Skip listening TCP ports when trying to bind a free port.

PiperOrigin-RevId: 327686558

4 files changed, 48 insertions, 35 deletions

diff --git a/pkg/tcpip/ports/ports.go b/pkg/tcpip/ports/ports.go
index f6d592eb5..d87193650 100644
--- a/pkg/tcpip/ports/ports.go
+++ b/pkg/tcpip/ports/ports.go
@@ -400,7 +400,11 @@ func (s *PortManager) isPortAvailableLocked(networks []tcpip.NetworkProtocolNumb
 // reserved by another endpoint. If port is zero, ReservePort will search for
 // an unreserved ephemeral port and reserve it, returning its value in the
 // "port" return value.
-func (s *PortManager) ReservePort(networks []tcpip.NetworkProtocolNumber, transport tcpip.TransportProtocolNumber, addr tcpip.Address, port uint16, flags Flags, bindToDevice tcpip.NICID, dest tcpip.FullAddress) (reservedPort uint16, err *tcpip.Error) {
+//
+// An optional testPort closure can be passed in which if provided will be used
+// to test if the picked port can be used. The function should return true if
+// the port is safe to use, false otherwise.
+func (s *PortManager) ReservePort(networks []tcpip.NetworkProtocolNumber, transport tcpip.TransportProtocolNumber, addr tcpip.Address, port uint16, flags Flags, bindToDevice tcpip.NICID, dest tcpip.FullAddress, testPort func(port uint16) bool) (reservedPort uint16, err *tcpip.Error) {
 	s.mu.Lock()
 	defer s.mu.Unlock()
 
@@ -412,12 +416,23 @@ func (s *PortManager) ReservePort(networks []tcpip.NetworkProtocolNumber, transp
 		if !s.reserveSpecificPort(networks, transport, addr, port, flags, bindToDevice, dst) {
 			return 0, tcpip.ErrPortInUse
 		}
+		if testPort != nil && !testPort(port) {
+			s.releasePortLocked(networks, transport, addr, port, flags.Bits(), bindToDevice, dst)
+			return 0, tcpip.ErrPortInUse
+		}
 		return port, nil
 	}
 
 	// A port wasn't specified, so try to find one.
 	return s.PickEphemeralPort(func(p uint16) (bool, *tcpip.Error) {
-		return s.reserveSpecificPort(networks, transport, addr, p, flags, bindToDevice, dst), nil
+		if !s.reserveSpecificPort(networks, transport, addr, p, flags, bindToDevice, dst) {
+			return false, nil
+		}
+		if testPort != nil && !testPort(p) {
+			s.releasePortLocked(networks, transport, addr, p, flags.Bits(), bindToDevice, dst)
+			return false, nil
+		}
+		return true, nil
 	})
 }
 
diff --git a/pkg/tcpip/ports/ports_test.go b/pkg/tcpip/ports/ports_test.go
index 58db5868c..4bc949fd8 100644
--- a/pkg/tcpip/ports/ports_test.go
+++ b/pkg/tcpip/ports/ports_test.go
@@ -332,7 +332,7 @@ func TestPortReservation(t *testing.T) {
 					pm.ReleasePort(net, fakeTransNumber, test.ip, test.port, test.flags, test.device, test.dest)
 					continue
 				}
-				gotPort, err := pm.ReservePort(net, fakeTransNumber, test.ip, test.port, test.flags, test.device, test.dest)
+				gotPort, err := pm.ReservePort(net, fakeTransNumber, test.ip, test.port, test.flags, test.device, test.dest, nil /* testPort */)
 				if err != test.want {
 					t.Fatalf("ReservePort(.., .., %s, %d, %+v, %d, %v) = %v, want %v", test.ip, test.port, test.flags, test.device, test.dest, err, test.want)
 				}
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 21a4b6e2f..9df22ac84 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -2169,7 +2169,7 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) *tc
 			if sameAddr && p == e.ID.RemotePort {
 				return false, nil
 			}
-			if _, err := e.stack.ReservePort(netProtos, ProtocolNumber, e.ID.LocalAddress, p, e.portFlags, e.bindToDevice, addr); err != nil {
+			if _, err := e.stack.ReservePort(netProtos, ProtocolNumber, e.ID.LocalAddress, p, e.portFlags, e.bindToDevice, addr, nil /* testPort */); err != nil {
 				if err != tcpip.ErrPortInUse || !reuse {
 					return false, nil
 				}
@@ -2207,7 +2207,7 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) *tc
 				tcpEP.notifyProtocolGoroutine(notifyAbort)
 				tcpEP.UnlockUser()
 				// Now try and Reserve again if it fails then we skip.
-				if _, err := e.stack.ReservePort(netProtos, ProtocolNumber, e.ID.LocalAddress, p, e.portFlags, e.bindToDevice, addr); err != nil {
+				if _, err := e.stack.ReservePort(netProtos, ProtocolNumber, e.ID.LocalAddress, p, e.portFlags, e.bindToDevice, addr, nil /* testPort */); err != nil {
 					return false, nil
 				}
 			}
@@ -2505,47 +2505,45 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) (err *tcpip.Error) {
 		}
 	}
 
-	port, err := e.stack.ReservePort(netProtos, ProtocolNumber, addr.Addr, addr.Port, e.portFlags, e.bindToDevice, tcpip.FullAddress{})
-	if err != nil {
-		return err
-	}
-
-	e.boundBindToDevice = e.bindToDevice
-	e.boundPortFlags = e.portFlags
-	e.isPortReserved = true
-	e.effectiveNetProtos = netProtos
-	e.ID.LocalPort = port
-
-	// Any failures beyond this point must remove the port registration.
-	defer func(portFlags ports.Flags, bindToDevice tcpip.NICID) {
-		if err != nil {
-			e.stack.ReleasePort(netProtos, ProtocolNumber, addr.Addr, port, portFlags, bindToDevice, tcpip.FullAddress{})
-			e.isPortReserved = false
-			e.effectiveNetProtos = nil
-			e.ID.LocalPort = 0
-			e.ID.LocalAddress = ""
-			e.boundNICID = 0
-			e.boundBindToDevice = 0
-			e.boundPortFlags = ports.Flags{}
-		}
-	}(e.boundPortFlags, e.boundBindToDevice)
-
+	var nic tcpip.NICID
 	// If an address is specified, we must ensure that it's one of our
 	// local addresses.
 	if len(addr.Addr) != 0 {
-		nic := e.stack.CheckLocalAddress(addr.NIC, netProto, addr.Addr)
+		nic = e.stack.CheckLocalAddress(addr.NIC, netProto, addr.Addr)
 		if nic == 0 {
 			return tcpip.ErrBadLocalAddress
 		}
-
-		e.boundNICID = nic
 		e.ID.LocalAddress = addr.Addr
 	}
 
-	if err := e.stack.CheckRegisterTransportEndpoint(e.boundNICID, e.effectiveNetProtos, ProtocolNumber, e.ID, e.boundPortFlags, e.boundBindToDevice); err != nil {
+	port, err := e.stack.ReservePort(netProtos, ProtocolNumber, addr.Addr, addr.Port, e.portFlags, e.bindToDevice, tcpip.FullAddress{}, func(p uint16) bool {
+		id := e.ID
+		id.LocalPort = p
+		// CheckRegisterTransportEndpoint should only return an error if there is a
+		// listening endpoint bound with the same id and portFlags and bindToDevice
+		// options.
+		//
+		// NOTE: Only listening and connected endpoint register with
+		// demuxer. Further connected endpoints always have a remote
+		// address/port. Hence this will only return an error if there is a matching
+		// listening endpoint.
+		if err := e.stack.CheckRegisterTransportEndpoint(nic, netProtos, ProtocolNumber, id, e.portFlags, e.bindToDevice); err != nil {
+			return false
+		}
+		return true
+	})
+	if err != nil {
 		return err
 	}
 
+	e.boundBindToDevice = e.bindToDevice
+	e.boundPortFlags = e.portFlags
+	// TODO(gvisor.dev/issue/3691): Add test to verify boundNICID is correct.
+	e.boundNICID = nic
+	e.isPortReserved = true
+	e.effectiveNetProtos = netProtos
+	e.ID.LocalPort = port
+
 	// Mark endpoint as bound.
 	e.setEndpointState(StateBound)
 
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 73608783c..c33434b75 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -1226,7 +1226,7 @@ func (*endpoint) Accept() (tcpip.Endpoint, *waiter.Queue, *tcpip.Error) {
 
 func (e *endpoint) registerWithStack(nicID tcpip.NICID, netProtos []tcpip.NetworkProtocolNumber, id stack.TransportEndpointID) (stack.TransportEndpointID, tcpip.NICID, *tcpip.Error) {
 	if e.ID.LocalPort == 0 {
-		port, err := e.stack.ReservePort(netProtos, ProtocolNumber, id.LocalAddress, id.LocalPort, e.portFlags, e.bindToDevice, tcpip.FullAddress{})
+		port, err := e.stack.ReservePort(netProtos, ProtocolNumber, id.LocalAddress, id.LocalPort, e.portFlags, e.bindToDevice, tcpip.FullAddress{}, nil /* testPort */)
 		if err != nil {
 			return id, e.bindToDevice, err
 		}