Add O_DIRECTORY support to openat(O_PATH) in VFS2.

VFS2 earlier was ignoring the effect of O_DIRECTORY with O_PATH.

PiperOrigin-RevId: 456147699

pkg/sentry/vfs/opath.go

@@ -137,3 +137,32 @@ func (fd *opathFD) StatFS(ctx context.Context) (linux.Statfs, error) {
 	rp.Release(ctx)
 	return statfs, err
 }
+
+func (vfs *VirtualFilesystem) openOPathFD(ctx context.Context, creds *auth.Credentials, pop *PathOperation, flags uint32) (*FileDescription, error) {
+	vd, err := vfs.GetDentryAt(ctx, creds, pop, &GetDentryOptions{})
+	if err != nil {
+		return nil, err
+	}
+	defer vd.DecRef(ctx)
+
+	if flags&linux.O_DIRECTORY != 0 {
+		stat, err := vfs.StatAt(ctx, creds, &PathOperation{
+			Root:  vd,
+			Start: vd,
+		}, &StatOptions{
+			Mask: linux.STATX_MODE,
+		})
+		if err != nil {
+			return nil, err
+		}
+		if stat.Mode&linux.S_IFDIR == 0 {
+			return nil, linuxerr.ENOTDIR
+		}
+	}
+
+	fd := &opathFD{}
+	if err := fd.vfsfd.Init(fd, flags, vd.Mount(), vd.Dentry(), &FileDescriptionOptions{}); err != nil {
+		return nil, err
+	}
+	return &fd.vfsfd, err
+}

pkg/sentry/vfs/vfs.go

@@ -417,22 +417,13 @@ func (vfs *VirtualFilesystem) OpenAt(ctx context.Context, creds *auth.Credential
 	if opts.Flags&linux.O_NOFOLLOW != 0 {
 		pop.FollowFinalSymlink = false
 	}
+	if opts.Flags&linux.O_PATH != 0 {
+		return vfs.openOPathFD(ctx, creds, pop, opts.Flags)
+	}
 	rp := vfs.getResolvingPath(creds, pop)
 	if opts.Flags&linux.O_DIRECTORY != 0 {
 		rp.mustBeDir = true
 	}
-	if opts.Flags&linux.O_PATH != 0 {
-		vd, err := vfs.GetDentryAt(ctx, creds, pop, &GetDentryOptions{})
-		if err != nil {
-			return nil, err
-		}
-		fd := &opathFD{}
-		if err := fd.vfsfd.Init(fd, opts.Flags, vd.Mount(), vd.Dentry(), &FileDescriptionOptions{}); err != nil {
-			return nil, err
-		}
-		vd.DecRef(ctx)
-		return &fd.vfsfd, err
-	}
 	for {
 		fd, err := rp.mount.fs.impl.OpenAt(ctx, rp, *opts)
 		if err == nil {

test/syscalls/linux/open.cc

@@ -523,6 +523,14 @@ TEST_F(OpenTest, OpenWithOpath) {
   ASSERT_NO_ERRNO(Open(path, O_PATH));
 }
 
+// NOTE(b/236445327): Regression test. Opening a non-directory with O_PATH and
+// O_DIRECTORY should fail with ENOTDIR.
+TEST_F(OpenTest, OPathWithODirectory) {
+  auto newFile = ASSERT_NO_ERRNO_AND_VALUE(TempPath::CreateFile());
+  EXPECT_THAT(open(newFile.path().c_str(), O_RDONLY | O_DIRECTORY | O_PATH),
+              SyscallFailsWithErrno(ENOTDIR));
+}
+
 }  // namespace
 
 }  // namespace testing