net/ipv6: Extract table lookup from ip6_pol_route

ip6_pol_route is used for ingress and egress FIB lookups. Refactor it
moving the table lookup into a separate fib6_table_lookup that can be
invoked separately and export the new function.

ip6_pol_route now calls fib6_table_lookup and uses the result to generate
a dst based rt6_info.

Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

include/net/ip6_fib.h

@@ -376,6 +376,10 @@ struct dst_entry *fib6_rule_lookup(struct net *net, struct flowi6 *fl6,
 				   const struct sk_buff *skb,
 				   int flags, pol_lookup_t lookup);
 
+/* called with rcu lock held; caller needs to select path */
+struct fib6_info *fib6_table_lookup(struct net *net, struct fib6_table *table,
+				    int oif, struct flowi6 *fl6, int strict);
+
 struct fib6_info *fib6_multipath_select(const struct net *net,
 					struct fib6_info *match,
 					struct flowi6 *fl6, int oif,

net/ipv6/route.c

@@ -1800,21 +1800,12 @@ void rt6_age_exceptions(struct fib6_info *rt,
 	rcu_read_unlock_bh();
 }
 
-struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
-			       int oif, struct flowi6 *fl6,
-			       const struct sk_buff *skb, int flags)
+/* must be called with rcu lock held */
+struct fib6_info *fib6_table_lookup(struct net *net, struct fib6_table *table,
+				    int oif, struct flowi6 *fl6, int strict)
 {
 	struct fib6_node *fn, *saved_fn;
 	struct fib6_info *f6i;
-	struct rt6_info *rt;
-	int strict = 0;
-
-	strict |= flags & RT6_LOOKUP_F_IFACE;
-	strict |= flags & RT6_LOOKUP_F_IGNORE_LINKSTATE;
-	if (net->ipv6.devconf_all->forwarding == 0)
-		strict |= RT6_LOOKUP_F_REACHABLE;
-
-	rcu_read_lock();
 
 	fn = fib6_node_lookup(&table->tb6_root, &fl6->daddr, &fl6->saddr);
 	saved_fn = fn;
@@ -1824,8 +1815,6 @@ struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
 
 redo_rt6_select:
 	f6i = rt6_select(net, fn, oif, strict);
-	if (f6i->fib6_nsiblings)
-		f6i = fib6_multipath_select(net, f6i, fl6, oif, skb, strict);
 	if (f6i == net->ipv6.fib6_null_entry) {
 		fn = fib6_backtrack(fn, &fl6->saddr);
 		if (fn)
@@ -1838,6 +1827,28 @@ redo_rt6_select:
 		}
 	}
 
+	return f6i;
+}
+
+struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
+			       int oif, struct flowi6 *fl6,
+			       const struct sk_buff *skb, int flags)
+{
+	struct fib6_info *f6i;
+	struct rt6_info *rt;
+	int strict = 0;
+
+	strict |= flags & RT6_LOOKUP_F_IFACE;
+	strict |= flags & RT6_LOOKUP_F_IGNORE_LINKSTATE;
+	if (net->ipv6.devconf_all->forwarding == 0)
+		strict |= RT6_LOOKUP_F_REACHABLE;
+
+	rcu_read_lock();
+
+	f6i = fib6_table_lookup(net, table, oif, fl6, strict);
+	if (f6i->fib6_nsiblings)
+		f6i = fib6_multipath_select(net, f6i, fl6, oif, skb, strict);
+
 	if (f6i == net->ipv6.fib6_null_entry) {
 		rt = net->ipv6.ip6_null_entry;
 		rcu_read_unlock();