feature/relayserver,net/udprelay: add IPv6 support (#16442)

Updates tailscale/corp#27502
Updates tailscale/corp#30043

Signed-off-by: Jordan Whited <jordan@tailscale.com>

feature/relayserver/relayserver.go

@@ -137,7 +137,7 @@ func (e *extension) relayServerOrInit() (relayServer, error) {
 		return nil, errors.New("TAILSCALE_USE_WIP_CODE envvar is not set")
 	}
 	var err error
-	e.server, _, err = udprelay.NewServer(e.logf, *e.port, nil)
+	e.server, err = udprelay.NewServer(e.logf, *e.port, nil)
 	if err != nil {
 		return nil, err
 	}

net/udprelay/server.go

@@ -57,7 +57,10 @@ type Server struct {
 	bindLifetime        time.Duration
 	steadyStateLifetime time.Duration
 	bus                 *eventbus.Bus
-	uc                  *net.UDPConn
+	uc4                 *net.UDPConn // always non-nil
+	uc4Port             uint16       // always nonzero
+	uc6                 *net.UDPConn // may be nil if IPv6 bind fails during initialization
+	uc6Port             uint16       // may be zero if IPv6 bind fails during initialization
 	closeOnce           sync.Once
 	wg                  sync.WaitGroup
 	closeCh             chan struct{}
@@ -278,13 +281,11 @@ func (e *serverEndpoint) isBound() bool {
 		e.boundAddrPorts[1].IsValid()
 }
 
-// NewServer constructs a [Server] listening on 0.0.0.0:'port'. IPv6 is not yet
+// NewServer constructs a [Server] listening on port. If port is zero, then
-// supported. Port may be 0, and what ultimately gets bound is returned as
+// port selection is left up to the host networking stack. If
-// 'boundPort'. If len(overrideAddrs) > 0 these will be used in place of dynamic
+// len(overrideAddrs) > 0 these will be used in place of dynamic discovery,
-// discovery, which is useful to override in tests.
+// which is useful to override in tests.
-//
+func NewServer(logf logger.Logf, port int, overrideAddrs []netip.Addr) (s *Server, err error) {
-// TODO: IPv6 support
-func NewServer(logf logger.Logf, port int, overrideAddrs []netip.Addr) (s *Server, boundPort uint16, err error) {
 	s = &Server{
 		logf:                logger.WithPrefix(logf, "relayserver"),
 		disco:               key.NewDisco(),
@@ -306,30 +307,36 @@ func NewServer(logf logger.Logf, port int, overrideAddrs []netip.Addr) (s *Serve
 	s.bus = bus
 	netMon, err := netmon.New(s.bus, logf)
 	if err != nil {
-		return nil, 0, err
+		return nil, err
 	}
 	s.netChecker = &netcheck.Client{
 		NetMon: netMon,
 		Logf:   logger.WithPrefix(logf, "relayserver: netcheck:"),
 		SendPacket: func(b []byte, addrPort netip.AddrPort) (int, error) {
-			return s.uc.WriteToUDPAddrPort(b, addrPort)
+			if addrPort.Addr().Is4() {
+				return s.uc4.WriteToUDPAddrPort(b, addrPort)
+			} else if s.uc6 != nil {
+				return s.uc6.WriteToUDPAddrPort(b, addrPort)
+			} else {
+				return 0, errors.New("IPv6 socket is not bound")
+			}
 		},
 	}
 
-	boundPort, err = s.listenOn(port)
+	err = s.listenOn(port)
 	if err != nil {
-		return nil, 0, err
+		return nil, err
 	}
 
-	s.wg.Add(1)
-	go s.packetReadLoop()
-	s.wg.Add(1)
-	go s.endpointGCLoop()
 	if len(overrideAddrs) > 0 {
 		addrPorts := make(set.Set[netip.AddrPort], len(overrideAddrs))
 		for _, addr := range overrideAddrs {
 			if addr.IsValid() {
-				addrPorts.Add(netip.AddrPortFrom(addr, boundPort))
+				if addr.Is4() {
+					addrPorts.Add(netip.AddrPortFrom(addr, s.uc4Port))
+				} else if s.uc6 != nil {
+					addrPorts.Add(netip.AddrPortFrom(addr, s.uc6Port))
+				}
 			}
 		}
 		s.addrPorts = addrPorts.Slice()
@@ -337,7 +344,17 @@ func NewServer(logf logger.Logf, port int, overrideAddrs []netip.Addr) (s *Serve
 		s.wg.Add(1)
 		go s.addrDiscoveryLoop()
 	}
-	return s, boundPort, nil
+
+	s.wg.Add(1)
+	go s.packetReadLoop(s.uc4)
+	if s.uc6 != nil {
+		s.wg.Add(1)
+		go s.packetReadLoop(s.uc6)
+	}
+	s.wg.Add(1)
+	go s.endpointGCLoop()
+
+	return s, nil
 }
 
 func (s *Server) addrDiscoveryLoop() {
@@ -351,14 +368,17 @@ func (s *Server) addrDiscoveryLoop() {
 		addrPorts.Make()
 
 		// get local addresses
-		localPort := s.uc.LocalAddr().(*net.UDPAddr).Port
 		ips, _, err := netmon.LocalAddresses()
 		if err != nil {
 			return nil, err
 		}
 		for _, ip := range ips {
 			if ip.IsValid() {
-				addrPorts.Add(netip.AddrPortFrom(ip, uint16(localPort)))
+				if ip.Is4() {
+					addrPorts.Add(netip.AddrPortFrom(ip, s.uc4Port))
+				} else {
+					addrPorts.Add(netip.AddrPortFrom(ip, s.uc6Port))
+				}
 			}
 		}
 
@@ -413,24 +433,52 @@ func (s *Server) addrDiscoveryLoop() {
 	}
 }
 
-func (s *Server) listenOn(port int) (uint16, error) {
+// listenOn binds an IPv4 and IPv6 socket to port. We consider it successful if
-	uc, err := net.ListenUDP("udp4", &net.UDPAddr{Port: port})
+// we manage to bind the IPv4 socket.
+//
+// The requested port may be zero, in which case port selection is left up to
+// the host networking stack. We make no attempt to bind a consistent port
+// across IPv4 and IPv6 if the requested port is zero.
+//
+// TODO: make these "re-bindable" in similar fashion to magicsock as a means to
+// deal with EDR software closing them. http://go/corp/30118
+func (s *Server) listenOn(port int) error {
+	for _, network := range []string{"udp4", "udp6"} {
+		uc, err := net.ListenUDP(network, &net.UDPAddr{Port: port})
 		if err != nil {
-		return 0, err
+			if network == "udp4" {
+				return err
+			} else {
+				s.logf("ignoring IPv6 bind failure: %v", err)
+				break
+			}
 		}
 		// TODO: set IP_PKTINFO sockopt
 		_, boundPortStr, err := net.SplitHostPort(uc.LocalAddr().String())
 		if err != nil {
-		s.uc.Close()
+			uc.Close()
-		return 0, err
+			if s.uc4 != nil {
+				s.uc4.Close()
 			}
-	boundPort, err := strconv.ParseUint(boundPortStr, 10, 16)
+			return err
+		}
+		portUint, err := strconv.ParseUint(boundPortStr, 10, 16)
 		if err != nil {
-		s.uc.Close()
+			uc.Close()
-		return 0, err
+			if s.uc4 != nil {
+				s.uc4.Close()
 			}
-	s.uc = uc
+			return err
-	return uint16(boundPort), nil
+		}
+		if network == "udp4" {
+			s.uc4 = uc
+			s.uc4Port = uint16(portUint)
+		} else {
+			s.uc6 = uc
+			s.uc6Port = uint16(portUint)
+		}
+	}
+	return nil
 }
 
 // Close closes the server.
@@ -438,7 +486,10 @@ func (s *Server) Close() error {
 	s.closeOnce.Do(func() {
 		s.mu.Lock()
 		defer s.mu.Unlock()
-		s.uc.Close()
+		s.uc4.Close()
+		if s.uc6 != nil {
+			s.uc6.Close()
+		}
 		close(s.closeCh)
 		s.wg.Wait()
 		clear(s.byVNI)
@@ -507,7 +558,7 @@ func (s *Server) handlePacket(from netip.AddrPort, b []byte, uw udpWriter) {
 	e.handlePacket(from, gh, b, uw, s.discoPublic)
 }
 
-func (s *Server) packetReadLoop() {
+func (s *Server) packetReadLoop(uc *net.UDPConn) {
 	defer func() {
 		s.wg.Done()
 		s.Close()
@@ -515,11 +566,11 @@ func (s *Server) packetReadLoop() {
 	b := make([]byte, 1<<16-1)
 	for {
 		// TODO: extract laddr from IP_PKTINFO for use in reply
-		n, from, err := s.uc.ReadFromUDPAddrPort(b)
+		n, from, err := uc.ReadFromUDPAddrPort(b)
 		if err != nil {
 			return
 		}
-		s.handlePacket(from, b[:n], s.uc)
+		s.handlePacket(from, b[:n], uc)
 	}
 }
 

net/udprelay/server_test.go

@@ -29,7 +29,7 @@ type testClient struct {
 
 func newTestClient(t *testing.T, vni uint32, serverEndpoint netip.AddrPort, local key.DiscoPrivate, remote, server key.DiscoPublic) *testClient {
 	rAddr := &net.UDPAddr{IP: serverEndpoint.Addr().AsSlice(), Port: int(serverEndpoint.Port())}
-	uc, err := net.DialUDP("udp4", nil, rAddr)
+	uc, err := net.DialUDP("udp", nil, rAddr)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -180,9 +180,23 @@ func TestServer(t *testing.T) {
 	discoA := key.NewDisco()
 	discoB := key.NewDisco()
 
-	ipv4LoopbackAddr := netip.MustParseAddr("127.0.0.1")
+	cases := []struct {
+		name          string
+		overrideAddrs []netip.Addr
+	}{
+		{
+			name:          "over ipv4",
+			overrideAddrs: []netip.Addr{netip.MustParseAddr("127.0.0.1")},
+		},
+		{
+			name:          "over ipv6",
+			overrideAddrs: []netip.Addr{netip.MustParseAddr("::1")},
+		},
+	}
 
-	server, _, err := NewServer(t.Logf, 0, []netip.Addr{ipv4LoopbackAddr})
+	for _, tt := range cases {
+		t.Run(tt.name, func(t *testing.T) {
+			server, err := NewServer(t.Logf, 0, tt.overrideAddrs)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -261,4 +275,6 @@ func TestServer(t *testing.T) {
 			if !bytes.Equal(txToBOnNewPort, rxFromA) {
 				t.Fatal("unexpected msg A->B")
 			}
+		})
+	}
 }