can: dev: __can_get_echo_skb(): Don't crash the kernel if can_priv::echo_skb...

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

If the "struct can_priv::echo_skb" is accessed out of bounds would lead
to a kernel crash. Better print a sensible warning message instead and
try to recover.

Cc: linux-stable <stable@vger.kernel.org>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/dev.c

@@ -481,7 +481,11 @@ struct sk_buff *__can_get_echo_skb(struct net_device *dev, unsigned int idx, u8
 {
 	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 NULL;
+	}
 
 	if (priv->echo_skb[idx]) {
 		/* Using "struct canfd_frame::len" for the frame