ipmr: Don't leak memory if fib lookup fails.

This was detected using two mcast router tables.  The
pimreg for the second interface did not have a specific
mrule, so packets received by it were handled by the
default table, which had nothing configured.

This caused the ipmr_fib_lookup to fail, causing
the memory leak.
Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/ipmr.c

@@ -442,8 +442,10 @@ static netdev_tx_t reg_vif_xmit(struct sk_buff *skb, struct net_device *dev)
 	int err;
 
 	err = ipmr_fib_lookup(net, &fl, &mrt);
-	if (err < 0)
+	if (err < 0) {
+		kfree_skb(skb);
 		return err;
+	}
 
 	read_lock(&mrt_lock);
 	dev->stats.tx_bytes += skb->len;
@@ -1728,8 +1730,10 @@ int ip_mr_input(struct sk_buff *skb)
 		goto dont_forward;
 
 	err = ipmr_fib_lookup(net, &skb_rtable(skb)->fl, &mrt);
-	if (err < 0)
+	if (err < 0) {
+		kfree_skb(skb);
 		return err;
+	}
 
 	if (!local) {
 		    if (IPCB(skb)->opt.router_alert) {