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
---
 fs/ocfs2/inode.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 14bf440ea4df..6641caa45292 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1456,6 +1456,13 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 		goto bail;
 	}
 
+	if (!di->i_links_count || !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

On Tue, Nov 18, 2025 at 01:35:07AM +0300, Ahmet Eray Karadag wrote:
> 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
> ---
>  fs/ocfs2/inode.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
> index 14bf440ea4df..6641caa45292 100644
> --- a/fs/ocfs2/inode.c
> +++ b/fs/ocfs2/inode.c
> @@ -1456,6 +1456,13 @@ int ocfs2_validate_inode_block(struct super_block *sb,
>  		goto bail;
>  	}
>  
> +	if (!di->i_links_count || !di->i_mode) {

question:
Why does this code not check both di->i_link_count and di->i_links_count_hi here?

- Heming
> +		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
> 
>