cmd/tailscaled, wgengine/netstack: always wire up netstack

Even if not in use. We plan to use it for more stuff later.

(not for iOS or macOS-GUIs yet; only tailscaled)

Change-Id: Idaef719d2a009be6a39f158fd8f57f8cca68e0ee
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/tailscaled.go

@@ -289,10 +289,14 @@ func run() error {
 		return err
 	}
 
-	var ns *netstack.Impl
-	if useNetstack || wrapNetstack {
-		onlySubnets := wrapNetstack && !useNetstack
-		ns = mustStartNetstack(logf, e, onlySubnets)
+	ns, err := newNetstack(logf, 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 socksListener != nil || httpProxyListener != nil {
@@ -453,19 +457,12 @@ func runDebugServer(mux *http.ServeMux, addr string) {
 	}
 }
 
-func mustStartNetstack(logf logger.Logf, e wgengine.Engine, onlySubnets bool) *netstack.Impl {
+func newNetstack(logf logger.Logf, e wgengine.Engine) (*netstack.Impl, error) {
 	tunDev, magicConn, ok := e.(wgengine.InternalsGetter).GetInternals()
 	if !ok {
-		log.Fatalf("%T is not a wgengine.InternalsGetter", e)
-	}
-	ns, err := netstack.Create(logf, tunDev, e, magicConn, onlySubnets)
-	if err != nil {
-		log.Fatalf("netstack.Create: %v", err)
-	}
-	if err := ns.Start(); err != nil {
-		log.Fatalf("failed to start netstack: %v", err)
+		return nil, fmt.Errorf("%T is not a wgengine.InternalsGetter", e)
 	}
-	return ns
+	return netstack.Create(logf, tunDev, e, magicConn)
 }
 
 func mustStartTCPListener(name, addr string) net.Listener {

cmd/tailscaled/tailscaled_windows.go

@@ -202,9 +202,14 @@ func startIPNServer(ctx context.Context, logid string) error {
 			dev.Close()
 			return nil, fmt.Errorf("engine: %w", err)
 		}
-		onlySubnets := true
-		if wrapNetstack {
-			mustStartNetstack(logf, eng, onlySubnets)
+		ns, err := newNetstack(logf, eng)
+		if err != nil {
+			return nil, fmt.Errorf("newNetstack: %w", err)
+		}
+		ns.ProcessLocalIPs = false
+		ns.ProcessSubnets = wrapNetstack
+		if err := ns.Start(); err != nil {
+			return nil, fmt.Errorf("failed to start netstack: %w", err)
 		}
 		return wgengine.NewWatchdog(eng), nil
 	}

tsnet/tsnet.go

@@ -127,10 +127,11 @@ func (s *Server) start() error {
 		return fmt.Errorf("%T is not a wgengine.InternalsGetter", eng)
 	}
 
-	ns, err := netstack.Create(logf, tunDev, eng, magicConn, false)
+	ns, err := netstack.Create(logf, tunDev, eng, magicConn)
 	if err != nil {
 		return fmt.Errorf("netstack.Create: %w", err)
 	}
+	ns.ProcessLocalIPs = true
 	ns.ForwardTCPIn = s.forwardTCP
 	if err := ns.Start(); err != nil {
 		return fmt.Errorf("failed to start netstack: %w", err)

wgengine/netstack/netstack.go

@@ -54,13 +54,23 @@ type Impl struct {
 	// port other than accepting it and closing it.
 	ForwardTCPIn func(c net.Conn, port uint16)
 
+	// ProcessLocalIPs is whether netstack should handle incoming
+	// traffic directed at the Node.Addresses (local IPs).
+	// It can only be set before calling Start.
+	ProcessLocalIPs bool
+
+	// ProcessSubnets is whether netstack should handle incoming
+	// traffic destined to non-local IPs (i.e. whether it should
+	// be a subnet router).
+	// It can only be set before calling Start.
+	ProcessSubnets bool
+
 	ipstack *stack.Stack
 	linkEP  *channel.Endpoint
 	tundev  *tstun.Wrapper
 	e       wgengine.Engine
 	mc      *magicsock.Conn
 	logf    logger.Logf
-	onlySubnets bool // whether we only want to handle subnet relaying
 
 	// atomicIsLocalIPFunc holds a func that reports whether an IP
 	// is a local (non-subnet) Tailscale IP address of this
@@ -81,7 +91,7 @@ const nicID = 1
 const mtu = 1500
 
 // Create creates and populates a new Impl.
-func Create(logf logger.Logf, tundev *tstun.Wrapper, e wgengine.Engine, mc *magicsock.Conn, onlySubnets bool) (*Impl, error) {
+func Create(logf logger.Logf, tundev *tstun.Wrapper, e wgengine.Engine, mc *magicsock.Conn) (*Impl, error) {
 	if mc == nil {
 		return nil, errors.New("nil magicsock.Conn")
 	}
@@ -130,7 +140,6 @@ func Create(logf logger.Logf, tundev *tstun.Wrapper, e wgengine.Engine, mc *magi
 		e:                   e,
 		mc:                  mc,
 		connsOpenBySubnetIP: make(map[netaddr.IP]int),
-		onlySubnets:         onlySubnets,
 	}
 	ns.atomicIsLocalIPFunc.Store(tsaddr.NewContainsIPFunc(nil))
 	return ns, nil
@@ -275,11 +284,11 @@ func (ns *Impl) updateIPs(nm *netmap.NetworkMap) {
 		isAddr[ipp] = true
 	}
 	for _, ipp := range nm.SelfNode.AllowedIPs {
-		if ns.onlySubnets && isAddr[ipp] {
-			continue
-		}
+		local := isAddr[ipp]
+		if local && ns.ProcessLocalIPs || !local && ns.ProcessSubnets {
 			newIPs[ipPrefixToAddressWithPrefix(ipp)] = true
 		}
+	}
 
 	ipsToBeAdded := make(map[tcpip.AddressWithPrefix]bool)
 	for ipp := range newIPs {
@@ -446,11 +455,27 @@ func (ns *Impl) isLocalIP(ip netaddr.IP) bool {
 	return ns.atomicIsLocalIPFunc.Load().(func(netaddr.IP) bool)(ip)
 }
 
+// shouldProcessInbound reports whether an inbound packet should be
+// handled by netstack.
+func (ns *Impl) shouldProcessInbound(p *packet.Parsed, t *tstun.Wrapper) bool {
+	if !ns.ProcessLocalIPs && !ns.ProcessSubnets {
+		// Fast path for common case (e.g. Linux server in TUN mode) where
+		// netstack isn't used at all; don't even do an isLocalIP lookup.
+		return false
+	}
+	isLocal := ns.isLocalIP(p.Dst.IP())
+	if ns.ProcessLocalIPs && isLocal {
+		return true
+	}
+	if ns.ProcessSubnets && !isLocal {
+		return true
+	}
+	return false
+}
+
 func (ns *Impl) injectInbound(p *packet.Parsed, t *tstun.Wrapper) filter.Response {
-	if ns.onlySubnets && ns.isLocalIP(p.Dst.IP()) {
-		// In hybrid ("only subnets") mode, bail out early if
-		// the traffic is destined for an actual Tailscale
-		// address. The real host OS interface will handle it.
+	if !ns.shouldProcessInbound(p, t) {
+		// Let the host network stack (if any) deal with it.
 		return filter.Accept
 	}
 	var pn tcpip.NetworkProtocolNumber