can: dev: can_put_echo_skb(): don't crash kernel if can_priv::echo_skb is accessed out of bounds

If the "struct can_priv::echoo_skb" is accessed out of bounds, this
would cause a kernel crash. Instead, issue a meaningful warning
message and return with an error.

Fixes: a6e4bc53 ("can: make the number of echo skb's configurable")
Link: https://lore.kernel.org/all/20231005-can-dev-fix-can-restart-v2-5-91b5c1fd922c@pengutronix.deReviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/dev/skb.c

@@ -49,7 +49,11 @@ int can_put_echo_skb(struct sk_buff *skb, struct net_device *dev,
 {
 	struct can_priv *priv = netdev_priv(dev);
 
-	BUG_ON(idx >= priv->echo_skb_max);
+	if (idx >= priv->echo_skb_max) {
+		netdev_err(dev, "%s: BUG! Trying to access can_priv::echo_skb out of bounds (%u/max %u)\n",
+			   __func__, idx, priv->echo_skb_max);
+		return -EINVAL;
+	}
 
 	/* check flag whether this packet has to be looped back */
 	if (!(dev->flags & IFF_ECHO) ||