linux-kernel - Re: [PATCH] fs/jfs: Add checking for out-of-bounds index in binary search in xtSearch

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Date:   Tue, 3 Oct 2023 18:36:25 -0500
From:   Dave Kleikamp <dave.kleikamp@...cle.com>
To:     Juntong Deng <juntong.deng@...look.com>, cuigaosheng1@...wei.com
Cc:     jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        syzbot+76a072c2f8a60280bd70@...kaller.appspotmail.com
Subject: Re: [PATCH] fs/jfs: Add checking for out-of-bounds index in binary
 search in xtSearch

On 10/3/23 5:49AM, Juntong Deng wrote:
> There is currently no out-of-bounds check for the index in a binary
> search, which may cause errors.
> 
> The following is related bug reported by Syzbot:
> 
> UBSAN: array-index-out-of-bounds in fs/jfs/jfs_xtree.c:360:4
> index 18 is out of range for type 'xad_t [18]'
> 
> Checking if the index exceeds the size of the xad array can solve
> this bug.

This won't work for the same reason I talk about here:
https://sourceforge.net/p/jfs/mailman/message/40826617/

The xad array can be either XTROOTMAXSLOT or XTPAGEMAXSLOT entries long 
and it is declared with the smaller number since it's included in the 
inode. I will fix the declarations so that we can use the larger number 
without triggering code checkers.

Thanks,
Shaggy

> 
> Reported-by: syzbot+76a072c2f8a60280bd70@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=76a072c2f8a60280bd70
> Signed-off-by: Juntong Deng <juntong.deng@...look.com>
> ---
>   fs/jfs/jfs_xtree.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/fs/jfs/jfs_xtree.c b/fs/jfs/jfs_xtree.c
> index 2d304cee884c..6b55bb1e4089 100644
> --- a/fs/jfs/jfs_xtree.c
> +++ b/fs/jfs/jfs_xtree.c
> @@ -356,6 +356,8 @@ static int xtSearch(struct inode *ip, s64 xoff,	s64 *nextp,
>   		 */
>   		for (base = XTENTRYSTART; lim; lim >>= 1) {
>   			index = base + (lim >> 1);
> +			if (index >= XTROOTMAXSLOT)
> +				break;
>   
>   			XT_CMP(cmp, xoff, &p->xad[index], t64);
>   			if (cmp == 0) {