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Date:   Wed, 24 Jul 2019 10:30:48 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     syzbot <syzbot+79f5f028005a77ecb6bb@...kaller.appspotmail.com>,
        bpf <bpf@...r.kernel.org>, David Airlie <airlied@...ux.ie>,
        alexander.deucher@....com, amd-gfx@...ts.freedesktop.org,
        Alexei Starovoitov <ast@...nel.org>, christian.koenig@....com,
        Daniel Borkmann <daniel@...earbox.net>, david1.zhou@....com,
        DRI <dri-devel@...ts.freedesktop.org>, leo.liu@....com,
        LKML <linux-kernel@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Marco Elver <elver@...gle.com>
Subject: Re: kernel panic: stack is corrupted in pointer

On Tue, Jul 23, 2019 at 7:26 PM John Fastabend <john.fastabend@...il.com> wrote:
>
> Dmitry Vyukov wrote:
> > On Wed, Jul 17, 2019 at 10:58 AM syzbot
> > <syzbot+79f5f028005a77ecb6bb@...kaller.appspotmail.com> wrote:
> > >
> > > Hello,
> > >
> > > syzbot found the following crash on:
> > >
> > > HEAD commit:    1438cde7 Add linux-next specific files for 20190716
> > > git tree:       linux-next
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=13988058600000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=3430a151e1452331
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=79f5f028005a77ecb6bb
> > > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=111fc8afa00000
> >
> > From the repro it looks like the same bpf stack overflow bug. +John
> > We need to dup them onto some canonical report for this bug, or this
> > becomes unmanageable.
>
> Fixes in bpf tree should fix this. Hopefully, we will squash this once fixes
> percolate up.
>
> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf.git

Cool! What is the fix?
We don't need to wait for the fix to percolate up (and then down
too!). syzbot gracefully handles when a patch is not yet present
everywhere (it happens all the time).

Btw, this was due to a stack overflow, right? Or something else?
We are trying to make KASAN configuration detect stack overflows too,
so that it does not cause havoc next time. But it turns out to be
non-trivial and our current attempt seems to fail:
https://groups.google.com/forum/#!topic/kasan-dev/IhYv7QYhLfY


> > #syz dup: kernel panic: corrupted stack end in dput
> >
> > > The bug was bisected to:
> > >
> > > commit 96a5d8d4915f3e241ebb48d5decdd110ab9c7dcf
> > > Author: Leo Liu <leo.liu@....com>
> > > Date:   Fri Jul 13 15:26:28 2018 +0000
> > >
> > >      drm/amdgpu: Make sure IB tests flushed after IP resume
> > >
> > > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14a46200600000
> > > final crash:    https://syzkaller.appspot.com/x/report.txt?x=16a46200600000
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=12a46200600000
> > >
> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > Reported-by: syzbot+79f5f028005a77ecb6bb@...kaller.appspotmail.com
> > > Fixes: 96a5d8d4915f ("drm/amdgpu: Make sure IB tests flushed after IP
> > > resume")
> > >
> > > Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in:
> > > pointer+0x702/0x750 lib/vsprintf.c:2187
> > > Shutting down cpus with NMI
> > > Kernel Offset: disabled
> > >
> > >
> > > ---
> > > This bug is generated by a bot. It may contain errors.
> > > See https://goo.gl/tpsmEJ for more information about syzbot.
> > > syzbot engineers can be reached at syzkaller@...glegroups.com.
> > >
> > > syzbot will keep track of this bug report. See:
> > > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > > For information about bisection process see: https://goo.gl/tpsmEJ#bisection
> > > syzbot can test patches for this bug, for details see:
> > > https://goo.gl/tpsmEJ#testing-patches
>
>
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