[canxl v3 15/17] can: raw: instantly reject unsupported CAN frames

Oliver Hartkopp
2025-11-20T18:48:26Z

For real CAN interfaces the CAN_CTRLMODE_FD and CAN_CTRLMODE_XL control
modes indicate whether an interface can handle those CAN FD/XL frames.

In the case a CAN XL interface is configured in CANXL-only mode with
disabled error-signalling neither CAN CC nor CAN FD frames can be sent.

The checks are performed on CAN_RAW sockets to give an instant feedback
to the user when writing unsupported CAN frames to the interface.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
---
net/can/raw.c | 54 +++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 46 insertions(+), 8 deletions(-)

diff --git a/net/can/raw.c b/net/can/raw.c
index a53853f5e9af..223630f0f9e9 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -890,24 +890,62 @@ static void raw_put_canxl_vcid(struct raw_sock *ro, struct sk_buff *skb)
cxl->prio &= CANXL_PRIO_MASK;
cxl->prio |= ro->tx_vcid_shifted;
}
}

-static unsigned int raw_check_txframe(struct raw_sock *ro, struct sk_buff *skb, int mtu)
+static inline bool raw_dev_cc_enabled(struct net_device *dev,
+ struct can_priv *priv)
{
- /* Classical CAN -> no checks for flags and device capabilities */
- if (can_is_can_skb(skb))
+ /* The CANXL-only mode disables error-signalling on the CAN bus
+ * which is needed to send CAN CC/FD frames
+ */
+ if (priv)
+ return !can_dev_in_xl_only_mode(priv);
+
+ /* virtual CAN interfaces always support CAN CC */
+ return true;
+}
+
+static inline bool raw_dev_fd_enabled(struct net_device *dev,
+ struct can_priv *priv)
+{
+ /* check FD ctrlmode on real CAN interfaces */
+ if (priv)
+ return (priv->ctrlmode & CAN_CTRLMODE_FD);
+
+ /* check MTU for virtual CAN FD interfaces */
+ return (READ_ONCE(dev->mtu) >= CANFD_MTU);
+}
+
+static inline bool raw_dev_xl_enabled(struct net_device *dev,
+ struct can_priv *priv)
+{
+ /* check XL ctrlmode on real CAN interfaces */
+ if (priv)
+ return (priv->ctrlmode & CAN_CTRLMODE_XL);
+
+ /* check MTU for virtual CAN XL interfaces */
+ return can_is_canxl_dev_mtu(READ_ONCE(dev->mtu));
+}
+
+static unsigned int raw_check_txframe(struct raw_sock *ro, struct sk_buff *skb,
+ struct net_device *dev)
+{
+ struct can_priv *priv = safe_candev_priv(dev);
+
+ /* Classical CAN */
+ if (can_is_can_skb(skb) && raw_dev_cc_enabled(dev, priv))
return CAN_MTU;

- /* CAN FD -> needs to be enabled and a CAN FD or CAN XL device */
+ /* CAN FD */
if (ro->fd_frames && can_is_canfd_skb(skb) &&
- (mtu == CANFD_MTU || can_is_canxl_dev_mtu(mtu)))
+ raw_dev_fd_enabled(dev, priv))
return CANFD_MTU;

- /* CAN XL -> needs to be enabled and a CAN XL device */
+ /* CAN XL */
if (ro->xl_frames && can_is_canxl_skb(skb) &&
- can_is_canxl_dev_mtu(mtu))
+ raw_dev_xl_enabled(dev, priv))
return CANXL_MTU;

return 0;
}

@@ -959,11 +997,11 @@ static int raw_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
goto free_skb;

err = -EINVAL;

/* check for valid CAN (CC/FD/XL) frame content */
- txmtu = raw_check_txframe(ro, skb, READ_ONCE(dev->mtu));
+ txmtu = raw_check_txframe(ro, skb, dev);
if (!txmtu)
goto free_skb;

/* only CANXL: clear/forward/set VCID value */
if (txmtu == CANXL_MTU)
--
2.47.3