wip

Updates #311

wgengine/magicsock/magicsock.go

@@ -1176,6 +1176,9 @@ func (c *Conn) mkReceiveFunc(ruc *RebindingUDPConn, healthItem *health.ReceiveFu
 				if neterror.PacketWasTruncated(err) {
 					continue
 				}
+				if c.peerMTUEnabled.Load() {
+					ruc.ReadICMPErrors(batch.msgs[:len(buffs)], c.logf)
+				}
 				return 0, err
 			}
 
@@ -2377,7 +2380,9 @@ func (c *Conn) bindSocket(ruc *RebindingUDPConn, network string, curPortFate cur
 			}
 		}
 		trySetSocketBuffer(pconn, c.logf)
-
+		if c.peerMTUEnabled.Load() {
+			trySetIPRECEVRR(pconn, c.logf)
+		}
 		// Success.
 		if debugBindSocket() {
 			c.logf("magicsock: bindSocket: successfully listened %v port %d", network, port)

wgengine/magicsock/magicsock_default.go

@@ -31,6 +31,8 @@ func getGSOSizeFromControl(control []byte) (int, error) {
 
 func setGSOSizeInControl(control *[]byte, gso uint16) {}
 
+func trySetIPRECEVRR(pconn nettype.PacketConn, logf logger.Logf) {}
+
 const (
 	controlMessageSize = 0
 )

wgengine/magicsock/magicsock_linux.go

@@ -318,6 +318,25 @@ func trySetSocketBuffer(pconn nettype.PacketConn, logf logger.Logf) {
 	}
 }
 
+// trySetSocketBuffer attempts to set SO_SNDBUFFORCE and SO_RECVBUFFORCE which
+// can overcome the limit of net.core.{r,w}mem_max, but require CAP_NET_ADMIN.
+// It falls back to the portable implementation if that fails, which may be
+// silently capped to net.core.{r,w}mem_max.
+func trySetIPRECEVRR(pconn nettype.PacketConn, logf logger.Logf) {
+	if c, ok := pconn.(*net.UDPConn); ok {
+		var errRcv error
+		rc, err := c.SyscallConn()
+		if err == nil {
+			rc.Control(func(fd uintptr) {
+				err = syscall.SetsockoptInt(int(fd), syscall.SOL_IP, syscall.IP_RECVERR, 1)
+				if errRcv != nil {
+					logf("magicsock: [warning] failed to enable IP_RECVERR: %v", errRcv)
+				}
+			})
+		}
+	}
+}
+
 // tryEnableUDPOffload attempts to enable the UDP_GRO socket option on pconn,
 // and returns two booleans indicating TX and RX UDP offload support.
 func tryEnableUDPOffload(pconn nettype.PacketConn) (hasTX bool, hasRX bool) {

wgengine/magicsock/rebinding_conn.go

@@ -10,9 +10,12 @@ import (
 	"sync"
 	"sync/atomic"
 	"syscall"
+	"unsafe"
 
 	"golang.org/x/net/ipv6"
+	"golang.org/x/sys/unix"
 	"tailscale.com/net/netaddr"
+	"tailscale.com/types/logger"
 	"tailscale.com/types/nettype"
 )
 
@@ -177,3 +180,26 @@ func (c *RebindingUDPConn) SyscallConn() (syscall.RawConn, error) {
 	}
 	return sc.SyscallConn()
 }
+
+func (c *RebindingUDPConn) ReadICMPErrors(msgs []ipv6.Message, logf logger.Logf) (int, error) {
+	for {
+		rc, err := c.SyscallConn()
+		if err == nil {
+			rc.Control(func(fd uintptr) {
+				err = syscall.SetsockoptInt(int(fd), syscall.SOL_IP, syscall.IP_RECVERR, 1)
+				var p = make([]byte, 1500)
+				var oob = make([]byte, 1500)
+				_, oobn, _, _, err := syscall.Recvmsg(int(fd), p, oob, syscall.MSG_ERRQUEUE)
+				if err != nil {
+					logf("magicsock: failed to receive ICMP message %v", err)
+				} else if oobn <= 0 {
+					logf("magicsock: failed to receive ICMP message oobn")
+				}
+				se := (*unix.SockExtendedErr)(unsafe.Pointer(&oob[syscall.SizeofCmsghdr]))
+				if se.Origin == 2 {
+					logf("magicsock: received ICMP error type %v info %v", se.Type, se.Info)
+				}
+			})
+		}
+	}
+}