From: Oliver Hartkopp <socketcan@hartkopp.net>

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>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 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 f36a83d3447c..be1ef7cf4204 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -892,20 +892,58 @@ static void raw_put_canxl_vcid(struct raw_sock *ro, struct sk_buff *skb)
 	}
 }
 
-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;
@@ -961,7 +999,7 @@ static int raw_sendmsg(struct socket *sock, struct msghdr *msg, size_t size)
 	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;
 

-- 
2.51.0