netfilter: xt_connlimit: connlimit-above early loop termination

The patch below introduces an early termination of the loop that is
counting matches. It terminates once the counter has exceeded the
threshold provided by the user. There's no point in continuing the loop
afterwards and looking at other entries.

It plays together with the following code further below:

return (connections > info->limit) ^ info->inverse;

where connections is the result of the counted connection, which in turn
is the matches variable in the loop. So once

        -> matches = info->limit + 1
alias   -> matches > info->limit
alias   -> matches > threshold

we can terminate the loop.
Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

net/netfilter/xt_connlimit.c

@@ -97,7 +97,8 @@ static int count_them(struct net *net,
 		      const struct nf_conntrack_tuple *tuple,
 		      const union nf_inet_addr *addr,
 		      const union nf_inet_addr *mask,
-		      u_int8_t family)
+		      u_int8_t family,
+		      unsigned int threshold)
 {
 	const struct nf_conntrack_tuple_hash *found;
 	struct xt_connlimit_conn *conn;
@@ -151,9 +152,14 @@ static int count_them(struct net *net,
 			continue;
 		}
 
-		if (same_source_net(addr, mask, &conn->tuple.src.u3, family))
+		if (same_source_net(addr, mask, &conn->tuple.src.u3, family)) {
 			/* same source network -> be counted! */
 			++matches;
+			if (matches > threshold) {
+				nf_ct_put(found_ct);
+				break;
+			}
+		}
 		nf_ct_put(found_ct);
 	}
 
@@ -207,7 +213,8 @@ connlimit_mt(const struct sk_buff *skb, struct xt_action_param *par)
 
 	spin_lock_bh(&info->data->lock);
 	connections = count_them(net, info->data, tuple_ptr, &addr,
-	                         &info->mask, par->family);
+	                         &info->mask, par->family,
+	                         info->limit);
 	spin_unlock_bh(&info->data->lock);
 
 	if (connections < 0)