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Subject: Re: WARNING in can_rcv
To:     Marc Kleine-Budde <mkl@pengutronix.de>,
        Eric Biggers <ebiggers3@gmail.com>
Cc:     Dmitry Vyukov <dvyukov@google.com>,
        syzbot <syzbot+4386709c0c1284dca827@syzkaller.appspotmail.com>,
        David Miller <davem@davemloft.net>, linux-can@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>,
        netdev <netdev@vger.kernel.org>, syzkaller-bugs@googlegroups.com
References: <001a11c16b40d795350562e878cc@google.com>
 <a48197ff-9270-8af7-a814-56af53093b3c@pengutronix.de>
 <CACT4Y+b0oUPVr7f973ZgBm9rUog=-mRWDFpcr-EzKaGYRnn8mQ@mail.gmail.com>
 <48c5623e-de78-5cfa-b537-2acf9a44ae51@hartkopp.net>
 <20180117071204.GG15527@zzz.localdomain>
 <dd50dd71-d552-1955-ebab-de1982ec9298@hartkopp.net>
 <359313e4-6280-8c97-a424-4f962b11c907@pengutronix.de>
From:   Oliver Hartkopp <socketcan@hartkopp.net>
Message-ID: <c26d5474-d990-65cb-c7dc-27a694ae5245@hartkopp.net>
Date:   Wed, 17 Jan 2018 17:29:05 +0100
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On 01/17/2018 10:43 AM, Marc Kleine-Budde wrote:
> On 01/17/2018 09:07 AM, Oliver Hartkopp wrote:
>>
>>
>> On 01/17/2018 08:12 AM, Eric Biggers wrote:
>>> On Wed, Jan 17, 2018 at 07:39:24AM +0100, Oliver Hartkopp wrote:
>>>>
>>>>
>>>> On 01/16/2018 07:11 PM, Dmitry Vyukov wrote:
>>>>> On Tue, Jan 16, 2018 at 7:07 PM, Marc Kleine-Budde <mkl@pengutronix.de> wrote:
>>>>>> On 01/16/2018 06:58 PM, syzbot wrote:
>>>>>>> Hello,
>>>>>>>
>>>>>>> syzkaller hit the following crash on
>>>>>>> a8750ddca918032d6349adbf9a4b6555e7db20da
>>>>>>> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
>>>>>>> compiler: gcc (GCC) 7.1.1 20170620
>>>>>>> .config is attached
>>>>>>> Raw console output is attached.
>>>>>>> C reproducer is attached
>>>>>>> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
>>>>>>> for information about syzkaller reproducers
>>>>>>>
>>>>>>>
>>>>>>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
>>>>>>> Reported-by: syzbot+4386709c0c1284dca827@syzkaller.appspotmail.com
>>>>>>> It will help syzbot understand when the bug is fixed. See footer for
>>>>>>> details.
>>>>>>> If you forward the report, please keep this part and the footer.
>>>>>>>
>>>>>>> device eql entered promiscuous mode
>>>>>>> ------------[ cut here ]------------
>>>>>>> PF_CAN: dropped non conform CAN skbuf: dev type 65534, len 42, datalen 0
>>>>>>> WARNING: CPU: 0 PID: 3650 at net/can/af_can.c:729 can_rcv+0x1c5/0x200
>>>>>>> net/can/af_can.c:724
>>>>>>> Kernel panic - not syncing: panic_on_warn set ...
>>>>>>
>>>>>> Invalid packages generate a warning (WARN_ONCE()), and you have
>>>>>> panic_on_warn active. Should we better silently drop these CAN packages?
>>>>>
>>>>> Hi,
>>>>>
>>>>> pr_warn_once() will be more appropriate. It prints a single line.
>>>>>
>>>>
>>>> The idea behind this WARN() is to detect really bad things that might have
>>>> happen on network driver level:
>>>>
>>>> The CAN subsystem registers with dev_add_pack() for ETH_P_CAN and
>>>> ETH_P_CANFD only. These ETH_P_ types are only allowed to be created by CAN
>>>> network devices (like vcan, vxcan, and real CAN drivers).
>>>>
>>>> I don't have any strong opinion on using WARN() or pr_warn_once().
>>>> Is this detected violation worth using WARN(), as something already must
>>>> have gone really wrong to trigger this issue?
>>>>
>>>
>>> WARN() indicates a kernel bug.  If it's instead "userspace did something
>>> stupid", or "someone sent some unexpected network packet", it needs to be
>>> pr_warn_once(), pr_warn_ratelimited(), or removed entirely.
>>
>> Ok. Thanks for the explanation!
>> It is "some bogus network driver sent something unexpected" - but that
>> does not harm the entire system.
>>
>> pr_warn_once() seems the right way to go then.
> 
> Is this an Acked-by for both patches?
> 

Yes :-)

Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>

I just did not expect that you wanted to update the patches before 
sending ...

Thanks,
Oliver