vrf: check forwarding on the original netdevice when generating ICMP dest unreachable

When ip_error() is called the device is the l3mdev master instead of the
original device. So the forwarding check should be on the original one.

Changes from v2:
- Handle the original device disappearing (per David Ahern)
- Minimize the change in code order

Changes from v1:
- Only need to reset the device on which __in_dev_get_rcu() is done (per
  David Ahern).
Signed-off-by: Stephen Suryaputra <ssuryaextr@gmail.com>
Acked-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/route.c

@@ -931,14 +931,23 @@ void ip_rt_send_redirect(struct sk_buff *skb)
 
 static int ip_error(struct sk_buff *skb)
 {
-	struct in_device *in_dev = __in_dev_get_rcu(skb->dev);
 	struct rtable *rt = skb_rtable(skb);
+	struct net_device *dev = skb->dev;
+	struct in_device *in_dev;
 	struct inet_peer *peer;
 	unsigned long now;
 	struct net *net;
 	bool send;
 	int code;
 
+	if (netif_is_l3_master(skb->dev)) {
+		dev = __dev_get_by_index(dev_net(skb->dev), IPCB(skb)->iif);
+		if (!dev)
+			goto out;
+	}
+
+	in_dev = __in_dev_get_rcu(dev);
+
 	/* IP on this device is disabled. */
 	if (!in_dev)
 		goto out;