linux-kernel - Re: [PATCH v5] ocfs2: Invalidate inode if i

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Message-ID: <r3mqyzrky6pamao7b4tsobdqqybhmyt6dg7jao76ho24kph3aq@wfwbzjqzury5>
Date: Tue, 2 Dec 2025 14:15:18 +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 v5] ocfs2: Invalidate inode if i_mode is zero after block
 read

On Tue, Dec 02, 2025 at 06:52:14AM +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
> ---
> v4:
>  - Reading i_links_count hi and low bits without helper function
>   to save few cpu cycles
> ---
> v5:
>  - Clear i_links_count check
>  - Log the actual i_nlink/i_mode
> ---
>  fs/ocfs2/inode.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
> index 14bf440ea4df..08ce0846289c 100644
> --- a/fs/ocfs2/inode.c
> +++ b/fs/ocfs2/inode.c
> @@ -1456,6 +1456,14 @@ int ocfs2_validate_inode_block(struct super_block *sb,
>  		goto bail;
>  	}
>  
> +	if ((!di->i_links_count && !di->i_links_count_hi) || !di->i_mode) {
> +		mlog(ML_ERROR, "Invalid dinode #%llu: "
> +			"Corrupt state (nlink = %u or mode = %u) detected!\n",
> +		        (unsigned long long)bh->b_blocknr,
> +			(di->i_links_count_hi | di->i_links_count), di->i_mode);

The '|' logic is meaningless here. Because the error case is rare, you can simply
call ocfs2_read_links_count(di).

- Heming
> +		rc = -EFSCORRUPTED;
> +		goto bail;
> +	}
>  	/*
>  	 * Errors after here are fatal.
>  	 */
> -- 
> 2.43.0
> 
>