Re: [PATCH v4] ocfs2: Invalidate inode if i_mode is zero after block read

[Joseph Qi]

On 2025/12/2 08:32, 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@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: https://syzkaller.appspot.com/bug?extid=55c40ae8a0e5f3659f2b
> Co-developed-by: Albin Babu Varghese <albinbabuvarghese20@xxxxxxxxx>
> Signed-off-by: Albin Babu Varghese <albinbabuvarghese20@xxxxxxxxx>
> Signed-off-by: Ahmet Eray Karadag <eraykrdg1@xxxxxxxxx>
> Previous link: https://lore.kernel.org/all/20251022222752.46758-2-eraykrdg1@xxxxxxxxx/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) {

"(di->i_links_count | di->i_links_count_hi)" looks meaningless.
So if we don't want to introduce the endian coversion here, how about:

if ((!di->i_links_count && !di->i_links_count_hi) || !di->i_mode) {
	...
}

Heming, what's your opinion?

> +		mlog(ML_ERROR, "Invalid dinode #%llu: "
> +			"Corrupt state (nlink=0 or mode=0,) detected!\n",

Better to log the actual i_nlink/i_mode. e.g.

"corrupted i_nlink %u or i_mode %u\n"
...

Joseph

> +		        (unsigned long long)bh->b_blocknr);
> +		rc = -EFSCORRUPTED;
> +		goto bail;
> +	}
>  	/*
>  	 * Errors after here are fatal.
>  	 */