linux-kernel - Re: BUG: unable to handle kernel paging request in pcpu

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Message-ID: <871rtiex4e.fsf@dja-thinkpad.axtens.net>
Date:   Fri, 06 Dec 2019 00:10:41 +1100
From:   Daniel Axtens <dja@...ens.net>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        syzbot <syzbot+82e323920b78d54aaed5@...kaller.appspotmail.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Andrii Nakryiko <andriin@...com>,
        Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        Song Liu <songliubraving@...com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Yonghong Song <yhs@...com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: Re: BUG: unable to handle kernel paging request in pcpu_alloc

Daniel Borkmann <daniel@...earbox.net> writes:

> On Thu, Dec 05, 2019 at 03:35:21PM +1100, Daniel Axtens wrote:
>> >> HEAD commit:    1ab75b2e Add linux-next specific files for 20191203
>> >> git tree:       linux-next
>> >> console output: https://syzkaller.appspot.com/x/log.txt?x=10edf2eae00000
>> >> kernel config:  https://syzkaller.appspot.com/x/.config?x=de1505c727f0ec20
>> >> dashboard link: https://syzkaller.appspot.com/bug?extid=82e323920b78d54aaed5
>> >> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>> >> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=156ef061e00000
>> >> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11641edae00000
>> >>
>> >> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>> >> Reported-by: syzbot+82e323920b78d54aaed5@...kaller.appspotmail.com
>> >
>> > +Daniel, is it the same as:
>> > https://syzkaller.appspot.com/bug?id=f6450554481c55c131cc23d581fbd8ea42e63e18
>> > If so, is it possible to make KASAN detect this consistently with the
>> > same crash type so that syzbot does not report duplicates?
>> 
>> It looks like both of these occur immediately after failure injection. I
>> think my assumption that I could ignore the chance of failures in the
>> per-cpu allocation path will have to be revisited. That's annoying.
>> 
>> I'll try to spin something today but Andrey feel free to pip me at the
>> post again :)
>> 
>> I'm not 100% confident to call them dups just yet, but I'm about 80%
>> confident that they are.
>
> Ok. Double checked BPF side yesterday night, but looks sane to me and the
> fault also hints into pcpu_alloc() rather than BPF code. Daniel, from your
> above reply, I read that you are aware of how the bisected commit would
> have caused the fault?

Yes, this one is on me - I did not take into account the brutal
efficiency of the fault injector when implementing my KASAN support for
vmalloc areas. I have a fix, I'm just doing final tests now.

Regards,
Daniel

>
> Thanks,
> Daniel
>
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