linux-kernel - Re: [PATCH v3] ocfs2: Avoid NULL pointer dereference in dx_dir_lookup

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Message-ID: <3ac6bcb9-ac73-492c-a9f6-fbfb827c5967@linux.alibaba.com>
Date: Tue, 8 Jul 2025 08:59:12 +0800
From: Joseph Qi <joseph.qi@...ux.alibaba.com>
To: Ivan Pravdin <ipravdin.official@...il.com>, mark@...heh.com,
 jlbec@...lplan.org, ocfs2-devel@...ts.linux.dev,
 linux-kernel@...r.kernel.org, akpm <akpm@...ux-foundation.org>
Cc: syzbot+20282c1b2184a857ac4c@...kaller.appspotmail.com
Subject: Re: [PATCH v3] ocfs2: Avoid NULL pointer dereference in
 dx_dir_lookup_rec()



On 2025/7/8 08:10, Ivan Pravdin wrote:
> When a directory entry is not found, ocfs2_dx_dir_lookup_rec() prints an
> error message that unconditionally dereferences the 'rec' pointer.
> However, if 'rec' is NULL, this leads to a NULL pointer dereference and
> a kernel panic.
> 
> Add an explicit check empty extent list to avoid dereferencing NULL
> 'rec' pointer.
> 
> Reported-by: syzbot+20282c1b2184a857ac4c@...kaller.appspotmail.com
> Closes: https://lore.kernel.org/all/67cd7e29.050a0220.e1a89.0007.GAE@google.com/
> Signed-off-by: Ivan Pravdin <ipravdin.official@...il.com>

Looks fine.

Reviewed-by: Joseph Qi <joseph.qi@...ux.alibaba.com>
> ---
> v1 -> v2: Changed 'Closes:' tag to point to the correct bug report.
> v2 -> v3: Added an explicit check for empty extent list before dereferencing 'rec'.
> 
>  fs/ocfs2/dir.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/ocfs2/dir.c b/fs/ocfs2/dir.c
> index 7799f4d16ce9..acbae902ae3a 100644
> --- a/fs/ocfs2/dir.c
> +++ b/fs/ocfs2/dir.c
> @@ -798,6 +798,14 @@ static int ocfs2_dx_dir_lookup_rec(struct inode *inode,
>  		}
>  	}
>  
> +	if (le16_to_cpu(el->l_next_free_rec) == 0) {
> +		ret = ocfs2_error(inode->i_sb,
> +				  "Inode %lu has empty extent list at depth %u\n",
> +				  inode->i_ino, 
> +				  le16_to_cpu(el->l_tree_depth));
> +		goto out;
> +	}
> +
>  	found = 0;
>  	for (i = le16_to_cpu(el->l_next_free_rec) - 1; i >= 0; i--) {
>  		rec = &el->l_recs[i];