ipv6 route: Prefer outgoing interface with source address assigned.

Outgoing interface is selected by the route decision if unspecified.
Let's prefer routes via interface(s) with the address assigned if we
have multiple routes with same cost.
With help from Naohiro Ooiwa <nooiwa@miraclelinux.com>.
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>

net/ipv6/route.c

@@ -237,15 +237,20 @@ static inline int rt6_need_strict(struct in6_addr *daddr)
 
 static inline struct rt6_info *rt6_device_match(struct net *net,
 						    struct rt6_info *rt,
+						    struct in6_addr *saddr,
 						    int oif,
 						    int flags)
 {
 	struct rt6_info *local = NULL;
 	struct rt6_info *sprt;
 
-	if (oif) {
-		for (sprt = rt; sprt; sprt = sprt->u.dst.rt6_next) {
-			struct net_device *dev = sprt->rt6i_dev;
+	if (!oif && ipv6_addr_any(saddr))
+		goto out;
+
+	for (sprt = rt; sprt; sprt = sprt->u.dst.rt6_next) {
+		struct net_device *dev = sprt->rt6i_dev;
+
+		if (oif) {
 			if (dev->ifindex == oif)
 				return sprt;
 			if (dev->flags & IFF_LOOPBACK) {
@@ -259,14 +264,21 @@ static inline struct rt6_info *rt6_device_match(struct net *net,
 				}
 				local = sprt;
 			}
+		} else {
+			if (ipv6_chk_addr(net, saddr, dev,
+					  flags & RT6_LOOKUP_F_IFACE))
+				return sprt;
 		}
+	}
 
+	if (oif) {
 		if (local)
 			return local;
 
 		if (flags & RT6_LOOKUP_F_IFACE)
 			return net->ipv6.ip6_null_entry;
 	}
+out:
 	return rt;
 }
 
@@ -539,7 +551,7 @@ static struct rt6_info *ip6_pol_route_lookup(struct net *net,
 	fn = fib6_lookup(&table->tb6_root, &fl->fl6_dst, &fl->fl6_src);
 restart:
 	rt = fn->leaf;
-	rt = rt6_device_match(net, rt, fl->oif, flags);
+	rt = rt6_device_match(net, rt, &fl->fl6_src, fl->oif, flags);
 	BACKTRACK(net, &fl->fl6_src);
 out:
 	dst_use(&rt->u.dst, jiffies);