linux-kernel - Re: KASAN: null-ptr-deref Write in io_wq_cancel

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Message-ID: <0e1b3410-95b0-f9d9-6838-486eae0bf5d7@kernel.dk>
Date:   Fri, 25 Oct 2019 07:50:42 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+d958a65633ea70280b23@...kaller.appspotmail.com>
Cc:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: KASAN: null-ptr-deref Write in io_wq_cancel_all

On 10/25/19 5:58 AM, Dmitry Vyukov wrote:
> On Fri, Oct 25, 2019 at 1:51 PM syzbot
> <syzbot+d958a65633ea70280b23@...kaller.appspotmail.com> wrote:
>>
>> Hello,
>>
>> syzbot found the following crash on:
>>
>> HEAD commit:    139c2d13 Add linux-next specific files for 20191025
>> git tree:       linux-next
>> console output: https://syzkaller.appspot.com/x/log.txt?x=17ab5a70e00000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=28fd7a693df38d29
>> dashboard link: https://syzkaller.appspot.com/bug?extid=d958a65633ea70280b23
>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>>
>> Unfortunately, I don't have any reproducer for this crash yet.
>>
>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> Reported-by: syzbot+d958a65633ea70280b23@...kaller.appspotmail.com
> 
> +Jens

Let me know if/when you have a reproducer for this one. I initially thought
this was a basic NULL pointer check, but it doesn't look like it. I wonder
if the thread handling the request got a signal, and since it had the
task file_table with the io_uring fd attached, it's triggering an exit.

I'll poke at it, but don't immediately see the issue.

-- 
Jens Axboe