wgengine/magicsock: listen on udp6, use it for STUN, report endpoint

More steps towards IPv6 transport.

We now send it to tailcontrol, which ignores it.

But it doesn't actually actually support IPv6 yet (outside of STUN).

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

wgengine/magicsock/magicsock.go

@@ -45,8 +45,9 @@
 // A Conn routes UDP packets and actively manages a list of its endpoints.
 // It implements wireguard/device.Bind.
 type Conn struct {
+	pconnPort    uint16 // the preferred port from opts.Port; 0 means auto
 	pconn4       *RebindingUDPConn
-	pconnPort    uint16
+	pconn6       *RebindingUDPConn // non-nil if IPv6 available
 	epFunc       func(endpoints []string)
 	logf         logger.Logf
 	sendLogLimit *rate.Limiter
@@ -137,6 +138,8 @@ type udpAddr struct {
 
 // Options contains options for Listen.
 type Options struct {
+	// Logf optionally provides a log function to use.
+	// If nil, log.Printf is used.
 	Logf logger.Logf
 
 	// Port is the port to listen on.
@@ -153,6 +156,13 @@ type Options struct {
 	derpTLSConfig *tls.Config // normally nil; used by tests
 }
 
+func (o *Options) logf() logger.Logf {
+	if o.Logf != nil {
+		return o.Logf
+	}
+	return log.Printf
+}
+
 func (o *Options) endpointsFunc() func([]string) {
 	if o == nil || o.EndpointsFunc == nil {
 		return func([]string) {}
@@ -164,41 +174,11 @@ func (o *Options) endpointsFunc() func([]string) {
 // As the set of possible endpoints for a Conn changes, the
 // callback opts.EndpointsFunc is called.
 func Listen(opts Options) (*Conn, error) {
-	var packetConn net.PacketConn
-	var err error
-
-	logf := log.Printf
-	if opts.Logf != nil {
-		logf = opts.Logf
-	}
-
-	if opts.Port == 0 {
-		// Our choice of port. Start with DefaultPort.
-		// If unavailable, pick any port.
-		want := fmt.Sprintf(":%d", DefaultPort)
-		logf("magicsock: bind: trying %v\n", want)
-		packetConn, err = net.ListenPacket("udp4", want)
-		if err != nil {
-			want = ":0"
-			logf("magicsock: bind: falling back to %v (%v)\n", want, err)
-			packetConn, err = net.ListenPacket("udp4", want)
-		}
-	} else {
-		packetConn, err = net.ListenPacket("udp4", fmt.Sprintf(":%d", opts.Port))
-	}
-	if err != nil {
-		return nil, fmt.Errorf("magicsock.Listen: %v", err)
-	}
-
-	connCtx, connCtxCancel := context.WithCancel(context.Background())
 	c := &Conn{
-		pconn4:        new(RebindingUDPConn),
 		pconnPort:     opts.Port,
-		sendLogLimit:  rate.NewLimiter(rate.Every(1*time.Minute), 1),
-		connCtx:       connCtx,
-		connCtxCancel: connCtxCancel,
+		logf:          opts.logf(),
 		epFunc:        opts.endpointsFunc(),
-		logf:          logf,
+		sendLogLimit:  rate.NewLimiter(rate.Every(1*time.Minute), 1),
 		addrsByUDP:    make(map[udpAddr]*AddrSet),
 		addrsByKey:    make(map[key.Public]*AddrSet),
 		wantDerp:      true,
@@ -207,6 +187,12 @@ func Listen(opts Options) (*Conn, error) {
 		derpTLSConfig: opts.derpTLSConfig,
 		derps:         opts.DERPs,
 	}
+
+	if err := c.initialBind(); err != nil {
+		return nil, err
+	}
+
+	c.connCtx, c.connCtxCancel = context.WithCancel(context.Background())
 	if c.derps == nil {
 		c.derps = derpmap.Prod()
 	}
@@ -214,11 +200,12 @@ func Listen(opts Options) (*Conn, error) {
 		DERP:         c.derps,
 		Logf:         logger.WithPrefix(c.logf, "netcheck: "),
 		GetSTUNConn4: func() netcheck.STUNConn { return c.pconn4 },
-		// TODO: add GetSTUNConn6 once Conn has a pconn6
+	}
+	if c.pconn6 != nil {
+		c.netChecker.GetSTUNConn6 = func() netcheck.STUNConn { return c.pconn6 }
 	}
 
 	c.ignoreSTUNPackets()
-	c.pconn4.Reset(packetConn.(*net.UDPConn))
 	c.ReSTUN("initial")
 
 	// We assume that LinkChange notifications are plumbed through well
@@ -438,8 +425,7 @@ func (c *Conn) determineEndpoints(ctx context.Context) (ipPorts []string, err er
 	if nr.GlobalV4 != "" {
 		addAddr(nr.GlobalV4, "stun")
 	}
-	const tailControlDoesIPv6 = false // TODO: when IPv6 filtering/splitting is enabled in tailcontrol
-	if nr.GlobalV6 != "" && tailControlDoesIPv6 {
+	if nr.GlobalV6 != "" {
 		addAddr(nr.GlobalV6, "stun")
 	}
 
@@ -1005,9 +991,23 @@ func (c *Conn) ReceiveIPv4(b []byte) (n int, ep conn.Endpoint, addr *net.UDPAddr
 	return n, ep, addr, nil
 }
 
-func (c *Conn) ReceiveIPv6(buff []byte) (int, conn.Endpoint, *net.UDPAddr, error) {
-	// TODO(crawshaw): IPv6 support
-	return 0, nil, nil, syscall.EAFNOSUPPORT
+func (c *Conn) ReceiveIPv6(b []byte) (int, conn.Endpoint, *net.UDPAddr, error) {
+	if c.pconn6 == nil {
+		return 0, nil, nil, syscall.EAFNOSUPPORT
+	}
+	for {
+		n, pAddr, err := c.pconn6.ReadFrom(b)
+		if err != nil {
+			return 0, nil, nil, err
+		}
+		addr := pAddr.(*net.UDPAddr)
+		if stun.Is(b[:n]) {
+			c.stunReceiveFunc.Load().(func([]byte, *net.UDPAddr))(b, addr)
+			continue
+		}
+		// TODO(bradfitz): finish. look up addrset, return etc.
+		// For now we're only using this for STUN.
+	}
 }
 
 // SetPrivateKey sets the connection's private key.
@@ -1107,6 +1107,9 @@ func (c *Conn) Close() error {
 	c.closed = true
 	c.connCtxCancel()
 	c.closeAllDerpLocked()
+	if c.pconn6 != nil {
+		c.pconn6.Close()
+	}
 	return c.pconn4.Close()
 }
 
@@ -1152,6 +1155,40 @@ func (c *Conn) ReSTUN(why string) {
 	}
 }
 
+func (c *Conn) initialBind() error {
+	if err := c.bind1(&c.pconn4, "udp4"); err != nil {
+		return err
+	}
+	if err := c.bind1(&c.pconn6, "udp6"); err != nil {
+		c.logf("ignoring IPv6 bind failure: %v", err)
+	}
+	return nil
+}
+
+func (c *Conn) bind1(ruc **RebindingUDPConn, which string) error {
+	var pc net.PacketConn
+	var err error
+	if c.pconnPort == 0 && DefaultPort != 0 {
+		pc, err = net.ListenPacket(which, fmt.Sprintf(":%d", DefaultPort))
+		if err != nil {
+			c.logf("magicsock: bind: default port %s/%v unavailable; picking random", which, DefaultPort)
+		}
+	}
+	if pc == nil {
+		// If unavailable, pick any port.
+		pc, err = net.ListenPacket(which, fmt.Sprintf(":%d", c.pconnPort))
+	}
+	if err != nil {
+		c.logf("magicsock: bind(%s/%v): %v", which, c.pconnPort, err)
+		return fmt.Errorf("magicsock: bind: %s/%d: %v", which, c.pconnPort, err)
+	}
+	if *ruc == nil {
+		*ruc = new(RebindingUDPConn)
+	}
+	(*ruc).Reset(pc.(*net.UDPConn))
+	return nil
+}
+
 // Rebind closes and re-binds the UDP sockets.
 // It should be followed by a call to ReSTUN.
 func (c *Conn) Rebind() {