cmd/derpprobe: check derper TLS certs too

Change-Id: If8c48e012b294570ebbb1a46bacdc58fafbfbcc5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

.gitattributes

@@ -1 +1,2 @@
 go.mod filter=go-mod
+*.go  diff=golang

.github/ISSUE_TEMPLATE/config.yml

@@ -1,5 +1,8 @@
 blank_issues_enabled: true
 contact_links:
-  - name: Support requests and Troubleshooting
+  - name: Support
+    url: https://tailscale.com/contact/support/
+    about: Contact us for support
+  - name: Troubleshooting
     url: https://tailscale.com/kb/1023/troubleshooting
-    about: Troubleshoot common issues. Contact us by email at support@tailscale.com.
+    about: Troubleshoot common issues

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -7,14 +7,7 @@ body:
     attributes:
       value: |
         Please check if your feature request is [already filed](https://github.com/tailscale/tailscale/issues).
-  - type: input
-    id: request
-    attributes:
-      label: Tell us about your idea!
-      description: What is your feature request?
-      placeholder: e.g., A pet pangolin
-    validations:
-      required: true
+        Tell us about your idea!
   - type: textarea
     id: problem
     attributes:

.github/dependabot.yml

@@ -2,15 +2,20 @@
 # https://docs.github.com/en/code-security/supply-chain-security/keeping-your-dependencies-updated-automatically/configuration-options-for-dependency-updates
 version: 2
 updates:
-  - package-ecosystem: "gomod"
-    directory: "/"
-    schedule:
-      interval: "daily"
-    commit-message:
-      prefix: "go.mod:"
+  ## Disabled between releases. We reenable it briefly after every
+  ## stable release, pull in all changes, and close it again so that
+  ## the tree remains more stable during development and the upstream
+  ## changes have time to soak before the next release.
+  # - package-ecosystem: "gomod"
+  #   directory: "/"
+  #   schedule:
+  #     interval: "daily"
+  #   commit-message:
+  #     prefix: "go.mod:"
+  #   open-pull-requests-limit: 100
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      interval: "daily"
+      interval: "weekly"
     commit-message:
       prefix: ".github:"

.github/workflows/cifuzz.yml

@@ -0,0 +1,26 @@
+name: CIFuzz
+on: [pull_request]
+jobs:
+  Fuzzing:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Build Fuzzers
+      id: build
+      uses: google/oss-fuzz/infra/cifuzz/actions/build_fuzzers@master
+      with:
+        oss-fuzz-project-name: 'tailscale'
+        dry-run: false
+        language: go
+    - name: Run Fuzzers
+      uses: google/oss-fuzz/infra/cifuzz/actions/run_fuzzers@master
+      with:
+        oss-fuzz-project-name: 'tailscale'
+        fuzz-seconds: 300
+        dry-run: false
+        language: go
+    - name: Upload Crash
+      uses: actions/upload-artifact@v2.3.1
+      if: failure() && steps.build.outcome == 'success'
+      with:
+        name: artifacts
+        path: ./out/artifacts

.github/workflows/cross-darwin.yml

@@ -17,7 +17,7 @@ jobs:
     steps:
 
     - name: Set up Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17
       id: go

.github/workflows/cross-freebsd.yml

@@ -17,7 +17,7 @@ jobs:
     steps:
 
     - name: Set up Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17
       id: go

.github/workflows/cross-openbsd.yml

@@ -17,7 +17,7 @@ jobs:
     steps:
 
     - name: Set up Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17
       id: go

.github/workflows/cross-windows.yml

@@ -17,7 +17,7 @@ jobs:
     steps:
 
     - name: Set up Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17
       id: go

.github/workflows/depaware.yml

@@ -14,7 +14,7 @@ jobs:
 
     steps:
     - name: Set up Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17
 

.github/workflows/go_generate.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
       - name: Set up Go
-        uses: actions/setup-go@v2.1.4
+        uses: actions/setup-go@v2.1.5
         with:
           go-version: 1.17
 

.github/workflows/license.yml

@@ -14,7 +14,7 @@ jobs:
 
     steps:
     - name: Set up Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17
 

.github/workflows/linux-race.yml

@@ -17,7 +17,7 @@ jobs:
     steps:
 
     - name: Set up Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17
       id: go
@@ -31,6 +31,21 @@ jobs:
     - name: Run tests and benchmarks with -race flag on linux
       run: go test -race -bench=. -benchtime=1x ./...
 
+    - name: Check that no tracked files in the repo have been modified
+      run: git diff --no-ext-diff --name-only --exit-code || (echo "Build/test modified the files above."; exit 1)
+
+    - name: Check that no files have been added to the repo
+      run: |
+        # Note: The "error: pathspec..." you see below is normal!
+        # In the success case in which there are no new untracked files,
+        # git ls-files complains about the pathspec not matching anything.
+        # That's OK. It's not worth the effort to suppress. Please ignore it.
+        if git ls-files --others --exclude-standard --directory --no-empty-directory --error-unmatch -- ':/*'
+        then
+          echo "Build/test created untracked files in the repo (file names above)."
+          exit 1
+        fi
+
     - uses: k0kubun/action-slack@v2.0.0
       with:
         payload: |

.github/workflows/linux.yml

@@ -17,7 +17,7 @@ jobs:
     steps:
 
     - name: Set up Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17
       id: go
@@ -40,6 +40,21 @@ jobs:
     - name: Run tests on linux
       run: go test -bench=. -benchtime=1x ./...
 
+    - name: Check that no tracked files in the repo have been modified
+      run: git diff --no-ext-diff --name-only --exit-code || (echo "Build/test modified the files above."; exit 1)
+
+    - name: Check that no files have been added to the repo
+      run: |
+        # Note: The "error: pathspec..." you see below is normal!
+        # In the success case in which there are no new untracked files,
+        # git ls-files complains about the pathspec not matching anything.
+        # That's OK. It's not worth the effort to suppress. Please ignore it.
+        if git ls-files --others --exclude-standard --directory --no-empty-directory --error-unmatch -- ':/*'
+        then
+          echo "Build/test created untracked files in the repo (file names above)."
+          exit 1
+        fi
+
     - uses: k0kubun/action-slack@v2.0.0
       with:
         payload: |

.github/workflows/linux32.yml

@@ -17,7 +17,7 @@ jobs:
     steps:
 
     - name: Set up Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17
       id: go
@@ -31,6 +31,21 @@ jobs:
     - name: Run tests on linux
       run: GOARCH=386 go test -bench=. -benchtime=1x ./...
 
+    - name: Check that no tracked files in the repo have been modified
+      run: git diff --no-ext-diff --name-only --exit-code || (echo "Build/test modified the files above."; exit 1)
+
+    - name: Check that no files have been added to the repo
+      run: |
+        # Note: The "error: pathspec..." you see below is normal!
+        # In the success case in which there are no new untracked files,
+        # git ls-files complains about the pathspec not matching anything.
+        # That's OK. It's not worth the effort to suppress. Please ignore it.
+        if git ls-files --others --exclude-standard --directory --no-empty-directory --error-unmatch -- ':/*'
+        then
+          echo "Build/test created untracked files in the repo (file names above)."
+          exit 1
+        fi
+
     - uses: k0kubun/action-slack@v2.0.0
       with:
         payload: |

.github/workflows/staticcheck.yml

@@ -14,7 +14,7 @@ jobs:
 
     steps:
     - name: Set up Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17
 

.github/workflows/vm.yml

@@ -12,11 +12,13 @@ jobs:
     if: "!contains(github.event.head_commit.message, '[ci skip]')"
 
     steps:
+      - name: Set GOPATH
+        run: echo "GOPATH=$HOME/go" >> $GITHUB_ENV
+
       - name: Set up Go
-        uses: actions/setup-go@v1
+        uses: actions/setup-go@v2.1.5
         with:
           go-version: 1.17
-        id: go
 
       - name: Checkout Code
         uses: actions/checkout@v1

.github/workflows/windows-race.yml

@@ -17,7 +17,7 @@ jobs:
     steps:
 
     - name: Install Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17.x
 

.github/workflows/windows.yml

@@ -17,7 +17,7 @@ jobs:
     steps:
 
     - name: Install Go
-      uses: actions/setup-go@v2.1.4
+      uses: actions/setup-go@v2.1.5
       with:
         go-version: 1.17.x
 

.gitignore

@@ -5,6 +5,7 @@
 *.dll
 *.so
 *.dylib
+*.spk
 
 cmd/tailscale/tailscale
 cmd/tailscaled/tailscaled

Dockerfile

@@ -50,12 +50,11 @@ ARG VERSION_GIT_HASH=""
 ENV VERSION_GIT_HASH=$VERSION_GIT_HASH
 ARG TARGETARCH
 
-RUN GOARCH=$TARGETARCH go install -tags=xversion -ldflags="\
+RUN GOARCH=$TARGETARCH go install -ldflags="\
       -X tailscale.com/version.Long=$VERSION_LONG \
       -X tailscale.com/version.Short=$VERSION_SHORT \
       -X tailscale.com/version.GitCommit=$VERSION_GIT_HASH" \
       -v ./cmd/tailscale ./cmd/tailscaled
 
-FROM alpine:3.14
-RUN apk add --no-cache ca-certificates iptables iproute2 ip6tables
+FROM ghcr.io/tailscale/alpine-base:3.14
 COPY --from=build-env /go/bin/* /usr/local/bin/

Dockerfile.base

@@ -0,0 +1,6 @@
+# Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+FROM alpine:3.15
+RUN apk add --no-cache ca-certificates iptables iproute2 ip6tables

Makefile

@@ -1,4 +1,6 @@
 IMAGE_REPO ?= tailscale/tailscale
+SYNO_ARCH ?= "amd64"
+SYNO_DSM ?= "7"
 
 usage:
 	echo "See Makefile"
@@ -23,11 +25,22 @@ build386:
 buildlinuxarm:
 	GOOS=linux GOARCH=arm go install tailscale.com/cmd/tailscale tailscale.com/cmd/tailscaled
 
-
 buildmultiarchimage:
-	docker buildx build --platform linux/amd64,linux/arm64,linux/arm/v7 -t ${IMAGE_REPO}:latest --push -f Dockerfile .
+	./build_docker.sh
 
 check: staticcheck vet depaware buildwindows build386 buildlinuxarm
 
 staticcheck:
 	go run honnef.co/go/tools/cmd/staticcheck -- $$(go list ./... | grep -v tempfork)
+
+spk:
+	PATH="${PWD}/tool:${PATH}" ./tool/go run github.com/tailscale/tailscale-synology@main -o tailscale.spk --source=. --goarch=${SYNO_ARCH} --dsm-version=${SYNO_DSM}
+
+spkall:
+	mkdir -p spks
+	PATH="${PWD}/tool:${PATH}" ./tool/go run github.com/tailscale/tailscale-synology@main -o spks --source=. --goarch=all --dsm-version=all
+
+pushspk: spk
+	echo "Pushing SPK to root@${SYNO_HOST} (env var SYNO_HOST) ..."
+	scp tailscale.spk root@${SYNO_HOST}:
+	ssh root@${SYNO_HOST} /usr/syno/bin/synopkg install tailscale.spk

README.md

@@ -8,11 +8,12 @@ Private WireGuard® networks made easy
 
 This repository contains all the open source Tailscale client code and
 the `tailscaled` daemon and `tailscale` CLI tool. The `tailscaled`
-daemon runs primarily on Linux; it also works to varying degrees on
-FreeBSD, OpenBSD, Darwin, and Windows.
+daemon runs on Linux, Windows and [macOS](https://tailscale.com/kb/1065/macos-variants/), and to varying degrees on FreeBSD, OpenBSD, and Darwin. (The Tailscale iOS and Android apps use this repo's code, but this repo doesn't contain the mobile GUI code.)
 
 The Android app is at https://github.com/tailscale/tailscale-android
 
+The Synology package is at https://github.com/tailscale/tailscale-synology
+
 ## Using
 
 We serve packages for a variety of distros at

VERSION.txt

@@ -1 +1 @@
-1.19.0
+1.21.0

api.md

@@ -23,6 +23,11 @@ Currently based on {some authentication method}. Visit the [admin panel](https:/
 	- [POST tailnet ACL validate](#tailnet-acl-validate-post): run validation tests against the tailnet's existing ACL
   - [Devices](#tailnet-devices)
     - [GET tailnet devices](#tailnet-devices-get)
+  - [Keys](#tailnet-keys)
+    - [GET tailnet keys](#tailnet-keys-get)
+    - [POST tailnet key](#tailnet-keys-post)
+    - [GET tailnet key](#tailnet-keys-key-get)
+    - [DELETE tailnet key](#tailnet-keys-key-delete)
   - [DNS](#tailnet-dns)
     - [GET tailnet DNS nameservers](#tailnet-dns-nameservers-get)
     - [POST tailnet DNS nameservers](#tailnet-dns-nameservers-post)
@@ -670,6 +675,159 @@ Response
 }
 ```
 
+<a name=tailnet-keys></a>
+
+### Keys
+
+<a name=tailnet-keys-get></a>
+
+#### `GET /api/v2/tailnet/:tailnet/keys` - list the keys for a tailnet
+
+Returns a list of active keys for a tailnet
+for the user who owns the API key used to perform this query.
+Supply the tailnet of interest in the path.
+
+##### Parameters
+No parameters.
+
+##### Returns
+
+Returns a JSON object with the IDs of all active keys.
+This includes both API keys and also machine authentication keys.
+In the future, this may provide more information about each key than just the ID.
+
+##### Example
+
+```
+curl 'https://api.tailscale.com/api/v2/tailnet/example.com/keys' \
+  -u "tskey-yourapikey123:"
+```
+
+Response:
+```
+{"keys": [
+	{"id": "kYKVU14CNTRL"},
+	{"id": "k68VdZ3CNTRL"},
+	{"id": "kJ9nq43CNTRL"},
+	{"id": "kkThgj1CNTRL"}
+]}
+```
+
+<a name=tailnet-keys-post></a>
+
+#### `POST /api/v2/tailnet/:tailnet/keys` - create a new key for a tailnet
+
+Create a new key in a tailnet associated
+with the user who owns the API key used to perform this request.
+Supply the tailnet in the path.
+
+##### Parameters
+
+###### POST Body
+`capabilities` - A mapping of resources to permissible actions.
+```
+{
+	"capabilities": {
+    "devices": {
+      "create": {
+        "reusable": false,
+        "ephemeral": false
+      }
+    }
+  }
+}
+```
+
+##### Returns
+
+Returns a JSON object with the provided capabilities in addition to the
+generated key. The key should be recorded and kept safe and secure as it
+wields the capabilities specified in the request. The identity of the key
+is embedded in the key itself and can be used to perform operations on
+the key (e.g., revoking it or retrieving information about it).
+The full key can no longer be retrieved by the server.
+
+##### Example
+
+```
+echo '{
+	"capabilities": {
+    "devices": {
+      "create": {
+        "reusable": false,
+        "ephemeral": false
+      }
+    }
+  }
+}' | curl -X POST --data-binary @- https://api.tailscale.com/api/v2/tailnet/example.com/keys \
+  -u "tskey-yourapikey123:" \
+  -H "Content-Type: application/json" | jsonfmt
+```
+
+Response:
+```
+{
+	"id":           "k123456CNTRL",
+	"key":          "tskey-k123456CNTRL-abcdefghijklmnopqrstuvwxyz",
+	"created":      "2021-12-09T23:22:39Z",
+	"expires":      "2022-03-09T23:22:39Z",
+	"capabilities": {"devices": {"create": {"reusable": false, "ephemeral": false}}}
+}
+```
+
+<a name=tailnet-keys-key-get></a>
+
+#### `GET /api/v2/tailnet/:tailnet/keys/:keyid` - get information for a specific key
+
+Returns a JSON object with information about specific key.
+Supply the tailnet and key ID of interest in the path.
+
+##### Parameters
+No parameters.
+
+##### Returns
+
+Returns a JSON object with information about the key such as
+when it was created and when it expires.
+It also lists the capabilities associated with the key.
+
+##### Example
+
+```
+curl 'https://api.tailscale.com/api/v2/tailnet/example.com/keys/k123456CNTRL' \
+  -u "tskey-yourapikey123:"
+```
+
+Response:
+```
+{
+	"id":           "k123456CNTRL",
+	"created":      "2021-12-09T22:13:53Z",
+	"expires":      "2022-03-09T22:13:53Z",
+	"capabilities": {"devices": {"create": {"reusable": false, "ephemeral": false}}}
+}
+```
+
+<a name=tailnet-keys-key-delete></a>
+
+#### `DELETE /api/v2/tailnet/:tailnet/keys/:keyid` - delete a specific key
+
+Deletes a specific key.
+Supply the tailnet and key ID of interest in the path.
+
+##### Parameters
+No parameters.
+
+##### Returns
+This reports status 200 upon success.
+
+##### Example
+
+```
+curl -X DELETE 'https://api.tailscale.com/api/v2/tailnet/example.com/keys/k123456CNTRL' \
+  -u "tskey-yourapikey123:"
+```
+
 <a name=tailnet-dns></a>
 
 ### DNS

build_dist.sh

@@ -30,12 +30,14 @@ else
 fi
 
 long_suffix="$change_suffix-t$short_hash"
-SHORT="$major.$minor.$patch"
+MINOR="$major.$minor"
+SHORT="$MINOR.$patch"
 LONG="${SHORT}$long_suffix"
 GIT_HASH="$git_hash"
 
 if [ "$1" = "shellvars" ]; then
 	cat <<EOF
+VERSION_MINOR="$MINOR"
 VERSION_SHORT="$SHORT"
 VERSION_LONG="$LONG"
 VERSION_GIT_HASH="$GIT_HASH"
@@ -43,4 +45,4 @@ EOF
 	exit 0
 fi
 
-exec go build -ldflags "-X tailscale.com/version.Long=${LONG} -X tailscale.com/version.Short=${SHORT} -X tailscale.com/version.GitCommit=${GIT_HASH}" "$@"
+exec ./tool/go build -ldflags "-X tailscale.com/version.Long=${LONG} -X tailscale.com/version.Short=${SHORT} -X tailscale.com/version.GitCommit=${GIT_HASH}" "$@"

build_docker.sh

@@ -19,10 +19,28 @@
 
 set -eu
 
-eval $(./build_dist.sh shellvars)
+# Use the "go" binary from the "tool" directory (which is github.com/tailscale/go)
+export PATH=$PWD/tool:$PATH
 
-docker build \
-  --build-arg VERSION_LONG=$VERSION_LONG \
-  --build-arg VERSION_SHORT=$VERSION_SHORT \
-  --build-arg VERSION_GIT_HASH=$VERSION_GIT_HASH \
-  -t tailscale:$VERSION_SHORT -t tailscale:latest .
+eval $(./build_dist.sh shellvars)
+DEFAULT_TAGS="v${VERSION_SHORT},v${VERSION_MINOR}"
+DEFAULT_REPOS="tailscale/tailscale,ghcr.io/tailscale/tailscale"
+DEFAULT_BASE="ghcr.io/tailscale/alpine-base:3.14"
+
+PUSH="${PUSH:-false}"
+REPOS="${REPOS:-${DEFAULT_REPOS}}"
+TAGS="${TAGS:-${DEFAULT_TAGS}}"
+BASE="${BASE:-${DEFAULT_BASE}}"
+
+go run github.com/tailscale/mkctr@latest \
+  --gopaths="\
+    tailscale.com/cmd/tailscale:/usr/local/bin/tailscale, \
+    tailscale.com/cmd/tailscaled:/usr/local/bin/tailscaled" \
+  --ldflags="\
+    -X tailscale.com/version.Long=${VERSION_LONG} \
+    -X tailscale.com/version.Short=${VERSION_SHORT} \
+    -X tailscale.com/version.GitCommit=${VERSION_GIT_HASH}" \
+  --base="${BASE}" \
+  --tags="${TAGS}" \
+  --repos="${REPOS}" \
+  --push="${PUSH}"

client/tailscale/tailscale.go

@@ -38,6 +38,9 @@ var (
 	// TailscaledSocket is the tailscaled Unix socket. It's used by the TailscaledDialer.
 	TailscaledSocket = paths.DefaultTailscaledSocket()
 
+	// TailscaledSocketSetExplicitly reports whether the user explicitly set TailscaledSocket.
+	TailscaledSocketSetExplicitly bool
+
 	// TailscaledDialer is the DialContext func that connects to the local machine's
 	// tailscaled or equivalent.
 	TailscaledDialer = defaultDialer
@@ -47,7 +50,8 @@ func defaultDialer(ctx context.Context, network, addr string) (net.Conn, error)
 	if addr != "local-tailscaled.sock:80" {
 		return nil, fmt.Errorf("unexpected URL address %q", addr)
 	}
-	if TailscaledSocket == paths.DefaultTailscaledSocket() {
+	// TODO: make this part of a safesocket.ConnectionStrategy
+	if !TailscaledSocketSetExplicitly {
 		// On macOS, when dialing from non-sandboxed program to sandboxed GUI running
 		// a TCP server on a random port, find the random port. For HTTP connections,
 		// we don't send the token. It gets added in an HTTP Basic-Auth header.
@@ -56,7 +60,11 @@ func defaultDialer(ctx context.Context, network, addr string) (net.Conn, error)
 			return d.DialContext(ctx, "tcp", "localhost:"+strconv.Itoa(port))
 		}
 	}
-	return safesocket.Connect(TailscaledSocket, safesocket.WindowsLocalPort)
+	s := safesocket.DefaultConnectionStrategy(TailscaledSocket)
+	// The user provided a non-default tailscaled socket address.
+	// Connect only to exactly what they provided.
+	s.UseFallback(false)
+	return safesocket.Connect(s)
 }
 
 var (
@@ -90,6 +98,31 @@ func DoLocalRequest(req *http.Request) (*http.Response, error) {
 	return tsClient.Do(req)
 }
 
+func doLocalRequestNiceError(req *http.Request) (*http.Response, error) {
+	res, err := DoLocalRequest(req)
+	if err == nil {
+		if server := res.Header.Get("Tailscale-Version"); server != "" && server != version.Long && onVersionMismatch != nil {
+			onVersionMismatch(version.Long, server)
+		}
+		if res.StatusCode == 403 {
+			all, _ := ioutil.ReadAll(res.Body)
+			return nil, &AccessDeniedError{errors.New(errorMessageFromBody(all))}
+		}
+		return res, nil
+	}
+	if ue, ok := err.(*url.Error); ok {
+		if oe, ok := ue.Err.(*net.OpError); ok && oe.Op == "dial" {
+			path := req.URL.Path
+			pathPrefix := path
+			if i := strings.Index(path, "?"); i != -1 {
+				pathPrefix = path[:i]
+			}
+			return nil, fmt.Errorf("Failed to connect to local Tailscale daemon for %s; %s Error: %w", pathPrefix, tailscaledConnectHint(), oe)
+		}
+	}
+	return nil, err
+}
+
 type errorJSON struct {
 	Error string
 }
@@ -140,32 +173,16 @@ func send(ctx context.Context, method, path string, wantStatus int, body io.Read
 	if err != nil {
 		return nil, err
 	}
-	res, err := DoLocalRequest(req)
+	res, err := doLocalRequestNiceError(req)
 	if err != nil {
-		if ue, ok := err.(*url.Error); ok {
-			if oe, ok := ue.Err.(*net.OpError); ok && oe.Op == "dial" {
-				pathPrefix := path
-				if i := strings.Index(path, "?"); i != -1 {
-					pathPrefix = path[:i]
-				}
-				return nil, fmt.Errorf("Failed to connect to local Tailscale daemon for %s; %s Error: %w", pathPrefix, tailscaledConnectHint(), oe)
-			}
-		}
 		return nil, err
 	}
 	defer res.Body.Close()
-	if server := res.Header.Get("Tailscale-Version"); server != "" && server != version.Long && onVersionMismatch != nil {
-		onVersionMismatch(version.Long, server)
-	}
 	slurp, err := ioutil.ReadAll(res.Body)
 	if err != nil {
 		return nil, err
 	}
 	if res.StatusCode != wantStatus {
-		if res.StatusCode == 403 {
-			return nil, &AccessDeniedError{errors.New(errorMessageFromBody(slurp))}
-		}
-		err := fmt.Errorf("HTTP %s: %s (expected %v)", res.Status, slurp, wantStatus)
 		return nil, bestError(err, slurp)
 	}
 	return slurp, nil
@@ -223,12 +240,22 @@ func BugReport(ctx context.Context, note string) (string, error) {
 	return strings.TrimSpace(string(body)), nil
 }
 
+// DebugAction invokes a debug action, such as "rebind" or "restun".
+// These are development tools and subject to change or removal over time.
+func DebugAction(ctx context.Context, action string) error {
+	body, err := send(ctx, "POST", "/localapi/v0/debug?action="+url.QueryEscape(action), 200, nil)
+	if err != nil {
+		return fmt.Errorf("error %w: %s", err, body)
+	}
+	return nil
+}
+
 // Status returns the Tailscale daemon's status.
 func Status(ctx context.Context) (*ipnstate.Status, error) {
 	return status(ctx, "")
 }
 
-// StatusWithPeers returns the Tailscale daemon's status, without the peer info.
+// StatusWithoutPeers returns the Tailscale daemon's status, without the peer info.
 func StatusWithoutPeers(ctx context.Context) (*ipnstate.Status, error) {
 	return status(ctx, "?peers=false")
 }
@@ -267,7 +294,7 @@ func GetWaitingFile(ctx context.Context, baseName string) (rc io.ReadCloser, siz
 	if err != nil {
 		return nil, 0, err
 	}
-	res, err := DoLocalRequest(req)
+	res, err := doLocalRequestNiceError(req)
 	if err != nil {
 		return nil, 0, err
 	}
@@ -295,6 +322,30 @@ func FileTargets(ctx context.Context) ([]apitype.FileTarget, error) {
 	return fts, nil
 }
 
+// PushFile sends Taildrop file r to target.
+//
+// A size of -1 means unknown.
+// The name parameter is the original filename, not escaped.
+func PushFile(ctx context.Context, target tailcfg.StableNodeID, size int64, name string, r io.Reader) error {
+	req, err := http.NewRequestWithContext(ctx, "PUT", "http://local-tailscaled.sock/localapi/v0/file-put/"+string(target)+"/"+url.PathEscape(name), r)
+	if err != nil {
+		return err
+	}
+	if size != -1 {
+		req.ContentLength = size
+	}
+	res, err := doLocalRequestNiceError(req)
+	if err != nil {
+		return err
+	}
+	if res.StatusCode == 200 {
+		io.Copy(io.Discard, res.Body)
+		return nil
+	}
+	all, _ := io.ReadAll(res.Body)
+	return bestError(fmt.Errorf("%s: %s", res.Status, all), all)
+}
+
 func CheckIPForwarding(ctx context.Context) error {
 	body, err := get200(ctx, "/localapi/v0/check-ip-forwarding")
 	if err != nil {

cmd/derper/cert.go

@@ -67,8 +67,8 @@ func NewManualCertManager(certdir, hostname string) (certProvider, error) {
 	if err != nil {
 		return nil, fmt.Errorf("can not load cert: %w", err)
 	}
-	if x509Cert.VerifyHostname(hostname) != nil {
-		return nil, errors.New("refuse to load cert: hostname mismatch with key")
+	if err := x509Cert.VerifyHostname(hostname); err != nil {
+		return nil, fmt.Errorf("cert invalid for hostname %q: %w", hostname, err)
 	}
 	return &manualCertManager{cert: &cert, hostname: hostname}, nil
 }

cmd/derper/derper.go

@@ -12,6 +12,7 @@ import (
 	"errors"
 	"expvar"
 	"flag"
+	"fmt"
 	"io"
 	"io/ioutil"
 	"log"
@@ -36,6 +37,7 @@ import (
 var (
 	dev           = flag.Bool("dev", false, "run in localhost development mode")
 	addr          = flag.String("a", ":443", "server address")
+	httpPort      = flag.Int("http-port", 80, "The port on which to serve HTTP. Set to -1 to disable")
 	configPath    = flag.String("c", "", "config file path")
 	certMode      = flag.String("certmode", "letsencrypt", "mode for getting a cert. possible options: manual, letsencrypt")
 	certDir       = flag.String("certdir", tsweb.DefaultCertDir("derper-certs"), "directory to store LetsEncrypt certs, if addr's port is :443")
@@ -49,9 +51,11 @@ var (
 )
 
 var (
-	stats           = new(metrics.Set)
-	stunDisposition = &metrics.LabelMap{Label: "disposition"}
-	stunAddrFamily  = &metrics.LabelMap{Label: "family"}
+	stats             = new(metrics.Set)
+	stunDisposition   = &metrics.LabelMap{Label: "disposition"}
+	stunAddrFamily    = &metrics.LabelMap{Label: "family"}
+	tlsRequestVersion = &metrics.LabelMap{Label: "version"}
+	tlsActiveVersion  = &metrics.LabelMap{Label: "version"}
 
 	stunReadError  = stunDisposition.Get("read_error")
 	stunNotSTUN    = stunDisposition.Get("not_stun")
@@ -66,6 +70,8 @@ func init() {
 	stats.Set("counter_requests", stunDisposition)
 	stats.Set("counter_addrfamily", stunAddrFamily)
 	expvar.Publish("stun", stats)
+	expvar.Publish("derper_tls_request_version", tlsRequestVersion)
+	expvar.Publish("gauge_derper_tls_active_version", tlsActiveVersion)
 }
 
 type config struct {
@@ -235,24 +241,58 @@ func main() {
 			cert.Certificate = append(cert.Certificate, s.MetaCert())
 			return cert, nil
 		}
-		go func() {
-			port80srv := &http.Server{
-				Addr:        net.JoinHostPort(listenHost, "80"),
-				Handler:     certManager.HTTPHandler(tsweb.Port80Handler{Main: mux}),
-				ReadTimeout: 30 * time.Second,
-				// Crank up WriteTimeout a bit more than usually
-				// necessary just so we can do long CPU profiles
-				// and not hit net/http/pprof's "profile
-				// duration exceeds server's WriteTimeout".
-				WriteTimeout: 5 * time.Minute,
-			}
-			err := port80srv.ListenAndServe()
-			if err != nil {
-				if err != http.ErrServerClosed {
-					log.Fatal(err)
+		httpsrv.Handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if r.TLS != nil {
+				label := "unknown"
+				switch r.TLS.Version {
+				case tls.VersionTLS10:
+					label = "1.0"
+				case tls.VersionTLS11:
+					label = "1.1"
+				case tls.VersionTLS12:
+					label = "1.2"
+				case tls.VersionTLS13:
+					label = "1.3"
 				}
+				tlsRequestVersion.Add(label, 1)
+				tlsActiveVersion.Add(label, 1)
+				defer tlsActiveVersion.Add(label, -1)
 			}
-		}()
+
+			// Set HTTP headers to appease automated security scanners.
+			//
+			// Security automation gets cranky when HTTPS sites don't
+			// set HSTS, and when they don't specify a content
+			// security policy for XSS mitigation.
+			//
+			// DERP's HTTP interface is only ever used for debug
+			// access (for which trivial safe policies work just
+			// fine), and by DERP clients which don't obey any of
+			// these browser-centric headers anyway.
+			w.Header().Set("Strict-Transport-Security", "max-age=63072000; includeSubDomains")
+			w.Header().Set("Content-Security-Policy", "default-src 'none'; frame-ancestors 'none'; form-action 'none'; base-uri 'self'; block-all-mixed-content; plugin-types 'none'")
+			mux.ServeHTTP(w, r)
+		})
+		if *httpPort > -1 {
+			go func() {
+				port80srv := &http.Server{
+					Addr:        net.JoinHostPort(listenHost, fmt.Sprintf("%d", *httpPort)),
+					Handler:     certManager.HTTPHandler(tsweb.Port80Handler{Main: mux}),
+					ReadTimeout: 30 * time.Second,
+					// Crank up WriteTimeout a bit more than usually
+					// necessary just so we can do long CPU profiles
+					// and not hit net/http/pprof's "profile
+					// duration exceeds server's WriteTimeout".
+					WriteTimeout: 5 * time.Minute,
+				}
+				err := port80srv.ListenAndServe()
+				if err != nil {
+					if err != http.ErrServerClosed {
+						log.Fatal(err)
+					}
+				}
+			}()
+		}
 		err = httpsrv.ListenAndServeTLS("", "")
 	} else {
 		log.Printf("derper: serving on %s", *addr)

cmd/derpprobe/derpprobe.go

@@ -9,7 +9,9 @@ import (
 	"bytes"
 	"context"
 	crand "crypto/rand"
+	"crypto/x509"
 	"encoding/json"
+	"errors"
 	"flag"
 	"fmt"
 	"html"
@@ -38,6 +40,7 @@ var (
 	state         = map[nodePair]pairStatus{}
 	lastDERPMap   *tailcfg.DERPMap
 	lastDERPMapAt time.Time
+	certs         = map[string]*x509.Certificate{}
 )
 
 func main() {
@@ -46,6 +49,13 @@ func main() {
 	log.Fatal(http.ListenAndServe(*listen, http.HandlerFunc(serve)))
 }
 
+func setCert(name string, cert *x509.Certificate) {
+	mu.Lock()
+	defer mu.Unlock()
+	certs[name] = cert
+	log.Printf("Cert %q: not before/after: %v, %v", name, cert.NotBefore, cert.NotAfter)
+}
+
 type overallStatus struct {
 	good, bad []string
 }
@@ -93,6 +103,27 @@ func getOverallStatus() (o overallStatus) {
 			}
 		}
 	}
+
+	var subjs []string
+	for k := range certs {
+		subjs = append(subjs, k)
+	}
+	sort.Strings(subjs)
+	reissueTime := time.Unix(1643226768, 0)     // assume certs before this need reissuance by LetsEncrypt due to ALPN bug
+	soon := time.Now().Add(14 * 24 * time.Hour) // in 2 weeks; autocert does 30 days by default
+	for _, s := range subjs {
+		cert := certs[s]
+		if cert.NotBefore.Before(reissueTime) {
+			o.addBadf("cert %q needs reissuing; NotBefore=%v", s, cert.NotBefore.Format(time.RFC3339))
+			continue
+		}
+		if cert.NotAfter.Before(soon) {
+			o.addBadf("cert %q expiring soon (%v); wasn't auto-refreshed", s, cert.NotAfter.Format(time.RFC3339))
+			continue
+		}
+		o.addGoodf("cert %q good %v - %v", s, cert.NotBefore.Format(time.RFC3339), cert.NotAfter.Format(time.RFC3339))
+	}
+
 	return
 }
 
@@ -359,6 +390,21 @@ func newConn(ctx context.Context, dm *tailcfg.DERPMap, n *tailcfg.DERPNode) (*de
 	if err != nil {
 		return nil, err
 	}
+	cs, ok := dc.TLSConnectionState()
+	if !ok {
+		dc.Close()
+		return nil, errors.New("no TLS state")
+	}
+	if len(cs.PeerCertificates) == 0 {
+		dc.Close()
+		return nil, errors.New("no peer certificates")
+	}
+	if cs.ServerName != n.HostName {
+		dc.Close()
+		return nil, fmt.Errorf("TLS server name %q != derp hostname %q", cs.ServerName, n.HostName)
+	}
+	setCert(cs.ServerName, cs.PeerCertificates[0])
+
 	errc := make(chan error, 1)
 	go func() {
 		m, err := dc.Recv()

cmd/hello/hello.go

@@ -2,13 +2,15 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// The hello binary runs hello.ipn.dev.
+// The hello binary runs hello.ts.net.
 package main // import "tailscale.com/cmd/hello"
 
 import (
 	"context"
+	"crypto/tls"
 	_ "embed"
 	"encoding/json"
+	"errors"
 	"flag"
 	"html/template"
 	"io/ioutil"
@@ -16,6 +18,7 @@ import (
 	"net/http"
 	"os"
 	"strings"
+	"time"
 
 	"tailscale.com/client/tailscale"
 	"tailscale.com/client/tailscale/apitype"
@@ -69,11 +72,31 @@ func main() {
 	if *httpsAddr != "" {
 		log.Printf("running HTTPS server on %s", *httpsAddr)
 		go func() {
-			errc <- http.ListenAndServeTLS(*httpsAddr,
-				"/etc/hello/hello.ipn.dev.crt",
-				"/etc/hello/hello.ipn.dev.key",
-				nil,
-			)
+			hs := &http.Server{
+				Addr: *httpsAddr,
+				TLSConfig: &tls.Config{
+					GetCertificate: func(hi *tls.ClientHelloInfo) (*tls.Certificate, error) {
+						switch hi.ServerName {
+						case "hello.ts.net":
+							return tailscale.GetCertificate(hi)
+						case "hello.ipn.dev":
+							c, err := tls.LoadX509KeyPair(
+								"/etc/hello/hello.ipn.dev.crt",
+								"/etc/hello/hello.ipn.dev.key",
+							)
+							if err != nil {
+								return nil, err
+							}
+							return &c, nil
+						}
+						return nil, errors.New("invalid SNI name")
+					},
+				},
+				IdleTimeout:       30 * time.Second,
+				ReadHeaderTimeout: 20 * time.Second,
+				MaxHeaderBytes:    10 << 10,
+			}
+			errc <- hs.ListenAndServeTLS("", "")
 		}()
 	}
 	log.Fatal(<-errc)
@@ -127,8 +150,9 @@ func tailscaleIP(who *apitype.WhoIsResponse) string {
 func root(w http.ResponseWriter, r *http.Request) {
 	if r.TLS == nil && *httpsAddr != "" {
 		host := r.Host
-		if strings.Contains(r.Host, "100.101.102.103") {
-			host = "hello.ipn.dev"
+		if strings.Contains(r.Host, "100.101.102.103") ||
+			strings.Contains(r.Host, "hello.ipn.dev") {
+			host = "hello.ts.net"
 		}
 		http.Redirect(w, r, "https://"+host, http.StatusFound)
 		return
@@ -137,6 +161,10 @@ func root(w http.ResponseWriter, r *http.Request) {
 		http.Redirect(w, r, "/", http.StatusFound)
 		return
 	}
+	if r.TLS != nil && *httpsAddr != "" && strings.Contains(r.Host, "hello.ipn.dev") {
+		http.Redirect(w, r, "https://hello.ts.net", http.StatusFound)
+		return
+	}
 	tmpl, err := getTmpl()
 	if err != nil {
 		w.Header().Set("Content-Type", "text/plain")

cmd/printdep/printdep.go

@@ -0,0 +1,46 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// The printdep command is a build system tool for printing out information
+// about dependencies.
+package main
+
+import (
+	"flag"
+	"fmt"
+	"log"
+	"runtime"
+	"strings"
+
+	ts "tailscale.com"
+)
+
+var (
+	goToolchain    = flag.Bool("go", false, "print the supported Go toolchain git hash (a github.com/tailscale/go commit)")
+	goToolchainURL = flag.Bool("go-url", false, "print the URL to the tarball of the Tailscale Go toolchain")
+)
+
+func main() {
+	flag.Parse()
+	if *goToolchain {
+		fmt.Println(strings.TrimSpace(ts.GoToolchainRev))
+	}
+	if *goToolchainURL {
+		var suffix string
+		switch runtime.GOARCH {
+		case "amd64":
+			// None
+		case "arm64":
+			suffix = "-" + runtime.GOARCH
+		default:
+			log.Fatalf("unsupported GOARCH %q", runtime.GOARCH)
+		}
+		switch runtime.GOOS {
+		case "linux", "darwin":
+		default:
+			log.Fatalf("unsupported GOOS %q", runtime.GOOS)
+		}
+		fmt.Printf("https://github.com/tailscale/go/releases/download/build-%s/%s%s.tar.gz\n", strings.TrimSpace(ts.GoToolchainRev), runtime.GOOS, suffix)
+	}
+}

cmd/tailscale/cli/cert.go

@@ -13,7 +13,6 @@ import (
 	"log"
 	"net/http"
 	"os"
-	"runtime"
 	"strings"
 
 	"github.com/peterbourgon/ff/v3/ffcli"
@@ -92,9 +91,6 @@ func runCert(ctx context.Context, args []string) error {
 		certArgs.keyFile = domain + ".key"
 	}
 	certPEM, keyPEM, err := tailscale.CertPair(ctx, domain)
-	if tailscale.IsAccessDeniedError(err) && os.Getuid() != 0 && runtime.GOOS != "windows" {
-		return fmt.Errorf("%v\n\nUse 'sudo tailscale cert' or 'tailscale up --operator=$USER' to not require root.", err)
-	}
 	if err != nil {
 		return err
 	}
@@ -108,7 +104,7 @@ func runCert(ctx context.Context, args []string) error {
 		if version.IsMacSysExt() {
 			dir = "io.tailscale.ipn.macsys"
 		}
-		printf("Warning: the macOS CLI runs in a sandbox; this binary's filesystem writes go to $HOME/Library/Containers/%s\n", dir)
+		printf("Warning: the macOS CLI runs in a sandbox; this binary's filesystem writes go to $HOME/Library/Containers/%s/Data\n", dir)
 	}
 	if certArgs.certFile != "" {
 		certChanged, err := writeIfChanged(certArgs.certFile, certPEM, 0644)

cmd/tailscale/cli/cli.go

@@ -164,8 +164,16 @@ change in the future.
 	}
 
 	tailscale.TailscaledSocket = rootArgs.socket
+	rootfs.Visit(func(f *flag.Flag) {
+		if f.Name == "socket" {
+			tailscale.TailscaledSocketSetExplicitly = true
+		}
+	})
 
 	err := rootCmd.Run(context.Background())
+	if tailscale.IsAccessDeniedError(err) && os.Getuid() != 0 && runtime.GOOS != "windows" {
+		return fmt.Errorf("%v\n\nUse 'sudo tailscale %s' or 'tailscale up --operator=$USER' to not require root.", err, strings.Join(args, " "))
+	}
 	if errors.Is(err, flag.ErrHelp) {
 		return nil
 	}
@@ -191,7 +199,8 @@ var rootArgs struct {
 var gotSignal syncs.AtomicBool
 
 func connect(ctx context.Context) (net.Conn, *ipn.BackendClient, context.Context, context.CancelFunc) {
-	c, err := safesocket.Connect(rootArgs.socket, safesocket.WindowsLocalPort)
+	s := safesocket.DefaultConnectionStrategy(rootArgs.socket)
+	c, err := safesocket.Connect(s)
 	if err != nil {
 		if runtime.GOOS != "windows" && rootArgs.socket == "" {
 			fatalf("--socket cannot be empty")

cmd/tailscale/cli/cli_test.go

@@ -18,8 +18,10 @@ import (
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/tstest"
+	"tailscale.com/types/key"
 	"tailscale.com/types/persist"
 	"tailscale.com/types/preftype"
+	"tailscale.com/version/distro"
 )
 
 // geese is a collection of gooses. It need not be complete.
@@ -57,6 +59,7 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 		curExitNodeIP netaddr.IP
 		curUser       string // os.Getenv("USER") on the client side
 		goos          string // empty means "linux"
+		distro        distro.Distro
 
 		want string
 	}{
@@ -313,6 +316,7 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 				ControlURL:       ipn.DefaultControlURL,
 				AllowSingleHosts: true,
 				CorpDNS:          true,
+				RouteAll:         true,
 
 				// And assume this no-op accidental pre-1.8 value:
 				NoSNAT: true,
@@ -329,7 +333,7 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 
 				NetfilterMode: preftype.NetfilterNoDivert, // we never had this bug, but pretend it got set non-zero on Windows somehow
 			},
-			goos: "windows",
+			goos: "openbsd",
 			want: "", // not an error
 		},
 		{
@@ -405,6 +409,21 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 			},
 			want: accidentalUpPrefix + " --hostname=foo --exit-node=100.64.5.7",
 		},
+		{
+			name:          "error_exit_node_and_allow_lan_omit_with_id_pref", // Isue 3480
+			flags:         []string{"--hostname=foo"},
+			curExitNodeIP: netaddr.MustParseIP("100.2.3.4"),
+			curPrefs: &ipn.Prefs{
+				ControlURL:       ipn.DefaultControlURL,
+				AllowSingleHosts: true,
+				CorpDNS:          true,
+				NetfilterMode:    preftype.NetfilterOn,
+
+				ExitNodeAllowLANAccess: true,
+				ExitNodeID:             "some_stable_id",
+			},
+			want: accidentalUpPrefix + " --hostname=foo --exit-node-allow-lan-access --exit-node=100.2.3.4",
+		},
 		{
 			name:  "ignore_login_server_synonym",
 			flags: []string{"--login-server=https://controlplane.tailscale.com"},
@@ -427,6 +446,38 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 			},
 			want: accidentalUpPrefix + " --netfilter-mode=off --accept-dns=false",
 		},
+		{
+			// Issue 3176: on Synology, don't require --accept-routes=false because user
+			// migth've had old an install, and we don't support --accept-routes anyway.
+			name:  "synology_permit_omit_accept_routes",
+			flags: []string{"--hostname=foo"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       "https://login.tailscale.com",
+				CorpDNS:          true,
+				AllowSingleHosts: true,
+				RouteAll:         true,
+				NetfilterMode:    preftype.NetfilterOn,
+			},
+			goos:   "linux",
+			distro: distro.Synology,
+			want:   "",
+		},
+		{
+			// Same test case as "synology_permit_omit_accept_routes" above, but
+			// on non-Synology distro.
+			name:  "not_synology_dont_permit_omit_accept_routes",
+			flags: []string{"--hostname=foo"},
+			curPrefs: &ipn.Prefs{
+				ControlURL:       "https://login.tailscale.com",
+				CorpDNS:          true,
+				AllowSingleHosts: true,
+				RouteAll:         true,
+				NetfilterMode:    preftype.NetfilterOn,
+			},
+			goos:   "linux",
+			distro: "", // not Synology
+			want:   accidentalUpPrefix + " --hostname=foo --accept-routes",
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -447,6 +498,7 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 				goos:          goos,
 				flagSet:       flagSet,
 				curExitNodeIP: tt.curExitNodeIP,
+				distro:        tt.distro,
 			}); err != nil {
 				got = err.Error()
 			}
@@ -495,6 +547,7 @@ func TestPrefsFromUpArgs(t *testing.T) {
 				WantRunning:      true,
 				CorpDNS:          true,
 				AllowSingleHosts: true,
+				RouteAll:         true,
 				NetfilterMode:    preftype.NetfilterOn,
 			},
 		},
@@ -532,7 +585,7 @@ func TestPrefsFromUpArgs(t *testing.T) {
 			args: upArgsT{
 				exitNodeIP: "foo",
 			},
-			wantErr: `invalid IP address "foo" for --exit-node: ParseIP("foo"): unable to parse IP`,
+			wantErr: `invalid value "foo" for --exit-node; must be IP or unique node name`,
 		},
 		{
 			name: "error_exit_node_allow_lan_without_exit_node",
@@ -733,6 +786,16 @@ func TestUpdatePrefs(t *testing.T) {
 			wantSimpleUp:   true,
 			wantJustEditMP: &ipn.MaskedPrefs{WantRunningSet: true},
 		},
+		{
+			name:  "just_edit_reset",
+			flags: []string{"--reset"},
+			curPrefs: &ipn.Prefs{
+				ControlURL: ipn.DefaultControlURL,
+				Persist:    &persist.Persist{LoginName: "crawshaw.github"},
+			},
+			env:            upCheckEnv{backendState: "Running"},
+			wantJustEditMP: &ipn.MaskedPrefs{WantRunningSet: true},
+		},
 		{
 			name:  "control_synonym",
 			flags: []string{},
@@ -806,3 +869,133 @@ func TestUpdatePrefs(t *testing.T) {
 		})
 	}
 }
+
+func TestExitNodeIPOfArg(t *testing.T) {
+	mustIP := netaddr.MustParseIP
+	tests := []struct {
+		name    string
+		arg     string
+		st      *ipnstate.Status
+		want    netaddr.IP
+		wantErr string
+	}{
+		{
+			name: "ip_while_stopped_okay",
+			arg:  "1.2.3.4",
+			st: &ipnstate.Status{
+				BackendState: "Stopped",
+			},
+			want: mustIP("1.2.3.4"),
+		},
+		{
+			name: "ip_not_found",
+			arg:  "1.2.3.4",
+			st: &ipnstate.Status{
+				BackendState: "Running",
+			},
+			wantErr: `no node found in netmap with IP 1.2.3.4`,
+		},
+		{
+			name: "ip_not_exit",
+			arg:  "1.2.3.4",
+			st: &ipnstate.Status{
+				BackendState: "Running",
+				Peer: map[key.NodePublic]*ipnstate.PeerStatus{
+					key.NewNode().Public(): {
+						TailscaleIPs: []netaddr.IP{mustIP("1.2.3.4")},
+					},
+				},
+			},
+			wantErr: `node 1.2.3.4 is not advertising an exit node`,
+		},
+		{
+			name: "ip",
+			arg:  "1.2.3.4",
+			st: &ipnstate.Status{
+				BackendState: "Running",
+				Peer: map[key.NodePublic]*ipnstate.PeerStatus{
+					key.NewNode().Public(): {
+						TailscaleIPs:   []netaddr.IP{mustIP("1.2.3.4")},
+						ExitNodeOption: true,
+					},
+				},
+			},
+			want: mustIP("1.2.3.4"),
+		},
+		{
+			name:    "no_match",
+			arg:     "unknown",
+			st:      &ipnstate.Status{MagicDNSSuffix: ".foo"},
+			wantErr: `invalid value "unknown" for --exit-node; must be IP or unique node name`,
+		},
+		{
+			name: "name",
+			arg:  "skippy",
+			st: &ipnstate.Status{
+				MagicDNSSuffix: ".foo",
+				Peer: map[key.NodePublic]*ipnstate.PeerStatus{
+					key.NewNode().Public(): {
+						DNSName:        "skippy.foo.",
+						TailscaleIPs:   []netaddr.IP{mustIP("1.0.0.2")},
+						ExitNodeOption: true,
+					},
+				},
+			},
+			want: mustIP("1.0.0.2"),
+		},
+		{
+			name: "name_not_exit",
+			arg:  "skippy",
+			st: &ipnstate.Status{
+				MagicDNSSuffix: ".foo",
+				Peer: map[key.NodePublic]*ipnstate.PeerStatus{
+					key.NewNode().Public(): {
+						DNSName:      "skippy.foo.",
+						TailscaleIPs: []netaddr.IP{mustIP("1.0.0.2")},
+					},
+				},
+			},
+			wantErr: `node "skippy" is not advertising an exit node`,
+		},
+		{
+			name: "ambiguous",
+			arg:  "skippy",
+			st: &ipnstate.Status{
+				MagicDNSSuffix: ".foo",
+				Peer: map[key.NodePublic]*ipnstate.PeerStatus{
+					key.NewNode().Public(): {
+						DNSName:        "skippy.foo.",
+						TailscaleIPs:   []netaddr.IP{mustIP("1.0.0.2")},
+						ExitNodeOption: true,
+					},
+					key.NewNode().Public(): {
+						DNSName:        "SKIPPY.foo.",
+						TailscaleIPs:   []netaddr.IP{mustIP("1.0.0.2")},
+						ExitNodeOption: true,
+					},
+				},
+			},
+			wantErr: `ambiguous exit node name "skippy"`,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := exitNodeIPOfArg(tt.arg, tt.st)
+			if err != nil {
+				if err.Error() == tt.wantErr {
+					return
+				}
+				if tt.wantErr == "" {
+					t.Fatal(err)
+				}
+				t.Fatalf("error = %#q; want %#q", err, tt.wantErr)
+			}
+			if tt.wantErr != "" {
+				t.Fatalf("got %v; want error %#q", got, tt.wantErr)
+			}
+			if got != tt.want {
+				t.Fatalf("got %v; want %v", got, tt.want)
+			}
+		})
+	}
+}

cmd/tailscale/cli/debug.go

@@ -70,6 +70,16 @@ var debugCmd = &ffcli.Command{
 			Exec:      runLocalCreds,
 			ShortHelp: "print how to access Tailscale local API",
 		},
+		{
+			Name:      "restun",
+			Exec:      localAPIAction("restun"),
+			ShortHelp: "force a magicsock restun",
+		},
+		{
+			Name:      "rebind",
+			Exec:      localAPIAction("rebind"),
+			ShortHelp: "force a magicsock rebind",
+		},
 		{
 			Name:      "prefs",
 			Exec:      runPrefs,
@@ -244,6 +254,15 @@ func runDERPMap(ctx context.Context, args []string) error {
 	return nil
 }
 
+func localAPIAction(action string) func(context.Context, []string) error {
+	return func(ctx context.Context, args []string) error {
+		if len(args) > 0 {
+			return errors.New("unexpected arguments")
+		}
+		return tailscale.DebugAction(ctx, action)
+	}
+}
+
 func runEnv(ctx context.Context, args []string) error {
 	for _, e := range os.Environ() {
 		outln(e)

cmd/tailscale/cli/diag.go

@@ -25,23 +25,23 @@ func fixTailscaledConnectError(origErr error) error {
 	if err != nil {
 		return fmt.Errorf("failed to connect to local Tailscaled process and failed to enumerate processes while looking for it")
 	}
-	found := false
+	var foundProc ps.Process
 	for _, proc := range procs {
 		base := filepath.Base(proc.Executable())
 		if base == "tailscaled" {
-			found = true
+			foundProc = proc
 			break
 		}
 		if runtime.GOOS == "darwin" && base == "IPNExtension" {
-			found = true
+			foundProc = proc
 			break
 		}
 		if runtime.GOOS == "windows" && strings.EqualFold(base, "tailscaled.exe") {
-			found = true
+			foundProc = proc
 			break
 		}
 	}
-	if !found {
+	if foundProc == nil {
 		switch runtime.GOOS {
 		case "windows":
 			return fmt.Errorf("failed to connect to local tailscaled process; is the Tailscale service running?")
@@ -52,5 +52,5 @@ func fixTailscaledConnectError(origErr error) error {
 		}
 		return fmt.Errorf("failed to connect to local tailscaled process; it doesn't appear to be running")
 	}
-	return fmt.Errorf("failed to connect to local tailscaled (which appears to be running). Got error: %w", origErr)
+	return fmt.Errorf("failed to connect to local tailscaled (which appears to be running as %v, pid %v). Got error: %w", foundProc.Executable(), foundProc.Pid(), origErr)
 }

cmd/tailscale/cli/file.go

@@ -11,14 +11,11 @@ import (
 	"flag"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"log"
 	"mime"
 	"net/http"
-	"net/url"
 	"os"
 	"path/filepath"
-	"strconv"
 	"strings"
 	"time"
 	"unicode/utf8"
@@ -28,8 +25,10 @@ import (
 	"inet.af/netaddr"
 	"tailscale.com/client/tailscale"
 	"tailscale.com/client/tailscale/apitype"
+	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/net/tsaddr"
+	"tailscale.com/tailcfg"
 	"tailscale.com/version"
 )
 
@@ -96,7 +95,7 @@ func runCp(ctx context.Context, args []string) error {
 		return err
 	}
 
-	peerAPIBase, isOffline, err := discoverPeerAPIBase(ctx, ip)
+	stableID, isOffline, err := getTargetStableID(ctx, ip)
 	if err != nil {
 		return fmt.Errorf("can't send to %s: %v", target, err)
 	}
@@ -149,37 +148,26 @@ func runCp(ctx context.Context, args []string) error {
 				name = filepath.Base(fileArg)
 			}
 
-			if slow, _ := strconv.ParseBool(os.Getenv("TS_DEBUG_SLOW_PUSH")); slow {
+			if envknob.Bool("TS_DEBUG_SLOW_PUSH") {
 				fileContents = &slowReader{r: fileContents}
 			}
 		}
 
-		dstURL := peerAPIBase + "/v0/put/" + url.PathEscape(name)
-		req, err := http.NewRequestWithContext(ctx, "PUT", dstURL, fileContents)
-		if err != nil {
-			return err
-		}
-		req.ContentLength = contentLength
 		if cpArgs.verbose {
-			log.Printf("sending to %v ...", dstURL)
+			log.Printf("sending %q to %v/%v/%v ...", name, target, ip, stableID)
 		}
-		res, err := http.DefaultClient.Do(req)
+		err := tailscale.PushFile(ctx, stableID, contentLength, name, fileContents)
 		if err != nil {
 			return err
 		}
-		if res.StatusCode == 200 {
-			io.Copy(ioutil.Discard, res.Body)
-			res.Body.Close()
-			continue
+		if cpArgs.verbose {
+			log.Printf("sent %q", name)
 		}
-		io.Copy(Stdout, res.Body)
-		res.Body.Close()
-		return errors.New(res.Status)
 	}
 	return nil
 }
 
-func discoverPeerAPIBase(ctx context.Context, ipStr string) (base string, isOffline bool, err error) {
+func getTargetStableID(ctx context.Context, ipStr string) (id tailcfg.StableNodeID, isOffline bool, err error) {
 	ip, err := netaddr.ParseIP(ipStr)
 	if err != nil {
 		return "", false, err
@@ -195,7 +183,7 @@ func discoverPeerAPIBase(ctx context.Context, ipStr string) (base string, isOffl
 				continue
 			}
 			isOffline = n.Online != nil && !*n.Online
-			return ft.PeerAPIURL, isOffline, nil
+			return n.StableID, isOffline, nil
 		}
 	}
 	return "", false, fileTargetErrorDetail(ctx, ip)
@@ -336,7 +324,7 @@ func runFileGet(ctx context.Context, args []string) error {
 	for {
 		wfs, err = tailscale.WaitingFiles(ctx)
 		if err != nil {
-			return fmt.Errorf("getting WaitingFiles: %v", err)
+			return fmt.Errorf("getting WaitingFiles: %w", err)
 		}
 		if len(wfs) != 0 || !getArgs.wait {
 			break
@@ -391,7 +379,7 @@ func wipeInbox(ctx context.Context) error {
 	}
 	wfs, err := tailscale.WaitingFiles(ctx)
 	if err != nil {
-		return fmt.Errorf("getting WaitingFiles: %v", err)
+		return fmt.Errorf("getting WaitingFiles: %w", err)
 	}
 	deleted := 0
 	for _, wf := range wfs {

cmd/tailscale/cli/ip.go

@@ -18,12 +18,13 @@ import (
 
 var ipCmd = &ffcli.Command{
 	Name:       "ip",
-	ShortUsage: "ip [-4] [-6] [peername]",
-	ShortHelp:  "Show current Tailscale IP address(es)",
-	LongHelp:   "Shows the Tailscale IP address of the current machine without an argument. With an argument, it shows the IP of a named peer.",
+	ShortUsage: "ip [-1] [-4] [-6] [peer hostname or ip address]",
+	ShortHelp:  "Show Tailscale IP addresses",
+	LongHelp:   "Show Tailscale IP addresses for peer. Peer defaults to the current machine.",
 	Exec:       runIP,
 	FlagSet: (func() *flag.FlagSet {
 		fs := newFlagSet("ip")
+		fs.BoolVar(&ipArgs.want1, "1", false, "only print one IP address")
 		fs.BoolVar(&ipArgs.want4, "4", false, "only print IPv4 address")
 		fs.BoolVar(&ipArgs.want6, "6", false, "only print IPv6 address")
 		return fs
@@ -31,13 +32,14 @@ var ipCmd = &ffcli.Command{
 }
 
 var ipArgs struct {
+	want1 bool
 	want4 bool
 	want6 bool
 }
 
 func runIP(ctx context.Context, args []string) error {
 	if len(args) > 1 {
-		return errors.New("unknown arguments")
+		return errors.New("too many arguments, expected at most one peer")
 	}
 	var of string
 	if len(args) == 1 {
@@ -45,8 +47,14 @@ func runIP(ctx context.Context, args []string) error {
 	}
 
 	v4, v6 := ipArgs.want4, ipArgs.want6
-	if v4 && v6 {
-		return errors.New("tailscale ip -4 and -6 are mutually exclusive")
+	nflags := 0
+	for _, b := range []bool{ipArgs.want1, v4, v6} {
+		if b {
+			nflags++
+		}
+	}
+	if nflags > 1 {
+		return errors.New("tailscale ip -1, -4, and -6 are mutually exclusive")
 	}
 	if !v4 && !v6 {
 		v4, v6 = true, true
@@ -71,6 +79,9 @@ func runIP(ctx context.Context, args []string) error {
 		return fmt.Errorf("no current Tailscale IPs; state: %v", st.BackendState)
 	}
 
+	if ipArgs.want1 {
+		ips = ips[:1]
+	}
 	match := false
 	for _, ip := range ips {
 		if ip.Is4() && v4 || ip.Is6() && v6 {

cmd/tailscale/cli/netcheck.go

@@ -13,13 +13,13 @@ import (
 	"io/ioutil"
 	"log"
 	"net/http"
-	"os"
 	"sort"
 	"strings"
 	"time"
 
 	"github.com/peterbourgon/ff/v3/ffcli"
 	"tailscale.com/client/tailscale"
+	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/net/netcheck"
 	"tailscale.com/net/portmapper"
@@ -49,7 +49,7 @@ var netcheckArgs struct {
 
 func runNetcheck(ctx context.Context, args []string) error {
 	c := &netcheck.Client{
-		UDPBindAddr: os.Getenv("TS_DEBUG_NETCHECK_UDP_BIND"),
+		UDPBindAddr: envknob.String("TS_DEBUG_NETCHECK_UDP_BIND"),
 		PortMapper:  portmapper.NewClient(logger.WithPrefix(log.Printf, "portmap: "), nil),
 	}
 	if netcheckArgs.verbose {

cmd/tailscale/cli/ping.go

@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"log"
 	"net"
+	"os"
 	"strings"
 	"time"
 
@@ -64,6 +65,16 @@ var pingArgs struct {
 }
 
 func runPing(ctx context.Context, args []string) error {
+	st, err := tailscale.Status(ctx)
+	if err != nil {
+		return fixTailscaledConnectError(err)
+	}
+	description, ok := isRunningOrStarting(st)
+	if !ok {
+		printf("%s\n", description)
+		os.Exit(1)
+	}
+
 	c, bc, ctx, cancel := connect(ctx)
 	defer cancel()
 

cmd/tailscale/cli/status.go

@@ -29,7 +29,22 @@ var statusCmd = &ffcli.Command{
 	Name:       "status",
 	ShortUsage: "status [--active] [--web] [--json]",
 	ShortHelp:  "Show state of tailscaled and its connections",
-	Exec:       runStatus,
+	LongHelp: strings.TrimSpace(`
+
+JSON FORMAT
+
+Warning: this format has changed between releases and might change more
+in the future.
+
+For a description of the fields, see the "type Status" declaration at:
+
+https://github.com/tailscale/tailscale/blob/main/ipn/ipnstate/ipnstate.go
+
+(and be sure to select branch/tag that corresponds to the version
+ of Tailscale you're running)
+
+`),
+	Exec: runStatus,
 	FlagSet: (func() *flag.FlagSet {
 		fs := newFlagSet("status")
 		fs.BoolVar(&statusArgs.json, "json", false, "output in JSON format (WARNING: format subject to change)")
@@ -106,24 +121,10 @@ func runStatus(ctx context.Context, args []string) error {
 		return err
 	}
 
-	switch st.BackendState {
-	default:
-		fmt.Fprintf(Stderr, "unexpected state: %s\n", st.BackendState)
+	description, ok := isRunningOrStarting(st)
+	if !ok {
+		outln(description)
 		os.Exit(1)
-	case ipn.Stopped.String():
-		outln("Tailscale is stopped.")
-		os.Exit(1)
-	case ipn.NeedsLogin.String():
-		outln("Logged out.")
-		if st.AuthURL != "" {
-			printf("\nLog in at: %s\n", st.AuthURL)
-		}
-		os.Exit(1)
-	case ipn.NeedsMachineAuth.String():
-		outln("Machine is not yet authorized by tailnet admin.")
-		os.Exit(1)
-	case ipn.Running.String(), ipn.Starting.String():
-		// Run below.
 	}
 
 	if len(st.Health) > 0 {
@@ -145,11 +146,19 @@ func runStatus(ctx context.Context, args []string) error {
 		)
 		relay := ps.Relay
 		anyTraffic := ps.TxBytes != 0 || ps.RxBytes != 0
+		var offline string
+		if !ps.Online {
+			offline = "; offline"
+		}
 		if !ps.Active {
 			if ps.ExitNode {
-				f("idle; exit node")
+				f("idle; exit node" + offline)
+			} else if ps.ExitNodeOption {
+				f("idle; offers exit node" + offline)
 			} else if anyTraffic {
-				f("idle")
+				f("idle" + offline)
+			} else if !ps.Online {
+				f("offline")
 			} else {
 				f("-")
 			}
@@ -157,12 +166,17 @@ func runStatus(ctx context.Context, args []string) error {
 			f("active; ")
 			if ps.ExitNode {
 				f("exit node; ")
+			} else if ps.ExitNodeOption {
+				f("offers exit node; ")
 			}
 			if relay != "" && ps.CurAddr == "" {
 				f("relay %q", relay)
 			} else if ps.CurAddr != "" {
 				f("direct %s", ps.CurAddr)
 			}
+			if !ps.Online {
+				f("; offline")
+			}
 		}
 		if anyTraffic {
 			f(", tx %d rx %d", ps.TxBytes, ps.RxBytes)
@@ -194,6 +208,27 @@ func runStatus(ctx context.Context, args []string) error {
 	return nil
 }
 
+// isRunningOrStarting reports whether st is in state Running or Starting.
+// It also returns a description of the status suitable to display to a user.
+func isRunningOrStarting(st *ipnstate.Status) (description string, ok bool) {
+	switch st.BackendState {
+	default:
+		return fmt.Sprintf("unexpected state: %s", st.BackendState), false
+	case ipn.Stopped.String():
+		return "Tailscale is stopped.", false
+	case ipn.NeedsLogin.String():
+		s := "Logged out."
+		if st.AuthURL != "" {
+			s += fmt.Sprintf("\nLog in at: %s", st.AuthURL)
+		}
+		return s, false
+	case ipn.NeedsMachineAuth.String():
+		return "Machine is not yet authorized by tailnet admin.", false
+	case ipn.Running.String(), ipn.Starting.String():
+		return st.BackendState, true
+	}
+}
+
 func dnsOrQuoteHostname(st *ipnstate.Status, ps *ipnstate.PeerStatus) string {
 	baseName := dnsname.TrimSuffix(ps.DNSName, st.MagicDNSSuffix)
 	if baseName != "" {

cmd/tailscale/cli/up.go

@@ -6,6 +6,8 @@ package cli
 
 import (
 	"context"
+	"encoding/base64"
+	"encoding/json"
 	"errors"
 	"flag"
 	"fmt"
@@ -22,12 +24,15 @@ import (
 	qrcode "github.com/skip2/go-qrcode"
 	"inet.af/netaddr"
 	"tailscale.com/client/tailscale"
+	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/safesocket"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/preftype"
+	"tailscale.com/util/dnsname"
+	"tailscale.com/version"
 	"tailscale.com/version/distro"
 )
 
@@ -46,8 +51,10 @@ down").
 
 If flags are specified, the flags must be the complete set of desired
 settings. An error is returned if any setting would be changed as a
-result of an unspecified flag's default value, unless the --reset
-flag is also used.
+result of an unspecified flag's default value, unless the --reset flag
+is also used. (The flags --authkey, --force-reauth, and --qr are not
+considered settings that need to be re-specified when modifying
+settings.)
 `),
 	FlagSet: upFlagSet,
 	Exec:    runUp,
@@ -60,22 +67,41 @@ func effectiveGOOS() string {
 	return runtime.GOOS
 }
 
+// acceptRouteDefault returns the CLI's default value of --accept-routes as
+// a function of the platform it's running on.
+func acceptRouteDefault(goos string) bool {
+	switch goos {
+	case "windows":
+		return true
+	case "darwin":
+		return version.IsSandboxedMacOS()
+	default:
+		return false
+	}
+}
+
 var upFlagSet = newUpFlagSet(effectiveGOOS(), &upArgs)
 
+func inTest() bool { return flag.Lookup("test.v") != nil }
+
 func newUpFlagSet(goos string, upArgs *upArgsT) *flag.FlagSet {
 	upf := newFlagSet("up")
 
 	upf.BoolVar(&upArgs.qr, "qr", false, "show QR code for login URLs")
+	upf.BoolVar(&upArgs.json, "json", false, "output in JSON format (WARNING: format subject to change)")
 	upf.BoolVar(&upArgs.forceReauth, "force-reauth", false, "force reauthentication")
 	upf.BoolVar(&upArgs.reset, "reset", false, "reset unspecified settings to their default values")
 
 	upf.StringVar(&upArgs.server, "login-server", ipn.DefaultControlURL, "base URL of control server")
-	upf.BoolVar(&upArgs.acceptRoutes, "accept-routes", false, "accept routes advertised by other Tailscale nodes")
+	upf.BoolVar(&upArgs.acceptRoutes, "accept-routes", acceptRouteDefault(goos), "accept routes advertised by other Tailscale nodes")
 	upf.BoolVar(&upArgs.acceptDNS, "accept-dns", true, "accept DNS configuration from the admin panel")
 	upf.BoolVar(&upArgs.singleRoutes, "host-routes", true, "install host routes to other Tailscale nodes")
-	upf.StringVar(&upArgs.exitNodeIP, "exit-node", "", "Tailscale IP of the exit node for internet traffic, or empty string to not use an exit node")
+	upf.StringVar(&upArgs.exitNodeIP, "exit-node", "", "Tailscale exit node (IP or base name) for internet traffic, or empty string to not use an exit node")
 	upf.BoolVar(&upArgs.exitNodeAllowLANAccess, "exit-node-allow-lan-access", false, "Allow direct access to the local network when routing traffic via an exit node")
 	upf.BoolVar(&upArgs.shieldsUp, "shields-up", false, "don't allow incoming connections")
+	if envknob.UseWIPCode() || inTest() {
+		upf.BoolVar(&upArgs.runSSH, "ssh", false, "run an SSH server, permitting access per tailnet admin's declared policy")
+	}
 	upf.StringVar(&upArgs.advertiseTags, "advertise-tags", "", "comma-separated ACL tags to request; each must start with \"tag:\" (e.g. \"tag:eng,tag:montreal,tag:ssh\")")
 	upf.StringVar(&upArgs.authKeyOrFile, "authkey", "", `node authorization key; if it begins with "file:", then it's a path to a file containing the authkey`)
 	upf.StringVar(&upArgs.hostname, "hostname", "", "hostname to use instead of the one provided by the OS")
@@ -111,6 +137,7 @@ type upArgsT struct {
 	exitNodeIP             string
 	exitNodeAllowLANAccess bool
 	shieldsUp              bool
+	runSSH                 bool
 	forceReauth            bool
 	forceDaemon            bool
 	advertiseRoutes        string
@@ -121,6 +148,7 @@ type upArgsT struct {
 	authKeyOrFile          string // "secret" or "file:/path/to/secret"
 	hostname               string
 	opUser                 string
+	json                   bool
 }
 
 func (a upArgsT) getAuthKey() (string, error) {
@@ -138,6 +166,33 @@ func (a upArgsT) getAuthKey() (string, error) {
 
 var upArgs upArgsT
 
+// Fields output when `tailscale up --json` is used. Two JSON blocks will be output.
+//
+// When "tailscale up" is run it first outputs a block with AuthURL and QR populated,
+// providing the link for where to authenticate this client. BackendState would be
+// valid but boring, as it will almost certainly be "NeedsLogin". Error would be
+// populated if something goes badly wrong.
+//
+// When the client is authenticated by having someone visit the AuthURL, a second
+// JSON block will be output. The AuthURL and QR fields will not be present, the
+// BackendState and Error fields will give the result of the authentication.
+// Ex:
+// {
+//    "AuthURL": "https://login.tailscale.com/a/0123456789abcdef",
+//    "QR": "data:image/png;base64,0123...cdef"
+//    "BackendState": "NeedsLogin"
+// }
+// {
+//    "BackendState": "Running"
+// }
+//
+type upOutputJSON struct {
+	AuthURL      string `json:",omitempty"` // Authentication URL of the form https://login.tailscale.com/a/0123456789
+	QR           string `json:",omitempty"` // a DataURL (base64) PNG of a QR code AuthURL
+	BackendState string `json:",omitempty"` // name of state like Running or NeedsMachineAuth
+	Error        string `json:",omitempty"` // description of an error
+}
+
 func warnf(format string, args ...interface{}) {
 	printf("Warning: "+format+"\n", args...)
 }
@@ -190,6 +245,65 @@ func calcAdvertiseRoutes(advertiseRoutes string, advertiseDefaultRoute bool) ([]
 	return routes, nil
 }
 
+// peerWithTailscaleIP returns the peer in st with the provided
+// Tailscale IP.
+func peerWithTailscaleIP(st *ipnstate.Status, ip netaddr.IP) (ps *ipnstate.PeerStatus, ok bool) {
+	for _, ps := range st.Peer {
+		for _, ip2 := range ps.TailscaleIPs {
+			if ip == ip2 {
+				return ps, true
+			}
+		}
+	}
+	return nil, false
+}
+
+// exitNodeIPOfArg maps from a user-provided CLI flag value to an IP
+// address they want to use as an exit node.
+func exitNodeIPOfArg(arg string, st *ipnstate.Status) (ip netaddr.IP, err error) {
+	if arg == "" {
+		return ip, errors.New("invalid use of exitNodeIPOfArg with empty string")
+	}
+	ip, err = netaddr.ParseIP(arg)
+	if err == nil {
+		// If we're online already and have a netmap, double check that the IP
+		// address specified is valid.
+		if st.BackendState == "Running" {
+			ps, ok := peerWithTailscaleIP(st, ip)
+			if !ok {
+				return ip, fmt.Errorf("no node found in netmap with IP %v", ip)
+			}
+			if !ps.ExitNodeOption {
+				return ip, fmt.Errorf("node %v is not advertising an exit node", ip)
+			}
+		}
+		return ip, err
+	}
+	match := 0
+	for _, ps := range st.Peer {
+		baseName := dnsname.TrimSuffix(ps.DNSName, st.MagicDNSSuffix)
+		if !strings.EqualFold(arg, baseName) {
+			continue
+		}
+		match++
+		if len(ps.TailscaleIPs) == 0 {
+			return ip, fmt.Errorf("node %q has no Tailscale IP?", arg)
+		}
+		if !ps.ExitNodeOption {
+			return ip, fmt.Errorf("node %q is not advertising an exit node", arg)
+		}
+		ip = ps.TailscaleIPs[0]
+	}
+	switch match {
+	case 0:
+		return ip, fmt.Errorf("invalid value %q for --exit-node; must be IP or unique node name", arg)
+	case 1:
+		return ip, nil
+	default:
+		return ip, fmt.Errorf("ambiguous exit node name %q", arg)
+	}
+}
+
 // prefsFromUpArgs returns the ipn.Prefs for the provided args.
 //
 // Note that the parameters upArgs and warnf are named intentionally
@@ -205,9 +319,9 @@ func prefsFromUpArgs(upArgs upArgsT, warnf logger.Logf, st *ipnstate.Status, goo
 	var exitNodeIP netaddr.IP
 	if upArgs.exitNodeIP != "" {
 		var err error
-		exitNodeIP, err = netaddr.ParseIP(upArgs.exitNodeIP)
+		exitNodeIP, err = exitNodeIPOfArg(upArgs.exitNodeIP, st)
 		if err != nil {
-			return nil, fmt.Errorf("invalid IP address %q for --exit-node: %v", upArgs.exitNodeIP, err)
+			return nil, err
 		}
 	} else if upArgs.exitNodeAllowLANAccess {
 		return nil, fmt.Errorf("--exit-node-allow-lan-access can only be used with --exit-node")
@@ -245,6 +359,7 @@ func prefsFromUpArgs(upArgs upArgsT, warnf logger.Logf, st *ipnstate.Status, goo
 	prefs.CorpDNS = upArgs.acceptDNS
 	prefs.AllowSingleHosts = upArgs.singleRoutes
 	prefs.ShieldsUp = upArgs.shieldsUp
+	prefs.RunSSH = upArgs.runSSH
 	prefs.AdvertiseRoutes = routes
 	prefs.AdvertiseTags = tags
 	prefs.Hostname = upArgs.hostname
@@ -306,7 +421,6 @@ func updatePrefs(prefs, curPrefs *ipn.Prefs, env upCheckEnv) (simpleUp bool, jus
 
 	justEdit := env.backendState == ipn.Running.String() &&
 		!env.upArgs.forceReauth &&
-		!env.upArgs.reset &&
 		env.upArgs.authKeyOrFile == "" &&
 		!controlURLChanged &&
 		!tagsChanged
@@ -380,11 +494,12 @@ func runUp(ctx context.Context, args []string) error {
 
 	env := upCheckEnv{
 		goos:          effectiveGOOS(),
+		distro:        distro.Get(),
 		user:          os.Getenv("USER"),
 		flagSet:       upFlagSet,
 		upArgs:        upArgs,
 		backendState:  st.BackendState,
-		curExitNodeIP: exitNodeIP(prefs, st),
+		curExitNodeIP: exitNodeIP(curPrefs, st),
 	}
 	simpleUp, justEditMP, err := updatePrefs(prefs, curPrefs, env)
 	if err != nil {
@@ -435,10 +550,16 @@ func runUp(ctx context.Context, args []string) error {
 				startLoginInteractive()
 			case ipn.NeedsMachineAuth:
 				printed = true
-				fmt.Fprintf(Stderr, "\nTo authorize your machine, visit (as admin):\n\n\t%s\n\n", prefs.AdminPageURL())
+				if env.upArgs.json {
+					printUpDoneJSON(ipn.NeedsMachineAuth, "")
+				} else {
+					fmt.Fprintf(Stderr, "\nTo authorize your machine, visit (as admin):\n\n\t%s\n\n", prefs.AdminPageURL())
+				}
 			case ipn.Running:
 				// Done full authentication process
-				if printed {
+				if env.upArgs.json {
+					printUpDoneJSON(ipn.Running, "")
+				} else if printed {
 					// Only need to print an update if we printed the "please click" message earlier.
 					fmt.Fprintf(Stderr, "Success.\n")
 				}
@@ -451,15 +572,33 @@ func runUp(ctx context.Context, args []string) error {
 		}
 		if url := n.BrowseToURL; url != nil && printAuthURL(*url) {
 			printed = true
-			fmt.Fprintf(Stderr, "\nTo authenticate, visit:\n\n\t%s\n\n", *url)
-			if upArgs.qr {
+			if upArgs.json {
+				js := &upOutputJSON{AuthURL: *url, BackendState: st.BackendState}
+
 				q, err := qrcode.New(*url, qrcode.Medium)
-				if err != nil {
-					log.Printf("QR code error: %v", err)
-				} else {
-					fmt.Fprintf(Stderr, "%s\n", q.ToString(false))
+				if err == nil {
+					png, err := q.PNG(128)
+					if err == nil {
+						js.QR = "data:image/png;base64," + base64.StdEncoding.EncodeToString(png)
+					}
 				}
 
+				data, err := json.MarshalIndent(js, "", "\t")
+				if err != nil {
+					log.Printf("upOutputJSON marshalling error: %v", err)
+				} else {
+					fmt.Println(string(data))
+				}
+			} else {
+				fmt.Fprintf(Stderr, "\nTo authenticate, visit:\n\n\t%s\n\n", *url)
+				if upArgs.qr {
+					q, err := qrcode.New(*url, qrcode.Medium)
+					if err != nil {
+						log.Printf("QR code error: %v", err)
+					} else {
+						fmt.Fprintf(Stderr, "%s\n", q.ToString(false))
+					}
+				}
 			}
 		}
 	})
@@ -546,6 +685,16 @@ func runUp(ctx context.Context, args []string) error {
 	}
 }
 
+func printUpDoneJSON(state ipn.State, errorString string) {
+	js := &upOutputJSON{BackendState: state.String(), Error: errorString}
+	data, err := json.MarshalIndent(js, "", "  ")
+	if err != nil {
+		log.Printf("printUpDoneJSON marshalling error: %v", err)
+	} else {
+		fmt.Println(string(data))
+	}
+}
+
 var (
 	prefsOfFlag = map[string][]string{} // "exit-node" => ExitNodeIP, ExitNodeID
 )
@@ -571,6 +720,7 @@ func init() {
 	addPrefFlagMapping("exit-node-allow-lan-access", "ExitNodeAllowLANAccess")
 	addPrefFlagMapping("unattended", "ForceDaemon")
 	addPrefFlagMapping("operator", "OperatorUser")
+	addPrefFlagMapping("ssh", "RunSSH")
 }
 
 func addPrefFlagMapping(flagName string, prefNames ...string) {
@@ -588,7 +738,7 @@ func addPrefFlagMapping(flagName string, prefNames ...string) {
 // correspond to an ipn.Pref.
 func preflessFlag(flagName string) bool {
 	switch flagName {
-	case "authkey", "force-reauth", "reset", "qr":
+	case "authkey", "force-reauth", "reset", "qr", "json":
 		return true
 	}
 	return false
@@ -622,6 +772,7 @@ type upCheckEnv struct {
 	upArgs        upArgsT
 	backendState  string
 	curExitNodeIP netaddr.IP
+	distro        distro.Distro
 }
 
 // checkForAccidentalSettingReverts (the "up checker") checks for
@@ -672,6 +823,10 @@ func checkForAccidentalSettingReverts(newPrefs, curPrefs *ipn.Prefs, env upCheck
 		if flagName == "login-server" && ipn.IsLoginServerSynonym(valCur) && ipn.IsLoginServerSynonym(valNew) {
 			continue
 		}
+		if flagName == "accept-routes" && valNew == false && env.goos == "linux" && env.distro == distro.Synology {
+			// Issue 3176. Old prefs had 'RouteAll: true' on disk, so ignore that.
+			continue
+		}
 		missing = append(missing, fmtFlagValueArg(flagName, valCur))
 	}
 	if len(missing) == 0 {
@@ -756,6 +911,8 @@ func prefsToFlags(env upCheckEnv, prefs *ipn.Prefs) (flagVal map[string]interfac
 		switch f.Name {
 		default:
 			panic(fmt.Sprintf("unhandled flag %q", f.Name))
+		case "ssh":
+			set(prefs.RunSSH)
 		case "login-server":
 			set(prefs.ControlURL)
 		case "accept-routes":

cmd/tailscale/cli/web.go

@@ -270,14 +270,14 @@ func synoTokenRedirect(w http.ResponseWriter, r *http.Request) bool {
 	// We need a SynoToken for authenticate.cgi.
 	// So we tell the client to get one.
 	serverURL := r.URL.Scheme + "://" + r.URL.Host
-	fmt.Fprintf(w, synoTokenRedirectHTML, serverURL)
+	synoTokenRedirectHTML.Execute(w, serverURL)
 	return true
 }
 
-const synoTokenRedirectHTML = `<html><body>
+var synoTokenRedirectHTML = template.Must(template.New("redirect").Parse(`<html><body>
 Redirecting with session token...
 <script>
-var serverURL = %q;
+var serverURL = {{ . }};
 var req = new XMLHttpRequest();
 req.overrideMimeType("application/json");
 req.open("GET", serverURL + "/webman/login.cgi", true);
@@ -289,7 +289,7 @@ req.onload = function() {
 req.send(null);
 </script>
 </body></html>
-`
+`))
 
 func webHandler(w http.ResponseWriter, r *http.Request) {
 	if authRedirect(w, r) {
@@ -375,7 +375,7 @@ func webHandler(w http.ResponseWriter, r *http.Request) {
 			data.AdvertiseExitNode = true
 		} else {
 			if data.AdvertiseRoutes != "" {
-				data.AdvertiseRoutes = ","
+				data.AdvertiseRoutes += ","
 			}
 			data.AdvertiseRoutes += r.String()
 		}

cmd/tailscale/depaware.txt

@@ -3,6 +3,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
    W 💣 github.com/alexbrainman/sspi                                 from github.com/alexbrainman/sspi/negotiate+
    W    github.com/alexbrainman/sspi/internal/common                 from github.com/alexbrainman/sspi/negotiate
    W 💣 github.com/alexbrainman/sspi/negotiate                       from tailscale.com/net/tshttpproxy
+        github.com/golang/groupcache/lru                             from tailscale.com/net/dnscache
         github.com/kballard/go-shellquote                            from tailscale.com/cmd/tailscale/cli
    L    github.com/klauspost/compress/flate                          from nhooyr.io/websocket
      💣 github.com/mitchellh/go-ps                                   from tailscale.com/cmd/tailscale/cli+
@@ -37,6 +38,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/derp/derphttp                                  from tailscale.com/net/netcheck
    L    tailscale.com/derp/wsconn                                    from tailscale.com/derp/derphttp
         tailscale.com/disco                                          from tailscale.com/derp
+        tailscale.com/envknob                                        from tailscale.com/cmd/tailscale/cli+
         tailscale.com/hostinfo                                       from tailscale.com/net/interfaces
         tailscale.com/ipn                                            from tailscale.com/cmd/tailscale/cli+
         tailscale.com/ipn/ipnstate                                   from tailscale.com/cmd/tailscale/cli+
@@ -46,6 +48,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/net/flowtrack                                  from tailscale.com/wgengine/filter+
      💣 tailscale.com/net/interfaces                                 from tailscale.com/cmd/tailscale/cli+
         tailscale.com/net/netcheck                                   from tailscale.com/cmd/tailscale/cli
+        tailscale.com/net/neterror                                   from tailscale.com/net/netcheck+
         tailscale.com/net/netknob                                    from tailscale.com/net/netns
         tailscale.com/net/netns                                      from tailscale.com/derp/derphttp+
         tailscale.com/net/packet                                     from tailscale.com/wgengine/filter
@@ -72,7 +75,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         tailscale.com/types/persist                                  from tailscale.com/ipn
         tailscale.com/types/preftype                                 from tailscale.com/cmd/tailscale/cli+
         tailscale.com/types/structs                                  from tailscale.com/ipn+
-        tailscale.com/util/clientmetric                              from tailscale.com/net/netcheck
+        tailscale.com/util/clientmetric                              from tailscale.com/net/netcheck+
         tailscale.com/util/dnsname                                   from tailscale.com/cmd/tailscale/cli+
    W    tailscale.com/util/endian                                    from tailscale.com/net/netns
         tailscale.com/util/groupmember                               from tailscale.com/cmd/tailscale/cli
@@ -91,7 +94,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         golang.org/x/crypto/nacl/secretbox                           from golang.org/x/crypto/nacl/box
         golang.org/x/crypto/poly1305                                 from golang.org/x/crypto/chacha20poly1305
         golang.org/x/crypto/salsa20/salsa                            from golang.org/x/crypto/nacl/box+
-        golang.org/x/net/dns/dnsmessage                              from net
+        golang.org/x/net/dns/dnsmessage                              from net+
         golang.org/x/net/http/httpguts                               from net/http+
         golang.org/x/net/http/httpproxy                              from net/http
         golang.org/x/net/http2/hpack                                 from net/http
@@ -103,7 +106,7 @@ tailscale.com/cmd/tailscale dependencies: (generated by github.com/tailscale/dep
         golang.org/x/sys/cpu                                         from golang.org/x/crypto/blake2b+
   LD    golang.org/x/sys/unix                                        from tailscale.com/net/netns+
    W    golang.org/x/sys/windows                                     from golang.org/x/sys/windows/registry+
-   W    golang.org/x/sys/windows/registry                            from golang.zx2c4.com/wireguard/windows/tunnel/winipcfg
+   W    golang.org/x/sys/windows/registry                            from golang.zx2c4.com/wireguard/windows/tunnel/winipcfg+
         golang.org/x/text/secure/bidirule                            from golang.org/x/net/idna
         golang.org/x/text/transform                                  from golang.org/x/text/secure/bidirule+
         golang.org/x/text/unicode/bidi                               from golang.org/x/net/idna+

cmd/tailscaled/debug.go

@@ -24,6 +24,7 @@ import (
 
 	"inet.af/netaddr"
 	"tailscale.com/derp/derphttp"
+	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/net/interfaces"
 	"tailscale.com/net/portmapper"
@@ -224,7 +225,7 @@ func debugPortmap(ctx context.Context) error {
 	defer cancel()
 
 	portmapper.VerboseLogs = true
-	switch os.Getenv("TS_DEBUG_PORTMAP_TYPE") {
+	switch envknob.String("TS_DEBUG_PORTMAP_TYPE") {
 	case "":
 	case "pmp":
 		portmapper.DisablePCP = true

cmd/tailscaled/depaware.txt

@@ -3,6 +3,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
    W 💣 github.com/alexbrainman/sspi                                 from github.com/alexbrainman/sspi/internal/common+
    W    github.com/alexbrainman/sspi/internal/common                 from github.com/alexbrainman/sspi/negotiate
    W 💣 github.com/alexbrainman/sspi/negotiate                       from tailscale.com/net/tshttpproxy
+   L    github.com/anmitsu/go-shlex                                  from github.com/gliderlabs/ssh
    L    github.com/aws/aws-sdk-go-v2                                 from github.com/aws/aws-sdk-go-v2/internal/ini
    L    github.com/aws/aws-sdk-go-v2/aws                             from github.com/aws/aws-sdk-go-v2/aws/middleware+
    L    github.com/aws/aws-sdk-go-v2/aws/arn                         from tailscale.com/ipn/store/aws
@@ -25,7 +26,8 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
    L    github.com/aws/aws-sdk-go-v2/credentials/stscreds            from github.com/aws/aws-sdk-go-v2/config
    L    github.com/aws/aws-sdk-go-v2/feature/ec2/imds                from github.com/aws/aws-sdk-go-v2/config+
    L    github.com/aws/aws-sdk-go-v2/feature/ec2/imds/internal/config from github.com/aws/aws-sdk-go-v2/feature/ec2/imds
-   L    github.com/aws/aws-sdk-go-v2/internal/endpoints              from github.com/aws/aws-sdk-go-v2/service/ssm/internal/endpoints+
+   L    github.com/aws/aws-sdk-go-v2/internal/configsources          from github.com/aws/aws-sdk-go-v2/service/ssm+
+   L    github.com/aws/aws-sdk-go-v2/internal/endpoints/v2           from github.com/aws/aws-sdk-go-v2/service/ssm/internal/endpoints+
    L    github.com/aws/aws-sdk-go-v2/internal/ini                    from github.com/aws/aws-sdk-go-v2/config
    L    github.com/aws/aws-sdk-go-v2/internal/rand                   from github.com/aws/aws-sdk-go-v2/aws+
    L    github.com/aws/aws-sdk-go-v2/internal/sdk                    from github.com/aws/aws-sdk-go-v2/aws+
@@ -59,10 +61,13 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
    L    github.com/aws/smithy-go/transport/http/internal/io          from github.com/aws/smithy-go/transport/http
    L    github.com/aws/smithy-go/waiter                              from github.com/aws/aws-sdk-go-v2/service/ssm
    L    github.com/coreos/go-iptables/iptables                       from tailscale.com/wgengine/router
+   L 💣 github.com/creack/pty                                        from tailscale.com/wgengine/netstack
+   L    github.com/gliderlabs/ssh                                    from tailscale.com/wgengine/netstack
    W 💣 github.com/go-ole/go-ole                                     from github.com/go-ole/go-ole/oleutil+
    W 💣 github.com/go-ole/go-ole/oleutil                             from tailscale.com/wgengine/winnet
    L 💣 github.com/godbus/dbus/v5                                    from tailscale.com/net/dns
-        github.com/google/btree                                      from inet.af/netstack/tcpip/header+
+        github.com/golang/groupcache/lru                             from tailscale.com/net/dnscache
+        github.com/google/btree                                      from gvisor.dev/gvisor/pkg/tcpip/header+
    L    github.com/insomniacslk/dhcp/dhcpv4                          from tailscale.com/net/tstun
    L    github.com/insomniacslk/dhcp/iana                            from github.com/insomniacslk/dhcp/dhcpv4
    L    github.com/insomniacslk/dhcp/interfaces                      from github.com/insomniacslk/dhcp/dhcpv4
@@ -113,39 +118,46 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         golang.zx2c4.com/wireguard/tai64n                            from golang.zx2c4.com/wireguard/device
      💣 golang.zx2c4.com/wireguard/tun                               from golang.zx2c4.com/wireguard/device+
    W 💣 golang.zx2c4.com/wireguard/windows/tunnel/winipcfg           from tailscale.com/cmd/tailscaled+
+        gvisor.dev/gvisor/pkg/atomicbitops                           from gvisor.dev/gvisor/pkg/tcpip+
+     💣 gvisor.dev/gvisor/pkg/buffer                                 from gvisor.dev/gvisor/pkg/tcpip/stack
+        gvisor.dev/gvisor/pkg/context                                from gvisor.dev/gvisor/pkg/refs+
+     💣 gvisor.dev/gvisor/pkg/gohacks                                from gvisor.dev/gvisor/pkg/state/wire+
+        gvisor.dev/gvisor/pkg/linewriter                             from gvisor.dev/gvisor/pkg/log
+        gvisor.dev/gvisor/pkg/log                                    from gvisor.dev/gvisor/pkg/context+
+        gvisor.dev/gvisor/pkg/rand                                   from gvisor.dev/gvisor/pkg/tcpip/network/hash+
+        gvisor.dev/gvisor/pkg/refs                                   from gvisor.dev/gvisor/pkg/refsvfs2
+        gvisor.dev/gvisor/pkg/refsvfs2                               from gvisor.dev/gvisor/pkg/tcpip/stack
+     💣 gvisor.dev/gvisor/pkg/sleep                                  from gvisor.dev/gvisor/pkg/tcpip/transport/tcp
+     💣 gvisor.dev/gvisor/pkg/state                                  from gvisor.dev/gvisor/pkg/atomicbitops+
+        gvisor.dev/gvisor/pkg/state/wire                             from gvisor.dev/gvisor/pkg/state
+     💣 gvisor.dev/gvisor/pkg/sync                                   from gvisor.dev/gvisor/pkg/linewriter+
+        gvisor.dev/gvisor/pkg/tcpip                                  from gvisor.dev/gvisor/pkg/tcpip/adapters/gonet+
+        gvisor.dev/gvisor/pkg/tcpip/adapters/gonet                   from tailscale.com/wgengine/netstack
+     💣 gvisor.dev/gvisor/pkg/tcpip/buffer                           from gvisor.dev/gvisor/pkg/tcpip/adapters/gonet+
+        gvisor.dev/gvisor/pkg/tcpip/hash/jenkins                     from gvisor.dev/gvisor/pkg/tcpip/stack+
+        gvisor.dev/gvisor/pkg/tcpip/header                           from gvisor.dev/gvisor/pkg/tcpip/header/parse+
+        gvisor.dev/gvisor/pkg/tcpip/header/parse                     from gvisor.dev/gvisor/pkg/tcpip/network/ipv4+
+        gvisor.dev/gvisor/pkg/tcpip/internal/tcp                     from gvisor.dev/gvisor/pkg/tcpip/stack+
+        gvisor.dev/gvisor/pkg/tcpip/link/channel                     from tailscale.com/wgengine/netstack
+        gvisor.dev/gvisor/pkg/tcpip/network/hash                     from gvisor.dev/gvisor/pkg/tcpip/network/ipv4+
+        gvisor.dev/gvisor/pkg/tcpip/network/internal/fragmentation   from gvisor.dev/gvisor/pkg/tcpip/network/ipv4+
+        gvisor.dev/gvisor/pkg/tcpip/network/internal/ip              from gvisor.dev/gvisor/pkg/tcpip/network/ipv4+
+        gvisor.dev/gvisor/pkg/tcpip/network/ipv4                     from tailscale.com/net/tstun+
+        gvisor.dev/gvisor/pkg/tcpip/network/ipv6                     from tailscale.com/wgengine/netstack
+        gvisor.dev/gvisor/pkg/tcpip/ports                            from gvisor.dev/gvisor/pkg/tcpip/stack+
+        gvisor.dev/gvisor/pkg/tcpip/seqnum                           from gvisor.dev/gvisor/pkg/tcpip/header+
+     💣 gvisor.dev/gvisor/pkg/tcpip/stack                            from gvisor.dev/gvisor/pkg/tcpip/adapters/gonet+
+        gvisor.dev/gvisor/pkg/tcpip/transport                        from gvisor.dev/gvisor/pkg/tcpip/transport/icmp+
+        gvisor.dev/gvisor/pkg/tcpip/transport/icmp                   from tailscale.com/wgengine/netstack
+        gvisor.dev/gvisor/pkg/tcpip/transport/internal/network       from gvisor.dev/gvisor/pkg/tcpip/transport/icmp+
+        gvisor.dev/gvisor/pkg/tcpip/transport/internal/noop          from gvisor.dev/gvisor/pkg/tcpip/transport/raw
+        gvisor.dev/gvisor/pkg/tcpip/transport/packet                 from gvisor.dev/gvisor/pkg/tcpip/transport/raw
+        gvisor.dev/gvisor/pkg/tcpip/transport/raw                    from gvisor.dev/gvisor/pkg/tcpip/transport/icmp+
+     💣 gvisor.dev/gvisor/pkg/tcpip/transport/tcp                    from gvisor.dev/gvisor/pkg/tcpip/adapters/gonet+
+        gvisor.dev/gvisor/pkg/tcpip/transport/tcpconntrack           from gvisor.dev/gvisor/pkg/tcpip/stack
+        gvisor.dev/gvisor/pkg/tcpip/transport/udp                    from gvisor.dev/gvisor/pkg/tcpip/adapters/gonet+
+        gvisor.dev/gvisor/pkg/waiter                                 from gvisor.dev/gvisor/pkg/context+
         inet.af/netaddr                                              from inet.af/wf+
-        inet.af/netstack/atomicbitops                                from inet.af/netstack/tcpip+
-     💣 inet.af/netstack/buffer                                      from inet.af/netstack/tcpip/stack
-     💣 inet.af/netstack/gohacks                                     from inet.af/netstack/state/wire+
-        inet.af/netstack/linewriter                                  from inet.af/netstack/log
-        inet.af/netstack/log                                         from inet.af/netstack/state+
-        inet.af/netstack/rand                                        from inet.af/netstack/tcpip/network/hash+
-     💣 inet.af/netstack/sleep                                       from inet.af/netstack/tcpip/transport/tcp
-     💣 inet.af/netstack/state                                       from inet.af/netstack/atomicbitops+
-        inet.af/netstack/state/wire                                  from inet.af/netstack/state
-     💣 inet.af/netstack/sync                                        from inet.af/netstack/linewriter+
-        inet.af/netstack/tcpip                                       from inet.af/netstack/tcpip/adapters/gonet+
-        inet.af/netstack/tcpip/adapters/gonet                        from tailscale.com/wgengine/netstack
-     💣 inet.af/netstack/tcpip/buffer                                from inet.af/netstack/tcpip/adapters/gonet+
-        inet.af/netstack/tcpip/hash/jenkins                          from inet.af/netstack/tcpip/stack+
-        inet.af/netstack/tcpip/header                                from inet.af/netstack/tcpip/header/parse+
-        inet.af/netstack/tcpip/header/parse                          from inet.af/netstack/tcpip/network/ipv4+
-        inet.af/netstack/tcpip/link/channel                          from tailscale.com/wgengine/netstack
-        inet.af/netstack/tcpip/network/hash                          from inet.af/netstack/tcpip/network/ipv4+
-        inet.af/netstack/tcpip/network/internal/fragmentation        from inet.af/netstack/tcpip/network/ipv4+
-        inet.af/netstack/tcpip/network/internal/ip                   from inet.af/netstack/tcpip/network/ipv4+
-        inet.af/netstack/tcpip/network/ipv4                          from tailscale.com/net/tstun+
-        inet.af/netstack/tcpip/network/ipv6                          from tailscale.com/wgengine/netstack
-        inet.af/netstack/tcpip/ports                                 from inet.af/netstack/tcpip/stack+
-        inet.af/netstack/tcpip/seqnum                                from inet.af/netstack/tcpip/header+
-     💣 inet.af/netstack/tcpip/stack                                 from inet.af/netstack/tcpip/adapters/gonet+
-        inet.af/netstack/tcpip/transport/icmp                        from tailscale.com/wgengine/netstack
-        inet.af/netstack/tcpip/transport/packet                      from inet.af/netstack/tcpip/transport/raw
-        inet.af/netstack/tcpip/transport/raw                         from inet.af/netstack/tcpip/transport/icmp+
-     💣 inet.af/netstack/tcpip/transport/tcp                         from inet.af/netstack/tcpip/adapters/gonet+
-        inet.af/netstack/tcpip/transport/tcpconntrack                from inet.af/netstack/tcpip/stack
-        inet.af/netstack/tcpip/transport/udp                         from inet.af/netstack/tcpip/adapters/gonet+
-        inet.af/netstack/waiter                                      from inet.af/netstack/tcpip+
         inet.af/peercred                                             from tailscale.com/ipn/ipnserver
    W 💣 inet.af/wf                                                   from tailscale.com/wf
    L    nhooyr.io/websocket                                          from tailscale.com/derp/derphttp+
@@ -162,6 +174,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/derp/derphttp                                  from tailscale.com/cmd/tailscaled+
    L    tailscale.com/derp/wsconn                                    from tailscale.com/derp/derphttp
         tailscale.com/disco                                          from tailscale.com/derp+
+        tailscale.com/envknob                                        from tailscale.com/cmd/tailscaled+
         tailscale.com/health                                         from tailscale.com/control/controlclient+
         tailscale.com/hostinfo                                       from tailscale.com/control/controlclient+
         tailscale.com/ipn                                            from tailscale.com/client/tailscale+
@@ -172,13 +185,13 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/ipn/policy                                     from tailscale.com/ipn/ipnlocal
         tailscale.com/ipn/store/aws                                  from tailscale.com/ipn/ipnserver
         tailscale.com/kube                                           from tailscale.com/ipn
-        tailscale.com/log/filelogger                                 from tailscale.com/ipn/ipnserver
+        tailscale.com/log/filelogger                                 from tailscale.com/logpolicy
         tailscale.com/log/logheap                                    from tailscale.com/control/controlclient
-        tailscale.com/logpolicy                                      from tailscale.com/cmd/tailscaled
+        tailscale.com/logpolicy                                      from tailscale.com/cmd/tailscaled+
         tailscale.com/logtail                                        from tailscale.com/logpolicy+
         tailscale.com/logtail/backoff                                from tailscale.com/cmd/tailscaled+
         tailscale.com/logtail/filch                                  from tailscale.com/logpolicy
-     💣 tailscale.com/metrics                                        from tailscale.com/derp
+     💣 tailscale.com/metrics                                        from tailscale.com/derp+
         tailscale.com/net/dns                                        from tailscale.com/cmd/tailscaled+
         tailscale.com/net/dns/resolver                               from tailscale.com/net/dns+
         tailscale.com/net/dnscache                                   from tailscale.com/control/controlclient+
@@ -186,16 +199,18 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/net/flowtrack                                  from tailscale.com/net/packet+
      💣 tailscale.com/net/interfaces                                 from tailscale.com/cmd/tailscaled+
         tailscale.com/net/netcheck                                   from tailscale.com/wgengine/magicsock
-        tailscale.com/net/netknob                                    from tailscale.com/ipn/localapi+
+        tailscale.com/net/neterror                                   from tailscale.com/net/netcheck+
+        tailscale.com/net/netknob                                    from tailscale.com/logpolicy+
         tailscale.com/net/netns                                      from tailscale.com/cmd/tailscaled+
      💣 tailscale.com/net/netstat                                    from tailscale.com/ipn/ipnserver
         tailscale.com/net/packet                                     from tailscale.com/net/tstun+
         tailscale.com/net/portmapper                                 from tailscale.com/cmd/tailscaled+
-        tailscale.com/net/socks5                                     from tailscale.com/net/socks5/tssocks
-        tailscale.com/net/socks5/tssocks                             from tailscale.com/cmd/tailscaled
+        tailscale.com/net/proxymux                                   from tailscale.com/cmd/tailscaled
+        tailscale.com/net/socks5                                     from tailscale.com/cmd/tailscaled
         tailscale.com/net/stun                                       from tailscale.com/net/netcheck+
         tailscale.com/net/tlsdial                                    from tailscale.com/control/controlclient+
         tailscale.com/net/tsaddr                                     from tailscale.com/ipn/ipnlocal+
+        tailscale.com/net/tsdial                                     from tailscale.com/cmd/tailscaled+
      💣 tailscale.com/net/tshttpproxy                                from tailscale.com/cmd/tailscaled+
         tailscale.com/net/tstun                                      from tailscale.com/cmd/tailscaled+
      💣 tailscale.com/paths                                          from tailscale.com/client/tailscale+
@@ -208,6 +223,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/tstime                                         from tailscale.com/wgengine/magicsock
      💣 tailscale.com/tstime/mono                                    from tailscale.com/net/tstun+
         tailscale.com/tstime/rate                                    from tailscale.com/wgengine/filter
+        tailscale.com/tsweb                                          from tailscale.com/cmd/tailscaled
         tailscale.com/types/dnstype                                  from tailscale.com/ipn/ipnlocal+
         tailscale.com/types/empty                                    from tailscale.com/control/controlclient+
         tailscale.com/types/flagtype                                 from tailscale.com/cmd/tailscaled
@@ -217,7 +233,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/types/netmap                                   from tailscale.com/control/controlclient+
         tailscale.com/types/nettype                                  from tailscale.com/wgengine/magicsock
         tailscale.com/types/opt                                      from tailscale.com/control/controlclient+
-        tailscale.com/types/pad32                                    from tailscale.com/derp+
+        tailscale.com/types/pad32                                    from tailscale.com/derp
         tailscale.com/types/persist                                  from tailscale.com/control/controlclient+
         tailscale.com/types/preftype                                 from tailscale.com/ipn+
         tailscale.com/types/structs                                  from tailscale.com/control/controlclient+
@@ -243,7 +259,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/wgengine/filter                                from tailscale.com/control/controlclient+
         tailscale.com/wgengine/magicsock                             from tailscale.com/wgengine+
         tailscale.com/wgengine/monitor                               from tailscale.com/cmd/tailscaled+
-        tailscale.com/wgengine/netstack                              from tailscale.com/cmd/tailscaled+
+     💣 tailscale.com/wgengine/netstack                              from tailscale.com/cmd/tailscaled
         tailscale.com/wgengine/router                                from tailscale.com/cmd/tailscaled+
         tailscale.com/wgengine/wgcfg                                 from tailscale.com/ipn/ipnlocal+
         tailscale.com/wgengine/wgcfg/nmcfg                           from tailscale.com/ipn/ipnlocal
@@ -252,21 +268,26 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         golang.org/x/crypto/acme                                     from tailscale.com/ipn/localapi
         golang.org/x/crypto/blake2b                                  from golang.org/x/crypto/nacl/box
         golang.org/x/crypto/blake2s                                  from golang.zx2c4.com/wireguard/device
-        golang.org/x/crypto/chacha20                                 from golang.org/x/crypto/chacha20poly1305
+   L    golang.org/x/crypto/blowfish                                 from golang.org/x/crypto/ssh/internal/bcrypt_pbkdf
+        golang.org/x/crypto/chacha20                                 from golang.org/x/crypto/chacha20poly1305+
         golang.org/x/crypto/chacha20poly1305                         from crypto/tls+
         golang.org/x/crypto/cryptobyte                               from crypto/ecdsa+
         golang.org/x/crypto/cryptobyte/asn1                          from crypto/ecdsa+
         golang.org/x/crypto/curve25519                               from crypto/tls+
+   L    golang.org/x/crypto/ed25519                                  from golang.org/x/crypto/ssh
         golang.org/x/crypto/hkdf                                     from crypto/tls
         golang.org/x/crypto/nacl/box                                 from tailscale.com/types/key
         golang.org/x/crypto/nacl/secretbox                           from golang.org/x/crypto/nacl/box
         golang.org/x/crypto/poly1305                                 from golang.org/x/crypto/chacha20poly1305+
         golang.org/x/crypto/salsa20/salsa                            from golang.org/x/crypto/nacl/box+
+   L    golang.org/x/crypto/ssh                                      from github.com/gliderlabs/ssh+
         golang.org/x/net/bpf                                         from github.com/mdlayher/netlink+
         golang.org/x/net/dns/dnsmessage                              from net+
         golang.org/x/net/http/httpguts                               from net/http+
         golang.org/x/net/http/httpproxy                              from net/http
-        golang.org/x/net/http2/hpack                                 from net/http
+        golang.org/x/net/http2                                       from golang.org/x/net/http2/h2c+
+        golang.org/x/net/http2/h2c                                   from tailscale.com/ipn/ipnlocal
+        golang.org/x/net/http2/hpack                                 from net/http+
         golang.org/x/net/idna                                        from golang.org/x/net/http/httpguts+
         golang.org/x/net/ipv4                                        from golang.zx2c4.com/wireguard/device
         golang.org/x/net/ipv6                                        from golang.zx2c4.com/wireguard/device+
@@ -285,26 +306,26 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         golang.org/x/text/transform                                  from golang.org/x/text/secure/bidirule+
         golang.org/x/text/unicode/bidi                               from golang.org/x/net/idna+
         golang.org/x/text/unicode/norm                               from golang.org/x/net/idna
-        golang.org/x/time/rate                                       from inet.af/netstack/tcpip/stack+
+        golang.org/x/time/rate                                       from gvisor.dev/gvisor/pkg/tcpip/stack+
         bufio                                                        from compress/flate+
         bytes                                                        from bufio+
         compress/flate                                               from compress/gzip+
         compress/gzip                                                from internal/profile+
-        container/heap                                               from inet.af/netstack/tcpip/transport/tcp
+        container/heap                                               from gvisor.dev/gvisor/pkg/tcpip/transport/tcp
         container/list                                               from crypto/tls+
         context                                                      from crypto/tls+
         crypto                                                       from crypto/ecdsa+
         crypto/aes                                                   from crypto/ecdsa+
         crypto/cipher                                                from crypto/aes+
         crypto/des                                                   from crypto/tls+
-        crypto/dsa                                                   from crypto/x509
+        crypto/dsa                                                   from crypto/x509+
         crypto/ecdsa                                                 from crypto/tls+
         crypto/ed25519                                               from crypto/tls+
         crypto/elliptic                                              from crypto/ecdsa+
         crypto/hmac                                                  from crypto/tls+
         crypto/md5                                                   from crypto/tls+
         crypto/rand                                                  from crypto/ed25519+
-        crypto/rc4                                                   from crypto/tls
+        crypto/rc4                                                   from crypto/tls+
         crypto/rsa                                                   from crypto/tls+
         crypto/sha1                                                  from crypto/tls+
         crypto/sha256                                                from crypto/tls+
@@ -328,7 +349,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         fmt                                                          from compress/flate+
         hash                                                         from crypto+
         hash/crc32                                                   from compress/gzip+
-        hash/fnv                                                     from inet.af/netstack/tcpip/network/ipv6+
+        hash/fnv                                                     from gvisor.dev/gvisor/pkg/tcpip/network/ipv6+
         hash/maphash                                                 from go4.org/mem
         html                                                         from net/http/pprof+
         io                                                           from bufio+
@@ -357,7 +378,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         path                                                         from github.com/aws/aws-sdk-go-v2/credentials/ec2rolecreds+
         path/filepath                                                from crypto/x509+
         reflect                                                      from crypto/x509+
-        regexp                                                       from github.com/aws/aws-sdk-go-v2/internal/endpoints+
+        regexp                                                       from github.com/aws/aws-sdk-go-v2/internal/endpoints/v2+
         regexp/syntax                                                from regexp
         runtime/debug                                                from github.com/klauspost/compress/zstd+
         runtime/pprof                                                from net/http/pprof+

cmd/tailscaled/tailscaled.go

@@ -23,21 +23,25 @@ import (
 	"path/filepath"
 	"runtime"
 	"runtime/debug"
-	"strconv"
 	"strings"
 	"syscall"
 	"time"
 
+	"inet.af/netaddr"
+	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnserver"
 	"tailscale.com/logpolicy"
 	"tailscale.com/logtail"
 	"tailscale.com/net/dns"
 	"tailscale.com/net/netns"
-	"tailscale.com/net/socks5/tssocks"
+	"tailscale.com/net/proxymux"
+	"tailscale.com/net/socks5"
+	"tailscale.com/net/tsdial"
 	"tailscale.com/net/tstun"
 	"tailscale.com/paths"
 	"tailscale.com/safesocket"
+	"tailscale.com/tsweb"
 	"tailscale.com/types/flagtype"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/clientmetric"
@@ -175,8 +179,7 @@ func main() {
 	osshare.SetFileSharingEnabled(false, logger.Discard)
 
 	if err != nil {
-		// No need to log; the func already did
-		os.Exit(1)
+		log.Fatal(err)
 	}
 }
 
@@ -221,7 +224,7 @@ func statePathOrDefault() string {
 func ipnServerOpts() (o ipnserver.Options) {
 	// Allow changing the OS-specific IPN behavior for tests
 	// so we can e.g. test Windows-specific behaviors on Linux.
-	goos := os.Getenv("TS_DEBUG_TAILSCALED_IPN_GOOS")
+	goos := envknob.String("TS_DEBUG_TAILSCALED_IPN_GOOS")
 	if goos == "" {
 		goos = runtime.GOOS
 	}
@@ -269,13 +272,13 @@ func run() error {
 	}
 
 	var logf logger.Logf = log.Printf
-	if v, _ := strconv.ParseBool(os.Getenv("TS_DEBUG_MEMORY")); v {
+	if envknob.Bool("TS_DEBUG_MEMORY") {
 		logf = logger.RusagePrefixLog(logf)
 	}
 	logf = logger.RateLimitedFn(logf, 5*time.Second, 5, 100)
 
 	if args.cleanup {
-		if os.Getenv("TS_PLEASE_PANIC") != "" {
+		if envknob.Bool("TS_PLEASE_PANIC") {
 			panic("TS_PLEASE_PANIC asked us to panic")
 		}
 		dns.Cleanup(logf, args.tunname)
@@ -293,45 +296,63 @@ func run() error {
 	var debugMux *http.ServeMux
 	if args.debug != "" {
 		debugMux = newDebugMux()
-		go runDebugServer(debugMux, args.debug)
 	}
 
 	linkMon, err := monitor.New(logf)
 	if err != nil {
-		log.Fatalf("creating link monitor: %v", err)
+		return fmt.Errorf("monitor.New: %w", err)
 	}
 	pol.Logtail.SetLinkMonitor(linkMon)
 
-	socksListener := mustStartTCPListener("SOCKS5", args.socksAddr)
-	httpProxyListener := mustStartTCPListener("HTTP proxy", args.httpProxyAddr)
+	socksListener, httpProxyListener := mustStartProxyListeners(args.socksAddr, args.httpProxyAddr)
 
-	e, useNetstack, err := createEngine(logf, linkMon)
+	dialer := new(tsdial.Dialer) // mutated below (before used)
+	e, useNetstack, err := createEngine(logf, linkMon, dialer)
 	if err != nil {
-		logf("wgengine.New: %v", err)
-		return err
+		return fmt.Errorf("createEngine: %w", err)
+	}
+	if _, ok := e.(wgengine.ResolvingEngine).GetResolver(); !ok {
+		panic("internal error: exit node resolver not wired up")
+	}
+	if debugMux != nil {
+		if ig, ok := e.(wgengine.InternalsGetter); ok {
+			if _, mc, ok := ig.GetInternals(); ok {
+				debugMux.HandleFunc("/debug/magicsock", mc.ServeHTTPDebug)
+			}
+		}
+		go runDebugServer(debugMux, args.debug)
 	}
 
-	ns, err := newNetstack(logf, e)
+	ns, err := newNetstack(logf, dialer, e)
 	if err != nil {
 		return fmt.Errorf("newNetstack: %w", err)
 	}
 	ns.ProcessLocalIPs = useNetstack
 	ns.ProcessSubnets = useNetstack || wrapNetstack
-	if err := ns.Start(); err != nil {
-		log.Fatalf("failed to start netstack: %v", err)
-	}
 
+	if useNetstack {
+		dialer.UseNetstackForIP = func(ip netaddr.IP) bool {
+			_, ok := e.PeerForIP(ip)
+			return ok
+		}
+		dialer.NetstackDialTCP = func(ctx context.Context, dst netaddr.IPPort) (net.Conn, error) {
+			return ns.DialContextTCP(ctx, dst)
+		}
+	}
 	if socksListener != nil || httpProxyListener != nil {
-		srv := tssocks.NewServer(logger.WithPrefix(logf, "socks5: "), e, ns)
 		if httpProxyListener != nil {
-			hs := &http.Server{Handler: httpProxyHandler(srv.Dialer)}
+			hs := &http.Server{Handler: httpProxyHandler(dialer.UserDial)}
 			go func() {
 				log.Fatalf("HTTP proxy exited: %v", hs.Serve(httpProxyListener))
 			}()
 		}
 		if socksListener != nil {
+			ss := &socks5.Server{
+				Logf:   logger.WithPrefix(logf, "socks5: "),
+				Dialer: dialer.UserDial,
+			}
 			go func() {
-				log.Fatalf("SOCKS5 server exited: %v", srv.Serve(socksListener))
+				log.Fatalf("SOCKS5 server exited: %v", ss.Serve(socksListener))
 			}()
 		}
 	}
@@ -361,12 +382,15 @@ func run() error {
 
 	store, err := ipnserver.StateStore(statePathOrDefault(), logf)
 	if err != nil {
-		return err
+		return fmt.Errorf("ipnserver.StateStore: %w", err)
 	}
-	srv, err := ipnserver.New(logf, pol.PublicID.String(), store, e, nil, opts)
+	srv, err := ipnserver.New(logf, pol.PublicID.String(), store, e, dialer, nil, opts)
 	if err != nil {
-		logf("ipnserver.New: %v", err)
-		return err
+		return fmt.Errorf("ipnserver.New: %w", err)
+	}
+	ns.SetLocalBackend(srv.LocalBackend())
+	if err := ns.Start(); err != nil {
+		log.Fatalf("failed to start netstack: %v", err)
 	}
 
 	if debugMux != nil {
@@ -381,21 +405,20 @@ func run() error {
 	err = srv.Run(ctx, ln)
 	// Cancelation is not an error: it is the only way to stop ipnserver.
 	if err != nil && err != context.Canceled {
-		logf("ipnserver.Run: %v", err)
-		return err
+		return fmt.Errorf("ipnserver.Run: %w", err)
 	}
 
 	return nil
 }
 
-func createEngine(logf logger.Logf, linkMon *monitor.Mon) (e wgengine.Engine, useNetstack bool, err error) {
+func createEngine(logf logger.Logf, linkMon *monitor.Mon, dialer *tsdial.Dialer) (e wgengine.Engine, useNetstack bool, err error) {
 	if args.tunname == "" {
 		return nil, false, errors.New("no --tun value specified")
 	}
 	var errs []error
 	for _, name := range strings.Split(args.tunname, ",") {
 		logf("wgengine.NewUserspaceEngine(tun %q) ...", name)
-		e, useNetstack, err = tryEngine(logf, linkMon, name)
+		e, useNetstack, err = tryEngine(logf, linkMon, dialer, name)
 		if err == nil {
 			return e, useNetstack, nil
 		}
@@ -408,11 +431,7 @@ func createEngine(logf logger.Logf, linkMon *monitor.Mon) (e wgengine.Engine, us
 var wrapNetstack = shouldWrapNetstack()
 
 func shouldWrapNetstack() bool {
-	if e := os.Getenv("TS_DEBUG_WRAP_NETSTACK"); e != "" {
-		v, err := strconv.ParseBool(e)
-		if err != nil {
-			log.Fatalf("invalid TS_DEBUG_WRAP_NETSTACK value: %v", err)
-		}
+	if v, ok := envknob.LookupBool("TS_DEBUG_WRAP_NETSTACK"); ok {
 		return v
 	}
 	if distro.Get() == distro.Synology {
@@ -427,10 +446,11 @@ func shouldWrapNetstack() bool {
 	return false
 }
 
-func tryEngine(logf logger.Logf, linkMon *monitor.Mon, name string) (e wgengine.Engine, useNetstack bool, err error) {
+func tryEngine(logf logger.Logf, linkMon *monitor.Mon, dialer *tsdial.Dialer, name string) (e wgengine.Engine, useNetstack bool, err error) {
 	conf := wgengine.Config{
 		ListenPort:  args.port,
 		LinkMonitor: linkMon,
+		Dialer:      dialer,
 	}
 
 	useNetstack = name == "userspace-networking"
@@ -440,14 +460,14 @@ func tryEngine(logf logger.Logf, linkMon *monitor.Mon, name string) (e wgengine.
 		log.Printf("Connecting to BIRD at %s ...", args.birdSocketPath)
 		conf.BIRDClient, err = createBIRDClient(args.birdSocketPath)
 		if err != nil {
-			return nil, false, err
+			return nil, false, fmt.Errorf("createBIRDClient: %w", err)
 		}
 	}
 	if !useNetstack {
 		dev, devName, err := tstun.New(logf, name)
 		if err != nil {
 			tstun.Diagnose(logf, name)
-			return nil, false, err
+			return nil, false, fmt.Errorf("tstun.New(%q): %w", name, err)
 		}
 		conf.Tun = dev
 		if strings.HasPrefix(name, "tap:") {
@@ -459,11 +479,11 @@ func tryEngine(logf logger.Logf, linkMon *monitor.Mon, name string) (e wgengine.
 		r, err := router.New(logf, dev, linkMon)
 		if err != nil {
 			dev.Close()
-			return nil, false, err
+			return nil, false, fmt.Errorf("creating router: %w", err)
 		}
 		d, err := dns.NewOSConfigurator(logf, devName)
 		if err != nil {
-			return nil, false, err
+			return nil, false, fmt.Errorf("dns.NewOSConfigurator: %w", err)
 		}
 		conf.DNS = d
 		conf.Router = r
@@ -491,6 +511,7 @@ func newDebugMux() *http.ServeMux {
 
 func servePrometheusMetrics(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "text/plain")
+	tsweb.VarzHandler(w, r)
 	clientmetric.WritePrometheusExpositionFormat(w)
 }
 
@@ -504,26 +525,54 @@ func runDebugServer(mux *http.ServeMux, addr string) {
 	}
 }
 
-func newNetstack(logf logger.Logf, e wgengine.Engine) (*netstack.Impl, error) {
+func newNetstack(logf logger.Logf, dialer *tsdial.Dialer, e wgengine.Engine) (*netstack.Impl, error) {
 	tunDev, magicConn, ok := e.(wgengine.InternalsGetter).GetInternals()
 	if !ok {
 		return nil, fmt.Errorf("%T is not a wgengine.InternalsGetter", e)
 	}
-	return netstack.Create(logf, tunDev, e, magicConn)
+	return netstack.Create(logf, tunDev, e, magicConn, dialer)
 }
 
-func mustStartTCPListener(name, addr string) net.Listener {
-	if addr == "" {
-		return nil
+// mustStartProxyListeners creates listeners for local SOCKS and HTTP
+// proxies, if the respective addresses are not empty. socksAddr and
+// httpAddr can be the same, in which case socksListener will receive
+// connections that look like they're speaking SOCKS and httpListener
+// will receive everything else.
+//
+// socksListener and httpListener can be nil, if their respective
+// addrs are empty.
+func mustStartProxyListeners(socksAddr, httpAddr string) (socksListener, httpListener net.Listener) {
+	if socksAddr == httpAddr && socksAddr != "" && !strings.HasSuffix(socksAddr, ":0") {
+		ln, err := net.Listen("tcp", socksAddr)
+		if err != nil {
+			log.Fatalf("proxy listener: %v", err)
+		}
+		return proxymux.SplitSOCKSAndHTTP(ln)
 	}
-	ln, err := net.Listen("tcp", addr)
-	if err != nil {
-		log.Fatalf("%v listener: %v", name, err)
+
+	var err error
+	if socksAddr != "" {
+		socksListener, err = net.Listen("tcp", socksAddr)
+		if err != nil {
+			log.Fatalf("SOCKS5 listener: %v", err)
+		}
+		if strings.HasSuffix(socksAddr, ":0") {
+			// Log kernel-selected port number so integration tests
+			// can find it portably.
+			log.Printf("SOCKS5 listening on %v", socksListener.Addr())
+		}
 	}
-	if strings.HasSuffix(addr, ":0") {
-		// Log kernel-selected port number so integration tests
-		// can find it portably.
-		log.Printf("%v listening on %v", name, ln.Addr())
+	if httpAddr != "" {
+		httpListener, err = net.Listen("tcp", httpAddr)
+		if err != nil {
+			log.Fatalf("HTTP proxy listener: %v", err)
+		}
+		if strings.HasSuffix(httpAddr, ":0") {
+			// Log kernel-selected port number so integration tests
+			// can find it portably.
+			log.Printf("HTTP proxy listening on %v", httpListener.Addr())
+		}
 	}
-	return ln
+
+	return socksListener, httpListener
 }

cmd/tailscaled/tailscaled_windows.go

@@ -29,9 +29,11 @@ import (
 	"golang.org/x/sys/windows/svc"
 	"golang.zx2c4.com/wireguard/windows/tunnel/winipcfg"
 	"inet.af/netaddr"
+	"tailscale.com/envknob"
 	"tailscale.com/ipn/ipnserver"
 	"tailscale.com/logpolicy"
 	"tailscale.com/net/dns"
+	"tailscale.com/net/tsdial"
 	"tailscale.com/net/tstun"
 	"tailscale.com/safesocket"
 	"tailscale.com/types/logger"
@@ -39,6 +41,7 @@ import (
 	"tailscale.com/version"
 	"tailscale.com/wf"
 	"tailscale.com/wgengine"
+	"tailscale.com/wgengine/monitor"
 	"tailscale.com/wgengine/netstack"
 	"tailscale.com/wgengine/router"
 )
@@ -53,6 +56,11 @@ func isWindowsService() bool {
 	return v
 }
 
+// runWindowsService starts running Tailscale under the Windows
+// Service environment.
+//
+// At this point we're still the parent process that
+// Windows started.
 func runWindowsService(pol *logpolicy.Policy) error {
 	return svc.Run(serviceName, &ipnService{Policy: pol})
 }
@@ -78,7 +86,10 @@ func (service *ipnService) Execute(args []string, r <-chan svc.ChangeRequest, ch
 		// Make a logger without a date prefix, as filelogger
 		// and logtail both already add their own. All we really want
 		// from the log package is the automatic newline.
-		logger := log.New(os.Stderr, "", 0)
+		// We start with log.Default().Writer(), which is the logtail
+		// writer that logpolicy already installed as the global
+		// output.
+		logger := log.New(log.Default().Writer(), "", 0)
 		ipnserver.BabysitProc(ctx, args, logger.Printf)
 	}()
 
@@ -88,6 +99,7 @@ func (service *ipnService) Execute(args []string, r <-chan svc.ChangeRequest, ch
 		select {
 		case <-doneCh:
 		case cmd := <-r:
+			log.Printf("Got Windows Service event: %v", cmdName(cmd.Cmd))
 			switch cmd.Cmd {
 			case svc.Stop:
 				cancel()
@@ -104,6 +116,42 @@ func (service *ipnService) Execute(args []string, r <-chan svc.ChangeRequest, ch
 	return false, windows.NO_ERROR
 }
 
+func cmdName(c svc.Cmd) string {
+	switch c {
+	case svc.Stop:
+		return "Stop"
+	case svc.Pause:
+		return "Pause"
+	case svc.Continue:
+		return "Continue"
+	case svc.Interrogate:
+		return "Interrogate"
+	case svc.Shutdown:
+		return "Shutdown"
+	case svc.ParamChange:
+		return "ParamChange"
+	case svc.NetBindAdd:
+		return "NetBindAdd"
+	case svc.NetBindRemove:
+		return "NetBindRemove"
+	case svc.NetBindEnable:
+		return "NetBindEnable"
+	case svc.NetBindDisable:
+		return "NetBindDisable"
+	case svc.DeviceEvent:
+		return "DeviceEvent"
+	case svc.HardwareProfileChange:
+		return "HardwareProfileChange"
+	case svc.PowerEvent:
+		return "PowerEvent"
+	case svc.SessionChange:
+		return "SessionChange"
+	case svc.PreShutdown:
+		return "PreShutdown"
+	}
+	return fmt.Sprintf("Unknown-Service-Cmd-%d", c)
+}
+
 func beWindowsSubprocess() bool {
 	if beFirewallKillswitch() {
 		return true
@@ -114,6 +162,9 @@ func beWindowsSubprocess() bool {
 	}
 	logid := os.Args[2]
 
+	// Remove the date/time prefix; the logtail + file logggers add it.
+	log.SetFlags(0)
+
 	log.Printf("Program starting: v%v: %#v", version.Long, os.Args)
 	log.Printf("subproc mode: logid=%v", logid)
 
@@ -177,6 +228,12 @@ func beFirewallKillswitch() bool {
 func startIPNServer(ctx context.Context, logid string) error {
 	var logf logger.Logf = log.Printf
 
+	linkMon, err := monitor.New(logf)
+	if err != nil {
+		return err
+	}
+	dialer := new(tsdial.Dialer)
+
 	getEngineRaw := func() (wgengine.Engine, error) {
 		dev, devName, err := tstun.New(logf, "Tailscale")
 		if err != nil {
@@ -197,17 +254,19 @@ func startIPNServer(ctx context.Context, logid string) error {
 			return nil, fmt.Errorf("DNS: %w", err)
 		}
 		eng, err := wgengine.NewUserspaceEngine(logf, wgengine.Config{
-			Tun:        dev,
-			Router:     r,
-			DNS:        d,
-			ListenPort: 41641,
+			Tun:         dev,
+			Router:      r,
+			DNS:         d,
+			ListenPort:  41641,
+			LinkMonitor: linkMon,
+			Dialer:      dialer,
 		})
 		if err != nil {
 			r.Close()
 			dev.Close()
 			return nil, fmt.Errorf("engine: %w", err)
 		}
-		ns, err := newNetstack(logf, eng)
+		ns, err := newNetstack(logf, dialer, eng)
 		if err != nil {
 			return nil, fmt.Errorf("newNetstack: %w", err)
 		}
@@ -256,7 +315,7 @@ func startIPNServer(ctx context.Context, logid string) error {
 	// not called concurrently and is not called again once it
 	// successfully returns an engine.
 	getEngine := func() (wgengine.Engine, error) {
-		if msg := os.Getenv("TS_DEBUG_WIN_FAIL"); msg != "" {
+		if msg := envknob.String("TS_DEBUG_WIN_FAIL"); msg != "" {
 			return nil, fmt.Errorf("pretending to be a service failure: %v", msg)
 		}
 		for {
@@ -287,7 +346,7 @@ func startIPNServer(ctx context.Context, logid string) error {
 		return fmt.Errorf("safesocket.Listen: %v", err)
 	}
 
-	err = ipnserver.Run(ctx, logf, ln, store, logid, getEngine, ipnServerOpts())
+	err = ipnserver.Run(ctx, logf, ln, store, linkMon, dialer, logid, getEngine, ipnServerOpts())
 	if err != nil {
 		logf("ipnserver.Run: %v", err)
 	}

cmd/tsshd/tsshd.go

@@ -157,8 +157,9 @@ func handleSSH(s ssh.Session) {
 		cmd.Process.Kill()
 		if err := cmd.Wait(); err != nil {
 			s.Exit(1)
+		} else {
+			s.Exit(0)
 		}
-		s.Exit(0)
 		return
 	}
 

control/controlbase/conn.go

@@ -2,12 +2,12 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package noise implements the base transport of the Tailscale 2021
-// control protocol.
+// Package controlbase implements the base transport of the Tailscale
+// 2021 control protocol.
 //
 // The base transport implements Noise IK, instantiated with
 // Curve25519, ChaCha20Poly1305 and BLAKE2s.
-package noise
+package controlbase
 
 import (
 	"crypto/cipher"

control/controlbase/conn_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package noise
+package controlbase
 
 import (
 	"bufio"
@@ -202,7 +202,7 @@ func TestConnStd(t *testing.T) {
 		serverErr := make(chan error, 1)
 		go func() {
 			var err error
-			c2, err = Server(context.Background(), s2, controlKey)
+			c2, err = Server(context.Background(), s2, controlKey, nil)
 			serverErr <- err
 		}()
 		c1, err = Client(context.Background(), s1, machineKey, controlKey.Public())
@@ -319,7 +319,7 @@ func pairWithConns(t *testing.T, clientConn, serverConn net.Conn) (*Conn, *Conn)
 	)
 	go func() {
 		var err error
-		server, err = Server(context.Background(), serverConn, controlKey)
+		server, err = Server(context.Background(), serverConn, controlKey, nil)
 		serverErr <- err
 	}()
 

control/controlbase/handshake.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package noise
+package controlbase
 
 import (
 	"context"
@@ -50,21 +50,23 @@ func protocolVersionPrologue(version uint16) []byte {
 	return strconv.AppendUint(ret, uint64(version), 10)
 }
 
-// Client initiates a control client handshake, returning the resulting
-// control connection.
-//
-// The context deadline, if any, covers the entire handshaking
-// process. Any preexisting Conn deadline is removed.
-func Client(ctx context.Context, conn net.Conn, machineKey key.MachinePrivate, controlKey key.MachinePublic) (*Conn, error) {
-	if deadline, ok := ctx.Deadline(); ok {
-		if err := conn.SetDeadline(deadline); err != nil {
-			return nil, fmt.Errorf("setting conn deadline: %w", err)
-		}
-		defer func() {
-			conn.SetDeadline(time.Time{})
-		}()
-	}
+// HandshakeContinuation upgrades a net.Conn to a Conn. The net.Conn
+// is assumed to have already sent the client>server handshake
+// initiation message.
+type HandshakeContinuation func(context.Context, net.Conn) (*Conn, error)
 
+// ClientDeferred initiates a control client handshake, returning the
+// initial message to send to the server and a continuation to
+// finalize the handshake.
+//
+// ClientDeferred is split in this way for RTT reduction: we run this
+// protocol after negotiating a protocol switch from HTTP/HTTPS. If we
+// completely serialized the negotiation followed by the handshake,
+// we'd pay an extra RTT to transmit the handshake initiation after
+// protocol switching. By splitting the handshake into an initial
+// message and a continuation, we can embed the handshake initiation
+// into the HTTP protocol switching request and avoid a bit of delay.
+func ClientDeferred(machineKey key.MachinePrivate, controlKey key.MachinePublic) (initialHandshake []byte, continueHandshake HandshakeContinuation, err error) {
 	var s symmetricState
 	s.Initialize()
 
@@ -83,18 +85,53 @@ func Client(ctx context.Context, conn net.Conn, machineKey key.MachinePrivate, c
 	s.MixHash(machineEphemeralPub.UntypedBytes())
 	cipher, err := s.MixDH(machineEphemeral, controlKey)
 	if err != nil {
-		return nil, fmt.Errorf("computing es: %w", err)
+		return nil, nil, fmt.Errorf("computing es: %w", err)
 	}
 	machineKeyPub := machineKey.Public()
 	s.EncryptAndHash(cipher, init.MachinePub(), machineKeyPub.UntypedBytes())
 	cipher, err = s.MixDH(machineKey, controlKey)
 	if err != nil {
-		return nil, fmt.Errorf("computing ss: %w", err)
+		return nil, nil, fmt.Errorf("computing ss: %w", err)
 	}
 	s.EncryptAndHash(cipher, init.Tag(), nil) // empty message payload
 
-	if _, err := conn.Write(init[:]); err != nil {
-		return nil, fmt.Errorf("writing initiation: %w", err)
+	cont := func(ctx context.Context, conn net.Conn) (*Conn, error) {
+		return continueClientHandshake(ctx, conn, &s, machineKey, machineEphemeral, controlKey)
+	}
+	return init[:], cont, nil
+}
+
+// Client wraps ClientDeferred and immediately invokes the returned
+// continuation with conn.
+//
+// This is a helper for when you don't need the fancy
+// continuation-style handshake, and just want to synchronously
+// upgrade a net.Conn to a secure transport.
+func Client(ctx context.Context, conn net.Conn, machineKey key.MachinePrivate, controlKey key.MachinePublic) (*Conn, error) {
+	init, cont, err := ClientDeferred(machineKey, controlKey)
+	if err != nil {
+		return nil, err
+	}
+	if _, err := conn.Write(init); err != nil {
+		return nil, err
+	}
+	return cont(ctx, conn)
+}
+
+func continueClientHandshake(ctx context.Context, conn net.Conn, s *symmetricState, machineKey, machineEphemeral key.MachinePrivate, controlKey key.MachinePublic) (*Conn, error) {
+	// No matter what, this function can only run once per s. Ensure
+	// attempted reuse causes a panic.
+	defer func() {
+		s.finished = true
+	}()
+
+	if deadline, ok := ctx.Deadline(); ok {
+		if err := conn.SetDeadline(deadline); err != nil {
+			return nil, fmt.Errorf("setting conn deadline: %w", err)
+		}
+		defer func() {
+			conn.SetDeadline(time.Time{})
+		}()
 	}
 
 	// Read in the payload and look for errors/protocol violations from the server.
@@ -122,10 +159,10 @@ func Client(ctx context.Context, conn net.Conn, machineKey key.MachinePrivate, c
 	// <- e, ee, se
 	controlEphemeralPub := key.MachinePublicFromRaw32(mem.B(resp.EphemeralPub()))
 	s.MixHash(controlEphemeralPub.UntypedBytes())
-	if _, err = s.MixDH(machineEphemeral, controlEphemeralPub); err != nil {
+	if _, err := s.MixDH(machineEphemeral, controlEphemeralPub); err != nil {
 		return nil, fmt.Errorf("computing ee: %w", err)
 	}
-	cipher, err = s.MixDH(machineKey, controlEphemeralPub)
+	cipher, err := s.MixDH(machineKey, controlEphemeralPub)
 	if err != nil {
 		return nil, fmt.Errorf("computing se: %w", err)
 	}
@@ -156,9 +193,13 @@ func Client(ctx context.Context, conn net.Conn, machineKey key.MachinePrivate, c
 // Server initiates a control server handshake, returning the resulting
 // control connection.
 //
+// optionalInit can be the client's initial handshake message as
+// returned by ClientDeferred, or nil in which case the initial
+// message is read from conn.
+//
 // The context deadline, if any, covers the entire handshaking
 // process.
-func Server(ctx context.Context, conn net.Conn, controlKey key.MachinePrivate) (*Conn, error) {
+func Server(ctx context.Context, conn net.Conn, controlKey key.MachinePrivate, optionalInit []byte) (*Conn, error) {
 	if deadline, ok := ctx.Deadline(); ok {
 		if err := conn.SetDeadline(deadline); err != nil {
 			return nil, fmt.Errorf("setting conn deadline: %w", err)
@@ -190,7 +231,12 @@ func Server(ctx context.Context, conn net.Conn, controlKey key.MachinePrivate) (
 	s.Initialize()
 
 	var init initiationMessage
-	if _, err := io.ReadFull(conn, init.Header()); err != nil {
+	if optionalInit != nil {
+		if len(optionalInit) != len(init) {
+			return nil, sendErr("wrong handshake initiation size")
+		}
+		copy(init[:], optionalInit)
+	} else if _, err := io.ReadFull(conn, init.Header()); err != nil {
 		return nil, err
 	}
 	if init.Version() != protocolVersion {
@@ -202,8 +248,11 @@ func Server(ctx context.Context, conn net.Conn, controlKey key.MachinePrivate) (
 	if init.Length() != len(init.Payload()) {
 		return nil, sendErr("wrong handshake initiation length")
 	}
-	if _, err := io.ReadFull(conn, init.Payload()); err != nil {
-		return nil, err
+	// if optionalInit was provided, we have the payload already.
+	if optionalInit == nil {
+		if _, err := io.ReadFull(conn, init.Payload()); err != nil {
+			return nil, err
+		}
 	}
 
 	// prologue. Can only do this once we at least think the client is

control/controlbase/handshake_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package noise
+package controlbase
 
 import (
 	"bytes"
@@ -26,7 +26,7 @@ func TestHandshake(t *testing.T) {
 	)
 	go func() {
 		var err error
-		server, err = Server(context.Background(), serverConn, serverKey)
+		server, err = Server(context.Background(), serverConn, serverKey, nil)
 		serverErr <- err
 	}()
 
@@ -78,7 +78,7 @@ func TestNoReuse(t *testing.T) {
 		)
 		go func() {
 			var err error
-			server, err = Server(context.Background(), serverConn, serverKey)
+			server, err = Server(context.Background(), serverConn, serverKey, nil)
 			serverErr <- err
 		}()
 
@@ -139,6 +139,9 @@ func TestNoReuse(t *testing.T) {
 			t.Fatalf("server wire traffic seen twice")
 		}
 		packets[serverWire] = true
+
+		server.Close()
+		client.Close()
 	}
 }
 
@@ -169,7 +172,7 @@ func TestTampering(t *testing.T) {
 			serverErr             = make(chan error, 1)
 		)
 		go func() {
-			_, err := Server(context.Background(), serverConn, serverKey)
+			_, err := Server(context.Background(), serverConn, serverKey, nil)
 			// If the server failed, we have to close the Conn to
 			// unblock the client.
 			if err != nil {
@@ -197,7 +200,7 @@ func TestTampering(t *testing.T) {
 			serverErr             = make(chan error, 1)
 		)
 		go func() {
-			_, err := Server(context.Background(), serverConn, serverKey)
+			_, err := Server(context.Background(), serverConn, serverKey, nil)
 			serverErr <- err
 		}()
 
@@ -222,7 +225,7 @@ func TestTampering(t *testing.T) {
 			serverErr             = make(chan error, 1)
 		)
 		go func() {
-			server, err := Server(context.Background(), serverConn, serverKey)
+			server, err := Server(context.Background(), serverConn, serverKey, nil)
 			serverErr <- err
 			_, err = io.WriteString(server, strings.Repeat("a", 14))
 			serverErr <- err
@@ -263,7 +266,7 @@ func TestTampering(t *testing.T) {
 			serverErr             = make(chan error, 1)
 		)
 		go func() {
-			server, err := Server(context.Background(), serverConn, serverKey)
+			server, err := Server(context.Background(), serverConn, serverKey, nil)
 			serverErr <- err
 			var bs [100]byte
 			// The server needs a timeout if the tampering is hitting the length header.

control/controlbase/interop_test.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package noise
+package controlbase
 
 import (
 	"context"
@@ -29,7 +29,7 @@ func TestInteropClient(t *testing.T) {
 	)
 
 	go func() {
-		server, err := Server(context.Background(), s2, controlKey)
+		server, err := Server(context.Background(), s2, controlKey, nil)
 		serverErr <- err
 		if err != nil {
 			return

control/controlbase/messages.go

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package noise
+package controlbase
 
 import "encoding/binary"
 

control/controlbase/noiseexplorer_test.go

@@ -24,7 +24,7 @@ IK:
  * PARAMETERS                                                       *
  * ---------------------------------------------------------------- */
 
-package noise
+package controlbase
 
 import (
 	"crypto/rand"

control/controlclient/auto.go

@@ -339,11 +339,9 @@ func (c *Auto) authRoutine() {
 				continue
 			}
 			if url != "" {
-				if goal.url != "" {
-					err = fmt.Errorf("[unexpected] server required a new URL?")
-					report(err, "WaitLoginURL")
-				}
-
+				// goal.url ought to be empty here.
+				// However, not all control servers get this right,
+				// and logging about it here just generates noise.
 				c.mu.Lock()
 				c.loginGoal = &LoginGoal{
 					wantLoggedIn: true,

control/controlclient/direct.go

@@ -21,7 +21,6 @@ import (
 	"os/exec"
 	"reflect"
 	"runtime"
-	"strconv"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -30,6 +29,7 @@ import (
 	"go4.org/mem"
 	"inet.af/netaddr"
 	"tailscale.com/control/controlknobs"
+	"tailscale.com/envknob"
 	"tailscale.com/health"
 	"tailscale.com/hostinfo"
 	"tailscale.com/ipn/ipnstate"
@@ -874,8 +874,8 @@ func decode(res *http.Response, v interface{}, serverKey key.MachinePublic, mkey
 }
 
 var (
-	debugMap, _      = strconv.ParseBool(os.Getenv("TS_DEBUG_MAP"))
-	debugRegister, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_REGISTER"))
+	debugMap      = envknob.Bool("TS_DEBUG_MAP")
+	debugRegister = envknob.Bool("TS_DEBUG_REGISTER")
 )
 
 var jsonEscapedZero = []byte(`\u0000`)
@@ -985,26 +985,14 @@ type debug struct {
 
 func initDebug() debug {
 	return debug{
-		NetMap:         envBool("TS_DEBUG_NETMAP"),
-		ProxyDNS:       envBool("TS_DEBUG_PROXY_DNS"),
-		StripEndpoints: envBool("TS_DEBUG_STRIP_ENDPOINTS"),
-		StripCaps:      envBool("TS_DEBUG_STRIP_CAPS"),
-		Disco:          os.Getenv("TS_DEBUG_USE_DISCO") == "" || envBool("TS_DEBUG_USE_DISCO"),
+		NetMap:         envknob.Bool("TS_DEBUG_NETMAP"),
+		ProxyDNS:       envknob.Bool("TS_DEBUG_PROXY_DNS"),
+		StripEndpoints: envknob.Bool("TS_DEBUG_STRIP_ENDPOINTS"),
+		StripCaps:      envknob.Bool("TS_DEBUG_STRIP_CAPS"),
+		Disco:          envknob.BoolDefaultTrue("TS_DEBUG_USE_DISCO"),
 	}
 }
 
-func envBool(k string) bool {
-	e := os.Getenv(k)
-	if e == "" {
-		return false
-	}
-	v, err := strconv.ParseBool(e)
-	if err != nil {
-		panic(fmt.Sprintf("invalid non-bool %q for env var %q", e, k))
-	}
-	return v
-}
-
 var clockNow = time.Now
 
 // opt.Bool configs from control.

control/controlclient/map.go

@@ -6,11 +6,10 @@ package controlclient
 
 import (
 	"log"
-	"os"
 	"sort"
-	"strconv"
 
 	"inet.af/netaddr"
+	"tailscale.com/envknob"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/key"
 	"tailscale.com/types/logger"
@@ -289,7 +288,7 @@ func cloneNodes(v1 []*tailcfg.Node) []*tailcfg.Node {
 	return v2
 }
 
-var debugSelfIPv6Only, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_SELF_V6_ONLY"))
+var debugSelfIPv6Only = envknob.Bool("TS_DEBUG_SELF_V6_ONLY")
 
 func filterSelfAddresses(in []netaddr.IPPrefix) (ret []netaddr.IPPrefix) {
 	switch {

control/controlhttp/client.go

@@ -0,0 +1,242 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package controlhttp implements the Tailscale 2021 control protocol
+// base transport over HTTP.
+//
+// This tunnels the protocol in control/controlbase over HTTP with a
+// variety of compatibility fallbacks for handling picky or deep
+// inspecting proxies.
+//
+// In the happy path, a client makes a single cleartext HTTP request
+// to the server, the server responds with 101 Switching Protocols,
+// and the control base protocol takes place over plain TCP.
+//
+// In the compatibility path, the client does the above over HTTPS,
+// resulting in double encryption (once for the control transport, and
+// once for the outer TLS layer).
+package controlhttp
+
+import (
+	"context"
+	"crypto/tls"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"net/http"
+	"net/http/httptrace"
+	"net/url"
+
+	"tailscale.com/control/controlbase"
+	"tailscale.com/net/dnscache"
+	"tailscale.com/net/dnsfallback"
+	"tailscale.com/net/netns"
+	"tailscale.com/net/tlsdial"
+	"tailscale.com/net/tshttpproxy"
+	"tailscale.com/types/key"
+)
+
+// upgradeHeader is the value of the Upgrade HTTP header used to
+// indicate the Tailscale control protocol.
+const (
+	upgradeHeaderValue  = "tailscale-control-protocol"
+	handshakeHeaderName = "X-Tailscale-Handshake"
+)
+
+// Dial connects to the HTTP server at addr, requests to switch to the
+// Tailscale control protocol, and returns an established control
+// protocol connection.
+//
+// If Dial fails to connect using addr, it also tries to tunnel over
+// TLS to <addr's host>:443 as a compatibility fallback.
+func Dial(ctx context.Context, addr string, machineKey key.MachinePrivate, controlKey key.MachinePublic) (*controlbase.Conn, error) {
+	host, port, err := net.SplitHostPort(addr)
+	if err != nil {
+		return nil, err
+	}
+	a := &dialParams{
+		ctx:        ctx,
+		host:       host,
+		httpPort:   port,
+		httpsPort:  "443",
+		machineKey: machineKey,
+		controlKey: controlKey,
+		proxyFunc:  tshttpproxy.ProxyFromEnvironment,
+	}
+	return a.dial()
+}
+
+type dialParams struct {
+	ctx        context.Context
+	host       string
+	httpPort   string
+	httpsPort  string
+	machineKey key.MachinePrivate
+	controlKey key.MachinePublic
+	proxyFunc  func(*http.Request) (*url.URL, error) // or nil
+
+	// For tests only
+	insecureTLS bool
+}
+
+func (a *dialParams) dial() (*controlbase.Conn, error) {
+	init, cont, err := controlbase.ClientDeferred(a.machineKey, a.controlKey)
+	if err != nil {
+		return nil, err
+	}
+
+	u := &url.URL{
+		Scheme: "http",
+		Host:   net.JoinHostPort(a.host, a.httpPort),
+		Path:   "/switch",
+	}
+	conn, httpErr := a.tryURL(u, init)
+	if httpErr == nil {
+		ret, err := cont(a.ctx, conn)
+		if err != nil {
+			conn.Close()
+			return nil, err
+		}
+		return ret, nil
+	}
+
+	// Connecting over plain HTTP failed, assume it's an HTTP proxy
+	// being difficult and see if we can get through over HTTPS.
+	u.Scheme = "https"
+	u.Host = net.JoinHostPort(a.host, a.httpsPort)
+	init, cont, err = controlbase.ClientDeferred(a.machineKey, a.controlKey)
+	if err != nil {
+		return nil, err
+	}
+	conn, tlsErr := a.tryURL(u, init)
+	if tlsErr == nil {
+		ret, err := cont(a.ctx, conn)
+		if err != nil {
+			conn.Close()
+			return nil, err
+		}
+		return ret, nil
+	}
+
+	return nil, fmt.Errorf("all connection attempts failed (HTTP: %v, HTTPS: %v)", httpErr, tlsErr)
+}
+
+func (a *dialParams) tryURL(u *url.URL, init []byte) (net.Conn, error) {
+	dns := &dnscache.Resolver{
+		Forward:          dnscache.Get().Forward,
+		LookupIPFallback: dnsfallback.Lookup,
+		UseLastGood:      true,
+	}
+	dialer := netns.NewDialer(log.Printf)
+	tr := http.DefaultTransport.(*http.Transport).Clone()
+	defer tr.CloseIdleConnections()
+	tr.Proxy = a.proxyFunc
+	tshttpproxy.SetTransportGetProxyConnectHeader(tr)
+	tr.DialContext = dnscache.Dialer(dialer.DialContext, dns)
+	// Disable HTTP2, since h2 can't do protocol switching.
+	tr.TLSClientConfig.NextProtos = []string{}
+	tr.TLSNextProto = map[string]func(string, *tls.Conn) http.RoundTripper{}
+	tr.TLSClientConfig = tlsdial.Config(a.host, tr.TLSClientConfig)
+	if a.insecureTLS {
+		tr.TLSClientConfig.InsecureSkipVerify = true
+		tr.TLSClientConfig.VerifyConnection = nil
+	}
+	tr.DialTLSContext = dnscache.TLSDialer(dialer.DialContext, dns, tr.TLSClientConfig)
+	tr.DisableCompression = true
+
+	// (mis)use httptrace to extract the underlying net.Conn from the
+	// transport. We make exactly 1 request using this transport, so
+	// there will be exactly 1 GotConn call. Additionally, the
+	// transport handles 101 Switching Protocols correctly, such that
+	// the Conn will not be reused or kept alive by the transport once
+	// the response has been handed back from RoundTrip.
+	//
+	// In theory, the machinery of net/http should make it such that
+	// the trace callback happens-before we get the response, but
+	// there's no promise of that. So, to make sure, we use a buffered
+	// channel as a synchronization step to avoid data races.
+	//
+	// Note that even though we're able to extract a net.Conn via this
+	// mechanism, we must still keep using the eventual resp.Body to
+	// read from, because it includes a buffer we can't get rid of. If
+	// the server never sends any data after sending the HTTP
+	// response, we could get away with it, but violating this
+	// assumption leads to very mysterious transport errors (lockups,
+	// unexpected EOFs...), and we're bound to forget someday and
+	// introduce a protocol optimization at a higher level that starts
+	// eagerly transmitting from the server.
+	connCh := make(chan net.Conn, 1)
+	trace := httptrace.ClientTrace{
+		GotConn: func(info httptrace.GotConnInfo) {
+			connCh <- info.Conn
+		},
+	}
+	ctx := httptrace.WithClientTrace(a.ctx, &trace)
+	req := &http.Request{
+		Method: "POST",
+		URL:    u,
+		Header: http.Header{
+			"Upgrade":           []string{upgradeHeaderValue},
+			"Connection":        []string{"upgrade"},
+			handshakeHeaderName: []string{base64.StdEncoding.EncodeToString(init)},
+		},
+	}
+	req = req.WithContext(ctx)
+
+	resp, err := tr.RoundTrip(req)
+	if err != nil {
+		return nil, err
+	}
+
+	if resp.StatusCode != http.StatusSwitchingProtocols {
+		return nil, fmt.Errorf("unexpected HTTP response: %s", resp.Status)
+	}
+
+	// From here on, the underlying net.Conn is ours to use, but there
+	// is still a read buffer attached to it within resp.Body. So, we
+	// must direct I/O through resp.Body, but we can still use the
+	// underlying net.Conn for stuff like deadlines.
+	var switchedConn net.Conn
+	select {
+	case switchedConn = <-connCh:
+	default:
+	}
+	if switchedConn == nil {
+		resp.Body.Close()
+		return nil, fmt.Errorf("httptrace didn't provide a connection")
+	}
+
+	if next := resp.Header.Get("Upgrade"); next != upgradeHeaderValue {
+		resp.Body.Close()
+		return nil, fmt.Errorf("server switched to unexpected protocol %q", next)
+	}
+
+	rwc, ok := resp.Body.(io.ReadWriteCloser)
+	if !ok {
+		resp.Body.Close()
+		return nil, errors.New("http Transport did not provide a writable body")
+	}
+
+	return &wrappedConn{switchedConn, rwc}, nil
+}
+
+type wrappedConn struct {
+	net.Conn
+	rwc io.ReadWriteCloser
+}
+
+func (w *wrappedConn) Read(bs []byte) (int, error) {
+	return w.rwc.Read(bs)
+}
+
+func (w *wrappedConn) Write(bs []byte) (int, error) {
+	return w.rwc.Write(bs)
+}
+
+func (w *wrappedConn) Close() error {
+	return w.rwc.Close()
+}

control/controlhttp/http_test.go

@@ -0,0 +1,398 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package controlhttp
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"strconv"
+	"sync"
+	"testing"
+
+	"tailscale.com/control/controlbase"
+	"tailscale.com/net/socks5"
+	"tailscale.com/types/key"
+)
+
+func TestControlHTTP(t *testing.T) {
+	tests := []struct {
+		name  string
+		proxy proxy
+	}{
+		// direct connection
+		{
+			name:  "no_proxy",
+			proxy: nil,
+		},
+		// SOCKS5
+		{
+			name:  "socks5",
+			proxy: &socksProxy{},
+		},
+		// HTTP->HTTP
+		{
+			name: "http_to_http",
+			proxy: &httpProxy{
+				useTLS:       false,
+				allowConnect: false,
+				allowHTTP:    true,
+			},
+		},
+		// HTTP->HTTPS
+		{
+			name: "http_to_https",
+			proxy: &httpProxy{
+				useTLS:       false,
+				allowConnect: true,
+				allowHTTP:    false,
+			},
+		},
+		// HTTP->any (will pick HTTP)
+		{
+			name: "http_to_any",
+			proxy: &httpProxy{
+				useTLS:       false,
+				allowConnect: true,
+				allowHTTP:    true,
+			},
+		},
+		// HTTPS->HTTP
+		{
+			name: "https_to_http",
+			proxy: &httpProxy{
+				useTLS:       true,
+				allowConnect: false,
+				allowHTTP:    true,
+			},
+		},
+		// HTTPS->HTTPS
+		{
+			name: "https_to_https",
+			proxy: &httpProxy{
+				useTLS:       true,
+				allowConnect: true,
+				allowHTTP:    false,
+			},
+		},
+		// HTTPS->any (will pick HTTP)
+		{
+			name: "https_to_any",
+			proxy: &httpProxy{
+				useTLS:       true,
+				allowConnect: true,
+				allowHTTP:    true,
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			testControlHTTP(t, test.proxy)
+		})
+	}
+}
+
+func testControlHTTP(t *testing.T, proxy proxy) {
+	client, server := key.NewMachine(), key.NewMachine()
+
+	sch := make(chan serverResult, 1)
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		conn, err := AcceptHTTP(context.Background(), w, r, server)
+		if err != nil {
+			log.Print(err)
+		}
+		res := serverResult{
+			err: err,
+		}
+		if conn != nil {
+			res.clientAddr = conn.RemoteAddr().String()
+			res.version = conn.ProtocolVersion()
+			res.peer = conn.Peer()
+			res.conn = conn
+		}
+		sch <- res
+	})
+
+	httpLn, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("HTTP listen: %v", err)
+	}
+	httpsLn, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("HTTPS listen: %v", err)
+	}
+
+	httpServer := &http.Server{Handler: handler}
+	go httpServer.Serve(httpLn)
+	defer httpServer.Close()
+
+	httpsServer := &http.Server{
+		Handler:   handler,
+		TLSConfig: tlsConfig(t),
+	}
+	go httpsServer.ServeTLS(httpsLn, "", "")
+	defer httpsServer.Close()
+
+	//ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	//defer cancel()
+
+	a := dialParams{
+		ctx:         context.Background(), //ctx,
+		host:        "localhost",
+		httpPort:    strconv.Itoa(httpLn.Addr().(*net.TCPAddr).Port),
+		httpsPort:   strconv.Itoa(httpsLn.Addr().(*net.TCPAddr).Port),
+		machineKey:  client,
+		controlKey:  server.Public(),
+		insecureTLS: true,
+	}
+
+	if proxy != nil {
+		proxyEnv := proxy.Start(t)
+		defer proxy.Close()
+		proxyURL, err := url.Parse(proxyEnv)
+		if err != nil {
+			t.Fatal(err)
+		}
+		a.proxyFunc = func(*http.Request) (*url.URL, error) {
+			return proxyURL, nil
+		}
+	} else {
+		a.proxyFunc = func(*http.Request) (*url.URL, error) {
+			return nil, nil
+		}
+	}
+
+	conn, err := a.dial()
+	if err != nil {
+		t.Fatalf("dialing controlhttp: %v", err)
+	}
+	defer conn.Close()
+	si := <-sch
+	if si.conn != nil {
+		defer si.conn.Close()
+	}
+	if si.err != nil {
+		t.Fatalf("controlhttp server got error: %v", err)
+	}
+	if clientVersion := conn.ProtocolVersion(); si.version != clientVersion {
+		t.Fatalf("client and server don't agree on protocol version: %d vs %d", clientVersion, si.version)
+	}
+	if si.peer != client.Public() {
+		t.Fatalf("server got peer pubkey %s, want %s", si.peer, client.Public())
+	}
+	if spub := conn.Peer(); spub != server.Public() {
+		t.Fatalf("client got peer pubkey %s, want %s", spub, server.Public())
+	}
+	if proxy != nil && !proxy.ConnIsFromProxy(si.clientAddr) {
+		t.Fatalf("client connected from %s, which isn't the proxy", si.clientAddr)
+	}
+}
+
+type serverResult struct {
+	err        error
+	clientAddr string
+	version    int
+	peer       key.MachinePublic
+	conn       *controlbase.Conn
+}
+
+type proxy interface {
+	Start(*testing.T) string
+	Close()
+	ConnIsFromProxy(string) bool
+}
+
+type socksProxy struct {
+	sync.Mutex
+	proxy           socks5.Server
+	ln              net.Listener
+	clientConnAddrs map[string]bool // addrs of the local end of outgoing conns from proxy
+}
+
+func (s *socksProxy) Start(t *testing.T) (url string) {
+	t.Helper()
+	s.Lock()
+	defer s.Unlock()
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("listening for SOCKS server: %v", err)
+	}
+	s.ln = ln
+	s.clientConnAddrs = map[string]bool{}
+	s.proxy.Logf = t.Logf
+	s.proxy.Dialer = s.dialAndRecord
+	go s.proxy.Serve(ln)
+	return fmt.Sprintf("socks5://%s", ln.Addr().String())
+}
+
+func (s *socksProxy) Close() {
+	s.Lock()
+	defer s.Unlock()
+	s.ln.Close()
+}
+
+func (s *socksProxy) dialAndRecord(ctx context.Context, network, addr string) (net.Conn, error) {
+	var d net.Dialer
+	conn, err := d.DialContext(ctx, network, addr)
+	if err != nil {
+		return nil, err
+	}
+	s.Lock()
+	defer s.Unlock()
+	s.clientConnAddrs[conn.LocalAddr().String()] = true
+	return conn, nil
+}
+
+func (s *socksProxy) ConnIsFromProxy(addr string) bool {
+	s.Lock()
+	defer s.Unlock()
+	return s.clientConnAddrs[addr]
+}
+
+type httpProxy struct {
+	useTLS       bool // take incoming connections over TLS
+	allowConnect bool // allow CONNECT for TLS
+	allowHTTP    bool // allow plain HTTP proxying
+
+	sync.Mutex
+	ln              net.Listener
+	rp              httputil.ReverseProxy
+	s               http.Server
+	clientConnAddrs map[string]bool // addrs of the local end of outgoing conns from proxy
+}
+
+func (h *httpProxy) Start(t *testing.T) (url string) {
+	t.Helper()
+	h.Lock()
+	defer h.Unlock()
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("listening for HTTP proxy: %v", err)
+	}
+	h.ln = ln
+	h.rp = httputil.ReverseProxy{
+		Director: func(*http.Request) {},
+		Transport: &http.Transport{
+			DialContext: h.dialAndRecord,
+			TLSClientConfig: &tls.Config{
+				InsecureSkipVerify: true,
+			},
+			TLSNextProto: map[string]func(string, *tls.Conn) http.RoundTripper{},
+		},
+	}
+	h.clientConnAddrs = map[string]bool{}
+	h.s.Handler = h
+	if h.useTLS {
+		h.s.TLSConfig = tlsConfig(t)
+		go h.s.ServeTLS(h.ln, "", "")
+		return fmt.Sprintf("https://%s", ln.Addr().String())
+	} else {
+		go h.s.Serve(h.ln)
+		return fmt.Sprintf("http://%s", ln.Addr().String())
+	}
+}
+
+func (h *httpProxy) Close() {
+	h.Lock()
+	defer h.Unlock()
+	h.s.Close()
+}
+
+func (h *httpProxy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if r.Method != "CONNECT" {
+		if !h.allowHTTP {
+			http.Error(w, "http proxy not allowed", 500)
+			return
+		}
+		h.rp.ServeHTTP(w, r)
+		return
+	}
+
+	if !h.allowConnect {
+		http.Error(w, "connect not allowed", 500)
+		return
+	}
+
+	dst := r.RequestURI
+	c, err := h.dialAndRecord(context.Background(), "tcp", dst)
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+	defer c.Close()
+
+	cc, ccbuf, err := w.(http.Hijacker).Hijack()
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+	defer cc.Close()
+
+	io.WriteString(cc, "HTTP/1.1 200 OK\r\n\r\n")
+
+	errc := make(chan error, 1)
+	go func() {
+		_, err := io.Copy(cc, c)
+		errc <- err
+	}()
+	go func() {
+		_, err := io.Copy(c, ccbuf)
+		errc <- err
+	}()
+	<-errc
+}
+
+func (h *httpProxy) dialAndRecord(ctx context.Context, network, addr string) (net.Conn, error) {
+	var d net.Dialer
+	conn, err := d.DialContext(ctx, network, addr)
+	if err != nil {
+		return nil, err
+	}
+	h.Lock()
+	defer h.Unlock()
+	h.clientConnAddrs[conn.LocalAddr().String()] = true
+	return conn, nil
+}
+
+func (h *httpProxy) ConnIsFromProxy(addr string) bool {
+	h.Lock()
+	defer h.Unlock()
+	return h.clientConnAddrs[addr]
+}
+
+func tlsConfig(t *testing.T) *tls.Config {
+	// Cert and key taken from the example code in the crypto/tls
+	// package.
+	certPem := []byte(`-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----`)
+	keyPem := []byte(`-----BEGIN EC PRIVATE KEY-----
+MHcCAQEEIIrYSSNQFaA2Hwf1duRSxKtLYX5CB04fSeQ6tF1aY/PuoAoGCCqGSM49
+AwEHoUQDQgAEPR3tU2Fta9ktY+6P9G0cWO+0kETA6SFs38GecTyudlHz6xvCdz8q
+EKTcWGekdmdDPsHloRNtsiCa697B2O9IFA==
+-----END EC PRIVATE KEY-----`)
+	cert, err := tls.X509KeyPair(certPem, keyPem)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return &tls.Config{
+		Certificates: []tls.Certificate{cert},
+	}
+}

control/controlhttp/server.go

@@ -0,0 +1,95 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package controlhttp
+
+import (
+	"bufio"
+	"context"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"net"
+	"net/http"
+
+	"tailscale.com/control/controlbase"
+	"tailscale.com/types/key"
+)
+
+// AcceptHTTP upgrades the HTTP request given by w and r into a
+// Tailscale control protocol base transport connection.
+//
+// AcceptHTTP always writes an HTTP response to w. The caller must not
+// attempt their own response after calling AcceptHTTP.
+func AcceptHTTP(ctx context.Context, w http.ResponseWriter, r *http.Request, private key.MachinePrivate) (*controlbase.Conn, error) {
+	next := r.Header.Get("Upgrade")
+	if next == "" {
+		http.Error(w, "missing next protocol", http.StatusBadRequest)
+		return nil, errors.New("no next protocol in HTTP request")
+	}
+	if next != upgradeHeaderValue {
+		http.Error(w, "unknown next protocol", http.StatusBadRequest)
+		return nil, fmt.Errorf("client requested unhandled next protocol %q", next)
+	}
+
+	initB64 := r.Header.Get(handshakeHeaderName)
+	if initB64 == "" {
+		http.Error(w, "missing Tailscale handshake header", http.StatusBadRequest)
+		return nil, errors.New("no tailscale handshake header in HTTP request")
+	}
+	init, err := base64.StdEncoding.DecodeString(initB64)
+	if err != nil {
+		http.Error(w, "invalid tailscale handshake header", http.StatusBadRequest)
+		return nil, fmt.Errorf("decoding base64 handshake header: %v", err)
+	}
+
+	hijacker, ok := w.(http.Hijacker)
+	if !ok {
+		http.Error(w, "make request over HTTP/1", http.StatusBadRequest)
+		return nil, errors.New("can't hijack client connection")
+	}
+
+	w.Header().Set("Upgrade", upgradeHeaderValue)
+	w.Header().Set("Connection", "upgrade")
+	w.WriteHeader(http.StatusSwitchingProtocols)
+
+	conn, brw, err := hijacker.Hijack()
+	if err != nil {
+		return nil, fmt.Errorf("hijacking client connection: %w", err)
+	}
+	if err := brw.Flush(); err != nil {
+		conn.Close()
+		return nil, fmt.Errorf("flushing hijacked HTTP buffer: %w", err)
+	}
+	if brw.Reader.Buffered() > 0 {
+		conn = &drainBufConn{conn, brw.Reader}
+	}
+
+	nc, err := controlbase.Server(ctx, conn, private, init)
+	if err != nil {
+		conn.Close()
+		return nil, fmt.Errorf("noise handshake failed: %w", err)
+	}
+
+	return nc, nil
+}
+
+// drainBufConn is a net.Conn with an initial bunch of bytes in a
+// bufio.Reader. Read drains the bufio.Reader until empty, then passes
+// through subsequent reads to the Conn directly.
+type drainBufConn struct {
+	net.Conn
+	r *bufio.Reader
+}
+
+func (b *drainBufConn) Read(bs []byte) (int, error) {
+	if b.r == nil {
+		return b.Conn.Read(bs)
+	}
+	n, err := b.r.Read(bs)
+	if b.r.Buffered() == 0 {
+		b.r = nil
+	}
+	return n, err
+}

control/controlknobs/controlknobs.go

@@ -7,9 +7,7 @@
 package controlknobs
 
 import (
-	"os"
-	"strconv"
-
+	"tailscale.com/envknob"
 	"tailscale.com/syncs"
 )
 
@@ -17,8 +15,7 @@ import (
 var disableUPnP syncs.AtomicBool
 
 func init() {
-	v, _ := strconv.ParseBool(os.Getenv("TS_DISABLE_UPNP"))
-	SetDisableUPnP(v)
+	SetDisableUPnP(envknob.Bool("TS_DISABLE_UPNP"))
 }
 
 // DisableUPnP reports the last reported value from control

derp/derp_client.go

@@ -12,10 +12,12 @@ import (
 	"fmt"
 	"io"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"go4.org/mem"
 	"golang.org/x/time/rate"
+	"inet.af/netaddr"
 	"tailscale.com/types/key"
 	"tailscale.com/types/logger"
 )
@@ -37,8 +39,8 @@ type Client struct {
 	rate *rate.Limiter // if non-nil, rate limiter to use
 
 	// Owned by Recv:
-	peeked  int   // bytes to discard on next Recv
-	readErr error // sticky read error
+	peeked  int          // bytes to discard on next Recv
+	readErr atomic.Value // of error; sticky (set by Recv)
 }
 
 // ClientOpt is an option passed to NewClient.
@@ -261,10 +263,18 @@ func (c *Client) ForwardPacket(srcKey, dstKey key.NodePublic, pkt []byte) (err e
 
 func (c *Client) writeTimeoutFired() { c.nc.Close() }
 
+func (c *Client) SendPing(data [8]byte) error {
+	return c.sendPingOrPong(framePing, data)
+}
+
 func (c *Client) SendPong(data [8]byte) error {
+	return c.sendPingOrPong(framePong, data)
+}
+
+func (c *Client) sendPingOrPong(typ frameType, data [8]byte) error {
 	c.wmu.Lock()
 	defer c.wmu.Unlock()
-	if err := writeFrameHeader(c.bw, framePong, 8); err != nil {
+	if err := writeFrameHeader(c.bw, typ, 8); err != nil {
 		return err
 	}
 	if _, err := c.bw.Write(data[:]); err != nil {
@@ -375,6 +385,12 @@ type PingMessage [8]byte
 
 func (PingMessage) msg() {}
 
+// PongMessage is a reply to a PingMessage from a client or server
+// with the payload sent previously in a PingMessage.
+type PongMessage [8]byte
+
+func (PongMessage) msg() {}
+
 // KeepAliveMessage is a one-way empty message from server to client, just to
 // keep the connection alive. It's like a PingMessage, but doesn't solicit
 // a reply from the client.
@@ -427,13 +443,14 @@ func (c *Client) Recv() (m ReceivedMessage, err error) {
 }
 
 func (c *Client) recvTimeout(timeout time.Duration) (m ReceivedMessage, err error) {
-	if c.readErr != nil {
-		return nil, c.readErr
+	readErr, _ := c.readErr.Load().(error)
+	if readErr != nil {
+		return nil, readErr
 	}
 	defer func() {
 		if err != nil {
 			err = fmt.Errorf("derp.Recv: %w", err)
-			c.readErr = err
+			c.readErr.Store(err)
 		}
 	}()
 
@@ -536,6 +553,15 @@ func (c *Client) recvTimeout(timeout time.Duration) (m ReceivedMessage, err erro
 			copy(pm[:], b[:])
 			return pm, nil
 
+		case framePong:
+			var pm PongMessage
+			if n < 8 {
+				c.logf("[unexpected] dropping short ping frame")
+				continue
+			}
+			copy(pm[:], b[:])
+			return pm, nil
+
 		case frameHealth:
 			return HealthMessage{Problem: string(b[:])}, nil
 
@@ -564,3 +590,22 @@ func (c *Client) setSendRateLimiter(sm ServerInfoMessage) {
 			sm.TokenBucketBytesBurst)
 	}
 }
+
+// LocalAddr returns the TCP connection's local address.
+//
+// If the client is broken in some previously detectable way, it
+// returns an error.
+func (c *Client) LocalAddr() (netaddr.IPPort, error) {
+	readErr, _ := c.readErr.Load().(error)
+	if readErr != nil {
+		return netaddr.IPPort{}, readErr
+	}
+	if c.nc == nil {
+		return netaddr.IPPort{}, errors.New("nil conn")
+	}
+	a := c.nc.LocalAddr()
+	if a == nil {
+		return netaddr.IPPort{}, errors.New("nil addr")
+	}
+	return netaddr.ParseIPPort(a.String())
+}

derp/derp_server.go

@@ -23,8 +23,8 @@ import (
 	"math"
 	"math/big"
 	"math/rand"
+	"net"
 	"net/http"
-	"os"
 	"os/exec"
 	"runtime"
 	"strconv"
@@ -39,6 +39,7 @@ import (
 	"inet.af/netaddr"
 	"tailscale.com/client/tailscale"
 	"tailscale.com/disco"
+	"tailscale.com/envknob"
 	"tailscale.com/metrics"
 	"tailscale.com/syncs"
 	"tailscale.com/types/key"
@@ -47,14 +48,14 @@ import (
 	"tailscale.com/version"
 )
 
-var debug, _ = strconv.ParseBool(os.Getenv("DERP_DEBUG_LOGS"))
+var debug = envknob.Bool("DERP_DEBUG_LOGS")
 
 // verboseDropKeys is the set of destination public keys that should
 // verbosely log whenever DERP drops a packet.
 var verboseDropKeys = map[key.NodePublic]bool{}
 
 func init() {
-	keys := os.Getenv("TS_DEBUG_VERBOSE_DROPS")
+	keys := envknob.String("TS_DEBUG_VERBOSE_DROPS")
 	if keys == "" {
 		return
 	}
@@ -124,6 +125,8 @@ type Server struct {
 	packetsForwardedOut          expvar.Int
 	packetsForwardedIn           expvar.Int
 	peerGoneFrames               expvar.Int // number of peer gone frames sent
+	gotPing                      expvar.Int // number of ping frames from client
+	sentPong                     expvar.Int // number of pong frames enqueued to client
 	accepts                      expvar.Int
 	curClients                   expvar.Int
 	curHomeClients               expvar.Int // ones with preferred
@@ -283,9 +286,8 @@ type PacketForwarder interface {
 // It is a defined type so that non-net connections can be used.
 type Conn interface {
 	io.WriteCloser
-
+	LocalAddr() net.Addr
 	// The *Deadline methods follow the semantics of net.Conn.
-
 	SetDeadline(time.Time) error
 	SetReadDeadline(time.Time) error
 	SetWriteDeadline(time.Time) error
@@ -662,6 +664,7 @@ func (s *Server) accept(nc Conn, brw *bufio.ReadWriter, remoteAddr string, connN
 		connectedAt:    time.Now(),
 		sendQueue:      make(chan pkt, perClientSendQueueDepth),
 		discoSendQueue: make(chan pkt, perClientSendQueueDepth),
+		sendPongCh:     make(chan [8]byte, 1),
 		peerGone:       make(chan key.NodePublic),
 		canMesh:        clientInfo.MeshKey != "" && clientInfo.MeshKey == s.meshKey,
 	}
@@ -729,6 +732,8 @@ func (c *sclient) run(ctx context.Context) error {
 			err = c.handleFrameWatchConns(ft, fl)
 		case frameClosePeer:
 			err = c.handleFrameClosePeer(ft, fl)
+		case framePing:
+			err = c.handleFramePing(ft, fl)
 		default:
 			err = c.handleUnknownFrame(ft, fl)
 		}
@@ -766,6 +771,33 @@ func (c *sclient) handleFrameWatchConns(ft frameType, fl uint32) error {
 	return nil
 }
 
+func (c *sclient) handleFramePing(ft frameType, fl uint32) error {
+	c.s.gotPing.Add(1)
+	var m PingMessage
+	if fl < uint32(len(m)) {
+		return fmt.Errorf("short ping: %v", fl)
+	}
+	if fl > 1000 {
+		// unreasonably extra large. We leave some extra
+		// space for future extensibility, but not too much.
+		return fmt.Errorf("ping body too large: %v", fl)
+	}
+	_, err := io.ReadFull(c.br, m[:])
+	if err != nil {
+		return err
+	}
+	if extra := int64(fl) - int64(len(m)); extra > 0 {
+		_, err = io.CopyN(ioutil.Discard, c.br, extra)
+	}
+	select {
+	case c.sendPongCh <- [8]byte(m):
+	default:
+		// They're pinging too fast. Ignore.
+		// TODO(bradfitz): add a rate limiter too.
+	}
+	return err
+}
+
 func (c *sclient) handleFrameClosePeer(ft frameType, fl uint32) error {
 	if fl != keyLen {
 		return fmt.Errorf("handleFrameClosePeer wrong size")
@@ -1202,6 +1234,7 @@ type sclient struct {
 	remoteIPPort   netaddr.IPPort      // zero if remoteAddr is not ip:port.
 	sendQueue      chan pkt            // packets queued to this client; never closed
 	discoSendQueue chan pkt            // important packets queued to this client; never closed
+	sendPongCh     chan [8]byte        // pong replies to send to the client; never closed
 	peerGone       chan key.NodePublic // write request that a previous sender has disconnected (not used by mesh peers)
 	meshUpdate     chan struct{}       // write request to write peerStateChange
 	canMesh        bool                // clientInfo had correct mesh token for inter-region routing
@@ -1342,6 +1375,9 @@ func (c *sclient) sendLoop(ctx context.Context) error {
 			werr = c.sendPacket(msg.src, msg.bs)
 			c.recordQueueTime(msg.enqueuedAt)
 			continue
+		case msg := <-c.sendPongCh:
+			werr = c.sendPong(msg)
+			continue
 		case <-keepAliveTick.C:
 			werr = c.sendKeepAlive()
 			continue
@@ -1368,6 +1404,9 @@ func (c *sclient) sendLoop(ctx context.Context) error {
 		case msg := <-c.discoSendQueue:
 			werr = c.sendPacket(msg.src, msg.bs)
 			c.recordQueueTime(msg.enqueuedAt)
+		case msg := <-c.sendPongCh:
+			werr = c.sendPong(msg)
+			continue
 		case <-keepAliveTick.C:
 			werr = c.sendKeepAlive()
 		}
@@ -1384,6 +1423,17 @@ func (c *sclient) sendKeepAlive() error {
 	return writeFrameHeader(c.bw.bw(), frameKeepAlive, 0)
 }
 
+// sendPong sends a pong reply, without flushing.
+func (c *sclient) sendPong(data [8]byte) error {
+	c.s.sentPong.Add(1)
+	c.setWriteDeadline()
+	if err := writeFrameHeader(c.bw.bw(), framePong, uint32(len(data))); err != nil {
+		return err
+	}
+	_, err := c.bw.Write(data[:])
+	return err
+}
+
 // sendPeerGone sends a peerGone frame, without flushing.
 func (c *sclient) sendPeerGone(peer key.NodePublic) error {
 	c.s.peerGoneFrames.Add(1)
@@ -1625,6 +1675,8 @@ func (s *Server) ExpVar() expvar.Var {
 	m.Set("unknown_frames", &s.unknownFrames)
 	m.Set("home_moves_in", &s.homeMovesIn)
 	m.Set("home_moves_out", &s.homeMovesOut)
+	m.Set("got_ping", &s.gotPing)
+	m.Set("sent_pong", &s.sentPong)
 	m.Set("peer_gone_frames", &s.peerGoneFrames)
 	m.Set("packets_forwarded_out", &s.packetsForwardedOut)
 	m.Set("packets_forwarded_in", &s.packetsForwardedIn)

derp/derp_test.go

@@ -812,6 +812,14 @@ func TestClientRecv(t *testing.T) {
 			},
 			want: PingMessage{1, 2, 3, 4, 5, 6, 7, 8},
 		},
+		{
+			name: "pong",
+			input: []byte{
+				byte(framePong), 0, 0, 0, 8,
+				1, 2, 3, 4, 5, 6, 7, 8,
+			},
+			want: PongMessage{1, 2, 3, 4, 5, 6, 7, 8},
+		},
 		{
 			name: "health_bad",
 			input: []byte{
@@ -858,6 +866,23 @@ func TestClientRecv(t *testing.T) {
 	}
 }
 
+func TestClientSendPing(t *testing.T) {
+	var buf bytes.Buffer
+	c := &Client{
+		bw: bufio.NewWriter(&buf),
+	}
+	if err := c.SendPing([8]byte{1, 2, 3, 4, 5, 6, 7, 8}); err != nil {
+		t.Fatal(err)
+	}
+	want := []byte{
+		byte(framePing), 0, 0, 0, 8,
+		1, 2, 3, 4, 5, 6, 7, 8,
+	}
+	if !bytes.Equal(buf.Bytes(), want) {
+		t.Errorf("unexpected output\nwrote: % 02x\n want: % 02x", buf.Bytes(), want)
+	}
+}
+
 func TestClientSendPong(t *testing.T) {
 	var buf bytes.Buffer
 	c := &Client{
@@ -873,7 +898,6 @@ func TestClientSendPong(t *testing.T) {
 	if !bytes.Equal(buf.Bytes(), want) {
 		t.Errorf("unexpected output\nwrote: % 02x\n want: % 02x", buf.Bytes(), want)
 	}
-
 }
 
 func TestServerDupClients(t *testing.T) {
@@ -1316,3 +1340,30 @@ func TestClientSendRateLimiting(t *testing.T) {
 		t.Errorf("limited conn's bytes count = %v; want >=%v, <%v", bytesLimited, bytes1K*2, bytes1K)
 	}
 }
+
+func TestServerRepliesToPing(t *testing.T) {
+	ts := newTestServer(t)
+	defer ts.close(t)
+
+	tc := newRegularClient(t, ts, "alice")
+
+	data := [8]byte{1, 2, 3, 4, 5, 6, 7, 42}
+
+	if err := tc.c.SendPing(data); err != nil {
+		t.Fatal(err)
+	}
+
+	for {
+		m, err := tc.c.recvTimeout(time.Second)
+		if err != nil {
+			t.Fatal(err)
+		}
+		switch m := m.(type) {
+		case PongMessage:
+			if ([8]byte(m)) != data {
+				t.Fatalf("got pong %2x; want %2x", [8]byte(m), data)
+			}
+			return
+		}
+	}
+}

derp/derphttp/derphttp_client.go

@@ -13,6 +13,7 @@ package derphttp
 import (
 	"bufio"
 	"context"
+	"crypto/rand"
 	"crypto/tls"
 	"crypto/x509"
 	"errors"
@@ -22,9 +23,7 @@ import (
 	"net"
 	"net/http"
 	"net/url"
-	"os"
 	"runtime"
-	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -32,6 +31,7 @@ import (
 	"go4.org/mem"
 	"inet.af/netaddr"
 	"tailscale.com/derp"
+	"tailscale.com/envknob"
 	"tailscale.com/net/dnscache"
 	"tailscale.com/net/netns"
 	"tailscale.com/net/tlsdial"
@@ -72,6 +72,8 @@ type Client struct {
 	client       *derp.Client
 	connGen      int // incremented once per new connection; valid values are >0
 	serverPubKey key.NodePublic
+	tlsState     *tls.ConnectionState
+	pingOut      map[derp.PingMessage]chan<- bool // chan to send to on pong
 }
 
 // NewRegionClient returns a new DERP-over-HTTP client. It connects lazily.
@@ -123,6 +125,17 @@ func (c *Client) Connect(ctx context.Context) error {
 	return err
 }
 
+// TLSConnectionState returns the last TLS connection state, if any.
+// The client must already be connected.
+func (c *Client) TLSConnectionState() (_ *tls.ConnectionState, ok bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.closed || c.client == nil {
+		return nil, false
+	}
+	return c.tlsState, c.tlsState != nil
+}
+
 // ServerPublicKey returns the server's public key.
 //
 // It only returns a non-zero value once a connection has succeeded
@@ -188,8 +201,7 @@ func useWebsockets() bool {
 		return true
 	}
 	if dialWebsocketFunc != nil {
-		v, _ := strconv.ParseBool(os.Getenv("TS_DEBUG_DERP_WS_CLIENT"))
-		return v
+		return envknob.Bool("TS_DEBUG_DERP_WS_CLIENT")
 	}
 	return false
 }
@@ -318,6 +330,7 @@ func (c *Client) connect(ctx context.Context, caller string) (client *derp.Clien
 	var httpConn net.Conn        // a TCP conn or a TLS conn; what we speak HTTP to
 	var serverPub key.NodePublic // or zero if unknown (if not using TLS or TLS middlebox eats it)
 	var serverProtoVersion int
+	var tlsState *tls.ConnectionState
 	if c.useHTTPS() {
 		tlsConn := c.tlsClient(tcpConn, node)
 		httpConn = tlsConn
@@ -340,9 +353,10 @@ func (c *Client) connect(ctx context.Context, caller string) (client *derp.Clien
 		// Note that we're not specifically concerned about TLS downgrade
 		// attacks. TLS handles that fine:
 		// https://blog.gypsyengineer.com/en/security/how-does-tls-1-3-protect-against-downgrade-attacks.html
-		connState := tlsConn.ConnectionState()
-		if connState.Version >= tls.VersionTLS13 {
-			serverPub, serverProtoVersion = parseMetaCert(connState.PeerCertificates)
+		cs := tlsConn.ConnectionState()
+		tlsState = &cs
+		if cs.Version >= tls.VersionTLS13 {
+			serverPub, serverProtoVersion = parseMetaCert(cs.PeerCertificates)
 		}
 	} else {
 		httpConn = tcpConn
@@ -409,6 +423,7 @@ func (c *Client) connect(ctx context.Context, caller string) (client *derp.Clien
 	c.serverPubKey = derpClient.ServerPublicKey()
 	c.client = derpClient
 	c.netConn = tcpConn
+	c.tlsState = tlsState
 	c.connGen++
 	return c.client, c.connGen, nil
 }
@@ -698,6 +713,95 @@ func (c *Client) Send(dstKey key.NodePublic, b []byte) error {
 	return err
 }
 
+func (c *Client) registerPing(m derp.PingMessage, ch chan<- bool) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	if c.pingOut == nil {
+		c.pingOut = map[derp.PingMessage]chan<- bool{}
+	}
+	c.pingOut[m] = ch
+}
+
+func (c *Client) unregisterPing(m derp.PingMessage) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	delete(c.pingOut, m)
+}
+
+func (c *Client) handledPong(m derp.PongMessage) bool {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	k := derp.PingMessage(m)
+	if ch, ok := c.pingOut[k]; ok {
+		ch <- true
+		delete(c.pingOut, k)
+		return true
+	}
+	return false
+}
+
+// Ping sends a ping to the peer and waits for it either to be
+// acknowledged (in which case Ping returns nil) or waits for ctx to
+// be over and returns an error. It will wait at most 5 seconds
+// before returning an error.
+//
+// Another goroutine must be in a loop calling Recv or
+// RecvDetail or ping responses won't be handled.
+func (c *Client) Ping(ctx context.Context) error {
+	maxDL := time.Now().Add(5 * time.Second)
+	if dl, ok := ctx.Deadline(); !ok || dl.After(maxDL) {
+		var cancel context.CancelFunc
+		ctx, cancel = context.WithDeadline(ctx, maxDL)
+		defer cancel()
+	}
+	var data derp.PingMessage
+	rand.Read(data[:])
+	gotPing := make(chan bool, 1)
+	c.registerPing(data, gotPing)
+	defer c.unregisterPing(data)
+	if err := c.SendPing(data); err != nil {
+		return err
+	}
+	select {
+	case <-gotPing:
+		return nil
+	case <-ctx.Done():
+		return ctx.Err()
+	}
+}
+
+// SendPing writes a ping message, without any implicit connect or
+// reconnect. This is a lower-level interface that writes a frame
+// without any implicit handling of the response pong, if any. For a
+// higher-level interface, use Ping.
+func (c *Client) SendPing(data [8]byte) error {
+	c.mu.Lock()
+	closed, client := c.closed, c.client
+	c.mu.Unlock()
+	if closed {
+		return ErrClientClosed
+	}
+	if client == nil {
+		return errors.New("client not connected")
+	}
+	return client.SendPing(data)
+}
+
+// LocalAddr reports c's local TCP address, without any implicit
+// connect or reconnect.
+func (c *Client) LocalAddr() (netaddr.IPPort, error) {
+	c.mu.Lock()
+	closed, client := c.closed, c.client
+	c.mu.Unlock()
+	if closed {
+		return netaddr.IPPort{}, ErrClientClosed
+	}
+	if client == nil {
+		return netaddr.IPPort{}, errors.New("client not connected")
+	}
+	return client.LocalAddr()
+}
+
 func (c *Client) ForwardPacket(from, to key.NodePublic, b []byte) error {
 	client, _, err := c.connect(context.TODO(), "derphttp.Client.ForwardPacket")
 	if err != nil {
@@ -805,14 +909,22 @@ func (c *Client) RecvDetail() (m derp.ReceivedMessage, connGen int, err error) {
 	if err != nil {
 		return nil, 0, err
 	}
-	m, err = client.Recv()
-	if err != nil {
-		c.closeForReconnect(client)
-		if c.isClosed() {
-			err = ErrClientClosed
+	for {
+		m, err = client.Recv()
+		switch m := m.(type) {
+		case derp.PongMessage:
+			if c.handledPong(m) {
+				continue
+			}
 		}
+		if err != nil {
+			c.closeForReconnect(client)
+			if c.isClosed() {
+				err = ErrClientClosed
+			}
+		}
+		return m, connGen, err
 	}
-	return m, connGen, err
 }
 
 func (c *Client) isClosed() bool {

derp/derphttp/derphttp_test.go

@@ -154,3 +154,55 @@ func waitConnect(t testing.TB, c *Client) {
 		t.Fatalf("client first Recv was unexpected type %T", v)
 	}
 }
+
+func TestPing(t *testing.T) {
+	serverPrivateKey := key.NewNode()
+	s := derp.NewServer(serverPrivateKey, t.Logf)
+	defer s.Close()
+
+	httpsrv := &http.Server{
+		TLSNextProto: make(map[string]func(*http.Server, *tls.Conn, http.Handler)),
+		Handler:      Handler(s),
+	}
+
+	ln, err := net.Listen("tcp4", "localhost:0")
+	if err != nil {
+		t.Fatal(err)
+	}
+	serverURL := "http://" + ln.Addr().String()
+	t.Logf("server URL: %s", serverURL)
+
+	go func() {
+		if err := httpsrv.Serve(ln); err != nil {
+			if err == http.ErrServerClosed {
+				return
+			}
+			panic(err)
+		}
+	}()
+
+	c, err := NewClient(key.NewNode(), serverURL, t.Logf)
+	if err != nil {
+		t.Fatalf("NewClient: %v", err)
+	}
+	defer c.Close()
+	if err := c.Connect(context.Background()); err != nil {
+		t.Fatalf("client Connect: %v", err)
+	}
+
+	errc := make(chan error, 1)
+	go func() {
+		for {
+			m, err := c.Recv()
+			if err != nil {
+				errc <- err
+				return
+			}
+			t.Logf("Recv: %T", m)
+		}
+	}()
+	err = c.Ping(context.Background())
+	if err != nil {
+		t.Fatalf("Ping: %v", err)
+	}
+}

envknob/envknob.go

@@ -0,0 +1,106 @@
+// Copyright (c) 2022 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package envknob provides access to environment-variable tweakable
+// debug settings.
+//
+// These are primarily knobs used by Tailscale developers during
+// development or by users when instructed to by Tailscale developers
+// when debugging something. They are not a stable interface and may
+// be removed or any time.
+//
+// A related package, control/controlknobs, are knobs that can be
+// changed at runtime by the control plane. Sometimes both are used:
+// an envknob for the default/explicit value, else falling back
+// to the controlknob value.
+package envknob
+
+import (
+	"log"
+	"os"
+	"strconv"
+
+	"tailscale.com/types/opt"
+)
+
+// String returns the named environment variable, using os.Getenv.
+//
+// In the future it will also track usage for reporting on debug pages.
+func String(envVar string) string {
+	return os.Getenv(envVar)
+}
+
+// Bool returns the boolean value of the named environment variable.
+// If the variable is not set, it returns false.
+// An invalid value exits the binary with a failure.
+func Bool(envVar string) bool {
+	return boolOr(envVar, false)
+}
+
+// BoolDefaultTrue is like Bool, but returns true by default if the
+// environment variable isn't present.
+func BoolDefaultTrue(envVar string) bool {
+	return boolOr(envVar, true)
+}
+
+func boolOr(envVar string, implicitValue bool) bool {
+	val := os.Getenv(envVar)
+	if val == "" {
+		return implicitValue
+	}
+	b, err := strconv.ParseBool(val)
+	if err == nil {
+		return b
+	}
+	log.Fatalf("invalid environment variable %s value %q: %v", envVar, val, err)
+	panic("unreachable")
+}
+
+// LookupBool returns the boolean value of the named environment value.
+// The ok result is whether a value was set.
+// If the value isn't a valid int, it exits the program with a failure.
+func LookupBool(envVar string) (v bool, ok bool) {
+	val := os.Getenv(envVar)
+	if val == "" {
+		return false, false
+	}
+	b, err := strconv.ParseBool(val)
+	if err == nil {
+		return b, true
+	}
+	log.Fatalf("invalid environment variable %s value %q: %v", envVar, val, err)
+	panic("unreachable")
+}
+
+// OptBool is like Bool, but returns an opt.Bool, so the caller can
+// distinguish between implicitly and explicitly false.
+func OptBool(envVar string) opt.Bool {
+	b, ok := LookupBool(envVar)
+	if !ok {
+		return ""
+	}
+	var ret opt.Bool
+	ret.Set(b)
+	return ret
+}
+
+// LookupInt returns the integer value of the named environment value.
+// The ok result is whether a value was set.
+// If the value isn't a valid int, it exits the program with a failure.
+func LookupInt(envVar string) (v int, ok bool) {
+	val := os.Getenv(envVar)
+	if val == "" {
+		return 0, false
+	}
+	v, err := strconv.Atoi(val)
+	if err == nil {
+		return v, true
+	}
+	log.Fatalf("invalid environment variable %s value %q: %v", envVar, val, err)
+	panic("unreachable")
+}
+
+// UseWIPCode is whether TAILSCALE_USE_WIP_CODE is set to permit use
+// of Work-In-Progress code.
+func UseWIPCode() bool { return Bool("TAILSCALE_USE_WIP_CODE") }

go.mod

@@ -7,208 +7,257 @@ require (
 	github.com/akutz/memconn v0.1.0
 	github.com/alexbrainman/sspi v0.0.0-20210105120005-909beea2cc74
 	github.com/anmitsu/go-shlex v0.0.0-20200514113438-38f4b401e2be // indirect
-	github.com/aws/aws-sdk-go v1.38.52
-	github.com/aws/aws-sdk-go-v2 v1.9.2
-	github.com/aws/aws-sdk-go-v2/config v1.8.3
-	github.com/aws/aws-sdk-go-v2/service/ssm v1.12.0
+	github.com/aws/aws-sdk-go-v2 v1.11.2
+	github.com/aws/aws-sdk-go-v2/config v1.11.0
+	github.com/aws/aws-sdk-go-v2/feature/s3/manager v1.7.4
+	github.com/aws/aws-sdk-go-v2/service/s3 v1.21.0
+	github.com/aws/aws-sdk-go-v2/service/ssm v1.17.1
 	github.com/coreos/go-iptables v0.6.0
 	github.com/creack/pty v1.1.17
 	github.com/dave/jennifer v1.4.1
 	github.com/frankban/quicktest v1.14.0
 	github.com/gliderlabs/ssh v0.3.3
-	github.com/go-ole/go-ole v1.2.6-0.20210915003542-8b1f7f90f6b1
-	github.com/godbus/dbus/v5 v5.0.5
+	github.com/go-ole/go-ole v1.2.6
+	github.com/godbus/dbus/v5 v5.0.6
+	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da
 	github.com/google/go-cmp v0.5.6
 	github.com/google/uuid v1.3.0
 	github.com/goreleaser/nfpm v1.10.3
 	github.com/iancoleman/strcase v0.2.0
-	github.com/insomniacslk/dhcp v0.0.0-20210621130208-1cac67f12b1e
-	github.com/jsimonetti/rtnetlink v0.0.0-20210525051524-4cc836578190
+	github.com/insomniacslk/dhcp v0.0.0-20211026125128-ad197bcd36fd
+	github.com/jsimonetti/rtnetlink v0.0.0-20211203074127-fd9a11f42291
 	github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51
 	github.com/klauspost/compress v1.13.6
-	github.com/mdlayher/netlink v1.4.1
+	github.com/mdlayher/netlink v1.4.2
 	github.com/mdlayher/sdnotify v0.0.0-20210228150836-ea3ec207d697
 	github.com/miekg/dns v1.1.43
 	github.com/mitchellh/go-ps v1.0.0
 	github.com/pborman/getopt v1.1.0
-	github.com/peterbourgon/ff/v3 v3.1.0
+	github.com/peterbourgon/ff/v3 v3.1.2
 	github.com/pkg/sftp v1.13.4
 	github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e
 	github.com/tailscale/certstore v0.0.0-20210528134328-066c94b793d3
-	github.com/tailscale/depaware v0.0.0-20201214215404-77d1e9757027
+	github.com/tailscale/depaware v0.0.0-20210622194025-720c4b409502
 	github.com/tailscale/goexpect v0.0.0-20210902213824-6e8c725cea41
 	github.com/tailscale/goupnp v1.0.1-0.20210804011211-c64d0f06ea05
-	github.com/tailscale/hujson v0.0.0-20200924210142-dde312d0d6a2
+	github.com/tailscale/hujson v0.0.0-20211105212140-3a0adc019d83
 	github.com/tailscale/netlink v1.1.1-0.20211101221916-cabfb018fe85
 	github.com/tcnksm/go-httpstat v0.2.0
 	github.com/toqueteos/webbrowser v1.2.0
 	github.com/ulikunitz/xz v0.5.10 // indirect
 	github.com/vishvananda/netlink v1.1.1-0.20211101163509-b10eb8fe5cf6
-	go4.org/mem v0.0.0-20201119185036-c04c5a6ff174
-	golang.org/x/crypto v0.0.0-20211108221036-ceb1ce70b4fa
-	golang.org/x/net v0.0.0-20211111083644-e5c967477495
+	go4.org/mem v0.0.0-20210711025021-927187094b94
+	golang.org/x/crypto v0.0.0-20211202192323-5770296d904e
+	golang.org/x/net v0.0.0-20211205041911-012df41ee64c
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
-	golang.org/x/sys v0.0.0-20211110154304-99a53858aa08
-	golang.org/x/term v0.0.0-20210503060354-a79de5458b56
-	golang.org/x/time v0.0.0-20210611083556-38a9dc6acbc6
-	golang.org/x/tools v0.1.7
+	golang.org/x/sys v0.0.0-20211205182925-97ca703d548d
+	golang.org/x/term v0.0.0-20210927222741-03fcf44c2211
+	golang.org/x/time v0.0.0-20211116232009-f0f3c7e86c11
+	golang.org/x/tools v0.1.8
 	golang.zx2c4.com/wireguard v0.0.0-20211116201604-de7c702ace45
 	golang.zx2c4.com/wireguard/windows v0.4.10
-	honnef.co/go/tools v0.2.1
+	gvisor.dev/gvisor v0.0.0-20220126021142-d8aa030b2591
+	honnef.co/go/tools v0.2.2
 	inet.af/netaddr v0.0.0-20211027220019-c74959edd3b6
-	inet.af/netstack v0.0.0-20211101182044-1c1bcf452982
-	inet.af/peercred v0.0.0-20210318190834-4259e17bb763
-	inet.af/wf v0.0.0-20210516214145-a5343001b756
+	inet.af/peercred v0.0.0-20210906144145-0893ea02156a
+	inet.af/wf v0.0.0-20211204062712-86aaea0a7310
 	nhooyr.io/websocket v1.8.7
 )
 
 require (
-	4d63.com/gochecknoglobals v0.0.0-20201008074935-acfc0b28355a // indirect
-	github.com/BurntSushi/toml v0.3.1 // indirect
+	4d63.com/gochecknoglobals v0.1.0 // indirect
+	github.com/Antonboom/errname v0.1.5 // indirect
+	github.com/Antonboom/nilnil v0.1.0 // indirect
+	github.com/BurntSushi/toml v0.4.1 // indirect
 	github.com/Djarvur/go-err113 v0.1.0 // indirect
-	github.com/Masterminds/goutils v1.1.0 // indirect
+	github.com/Masterminds/goutils v1.1.1 // indirect
 	github.com/Masterminds/semver v1.5.0 // indirect
 	github.com/Masterminds/semver/v3 v3.1.1 // indirect
 	github.com/Masterminds/sprig v2.22.0+incompatible // indirect
-	github.com/Microsoft/go-winio v0.4.16 // indirect
+	github.com/Microsoft/go-winio v0.5.1 // indirect
 	github.com/OpenPeeDeeP/depguard v1.0.1 // indirect
-	github.com/aws/aws-sdk-go-v2/credentials v1.4.3 // indirect
-	github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.6.0 // indirect
-	github.com/aws/aws-sdk-go-v2/internal/ini v1.2.4 // indirect
-	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.3.2 // indirect
-	github.com/aws/aws-sdk-go-v2/service/sso v1.4.2 // indirect
-	github.com/aws/aws-sdk-go-v2/service/sts v1.7.2 // indirect
-	github.com/aws/smithy-go v1.8.0 // indirect
+	github.com/ProtonMail/go-crypto v0.0.0-20211112122917-428f8eabeeb3 // indirect
+	github.com/acomagu/bufpipe v1.0.3 // indirect
+	github.com/alexkohler/prealloc v1.0.0 // indirect
+	github.com/ashanbrown/forbidigo v1.2.0 // indirect
+	github.com/ashanbrown/makezero v0.0.0-20210520155254-b6261585ddde // indirect
+	github.com/aws/aws-sdk-go-v2/aws/protocol/eventstream v1.0.0 // indirect
+	github.com/aws/aws-sdk-go-v2/credentials v1.6.4 // indirect
+	github.com/aws/aws-sdk-go-v2/feature/ec2/imds v1.8.2 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/configsources v1.1.2 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/endpoints/v2 v2.0.2 // indirect
+	github.com/aws/aws-sdk-go-v2/internal/ini v1.3.2 // indirect
+	github.com/aws/aws-sdk-go-v2/service/internal/accept-encoding v1.5.0 // indirect
+	github.com/aws/aws-sdk-go-v2/service/internal/presigned-url v1.5.2 // indirect
+	github.com/aws/aws-sdk-go-v2/service/internal/s3shared v1.9.2 // indirect
+	github.com/aws/aws-sdk-go-v2/service/sso v1.6.2 // indirect
+	github.com/aws/aws-sdk-go-v2/service/sts v1.11.1 // indirect
+	github.com/aws/smithy-go v1.9.0 // indirect
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/bkielbasa/cyclop v1.2.0 // indirect
 	github.com/blakesmith/ar v0.0.0-20190502131153-809d4375e1fb // indirect
-	github.com/bombsimon/wsl/v3 v3.1.0 // indirect
+	github.com/blizzy78/varnamelen v0.5.0 // indirect
+	github.com/bombsimon/wsl/v3 v3.3.0 // indirect
+	github.com/breml/bidichk v0.2.1 // indirect
+	github.com/butuzov/ireturn v0.1.1 // indirect
 	github.com/cavaliercoder/go-cpio v0.0.0-20180626203310-925f9528c45e // indirect
-	github.com/daixiang0/gci v0.2.7 // indirect
+	github.com/cespare/xxhash/v2 v2.1.2 // indirect
+	github.com/charithe/durationcheck v0.0.9 // indirect
+	github.com/chavacava/garif v0.0.0-20210405164556-e8a0a408d6af // indirect
+	github.com/daixiang0/gci v0.2.9 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
-	github.com/denis-tingajkin/go-header v0.3.1 // indirect
+	github.com/denis-tingajkin/go-header v0.4.2 // indirect
 	github.com/emirpasic/gods v1.12.0 // indirect
-	github.com/fatih/color v1.10.0 // indirect
-	github.com/fsnotify/fsnotify v1.4.9 // indirect
-	github.com/go-critic/go-critic v0.5.2 // indirect
+	github.com/esimonov/ifshort v1.0.3 // indirect
+	github.com/ettle/strcase v0.1.1 // indirect
+	github.com/fatih/color v1.13.0 // indirect
+	github.com/fatih/structtag v1.2.0 // indirect
+	github.com/fsnotify/fsnotify v1.5.1 // indirect
+	github.com/fzipp/gocyclo v0.3.1 // indirect
+	github.com/go-critic/go-critic v0.6.1 // indirect
 	github.com/go-git/gcfg v1.5.0 // indirect
-	github.com/go-git/go-billy/v5 v5.0.0 // indirect
-	github.com/go-git/go-git/v5 v5.2.0 // indirect
+	github.com/go-git/go-billy/v5 v5.3.1 // indirect
+	github.com/go-git/go-git/v5 v5.4.2 // indirect
 	github.com/go-toolsmith/astcast v1.0.0 // indirect
 	github.com/go-toolsmith/astcopy v1.0.0 // indirect
-	github.com/go-toolsmith/astequal v1.0.0 // indirect
+	github.com/go-toolsmith/astequal v1.0.1 // indirect
 	github.com/go-toolsmith/astfmt v1.0.0 // indirect
 	github.com/go-toolsmith/astp v1.0.0 // indirect
 	github.com/go-toolsmith/strparse v1.0.0 // indirect
 	github.com/go-toolsmith/typep v1.0.2 // indirect
-	github.com/go-xmlfmt/xmlfmt v0.0.0-20191208150333-d5b6f63a941b // indirect
+	github.com/go-xmlfmt/xmlfmt v0.0.0-20211206191508-7fd73a941850 // indirect
 	github.com/gobwas/glob v0.2.3 // indirect
-	github.com/gofrs/flock v0.8.0 // indirect
+	github.com/gofrs/flock v0.8.1 // indirect
+	github.com/golang/protobuf v1.5.2 // indirect
 	github.com/golangci/check v0.0.0-20180506172741-cfe4005ccda2 // indirect
 	github.com/golangci/dupl v0.0.0-20180902072040-3e9179ac440a // indirect
-	github.com/golangci/errcheck v0.0.0-20181223084120-ef45e06d44b6 // indirect
 	github.com/golangci/go-misc v0.0.0-20180628070357-927a3d87b613 // indirect
-	github.com/golangci/gocyclo v0.0.0-20180528144436-0a533e8fa43d // indirect
 	github.com/golangci/gofmt v0.0.0-20190930125516-244bba706f1a // indirect
-	github.com/golangci/golangci-lint v1.33.0 // indirect
-	github.com/golangci/ineffassign v0.0.0-20190609212857-42439a7714cc // indirect
+	github.com/golangci/golangci-lint v1.43.0 // indirect
 	github.com/golangci/lint-1 v0.0.0-20191013205115-297bf364a8e0 // indirect
 	github.com/golangci/maligned v0.0.0-20180506175553-b1d89398deca // indirect
 	github.com/golangci/misspell v0.3.5 // indirect
-	github.com/golangci/prealloc v0.0.0-20180630174525-215b22d4de21 // indirect
-	github.com/golangci/revgrep v0.0.0-20180812185044-276a5c0a1039 // indirect
+	github.com/golangci/revgrep v0.0.0-20210930125155-c22e5001d4f2 // indirect
 	github.com/golangci/unconvert v0.0.0-20180507085042-28b1c447d1f4 // indirect
 	github.com/google/btree v1.0.1 // indirect
-	github.com/google/goterm v0.0.0-20190703233501-fc88cf888a3f // indirect
+	github.com/google/goterm v0.0.0-20200907032337-555d40f16ae2 // indirect
 	github.com/google/rpmpack v0.0.0-20201206194719-59e495f2b7e1 // indirect
+	github.com/gordonklaus/ineffassign v0.0.0-20210914165742-4cc7213b9bc8 // indirect
 	github.com/goreleaser/chglog v0.1.2 // indirect
 	github.com/goreleaser/fileglob v0.3.1 // indirect
-	github.com/gostaticanalysis/analysisutil v0.6.1 // indirect
-	github.com/gostaticanalysis/comment v1.4.1 // indirect
+	github.com/gostaticanalysis/analysisutil v0.7.1 // indirect
+	github.com/gostaticanalysis/comment v1.4.2 // indirect
+	github.com/gostaticanalysis/forcetypeassert v0.1.0 // indirect
+	github.com/gostaticanalysis/nilerr v0.1.1 // indirect
+	github.com/hashicorp/errwrap v1.1.0 // indirect
+	github.com/hashicorp/go-multierror v1.1.1 // indirect
 	github.com/hashicorp/hcl v1.0.0 // indirect
 	github.com/huandu/xstrings v1.3.2 // indirect
-	github.com/imdario/mergo v0.3.11 // indirect
+	github.com/imdario/mergo v0.3.12 // indirect
 	github.com/inconshreveable/mousetrap v1.0.0 // indirect
 	github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99 // indirect
-	github.com/jgautheron/goconst v0.0.0-20201117150253-ccae5bf973f3 // indirect
-	github.com/jingyugao/rowserrcheck v0.0.0-20191204022205-72ab7603b68a // indirect
+	github.com/jgautheron/goconst v1.5.1 // indirect
+	github.com/jingyugao/rowserrcheck v1.1.1 // indirect
 	github.com/jirfag/go-printf-func-name v0.0.0-20200119135958-7558a9eaa5af // indirect
 	github.com/jmespath/go-jmespath v0.4.0 // indirect
 	github.com/josharian/native v0.0.0-20200817173448-b6b71def0850 // indirect
-	github.com/kevinburke/ssh_config v0.0.0-20201106050909-4977a11b4351 // indirect
+	github.com/julz/importas v0.0.0-20210922140945-27e0a5d4dee2 // indirect
+	github.com/kevinburke/ssh_config v1.1.0 // indirect
+	github.com/kisielk/errcheck v1.6.0 // indirect
 	github.com/kisielk/gotool v1.0.0 // indirect
 	github.com/kr/fs v0.1.0 // indirect
 	github.com/kr/pretty v0.3.0 // indirect
 	github.com/kr/text v0.2.0 // indirect
-	github.com/kunwardeep/paralleltest v1.0.2 // indirect
+	github.com/kulti/thelper v0.4.0 // indirect
+	github.com/kunwardeep/paralleltest v1.0.3 // indirect
 	github.com/kyoh86/exportloopref v0.1.8 // indirect
-	github.com/magiconair/properties v1.8.4 // indirect
+	github.com/ldez/gomoddirectives v0.2.2 // indirect
+	github.com/ldez/tagliatelle v0.2.0 // indirect
+	github.com/magiconair/properties v1.8.5 // indirect
 	github.com/maratori/testpackage v1.0.1 // indirect
-	github.com/matoous/godox v0.0.0-20200801072554-4fb83dc2941e // indirect
-	github.com/mattn/go-colorable v0.1.8 // indirect
-	github.com/mattn/go-isatty v0.0.12 // indirect
-	github.com/mbilski/exhaustivestruct v1.1.0 // indirect
-	github.com/mdlayher/socket v0.0.0-20210307095302-262dc9984e00 // indirect
-	github.com/mitchellh/copystructure v1.0.0 // indirect
+	github.com/matoous/godox v0.0.0-20210227103229-6504466cf951 // indirect
+	github.com/mattn/go-colorable v0.1.12 // indirect
+	github.com/mattn/go-isatty v0.0.14 // indirect
+	github.com/mattn/go-runewidth v0.0.13 // indirect
+	github.com/matttproud/golang_protobuf_extensions v1.0.1 // indirect
+	github.com/mbilski/exhaustivestruct v1.2.0 // indirect
+	github.com/mdlayher/socket v0.0.0-20211102153432-57e3fa563ecb // indirect
+	github.com/mgechev/dots v0.0.0-20210922191527-e955255bf517 // indirect
+	github.com/mgechev/revive v1.1.2 // indirect
+	github.com/mitchellh/copystructure v1.2.0 // indirect
 	github.com/mitchellh/go-homedir v1.1.0 // indirect
-	github.com/mitchellh/mapstructure v1.4.0 // indirect
-	github.com/mitchellh/reflectwalk v1.0.1 // indirect
+	github.com/mitchellh/mapstructure v1.4.3 // indirect
+	github.com/mitchellh/reflectwalk v1.0.2 // indirect
 	github.com/moricho/tparallel v0.2.1 // indirect
-	github.com/nakabonne/nestif v0.3.0 // indirect
-	github.com/nbutton23/zxcvbn-go v0.0.0-20180912185939-ae427f1e4c1d // indirect
-	github.com/nishanths/exhaustive v0.1.0 // indirect
+	github.com/nakabonne/nestif v0.3.1 // indirect
+	github.com/nbutton23/zxcvbn-go v0.0.0-20210217022336-fa2cb2858354 // indirect
+	github.com/nishanths/exhaustive v0.7.11 // indirect
+	github.com/nishanths/predeclared v0.2.1 // indirect
+	github.com/olekukonko/tablewriter v0.0.5 // indirect
 	github.com/op/go-logging v0.0.0-20160315200505-970db520ece7 // indirect
-	github.com/pelletier/go-toml v1.8.1 // indirect
+	github.com/pelletier/go-toml v1.9.4 // indirect
 	github.com/phayes/checkstyle v0.0.0-20170904204023-bfd46e6a821d // indirect
-	github.com/pkg/diff v0.0.0-20200914180035-5b29258ca4f7 // indirect
+	github.com/pkg/diff v0.0.0-20210226163009-20ebb0f2a09e // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
-	github.com/polyfloyd/go-errorlint v0.0.0-20201127212506-19bd8db6546f // indirect
-	github.com/quasilyte/go-ruleguard v0.2.1 // indirect
-	github.com/quasilyte/regex/syntax v0.0.0-20200805063351-8f842688393c // indirect
-	github.com/rogpeppe/go-internal v1.6.2 // indirect
-	github.com/ryancurrah/gomodguard v1.1.0 // indirect
+	github.com/polyfloyd/go-errorlint v0.0.0-20211125173453-6d6d39c5bb8b // indirect
+	github.com/prometheus/client_golang v1.11.0 // indirect
+	github.com/prometheus/client_model v0.2.0 // indirect
+	github.com/prometheus/common v0.32.1 // indirect
+	github.com/prometheus/procfs v0.7.3 // indirect
+	github.com/quasilyte/go-ruleguard v0.3.13 // indirect
+	github.com/quasilyte/regex/syntax v0.0.0-20210819130434-b3f0c404a727 // indirect
+	github.com/rivo/uniseg v0.2.0 // indirect
+	github.com/rogpeppe/go-internal v1.8.1-0.20211023094830-115ce09fd6b4 // indirect
+	github.com/ryancurrah/gomodguard v1.2.3 // indirect
 	github.com/ryanrolds/sqlclosecheck v0.3.0 // indirect
+	github.com/sanposhiho/wastedassign/v2 v2.0.7 // indirect
 	github.com/sassoftware/go-rpmutils v0.0.0-20190420191620-a8f1baeba37b // indirect
-	github.com/securego/gosec/v2 v2.5.0 // indirect
-	github.com/sergi/go-diff v1.1.0 // indirect
+	github.com/securego/gosec/v2 v2.9.3 // indirect
+	github.com/sergi/go-diff v1.2.0 // indirect
 	github.com/shazow/go-diff v0.0.0-20160112020656-b6b7b6733b8c // indirect
-	github.com/sirupsen/logrus v1.7.0 // indirect
+	github.com/sirupsen/logrus v1.8.1 // indirect
+	github.com/sivchari/tenv v1.4.7 // indirect
 	github.com/sonatard/noctx v0.0.1 // indirect
 	github.com/sourcegraph/go-diff v0.6.1 // indirect
-	github.com/spf13/afero v1.5.1 // indirect
-	github.com/spf13/cast v1.3.1 // indirect
-	github.com/spf13/cobra v1.1.1 // indirect
+	github.com/spf13/afero v1.6.0 // indirect
+	github.com/spf13/cast v1.4.1 // indirect
+	github.com/spf13/cobra v1.2.1 // indirect
 	github.com/spf13/jwalterweatherman v1.1.0 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
-	github.com/spf13/viper v1.7.1 // indirect
-	github.com/ssgreg/nlreturn/v2 v2.1.0 // indirect
+	github.com/spf13/viper v1.9.0 // indirect
+	github.com/ssgreg/nlreturn/v2 v2.2.1 // indirect
 	github.com/stretchr/objx v0.3.0 // indirect
 	github.com/stretchr/testify v1.7.0 // indirect
 	github.com/subosito/gotenv v1.2.0 // indirect
-	github.com/tdakkota/asciicheck v0.0.0-20200416200610-e657995f937b // indirect
-	github.com/tetafro/godot v1.3.2 // indirect
-	github.com/timakin/bodyclose v0.0.0-20200424151742-cb6215831a94 // indirect
-	github.com/tomarrell/wrapcheck v0.0.0-20201130113247-1683564d9756 // indirect
-	github.com/tommy-muehle/go-mnd v1.3.1-0.20200224220436-e6f9a994e8fa // indirect
+	github.com/sylvia7788/contextcheck v1.0.4 // indirect
+	github.com/tdakkota/asciicheck v0.1.1 // indirect
+	github.com/tetafro/godot v1.4.11 // indirect
+	github.com/timakin/bodyclose v0.0.0-20210704033933-f49887972144 // indirect
+	github.com/tomarrell/wrapcheck/v2 v2.4.0 // indirect
+	github.com/tommy-muehle/go-mnd/v2 v2.4.0 // indirect
 	github.com/u-root/uio v0.0.0-20210528114334-82958018845c // indirect
 	github.com/ultraware/funlen v0.0.3 // indirect
 	github.com/ultraware/whitespace v0.0.4 // indirect
-	github.com/uudashr/gocognit v1.0.1 // indirect
-	github.com/vishvananda/netns v0.0.0-20200728191858-db3c7e526aae // indirect
-	github.com/xanzy/ssh-agent v0.3.0 // indirect
+	github.com/uudashr/gocognit v1.0.5 // indirect
+	github.com/vishvananda/netns v0.0.0-20211101163701-50045581ed74 // indirect
+	github.com/xanzy/ssh-agent v0.3.1 // indirect
+	github.com/yeya24/promlinter v0.1.0 // indirect
 	go4.org/intern v0.0.0-20211027215823-ae77deb06f29 // indirect
 	go4.org/unsafe/assume-no-moving-gc v0.0.0-20211027215541-db492cf91b37 // indirect
-	golang.org/x/mod v0.4.2 // indirect
+	golang.org/x/mod v0.5.1 // indirect
 	golang.org/x/text v0.3.7 // indirect
 	golang.org/x/xerrors v0.0.0-20200804184101-5ec99f83aff1 // indirect
 	golang.zx2c4.com/wintun v0.0.0-20211104114900-415007cec224 // indirect
-	gopkg.in/ini.v1 v1.62.0 // indirect
+	google.golang.org/protobuf v1.27.1 // indirect
+	gopkg.in/ini.v1 v1.66.2 // indirect
 	gopkg.in/warnings.v0 v0.1.2 // indirect
 	gopkg.in/yaml.v2 v2.4.0 // indirect
-	gopkg.in/yaml.v3 v3.0.0-20200615113413-eeeca48fe776 // indirect
-	howett.net/plist v0.0.0-20181124034731-591f970eefbb // indirect
-	mvdan.cc/gofumpt v0.0.0-20201129102820-5c11c50e9475 // indirect
+	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
+	howett.net/plist v1.0.0 // indirect
+	mvdan.cc/gofumpt v0.2.0 // indirect
 	mvdan.cc/interfacer v0.0.0-20180901003855-c20040233aed // indirect
 	mvdan.cc/lint v0.0.0-20170908181259-adc824a0674b // indirect
-	mvdan.cc/unparam v0.0.0-20200501210554-b37ab49443f7 // indirect
-	software.sslmate.com/src/go-pkcs12 v0.0.0-20180114231543-2291e8f0f237 // indirect
+	mvdan.cc/unparam v0.0.0-20211002134041-24922b6997ca // indirect
+	software.sslmate.com/src/go-pkcs12 v0.0.0-20210415151418-c5206de65a78 // indirect
 )

go.toolchain.branch

@@ -0,0 +1 @@
+tailscale.go1.17

go.toolchain.rev

@@ -0,0 +1 @@
+25fe91a25c9630a50138a135105af19ae7c7c3e7

health/health.go

@@ -9,13 +9,14 @@ package health
 import (
 	"errors"
 	"fmt"
-	"os"
+	"net/http"
 	"runtime"
 	"sort"
 	"sync"
 	"sync/atomic"
 	"time"
 
+	"tailscale.com/envknob"
 	"tailscale.com/tailcfg"
 	"tailscale.com/util/multierr"
 )
@@ -28,6 +29,8 @@ var (
 	watchers = map[*watchHandle]func(Subsystem, error){} // opt func to run if error state changes
 	timer    *time.Timer
 
+	debugHandler = map[string]http.Handler{}
+
 	inMapPoll               bool
 	inMapPollSince          time.Time
 	lastMapPollEndedAt      time.Time
@@ -58,6 +61,9 @@ const (
 	// SysDNS is the name of the net/dns subsystem.
 	SysDNS = Subsystem("dns")
 
+	// SysDNSOS is the name of the net/dns OSConfigurator subsystem.
+	SysDNSOS = Subsystem("dns-os")
+
 	// SysNetworkCategory is the name of the subsystem that sets
 	// the Windows network adapter's "category" (public, private, domain).
 	// If it's unhealthy, the Windows firewall rules won't match.
@@ -101,12 +107,30 @@ func SetDNSHealth(err error) { set(SysDNS, err) }
 // DNSHealth returns the net/dns.Manager error state.
 func DNSHealth() error { return get(SysDNS) }
 
+// SetDNSOSHealth sets the state of the net/dns.OSConfigurator
+func SetDNSOSHealth(err error) { set(SysDNSOS, err) }
+
+// DNSOSHealth returns the net/dns.OSConfigurator error state.
+func DNSOSHealth() error { return get(SysDNSOS) }
+
 // SetNetworkCategoryHealth sets the state of setting the network adaptor's category.
 // This only applies on Windows.
 func SetNetworkCategoryHealth(err error) { set(SysNetworkCategory, err) }
 
 func NetworkCategoryHealth() error { return get(SysNetworkCategory) }
 
+func RegisterDebugHandler(typ string, h http.Handler) {
+	mu.Lock()
+	defer mu.Unlock()
+	debugHandler[typ] = h
+}
+
+func DebugHandler(typ string) http.Handler {
+	mu.Lock()
+	defer mu.Unlock()
+	return debugHandler[typ]
+}
+
 func get(key Subsystem) error {
 	mu.Lock()
 	defer mu.Unlock()
@@ -159,7 +183,8 @@ func GotStreamedMapResponse() {
 	selfCheckLocked()
 }
 
-// SetInPollNetMap records that we're in
+// SetInPollNetMap records whether the client has an open
+// HTTP long poll open to the control plane.
 func SetInPollNetMap(v bool) {
 	mu.Lock()
 	defer mu.Unlock()
@@ -174,6 +199,14 @@ func SetInPollNetMap(v bool) {
 	}
 }
 
+// GetInPollNetMap reports whether the client has an open
+// HTTP long poll open to the control plane.
+func GetInPollNetMap() bool {
+	mu.Lock()
+	defer mu.Unlock()
+	return inMapPoll
+}
+
 // SetMagicSockDERPHome notes what magicsock's view of its home DERP is.
 func SetMagicSockDERPHome(region int) {
 	mu.Lock()
@@ -275,7 +308,7 @@ func OverallError() error {
 	return overallErrorLocked()
 }
 
-var fakeErrForTesting = os.Getenv("TS_DEBUG_FAKE_HEALTH_ERROR")
+var fakeErrForTesting = envknob.String("TS_DEBUG_FAKE_HEALTH_ERROR")
 
 func overallErrorLocked() error {
 	if !anyInterfaceUp {

hostinfo/hostinfo.go

@@ -87,6 +87,7 @@ const (
 	AWSFargate      = EnvType("fg")
 	FlyDotIo        = EnvType("fly")
 	Kubernetes      = EnvType("k8s")
+	DockerDesktop   = EnvType("dde")
 )
 
 var envType atomic.Value // of EnvType
@@ -144,6 +145,9 @@ func getEnvType() EnvType {
 	if inKubernetes() {
 		return Kubernetes
 	}
+	if inDockerDesktop() {
+		return DockerDesktop
+	}
 	return ""
 }
 
@@ -228,6 +232,13 @@ func inKubernetes() bool {
 	return false
 }
 
+func inDockerDesktop() bool {
+	if os.Getenv("TS_HOST_ENV") == "dde" {
+		return true
+	}
+	return false
+}
+
 type etcAptSrcResult struct {
 	mod      time.Time
 	disabled bool

hostinfo/hostinfo_windows.go

@@ -5,10 +5,11 @@
 package hostinfo
 
 import (
-	"os/exec"
-	"strings"
+	"fmt"
 	"sync/atomic"
-	"syscall"
+
+	"golang.org/x/sys/windows"
+	"golang.org/x/sys/windows/registry"
 )
 
 func init() {
@@ -21,19 +22,37 @@ func osVersionWindows() string {
 	if s, ok := winVerCache.Load().(string); ok {
 		return s
 	}
-	cmd := exec.Command("cmd", "/c", "ver")
-	cmd.SysProcAttr = &syscall.SysProcAttr{HideWindow: true}
-	out, _ := cmd.Output() // "\nMicrosoft Windows [Version 10.0.19041.388]\n\n"
-	s := strings.TrimSpace(string(out))
-	s = strings.TrimPrefix(s, "Microsoft Windows [")
-	s = strings.TrimSuffix(s, "]")
-
-	// "Version 10.x.y.z", with "Version" localized. Keep only stuff after the space.
-	if sp := strings.Index(s, " "); sp != -1 {
-		s = s[sp+1:]
+	major, minor, build := windows.RtlGetNtVersionNumbers()
+	s := fmt.Sprintf("%d.%d.%d", major, minor, build)
+	// Windows 11 still uses 10 as its major number internally
+	if major == 10 {
+		if ubr, err := getUBR(); err == nil {
+			s += fmt.Sprintf(".%d", ubr)
+		}
 	}
 	if s != "" {
 		winVerCache.Store(s)
 	}
 	return s // "10.0.19041.388", ideally
 }
+
+// getUBR obtains a fourth version field, the "Update Build Revision",
+// from the registry. This field is only available beginning with Windows 10.
+func getUBR() (uint32, error) {
+	key, err := registry.OpenKey(registry.LOCAL_MACHINE,
+		`SOFTWARE\Microsoft\Windows NT\CurrentVersion`, registry.QUERY_VALUE|registry.WOW64_64KEY)
+	if err != nil {
+		return 0, err
+	}
+	defer key.Close()
+
+	val, valType, err := key.GetIntegerValue("UBR")
+	if err != nil {
+		return 0, err
+	}
+	if valType != registry.DWORD {
+		return 0, registry.ErrUnexpectedType
+	}
+
+	return uint32(val), nil
+}

ipn/ipnlocal/dnsconfig_test.go

@@ -111,7 +111,8 @@ func TestDNSConfigForNetmap(t *testing.T) {
 			},
 			prefs: &ipn.Prefs{},
 			want: &dns.Config{
-				Routes: map[dnsname.FQDN][]dnstype.Resolver{},
+				OnlyIPv6: true,
+				Routes:   map[dnsname.FQDN][]dnstype.Resolver{},
 				Hosts: map[dnsname.FQDN][]netaddr.IP{
 					"b.net.":       ips("fe75::2"),
 					"myname.net.":  ips("fe75::1"),
@@ -232,32 +233,11 @@ func TestDNSConfigForNetmap(t *testing.T) {
 			},
 		},
 		{
-			name: "android_does_need_fallbacks",
-			os:   "android",
-			nm: &netmap.NetworkMap{
-				DNS: tailcfg.DNSConfig{
-					FallbackResolvers: []dnstype.Resolver{
-						{Addr: "8.8.4.4"},
-					},
-					Routes: map[string][]dnstype.Resolver{
-						"foo.com.": {{Addr: "1.2.3.4"}},
-					},
-				},
-			},
-			prefs: &ipn.Prefs{
-				CorpDNS: true,
-			},
-			want: &dns.Config{
-				Hosts: map[dnsname.FQDN][]netaddr.IP{},
-				DefaultResolvers: []dnstype.Resolver{
-					{Addr: "8.8.4.4:53"},
-				},
-				Routes: map[dnsname.FQDN][]dnstype.Resolver{
-					"foo.com.": {{Addr: "1.2.3.4:53"}},
-				},
-			},
-		},
-		{
+			// Prior to fixing https://github.com/tailscale/tailscale/issues/2116,
+			// Android had cases where it needed FallbackResolvers. This was the
+			// negative test for the case where Override-local-DNS was set, so the
+			// fallback resolvers did not need to be used. This test is still valid
+			// so we keep it, but the fallback test has been removed.
 			name: "android_does_NOT_need_fallbacks",
 			os:   "android",
 			nm: &netmap.NetworkMap{
@@ -344,3 +324,48 @@ func TestDNSConfigForNetmap(t *testing.T) {
 		})
 	}
 }
+
+func TestAllowExitNodeDNSProxyToServeName(t *testing.T) {
+	b := &LocalBackend{}
+	if b.allowExitNodeDNSProxyToServeName("google.com") {
+		t.Fatal("unexpected true on backend with nil NetMap")
+	}
+
+	b.netMap = &netmap.NetworkMap{
+		DNS: tailcfg.DNSConfig{
+			ExitNodeFilteredSet: []string{
+				".ts.net",
+				"some.exact.bad",
+			},
+		},
+	}
+	tests := []struct {
+		name string
+		want bool
+	}{
+		// Allow by default:
+		{"google.com", true},
+		{"GOOGLE.com", true},
+
+		// Rejected by suffix:
+		{"foo.TS.NET", false},
+		{"foo.ts.net", false},
+
+		// Suffix doesn't match
+		{"ts.net", true},
+
+		// Rejected by exact match:
+		{"some.exact.bad", false},
+		{"SOME.EXACT.BAD", false},
+
+		// But a prefix is okay.
+		{"prefix-okay.some.exact.bad", true},
+	}
+	for _, tt := range tests {
+		got := b.allowExitNodeDNSProxyToServeName(tt.name)
+		if got != tt.want {
+			t.Errorf("for %q = %v; want %v", tt.name, got, tt.want)
+		}
+	}
+
+}

ipn/ipnlocal/local.go

@@ -22,12 +22,12 @@ import (
 	"strings"
 	"sync"
 	"sync/atomic"
-	"syscall"
 	"time"
 
 	"inet.af/netaddr"
 	"tailscale.com/client/tailscale/apitype"
 	"tailscale.com/control/controlclient"
+	"tailscale.com/envknob"
 	"tailscale.com/health"
 	"tailscale.com/hostinfo"
 	"tailscale.com/ipn"
@@ -36,8 +36,10 @@ import (
 	"tailscale.com/net/dns"
 	"tailscale.com/net/interfaces"
 	"tailscale.com/net/tsaddr"
+	"tailscale.com/net/tsdial"
 	"tailscale.com/paths"
 	"tailscale.com/portlist"
+	"tailscale.com/syncs"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/dnstype"
 	"tailscale.com/types/empty"
@@ -55,6 +57,7 @@ import (
 	"tailscale.com/version/distro"
 	"tailscale.com/wgengine"
 	"tailscale.com/wgengine/filter"
+	"tailscale.com/wgengine/magicsock"
 	"tailscale.com/wgengine/router"
 	"tailscale.com/wgengine/wgcfg"
 	"tailscale.com/wgengine/wgcfg/nmcfg"
@@ -63,7 +66,7 @@ import (
 var controlDebugFlags = getControlDebugFlags()
 
 func getControlDebugFlags() []string {
-	if e := os.Getenv("TS_DEBUG_CONTROL_FLAGS"); e != "" {
+	if e := envknob.String("TS_DEBUG_CONTROL_FLAGS"); e != "" {
 		return strings.Split(e, ",")
 	}
 	return nil
@@ -88,6 +91,7 @@ type LocalBackend struct {
 	statsLogf             logger.Logf        // for printing peers stats on change
 	e                     wgengine.Engine
 	store                 ipn.StateStore
+	dialer                *tsdial.Dialer // non-nil
 	backendLogID          string
 	unregisterLinkMon     func()
 	unregisterHealthWatch func()
@@ -97,9 +101,12 @@ type LocalBackend struct {
 	serverURL             string           // tailcontrol URL
 	newDecompressor       func() (controlclient.Decompressor, error)
 	varRoot               string // or empty if SetVarRoot never called
+	sshAtomicBool         syncs.AtomicBool
 
 	filterHash deephash.Sum
 
+	filterAtomic atomic.Value // of *filter.Filter
+
 	// The mutex protects the following elements.
 	mu             sync.Mutex
 	httpTestClient *http.Client // for controlclient. nil by default, used by tests.
@@ -139,7 +146,11 @@ type LocalBackend struct {
 	// same as the Network Extension lifetime and we can thus avoid
 	// double-copying files by writing them to the right location
 	// immediately.
-	directFileRoot string
+	// It's also used on Synology & TrueNAS, but in that case DoFinalRename
+	// is also set true, which moves the *.partial file to its final
+	// name on completion.
+	directFileRoot          string
+	directFileDoFinalRename bool // false on macOS, true on Synology & TrueNAS
 
 	// statusLock must be held before calling statusChanged.Wait() or
 	// statusChanged.Broadcast().
@@ -153,16 +164,18 @@ type clientGen func(controlclient.Options) (controlclient.Client, error)
 
 // NewLocalBackend returns a new LocalBackend that is ready to run,
 // but is not actually running.
-func NewLocalBackend(logf logger.Logf, logid string, store ipn.StateStore, e wgengine.Engine) (*LocalBackend, error) {
+//
+// If dialer is nil, a new one is made.
+func NewLocalBackend(logf logger.Logf, logid string, store ipn.StateStore, dialer *tsdial.Dialer, e wgengine.Engine) (*LocalBackend, error) {
 	if e == nil {
-		panic("ipn.NewLocalBackend: wgengine must not be nil")
+		panic("ipn.NewLocalBackend: engine must not be nil")
+	}
+	if dialer == nil {
+		dialer = new(tsdial.Dialer)
 	}
 
 	osshare.SetFileSharingEnabled(false, logf)
 
-	// Default filter blocks everything and logs nothing, until Start() is called.
-	e.SetFilter(filter.NewAllowNone(logf, &netaddr.IPSet{}))
-
 	ctx, cancel := context.WithCancel(context.Background())
 	portpoll, err := portlist.NewPoller()
 	if err != nil {
@@ -177,11 +190,16 @@ func NewLocalBackend(logf logger.Logf, logid string, store ipn.StateStore, e wge
 		statsLogf:      logger.LogOnChange(logf, 5*time.Minute, time.Now),
 		e:              e,
 		store:          store,
+		dialer:         dialer,
 		backendLogID:   logid,
 		state:          ipn.NoState,
 		portpoll:       portpoll,
 		gotPortPollRes: make(chan struct{}),
 	}
+
+	// Default filter blocks everything and logs nothing, until Start() is called.
+	b.setFilter(filter.NewAllowNone(logf, &netaddr.IPSet{}))
+
 	b.statusChanged = sync.NewCond(&b.statusLock)
 	b.e.SetStatusCallback(b.setWgengineStatus)
 
@@ -208,6 +226,11 @@ func NewLocalBackend(logf logger.Logf, logid string, store ipn.StateStore, e wge
 	return b, nil
 }
 
+// Dialer returns the backend's dialer.
+func (b *LocalBackend) Dialer() *tsdial.Dialer {
+	return b.dialer
+}
+
 // SetDirectFileRoot sets the directory to download files to directly,
 // without buffering them through an intermediate daemon-owned
 // tailcfg.UserID-specific directory.
@@ -219,6 +242,17 @@ func (b *LocalBackend) SetDirectFileRoot(dir string) {
 	b.directFileRoot = dir
 }
 
+// SetDirectFileDoFinalRename sets whether the peerapi file server should rename
+// a received "name.partial" file to "name" when the download is complete.
+//
+// This only applies when SetDirectFileRoot is non-empty.
+// The default is false.
+func (b *LocalBackend) SetDirectFileDoFinalRename(v bool) {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.directFileDoFinalRename = v
+}
+
 // b.mu must be held.
 func (b *LocalBackend) maybePauseControlClientLocked() {
 	if b.cc == nil {
@@ -347,11 +381,23 @@ func (b *LocalBackend) updateStatus(sb *ipnstate.StatusBuilder, extraLocked func
 		if b.netMap != nil {
 			s.MagicDNSSuffix = b.netMap.MagicDNSSuffix()
 			s.CertDomains = append([]string(nil), b.netMap.DNS.CertDomains...)
+			s.TailnetName = b.netMap.Domain
 		}
 	})
 	sb.MutateSelfStatus(func(ss *ipnstate.PeerStatus) {
-		if b.netMap != nil && b.netMap.SelfNode != nil {
-			ss.ID = b.netMap.SelfNode.StableID
+		ss.Online = health.GetInPollNetMap()
+		if b.netMap != nil {
+			ss.HostName = b.netMap.Hostinfo.Hostname
+			ss.DNSName = b.netMap.Name
+			ss.UserID = b.netMap.User
+			if sn := b.netMap.SelfNode; sn != nil {
+				ss.ID = sn.StableID
+				if c := sn.Capabilities; len(c) > 0 {
+					ss.Capabilities = append([]string(nil), c...)
+				}
+			}
+		} else {
+			ss.HostName, _ = os.Hostname()
 		}
 		for _, pln := range b.peerAPIListeners {
 			ss.PeerAPIURL = append(ss.PeerAPIURL, pln.urlStr)
@@ -377,33 +423,30 @@ func (b *LocalBackend) populatePeerStatusLocked(sb *ipnstate.StatusBuilder) {
 		if p.LastSeen != nil {
 			lastSeen = *p.LastSeen
 		}
-		var tailAddr4 string
 		var tailscaleIPs = make([]netaddr.IP, 0, len(p.Addresses))
 		for _, addr := range p.Addresses {
 			if addr.IsSingleIP() && tsaddr.IsTailscaleIP(addr.IP()) {
-				if addr.IP().Is4() && tailAddr4 == "" {
-					// The peer struct previously only allowed a single
-					// Tailscale IP address. For compatibility for a few releases starting
-					// with 1.8, keep it pulled out as IPv4-only for a bit.
-					tailAddr4 = addr.IP().String()
-				}
 				tailscaleIPs = append(tailscaleIPs, addr.IP())
 			}
 		}
+		exitNodeOption := tsaddr.PrefixesContainsFunc(p.AllowedIPs, func(r netaddr.IPPrefix) bool {
+			return r.Bits() == 0
+		})
 		sb.AddPeer(p.Key, &ipnstate.PeerStatus{
-			InNetworkMap:       true,
-			ID:                 p.StableID,
-			UserID:             p.User,
-			TailAddrDeprecated: tailAddr4,
-			TailscaleIPs:       tailscaleIPs,
-			HostName:           p.Hostinfo.Hostname,
-			DNSName:            p.Name,
-			OS:                 p.Hostinfo.OS,
-			KeepAlive:          p.KeepAlive,
-			Created:            p.Created,
-			LastSeen:           lastSeen,
-			ShareeNode:         p.Hostinfo.ShareeNode,
-			ExitNode:           p.StableID != "" && p.StableID == b.prefs.ExitNodeID,
+			InNetworkMap:   true,
+			ID:             p.StableID,
+			UserID:         p.User,
+			TailscaleIPs:   tailscaleIPs,
+			HostName:       p.Hostinfo.Hostname,
+			DNSName:        p.Name,
+			OS:             p.Hostinfo.OS,
+			KeepAlive:      p.KeepAlive,
+			Created:        p.Created,
+			LastSeen:       lastSeen,
+			Online:         p.Online != nil && *p.Online,
+			ShareeNode:     p.Hostinfo.ShareeNode,
+			ExitNode:       p.StableID != "" && p.StableID == b.prefs.ExitNodeID,
+			ExitNodeOption: exitNodeOption,
 		})
 	}
 }
@@ -499,6 +542,7 @@ func (b *LocalBackend) setClientStatus(st controlclient.Status) {
 		// Since st.NetMap==nil means "netmap is unchanged", there is
 		// no other way to represent this change.
 		b.setNetMapLocked(nil)
+		b.e.SetNetworkMap(new(netmap.NetworkMap))
 	}
 
 	prefs := b.prefs
@@ -588,6 +632,11 @@ func (b *LocalBackend) setClientStatus(st controlclient.Status) {
 // findExitNodeIDLocked updates b.prefs to reference an exit node by ID,
 // rather than by IP. It returns whether prefs was mutated.
 func (b *LocalBackend) findExitNodeIDLocked(nm *netmap.NetworkMap) (prefsChanged bool) {
+	if nm == nil {
+		// No netmap, can't resolve anything.
+		return false
+	}
+
 	// If we have a desired IP on file, try to find the corresponding
 	// node.
 	if b.prefs.ExitNodeIP.IsZero() {
@@ -976,7 +1025,12 @@ func (b *LocalBackend) updateFilter(netMap *netmap.NetworkMap, prefs *ipn.Prefs)
 				// wifi": you get internet access, but to additionally
 				// get LAN access the LAN(s) need to be offered
 				// explicitly as well.
-				s, err := shrinkDefaultRoute(r)
+				localInterfaceRoutes, hostIPs, err := interfaceRoutes()
+				if err != nil {
+					b.logf("getting local interface routes: %v", err)
+					continue
+				}
+				s, err := shrinkDefaultRoute(r, localInterfaceRoutes, hostIPs)
 				if err != nil {
 					b.logf("computing default route filter: %v", err)
 					continue
@@ -1001,20 +1055,25 @@ func (b *LocalBackend) updateFilter(netMap *netmap.NetworkMap, prefs *ipn.Prefs)
 
 	if !haveNetmap {
 		b.logf("netmap packet filter: (not ready yet)")
-		b.e.SetFilter(filter.NewAllowNone(b.logf, logNets))
+		b.setFilter(filter.NewAllowNone(b.logf, logNets))
 		return
 	}
 
 	oldFilter := b.e.GetFilter()
 	if shieldsUp {
 		b.logf("netmap packet filter: (shields up)")
-		b.e.SetFilter(filter.NewShieldsUpFilter(localNets, logNets, oldFilter, b.logf))
+		b.setFilter(filter.NewShieldsUpFilter(localNets, logNets, oldFilter, b.logf))
 	} else {
 		b.logf("netmap packet filter: %v filters", len(packetFilter))
-		b.e.SetFilter(filter.New(packetFilter, localNets, logNets, oldFilter, b.logf))
+		b.setFilter(filter.New(packetFilter, localNets, logNets, oldFilter, b.logf))
 	}
 }
 
+func (b *LocalBackend) setFilter(f *filter.Filter) {
+	b.filterAtomic.Store(f)
+	b.e.SetFilter(f)
+}
+
 var removeFromDefaultRoute = []netaddr.IPPrefix{
 	// RFC1918 LAN ranges
 	netaddr.MustParseIPPrefix("192.168.0.0/16"),
@@ -1115,17 +1174,14 @@ func interfaceRoutes() (ips *netaddr.IPSet, hostIPs []netaddr.IP, err error) {
 }
 
 // shrinkDefaultRoute returns an IPSet representing the IPs in route,
-// minus those in removeFromDefaultRoute and local interface subnets.
-func shrinkDefaultRoute(route netaddr.IPPrefix) (*netaddr.IPSet, error) {
-	interfaceRoutes, hostIPs, err := interfaceRoutes()
-	if err != nil {
-		return nil, err
-	}
+// minus those in removeFromDefaultRoute and localInterfaceRoutes,
+// plus the IPs in hostIPs.
+func shrinkDefaultRoute(route netaddr.IPPrefix, localInterfaceRoutes *netaddr.IPSet, hostIPs []netaddr.IP) (*netaddr.IPSet, error) {
 	var b netaddr.IPSetBuilder
 	// Add the default route.
 	b.AddPrefix(route)
 	// Remove the local interface routes.
-	b.RemoveSet(interfaceRoutes)
+	b.RemoveSet(localInterfaceRoutes)
 
 	// Having removed all the LAN subnets, re-add the hosts's own
 	// IPs. It's fine for clients to connect to an exit node's public
@@ -1242,7 +1298,7 @@ func (b *LocalBackend) send(n ipn.Notify) {
 		return
 	}
 
-	if apiSrv != nil && apiSrv.hasFilesWaiting() {
+	if apiSrv.hasFilesWaiting() {
 		n.FilesWaiting = &empty.Message{}
 	}
 
@@ -1297,7 +1353,7 @@ func (b *LocalBackend) popBrowserAuthNow() {
 }
 
 // For testing lazy machine key generation.
-var panicOnMachineKeyGeneration, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_PANIC_MACHINE_KEY"))
+var panicOnMachineKeyGeneration = envknob.Bool("TS_DEBUG_PANIC_MACHINE_KEY")
 
 func (b *LocalBackend) createGetMachinePrivateKeyFunc() func() (key.MachinePrivate, error) {
 	var cache atomic.Value
@@ -1483,6 +1539,9 @@ func (b *LocalBackend) loadStateLocked(key ipn.StateKey, prefs *ipn.Prefs) (err
 	}
 
 	b.logf("backend prefs for %q: %s", key, b.prefs.Pretty())
+
+	b.sshAtomicBool.Set(b.prefs != nil && b.prefs.RunSSH)
+
 	return nil
 }
 
@@ -1651,14 +1710,20 @@ func (b *LocalBackend) SetPrefs(newp *ipn.Prefs) {
 }
 
 // setPrefsLockedOnEntry requires b.mu be held to call it, but it
-// unlocks b.mu when done.
+// unlocks b.mu when done. newp ownership passes to this function.
 func (b *LocalBackend) setPrefsLockedOnEntry(caller string, newp *ipn.Prefs) {
 	netMap := b.netMap
 	stateKey := b.stateKey
 
+	b.sshAtomicBool.Set(newp.RunSSH)
+
 	oldp := b.prefs
 	newp.Persist = oldp.Persist // caller isn't allowed to override this
 	b.prefs = newp
+	// findExitNodeIDLocked returns whether it updated b.prefs, but
+	// everything in this function treats b.prefs as completely new
+	// anyway. No-op if no exit node resolution is needed.
+	b.findExitNodeIDLocked(netMap)
 	b.inServerMode = newp.ForceDaemon
 	// We do this to avoid holding the lock while doing everything else.
 	newp = b.prefs.Clone()
@@ -1694,7 +1759,7 @@ func (b *LocalBackend) setPrefsLockedOnEntry(caller string, newp *ipn.Prefs) {
 				// notified (to update its prefs/persist) on
 				// account switch.  Log this while we figure it
 				// out.
-				b.logf("active login: %s ([unexpected] corp#461, not %s)", newp.Persist.LoginName)
+				b.logf("active login: %q ([unexpected] corp#461, not %q)", newp.Persist.LoginName, login)
 			}
 		}
 	}
@@ -1736,15 +1801,24 @@ func (b *LocalBackend) getPeerAPIPortForTSMPPing(ip netaddr.IP) (port uint16, ok
 
 func (b *LocalBackend) peerAPIServicesLocked() (ret []tailcfg.Service) {
 	for _, pln := range b.peerAPIListeners {
-		proto := tailcfg.ServiceProto("peerapi4")
+		proto := tailcfg.PeerAPI4
 		if pln.ip.Is6() {
-			proto = "peerapi6"
+			proto = tailcfg.PeerAPI6
 		}
 		ret = append(ret, tailcfg.Service{
 			Proto: proto,
 			Port:  uint16(pln.port),
 		})
 	}
+	switch runtime.GOOS {
+	case "linux", "freebsd", "openbsd", "illumos", "darwin", "windows":
+		// These are the platforms currently supported by
+		// net/dns/resolver/tsdns.go:Resolver.HandleExitNodeDNSQuery.
+		ret = append(ret, tailcfg.Service{
+			Proto: tailcfg.PeerAPIDNS,
+			Port:  1, // version
+		})
+	}
 	return ret
 }
 
@@ -1845,6 +1919,15 @@ func (b *LocalBackend) authReconfig() {
 		}
 	}
 
+	// Keep the dialer updated about whether we're supposed to use
+	// an exit node's DNS server (so SOCKS5/HTTP outgoing dials
+	// can use it for name resolution)
+	if dohURL, ok := exitNodeCanProxyDNS(nm, prefs.ExitNodeID); ok {
+		b.dialer.SetExitDNSDoH(dohURL)
+	} else {
+		b.dialer.SetExitDNSDoH("")
+	}
+
 	cfg, err := nmcfg.WGCfg(nm, b.logf, flags, prefs.ExitNodeID)
 	if err != nil {
 		b.logf("wgcfg: %v", err)
@@ -1877,6 +1960,7 @@ func dnsConfigForNetmap(nm *netmap.NetworkMap, prefs *ipn.Prefs, logf logger.Log
 	// selfV6Only is whether we only have IPv6 addresses ourselves.
 	selfV6Only := tsaddr.PrefixesContainsFunc(nm.Addresses, tsaddr.PrefixIs6) &&
 		!tsaddr.PrefixesContainsFunc(nm.Addresses, tsaddr.PrefixIs4)
+	dcfg.OnlyIPv6 = selfV6Only
 
 	// Populate MagicDNS records. We do this unconditionally so that
 	// quad-100 can always respond to MagicDNS queries, even if the OS
@@ -1943,12 +2027,32 @@ func dnsConfigForNetmap(nm *netmap.NetworkMap, prefs *ipn.Prefs, logf logger.Log
 		return dcfg
 	}
 
+	for _, dom := range nm.DNS.Domains {
+		fqdn, err := dnsname.ToFQDN(dom)
+		if err != nil {
+			logf("[unexpected] non-FQDN search domain %q", dom)
+		}
+		dcfg.SearchDomains = append(dcfg.SearchDomains, fqdn)
+	}
+	if nm.DNS.Proxied { // actually means "enable MagicDNS"
+		for _, dom := range magicDNSRootDomains(nm) {
+			dcfg.Routes[dom] = nil // resolve internally with dcfg.Hosts
+		}
+	}
+
 	addDefault := func(resolvers []dnstype.Resolver) {
 		for _, r := range resolvers {
 			dcfg.DefaultResolvers = append(dcfg.DefaultResolvers, normalizeResolver(r))
 		}
 	}
 
+	// If we're using an exit node and that exit node is new enough (1.19.x+)
+	// to run a DoH DNS proxy, then send all our DNS traffic through it.
+	if dohURL, ok := exitNodeCanProxyDNS(nm, prefs.ExitNodeID); ok {
+		addDefault([]dnstype.Resolver{{Addr: dohURL}})
+		return dcfg
+	}
+
 	addDefault(nm.DNS.Resolvers)
 	for suffix, resolvers := range nm.DNS.Routes {
 		fqdn, err := dnsname.ToFQDN(suffix)
@@ -1970,18 +2074,6 @@ func dnsConfigForNetmap(nm *netmap.NetworkMap, prefs *ipn.Prefs, logf logger.Log
 			dcfg.Routes[fqdn] = append(dcfg.Routes[fqdn], normalizeResolver(r))
 		}
 	}
-	for _, dom := range nm.DNS.Domains {
-		fqdn, err := dnsname.ToFQDN(dom)
-		if err != nil {
-			logf("[unexpected] non-FQDN search domain %q", dom)
-		}
-		dcfg.SearchDomains = append(dcfg.SearchDomains, fqdn)
-	}
-	if nm.DNS.Proxied { // actually means "enable MagicDNS"
-		for _, dom := range magicDNSRootDomains(nm) {
-			dcfg.Routes[dom] = nil // resolve internally with dcfg.Hosts
-		}
-	}
 
 	// Set FallbackResolvers as the default resolvers in the
 	// scenarios that can't handle a purely split-DNS config. See
@@ -2005,9 +2097,6 @@ func dnsConfigForNetmap(nm *netmap.NetworkMap, prefs *ipn.Prefs, logf logger.Log
 		addDefault(nm.DNS.FallbackResolvers)
 	case len(dcfg.Routes) == 0:
 		// No settings requiring split DNS, no problem.
-	case versionOS == "android":
-		// We don't support split DNS at all on Android yet.
-		addDefault(nm.DNS.FallbackResolvers)
 	}
 
 	return dcfg
@@ -2041,7 +2130,7 @@ func (b *LocalBackend) TailscaleVarRoot() string {
 		return b.varRoot
 	}
 	switch runtime.GOOS {
-	case "ios", "android":
+	case "ios", "android", "darwin":
 		dir, _ := paths.AppSharedDir.Load().(string)
 		return dir
 	}
@@ -2054,7 +2143,7 @@ func (b *LocalBackend) fileRootLocked(uid tailcfg.UserID) string {
 	}
 	varRoot := b.TailscaleVarRoot()
 	if varRoot == "" {
-		b.logf("peerapi disabled; no state directory")
+		b.logf("Taildrop disabled; no state directory")
 		return ""
 	}
 	baseDir := fmt.Sprintf("%s-uid-%d",
@@ -2062,7 +2151,7 @@ func (b *LocalBackend) fileRootLocked(uid tailcfg.UserID) string {
 		uid)
 	dir := filepath.Join(varRoot, "files", baseDir)
 	if err := os.MkdirAll(dir, 0700); err != nil {
-		b.logf("peerapi disabled; error making directory: %v", err)
+		b.logf("Taildrop disabled; error making directory: %v", err)
 		return ""
 	}
 	return dir
@@ -2125,22 +2214,20 @@ func (b *LocalBackend) initPeerAPIListener() {
 
 	fileRoot := b.fileRootLocked(selfNode.User)
 	if fileRoot == "" {
-		return
-	}
-
-	var tunName string
-	if ge, ok := b.e.(wgengine.InternalsGetter); ok {
-		if tunWrap, _, ok := ge.GetInternals(); ok {
-			tunName, _ = tunWrap.Name()
-		}
+		b.logf("peerapi starting without Taildrop directory configured")
 	}
 
 	ps := &peerAPIServer{
-		b:              b,
-		rootDir:        fileRoot,
-		tunName:        tunName,
-		selfNode:       selfNode,
-		directFileMode: b.directFileRoot != "",
+		b:                       b,
+		rootDir:                 fileRoot,
+		selfNode:                selfNode,
+		directFileMode:          b.directFileRoot != "",
+		directFileDoFinalRename: b.directFileDoFinalRename,
+	}
+	if re, ok := b.e.(wgengine.ResolvingEngine); ok {
+		if r, ok := re.GetResolver(); ok {
+			ps.resolver = r
+		}
 	}
 	b.peerAPIServer = ps
 
@@ -2305,7 +2392,9 @@ func (b *LocalBackend) routerConfig(cfg *wgcfg.Config, prefs *ipn.Prefs) *router
 		}
 	}
 
-	rs.Routes = append(rs.Routes, netaddr.IPPrefixFrom(tsaddr.TailscaleServiceIP(), 32))
+	if tsaddr.PrefixesContainsFunc(rs.LocalAddrs, tsaddr.PrefixIs4) {
+		rs.Routes = append(rs.Routes, netaddr.IPPrefixFrom(tsaddr.TailscaleServiceIP(), 32))
+	}
 
 	return rs
 }
@@ -2537,8 +2626,11 @@ func (b *LocalBackend) ResetForClientDisconnect() {
 	b.authURL = ""
 	b.authURLSticky = ""
 	b.activeLogin = ""
+	b.sshAtomicBool.Set(false)
 }
 
+func (b *LocalBackend) ShouldRunSSH() bool { return b.sshAtomicBool.Get() }
+
 // Logout tells the controlclient that we want to log out, and
 // transitions the local engine to the logged-out state without
 // waiting for controlclient to be in that state.
@@ -2618,6 +2710,7 @@ func hasCapability(nm *netmap.NetworkMap, cap string) bool {
 }
 
 func (b *LocalBackend) setNetMapLocked(nm *netmap.NetworkMap) {
+	b.dialer.SetNetMap(nm)
 	var login string
 	if nm != nil {
 		login = nm.UserProfiles[nm.User].LoginName
@@ -2722,9 +2815,6 @@ func (b *LocalBackend) WaitingFiles() ([]apitype.WaitingFile, error) {
 	b.mu.Lock()
 	apiSrv := b.peerAPIServer
 	b.mu.Unlock()
-	if apiSrv == nil {
-		return nil, errors.New("peerapi disabled")
-	}
 	return apiSrv.WaitingFiles()
 }
 
@@ -2732,9 +2822,6 @@ func (b *LocalBackend) DeleteFile(name string) error {
 	b.mu.Lock()
 	apiSrv := b.peerAPIServer
 	b.mu.Unlock()
-	if apiSrv == nil {
-		return errors.New("peerapi disabled")
-	}
 	return apiSrv.DeleteFile(name)
 }
 
@@ -2742,9 +2829,6 @@ func (b *LocalBackend) OpenFile(name string) (rc io.ReadCloser, size int64, err
 	b.mu.Lock()
 	apiSrv := b.peerAPIServer
 	b.mu.Unlock()
-	if apiSrv == nil {
-		return nil, 0, errors.New("peerapi disabled")
-	}
 	return apiSrv.OpenFile(name)
 }
 
@@ -2858,9 +2942,9 @@ func peerAPIBase(nm *netmap.NetworkMap, peer *tailcfg.Node) string {
 	var p4, p6 uint16
 	for _, s := range peer.Hostinfo.Services {
 		switch s.Proto {
-		case "peerapi4":
+		case tailcfg.PeerAPI4:
 			p4 = s.Port
-		case "peerapi6":
+		case tailcfg.PeerAPI6:
 			p6 = s.Port
 		}
 	}
@@ -2894,48 +2978,97 @@ func (b *LocalBackend) CheckIPForwarding() error {
 	if wgengine.IsNetstackRouter(b.e) {
 		return nil
 	}
-	if isBSD(runtime.GOOS) {
+
+	switch {
+	case isBSD(runtime.GOOS):
 		return fmt.Errorf("Subnet routing and exit nodes only work with additional manual configuration on %v, and is not currently officially supported.", runtime.GOOS)
+	case runtime.GOOS == "linux":
+		return checkIPForwardingLinux()
+	default:
+		// TODO: subnet routing and exit nodes probably don't work
+		// correctly on non-linux, non-netstack OSes either. Warn
+		// instead of being silent?
+		return nil
+	}
+}
+
+// checkIPForwardingLinux checks if IP forwarding is enabled correctly
+// for subnet routing and exit node functionality. Returns an error
+// describing configuration issues if the configuration is not
+// definitely good.
+func checkIPForwardingLinux() error {
+	const kbLink = "\nSee https://tailscale.com/kb/1104/enable-ip-forwarding/"
+
+	disabled, err := disabledSysctls("net.ipv4.ip_forward", "net.ipv6.conf.all.forwarding")
+	if err != nil {
+		return fmt.Errorf("Couldn't check system's IP forwarding configuration, subnet routing/exit nodes may not work: %w%s", err, kbLink)
 	}
 
-	var keys []string
-
-	if runtime.GOOS == "linux" {
-		keys = append(keys, "net.ipv4.ip_forward", "net.ipv6.conf.all.forwarding")
-	} else if isBSD(runtime.GOOS) {
-		keys = append(keys, "net.inet.ip.forwarding")
-	} else {
+	if len(disabled) == 0 {
+		// IP forwarding is enabled systemwide, all is well.
 		return nil
 	}
 
-	const suffix = "\nSubnet routes won't work without IP forwarding.\nSee https://tailscale.com/kb/1104/enable-ip-forwarding/"
-	for _, key := range keys {
-		bs, err := exec.Command("sysctl", "-n", key).Output()
-		if err != nil {
-			return fmt.Errorf("couldn't check %s (%v)%s", key, err, suffix)
+	// IP forwarding isn't enabled globally, but it might be enabled
+	// on a per-interface basis. Check if it's on for all interfaces,
+	// and warn appropriately if it's not.
+	ifaces, err := interfaces.GetList()
+	if err != nil {
+		return fmt.Errorf("Couldn't enumerate network interfaces, subnet routing/exit nodes may not work: %w%s", err, kbLink)
+	}
+
+	var (
+		warnings   []string
+		anyEnabled bool
+	)
+	for _, iface := range ifaces {
+		if iface.Name == "lo" {
+			continue
 		}
-		on, err := strconv.ParseBool(string(bytes.TrimSpace(bs)))
+		disabled, err = disabledSysctls(fmt.Sprintf("net.ipv4.conf.%s.forwarding", iface.Name), fmt.Sprintf("net.ipv6.conf.%s.forwarding", iface.Name))
 		if err != nil {
-			return fmt.Errorf("couldn't parse %s (%v)%s.", key, err, suffix)
+			return fmt.Errorf("Couldn't check system's IP forwarding configuration, subnet routing/exit nodes may not work: %w%s", err, kbLink)
 		}
-		if !on {
-			return fmt.Errorf("%s is disabled.%s", key, suffix)
+		if len(disabled) > 0 {
+			warnings = append(warnings, fmt.Sprintf("Traffic received on %s won't be forwarded (%s disabled)", iface.Name, strings.Join(disabled, ", ")))
+		} else {
+			anyEnabled = true
 		}
 	}
+	if !anyEnabled {
+		// IP forwarding is compeltely disabled, just say that rather
+		// than enumerate all the interfaces on the system.
+		return fmt.Errorf("IP forwarding is disabled, subnet routing/exit nodes will not work.%s", kbLink)
+	}
+	if len(warnings) > 0 {
+		// If partially enabled, enumerate the bits that won't work.
+		return fmt.Errorf("%s\nSubnet routes and exit nodes may not work correctly.%s", strings.Join(warnings, "\n"), kbLink)
+	}
+
 	return nil
 }
 
-// peerDialControlFunc is non-nil on platforms that require a way to
-// bind to dial out to other peers.
-var peerDialControlFunc func(*LocalBackend) func(network, address string, c syscall.RawConn) error
-
-// PeerDialControlFunc returns a net.Dialer.Control func (possibly nil) to use to
-// dial other Tailscale peers from the current environment.
-func (b *LocalBackend) PeerDialControlFunc() func(network, address string, c syscall.RawConn) error {
-	if peerDialControlFunc != nil {
-		return peerDialControlFunc(b)
+// disabledSysctls checks if the given sysctl keys are off, according
+// to strconv.ParseBool. Returns a list of keys that are disabled, or
+// err if something went wrong which prevented the lookups from
+// completing.
+func disabledSysctls(sysctls ...string) (disabled []string, err error) {
+	for _, k := range sysctls {
+		// TODO: on linux, we can get at these values via /proc/sys,
+		// rather than fork subcommands that may not be installed.
+		bs, err := exec.Command("sysctl", "-n", k).Output()
+		if err != nil {
+			return nil, fmt.Errorf("couldn't check %s (%v)", k, err)
+		}
+		on, err := strconv.ParseBool(string(bytes.TrimSpace(bs)))
+		if err != nil {
+			return nil, fmt.Errorf("couldn't parse %s (%v)", k, err)
+		}
+		if !on {
+			disabled = append(disabled, k)
+		}
 	}
-	return nil
+	return disabled, nil
 }
 
 // DERPMap returns the current DERPMap in use, or nil if not connected.
@@ -2947,3 +3080,107 @@ func (b *LocalBackend) DERPMap() *tailcfg.DERPMap {
 	}
 	return b.netMap.DERPMap
 }
+
+// OfferingExitNode reports whether b is currently offering exit node
+// access.
+func (b *LocalBackend) OfferingExitNode() bool {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.prefs == nil {
+		return false
+	}
+	var def4, def6 bool
+	for _, r := range b.prefs.AdvertiseRoutes {
+		if r.Bits() != 0 {
+			continue
+		}
+		if r.IP().Is4() {
+			def4 = true
+		} else if r.IP().Is6() {
+			def6 = true
+		}
+	}
+	return def4 && def6
+}
+
+// allowExitNodeDNSProxyToServeName reports whether the Exit Node DNS
+// proxy is allowed to serve responses for the provided DNS name.
+func (b *LocalBackend) allowExitNodeDNSProxyToServeName(name string) bool {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	nm := b.netMap
+	if nm == nil {
+		return false
+	}
+	name = strings.ToLower(name)
+	for _, bad := range nm.DNS.ExitNodeFilteredSet {
+		if bad == "" {
+			// Invalid, ignore.
+			continue
+		}
+		if bad[0] == '.' {
+			// Entries beginning with a dot are suffix matches.
+			if dnsname.HasSuffix(name, bad) {
+				return false
+			}
+			continue
+		}
+		// Otherwise entries are exact matches. They're
+		// guaranteed to be lowercase already.
+		if name == bad {
+			return false
+		}
+	}
+	return true
+}
+
+// exitNodeCanProxyDNS reports the DoH base URL ("http://foo/dns-query") without query parameters
+// to exitNodeID's DoH service, if available.
+//
+// If exitNodeID is the zero valid, it returns "", false.
+func exitNodeCanProxyDNS(nm *netmap.NetworkMap, exitNodeID tailcfg.StableNodeID) (dohURL string, ok bool) {
+	if exitNodeID.IsZero() {
+		return "", false
+	}
+	for _, p := range nm.Peers {
+		if p.StableID != exitNodeID {
+			continue
+		}
+		for _, s := range p.Hostinfo.Services {
+			if s.Proto == tailcfg.PeerAPIDNS && s.Port >= 1 {
+				return peerAPIBase(nm, p) + "/dns-query", true
+			}
+		}
+	}
+	return "", false
+}
+
+func (b *LocalBackend) DebugRebind() error {
+	mc, err := b.magicConn()
+	if err != nil {
+		return err
+	}
+	mc.Rebind()
+	return nil
+}
+
+func (b *LocalBackend) DebugReSTUN() error {
+	mc, err := b.magicConn()
+	if err != nil {
+		return err
+	}
+	mc.ReSTUN("explicit-debug")
+	return nil
+}
+
+func (b *LocalBackend) magicConn() (*magicsock.Conn, error) {
+	ig, ok := b.e.(wgengine.InternalsGetter)
+	if !ok {
+		return nil, errors.New("engine isn't InternalsGetter")
+	}
+	_, mc, ok := ig.GetInternals()
+	if !ok {
+		return nil, errors.New("failed to get internals")
+	}
+	return mc, nil
+}

ipn/ipnlocal/local_test.go

@@ -92,14 +92,14 @@ func TestNetworkMapCompare(t *testing.T) {
 		},
 		{
 			"Node names identical",
-			&netmap.NetworkMap{Peers: []*tailcfg.Node{&tailcfg.Node{Name: "A"}}},
-			&netmap.NetworkMap{Peers: []*tailcfg.Node{&tailcfg.Node{Name: "A"}}},
+			&netmap.NetworkMap{Peers: []*tailcfg.Node{{Name: "A"}}},
+			&netmap.NetworkMap{Peers: []*tailcfg.Node{{Name: "A"}}},
 			true,
 		},
 		{
 			"Node names differ",
-			&netmap.NetworkMap{Peers: []*tailcfg.Node{&tailcfg.Node{Name: "A"}}},
-			&netmap.NetworkMap{Peers: []*tailcfg.Node{&tailcfg.Node{Name: "B"}}},
+			&netmap.NetworkMap{Peers: []*tailcfg.Node{{Name: "A"}}},
+			&netmap.NetworkMap{Peers: []*tailcfg.Node{{Name: "B"}}},
 			false,
 		},
 		{
@@ -117,8 +117,8 @@ func TestNetworkMapCompare(t *testing.T) {
 		{
 			"Node Users differ",
 			// User field is not checked.
-			&netmap.NetworkMap{Peers: []*tailcfg.Node{&tailcfg.Node{User: 0}}},
-			&netmap.NetworkMap{Peers: []*tailcfg.Node{&tailcfg.Node{User: 1}}},
+			&netmap.NetworkMap{Peers: []*tailcfg.Node{{User: 0}}},
+			&netmap.NetworkMap{Peers: []*tailcfg.Node{{User: 1}}},
 			true,
 		},
 	}
@@ -178,9 +178,31 @@ func TestShrinkDefaultRoute(t *testing.T) {
 		},
 	}
 
+	// Construct a fake local network environment to make this test hermetic.
+	// localInterfaceRoutes and hostIPs would normally come from calling interfaceRoutes,
+	// and localAddresses would normally come from calling interfaces.LocalAddresses.
+	var b netaddr.IPSetBuilder
+	for _, c := range []string{"127.0.0.0/8", "192.168.9.0/24", "fe80::/32"} {
+		p := netaddr.MustParseIPPrefix(c)
+		b.AddPrefix(p)
+	}
+	localInterfaceRoutes, err := b.IPSet()
+	if err != nil {
+		t.Fatal(err)
+	}
+	hostIPs := []netaddr.IP{
+		netaddr.MustParseIP("127.0.0.1"),
+		netaddr.MustParseIP("192.168.9.39"),
+		netaddr.MustParseIP("fe80::1"),
+		netaddr.MustParseIP("fe80::437d:feff:feca:49a7"),
+	}
+	localAddresses := []netaddr.IP{
+		netaddr.MustParseIP("192.168.9.39"),
+	}
+
 	for _, test := range tests {
 		def := netaddr.MustParseIPPrefix(test.route)
-		got, err := shrinkDefaultRoute(def)
+		got, err := shrinkDefaultRoute(def, localInterfaceRoutes, hostIPs)
 		if err != nil {
 			t.Fatalf("shrinkDefaultRoute(%q): %v", test.route, err)
 		}
@@ -194,11 +216,7 @@ func TestShrinkDefaultRoute(t *testing.T) {
 				t.Errorf("shrink(%q).Contains(%v) = true, want false", test.route, ip)
 			}
 		}
-		ips, _, err := interfaces.LocalAddresses()
-		if err != nil {
-			t.Fatal(err)
-		}
-		for _, ip := range ips {
+		for _, ip := range localAddresses {
 			want := test.localIPFn(ip)
 			if gotContains := got.Contains(ip); gotContains != want {
 				t.Errorf("shrink(%q).Contains(%v) = %v, want %v", test.route, ip, gotContains, want)
@@ -445,7 +463,7 @@ func TestLazyMachineKeyGeneration(t *testing.T) {
 		t.Fatalf("NewFakeUserspaceEngine: %v", err)
 	}
 	t.Cleanup(eng.Close)
-	lb, err := NewLocalBackend(logf, "logid", store, eng)
+	lb, err := NewLocalBackend(logf, "logid", store, nil, eng)
 	if err != nil {
 		t.Fatalf("NewLocalBackend: %v", err)
 	}

ipn/ipnlocal/loglines_test.go

@@ -54,7 +54,7 @@ func TestLocalLogLines(t *testing.T) {
 	}
 	t.Cleanup(e.Close)
 
-	lb, err := NewLocalBackend(logf, idA.String(), store, e)
+	lb, err := NewLocalBackend(logf, idA.String(), store, nil, e)
 	if err != nil {
 		t.Fatal(err)
 	}

ipn/ipnlocal/peerapi.go

@@ -6,6 +6,7 @@ package ipnlocal
 
 import (
 	"context"
+	"encoding/base64"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -28,34 +29,49 @@ import (
 	"unicode"
 	"unicode/utf8"
 
+	"golang.org/x/net/dns/dnsmessage"
 	"inet.af/netaddr"
 	"tailscale.com/client/tailscale/apitype"
+	"tailscale.com/health"
 	"tailscale.com/hostinfo"
 	"tailscale.com/ipn"
 	"tailscale.com/logtail/backoff"
+	"tailscale.com/net/dns/resolver"
 	"tailscale.com/net/interfaces"
 	"tailscale.com/syncs"
 	"tailscale.com/tailcfg"
 	"tailscale.com/util/clientmetric"
 	"tailscale.com/wgengine"
+	"tailscale.com/wgengine/filter"
 )
 
 var initListenConfig func(*net.ListenConfig, netaddr.IP, *interfaces.State, string) error
 
+// addH2C is non-nil on platforms where we want to add H2C
+// ("cleartext" HTTP/2) support to the peerAPI.
+var addH2C func(*http.Server)
+
 type peerAPIServer struct {
 	b          *LocalBackend
-	rootDir    string
-	tunName    string
+	rootDir    string // empty means file receiving unavailable
 	selfNode   *tailcfg.Node
 	knownEmpty syncs.AtomicBool
+	resolver   *resolver.Resolver
 
 	// directFileMode is whether we're writing files directly to a
 	// download directory (as *.partial files), rather than making
 	// the frontend retrieve it over localapi HTTP and write it
-	// somewhere itself. This is used on GUI macOS version.
+	// somewhere itself. This is used on the GUI macOS versions
+	// and on Synology.
 	// In directFileMode, the peerapi doesn't do the final rename
-	// from "foo.jpg.partial" to "foo.jpg".
+	// from "foo.jpg.partial" to "foo.jpg" unless
+	// directFileDoFinalRename is set.
 	directFileMode bool
+
+	// directFileDoFinalRename is whether in directFileMode we
+	// additionally move the *.direct file to its final name after
+	// it's received.
+	directFileDoFinalRename bool
 }
 
 const (
@@ -72,6 +88,10 @@ const (
 	deletedSuffix = ".deleted"
 )
 
+func (s *peerAPIServer) canReceiveFiles() bool {
+	return s != nil && s.rootDir != ""
+}
+
 func validFilenameRune(r rune) bool {
 	switch r {
 	case '/':
@@ -118,7 +138,7 @@ func (s *peerAPIServer) diskPath(baseName string) (fullPath string, ok bool) {
 // hasFilesWaiting reports whether any files are buffered in the
 // tailscaled daemon storage.
 func (s *peerAPIServer) hasFilesWaiting() bool {
-	if s.rootDir == "" || s.directFileMode {
+	if s == nil || s.rootDir == "" || s.directFileMode {
 		return false
 	}
 	if s.knownEmpty.Get() {
@@ -178,8 +198,11 @@ func (s *peerAPIServer) hasFilesWaiting() bool {
 // As a side effect, it also does any lazy deletion of files as
 // required by Windows.
 func (s *peerAPIServer) WaitingFiles() (ret []apitype.WaitingFile, err error) {
+	if s == nil {
+		return nil, errNilPeerAPIServer
+	}
 	if s.rootDir == "" {
-		return nil, errors.New("peerapi disabled; no storage configured")
+		return nil, errNoTaildrop
 	}
 	if s.directFileMode {
 		return nil, nil
@@ -243,6 +266,11 @@ func (s *peerAPIServer) WaitingFiles() (ret []apitype.WaitingFile, err error) {
 	return ret, nil
 }
 
+var (
+	errNilPeerAPIServer = errors.New("peerapi unavailable; not listening")
+	errNoTaildrop       = errors.New("Taildrop disabled; no storage directory")
+)
+
 // tryDeleteAgain tries to delete path (and path+deletedSuffix) after
 // it failed earlier.  This happens on Windows when various anti-virus
 // tools hook into filesystem operations and have the file open still
@@ -258,8 +286,11 @@ func tryDeleteAgain(fullPath string) {
 }
 
 func (s *peerAPIServer) DeleteFile(baseName string) error {
+	if s == nil {
+		return errNilPeerAPIServer
+	}
 	if s.rootDir == "" {
-		return errors.New("peerapi disabled; no storage configured")
+		return errNoTaildrop
 	}
 	if s.directFileMode {
 		return errors.New("deletes not allowed in direct mode")
@@ -324,8 +355,11 @@ func touchFile(path string) error {
 }
 
 func (s *peerAPIServer) OpenFile(baseName string) (rc io.ReadCloser, size int64, err error) {
+	if s == nil {
+		return nil, 0, errNilPeerAPIServer
+	}
 	if s.rootDir == "" {
-		return nil, 0, errors.New("peerapi disabled; no storage configured")
+		return nil, 0, errNoTaildrop
 	}
 	if s.directFileMode {
 		return nil, 0, errors.New("opens not allowed in direct mode")
@@ -358,7 +392,7 @@ func (s *peerAPIServer) listen(ip netaddr.IP, ifState *interfaces.State) (ln net
 		// On iOS/macOS, this sets the lc.Control hook to
 		// setsockopt the interface index to bind to, to get
 		// out of the network sandbox.
-		if err := initListenConfig(&lc, ip, ifState, s.tunName); err != nil {
+		if err := initListenConfig(&lc, ip, ifState, s.b.dialer.TUNName()); err != nil {
 			return nil, err
 		}
 		if runtime.GOOS == "darwin" || runtime.GOOS == "ios" {
@@ -463,6 +497,9 @@ func (pln *peerAPIListener) serve() {
 		httpServer := &http.Server{
 			Handler: h,
 		}
+		if addH2C != nil {
+			addH2C(httpServer)
+		}
 		go httpServer.Serve(&oneConnListener{Listener: pln.ln, conn: c})
 	}
 }
@@ -503,6 +540,10 @@ func (h *peerAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		h.handlePeerPut(w, r)
 		return
 	}
+	if strings.HasPrefix(r.URL.Path, "/dns-query") {
+		h.handleDNSQuery(w, r)
+		return
+	}
 	switch r.URL.Path {
 	case "/v0/goroutines":
 		h.handleServeGoroutines(w, r)
@@ -513,6 +554,12 @@ func (h *peerAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	case "/v0/metrics":
 		h.handleServeMetrics(w, r)
 		return
+	case "/v0/magicsock":
+		h.handleServeMagicsock(w, r)
+		return
+	case "/v0/dnsfwd":
+		h.handleServeDNSFwd(w, r)
+		return
 	}
 	who := h.peerUser.DisplayName
 	fmt.Fprintf(w, `<html>
@@ -599,7 +646,7 @@ func (h *peerAPIHandler) handlePeerPut(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	if h.ps.rootDir == "" {
-		http.Error(w, "no rootdir", http.StatusInternalServerError)
+		http.Error(w, errNoTaildrop.Error(), http.StatusInternalServerError)
 		return
 	}
 	rawPath := r.URL.EscapedPath()
@@ -671,7 +718,7 @@ func (h *peerAPIHandler) handlePeerPut(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}
-	if h.ps.directFileMode {
+	if h.ps.directFileMode && !h.ps.directFileDoFinalRename {
 		if inFile != nil { // non-zero length; TODO: notify even for zero length
 			inFile.markAndNotifyDone()
 		}
@@ -741,6 +788,21 @@ func (h *peerAPIHandler) handleServeEnv(w http.ResponseWriter, r *http.Request)
 	json.NewEncoder(w).Encode(data)
 }
 
+func (h *peerAPIHandler) handleServeMagicsock(w http.ResponseWriter, r *http.Request) {
+	if !h.isSelf {
+		http.Error(w, "not owner", http.StatusForbidden)
+		return
+	}
+	eng := h.ps.b.e
+	if ig, ok := eng.(wgengine.InternalsGetter); ok {
+		if _, mc, ok := ig.GetInternals(); ok {
+			mc.ServeHTTPDebug(w, r)
+			return
+		}
+	}
+	http.Error(w, "miswired", 500)
+}
+
 func (h *peerAPIHandler) handleServeMetrics(w http.ResponseWriter, r *http.Request) {
 	if !h.isSelf {
 		http.Error(w, "not owner", http.StatusForbidden)
@@ -749,3 +811,231 @@ func (h *peerAPIHandler) handleServeMetrics(w http.ResponseWriter, r *http.Reque
 	w.Header().Set("Content-Type", "text/plain")
 	clientmetric.WritePrometheusExpositionFormat(w)
 }
+
+func (h *peerAPIHandler) handleServeDNSFwd(w http.ResponseWriter, r *http.Request) {
+	if !h.isSelf {
+		http.Error(w, "not owner", http.StatusForbidden)
+		return
+	}
+	dh := health.DebugHandler("dnsfwd")
+	if dh == nil {
+		http.Error(w, "not wired up", 500)
+		return
+	}
+	dh.ServeHTTP(w, r)
+}
+
+func (h *peerAPIHandler) replyToDNSQueries() bool {
+	if h.isSelf {
+		// If the peer is owned by the same user, just allow it
+		// without further checks.
+		return true
+	}
+	b := h.ps.b
+	if !b.OfferingExitNode() {
+		// If we're not an exit node, there's no point to
+		// being a DNS server for somebody.
+		return false
+	}
+	if !h.remoteAddr.IsValid() {
+		// This should never be the case if the peerAPIHandler
+		// was wired up correctly, but just in case.
+		return false
+	}
+	// Otherwise, we're an exit node but the peer is not us, so
+	// we need to check if they're allowed access to the internet.
+	// As peerapi bypasses wgengine/filter checks, we need to check
+	// ourselves. As a proxy for autogroup:internet access, we see
+	// if we would've accepted a packet to 0.0.0.0:53. We treat
+	// the IP 0.0.0.0 as being "the internet".
+	f, ok := b.filterAtomic.Load().(*filter.Filter)
+	if !ok {
+		return false
+	}
+	// Note: we check TCP here because the Filter type already had
+	// a CheckTCP method (for unit tests), but it's pretty
+	// arbitrary. DNS runs over TCP and UDP, so sure... we check
+	// TCP.
+	dstIP := netaddr.IPv4(0, 0, 0, 0)
+	remoteIP := h.remoteAddr.IP()
+	if remoteIP.Is6() {
+		// autogroup:internet for IPv6 is defined to start with 2000::/3,
+		// so use 2000::0 as the probe "the internet" address.
+		dstIP = netaddr.MustParseIP("2000::")
+	}
+	verdict := f.CheckTCP(remoteIP, dstIP, 53)
+	return verdict == filter.Accept
+}
+
+// handleDNSQuery implements a DoH server (RFC 8484) over the peerapi.
+// It's not over HTTPS as the spec dictates, but rather HTTP-over-WireGuard.
+func (h *peerAPIHandler) handleDNSQuery(w http.ResponseWriter, r *http.Request) {
+	if h.ps.resolver == nil {
+		http.Error(w, "DNS not wired up", http.StatusNotImplemented)
+		return
+	}
+	if !h.replyToDNSQueries() {
+		http.Error(w, "DNS access denied", http.StatusForbidden)
+		return
+	}
+	pretty := false // non-DoH debug mode for humans
+	q, publicError := dohQuery(r)
+	if publicError != "" && r.Method == "GET" {
+		if name := r.FormValue("q"); name != "" {
+			pretty = true
+			publicError = ""
+			q = dnsQueryForName(name, r.FormValue("t"))
+		}
+	}
+	if publicError != "" {
+		http.Error(w, publicError, http.StatusBadRequest)
+		return
+	}
+
+	// Some timeout that's short enough to be noticed by humans
+	// but long enough that it's longer than real DNS timeouts.
+	const arbitraryTimeout = 5 * time.Second
+
+	ctx, cancel := context.WithTimeout(r.Context(), arbitraryTimeout)
+	defer cancel()
+	res, err := h.ps.resolver.HandleExitNodeDNSQuery(ctx, q, h.remoteAddr, h.ps.b.allowExitNodeDNSProxyToServeName)
+	if err != nil {
+		h.logf("handleDNS fwd error: %v", err)
+		if err := ctx.Err(); err != nil {
+			http.Error(w, err.Error(), 500)
+		} else {
+			http.Error(w, "DNS forwarding error", 500)
+		}
+		return
+	}
+	if pretty {
+		// Non-standard response for interactive debugging.
+		w.Header().Set("Content-Type", "application/json")
+		writePrettyDNSReply(w, res)
+		return
+	}
+	w.Header().Set("Content-Type", "application/dns-message")
+	w.Header().Set("Content-Length", strconv.Itoa(len(res)))
+	w.Write(res)
+}
+
+func dohQuery(r *http.Request) (dnsQuery []byte, publicErr string) {
+	const maxQueryLen = 256 << 10
+	switch r.Method {
+	default:
+		return nil, "bad HTTP method"
+	case "GET":
+		q64 := r.FormValue("dns")
+		if q64 == "" {
+			return nil, "missing 'dns' parameter"
+		}
+		if base64.RawURLEncoding.DecodedLen(len(q64)) > maxQueryLen {
+			return nil, "query too large"
+		}
+		q, err := base64.RawURLEncoding.DecodeString(q64)
+		if err != nil {
+			return nil, "invalid 'dns' base64 encoding"
+		}
+		return q, ""
+	case "POST":
+		if r.Header.Get("Content-Type") != "application/dns-message" {
+			return nil, "unexpected Content-Type"
+		}
+		q, err := io.ReadAll(io.LimitReader(r.Body, maxQueryLen+1))
+		if err != nil {
+			return nil, "error reading post body with DNS query"
+		}
+		if len(q) > maxQueryLen {
+			return nil, "query too large"
+		}
+		return q, ""
+	}
+}
+
+func dnsQueryForName(name, typStr string) []byte {
+	typ := dnsmessage.TypeA
+	switch strings.ToLower(typStr) {
+	case "aaaa":
+		typ = dnsmessage.TypeAAAA
+	case "txt":
+		typ = dnsmessage.TypeTXT
+	}
+	b := dnsmessage.NewBuilder(nil, dnsmessage.Header{
+		OpCode:           0, // query
+		RecursionDesired: true,
+		ID:               0,
+	})
+	if !strings.HasSuffix(name, ".") {
+		name += "."
+	}
+	b.StartQuestions()
+	b.Question(dnsmessage.Question{
+		Name:  dnsmessage.MustNewName(name),
+		Type:  typ,
+		Class: dnsmessage.ClassINET,
+	})
+	msg, _ := b.Finish()
+	return msg
+}
+
+func writePrettyDNSReply(w io.Writer, res []byte) (err error) {
+	defer func() {
+		if err != nil {
+			j, _ := json.Marshal(struct {
+				Error string
+			}{err.Error()})
+			j = append(j, '\n')
+			w.Write(j)
+			return
+		}
+	}()
+	var p dnsmessage.Parser
+	hdr, err := p.Start(res)
+	if err != nil {
+		return err
+	}
+	if hdr.RCode != dnsmessage.RCodeSuccess {
+		return fmt.Errorf("DNS RCode = %v", hdr.RCode)
+	}
+	if err := p.SkipAllQuestions(); err != nil {
+		return err
+	}
+
+	var gotIPs []string
+	for {
+		h, err := p.AnswerHeader()
+		if err == dnsmessage.ErrSectionDone {
+			break
+		}
+		if err != nil {
+			return err
+		}
+		if h.Class != dnsmessage.ClassINET {
+			continue
+		}
+		switch h.Type {
+		case dnsmessage.TypeA:
+			r, err := p.AResource()
+			if err != nil {
+				return err
+			}
+			gotIPs = append(gotIPs, net.IP(r.A[:]).String())
+		case dnsmessage.TypeAAAA:
+			r, err := p.AAAAResource()
+			if err != nil {
+				return err
+			}
+			gotIPs = append(gotIPs, net.IP(r.AAAA[:]).String())
+		case dnsmessage.TypeTXT:
+			r, err := p.TXTResource()
+			if err != nil {
+				return err
+			}
+			gotIPs = append(gotIPs, r.TXT...)
+		}
+	}
+	j, _ := json.Marshal(gotIPs)
+	j = append(j, '\n')
+	w.Write(j)
+	return nil
+}

ipn/ipnlocal/peerapi_h2c.go

@@ -0,0 +1,22 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !ios && !android
+// +build !ios,!android
+
+package ipnlocal
+
+import (
+	"net/http"
+
+	"golang.org/x/net/http2"
+	"golang.org/x/net/http2/h2c"
+)
+
+func init() {
+	addH2C = func(s *http.Server) {
+		h2s := &http2.Server{}
+		s.Handler = h2c.NewHandler(s.Handler, h2s)
+	}
+}

ipn/ipnlocal/peerapi_macios_ext.go

@@ -9,10 +9,8 @@
 package ipnlocal
 
 import (
-	"errors"
 	"fmt"
 	"net"
-	"syscall"
 
 	"inet.af/netaddr"
 	"tailscale.com/net/interfaces"
@@ -21,7 +19,6 @@ import (
 
 func init() {
 	initListenConfig = initListenConfigNetworkExtension
-	peerDialControlFunc = peerDialControlFuncNetworkExtension
 }
 
 // initListenConfigNetworkExtension configures nc for listening on IP
@@ -34,24 +31,3 @@ func initListenConfigNetworkExtension(nc *net.ListenConfig, ip netaddr.IP, st *i
 	}
 	return netns.SetListenConfigInterfaceIndex(nc, tunIf.Index)
 }
-
-func peerDialControlFuncNetworkExtension(b *LocalBackend) func(network, address string, c syscall.RawConn) error {
-	b.mu.Lock()
-	defer b.mu.Unlock()
-	st := b.prevIfState
-	pas := b.peerAPIServer
-	index := -1
-	if st != nil && pas != nil && pas.tunName != "" {
-		if tunIf, ok := st.Interface[pas.tunName]; ok {
-			index = tunIf.Index
-		}
-	}
-	var lc net.ListenConfig
-	netns.SetListenConfigInterfaceIndex(&lc, index)
-	return func(network, address string, c syscall.RawConn) error {
-		if index == -1 {
-			return errors.New("failed to find TUN interface to bind to")
-		}
-		return lc.Control(network, address, c)
-	}
-}

ipn/ipnlocal/peerapi_test.go

@@ -19,8 +19,13 @@ import (
 	"strings"
 	"testing"
 
+	"inet.af/netaddr"
+	"tailscale.com/ipn"
 	"tailscale.com/tailcfg"
 	"tailscale.com/tstest"
+	"tailscale.com/types/logger"
+	"tailscale.com/wgengine"
+	"tailscale.com/wgengine/filter"
 )
 
 type peerAPITestEnv struct {
@@ -174,7 +179,7 @@ func TestHandlePeerAPI(t *testing.T) {
 			req:        httptest.NewRequest("PUT", "/v0/put/foo", nil),
 			checks: checks(
 				httpStatus(http.StatusInternalServerError),
-				bodyContains("no rootdir"),
+				bodyContains("Taildrop disabled; no storage directory"),
 			),
 		},
 		{
@@ -568,3 +573,55 @@ func TestDeletedMarkers(t *testing.T) {
 	}
 
 }
+
+func TestPeerAPIReplyToDNSQueries(t *testing.T) {
+	var h peerAPIHandler
+
+	h.isSelf = true
+	if !h.replyToDNSQueries() {
+		t.Errorf("for isSelf = false; want true")
+	}
+	h.isSelf = false
+	h.remoteAddr = netaddr.MustParseIPPort("100.150.151.152:12345")
+
+	eng, _ := wgengine.NewFakeUserspaceEngine(logger.Discard, 0)
+	h.ps = &peerAPIServer{
+		b: &LocalBackend{
+			e: eng,
+		},
+	}
+	if h.ps.b.OfferingExitNode() {
+		t.Fatal("unexpectedly offering exit node")
+	}
+	h.ps.b.prefs = &ipn.Prefs{
+		AdvertiseRoutes: []netaddr.IPPrefix{
+			netaddr.MustParseIPPrefix("0.0.0.0/0"),
+			netaddr.MustParseIPPrefix("::/0"),
+		},
+	}
+	if !h.ps.b.OfferingExitNode() {
+		t.Fatal("unexpectedly not offering exit node")
+	}
+
+	if h.replyToDNSQueries() {
+		t.Errorf("unexpectedly doing DNS without filter")
+	}
+
+	h.ps.b.setFilter(filter.NewAllowNone(logger.Discard, new(netaddr.IPSet)))
+	if h.replyToDNSQueries() {
+		t.Errorf("unexpectedly doing DNS without filter")
+	}
+
+	f := filter.NewAllowAllForTest(logger.Discard)
+
+	h.ps.b.setFilter(f)
+	if !h.replyToDNSQueries() {
+		t.Errorf("unexpectedly deny; wanted to be a DNS server")
+	}
+
+	// Also test IPv6.
+	h.remoteAddr = netaddr.MustParseIPPort("[fe70::1]:12345")
+	if !h.replyToDNSQueries() {
+		t.Errorf("unexpectedly IPv6 deny; wanted to be a DNS server")
+	}
+}

ipn/ipnlocal/state_test.go

@@ -87,8 +87,9 @@ func (nt *notifyThrottler) drain(count int) []ipn.Notify {
 type mockControl struct {
 	tb         testing.TB
 	opts       controlclient.Options
-	logf       logger.Logf
+	logfActual logger.Logf
 	statusFunc func(controlclient.Status)
+	preventLog syncs.AtomicBool
 
 	mu          sync.Mutex
 	calls       []string
@@ -104,6 +105,13 @@ func newMockControl(tb testing.TB) *mockControl {
 	}
 }
 
+func (cc *mockControl) logf(format string, args ...interface{}) {
+	if cc.preventLog.Get() || cc.logfActual == nil {
+		return
+	}
+	cc.logfActual(format, args...)
+}
+
 func (cc *mockControl) SetStatusFunc(fn func(controlclient.Status)) {
 	cc.statusFunc = fn
 }
@@ -284,14 +292,15 @@ func TestStateMachine(t *testing.T) {
 	t.Cleanup(e.Close)
 
 	cc := newMockControl(t)
-	b, err := NewLocalBackend(logf, "logid", store, e)
+	t.Cleanup(func() { cc.preventLog.Set(true) }) // hacky way to pacify issue 3020
+	b, err := NewLocalBackend(logf, "logid", store, nil, e)
 	if err != nil {
 		t.Fatalf("NewLocalBackend: %v", err)
 	}
 	b.SetControlClientGetterForTesting(func(opts controlclient.Options) (controlclient.Client, error) {
 		cc.mu.Lock()
 		cc.opts = opts
-		cc.logf = opts.Logf
+		cc.logfActual = opts.Logf
 		cc.authBlocked = true
 		cc.persist = cc.opts.Persist
 		cc.mu.Unlock()
@@ -305,6 +314,9 @@ func TestStateMachine(t *testing.T) {
 	notifies.expect(0)
 
 	b.SetNotifyCallback(func(n ipn.Notify) {
+		if cc.preventLog.Get() {
+			return
+		}
 		if n.State != nil ||
 			n.Prefs != nil ||
 			n.BrowseToURL != nil ||
@@ -315,6 +327,7 @@ func TestStateMachine(t *testing.T) {
 			logf("\n(ignored) %v\n\n", n)
 		}
 	})
+	t.Cleanup(func() { b.SetNotifyCallback(nil) }) // hacky way to pacify issue 3020
 
 	// Check that it hasn't called us right away.
 	// The state machine should be idle until we call Start().
@@ -941,14 +954,14 @@ func TestWGEngineStatusRace(t *testing.T) {
 	eng, err := wgengine.NewFakeUserspaceEngine(logf, 0)
 	c.Assert(err, qt.IsNil)
 	t.Cleanup(eng.Close)
-	b, err := NewLocalBackend(logf, "logid", new(ipn.MemoryStore), eng)
+	b, err := NewLocalBackend(logf, "logid", new(ipn.MemoryStore), nil, eng)
 	c.Assert(err, qt.IsNil)
 
 	cc := newMockControl(t)
 	b.SetControlClientGetterForTesting(func(opts controlclient.Options) (controlclient.Client, error) {
 		cc.mu.Lock()
 		defer cc.mu.Unlock()
-		cc.logf = opts.Logf
+		cc.logfActual = opts.Logf
 		return cc, nil
 	})
 

ipn/ipnserver/proxyconnect.go

@@ -0,0 +1,74 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ipnserver
+
+import (
+	"bufio"
+	"context"
+	"io"
+	"net"
+	"net/http"
+	"time"
+
+	"tailscale.com/logpolicy"
+	"tailscale.com/types/logger"
+)
+
+// handleProxyConnectConn handles a CONNECT request to
+// log.tailscale.io (or whatever the configured log server is). This
+// is intended for use by the Windows GUI client to log via when an
+// exit node is in use, so the logs don't go out via the exit node and
+// instead go directly, like tailscaled's. The dialer tried to do that
+// in the unprivileged GUI by binding to a specific interface, but the
+// "Internet Kill Switch" installed by tailscaled for exit nodes
+// precludes that from working and instead the GUI fails to dial out.
+// So, go through tailscaled (with a CONNECT request) instead.
+func (s *Server) handleProxyConnectConn(ctx context.Context, br *bufio.Reader, c net.Conn, logf logger.Logf) {
+	defer c.Close()
+
+	c.SetReadDeadline(time.Now().Add(5 * time.Second)) // should be long enough to send the HTTP headers
+	req, err := http.ReadRequest(br)
+	if err != nil {
+		logf("ReadRequest: %v", err)
+		return
+	}
+	c.SetReadDeadline(time.Time{})
+
+	if req.Method != "CONNECT" {
+		logf("ReadRequest: unexpected method %q, not CONNECT", req.Method)
+		return
+	}
+
+	hostPort := req.RequestURI
+	logHost := logpolicy.LogHost()
+	allowed := net.JoinHostPort(logHost, "443")
+	if hostPort != allowed {
+		logf("invalid CONNECT target %q; want %q", hostPort, allowed)
+		io.WriteString(c, "HTTP/1.1 403 Forbidden\r\n\r\nBad CONNECT target.\n")
+		return
+	}
+
+	tr := logpolicy.NewLogtailTransport(logHost)
+	back, err := tr.DialContext(ctx, "tcp", hostPort)
+	if err != nil {
+		logf("error CONNECT dialing %v: %v", hostPort, err)
+		io.WriteString(c, "HTTP/1.1 502 Fail\r\n\r\nConnect failure.\n")
+		return
+	}
+	defer back.Close()
+
+	io.WriteString(c, "HTTP/1.1 200 OK\r\n\r\n")
+
+	errc := make(chan error, 2)
+	go func() {
+		_, err := io.Copy(c, back)
+		errc <- err
+	}()
+	go func() {
+		_, err := io.Copy(back, br)
+		errc <- err
+	}()
+	<-errc
+}

ipn/ipnserver/server.go

@@ -20,6 +20,7 @@ import (
 	"os/exec"
 	"os/signal"
 	"os/user"
+	"path/filepath"
 	"runtime"
 	"strconv"
 	"strings"
@@ -31,13 +32,14 @@ import (
 	"inet.af/netaddr"
 	"inet.af/peercred"
 	"tailscale.com/control/controlclient"
+	"tailscale.com/envknob"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnlocal"
 	"tailscale.com/ipn/localapi"
 	"tailscale.com/ipn/store/aws"
-	"tailscale.com/log/filelogger"
 	"tailscale.com/logtail/backoff"
 	"tailscale.com/net/netstat"
+	"tailscale.com/net/tsdial"
 	"tailscale.com/paths"
 	"tailscale.com/safesocket"
 	"tailscale.com/smallzstd"
@@ -48,6 +50,7 @@ import (
 	"tailscale.com/version"
 	"tailscale.com/version/distro"
 	"tailscale.com/wgengine"
+	"tailscale.com/wgengine/monitor"
 )
 
 // Options is the configuration of the Tailscale node agent.
@@ -237,12 +240,28 @@ func bufferHasHTTPRequest(br *bufio.Reader) bool {
 		mem.Contains(mem.B(peek), mem.S(" HTTP/"))
 }
 
+// bufferIsConnect reports whether br looks like it's likely an HTTP
+// CONNECT request.
+//
+// Invariant: br has already had at least 4 bytes Peek'ed.
+func bufferIsConnect(br *bufio.Reader) bool {
+	peek, _ := br.Peek(br.Buffered())
+	return mem.HasPrefix(mem.B(peek), mem.S("CONN"))
+}
+
 func (s *Server) serveConn(ctx context.Context, c net.Conn, logf logger.Logf) {
 	// First see if it's an HTTP request.
 	br := bufio.NewReader(c)
 	c.SetReadDeadline(time.Now().Add(time.Second))
 	br.Peek(4)
 	c.SetReadDeadline(time.Time{})
+
+	// Handle logtail CONNECT requests early. (See docs on handleProxyConnectConn)
+	if bufferIsConnect(br) {
+		s.handleProxyConnectConn(ctx, br, c, logf)
+		return
+	}
+
 	isHTTPReq := bufferHasHTTPRequest(br)
 
 	ci, err := s.addConn(c, isHTTPReq)
@@ -427,6 +446,26 @@ func (s *Server) localAPIPermissions(ci connIdentity) (read, write bool) {
 	return false, false
 }
 
+// connCanFetchCerts reports whether ci is allowed to fetch HTTPS
+// certs from this server when it wouldn't otherwise be able to.
+//
+// That is, this reports whether ci should grant additional
+// capabilities over what the conn would otherwise be able to do.
+//
+// For now this only returns true on Unix machines when
+// TS_PERMIT_CERT_UID is set the to the userid of the peer
+// connection. It's intended to give your non-root webserver access
+// (www-data, caddy, nginx, etc) to certs.
+func (s *Server) connCanFetchCerts(ci connIdentity) bool {
+	if ci.IsUnixSock && ci.Creds != nil {
+		connUID, ok := ci.Creds.UserID()
+		if ok && connUID == envknob.String("TS_PERMIT_CERT_UID") {
+			return true
+		}
+	}
+	return false
+}
+
 // registerDisconnectSub adds ch as a subscribe to connection disconnect
 // events. If add is false, the subscriber is removed.
 func (s *Server) registerDisconnectSub(ch chan<- struct{}, add bool) {
@@ -651,7 +690,7 @@ func StateStore(path string, logf logger.Logf) (ipn.StateStore, error) {
 // The getEngine func is called repeatedly, once per connection, until it returns an engine successfully.
 //
 // Deprecated: use New and Server.Run instead.
-func Run(ctx context.Context, logf logger.Logf, ln net.Listener, store ipn.StateStore, logid string, getEngine func() (wgengine.Engine, error), opts Options) error {
+func Run(ctx context.Context, logf logger.Logf, ln net.Listener, store ipn.StateStore, linkMon *monitor.Mon, dialer *tsdial.Dialer, logid string, getEngine func() (wgengine.Engine, error), opts Options) error {
 	getEngine = getEngineUntilItWorksWrapper(getEngine)
 	runDone := make(chan struct{})
 	defer close(runDone)
@@ -735,7 +774,7 @@ func Run(ctx context.Context, logf logger.Logf, ln net.Listener, store ipn.State
 		}
 	}
 
-	server, err := New(logf, logid, store, eng, serverModeUser, opts)
+	server, err := New(logf, logid, store, eng, dialer, serverModeUser, opts)
 	if err != nil {
 		return err
 	}
@@ -748,8 +787,8 @@ func Run(ctx context.Context, logf logger.Logf, ln net.Listener, store ipn.State
 // New returns a new Server.
 //
 // To start it, use the Server.Run method.
-func New(logf logger.Logf, logid string, store ipn.StateStore, eng wgengine.Engine, serverModeUser *user.User, opts Options) (*Server, error) {
-	b, err := ipnlocal.NewLocalBackend(logf, logid, store, eng)
+func New(logf logger.Logf, logid string, store ipn.StateStore, eng wgengine.Engine, dialer *tsdial.Dialer, serverModeUser *user.User, opts Options) (*Server, error) {
+	b, err := ipnlocal.NewLocalBackend(logf, logid, store, dialer, eng)
 	if err != nil {
 		return nil, fmt.Errorf("NewLocalBackend: %v", err)
 	}
@@ -758,6 +797,22 @@ func New(logf logger.Logf, logid string, store ipn.StateStore, eng wgengine.Engi
 		return smallzstd.NewDecoder(nil)
 	})
 
+	dg := distro.Get()
+	switch dg {
+	case distro.Synology, distro.TrueNAS:
+		// See if they have a "Taildrop" share.
+		// See https://github.com/tailscale/tailscale/issues/2179#issuecomment-982821319
+		path, err := findTaildropDir(dg)
+		if err != nil {
+			logf("%s Taildrop support: %v", dg, err)
+		} else {
+			logf("%s Taildrop: using %v", dg, path)
+			b.SetDirectFileRoot(path)
+			b.SetDirectFileDoFinalRename(true)
+		}
+
+	}
+
 	if opts.AutostartStateKey == "" {
 		autoStartKey, err := store.ReadState(ipn.ServerModeStartKey)
 		if err != nil && err != ipn.ErrStateNotExist {
@@ -851,14 +906,6 @@ func BabysitProc(ctx context.Context, args []string, logf logger.Logf) {
 		panic("cannot determine executable: " + err.Error())
 	}
 
-	if runtime.GOOS == "windows" {
-		if len(args) != 2 && args[0] != "/subproc" {
-			panic(fmt.Sprintf("unexpected arguments %q", args))
-		}
-		logID := args[1]
-		logf = filelogger.New("tailscale-service", logID, logf)
-	}
-
 	var proc struct {
 		mu sync.Mutex
 		p  *os.Process
@@ -890,6 +937,14 @@ func BabysitProc(ctx context.Context, args []string, logf logger.Logf) {
 		startTime := time.Now()
 		log.Printf("exec: %#v %v", executable, args)
 		cmd := exec.Command(executable, args...)
+		if runtime.GOOS == "windows" {
+			extraEnv, err := loadExtraEnv()
+			if err != nil {
+				logf("errors loading extra env file; ignoring: %v", err)
+			} else {
+				cmd.Env = append(os.Environ(), extraEnv...)
+			}
+		}
 
 		// Create a pipe object to use as the subproc's stdin.
 		// When the writer goes away, the reader gets EOF.
@@ -1041,6 +1096,7 @@ func (psc *protoSwitchConn) Close() error {
 func (s *Server) localhostHandler(ci connIdentity) http.Handler {
 	lah := localapi.NewHandler(s.b, s.logf, s.backendLogID)
 	lah.PermitRead, lah.PermitWrite = s.localAPIPermissions(ci)
+	lah.PermitCert = s.connCanFetchCerts(ci)
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		if strings.HasPrefix(r.URL.Path, "/localapi/") {
@@ -1112,3 +1168,94 @@ func (ln *listenerWithReadyConn) Accept() (net.Conn, error) {
 	}
 	return ln.Listener.Accept()
 }
+
+func findTaildropDir(dg distro.Distro) (string, error) {
+	const name = "Taildrop"
+	switch dg {
+	case distro.Synology:
+		return findSynologyTaildropDir(name)
+	case distro.TrueNAS:
+		return findTrueNASTaildropDir(name)
+	}
+	return "", fmt.Errorf("%s is an unsupported distro for Taildrop dir", dg)
+}
+
+// findSynologyTaildropDir looks for the first volume containing a
+// "Taildrop" directory.  We'd run "synoshare --get Taildrop" command
+// but on DSM7 at least, we lack permissions to run that.
+func findSynologyTaildropDir(name string) (dir string, err error) {
+	for i := 1; i <= 16; i++ {
+		dir = fmt.Sprintf("/volume%v/%s", i, name)
+		if fi, err := os.Stat(dir); err == nil && fi.IsDir() {
+			return dir, nil
+		}
+	}
+	return "", fmt.Errorf("shared folder %q not found", name)
+}
+
+// findTrueNASTaildropDir returns the first matching directory of
+// /mnt/{name} or /mnt/*/{name}
+func findTrueNASTaildropDir(name string) (dir string, err error) {
+	// If we're running in a jail, a mount point could just be added at /mnt/Taildrop
+	dir = fmt.Sprintf("/mnt/%s", name)
+	if fi, err := os.Stat(dir); err == nil && fi.IsDir() {
+		return dir, nil
+	}
+
+	// but if running on the host, it may be something like /mnt/Primary/Taildrop
+	fis, err := ioutil.ReadDir("/mnt")
+	if err != nil {
+		return "", fmt.Errorf("error reading /mnt: %w", err)
+	}
+	for _, fi := range fis {
+		dir = fmt.Sprintf("/mnt/%s/%s", fi.Name(), name)
+		if fi, err := os.Stat(dir); err == nil && fi.IsDir() {
+			return dir, nil
+		}
+	}
+	return "", fmt.Errorf("shared folder %q not found", name)
+}
+
+func loadExtraEnv() (env []string, err error) {
+	if runtime.GOOS != "windows" {
+		return nil, nil
+	}
+	name := filepath.Join(os.Getenv("ProgramData"), "Tailscale", "tailscaled-env.txt")
+	contents, err := os.ReadFile(name)
+	if os.IsNotExist(err) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	for _, line := range strings.Split(string(contents), "\n") {
+		line = strings.TrimSpace(line)
+		if line == "" || line[0] == '#' {
+			continue
+		}
+		k, v, ok := stringsCut(line, "=")
+		if !ok || k == "" {
+			continue
+		}
+		if strings.HasPrefix(v, `"`) {
+			var err error
+			v, err = strconv.Unquote(v)
+			if err != nil {
+				return nil, fmt.Errorf("invalid value in line %q: %v", line, err)
+			}
+			env = append(env, k+"="+v)
+		} else {
+			env = append(env, line)
+		}
+	}
+	return env, nil
+}
+
+// stringsCut is Go 1.18's strings.Cut.
+// TODO(bradfitz): delete this when we depend on Go 1.18.
+func stringsCut(s, sep string) (before, after string, found bool) {
+	if i := strings.Index(s, sep); i >= 0 {
+		return s[:i], s[i+len(sep):], true
+	}
+	return s, "", false
+}

ipn/ipnserver/server_test.go

@@ -13,6 +13,7 @@ import (
 
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnserver"
+	"tailscale.com/net/tsdial"
 	"tailscale.com/safesocket"
 	"tailscale.com/wgengine"
 )
@@ -32,10 +33,11 @@ func TestRunMultipleAccepts(t *testing.T) {
 		t.Logf(format, args...)
 	}
 
+	s := safesocket.DefaultConnectionStrategy(socketPath)
 	connect := func() {
 		for i := 1; i <= 2; i++ {
 			logf("connect %d ...", i)
-			c, err := safesocket.Connect(socketPath, 0)
+			c, err := safesocket.Connect(s)
 			if err != nil {
 				t.Fatalf("safesocket.Connect: %v\n", err)
 			}
@@ -72,6 +74,6 @@ func TestRunMultipleAccepts(t *testing.T) {
 	}
 	defer ln.Close()
 
-	err = ipnserver.Run(ctx, logTriggerTestf, ln, store, "dummy_logid", ipnserver.FixedEngine(eng), opts)
+	err = ipnserver.Run(ctx, logTriggerTestf, ln, store, nil /* mon */, new(tsdial.Dialer), "dummy_logid", ipnserver.FixedEngine(eng), opts)
 	t.Logf("ipnserver.Run = %v", err)
 }

ipn/ipnstate/ipnstate.go

@@ -33,6 +33,10 @@ type Status struct {
 	//  "Starting", "Running".
 	BackendState string
 
+	// TailnetName is the name of the network that's currently in
+	// use.
+	TailnetName string
+
 	AuthURL      string       // current URL provided by control to authorize client
 	TailscaleIPs []netaddr.IP // Tailscale IP(s) assigned to this node
 	Self         *PeerStatus
@@ -70,9 +74,14 @@ func (s *Status) Peers() []key.NodePublic {
 }
 
 type PeerStatusLite struct {
+	// TxBytes/RxBytes is the total number of bytes transmitted to/received from this peer.
 	TxBytes, RxBytes int64
-	LastHandshake    time.Time
-	NodeKey          key.NodePublic
+	// LastHandshake is the last time a handshake succeeded with this peer.
+	// (Or we got key confirmation via the first data message,
+	// which is approximately the same thing.)
+	LastHandshake time.Time
+	// NodeKey is this peer's public node key.
+	NodeKey key.NodePublic
 }
 
 type PeerStatus struct {
@@ -83,22 +92,23 @@ type PeerStatus struct {
 	OS        string // HostInfo.OS
 	UserID    tailcfg.UserID
 
-	TailAddrDeprecated string       `json:"TailAddr"` // Tailscale IP
-	TailscaleIPs       []netaddr.IP // Tailscale IP(s) assigned to this node
+	TailscaleIPs []netaddr.IP // Tailscale IP(s) assigned to this node
 
 	// Endpoints:
 	Addrs   []string
 	CurAddr string // one of Addrs, or unique if roaming
 	Relay   string // DERP region
 
-	RxBytes       int64
-	TxBytes       int64
-	Created       time.Time // time registered with tailcontrol
-	LastWrite     time.Time // time last packet sent
-	LastSeen      time.Time // last seen to tailcontrol
-	LastHandshake time.Time // with local wireguard
-	KeepAlive     bool
-	ExitNode      bool // true if this is the currently selected exit node.
+	RxBytes        int64
+	TxBytes        int64
+	Created        time.Time // time registered with tailcontrol
+	LastWrite      time.Time // time last packet sent
+	LastSeen       time.Time // last seen to tailcontrol; only present if offline
+	LastHandshake  time.Time // with local wireguard
+	Online         bool      // whether node is connected to the control plane
+	KeepAlive      bool
+	ExitNode       bool // true if this is the currently selected exit node.
+	ExitNodeOption bool // true if this node can be an exit node (offered && approved)
 
 	// Active is whether the node was recently active. The
 	// definition is somewhat undefined but has historically and
@@ -237,9 +247,6 @@ func (sb *StatusBuilder) AddPeer(peer key.NodePublic, st *PeerStatus) {
 	if v := st.UserID; v != 0 {
 		e.UserID = v
 	}
-	if v := st.TailAddrDeprecated; v != "" {
-		e.TailAddrDeprecated = v
-	}
 	if v := st.TailscaleIPs; v != nil {
 		e.TailscaleIPs = v
 	}
@@ -270,6 +277,9 @@ func (sb *StatusBuilder) AddPeer(peer key.NodePublic, st *PeerStatus) {
 	if v := st.LastWrite; !v.IsZero() {
 		e.LastWrite = v
 	}
+	if st.Online {
+		e.Online = true
+	}
 	if st.InNetworkMap {
 		e.InNetworkMap = true
 	}
@@ -285,6 +295,9 @@ func (sb *StatusBuilder) AddPeer(peer key.NodePublic, st *PeerStatus) {
 	if st.ExitNode {
 		e.ExitNode = true
 	}
+	if st.ExitNodeOption {
+		e.ExitNodeOption = true
+	}
 	if st.ShareeNode {
 		e.ShareeNode = true
 	}

ipn/localapi/cert.go

@@ -29,12 +29,12 @@ import (
 	"net/http"
 	"os"
 	"path/filepath"
-	"strconv"
 	"strings"
 	"sync"
 	"time"
 
 	"golang.org/x/crypto/acme"
+	"tailscale.com/envknob"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/types/logger"
 )
@@ -63,10 +63,10 @@ func (h *Handler) certDir() (string, error) {
 	return full, nil
 }
 
-var acmeDebug, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_ACME"))
+var acmeDebug = envknob.Bool("TS_DEBUG_ACME")
 
 func (h *Handler) serveCert(w http.ResponseWriter, r *http.Request) {
-	if !h.PermitWrite {
+	if !h.PermitWrite && !h.PermitCert {
 		http.Error(w, "cert access denied", http.StatusForbidden)
 		return
 	}

ipn/localapi/localapi.go

@@ -12,7 +12,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"net"
 	"net/http"
 	"net/http/httputil"
 	"net/url"
@@ -20,7 +19,6 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
-	"sync"
 	"time"
 
 	"inet.af/netaddr"
@@ -28,7 +26,6 @@ import (
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnlocal"
 	"tailscale.com/ipn/ipnstate"
-	"tailscale.com/net/netknob"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/clientmetric"
@@ -55,8 +52,15 @@ type Handler struct {
 	PermitRead bool
 
 	// PermitWrite is whether mutating HTTP handlers are allowed.
+	// If PermitWrite is true, everything is allowed.
+	// It effectively means that the user is root or the admin
+	// (operator user).
 	PermitWrite bool
 
+	// PermitCert is whether the client is additionally granted
+	// cert fetching access.
+	PermitCert bool
+
 	b            *ipnlocal.LocalBackend
 	logf         logger.Logf
 	backendLogID string
@@ -116,6 +120,8 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		h.serveDERPMap(w, r)
 	case "/localapi/v0/metrics":
 		h.serveMetrics(w, r)
+	case "/localapi/v0/debug":
+		h.serveDebug(w, r)
 	case "/":
 		io.WriteString(w, "tailscaled\n")
 	default:
@@ -198,6 +204,35 @@ func (h *Handler) serveMetrics(w http.ResponseWriter, r *http.Request) {
 	clientmetric.WritePrometheusExpositionFormat(w)
 }
 
+func (h *Handler) serveDebug(w http.ResponseWriter, r *http.Request) {
+	if !h.PermitWrite {
+		http.Error(w, "debug access denied", http.StatusForbidden)
+		return
+	}
+	if r.Method != "POST" {
+		http.Error(w, "POST required", http.StatusMethodNotAllowed)
+		return
+	}
+	action := r.FormValue("action")
+	var err error
+	switch action {
+	case "rebind":
+		err = h.b.DebugRebind()
+	case "restun":
+		err = h.b.DebugReSTUN()
+	case "":
+		err = fmt.Errorf("missing parameter 'action'")
+	default:
+		err = fmt.Errorf("unknown action %q", action)
+	}
+	if err != nil {
+		http.Error(w, err.Error(), 400)
+		return
+	}
+	w.Header().Set("Content-Type", "text/plain")
+	io.WriteString(w, "done\n")
+}
+
 // serveProfileFunc is the implementation of Handler.serveProfile, after auth,
 // for platforms where we want to link it in.
 var serveProfileFunc func(http.ResponseWriter, *http.Request)
@@ -376,6 +411,25 @@ func (h *Handler) serveFileTargets(w http.ResponseWriter, r *http.Request) {
 	json.NewEncoder(w).Encode(fts)
 }
 
+// serveFilePut sends a file to another node.
+//
+// It's sometimes possible for clients to do this themselves, without
+// tailscaled, except in the case of tailscaled running in
+// userspace-networking ("netstack") mode, in which case tailscaled
+// needs to a do a netstack dial out.
+//
+// Instead, the CLI also goes through tailscaled so it doesn't need to be
+// aware of the network mode in use.
+//
+// macOS/iOS have always used this localapi method to simplify the GUI
+// clients.
+//
+// The Windows client currently (2021-11-30) uses the peerapi (/v0/put/)
+// directly, as the Windows GUI always runs in tun mode anyway.
+//
+// URL format:
+//
+//    * PUT /localapi/v0/file-put/:stableID/:escaped-filename
 func (h *Handler) serveFilePut(w http.ResponseWriter, r *http.Request) {
 	if !h.PermitWrite {
 		http.Error(w, "file access denied", http.StatusForbidden)
@@ -423,7 +477,7 @@ func (h *Handler) serveFilePut(w http.ResponseWriter, r *http.Request) {
 	outReq.ContentLength = r.ContentLength
 
 	rp := httputil.NewSingleHostReverseProxy(dstURL)
-	rp.Transport = getDialPeerTransport(h.b)
+	rp.Transport = h.b.Dialer().PeerAPITransport()
 	rp.ServeHTTP(w, outReq)
 }
 
@@ -457,26 +511,6 @@ func (h *Handler) serveDERPMap(w http.ResponseWriter, r *http.Request) {
 	e.Encode(h.b.DERPMap())
 }
 
-var dialPeerTransportOnce struct {
-	sync.Once
-	v *http.Transport
-}
-
-func getDialPeerTransport(b *ipnlocal.LocalBackend) *http.Transport {
-	dialPeerTransportOnce.Do(func() {
-		t := http.DefaultTransport.(*http.Transport).Clone()
-		t.Dial = nil
-		dialer := net.Dialer{
-			Timeout:   30 * time.Second,
-			KeepAlive: netknob.PlatformTCPKeepAlive(),
-			Control:   b.PeerDialControlFunc(),
-		}
-		t.DialContext = dialer.DialContext
-		dialPeerTransportOnce.v = t
-	})
-	return dialPeerTransportOnce.v
-}
-
 func defBool(a string, def bool) bool {
 	if a == "" {
 		return def

ipn/policy/policy.go

@@ -14,7 +14,8 @@ import (
 // system (a version.OS value) is an interesting enough port to report
 // to our peer nodes for discovery purposes.
 func IsInterestingService(s tailcfg.Service, os string) bool {
-	if s.Proto == "peerapi4" || s.Proto == "peerapi6" {
+	switch s.Proto {
+	case tailcfg.PeerAPI4, tailcfg.PeerAPI6, tailcfg.PeerAPIDNS:
 		return true
 	}
 	if s.Proto != tailcfg.TCP {

ipn/prefs.go

@@ -98,6 +98,11 @@ type Prefs struct {
 	// DNS configuration, if it exists.
 	CorpDNS bool
 
+	// RunSSH bool is whether this node should run an SSH
+	// server, permitting access to peers according to the
+	// policies as configured by the Tailnet's admin(s).
+	RunSSH bool
+
 	// WantRunning indicates whether networking should be active on
 	// this node.
 	WantRunning bool
@@ -193,6 +198,7 @@ type MaskedPrefs struct {
 	ExitNodeIPSet             bool `json:",omitempty"`
 	ExitNodeAllowLANAccessSet bool `json:",omitempty"`
 	CorpDNSSet                bool `json:",omitempty"`
+	RunSSHSet                 bool `json:",omitempty"`
 	WantRunningSet            bool `json:",omitempty"`
 	LoggedOutSet              bool `json:",omitempty"`
 	ShieldsUpSet              bool `json:",omitempty"`
@@ -277,6 +283,9 @@ func (p *Prefs) pretty(goos string) string {
 		sb.WriteString("mesh=false ")
 	}
 	fmt.Fprintf(&sb, "dns=%v want=%v ", p.CorpDNS, p.WantRunning)
+	if p.RunSSH {
+		sb.WriteString("ssh=true ")
+	}
 	if p.LoggedOut {
 		sb.WriteString("loggedout=true ")
 	}
@@ -348,6 +357,7 @@ func (p *Prefs) Equals(p2 *Prefs) bool {
 		p.ExitNodeIP == p2.ExitNodeIP &&
 		p.ExitNodeAllowLANAccess == p2.ExitNodeAllowLANAccess &&
 		p.CorpDNS == p2.CorpDNS &&
+		p.RunSSH == p2.RunSSH &&
 		p.WantRunning == p2.WantRunning &&
 		p.LoggedOut == p2.LoggedOut &&
 		p.NotepadURLs == p2.NotepadURLs &&
@@ -426,6 +436,47 @@ func (p *Prefs) AdminPageURL() string {
 	return url + "/admin/machines"
 }
 
+// AdvertisesExitNode reports whether p is advertising both the v4 and
+// v6 /0 exit node routes.
+func (p *Prefs) AdvertisesExitNode() bool {
+	if p == nil {
+		return false
+	}
+	var v4, v6 bool
+	for _, r := range p.AdvertiseRoutes {
+		if r.Bits() != 0 {
+			continue
+		}
+		if r.IP().Is4() {
+			v4 = true
+		} else if r.IP().Is6() {
+			v6 = true
+		}
+	}
+	return v4 && v6
+}
+
+// SetAdvertiseExitNode mutates p (if non-nil) to add or remove the two
+// /0 exit node routes.
+func (p *Prefs) SetAdvertiseExitNode(runExit bool) {
+	if p == nil {
+		return
+	}
+	all := p.AdvertiseRoutes
+	p.AdvertiseRoutes = p.AdvertiseRoutes[:0]
+	for _, r := range all {
+		if r.Bits() != 0 {
+			p.AdvertiseRoutes = append(p.AdvertiseRoutes, r)
+		}
+	}
+	if !runExit {
+		return
+	}
+	p.AdvertiseRoutes = append(p.AdvertiseRoutes,
+		netaddr.IPPrefixFrom(netaddr.IPv4(0, 0, 0, 0), 0),
+		netaddr.IPPrefixFrom(netaddr.IPv6Unspecified(), 0))
+}
+
 // PrefsFromBytes deserializes Prefs from a JSON blob. If
 // enforceDefaults is true, Prefs.RouteAll and Prefs.AllowSingleHosts
 // are forced on.

ipn/prefs_clone.go

@@ -40,6 +40,7 @@ var _PrefsCloneNeedsRegeneration = Prefs(struct {
 	ExitNodeIP             netaddr.IP
 	ExitNodeAllowLANAccess bool
 	CorpDNS                bool
+	RunSSH                 bool
 	WantRunning            bool
 	LoggedOut              bool
 	ShieldsUp              bool

ipn/prefs_test.go

@@ -42,6 +42,7 @@ func TestPrefsEqual(t *testing.T) {
 		"ExitNodeIP",
 		"ExitNodeAllowLANAccess",
 		"CorpDNS",
+		"RunSSH",
 		"WantRunning",
 		"LoggedOut",
 		"ShieldsUp",
@@ -646,3 +647,35 @@ func TestMaskedPrefsPretty(t *testing.T) {
 		}
 	}
 }
+
+func TestPrefsExitNode(t *testing.T) {
+	var p *Prefs
+	if p.AdvertisesExitNode() {
+		t.Errorf("nil shouldn't advertise exit node")
+	}
+	p = NewPrefs()
+	if p.AdvertisesExitNode() {
+		t.Errorf("default shouldn't advertise exit node")
+	}
+	p.AdvertiseRoutes = []netaddr.IPPrefix{
+		netaddr.MustParseIPPrefix("10.0.0.0/16"),
+	}
+	p.SetAdvertiseExitNode(true)
+	if got, want := len(p.AdvertiseRoutes), 3; got != want {
+		t.Errorf("routes = %d; want %d", got, want)
+	}
+	p.SetAdvertiseExitNode(true)
+	if got, want := len(p.AdvertiseRoutes), 3; got != want {
+		t.Errorf("routes = %d; want %d", got, want)
+	}
+	if !p.AdvertisesExitNode() {
+		t.Errorf("not advertising after enable")
+	}
+	p.SetAdvertiseExitNode(false)
+	if p.AdvertisesExitNode() {
+		t.Errorf("advertising after disable")
+	}
+	if got, want := len(p.AdvertiseRoutes), 1; got != want {
+		t.Errorf("routes = %d; want %d", got, want)
+	}
+}

ipn/store/aws/store_aws.go

@@ -23,7 +23,7 @@ import (
 )
 
 const (
-	parameterNameRxStr = `^parameter/(.*)`
+	parameterNameRxStr = `^parameter(/.*)`
 )
 
 var parameterNameRx = regexp.MustCompile(parameterNameRxStr)

logpolicy/logpolicy.go

@@ -8,11 +8,14 @@
 package logpolicy
 
 import (
+	"bufio"
 	"bytes"
 	"context"
 	"crypto/tls"
 	"encoding/json"
+	"errors"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"log"
 	"net"
@@ -22,13 +25,14 @@ import (
 	"os/exec"
 	"path/filepath"
 	"runtime"
-	"strconv"
 	"strings"
 	"sync"
 	"time"
 
 	"golang.org/x/term"
 	"tailscale.com/atomicfile"
+	"tailscale.com/envknob"
+	"tailscale.com/log/filelogger"
 	"tailscale.com/logtail"
 	"tailscale.com/logtail/filch"
 	"tailscale.com/net/dnscache"
@@ -38,6 +42,7 @@ import (
 	"tailscale.com/net/tlsdial"
 	"tailscale.com/net/tshttpproxy"
 	"tailscale.com/paths"
+	"tailscale.com/safesocket"
 	"tailscale.com/smallzstd"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/clientmetric"
@@ -65,6 +70,15 @@ func getLogTarget() string {
 	return getLogTargetOnce.v
 }
 
+// LogHost returns the hostname only (without port) of the configured
+// logtail server, or the default.
+func LogHost() string {
+	if v := getLogTarget(); v != "" {
+		return v
+	}
+	return logtail.DefaultHost
+}
+
 // Config represents an instance of logs in a collection.
 type Config struct {
 	Collection string
@@ -213,7 +227,7 @@ func runningUnderSystemd() bool {
 }
 
 func redirectStderrToLogPanics() bool {
-	return runningUnderSystemd() || os.Getenv("TS_PLEASE_PANIC") != ""
+	return runningUnderSystemd() || envknob.Bool("TS_PLEASE_PANIC")
 }
 
 // winProgramDataAccessible reports whether the directory (assumed to
@@ -391,7 +405,7 @@ func New(collection string) *Policy {
 	} else {
 		lflags = log.LstdFlags
 	}
-	if v, _ := strconv.ParseBool(os.Getenv("TS_DEBUG_LOG_TIME")); v {
+	if envknob.Bool("TS_DEBUG_LOG_TIME") {
 		lflags = log.LstdFlags | log.Lmicroseconds
 	}
 	if runningUnderSystemd() {
@@ -501,7 +515,7 @@ func New(collection string) *Policy {
 			}
 			return w
 		},
-		HTTPC: &http.Client{Transport: newLogtailTransport(logtail.DefaultHost)},
+		HTTPC: &http.Client{Transport: NewLogtailTransport(logtail.DefaultHost)},
 	}
 	if collection == logtail.CollectionNode {
 		c.MetricsDelta = clientmetric.EncodeLogTailMetricsDelta
@@ -511,7 +525,7 @@ func New(collection string) *Policy {
 		log.Println("You have enabled a non-default log target. Doing without being told to by Tailscale staff or your network administrator will make getting support difficult.")
 		c.BaseURL = val
 		u, _ := url.Parse(val)
-		c.HTTPC = &http.Client{Transport: newLogtailTransport(u.Host)}
+		c.HTTPC = &http.Client{Transport: NewLogtailTransport(u.Host)}
 	}
 
 	filchBuf, filchErr := filch.New(filepath.Join(dir, cmdName), filch.Options{
@@ -524,8 +538,20 @@ func New(collection string) *Policy {
 		}
 	}
 	lw := logtail.NewLogger(c, log.Printf)
+
+	var logOutput io.Writer = lw
+
+	if runtime.GOOS == "windows" && c.Collection == logtail.CollectionNode {
+		logID := newc.PublicID.String()
+		exe, _ := os.Executable()
+		if strings.EqualFold(filepath.Base(exe), "tailscaled.exe") {
+			diskLogf := filelogger.New("tailscale-service", logID, lw.Logf)
+			logOutput = logger.FuncWriter(diskLogf)
+		}
+	}
+
 	log.SetFlags(0) // other logflags are set on console, not here
-	log.SetOutput(lw)
+	log.SetOutput(logOutput)
 
 	log.Printf("Program starting: v%v, Go %v: %#v",
 		version.Long,
@@ -571,9 +597,12 @@ func (p *Policy) Shutdown(ctx context.Context) error {
 	return nil
 }
 
-// newLogtailTransport returns the HTTP Transport we use for uploading
-// logs to the given host name.
-func newLogtailTransport(host string) *http.Transport {
+// NewLogtailTransport returns an HTTP Transport particularly suited to uploading
+// logs to the given host name. This includes:
+//   - If DNS lookup fails, consult the bootstrap DNS list of Tailscale hostnames.
+//   - If TLS connection fails, try again using LetsEncrypt's built-in root certificate,
+//     for the benefit of older OS platforms which might not include it.
+func NewLogtailTransport(host string) *http.Transport {
 	// Start with a copy of http.DefaultTransport and tweak it a bit.
 	tr := http.DefaultTransport.(*http.Transport).Clone()
 
@@ -599,6 +628,24 @@ func newLogtailTransport(host string) *http.Transport {
 			return c, nil
 		}
 
+		if version.IsWindowsGUI() && strings.HasPrefix(netw, "tcp") {
+			if c, err := safesocket.Connect(safesocket.DefaultConnectionStrategy("")); err == nil {
+				fmt.Fprintf(c, "CONNECT %s HTTP/1.0\r\n\r\n", addr)
+				br := bufio.NewReader(c)
+				res, err := http.ReadResponse(br, nil)
+				if err == nil && res.StatusCode != 200 {
+					err = errors.New(res.Status)
+				}
+				if err != nil {
+					log.Printf("logtail: CONNECT response from tailscaled: %v", err)
+					c.Close()
+				} else {
+					log.Printf("logtail: connected via tailscaled")
+					return c, nil
+				}
+			}
+		}
+
 		// If we failed to dial, try again with bootstrap DNS.
 		log.Printf("logtail: dial %q failed: %v (in %v), trying bootstrap...", addr, err, d)
 		dnsCache := &dnscache.Resolver{
@@ -623,7 +670,7 @@ func newLogtailTransport(host string) *http.Transport {
 	// TODO(bradfitz): remove this debug knob once we've decided
 	// to upload via HTTP/1 or HTTP/2 (probably HTTP/1). Or we might just enforce
 	// it server-side.
-	if h1, _ := strconv.ParseBool(os.Getenv("TS_DEBUG_FORCE_H1_LOGS")); h1 {
+	if envknob.Bool("TS_DEBUG_FORCE_H1_LOGS") {
 		tr.TLSClientConfig = nil // DefaultTransport's was already initialized w/ h2
 		tr.ForceAttemptHTTP2 = false
 		tr.TLSNextProto = map[string]func(authority string, c *tls.Conn) http.RoundTripper{}