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Date: Wed, 17 Jan 2018 09:07:51 +0100 From: Oliver Hartkopp <socketcan@...tkopp.net> To: Eric Biggers <ebiggers3@...il.com>, Marc Kleine-Budde <mkl@...gutronix.de> Cc: Dmitry Vyukov <dvyukov@...gle.com>, syzbot <syzbot+4386709c0c1284dca827@...kaller.appspotmail.com>, David Miller <davem@...emloft.net>, linux-can@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, netdev <netdev@...r.kernel.org>, syzkaller-bugs@...glegroups.com Subject: Re: WARNING in can_rcv 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@...gutronix.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@...kaller.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. Thanks, Oliver
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