Re: WARNING in can_rcv

[Marc Kleine-Budde]

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@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
>>>>>> 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?

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
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