Sanity test that open(2) on a UDS fails

Spoiler alert: it doesn't.

PiperOrigin-RevId: 272513529

test/syscalls/linux/BUILD

@@ -333,6 +333,7 @@ cc_binary(
     linkstatic = 1,
     deps = [
         ":socket_test_util",
+        "//test/util:file_descriptor",
         "//test/util:test_main",
         "//test/util:test_util",
         "@com_google_googletest//:gtest",

test/syscalls/linux/socket.cc

@@ -17,6 +17,7 @@
 
 #include "gtest/gtest.h"
 #include "test/syscalls/linux/socket_test_util.h"
+#include "test/util/file_descriptor.h"
 #include "test/util/test_util.h"
 
 namespace gvisor {
@@ -57,5 +58,28 @@ TEST(SocketTest, ProtocolInet) {
   }
 }
 
+using SocketOpenTest = ::testing::TestWithParam<int>;
+
+// UDS cannot be opened.
+TEST_P(SocketOpenTest, Unix) {
+  // FIXME(b/142001530): Open incorrectly succeeds on gVisor.
+  SKIP_IF(IsRunningOnGvisor());
+
+  FileDescriptor bound =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(AF_UNIX, SOCK_STREAM, PF_UNIX));
+
+  struct sockaddr_un addr =
+      ASSERT_NO_ERRNO_AND_VALUE(UniqueUnixAddr(/*abstract=*/false, AF_UNIX));
+
+  ASSERT_THAT(bind(bound.get(), reinterpret_cast<struct sockaddr*>(&addr),
+                   sizeof(addr)),
+              SyscallSucceeds());
+
+  EXPECT_THAT(open(addr.sun_path, GetParam()), SyscallFailsWithErrno(ENXIO));
+}
+
+INSTANTIATE_TEST_SUITE_P(OpenModes, SocketOpenTest,
+                         ::testing::Values(O_RDONLY, O_RDWR));
+
 }  // namespace testing
 }  // namespace gvisor

test/syscalls/linux/socket_test_util.h

@@ -83,6 +83,8 @@ inline ssize_t SendFd(int fd, void* buf, size_t count, int flags) {
       count);
 }
 
+PosixErrorOr<struct sockaddr_un> UniqueUnixAddr(bool abstract, int domain);
+
 // A Creator<T> is a function that attempts to create and return a new T. (This
 // is copy/pasted from cloud/gvisor/api/sandbox_util.h and is just duplicated
 // here for clarity.)