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 <ssu...@ieee.org>
---
net/ipv4/route.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 62d4d90c1389..2a57566e6e91 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -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);
--
2.7.4
