A panic occurs in ocfs2_unlink due to WARN_ON(inode->i_nlink == 0) when
handling a corrupted inode with i_mode=0 and i_nlink=0 in memory.
This "zombie" inode is created because ocfs2_read_locked_inode proceeds
even after ocfs2_validate_inode_block successfully validates a block
that structurally looks okay (passes checksum, signature etc.) but
contains semantically invalid data (specifically i_mode=0). The current
validation function doesn't check for i_mode being zero.
This results in an in-memory inode with i_mode=0 being added to the VFS
cache, which later triggers the panic during unlink.
Prevent this by adding an explicit check for (i_mode == 0, i_nlink == 0, non-orphan)
within ocfs2_validate_inode_block. If the check is true, return -EFSCORRUPTED to signal
corruption. This causes the caller (ocfs2_read_locked_inode) to invoke
make_bad_inode(), correctly preventing the zombie inode from entering
the cache.
Reported-by: syzbot+55c40ae8a0e5f3659f2b@syzkaller.appspotmail.com
Fixes: https://syzkaller.appspot.com/bug?extid=55c40ae8a0e5f3659f2b
Co-developed-by: Albin Babu Varghese <albinbabuvarghese20@gmail.com>
Signed-off-by: Albin Babu Varghese <albinbabuvarghese20@gmail.com>
Signed-off-by: Ahmet Eray Karadag <eraykrdg1@gmail.com>
Previous link: https://lore.kernel.org/all/20251022222752.46758-2-eraykrdg1@gmail.com/T/
---
v2:
- Only checking either i_links_count == 0 or i_mode == 0
- Not performing le16_to_cpu() anymore
- Tested with ocfs2-test
---
v3:
- Add checking both high and low bits of i_links_count
---
v4:
- Reading i_links_count hi and low bits without helper function
to save few cpu cycles
---
fs/ocfs2/inode.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 14bf440ea4df..34c2882273ae 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1455,7 +1455,13 @@ int ocfs2_validate_inode_block(struct super_block *sb,
(unsigned long long)bh->b_blocknr);
goto bail;
}
-
+ if (!(di->i_links_count | di->i_links_count_hi) || !di->i_mode) {
+ mlog(ML_ERROR, "Invalid dinode #%llu: "
+ "Corrupt state (nlink=0 or mode=0,) detected!\n",
+ (unsigned long long)bh->b_blocknr);
+ rc = -EFSCORRUPTED;
+ goto bail;
+ }
/*
* Errors after here are fatal.
*/
--
2.43.0