ipv6: Fixed source specific default route handling.

If there are only IPv6 source specific default routes present, the
host gets -ENETUNREACH on e.g. connect() because ip6_dst_lookup_tail
calls ip6_route_output first, and given source address any, it fails,
and ip6_route_get_saddr is never called.

The change is to use the ip6_route_get_saddr, even if the initial
ip6_route_output fails, and then doing ip6_route_output _again_ after
we have appropriate source address available.

Note that this is '99% fix' to the problem; a correct fix would be to
do route lookups only within addrconf.c when picking a source address,
and never call ip6_route_output before source address has been
populated.

Signed-off-by: Markus Stenberg <markus.stenberg@iki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 5c48293..d358888 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2245,9 +2245,10 @@
 			unsigned int prefs,
 			struct in6_addr *saddr)
 {
-	struct inet6_dev *idev = ip6_dst_idev((struct dst_entry *)rt);
+	struct inet6_dev *idev =
+		rt ? ip6_dst_idev((struct dst_entry *)rt) : NULL;
 	int err = 0;
-	if (rt->rt6i_prefsrc.plen)
+	if (rt && rt->rt6i_prefsrc.plen)
 		*saddr = rt->rt6i_prefsrc.addr;
 	else
 		err = ipv6_dev_get_saddr(net, idev ? idev->dev : NULL,