linux-kernel - Re: [PATCH] erofs: Prohibit access to excessive algorithmformat

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Message-ID: <c93c3ae0-2e72-48b3-9faf-956fd6f1a3d4@linux.alibaba.com>
Date: Sat, 23 Aug 2025 17:40:54 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: Edward Adam Davis <eadavis@...com>,
 syzbot+5a398eb460ddaa6f242f@...kaller.appspotmail.com
Cc: linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] erofs: Prohibit access to excessive algorithmformat

Hi,

On 2025/8/23 09:53, Edward Adam Davis wrote:
> syz reported a global-out-of-bounds Read in z_erofs_decompress_queue.
> 
> OOB occurs in z_erofs_decompress_queue() because algorithmformat is too
> large.
> 
> Added relevant checks when registering pcluster.
> 
> Reported-by: syzbot+5a398eb460ddaa6f242f@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=5a398eb460ddaa6f242f
> Tested-by: syzbot+5a398eb460ddaa6f242f@...kaller.appspotmail.com
> Signed-off-by: Edward Adam Davis <eadavis@...com>

Your analysis is correct, but the fix should be applied to zmap.c
instead since it parses the on-disk map format. Also, it's actually
a regression out of new encoded extents since the old compress
indexes already has the check.

I've submitted a formal fix:
https://lore.kernel.org/r/20250823093018.3117864-1-hsiangkao@linux.alibaba.com

Thanks,
Gao Xiang