Re: [PATCH v2] net/sched: em_canid: fix uninit-value in em_canid_match
From: Oliver Hartkopp <socketcan@hartkopp.net>
Date: 2025-11-26 08:03:14
Also in:
linux-can, linux-kernel-mentees, lkml
Hello Shaurya, many thanks that you picked up this KMSAN issue! On 26.11.25 08:06, ssrane_b23@ee.vjti.ac.in wrote:
quoted hunk ↗ jump to hunk
From: Shaurya Rane <redacted> 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@syzkaller.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 <redacted> --- 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) {