Commit 969447f2 authored Nov 10, 2016 by Stephen Suryaputra Lin Committed by David S. Miller Nov 13, 2016

ipv4: use new_gw for redirect neigh lookup



In v2.6, ip_rt_redirect() calls arp_bind_neighbour() which returns 0
and then the state of the neigh for the new_gw is checked. If the state
isn't valid then the redirected route is deleted. This behavior is
maintained up to v3.5.7 by check_peer_redirect() because rt->rt_gateway
is assigned to peer->redirect_learned.a4 before calling
ipv4_neigh_lookup().

After commit 5943634f ("ipv4: Maintain redirect and PMTU info in
struct rtable again."), ipv4_neigh_lookup() is performed without the
rt_gateway assigned to the new_gw. In the case when rt_gateway (old_gw)
isn't zero, the function uses it as the key. The neigh is most likely
valid since the old_gw is the one that sends the ICMP redirect message.
Then the new_gw is assigned to fib_nh_exception. The problem is: the
new_gw ARP may never gets resolved and the traffic is blackholed.

So, use the new_gw for neigh lookup.

Changes from v1:
 - use __ipv4_neigh_lookup instead (per Eric Dumazet).

Fixes: 5943634f ("ipv4: Maintain redirect and PMTU info in struct rtable again.")
Signed-off-by: Stephen Suryaputra Lin <ssurya@ieee.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent ca0a7531

net/ipv4/route.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -753,7 +753,9 @@ static void __ip_do_redirect(struct rtable rt, struct sk_buff skb, struct flow
		goto reject_redirect;
		}

		n = ipv4_neigh_lookup(&rt->dst, NULL, &new_gw);
		n = __ipv4_neigh_lookup(rt->dst.dev, new_gw);
		if (!n)
		n = neigh_create(&arp_tbl, &new_gw, rt->dst.dev);
		if (!IS_ERR(n)) {
		if (!(n->nud_state & NUD_VALID)) {
		neigh_event_send(n, NULL);

Admin message