linux-kernel - Re: [PATCH v2] net/sched: em_canid: fix uninit-value in em_canid

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <9c9e9356-55c2-4ec0-9a0e-742a374e0d04@hartkopp.net>
Date: Wed, 26 Nov 2025 09:02:54 +0100
From: Oliver Hartkopp <socketcan@...tkopp.net>
To: ssrane_b23@...vjti.ac.in, Marc Kleine-Budde <mkl@...gutronix.de>,
 Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang <xiyou.wangcong@...il.com>,
 Jiri Pirko <jiri@...nulli.us>, "David S . Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>
Cc: Simon Horman <horms@...nel.org>, Rostislav Lisovy <lisovy@...il.com>,
 linux-can@...r.kernel.org, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, skhan@...uxfoundation.org,
 linux-kernel-mentees@...ts.linux.dev, david.hunter.linux@...il.com,
 khalid@...nel.org, syzbot+5d8269a1e099279152bc@...kaller.appspotmail.com
Subject: Re: [PATCH v2] net/sched: em_canid: fix uninit-value in
 em_canid_match

Hello Shaurya,

many thanks that you picked up this KMSAN issue!

On 26.11.25 08:06, ssrane_b23@...vjti.ac.in wrote:
> From: Shaurya Rane <ssrane_b23@...vjti.ac.in>
> 
> Use pskb_may_pull() to ensure the CAN ID is accessible in the linear
> data buffer before reading it. A simple skb->len check is insufficient
> because it only verifies the total data length but does not guarantee
> the data is present in skb->data (it could be in fragments).
> 
> pskb_may_pull() both validates the length and pulls fragmented data
> into the linear buffer if necessary, making it safe to directly
> access skb->data.
> 
> Reported-by: syzbot+5d8269a1e099279152bc@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=5d8269a1e099279152bc
> Fixes: f057bbb6f9ed ("net: em_canid: Ematch rule to match CAN frames according to their identifiers")
> Signed-off-by: Shaurya Rane <ssrane_b23@...vjti.ac.in>
> ---
> v2: Use pskb_may_pull() instead of skb->len check to properly
>      handle fragmented skbs (Eric Dumazet)
> ---
>   net/sched/em_canid.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/net/sched/em_canid.c b/net/sched/em_canid.c
> index 5337bc462755..2214b548fab8 100644
> --- a/net/sched/em_canid.c
> +++ b/net/sched/em_canid.c
> @@ -99,6 +99,9 @@ static int em_canid_match(struct sk_buff *skb, struct tcf_ematch *m,
>   	int i;
>   	const struct can_filter *lp;
>   
> +	if (!pskb_may_pull(skb, sizeof(canid_t)))

The EM CANID handles struct CAN frames in skb->data.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/uapi/linux/can.h#n221

The smallest type of CAN frame that can be properly handled with EM 
CANID is a Classical CAN frame which has a length of 16 bytes.

Therefore I would suggest

	if (!pskb_may_pull(skb, CAN_MTU))

instead of only checking for the first element in struct can_frame.

Many thanks and best regards,
Oliver

> +		return 0;
> +
>   	can_id = em_canid_get_id(skb);
>   
>   	if (can_id & CAN_EFF_FLAG) {