On 01/16/2018 07:11 PM, Dmitry Vyukov wrote:

On Tue, Jan 16, 2018 at 7:07 PM, Marc Kleine-Budde [off-list ref] wrote:

quoted

On 01/16/2018 06:58 PM, syzbot wrote:

quoted

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?

Best regards,
Oliver