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

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Message-Id: <20251126070641.39532-1-ssranevjti@gmail.com>
Date: Wed, 26 Nov 2025 12:36:41 +0530
From: ssrane_b23@...vjti.ac.in
To: Oliver Hartkopp <socketcan@...tkopp.net>,
	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,
	Shaurya Rane <ssrane_b23@...vjti.ac.in>,
	syzbot+5d8269a1e099279152bc@...kaller.appspotmail.com
Subject: [PATCH v2] net/sched: em_canid: fix uninit-value in em_canid_match

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)))
+		return 0;
+
 	can_id = em_canid_get_id(skb);
 
 	if (can_id & CAN_EFF_FLAG) {
-- 
2.34.1