linux-kernel - Re: bpfilter breaks IPT_SO_GET

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Date:   Tue, 25 Sep 2018 19:59:00 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Michal Kubecek <mkubecek@...e.cz>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        David Miller <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>,
        NetFilter <netfilter-devel@...r.kernel.org>,
        Fabian Vogt <fvogt@...e.com>, Takashi Iwai <tiwai@...e.de>
Subject: Re: bpfilter breaks IPT_SO_GET_INFO

On Wed, Sep 19, 2018 at 10:29 AM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Wed, Sep 19, 2018 at 9:18 AM, Michal Kubecek <mkubecek@...e.cz> wrote:
>> On Mon, Sep 17, 2018 at 03:36:21PM +0200, Dmitry Vyukov wrote:
>>> Hi,
>>>
>>> I am having some problem with upstream kernel and bpfilter. The
>>> manifestation is that IPT_SO_GET_INFO on an ipv4 socket works, then
>>> something (that I can't fully localize but can reproduce) happens and
>>> then IPT_SO_GET_INFO starts permanently returning 256.
>> ...
>>> Now the litmus program always fails with:
>>>
>>> getsockopt(3, SOL_IP, 0x40 /* IP_??? */,
>>> "filter\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., [84])
>>> = 256
>>>
>>> I am currently on upstream commit
>>> 28619527b8a712590c93d0a9e24b4425b9376a8c, my .config is attached. I
>>> don't know what is bpfilter, I see it mentions some umh, if it
>>> requires some additional setup I don't it, i.e. I don't install any
>>> userspace modules/helpers.
>>
>> This looks similar to the fallback issue described here:
>>
>>   https://bugzilla.suse.com/show_bug.cgi?id=1106751#c1
>>
>> Unfortunately I didn't have time to look into it more closely yet.
>
> +Takashi
>
> But I already have CONFIG_BPFILTER_UMH=y in my config, so it does not
> help completely.
> Also in my case it is working initially, but breaks after I run the
> second program.


I've disabled CONFIG_BPFILTER for now, it causes too many failures.
https://github.com/google/syzkaller/commit/19a403430d8d5ae2472e16dab2f26ddd899cf552