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Subject: Re: [syzbot] KASAN: stack-out-of-bounds Read in iov_iter_revert
To:     Pavel Begunkov <asml.silence@gmail.com>,
        Lee Jones <lee.jones@linaro.org>,
        syzbot <syzbot+9671693590ef5aad8953@syzkaller.appspotmail.com>
Cc:     io-uring@vger.kernel.org, linux-kernel@vger.kernel.org,
        syzkaller-bugs@googlegroups.com
References: <6f7d4c1d-f923-3ab1-c525-45316b973c72@gmail.com>
 <00000000000047f3b805c962affb@google.com> <YYLAYvFU+9cnu+4H@google.com>
 <0b4a5ff8-12e5-3cc7-8971-49e576444c9a@gmail.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <dd122760-5f87-10b1-e50d-388c2631c01a@kernel.dk>
Date:   Mon, 8 Nov 2021 08:41:52 -0700
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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@syzkaller.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@kernel.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@kernel.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.

-- 
Jens Axboe