From: Marc Kleine-Budde <mkl@pengutronix.de>
To: Oliver Hartkopp <socketcan@hartkopp.net>,
syzbot <syzbot+b02ff0707a97e4e79ebb@syzkaller.appspotmail.com>,
davem@davemloft.net, glider@google.com,
linux-can@vger.kernel.org, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: KMSAN: uninit-value in can_receive
Date: Mon, 18 Nov 2019 22:15:29 +0100 [thread overview]
Message-ID: <7f5c4546-0c1a-86ae-581e-0203b5fca446@pengutronix.de> (raw)
In-Reply-To: <7934bc2b-597f-0bb3-be2d-32f3b07b4de9@hartkopp.net>
[-- Attachment #1.1: Type: text/plain, Size: 2188 bytes --]
On 11/18/19 9:49 PM, Oliver Hartkopp wrote:
>
>
> On 18/11/2019 21.29, Marc Kleine-Budde wrote:
>> On 11/18/19 9:25 PM, Oliver Hartkopp wrote:
>
>>>> 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
>
>>>
>>> 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?
>>
>> The packet is injected via the packet socket into the kernel. Where does
>> skb->head point to in this case? When the skb is a proper
>> kernel-generated skb containing a CAN-2.0 or CAN-FD frame skb->head is
>> maybe properly initialized?
>
> The packet is either received via vcan or vxcan which checks via
> can_dropped_invalid_skb() if we have a valid ETH_P_CAN type skb.
According to the call stack it's injected into the kernel via a packet
socket and not via v(x)can.
> We additionally might think about introducing a check whether we have a
> can_skb_reserve() created skbuff.
>
> But even if someone forged a skbuff without this reserved space the
> access to can_skb_prv(skb)->skbcnt would point into some CAN frame
> content - which is still no access to uninitialized content, right?
Marc
--
Pengutronix e.K. | Marc Kleine-Budde |
Embedded Linux | https://www.pengutronix.de |
Vertretung West/Dortmund | Phone: +49-231-2826-924 |
Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
next prev parent reply other threads:[~2019-11-18 21:15 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
2019-11-18 20:29 ` Marc Kleine-Budde
2019-11-18 20:49 ` Oliver Hartkopp
2019-11-18 21:15 ` Marc Kleine-Budde [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=7f5c4546-0c1a-86ae-581e-0203b5fca446@pengutronix.de \
--to=mkl@pengutronix.de \
--cc=davem@davemloft.net \
--cc=glider@google.com \
--cc=linux-can@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=socketcan@hartkopp.net \
--cc=syzbot+b02ff0707a97e4e79ebb@syzkaller.appspotmail.com \
--cc=syzkaller-bugs@googlegroups.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).