netfilter: conncount: Support count only use case

Currently, nf_conncount_count() counts the number of connections that
matches key and inserts a conntrack 'tuple' with the same key into the
accounting data structure. This patch supports another use case that only
counts the number of connections where 'tuple' is not provided. Therefore,
proper changes are made on nf_conncount_count() to support the case where
'tuple' is NULL. This could be useful for querying statistics or
debugging purpose.

Signed-off-by: Yi-Hung Wei <[e-mail]>
Acked-by: Florian Westphal <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/nf_conncount.c

···
 	struct nf_conn *found_ct;
 	unsigned int length = 0;
 
-	*addit = true;
+	*addit = tuple ? true : false;
 
 	/* check the saved connections */
 	hlist_for_each_entry_safe(conn, n, head, node) {
···
 
 		found_ct = nf_ct_tuplehash_to_ctrack(found);
 
-		if (nf_ct_tuple_equal(&conn->tuple, tuple)) {
+		if (tuple && nf_ct_tuple_equal(&conn->tuple, tuple)) {
 			/*
 			 * Just to be sure we have it only once in the list.
 			 * We should not see tuples twice unless someone hooks
···
 		goto restart;
 	}
 
+	if (!tuple)
+		return 0;
+
 	/* no match, need to insert new node */
 	rbconn = kmem_cache_alloc(conncount_rb_cachep, GFP_ATOMIC);
 	if (rbconn == NULL)
···
 	return 1;
 }
 
+/* Count and return number of conntrack entries in 'net' with particular 'key'.
+ * If 'tuple' is not null, insert it into the accounting data structure.
+ */
 unsigned int nf_conncount_count(struct net *net,
 				struct nf_conncount_data *data,
 				const u32 *key,