From: Kaixuan Li isotp_rcv() separates Classic CAN from CAN FD by skb->len alone: if (skb->len != so->ll.mtu) return; cf = (struct canfd_frame *)skb->data; A CAN XL frame with cxl->len 4 is CAN_MTU bytes, so it passes, and is then read as a canfd_frame whose len comes out of canxl_frame.flags: at least 0x80. Of the paths that follow, only the flow control one uses that length without bounding it first, so check_pad() walks to 255 over a 16-byte frame and the caller reports EBADMSG on an unrelated socket. bcm_rx_handler(), j1939_can_recv(), can_can_gw_rcv() and raw_rcv() check the frame type here, and can_dropped_invalid_skb() switches on skb->protocol on the transmit side. isotp_rcv() is the gap. Fixes: fb08cba12b52 ("can: canxl: update CAN infrastructure for CAN XL frames") Signed-off-by: Kaixuan Li Reviewed-by: Oliver Hartkopp Acked-by: Oliver Hartkopp Reviewed-by: Quchaosheng Link: https://patch.msgid.link/20260920035626.2581040-1-kaixuanli0131@gmail.com Cc: stable@vger.kernel.org Signed-off-by: Marc Kleine-Budde --- net/can/isotp.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/net/can/isotp.c b/net/can/isotp.c index 1a272ce6a2bd..5e1c3971ebfc 100644 --- a/net/can/isotp.c +++ b/net/can/isotp.c @@ -756,6 +756,14 @@ static void isotp_rcv(struct sk_buff *skb, void *data) if (skb->len != so->ll.mtu) return; + /* check for correct CAN CC/FD frame content */ + if (so->ll.mtu == CAN_MTU) { + if (!can_is_can_skb(skb)) + return; + } else if (!can_is_canfd_skb(skb)) { + return; + } + cf = (struct canfd_frame *)skb->data; /* if enabled: check reception of my configured extended address */ -- 2.53.0