root/net/ipv4/netfilter/ipt_NETMAP.c

DEFINITIONS

1. netmap_tg_check
2. netmap_tg
3. netmap_tg_init
4. netmap_tg_exit

/* NETMAP - static NAT mapping of IP network addresses (1:1).
 * The mapping can be applied to source (POSTROUTING),
 * destination (PREROUTING), or both (with separate rules).
 */

/* (C) 2000-2001 Svenning Soerensen <svenning@post5.tele.dk>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include <linux/ip.h>
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter/x_tables.h>
#include <net/netfilter/nf_nat_rule.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Svenning Soerensen <svenning@post5.tele.dk>");
MODULE_DESCRIPTION("Xtables: 1:1 NAT mapping of IPv4 subnets");

static bool netmap_tg_check(const struct xt_tgchk_param *par)
{
        const struct nf_nat_multi_range_compat *mr = par->targinfo;

        if (!(mr->range[0].flags & IP_NAT_RANGE_MAP_IPS)) {
                pr_debug("NETMAP:check: bad MAP_IPS.\n");
                return false;
        }
        if (mr->rangesize != 1) {
                pr_debug("NETMAP:check: bad rangesize %u.\n", mr->rangesize);
                return false;
        }
        return true;
}

static unsigned int
netmap_tg(struct sk_buff *skb, const struct xt_target_param *par)
{
        struct nf_conn *ct;
        enum ip_conntrack_info ctinfo;
        __be32 new_ip, netmask;
        const struct nf_nat_multi_range_compat *mr = par->targinfo;
        struct nf_nat_range newrange;

        NF_CT_ASSERT(par->hooknum == NF_INET_PRE_ROUTING ||
                     par->hooknum == NF_INET_POST_ROUTING ||
                     par->hooknum == NF_INET_LOCAL_OUT);
        ct = nf_ct_get(skb, &ctinfo);

        netmask = ~(mr->range[0].min_ip ^ mr->range[0].max_ip);

        if (par->hooknum == NF_INET_PRE_ROUTING ||
            par->hooknum == NF_INET_LOCAL_OUT)
                new_ip = ip_hdr(skb)->daddr & ~netmask;
        else
                new_ip = ip_hdr(skb)->saddr & ~netmask;
        new_ip |= mr->range[0].min_ip & netmask;

        newrange = ((struct nf_nat_range)
                { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
                  new_ip, new_ip,
                  mr->range[0].min, mr->range[0].max });

        /* Hand modified range to generic setup. */
        return nf_nat_setup_info(ct, &newrange, HOOK2MANIP(par->hooknum));
}

static struct xt_target netmap_tg_reg __read_mostly = {
        .name           = "NETMAP",
        .family         = NFPROTO_IPV4,
        .target         = netmap_tg,
        .targetsize     = sizeof(struct nf_nat_multi_range_compat),
        .table          = "nat",
        .hooks          = (1 << NF_INET_PRE_ROUTING) |
                          (1 << NF_INET_POST_ROUTING) |
                          (1 << NF_INET_LOCAL_OUT),
        .checkentry     = netmap_tg_check,
        .me             = THIS_MODULE
};

static int __init netmap_tg_init(void)
{
        return xt_register_target(&netmap_tg_reg);
}

static void __exit netmap_tg_exit(void)
{
        xt_unregister_target(&netmap_tg_reg);
}

module_init(netmap_tg_init);
module_exit(netmap_tg_exit);