On 9/16/16 6:55 AM, Vincent Bernat wrote:
> Commit 8c14586fc320 ("net: ipv6: Use passed in table for nexthop
> lookups") introduced a regression: insertion of an IPv6 route in a table
> not containing the appropriate connected route for the gateway but which
> contained a non-connected route (like a default gateway) fails while it
> was previously working:
>
> $ ip link add eth0 type dummy
> $ ip link set up dev eth0
> $ ip addr add 2001:db8::1/64 dev eth0
> $ ip route add ::/0 via 2001:db8::5 dev eth0 table 20
> $ ip route add 2001:db8:cafe::1/128 via 2001:db8::6 dev eth0 table 20
> RTNETLINK answers: No route to host
> $ ip -6 route show table 20
> default via 2001:db8::5 dev eth0 metric 1024 pref medium
so your table 20 is not complete in that it lacks a connected route to resolve
2001:db8::6 as a nexthop, so you are relying on a fallback to other tables
(main in this case).
-----8<-----
> @@ -1991,33 +2015,15 @@ static struct rt6_info *ip6_route_info_create(struct
> fib6_config *cfg)
> if (!(gwa_type & IPV6_ADDR_UNICAST))
> goto out;
>
> + err = -EHOSTUNREACH;
> if (cfg->fc_table)
> grt = ip6_nh_lookup_table(net, cfg, gw_addr);
-----8<-----
> - if (!(grt->rt6i_flags & RTF_GATEWAY))
> - err = 0;
This is the check that is failing for your use case. ip6_nh_lookup_table is
returning the default route and nexthops can not rely on a gateway. Given that
a simpler and more direct change is (whitespace mangled on paste):
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index ad4a7ff301fc..48bae2ee2e18 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1991,9 +1991,19 @@ static struct rt6_info *ip6_route_info_create(struct
fib6_config *cfg)
if (!(gwa_type & IPV6_ADDR_UNICAST))
goto out;
- if (cfg->fc_table)
+ if (cfg->fc_table) {
grt = ip6_nh_lookup_table(net, cfg, gw_addr);
+ /* a nexthop lookup can not go through a gw.
+ * if this happens on a table based lookup
+ * then fallback to a full lookup
+ */
+ if (grt && grt->rt6i_flags & RTF_GATEWAY) {
+ ip6_rt_put(grt);
+ grt = NULL;
+ }
+ }
+
if (!grt)
grt = rt6_lookup(net, gw_addr, NULL,
cfg->fc_ifindex, 1);
