[PATCH 2/3] netfilter: iptables: fix use of cluster match with 32 nodes

[Pablo Neira Ayuso <pablo@netfilter.org>]

This patch fixes a problem when you use 32 nodes in the cluster
match:

% iptables -I PREROUTING -t mangle -i eth0 -m cluster \
  --cluster-total-nodes  32  --cluster-local-node  32 \
  --cluster-hash-seed 0xdeadbeef -j MARK --set-mark 0xffff
iptables: Invalid argument. Run `dmesg' for more information.
% dmesg | tail -1
xt_cluster: this node mask cannot be higher than the total number of nodes

The problem is related to this checking:

if (info->node_mask >= (1 << info->total_nodes)) {
	printk(KERN_ERR "xt_cluster: this node mask cannot be "
			"higher than the total number of nodes\n");
	return false;
}

(1 << 32) is 1. Thus, the checking fails. This patch skips the case
in which total_nodes is 32 and it adds an extra validation to ensure
that we don't go over 32 nodes.

BTW, I said this before but I insist: I have only tested the cluster
match with 2 nodes getting ~45% extra performance in an active-active setup.
The maximum limit of 32 nodes is still completely arbitrary. I'd really
appreciate if people that have more nodes in their setups let me know.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
---

 include/linux/netfilter/xt_cluster.h |    2 ++
 net/netfilter/xt_cluster.c           |    8 +++++++-
 2 files changed, 9 insertions(+), 1 deletions(-)

diff --git a/include/linux/netfilter/xt_cluster.h b/include/linux/netfilter/xt_cluster.h
index 5e0a0d0..12c7b13 100644
--- a/include/linux/netfilter/xt_cluster.h
+++ b/include/linux/netfilter/xt_cluster.h
@@ -12,4 +12,6 @@ struct xt_cluster_match_info {
 	u_int32_t		flags;
 };
 
+#define XT_CLUSTER_NODES_MAX    32
+
 #endif /* _XT_CLUSTER_MATCH_H */
diff --git a/net/netfilter/xt_cluster.c b/net/netfilter/xt_cluster.c
index 6c48476..04af29e 100644
--- a/net/netfilter/xt_cluster.c
+++ b/net/netfilter/xt_cluster.c
@@ -135,7 +135,13 @@ static bool xt_cluster_mt_checkentry(const struct xt_mtchk_param *par)
 {
 	struct xt_cluster_match_info *info = par->matchinfo;
 
-	if (info->node_mask >= (1 << info->total_nodes)) {
+	if (info->total_nodes > XT_CLUSTER_NODES_MAX) {
+		printk(KERN_ERR "xt_cluster: too many total nodes (%u > %u)\n",
+				info->total_nodes, XT_CLUSTER_NODES_MAX);
+		return false;
+	}
+	if (info->total_nodes < XT_CLUSTER_NODES_MAX &&
+	    info->node_mask >= (1 << info->total_nodes)) {
 		printk(KERN_ERR "xt_cluster: this node mask cannot be "
 				"higher than the total number of nodes\n");
 		return false;