[PATCH] net: ipv6: fallback to full lookup if table lookup is unsuitable

[Vincent Bernat]

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

After this patch, we get:

    $ ip route add 2001:db8:cafe::1/128 via 2001:db8::6 dev eth0 table 20
    $ ip -6 route show table 20
    2001:db8:cafe::1 via 2001:db8::6 dev eth0  metric 1024  pref medium
    default via 2001:db8::5 dev eth0  metric 1024  pref medium

Signed-off-by: Vincent Bernat <vinc...@bernat.im>
---
 net/ipv6/route.c | 48 +++++++++++++++++++++++++++---------------------
 1 file changed, 27 insertions(+), 21 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index ad4a7ff301fc..c2aaddcfed9e 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1808,6 +1808,30 @@ static struct rt6_info *ip6_nh_lookup_table(struct net 
*net,
        return rt;
 }
 
+static int ip6_nh_valid(struct rt6_info *grt,
+                       struct net_device **dev, struct inet6_dev **idev) {
+       int ret = 0;
+
+       if (!grt)
+               goto out;
+       if (grt->rt6i_flags & RTF_GATEWAY)
+               goto out;
+       if (*dev) {
+               if (*dev != grt->dst.dev)
+                       goto out;
+       } else {
+               *dev = grt->dst.dev;
+               *idev = grt->rt6i_idev;
+               dev_hold(*dev);
+               in6_dev_hold(*idev);
+       }
+       ret = 1;
+out:
+       if (grt)
+               ip6_rt_put(grt);
+       return ret;
+}
+
 static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg)
 {
        struct net *net = cfg->fc_nlinfo.nl_net;
@@ -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);
-
-                       if (!grt)
+                       if (!ip6_nh_valid(grt, &dev, &idev)) {
                                grt = rt6_lookup(net, gw_addr, NULL,
                                                 cfg->fc_ifindex, 1);
-
-                       err = -EHOSTUNREACH;
-                       if (!grt)
-                               goto out;
-                       if (dev) {
-                               if (dev != grt->dst.dev) {
-                                       ip6_rt_put(grt);
+                               if (!ip6_nh_valid(grt, &dev, &idev))
                                        goto out;
-                               }
-                       } else {
-                               dev = grt->dst.dev;
-                               idev = grt->rt6i_idev;
-                               dev_hold(dev);
-                               in6_dev_hold(grt->rt6i_idev);
                        }
-                       if (!(grt->rt6i_flags & RTF_GATEWAY))
-                               err = 0;
-                       ip6_rt_put(grt);
-
-                       if (err)
-                               goto out;
                }
                err = -EINVAL;
                if (!dev || (dev->flags & IFF_LOOPBACK))
-- 
2.9.3