Make connect on socket returned by accept correctly error out with EISCONN

PiperOrigin-RevId: 279814493

pkg/tcpip/transport/tcp/accept.go

@@ -300,6 +300,7 @@ func (l *listenContext) createEndpointAndPerformHandshake(s *segment, opts *head
 	ep.mu.Lock()
 	ep.stack.Stats().TCP.CurrentEstablished.Increment()
 	ep.state = StateEstablished
+	ep.isConnectNotified = true
 	ep.mu.Unlock()
 
 	// Update the receive window scaling. We can't do it before the
@@ -539,6 +540,7 @@ func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) {
 		// Switch state to connected.
 		n.stack.Stats().TCP.CurrentEstablished.Increment()
 		n.state = StateEstablished
+		n.isConnectNotified = true
 
 		// Do the delivery in a separate goroutine so
 		// that we don't block the listen loop in case

pkg/tcpip/transport/tcp/tcp_test.go

@@ -4599,6 +4599,9 @@ func TestEndpointBindListenAcceptState(t *testing.T) {
 	if got, want := tcp.EndpointState(aep.State()), tcp.StateEstablished; got != want {
 		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
 	}
+	if err := aep.Connect(tcpip.FullAddress{Addr: context.TestAddr, Port: context.TestPort}); err != tcpip.ErrAlreadyConnected {
+		t.Errorf("Unexpected error attempting to call connect on an established endpoint, got: %v, want: %v", err, tcpip.ErrAlreadyConnected)
+	}
 	// Listening endpoint remains in listen state.
 	if got, want := tcp.EndpointState(ep.State()), tcp.StateListen; got != want {
 		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)

test/syscalls/linux/tcp_socket.cc

@@ -130,6 +130,19 @@ void TcpSocketTest::TearDown() {
   }
 }
 
+TEST_P(TcpSocketTest, ConnectOnEstablishedConnection) {
+  sockaddr_storage addr =
+      ASSERT_NO_ERRNO_AND_VALUE(InetLoopbackAddr(GetParam()));
+  socklen_t addrlen = sizeof(addr);
+
+  ASSERT_THAT(
+      connect(s_, reinterpret_cast<const struct sockaddr*>(&addr), addrlen),
+      SyscallFailsWithErrno(EISCONN));
+  ASSERT_THAT(
+      connect(t_, reinterpret_cast<const struct sockaddr*>(&addr), addrlen),
+      SyscallFailsWithErrno(EISCONN));
+}
+
 TEST_P(TcpSocketTest, DataCoalesced) {
   char buf[10];