linux-kernel - Re: [PATCH v3] ocfs2: Invalidate inode if i

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Message-ID: <lkeaoxtkqccd3knpskbewkbn4cimlxaufix4evugcfkplk6u4b@oi36e4iu3x3r>
Date: Thu, 20 Nov 2025 10:32:43 +0800
From: Heming Zhao <heming.zhao@...e.com>
To: Ahmet Eray Karadag <eraykrdg1@...il.com>
Cc: mark@...heh.com, jlbec@...lplan.org, joseph.qi@...ux.alibaba.com, 
	ocfs2-devel@...ts.linux.dev, linux-kernel@...r.kernel.org, david.hunter.linux@...il.com, 
	skhan@...uxfoundation.org, syzbot+55c40ae8a0e5f3659f2b@...kaller.appspotmail.com, 
	Albin Babu Varghese <albinbabuvarghese20@...il.com>
Subject: Re: [PATCH v3] ocfs2: Invalidate inode if i_mode is zero after block
 read

On Thu, Nov 20, 2025 at 01:17:24AM +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@...kaller.appspotmail.com
> Fixes: https://syzkaller.appspot.com/bug?extid=55c40ae8a0e5f3659f2b
> Co-developed-by: Albin Babu Varghese <albinbabuvarghese20@...il.com>
> Signed-off-by: Albin Babu Varghese <albinbabuvarghese20@...il.com>
> Signed-off-by: Ahmet Eray Karadag <eraykrdg1@...il.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
> ---
>  fs/ocfs2/inode.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
> index 14bf440ea4df..c8b129db756e 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 (!ocfs2_read_links_count(di) || !di->i_mode) {

the code logic looks good to me, but I prefer the following code to save a few
cpu cycles.

```
/* only check if the "link count" or i_mode is ZERO */
if (!(di->i_links_count | di->i_links_count_hi) || !di->i_mode)
```

@Joseph
which do you like?

- 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
> 
>