linux-kernel - Forwarded: [PATCH] f2fs: invalidate dentry cache on failed whiteout creation

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Message-ID: <68f906c1.050a0220.346f24.005b.GAE@google.com>
Date: Wed, 22 Oct 2025 09:30:57 -0700
From: syzbot <syzbot+632cf32276a9a564188d@...kaller.appspotmail.com>
To: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Forwarded: [PATCH] f2fs: invalidate dentry cache on failed whiteout creation

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linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com.

***

Subject: [PATCH] f2fs: invalidate dentry cache on failed whiteout creation
Author: kartikey406@...il.com

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

F2FS can mount filesystems with corrupted directory depth values that
get runtime-clamped to MAX_DIR_HASH_DEPTH. When RENAME_WHITEOUT
operations are performed on such directories, f2fs_rename performs
directory modifications (updating target entry and deleting source
entry) before attempting to add the whiteout entry via f2fs_add_link.

If f2fs_add_link fails due to the corrupted directory structure, the
function returns an error to VFS, but the partial directory
modifications have already been committed to disk. VFS assumes the
entire rename operation failed and does not update the dentry cache,
leaving stale mappings.

This causes subsequent operations to use cached dentry information that
no longer matches the on-disk state. When a second rename targets the
same entry, VFS attempts to decrement i_nlink on the stale inode, which
may already have i_nlink=0, triggering a WARNING in drop_nlink().

Example sequence:
1. First rename (RENAME_WHITEOUT): file2 → file1
   - f2fs updates file1 entry on disk (points to inode 8)
   - f2fs deletes file2 entry on disk
   - f2fs_add_link(whiteout) fails (corrupted directory)
   - Returns error to VFS
   - VFS cache still has: file1 → inode 7 (stale!)

2. Second rename: file3 → file1
   - VFS uses stale cache: file1 → inode 7
   - Tries to drop_nlink on inode 7 (i_nlink already 0)
   - WARNING in drop_nlink()

Fix this by explicitly invalidating old_dentry and new_dentry when
f2fs_add_link fails during whiteout creation. This forces VFS to
refresh from disk on subsequent operations, ensuring cache consistency
even when the rename partially succeeds.

Reproducer:
1. Mount F2FS image with corrupted i_current_depth
2. renameat2(file2, file1, RENAME_WHITEOUT)
3. renameat2(file3, file1, 0)
4. System triggers WARNING in drop_nlink()

Reported-by: syzbot+632cf32276a9a564188d@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=632cf32276a9a564188d
Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>
---
 fs/f2fs/namei.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
index b882771e4699..712479b7b93d 100644
--- a/fs/f2fs/namei.c
+++ b/fs/f2fs/namei.c
@@ -1053,9 +1053,11 @@ static int f2fs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 	if (whiteout) {
 		set_inode_flag(whiteout, FI_INC_LINK);
 		err = f2fs_add_link(old_dentry, whiteout);
-		if (err)
+		if (err) {
+			d_invalidate(old_dentry);
+			d_invalidate(new_dentry);
 			goto put_out_dir;
-
+		}
 		spin_lock(&whiteout->i_lock);
 		whiteout->i_state &= ~I_LINKABLE;
 		spin_unlock(&whiteout->i_lock);
-- 
2.43.0