From d037d05c2e32792a6fa572b0aa3c92a8ac78589d Mon Sep 17 00:00:00 2001 From: Vincent Mailhol Date: Wed, 26 Nov 2025 11:16:04 +0100 Subject: [PATCH] can: dev: can_dev_dropped_skb: drop CAN FD skbs if FD is off Currently, the CAN FD skb validation logic is based on the MTU: the interface is deemed FD capable if and only if its MTU is greater or equal to CANFD_MTU. This logic is showing its limit with the introduction of CAN XL. For example, consider the two scenarios below: 1. An interface configured with CAN FD on and CAN XL on 2. An interface configured with CAN FD off and CAN XL on In those two scenarios, the interfaces would have the same MTU: CANXL_MTU making it impossible to differentiate which one has CAN FD turned on and which one has it off. Because of the limitation, the only non-UAPI-breaking workaround is to do the check at the device level using the can_priv->ctrlmode flags. Unfortunately, the virtual interfaces (vcan, vxcan), which do not have a can_priv, are left behind. Add a check on the CAN_CTRLMODE_FD flag in can_dev_dropped_skb() and drop FD frames whenever the feature is turned off. Signed-off-by: Vincent Mailhol Signed-off-by: Oliver Hartkopp Link: https://patch.msgid.link/20251126-canxl-v8-3-e7e3eb74f889@pengutronix.de Signed-off-by: Marc Kleine-Budde --- include/linux/can/dev.h | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h index bd7410b5d8a67..a7a39a6101d94 100644 --- a/include/linux/can/dev.h +++ b/include/linux/can/dev.h @@ -103,12 +103,20 @@ static inline bool can_dev_dropped_skb(struct net_device *dev, struct sk_buff *s if (priv->ctrlmode & CAN_CTRLMODE_LISTENONLY) { netdev_info_once(dev, "interface in listen only mode, dropping skb\n"); - kfree_skb(skb); - dev->stats.tx_dropped++; - return true; + goto invalid_skb; + } + + if (!(priv->ctrlmode & CAN_CTRLMODE_FD) && can_is_canfd_skb(skb)) { + netdev_info_once(dev, "CAN FD is disabled, dropping skb\n"); + goto invalid_skb; } return can_dropped_invalid_skb(dev, skb); + +invalid_skb: + kfree_skb(skb); + dev->stats.tx_dropped++; + return true; } void can_setup(struct net_device *dev); -- 2.47.3