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Date:   Thu, 5 Dec 2019 13:59:00 +0100
From:   Daniel Borkmann <daniel@iogearbox.net>
To:     Daniel Axtens <dja@axtens.net>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        syzbot <syzbot+82e323920b78d54aaed5@syzkaller.appspotmail.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Andrii Nakryiko <andriin@fb.com>,
        Alexei Starovoitov <ast@kernel.org>, bpf <bpf@vger.kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>,
        Song Liu <songliubraving@fb.com>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
        Yonghong Song <yhs@fb.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>
Subject: Re: BUG: unable to handle kernel paging request in pcpu_alloc
Message-ID: <20191205125900.GB29780@localhost.localdomain>
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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@syzkaller.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?

Thanks,
Daniel