[vfs2] Fix tmpfs mounting.

Earlier we were using NLink to decide if /tmp is empty or not. However, NLink
at best tells us about the number of subdirectories (via the ".." entries).
NLink = n + 2 for n subdirectories. But it does not tell us if the directory is
empty. There still might be non-directory files. We could also not rely on
NLink because host overlayfs always returned 1.

VFS1 uses Readdir to decide if the directory is empty. Used a similar approach.
We now use IterDirents to decide if the "/tmp" directory is empty.

Fixes #3369

PiperOrigin-RevId: 325554234

1 files changed, 6 insertions, 4 deletions

diff --git a/pkg/sentry/fsimpl/overlay/directory.go b/pkg/sentry/fsimpl/overlay/directory.go
index fccb94105..6a79f7ffe 100644
--- a/pkg/sentry/fsimpl/overlay/directory.go
+++ b/pkg/sentry/fsimpl/overlay/directory.go
@@ -51,7 +51,7 @@ func (d *dentry) collectWhiteoutsForRmdirLocked(ctx context.Context) (map[string
 		// Reuse slice allocated for maybeWhiteouts from a previous layer to
 		// reduce allocations.
 		maybeWhiteouts = maybeWhiteouts[:0]
-		if err := layerFD.IterDirents(ctx, vfs.IterDirentsCallbackFunc(func(dirent vfs.Dirent) error {
+		err = layerFD.IterDirents(ctx, vfs.IterDirentsCallbackFunc(func(dirent vfs.Dirent) error {
 			if dirent.Name == "." || dirent.Name == ".." {
 				return nil
 			}
@@ -68,7 +68,8 @@ func (d *dentry) collectWhiteoutsForRmdirLocked(ctx context.Context) (map[string
 			}
 			// Non-whiteout file in the directory prevents rmdir.
 			return syserror.ENOTEMPTY
-		})); err != nil {
+		}))
+		if err != nil {
 			readdirErr = err
 			return false
 		}
@@ -182,7 +183,7 @@ func (d *dentry) getDirents(ctx context.Context) ([]vfs.Dirent, error) {
 		// Reuse slice allocated for maybeWhiteouts from a previous layer to
 		// reduce allocations.
 		maybeWhiteouts = maybeWhiteouts[:0]
-		if err := layerFD.IterDirents(ctx, vfs.IterDirentsCallbackFunc(func(dirent vfs.Dirent) error {
+		err = layerFD.IterDirents(ctx, vfs.IterDirentsCallbackFunc(func(dirent vfs.Dirent) error {
 			if dirent.Name == "." || dirent.Name == ".." {
 				return nil
 			}
@@ -201,7 +202,8 @@ func (d *dentry) getDirents(ctx context.Context) ([]vfs.Dirent, error) {
 			dirent.NextOff = int64(len(dirents) + 1)
 			dirents = append(dirents, dirent)
 			return nil
-		})); err != nil {
+		}))
+		if err != nil {
 			readdirErr = err
 			return false
 		}