linux-kernel - Re: [PATCH v2] loop: don't change loop device under exclusive opener in loop_set

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Message-ID: <9a687e88-7cf2-49ae-8b79-1b87a21c070f@kernel.dk>
Date: Tue, 6 Jan 2026 05:31:19 -0700
From: Jens Axboe <axboe@...nel.dk>
To: Jan Kara <jack@...e.cz>,
 Raphael Pinsonneault-Thibeault <rpthibeault@...il.com>
Cc: syzbot+3ee481e21fd75e14c397@...kaller.appspotmail.com,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kernel-mentees@...ts.linux.dev, Yongpeng Yang <yangyongpeng@...omi.com>
Subject: Re: [PATCH v2] loop: don't change loop device under exclusive opener
 in loop_set_status

On 1/6/26 5:08 AM, Jan Kara wrote:
> On Wed 17-12-25 14:00:40, Raphael Pinsonneault-Thibeault wrote:
>> loop_set_status() is allowed to change the loop device while there
>> are other openers of the device, even exclusive ones.
>>
>> In this case, it causes a KASAN: slab-out-of-bounds Read in
>> ext4_search_dir(), since when looking for an entry in an inlined
>> directory, e_value_offs is changed underneath the filesystem by
>> loop_set_status().
>>
>> Fix the problem by forbidding loop_set_status() from modifying the loop
>> device while there are exclusive openers of the device. This is similar
>> to the fix in loop_configure() by commit 33ec3e53e7b1 ("loop: Don't
>> change loop device under exclusive opener") alongside commit ecbe6bc0003b
>> ("block: use bd_prepare_to_claim directly in the loop driver").
>>
>> Reported-by: syzbot+3ee481e21fd75e14c397@...kaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=3ee481e21fd75e14c397
>> Tested-by: syzbot+3ee481e21fd75e14c397@...kaller.appspotmail.com
>> Tested-by: Yongpeng Yang <yangyongpeng@...omi.com>
>> Signed-off-by: Raphael Pinsonneault-Thibeault <rpthibeault@...il.com>
>> Reviewed-by: Jan Kara <jack@...e.cz>
> 
> Jens, ping?

Now applied. Heads up in general, don't nest v2 or later inside the
original thread. It just makes emails get lost, as it appears part
of the original discussion.

-- 
Jens Axboe