[PATCH] ovl: clean up dir on casefold mismatch

[Tao Cui <cui.tao@linux.dev>]

From: Tao Cui <cuitao@kylinos.cn>

In ovl_create_real(), the S_IFDIR case checks after a successful
ovl_do_mkdir() that the new directory inherited the expected casefold
flag.  On mismatch, err is set to -EINVAL but the directory that was
just created in the workdir or in the upper layer is left behind.

The mismatch is reachable: ofs->casefold is fixed at mount time, but
the casefold flag of the index dir can diverge.  With index=on, a
pre-existing "index" directory with +F is accepted at mount, and every
temp mkdir for an index entry inside it fails the check and leaks one
directory.  Measured on an ext4 casefold upper: 100 directory renames
left 100 "#nnnn" entries in the index dir, one per failed mkdir,
growing without bound.

Clean up the created directory with ovl_cleanup_locked() before
returning the error.  All callers of ovl_create_real() arrive with the
parent inode locked (via start_creating()), so the locked variant must
be used; ovl_cleanup() would deadlock on inode_lock().

Fixes: dfc7da402ccc9 ("ovl: Check for casefold consistency when creating new dentries")
Cc: stable@vger.kernel.org
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
---
 fs/overlayfs/dir.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 7beb0af26498..4e451bbd8f97 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -188,6 +188,7 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs, struct dentry *parent,
 			if (!err && ofs->casefold != ovl_dentry_casefolded(newdentry)) {
 				pr_warn_ratelimited("wrong inherited casefold (%pd2)\n",
 						    newdentry);
+				ovl_cleanup_locked(ofs, dir, newdentry);
 				err = -EINVAL;
 			}
 			break;
-- 
2.43.0