3.16.40-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Stephen Suryaputra Lin <stephen.suryaputra.lin@xxxxxxxxx> commit 969447f226b451c453ddc83cac6144eaeac6f2e3 upstream. 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 5943634fc559 ("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: 5943634fc559 ("ipv4: Maintain redirect and PMTU info in struct rtable again.") Signed-off-by: Stephen Suryaputra Lin <ssurya@xxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx> --- net/ipv4/route.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -746,7 +746,9 @@ static void __ip_do_redirect(struct rtab 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);