netfilter: nfnetlink: add netns refcount tracker to struct nfulnl_instance

If compiled with CONFIG_NET_NS_REFCNT_TRACKER=y,
using put_net_track() in nfulnl_instance_free_rcu()
and get_net_track() in instance_create()
might help us finding netns refcount imbalances.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nfnetlink_log.c

@@ -66,6 +66,7 @@ struct nfulnl_instance {
 	struct sk_buff *skb;		/* pre-allocatd skb */
 	struct timer_list timer;
 	struct net *net;
+	netns_tracker ns_tracker;
 	struct user_namespace *peer_user_ns;	/* User namespace of the peer process */
 	u32 peer_portid;		/* PORTID of the peer process */
 
@@ -140,7 +141,7 @@ static void nfulnl_instance_free_rcu(struct rcu_head *head)
 	struct nfulnl_instance *inst =
 		container_of(head, struct nfulnl_instance, rcu);
 
-	put_net(inst->net);
+	put_net_track(inst->net, &inst->ns_tracker);
 	kfree(inst);
 	module_put(THIS_MODULE);
 }
@@ -187,7 +188,7 @@ instance_create(struct net *net, u_int16_t group_num,
 
 	timer_setup(&inst->timer, nfulnl_timer, 0);
 
-	inst->net = get_net(net);
+	inst->net = get_net_track(net, &inst->ns_tracker, GFP_ATOMIC);
 	inst->peer_user_ns = user_ns;
 	inst->peer_portid = portid;
 	inst->group_num = group_num;