icmp: Don't leak original dst into ip_route_input()

ip_route_input() unconditionally overwrites the dst. Hide the original
dst attached to the skb by calling skb_dst_set(skb, NULL) prior to
ip_route_input().
Reported-by: NJulian Anastasov <ja@ssi.bg>
Signed-off-by: NThomas Graf <tgraf@suug.ch>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/icmp.c

@@ -496,6 +496,7 @@ static struct rtable *icmp_route_lookup(struct net *net,
 		}
 		/* Ugh! */
 		orefdst = skb_in->_skb_refdst; /* save old refdst */
+		skb_dst_set(skb_in, NULL);
 		err = ip_route_input(skb_in, fl4_dec.daddr, fl4_dec.saddr,
 				     RT_TOS(tos), rt2->dst.dev);