Commit 969447f2 authored by Stephen Suryaputra Lin's avatar Stephen Suryaputra Lin Committed by David S. Miller
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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

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: default avatarStephen Suryaputra Lin <>
Signed-off-by: default avatarDavid S. Miller <>
parent ca0a7531
......@@ -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->, new_gw);
if (!n)
n = neigh_create(&arp_tbl, &new_gw, rt->;
if (!IS_ERR(n)) {
if (!(n->nud_state & NUD_VALID)) {
neigh_event_send(n, NULL);
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