linux-kernel - Re: [syzbot] KASAN: stack-out-of-bounds Read in iov_iter

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Date:   Wed, 15 Dec 2021 11:16:04 +0000
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Lee Jones <lee.jones@...aro.org>, Jens Axboe <axboe@...nel.dk>
Cc:     syzbot <syzbot+9671693590ef5aad8953@...kaller.appspotmail.com>,
        io-uring@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [syzbot] KASAN: stack-out-of-bounds Read in iov_iter_revert

On 12/15/21 08:06, Lee Jones wrote:
> On Tue, 09 Nov 2021, Lee Jones wrote:
> 
>> On Mon, 08 Nov 2021, Jens Axboe wrote:
>>> On 11/8/21 8:29 AM, Pavel Begunkov wrote:
>>>> On 11/3/21 17:01, Lee Jones wrote:
>>>>> Good afternoon Pavel,
>>>>>
>>>>>> syzbot has tested the proposed patch and the reproducer did not trigger any issue:
>>>>>>
>>>>>> Reported-and-tested-by: syzbot+9671693590ef5aad8953@...kaller.appspotmail.com
>>>>>>
>>>>>> Tested on:
>>>>>>
>>>>>> commit:         bff2c168 io_uring: don't retry with truncated iter
>>>>>> git tree:       https://github.com/isilence/linux.git truncate
>>>>>> kernel config:  https://syzkaller.appspot.com/x/.config?x=730106bfb5bf8ace
>>>>>> dashboard link: https://syzkaller.appspot.com/bug?extid=9671693590ef5aad8953
>>>>>> compiler:       Debian clang version 11.0.1-2, GNU ld (GNU Binutils for Debian) 2.35.1
>>>>>>
>>>>>> Note: testing is done by a robot and is best-effort only.
>>>>>
>>>>> As you can see in the 'dashboard link' above this bug also affects
>>>>> android-5-10 which is currently based on v5.10.75.
>>>>>
>>>>> I see that the back-port of this patch failed in v5.10.y:
>>>>>
>>>>>     https://lore.kernel.org/stable/163152589512611@kroah.com/
>>>>>
>>>>> And after solving the build-error by back-porting both:
>>>>>
>>>>>     2112ff5ce0c11 iov_iter: track truncated size
>>>>>     89c2b3b749182 io_uring: reexpand under-reexpanded iters
>>>>>
>>>>> I now see execution tripping the WARN() in iov_iter_revert():
>>>>>
>>>>>     if (WARN_ON(unroll > MAX_RW_COUNT))
>>>>>         return
>>>>>
>>>>> Am I missing any additional patches required to fix stable/v5.10.y?
>>>>
>>>> Is it the same syz test? There was a couple more patches for
>>>> IORING_SETUP_IOPOLL, but strange if that's not the case.
>>>>
>>>>
>>>> fwiw, Jens decided to replace it with another mechanism shortly
>>>> after, so it may be a better idea to backport those. Jens,
>>>> what do you think?
>>>>
>>>>
>>>> commit 8fb0f47a9d7acf620d0fd97831b69da9bc5e22ed
>>>> Author: Jens Axboe <axboe@...nel.dk>
>>>> Date:   Fri Sep 10 11:18:36 2021 -0600
>>>>
>>>>       iov_iter: add helper to save iov_iter state
>>>>
>>>> commit cd65869512ab5668a5d16f789bc4da1319c435c4
>>>> Author: Jens Axboe <axboe@...nel.dk>
>>>> Date:   Fri Sep 10 11:19:14 2021 -0600
>>>>
>>>>       io_uring: use iov_iter state save/restore helpers
>>>
>>> Yes, I think backporting based on the save/restore setup is the
>>> sanest way by far.
>>
>> Would you be kind enough to attempt to send these patches to Stable?
>>
>> When I tried to back-port them, the second one gave me trouble.  And
>> without the in depth knowledge of the driver/subsystem that you guys
>> have, I found it almost impossible to resolve all of the conflicts:
> 
> Any movement on this chaps?
> 
> Not sure I am able to do this back-port without your help.

Apologies, slipped from my attention, we'll backport it,
and thanks for the reminder


-- 
Pavel Begunkov