can: Use WARN_ONCE() instead of BUG_ON() for sanity check in receive path

To ensure a proper handling of CAN frames transported in skbuffs some checks
need to be performed at receive time.

As stated by Michael Olbrich and Luotao Fu BUG_ON() might be to restrictive.
This is right as we can just drop the non conform skbuff and the Kernel can
continue working.

This patch replaces the BUG_ON() with a WARN_ONCE() so that the system remains
healthy but we made the problem visible (once).
Signed-off-by: Oliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: Urs Thuermann <urs@isnogud.escape.de>
CC: Michael Olbrich <m.olbrich@pengutronix.de>
CC: Luotao Fu <l.fu@pengutronix.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/can/af_can.c

@@ -651,12 +651,16 @@ static int can_rcv(struct sk_buff *skb, struct net_device *dev,
 	struct can_frame *cf = (struct can_frame *)skb->data;
 	int matches;
 
-	if (dev->type != ARPHRD_CAN || !net_eq(dev_net(dev), &init_net)) {
-		kfree_skb(skb);
-		return 0;
-	}
+	if (!net_eq(dev_net(dev), &init_net))
+		goto drop;
 
-	BUG_ON(skb->len != sizeof(struct can_frame) || cf->can_dlc > 8);
+	if (WARN_ONCE(dev->type != ARPHRD_CAN ||
+		      skb->len != sizeof(struct can_frame) ||
+		      cf->can_dlc > 8,
+		      "PF_CAN: dropped non conform skbuf: "
+		      "dev type %d, len %d, can_dlc %d\n",
+		      dev->type, skb->len, cf->can_dlc))
+		goto drop;
 
 	/* update statistics */
 	can_stats.rx_frames++;
@@ -683,6 +687,10 @@ static int can_rcv(struct sk_buff *skb, struct net_device *dev,
 	}
 
 	return 0;
+
+drop:
+	kfree_skb(skb);
+	return 0;
 }
 
 /*