ipv6: del unreachable route when an addr is deleted on lo

When an address is added on loopback (ip -6 a a 2002::1/128 dev lo), two routes
are added:
 - one in the local table:
    local 2002::1 via :: dev lo  proto none  metric 0
 - one the in main table (for the prefix):
    unreachable 2002::1 dev lo  proto kernel  metric 256  error -101

When the address is deleted, the route inserted in the main table remains
because we use rt6_lookup(), which returns NULL when dst->error is set, which
is the case here! Thus, it is better to use ip6_route_lookup() to avoid this
kind of filter.
Signed-off-by: NNicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -788,10 +788,16 @@ static void ipv6_del_addr(struct inet6_ifaddr *ifp)
 		struct in6_addr prefix;
 		struct rt6_info *rt;
 		struct net *net = dev_net(ifp->idev->dev);
+		struct flowi6 fl6 = {};
+
 		ipv6_addr_prefix(&prefix, &ifp->addr, ifp->prefix_len);
-		rt = rt6_lookup(net, &prefix, NULL, ifp->idev->dev->ifindex, 1);
+		fl6.flowi6_oif = ifp->idev->dev->ifindex;
+		fl6.daddr = prefix;
+		rt = (struct rt6_info *)ip6_route_lookup(net, &fl6,
+							 RT6_LOOKUP_F_IFACE);
 
-		if (rt && addrconf_is_prefix_route(rt)) {
+		if (rt != net->ipv6.ip6_null_entry &&
+		    addrconf_is_prefix_route(rt)) {
 			if (onlink == 0) {
 				ip6_del_rt(rt);
 				rt = NULL;