netdev - [v2] net: ipv6: fallback to full lookup if table lookup is unsuitable

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Date:   Fri, 16 Sep 2016 22:33:49 +0200
From:   Vincent Bernat <vincent@...nat.im>
To:     David Ahern <dsa@...ulusnetworks.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>, netdev@...r.kernel.org
Cc:     Vincent Bernat <vincent@...nat.im>
Subject: [v2] net: ipv6: fallback to full lookup if table lookup is unsuitable

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 <vincent@...nat.im>
---
 net/ipv6/route.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index ad4a7ff301fc..2c6c7257ff75 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1994,6 +1994,14 @@ static struct rt6_info *ip6_route_info_create(struct fib6_config *cfg)
 			if (cfg->fc_table)
 				grt = ip6_nh_lookup_table(net, cfg, gw_addr);
 
+			if (grt) {
+				if (grt->rt6i_flags & RTF_GATEWAY ||
+				    (dev && dev != grt->dst.dev)) {
+					ip6_rt_put(grt);
+					grt = NULL;
+				}
+			}
+
 			if (!grt)
 				grt = rt6_lookup(net, gw_addr, NULL,
 						 cfg->fc_ifindex, 1);
-- 
2.9.3