linux-kernel - Re: [syzbot] UBSAN: array-index-out-of-bounds in io_submit

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Message-ID: <7b07cce6-b8a8-7f0b-f4ab-285a9369ef0a@kernel.dk>
Date:   Tue, 31 May 2022 03:53:14 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Hao Xu <haoxu.linux@...oud.com>,
        syzbot <syzbot+b6c9b65b6753d333d833@...kaller.appspotmail.com>,
        asml.silence@...il.com, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] UBSAN: array-index-out-of-bounds in io_submit_sqes

On 5/31/22 3:14 AM, Dmitry Vyukov wrote:
> On Tue, 31 May 2022 at 11:07, Jens Axboe <axboe@...nel.dk> wrote:
>>
>> On 5/31/22 3:05 AM, Dmitry Vyukov wrote:
>>> On Tue, 31 May 2022 at 11:01, Jens Axboe <axboe@...nel.dk> wrote:
>>>>
>>>> On 5/31/22 3:00 AM, Hao Xu wrote:
>>>>> On 5/31/22 16:45, Jens Axboe wrote:
>>>>>> On 5/31/22 1:55 AM, syzbot wrote:
>>>>>>> Hello,
>>>>>>>
>>>>>>> syzbot found the following issue on:
>>>>>>>
>>>>>>> HEAD commit:    3b46e4e44180 Add linux-next specific files for 20220531
>>>>>>> git tree:       linux-next
>>>>>>> console output: https://syzkaller.appspot.com/x/log.txt?x=16e151f5f00000
>>>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=ccb8d66fc9489ef
>>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=b6c9b65b6753d333d833
>>>>>>> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>>>>>>>
>>>>>>> Unfortunately, I don't have any reproducer for this issue yet.
>>>>>>>
>>>>>>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>>>>>>> Reported-by: syzbot+b6c9b65b6753d333d833@...kaller.appspotmail.com
>>>>>>>
>>>>>>> ================================================================================
>>>>>>> ================================================================================
>>>>>>> UBSAN: array-index-out-of-bounds in fs/io_uring.c:8860:19
>>>>>>> index 75 is out of range for type 'io_op_def [47]'
>>>>>>
>>>>>> 'def' is just set here, it's not actually used after 'opcode' has been
>>>>>> verified.
>>>>>>
>>>>>
>>>>> Maybe we can move it to be below the opcode check to comfort UBSAN.
>>>>
>>>> Yeah that's what I did, just rebased it to get rid of it:
>>>>
>>>> https://git.kernel.dk/cgit/linux-block/commit/?h=io_uring-5.19&id=fcde59feb1affb6d56aecadc3868df4631480da5
>>>
>>> If you are rebasing it, please add the following tag so that the bug
>>> is closed later:
>>>
>>> Tested-by: syzbot+b6c9b65b6753d333d833@...kaller.appspotmail.com
>>
>> Sorry, missed that, would be a bit confusing?
> 
> Why confusing? It tested it, no?

Usually I'd use that tag if it's a separate commit that fixes an issue,
and someone (or a bot) has tested it. I think we both agree that the
change will fix it, but not really tested at that point. Or maybe it is
now :)

> 
>> 5.20 branch is rebased
>> on top of that too. Can we just do:
>>
>> #syz fix: io_uring: add io_op_defs 'def' pointer in req init and issue
>>
>> ?
> 
> In most cases it will work. However, there is no way to distinguish
> unfixed and fixed versions of the patch based on the title.
> So if the unfixed version manages to reach all syzbot builds, it will
> close the bug at that point. And then can start reporting duplicates
> since the bug is still present. But practically unlikely to happen.
> The tag allows to distinguish unfixed and fixed versions of the patch,
> so it will work reliably w/o possible duplicates.

Gotcha. Usually I don't rebase anyway, but easier in this case.

-- 
Jens Axboe