netdev - Re: WARNING in __debug_object

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Date:   Sun, 28 Oct 2018 23:47:33 -0700
From:   Song Liu <liu.song.a23@...il.com>
To:     eric.dumazet@...il.com
Cc:     dvyukov@...gle.com,
        syzbot+6e682caa546b7c96c859@...kaller.appspotmail.com,
        edumazet@...gle.com, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S . Miller" <davem@...emloft.net>,
        open list <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        syzkaller-bugs@...glegroups.com
Subject: Re: WARNING in __debug_object_init (3)

On Sun, Oct 28, 2018 at 10:45 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
>
> On 10/28/2018 08:13 AM, Dmitry Vyukov wrote:
> > On Sun, Oct 28, 2018 at 3:18 AM, syzbot
> > <syzbot+6e682caa546b7c96c859@...kaller.appspotmail.com> wrote:
> >> Hello,
> >>
> >> syzbot found the following crash on:
> >>
> >> HEAD commit:    8c60c36d0b8c Add linux-next specific files for 20181019
> >> git tree:       linux-next
> >> console output: https://syzkaller.appspot.com/x/log.txt?x=100feec5400000
> >> kernel config:  https://syzkaller.appspot.com/x/.config?x=8b6d7c4c81535e89
> >> dashboard link: https://syzkaller.appspot.com/bug?extid=6e682caa546b7c96c859
> >> compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> >> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13579abd400000
> >> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13654f6b400000
> >>
> >> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> >> Reported-by: syzbot+6e682caa546b7c96c859@...kaller.appspotmail.com
> >
> > +Eric knows what's wrong here. Something about "bpf: add tests for
> > direct packet access from CGROUP_SKB" commit. Was is amended to fix a
> > bug?
> >
>
> I know little.
>
> It seems that this linux-next tree contains a (buggy) pre-version of
> this commit :
>
> commit 2cb494a36c98279c5c6ce8e99cf9776f15449ade
> Author: Song Liu <songliubraving@...com>
> Date:   Fri Oct 19 09:57:58 2018 -0700
>
>     bpf: add tests for direct packet access from CGROUP_SKB
>
>     Tests are added to make sure CGROUP_SKB cannot access:
>       tc_classid, data_meta, flow_keys
>
>     and can read and write:
>       mark, prority, and cb[0-4]
>
>     and can read other fields.
>
>     To make selftest with skb->sk work, a dummy sk is added in
>     bpf_prog_test_run_skb().
>
>     Signed-off-by: Song Liu <songliubraving@...com>
>     Signed-off-by: Alexei Starovoitov <ast@...nel.org>
>
> Maybe bpf maintainers chose to pre-submit a buggy patch and rebased their tree.
>
> The buggy patch in linux-next was :
>
> commit 75079847e9d05d4cc1b7e09b29e22cbc8318a6b7
> Author: Song Liu <songliubraving@...com>
> Date:   Thu Oct 18 09:06:49 2018 -0700
>
>     bpf: add tests for direct packet access from CGROUP_SKB
>
>     Tests are added to make sure CGROUP_SKB cannot access:
>       tc_classid, data_meta, flow_keys
>
>     and can read and write:
>       mark, prority, and cb[0-4]
>
>     and can read other fields.
>
>     To make selftest with skb->sk work, a dummy sk is added in
>     bpf_prog_test_run_skb().
>
>     Signed-off-by: Song Liu <songliubraving@...com>
>     Signed-off-by: Alexei Starovoitov <ast@...nel.org>
>

Thanks Eric.

Yeah, the version in the linux-next tree was a buggy version. The one
in Linus' tree is correct. I confirmed that this issue doesn't repro in Linus'
tree.

Song