From: Oliver Hartkopp <socketcan@hartkopp.net>
To: syzbot <syzbot+b02ff0707a97e4e79ebb@syzkaller.appspotmail.com>,
davem@davemloft.net, glider@google.com,
linux-can@vger.kernel.org, linux-kernel@vger.kernel.org,
mkl@pengutronix.de, netdev@vger.kernel.org,
syzkaller-bugs@googlegroups.com
Subject: Re: KMSAN: uninit-value in can_receive
Date: Mon, 18 Nov 2019 21:25:18 +0100 [thread overview]
Message-ID: <a5f73d92-fdf2-2590-c863-39a181dca8e1@hartkopp.net> (raw)
In-Reply-To: <0000000000005c08d10597a3a05d@google.com>
On 18/11/2019 20.05, syzbot wrote:
> Hello,
>
> syzbot found the following crash on:
>
> HEAD commit: 9c6a7162 kmsan: remove unneeded annotations in bio
> git tree: https://github.com/google/kmsan.git master
> console output: https://syzkaller.appspot.com/x/log.txt?x=14563416e00000
> kernel config: https://syzkaller.appspot.com/x/.config?x=9e324dfe9c7b0360
> dashboard link:
> https://syzkaller.appspot.com/bug?extid=b02ff0707a97e4e79ebb
> compiler: clang version 9.0.0 (/home/glider/llvm/clang
> 80fee25776c2fb61e74c1ecb1a523375c2500b69)
>
> Unfortunately, I don't have any reproducer for this crash yet.
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+b02ff0707a97e4e79ebb@syzkaller.appspotmail.com
>
> =====================================================
> BUG: KMSAN: uninit-value in can_receive+0x23c/0x5e0 net/can/af_can.c:649
> CPU: 1 PID: 3490 Comm: syz-executor.2 Not tainted 5.4.0-rc5+ #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> Google 01/01/2011
> Call Trace:
> <IRQ>
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x191/0x1f0 lib/dump_stack.c:113
> kmsan_report+0x128/0x220 mm/kmsan/kmsan_report.c:108
> __msan_warning+0x73/0xe0 mm/kmsan/kmsan_instr.c:245
> can_receive+0x23c/0x5e0 net/can/af_can.c:649
> can_rcv+0x188/0x3a0 net/can/af_can.c:685
In line 649 of 5.4.0-rc5+ we can find a while() statement:
while (!(can_skb_prv(skb)->skbcnt))
can_skb_prv(skb)->skbcnt = atomic_inc_return(&skbcounter);
In linux/include/linux/can/skb.h we see:
static inline struct can_skb_priv *can_skb_prv(struct sk_buff *skb)
{
return (struct can_skb_priv *)(skb->head);
}
IMO accessing can_skb_prv(skb)->skbcnt at this point is a valid
operation which has no uninitialized value.
Can this probably be a false positive of KMSAN?
Regards,
Oliver
next prev parent reply other threads:[~2019-11-18 20:25 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-18 19:05 KMSAN: uninit-value in can_receive syzbot
2019-11-18 20:25 ` Oliver Hartkopp [this message]
2019-11-18 20:29 ` Marc Kleine-Budde
2019-11-18 20:49 ` Oliver Hartkopp
2019-11-18 21:15 ` Marc Kleine-Budde
2019-11-19 7:35 ` Oliver Hartkopp
2019-11-19 9:00 ` Oleksij Rempel
2019-11-19 10:08 ` Dmitry Vyukov
2019-11-19 13:06 ` Alexander Potapenko
2019-11-19 16:53 ` Eric Dumazet
2019-11-19 20:24 ` Oliver Hartkopp
2019-11-19 21:09 ` Eric Dumazet
2019-11-20 20:10 ` Oliver Hartkopp
2019-12-03 10:09 ` Marc Kleine-Budde
2019-12-03 10:37 ` Oliver Hartkopp
2019-12-03 10:40 ` Marc Kleine-Budde
2019-11-26 9:00 ` syzbot
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