can: dev: can_free_echo_skb(): don't crash the kernel if can_priv::echo_skb is...

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

A out of bounds access to "struct can_priv::echo_skb" leads to a
kernel crash. Better print a sensible warning message instead and try
to recover.

This patch is similar to:

| e7a6994d ("can: dev: __can_get_echo_skb(): Don't crash the kernel
|               if can_priv::echo_skb is accessed out of bounds")

Link: https://lore.kernel.org/r/20210319142700.305648-2-mkl@pengutronix.deSigned-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/dev/skb.c

@@ -157,7 +157,11 @@ void can_free_echo_skb(struct net_device *dev, unsigned int idx)
 {
 	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;
+	}
 
 	if (priv->echo_skb[idx]) {
 		dev_kfree_skb_any(priv->echo_skb[idx]);