netdev - Re: v4.14-rc3/arm64 DABT exception in atomic_inc() / __skb

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Message-ID: <CACT4Y+bjzzCv3LSxK12C1xB8GfR3UYCrX_5phRYJ8fpxh9vcvQ@mail.gmail.com>
Date:   Fri, 20 Oct 2017 17:14:55 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Wei Wei <dotweiba@...il.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>,
        Willem de Bruijn <willemb@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: v4.14-rc3/arm64 DABT exception in atomic_inc() / __skb_clone()

On Fri, Oct 20, 2017 at 4:40 PM, Wei Wei <dotweiba@...il.com> wrote:
> Sadly, the syzkaller characterized it as a non-reproducible bug and there were empty
>  repro files. But if manually executing in VM like this “./syz-execprog -executor=
> ./syz-executor -repeat=0 -procs=16 -cover=0 crash-log”, it crashed when executing exactly
> program 1056 using log0 provided.
>
> I failed to generate the C reproducer with syz-repro as it said “no target compiler”
> in the final step. I would appreciate if you could give some hints.

syzkaller tries to use aarch64-linux-gnu-gcc when cross-compiling to arm64:
https://github.com/google/syzkaller/blob/master/sys/targets/targets.go#L62
Try to install g++-aarch64-linux-gnu.
Or how should it be done on your system?


> Thanks,
> Wei
>> On 20 Oct 2017, at 7:14 AM, Mark Rutland <mark.rutland@....com> wrote:
>>
>> On Thu, Oct 19, 2017 at 10:16:08PM -0400, Wei Wei wrote:
>>> Hi all,
>>
>> Hi,
>>
>>> I have fuzzed v4.14-rc3 using syzkaller and found a bug similar to that one [1].
>>> But the call trace isn’t the same. The atomic_inc() might handle a corrupted
>>> skb_buff.
>>>
>>> The logs and config have been uploaded to my github repo [2].
>>>
>>> [1] https://lkml.org/lkml/2017/10/2/216
>>> [2] https://github.com/dotweiba/skb_clone_atomic_inc_bug
>>
>> These do look very similar to what I was hitting; all appear to be
>> misaligned atomics in the same path.
>>
>> I see that you have some empty repro files in [2]. If you have any
>> reproducers, would you mind sharing them?
>>
>> If any of those are smaller or more reliable than the one I was able to
>> generate [3], it might make it more obvious what's going on, and/or make
>> it simpler to come up with a plain C reproducer.
>>
>> Thanks,
>> Mark.
>>
>> [3] https://www.kernel.org/pub/linux/kernel/people/mark/bugs/20171002-skb_clone-misaligned-atomic/syzkaller.repro
>
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