netdev - [PATCH net 8/8] net/sched: em_canid: fix uninit-value in em_canid

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Message-ID: <20251126155713.217105-9-mkl@pengutronix.de>
Date: Wed, 26 Nov 2025 16:41:18 +0100
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	kuba@...nel.org,
	linux-can@...r.kernel.org,
	kernel@...gutronix.de,
	Shaurya Rane <ssrane_b23@...vjti.ac.in>,
	syzbot+5d8269a1e099279152bc@...kaller.appspotmail.com,
	Marc Kleine-Budde <mkl@...gutronix.de>
Subject: [PATCH net 8/8] 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 a complete CAN frame is present in the
linear data buffer before reading the CAN ID. 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>
Link: https://patch.msgid.link/20251126085718.50808-1-ssranevjti@gmail.com
Signed-off-by: Marc Kleine-Budde <mkl@...gutronix.de>
---
 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..2d27f91d8441 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, CAN_MTU))
+		return 0;
+
 	can_id = em_canid_get_id(skb);
 
 	if (can_id & CAN_EFF_FLAG) {
-- 
2.51.0