can: raw: instantly reject disabled CAN frames

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 now performed on CAN_RAW sockets to give an instant feedback
to the user when writing unsupported CAN frames to the interface or when
the CAN interface is in read-only mode.

Fixes: 1a620a723853 ("can: raw: instantly reject unsupported CAN frames")
Cc: Marc Kleine-Budde <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Vincent Mailhol <[e-mail]>
Signed-off-by: Oliver Hartkopp <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
[mkl: fix dev reference leak]
Link: https://lore.kernel.org/all/[e-mail]
Signed-off-by: Marc Kleine-Budde <[e-mail]>

net/can/raw.c

···
 #include <linux/if_arp.h>
 #include <linux/skbuff.h>
 #include <linux/can.h>
+#include <linux/can/can-ml.h>
 #include <linux/can/core.h>
-#include <linux/can/dev.h> /* for can_is_canxl_dev_mtu() */
 #include <linux/can/skb.h>
 #include <linux/can/raw.h>
 #include <net/sock.h>
···
 	}
 }
 
-static unsigned int raw_check_txframe(struct raw_sock *ro, struct sk_buff *skb, int mtu)
+static unsigned int raw_check_txframe(struct raw_sock *ro, struct sk_buff *skb,
+				      struct net_device *dev)
 {
-	/* Classical CAN -> no checks for flags and device capabilities */
-	if (can_is_can_skb(skb))
+	/* Classical CAN */
+	if (can_is_can_skb(skb) && can_cap_enabled(dev, CAN_CAP_CC))
 		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)))
+	    can_cap_enabled(dev, CAN_CAP_FD))
 		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))
+	    can_cap_enabled(dev, CAN_CAP_XL))
 		return CANXL_MTU;
 
 	return 0;
···
 	if (!dev)
 		return -ENXIO;
 
+	/* no sending on a CAN device in read-only mode */
+	if (can_cap_enabled(dev, CAN_CAP_RO)) {
+		err = -EACCES;
+		goto put_dev;
+	}
+
 	skb = sock_alloc_send_skb(sk, size + sizeof(struct can_skb_priv),
 				  msg->msg_flags & MSG_DONTWAIT, &err);
 	if (!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;