linux-kernel - Re: [PATCH] jfs: add a check to prevent array-index-out-of-bounds

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Message-ID: <f8ad2538-28e1-444e-94ca-1ede6e74e848@oracle.com>
Date: Tue, 29 Oct 2024 17:39:46 -0500
From: Dave Kleikamp <dave.kleikamp@...cle.com>
To: Nihar Chaithanya <niharchaithanya@...il.com>, shaggy@...nel.org
Cc: jfs-discussion@...ts.sourceforge.net, skhan@...uxfoundation.org,
        linux-bcachefs@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzbot+412dea214d8baa3f7483@...kaller.appspotmail.com
Subject: Re: [PATCH] jfs: add a check to prevent array-index-out-of-bounds

On 10/8/24 3:21PM, Nihar Chaithanya wrote:
> When the value of lp is 1 at the end of the iteration in the for loop,
> lp is modified in the next iteration to a negative value.
> Add a check to prevent this condition.
> 
> Reported-by: syzbot+412dea214d8baa3f7483@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=412dea214d8baa3f7483
> Tested-by: syzbot+412dea214d8baa3f7483@...kaller.appspotmail.com
> Signed-off-by: Nihar Chaithanya <niharchaithanya@...il.com>
> ---
>   fs/jfs/jfs_dmap.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/fs/jfs/jfs_dmap.c b/fs/jfs/jfs_dmap.c
> index 5713994328cb..3ebb2dfdd0b3 100644
> --- a/fs/jfs/jfs_dmap.c
> +++ b/fs/jfs/jfs_dmap.c
> @@ -2911,6 +2911,12 @@ static void dbAdjTree(dmtree_t *tp, int leafno, int newval, bool is_ctl)
>   		 */
>   		tp->dmt_stree[pp] = max;
>   
> +		/* check to prevent negative value of lp on the
> +		 * next iteration.
> +		 */
> +		if (lp == 1)
> +			break;
> +

I'm going to change this a little bit. I think it's a little cleaner to 
test lp for zero at the top of the loop.

>   		/* parent becomes leaf for next go-round.
>   		 */
>   		lp = pp;

That and rewording the commit message, I will apply this.

Thanks,
Shaggy