nf_conntrack_snmp.c

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/*
 *      SNMP service broadcast connection tracking helper
 *
 *      (c) 2011 Jiri Olsa <[email protected]>
 *
 *      This program is free software; you can redistribute it and/or
 *      modify it under the terms of the GNU General Public License
 *      as published by the Free Software Foundation; either version
 *      2 of the License, or (at your option) any later version.
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/in.h>

#include <net/netfilter/nf_conntrack.h>
#include <net/netfilter/nf_conntrack_helper.h>
#include <net/netfilter/nf_conntrack_expect.h>

#define SNMP_PORT   161

MODULE_AUTHOR("Jiri Olsa <[email protected]>");
MODULE_DESCRIPTION("SNMP service broadcast connection tracking helper");
MODULE_LICENSE("GPL");
MODULE_ALIAS_NFCT_HELPER("snmp");

static unsigned int timeout __read_mostly = 30;
module_param(timeout, uint, S_IRUSR);
MODULE_PARM_DESC(timeout, "timeout for master connection/replies in seconds");

int (*nf_nat_snmp_hook)(struct sk_buff *skb,
            unsigned int protoff,
            struct nf_conn *ct,
            enum ip_conntrack_info ctinfo);
EXPORT_SYMBOL_GPL(nf_nat_snmp_hook);

static int snmp_conntrack_help(struct sk_buff *skb, unsigned int protoff,
        struct nf_conn *ct, enum ip_conntrack_info ctinfo)
{
    typeof(nf_nat_snmp_hook) nf_nat_snmp;

    nf_conntrack_broadcast_help(skb, protoff, ct, ctinfo, timeout);

    nf_nat_snmp = rcu_dereference(nf_nat_snmp_hook);
    if (nf_nat_snmp && ct->status & IPS_NAT_MASK)
        return nf_nat_snmp(skb, protoff, ct, ctinfo);

    return NF_ACCEPT;
}

static struct nf_conntrack_expect_policy exp_policy = {
    .max_expected   = 1,
};

static struct nf_conntrack_helper helper __read_mostly = {
    .name           = "snmp",
    .tuple.src.l3num    = NFPROTO_IPV4,
    .tuple.src.u.udp.port   = cpu_to_be16(SNMP_PORT),
    .tuple.dst.protonum = IPPROTO_UDP,
    .me         = THIS_MODULE,
    .help           = snmp_conntrack_help,
    .expect_policy      = &exp_policy,
};

static int __init nf_conntrack_snmp_init(void)
{
    exp_policy.timeout = timeout;
    return nf_conntrack_helper_register(&helper);
}

static void __exit nf_conntrack_snmp_fini(void)
{
    nf_conntrack_helper_unregister(&helper);
}

module_init(nf_conntrack_snmp_init);
module_exit(nf_conntrack_snmp_fini);