unix: return ECONNREFUSE if a socket file exists but a socket isn't bound to it

PiperOrigin-RevId: 328843560

pkg/sentry/fsimpl/gofer/filesystem.go

@@ -1512,7 +1512,9 @@ func (fs *filesystem) BoundEndpointAt(ctx context.Context, rp *vfs.ResolvingPath
 				path:   opts.Addr,
 			}, nil
 		}
-		return d.endpoint, nil
+		if d.endpoint != nil {
+			return d.endpoint, nil
+		}
 	}
 	return nil, syserror.ECONNREFUSED
 }

pkg/sentry/fsimpl/tmpfs/filesystem.go

@@ -783,6 +783,9 @@ func (fs *filesystem) BoundEndpointAt(ctx context.Context, rp *vfs.ResolvingPath
 	}
 	switch impl := d.inode.impl.(type) {
 	case *socketFile:
+		if impl.ep == nil {
+			return nil, syserror.ECONNREFUSED
+		}
 		return impl.ep, nil
 	default:
 		return nil, syserror.ECONNREFUSED

test/syscalls/linux/mknod.cc

@@ -14,6 +14,7 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <sys/socket.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/un.h>
@@ -103,6 +104,24 @@ TEST(MknodTest, UnimplementedTypesReturnError) {
   ASSERT_THAT(mknod(path.c_str(), S_IFBLK, 0), SyscallFailsWithErrno(EPERM));
 }
 
+TEST(MknodTest, Socket) {
+  ASSERT_THAT(chdir(GetAbsoluteTestTmpdir().c_str()), SyscallSucceeds());
+
+  SKIP_IF(IsRunningOnGvisor() && IsRunningWithVFS1());
+
+  ASSERT_THAT(mknod("./file0", S_IFSOCK | S_IRUSR | S_IWUSR, 0),
+              SyscallSucceeds());
+
+  int sk;
+  ASSERT_THAT(sk = socket(AF_UNIX, SOCK_SEQPACKET, 0), SyscallSucceeds());
+  FileDescriptor fd(sk);
+
+  struct sockaddr_un addr = {.sun_family = AF_UNIX};
+  absl::SNPrintF(addr.sun_path, sizeof(addr.sun_path), "./file0");
+  ASSERT_THAT(connect(sk, (struct sockaddr *)&addr, sizeof(addr)),
+              SyscallFailsWithErrno(ECONNREFUSED));
+}
+
 TEST(MknodTest, Fifo) {
   const std::string fifo = NewTempAbsPath();
   ASSERT_THAT(mknod(fifo.c_str(), S_IFIFO | S_IRUSR | S_IWUSR, 0),