v4.14-rc3/arm64 DABT exception in atomic_inc() / __skb_clone()

On Fri, Oct 20, 2017 at 4:40 PM, Wei Wei [off-list ref] 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

quoted

On 20 Oct 2017, at 7:14 AM, Mark Rutland [off-list ref] wrote:

On Thu, Oct 19, 2017 at 10:16:08PM -0400, Wei Wei wrote:

quoted

Hi all,

Hi,

quoted

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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