Re: KASAN: null-ptr-deref Write in io_wq_cancel_all

From: Jens Axboe <axboe@kernel.dk>
To: Dmitry Vyukov <dvyukov@google.com>,
	syzbot <syzbot+d958a65633ea70280b23@syzkaller.appspotmail.com>
Cc: linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: KASAN: null-ptr-deref Write in io_wq_cancel_all
Date: Fri, 25 Oct 2019 07:50:42 -0600	[thread overview]
Message-ID: <0e1b3410-95b0-f9d9-6838-486eae0bf5d7@kernel.dk> (raw)
In-Reply-To: <CACT4Y+Y946C-kyiBSZtyKY7PU4qxrysOfukd42--pXdyTRyjbw@mail.gmail.com>

On 10/25/19 5:58 AM, Dmitry Vyukov wrote:
> On Fri, Oct 25, 2019 at 1:51 PM syzbot
> <syzbot+d958a65633ea70280b23@syzkaller.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@syzkaller.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