ipv6: honor RT6_LOOKUP_F_DST_NOREF in rule lookup logic

This patch specifically converts the rule lookup logic to honor this
flag and not release refcnt when traversing each rule and calling
lookup() on each routing table.
Similar to previous patch, we also need some special handling of dst
entries in uncached list because there is always 1 refcnt taken for them
even if RT6_LOOKUP_F_DST_NOREF flag is set.

Signed-off-by: Wei Wang <weiwan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/fib6_rules.c

@@ -113,14 +113,15 @@ struct dst_entry *fib6_rule_lookup(struct net *net, struct flowi6 *fl6,
 		rt = lookup(net, net->ipv6.fib6_local_tbl, fl6, skb, flags);
 		if (rt != net->ipv6.ip6_null_entry && rt->dst.error != -EAGAIN)
 			return &rt->dst;
-		ip6_rt_put(rt);
+		ip6_rt_put_flags(rt, flags);
 		rt = lookup(net, net->ipv6.fib6_main_tbl, fl6, skb, flags);
 		if (rt->dst.error != -EAGAIN)
 			return &rt->dst;
-		ip6_rt_put(rt);
+		ip6_rt_put_flags(rt, flags);
 	}
 
-	dst_hold(&net->ipv6.ip6_null_entry->dst);
+	if (!(flags & RT6_LOOKUP_F_DST_NOREF))
+		dst_hold(&net->ipv6.ip6_null_entry->dst);
 	return &net->ipv6.ip6_null_entry->dst;
 }
 
@@ -237,13 +238,14 @@ static int __fib6_rule_action(struct fib_rule *rule, struct flowi *flp,
 			goto out;
 	}
 again:
-	ip6_rt_put(rt);
+	ip6_rt_put_flags(rt, flags);
 	err = -EAGAIN;
 	rt = NULL;
 	goto out;
 
 discard_pkt:
-	dst_hold(&rt->dst);
+	if (!(flags & RT6_LOOKUP_F_DST_NOREF))
+		dst_hold(&rt->dst);
 out:
 	res->rt6 = rt;
 	return err;

net/ipv6/ip6_fib.c

@@ -316,9 +316,10 @@ struct dst_entry *fib6_rule_lookup(struct net *net, struct flowi6 *fl6,
 
 	rt = lookup(net, net->ipv6.fib6_main_tbl, fl6, skb, flags);
 	if (rt->dst.error == -EAGAIN) {
-		ip6_rt_put(rt);
+		ip6_rt_put_flags(rt, flags);
 		rt = net->ipv6.ip6_null_entry;
-		dst_hold(&rt->dst);
+		if (!(flags | RT6_LOOKUP_F_DST_NOREF))
+			dst_hold(&rt->dst);
 	}
 
 	return &rt->dst;