socket/unix: handle sendto address argument for connected sockets

In case of SOCK_SEQPACKET, it has to be ignored.
In case of SOCK_STREAM, EISCONN or EOPNOTSUPP has to be returned.

PiperOrigin-RevId: 315755972

pkg/sentry/socket/unix/unix.go

@@ -459,15 +459,25 @@ func (s *socketOpsCommon) SendMsg(t *kernel.Task, src usermem.IOSequence, to []b
 		To:       nil,
 	}
 	if len(to) > 0 {
-		ep, err := extractEndpoint(t, to)
-		if err != nil {
-			return 0, err
-		}
-		defer ep.Release()
-		w.To = ep
+		switch s.stype {
+		case linux.SOCK_SEQPACKET:
+			to = nil
+		case linux.SOCK_STREAM:
+			if s.State() == linux.SS_CONNECTED {
+				return 0, syserr.ErrAlreadyConnected
+			}
+			return 0, syserr.ErrNotSupported
+		default:
+			ep, err := extractEndpoint(t, to)
+			if err != nil {
+				return 0, err
+			}
+			defer ep.Release()
+			w.To = ep
 
-		if ep.Passcred() && w.Control.Credentials == nil {
-			w.Control.Credentials = control.MakeCreds(t)
+			if ep.Passcred() && w.Control.Credentials == nil {
+				w.Control.Credentials = control.MakeCreds(t)
+			}
 		}
 	}
 

test/syscalls/linux/socket_unix_seqpacket.cc

@@ -43,6 +43,24 @@ TEST_P(SeqpacketUnixSocketPairTest, ReadOneSideClosed) {
               SyscallSucceedsWithValue(0));
 }
 
+TEST_P(SeqpacketUnixSocketPairTest, Sendto) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+
+  struct sockaddr_un addr = {};
+  addr.sun_family = AF_UNIX;
+  constexpr char kPath[] = "\0nonexistent";
+  memcpy(addr.sun_path, kPath, sizeof(kPath));
+
+  constexpr char kStr[] = "abc";
+  ASSERT_THAT(sendto(sockets->second_fd(), kStr, 3, 0, (struct sockaddr*)&addr,
+                     sizeof(addr)),
+              SyscallSucceedsWithValue(3));
+
+  char data[10] = {};
+  ASSERT_THAT(read(sockets->first_fd(), data, sizeof(data)),
+              SyscallSucceedsWithValue(3));
+}
+
 }  // namespace
 
 }  // namespace testing

test/syscalls/linux/socket_unix_stream.cc

@@ -89,6 +89,20 @@ TEST_P(StreamUnixSocketPairTest, ReadOneSideClosedWithUnreadData) {
               SyscallFailsWithErrno(ECONNRESET));
 }
 
+TEST_P(StreamUnixSocketPairTest, Sendto) {
+  auto sockets = ASSERT_NO_ERRNO_AND_VALUE(NewSocketPair());
+
+  struct sockaddr_un addr = {};
+  addr.sun_family = AF_UNIX;
+  constexpr char kPath[] = "\0nonexistent";
+  memcpy(addr.sun_path, kPath, sizeof(kPath));
+
+  constexpr char kStr[] = "abc";
+  ASSERT_THAT(sendto(sockets->second_fd(), kStr, 3, 0, (struct sockaddr*)&addr,
+                     sizeof(addr)),
+              SyscallFailsWithErrno(EISCONN));
+}
+
 INSTANTIATE_TEST_SUITE_P(
     AllUnixDomainSockets, StreamUnixSocketPairTest,
     ::testing::ValuesIn(IncludeReversals(VecCat<SocketPairKind>(