Fix TCP wildcard bind failure when netstack is v6 only

TCP endpoint unconditionly binds to v4 even when the stack only supports v6.

PiperOrigin-RevId: 339739392

pkg/tcpip/transport/tcp/dual_stack_test.go

@@ -236,6 +236,25 @@ func TestV6ConnectWhenBoundToWildcard(t *testing.T) {
 	testV6Connect(t, c)
 }
 
+func TestStackV6OnlyConnectWhenBoundToWildcard(t *testing.T) {
+	c := context.NewWithOpts(t, context.Options{
+		EnableV6: true,
+		MTU:      defaultMTU,
+	})
+	defer c.Cleanup()
+
+	// Create a v6 endpoint but don't set the v6-only TCP option.
+	c.CreateV6Endpoint(false)
+
+	// Bind to wildcard.
+	if err := c.EP.Bind(tcpip.FullAddress{}); err != nil {
+		t.Fatalf("Bind failed: %v", err)
+	}
+
+	// Test the connection request.
+	testV6Connect(t, c)
+}
+
 func TestV6ConnectWhenBoundToLocalAddress(t *testing.T) {
 	c := context.New(t, defaultMTU)
 	defer c.Cleanup()

pkg/tcpip/transport/tcp/endpoint.go

@@ -2690,14 +2690,16 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) (err *tcpip.Error) {
 		return err
 	}
 
-	// Expand netProtos to include v4 and v6 if the caller is binding to a
-	// wildcard (empty) address, and this is an IPv6 endpoint with v6only
-	// set to false.
 	netProtos := []tcpip.NetworkProtocolNumber{netProto}
-	if netProto == header.IPv6ProtocolNumber && !e.v6only && addr.Addr == "" {
-		netProtos = []tcpip.NetworkProtocolNumber{
-			header.IPv6ProtocolNumber,
-			header.IPv4ProtocolNumber,
+
+	// Expand netProtos to include v4 and v6 under dual-stack if the caller is
+	// binding to a wildcard (empty) address, and this is an IPv6 endpoint with
+	// v6only set to false.
+	if netProto == header.IPv6ProtocolNumber {
+		stackHasV4 := e.stack.CheckNetworkProtocol(header.IPv4ProtocolNumber)
+		alsoBindToV4 := !e.v6only && addr.Addr == "" && stackHasV4
+		if alsoBindToV4 {
+			netProtos = append(netProtos, header.IPv4ProtocolNumber)
 		}
 	}
 

pkg/tcpip/transport/tcp/testing/context/context.go

@@ -112,6 +112,18 @@ type Headers struct {
 	TCPOpts []byte
 }
 
+// Options contains options for creating a new test context.
+type Options struct {
+	// EnableV4 indicates whether IPv4 should be enabled.
+	EnableV4 bool
+
+	// EnableV6 indicates whether IPv4 should be enabled.
+	EnableV6 bool
+
+	// MTU indicates the maximum transmission unit on the link layer.
+	MTU uint32
+}
+
 // Context provides an initialized Network stack and a link layer endpoint
 // for use in TCP tests.
 type Context struct {
@@ -154,10 +166,30 @@ type Context struct {
 // New allocates and initializes a test context containing a new
 // stack and a link-layer endpoint.
 func New(t *testing.T, mtu uint32) *Context {
-	s := stack.New(stack.Options{
-		NetworkProtocols:   []stack.NetworkProtocolFactory{ipv4.NewProtocol, ipv6.NewProtocol},
-		TransportProtocols: []stack.TransportProtocolFactory{tcp.NewProtocol},
+	return NewWithOpts(t, Options{
+		EnableV4: true,
+		EnableV6: true,
+		MTU:      mtu,
 	})
+}
+
+// NewWithOpts allocates and initializes a test context containing a new
+// stack and a link-layer endpoint with specific options.
+func NewWithOpts(t *testing.T, opts Options) *Context {
+	if opts.MTU == 0 {
+		panic("MTU must be greater than 0")
+	}
+
+	stackOpts := stack.Options{
+		TransportProtocols: []stack.TransportProtocolFactory{tcp.NewProtocol},
+	}
+	if opts.EnableV4 {
+		stackOpts.NetworkProtocols = append(stackOpts.NetworkProtocols, ipv4.NewProtocol)
+	}
+	if opts.EnableV6 {
+		stackOpts.NetworkProtocols = append(stackOpts.NetworkProtocols, ipv6.NewProtocol)
+	}
+	s := stack.New(stackOpts)
 
 	const sendBufferSize = 1 << 20 // 1 MiB
 	const recvBufferSize = 1 << 20 // 1 MiB
@@ -182,50 +214,55 @@ func New(t *testing.T, mtu uint32) *Context {
 
 	// Some of the congestion control tests send up to 640 packets, we so
 	// set the channel size to 1000.
-	ep := channel.New(1000, mtu, "")
+	ep := channel.New(1000, opts.MTU, "")
 	wep := stack.LinkEndpoint(ep)
 	if testing.Verbose() {
 		wep = sniffer.New(ep)
 	}
-	opts := stack.NICOptions{Name: "nic1"}
-	if err := s.CreateNICWithOptions(1, wep, opts); err != nil {
+	nicOpts := stack.NICOptions{Name: "nic1"}
+	if err := s.CreateNICWithOptions(1, wep, nicOpts); err != nil {
 		t.Fatalf("CreateNICWithOptions(_, _, %+v) failed: %v", opts, err)
 	}
-	wep2 := stack.LinkEndpoint(channel.New(1000, mtu, ""))
+	wep2 := stack.LinkEndpoint(channel.New(1000, opts.MTU, ""))
 	if testing.Verbose() {
-		wep2 = sniffer.New(channel.New(1000, mtu, ""))
+		wep2 = sniffer.New(channel.New(1000, opts.MTU, ""))
 	}
 	opts2 := stack.NICOptions{Name: "nic2"}
 	if err := s.CreateNICWithOptions(2, wep2, opts2); err != nil {
 		t.Fatalf("CreateNICWithOptions(_, _, %+v) failed: %v", opts2, err)
 	}
 
-	v4ProtocolAddr := tcpip.ProtocolAddress{
-		Protocol:          ipv4.ProtocolNumber,
-		AddressWithPrefix: StackAddrWithPrefix,
-	}
-	if err := s.AddProtocolAddress(1, v4ProtocolAddr); err != nil {
-		t.Fatalf("AddProtocolAddress(1, %#v): %s", v4ProtocolAddr, err)
-	}
+	var routeTable []tcpip.Route
 
-	v6ProtocolAddr := tcpip.ProtocolAddress{
-		Protocol:          ipv6.ProtocolNumber,
-		AddressWithPrefix: StackV6AddrWithPrefix,
-	}
-	if err := s.AddProtocolAddress(1, v6ProtocolAddr); err != nil {
-		t.Fatalf("AddProtocolAddress(1, %#v): %s", v6ProtocolAddr, err)
-	}
-
-	s.SetRouteTable([]tcpip.Route{
-		{
+	if opts.EnableV4 {
+		v4ProtocolAddr := tcpip.ProtocolAddress{
+			Protocol:          ipv4.ProtocolNumber,
+			AddressWithPrefix: StackAddrWithPrefix,
+		}
+		if err := s.AddProtocolAddress(1, v4ProtocolAddr); err != nil {
+			t.Fatalf("AddProtocolAddress(1, %#v): %s", v4ProtocolAddr, err)
+		}
+		routeTable = append(routeTable, tcpip.Route{
 			Destination: header.IPv4EmptySubnet,
 			NIC:         1,
-		},
-		{
+		})
+	}
+
+	if opts.EnableV6 {
+		v6ProtocolAddr := tcpip.ProtocolAddress{
+			Protocol:          ipv6.ProtocolNumber,
+			AddressWithPrefix: StackV6AddrWithPrefix,
+		}
+		if err := s.AddProtocolAddress(1, v6ProtocolAddr); err != nil {
+			t.Fatalf("AddProtocolAddress(1, %#v): %s", v6ProtocolAddr, err)
+		}
+		routeTable = append(routeTable, tcpip.Route{
 			Destination: header.IPv6EmptySubnet,
 			NIC:         1,
-		},
-	})
+		})
+	}
+
+	s.SetRouteTable(routeTable)
 
 	return &Context{
 		t:           t,