Fix SO_ACCEPTCONN option for unix sockets.

SO_ACCEPTCONN returns true for TCP sockets which are in a listening state.
Added this socket option support for unix sockets.

PiperOrigin-RevId: 577008617

pkg/sentry/socket/netstack/netstack.go

@@ -1076,13 +1076,8 @@ func getSockOptSocket(t *kernel.Task, s socket.Socket, ep commonEndpoint, family
 			return nil, syserr.ErrInvalidArgument
 		}
 
-		// This option is only viable for TCP endpoints.
-		var v bool
-		if socket.IsTCP(s) {
-			v = tcp.EndpointState(ep.State()) == tcp.StateListen
-		}
-		vP := primitive.Int32(boolToInt32(v))
-		return &vP, nil
+		v := primitive.Int32(boolToInt32(ep.SocketOptions().GetAcceptConn()))
+		return &v, nil
 
 	case linux.SO_RCVLOWAT:
 		if outLen < sizeOfInt32 {

pkg/sentry/socket/unix/transport/connectioned.go

@@ -645,3 +645,7 @@ func (e *connectionedEndpoint) EventUnregister(we *waiter.Entry) {
 		fdnotifier.UpdateFD(bsFD.NotificationFD())
 	}
 }
+
+func (e *connectionedEndpoint) GetAcceptConn() bool {
+	return e.Listening()
+}

pkg/tcpip/socketops.go

@@ -63,6 +63,10 @@ type SocketOptionsHandler interface {
 	// changed. The handler notifies the writers if the send buffer size is
 	// increased with setsockopt(2) for TCP endpoints.
 	WakeupWriters()
+
+	// GetAcceptConn returns true if the socket is a TCP socket and is in
+	// listening state.
+	GetAcceptConn() bool
 }
 
 // DefaultSocketOptionsHandler is an embeddable type that implements no-op
@@ -112,6 +116,11 @@ func (*DefaultSocketOptionsHandler) OnSetReceiveBufferSize(v, oldSz int64) (newS
 	return v, nil
 }
 
+// GetAcceptConn implements SocketOptionsHandler.GetAcceptConn.
+func (*DefaultSocketOptionsHandler) GetAcceptConn() bool {
+	return false
+}
+
 // StackHandler holds methods to access the stack options. These must be
 // implemented by the stack.
 type StackHandler interface {
@@ -742,3 +751,8 @@ func (so *SocketOptions) SetRcvlowat(rcvlowat int32) Error {
 	so.rcvlowat.Store(rcvlowat)
 	return nil
 }
+
+// GetAcceptConn gets value for SO_ACCEPTCONN option.
+func (so *SocketOptions) GetAcceptConn() bool {
+	return so.handler.GetAcceptConn()
+}

pkg/tcpip/transport/tcp/endpoint.go

@@ -3325,3 +3325,7 @@ func (e *endpoint) computeTCPSendBufferSize() int64 {
 
 	return newSndBufSz
 }
+
+func (e *endpoint) GetAcceptConn() bool {
+	return EndpointState(e.State()) == StateListen
+}

test/syscalls/linux/socket_unix_stream.cc

@@ -229,6 +229,27 @@ TEST_P(StreamUnixSocketPairTest, IncreasedSocketSendBufUnblocksWrites) {
               SyscallSucceeds());
 }
 
+TEST_P(StreamUnixSocketPairTest, GetAcceptConn) {
+  auto bound = ASSERT_NO_ERRNO_AND_VALUE(Socket(AF_UNIX, SOCK_STREAM, 0));
+  struct sockaddr_un bind_addr =
+      ASSERT_NO_ERRNO_AND_VALUE(UniqueUnixAddr(true, AF_UNIX));
+  ASSERT_THAT(bind(bound.get(), AsSockAddr(&bind_addr), sizeof(bind_addr)),
+              SyscallSucceeds());
+  int opt = 0;
+  socklen_t opt_len = sizeof(opt);
+  ASSERT_THAT(
+      getsockopt(bound.get(), SOL_SOCKET, SO_ACCEPTCONN, &opt, &opt_len),
+      SyscallSucceeds());
+  ASSERT_EQ(opt, 0);
+  ASSERT_THAT(listen(bound.get(),
+                     /* backlog = */ 5),  // NOLINT(bugprone-argument-comment)
+              SyscallSucceeds());
+  ASSERT_THAT(
+      getsockopt(bound.get(), SOL_SOCKET, SO_ACCEPTCONN, &opt, &opt_len),
+      SyscallSucceeds());
+  ASSERT_EQ(opt, 1);
+}
+
 INSTANTIATE_TEST_SUITE_P(
     AllUnixDomainSockets, StreamUnixSocketPairTest,
     ::testing::ValuesIn(IncludeReversals(VecCat<SocketPairKind>(