root/net/ipv4/netfilter/ipt_MASQUERADE.c

DEFINITIONS

1. masquerade_tg_check
2. masquerade_tg
3. device_cmp
4. masq_device_event
5. masq_inet_event
6. masquerade_tg_init
7. masquerade_tg_exit

/* Masquerade.  Simple mapping which alters range to a local IP address
   (depending on route). */

/* (C) 1999-2001 Paul `Rusty' Russell
 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
 *
 * 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/types.h>
#include <linux/inetdevice.h>
#include <linux/ip.h>
#include <linux/timer.h>
#include <linux/module.h>
#include <linux/netfilter.h>
#include <net/protocol.h>
#include <net/ip.h>
#include <net/checksum.h>
#include <net/route.h>
#include <net/netfilter/nf_nat_rule.h>
#include <linux/netfilter_ipv4.h>
#include <linux/netfilter/x_tables.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Netfilter Core Team <coreteam@netfilter.org>");
MODULE_DESCRIPTION("Xtables: automatic-address SNAT");

/* Lock protects masq region inside conntrack */
static DEFINE_RWLOCK(masq_lock);

/* FIXME: Multiple targets. --RR */
static bool masquerade_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("masquerade_check: bad MAP_IPS.\n");
                return false;
        }
        if (mr->rangesize != 1) {
                pr_debug("masquerade_check: bad rangesize %u\n", mr->rangesize);
                return false;
        }
        return true;
}

static unsigned int
masquerade_tg(struct sk_buff *skb, const struct xt_target_param *par)
{
        struct nf_conn *ct;
        struct nf_conn_nat *nat;
        enum ip_conntrack_info ctinfo;
        struct nf_nat_range newrange;
        const struct nf_nat_multi_range_compat *mr;
        const struct rtable *rt;
        __be32 newsrc;

        NF_CT_ASSERT(par->hooknum == NF_INET_POST_ROUTING);

        ct = nf_ct_get(skb, &ctinfo);
        nat = nfct_nat(ct);

        NF_CT_ASSERT(ct && (ctinfo == IP_CT_NEW || ctinfo == IP_CT_RELATED
                            || ctinfo == IP_CT_RELATED + IP_CT_IS_REPLY));

        /* Source address is 0.0.0.0 - locally generated packet that is
         * probably not supposed to be masqueraded.
         */
        if (ct->tuplehash[IP_CT_DIR_ORIGINAL].tuple.src.u3.ip == 0)
                return NF_ACCEPT;

        mr = par->targinfo;
        rt = skb->rtable;
        newsrc = inet_select_addr(par->out, rt->rt_gateway, RT_SCOPE_UNIVERSE);
        if (!newsrc) {
                printk("MASQUERADE: %s ate my IP address\n", par->out->name);
                return NF_DROP;
        }

        write_lock_bh(&masq_lock);
        nat->masq_index = par->out->ifindex;
        write_unlock_bh(&masq_lock);

        /* Transfer from original range. */
        newrange = ((struct nf_nat_range)
                { mr->range[0].flags | IP_NAT_RANGE_MAP_IPS,
                  newsrc, newsrc,
                  mr->range[0].min, mr->range[0].max });

        /* Hand modified range to generic setup. */
        return nf_nat_setup_info(ct, &newrange, IP_NAT_MANIP_SRC);
}

static int
device_cmp(struct nf_conn *i, void *ifindex)
{
        const struct nf_conn_nat *nat = nfct_nat(i);
        int ret;

        if (!nat)
                return 0;

        read_lock_bh(&masq_lock);
        ret = (nat->masq_index == (int)(long)ifindex);
        read_unlock_bh(&masq_lock);

        return ret;
}

static int masq_device_event(struct notifier_block *this,
                             unsigned long event,
                             void *ptr)
{
        const struct net_device *dev = ptr;
        struct net *net = dev_net(dev);

        if (event == NETDEV_DOWN) {
                /* Device was downed.  Search entire table for
                   conntracks which were associated with that device,
                   and forget them. */
                NF_CT_ASSERT(dev->ifindex != 0);

                nf_ct_iterate_cleanup(net, device_cmp,
                                      (void *)(long)dev->ifindex);
        }

        return NOTIFY_DONE;
}

static int masq_inet_event(struct notifier_block *this,
                           unsigned long event,
                           void *ptr)
{
        struct net_device *dev = ((struct in_ifaddr *)ptr)->ifa_dev->dev;
        return masq_device_event(this, event, dev);
}

static struct notifier_block masq_dev_notifier = {
        .notifier_call  = masq_device_event,
};

static struct notifier_block masq_inet_notifier = {
        .notifier_call  = masq_inet_event,
};

static struct xt_target masquerade_tg_reg __read_mostly = {
        .name           = "MASQUERADE",
        .family         = NFPROTO_IPV4,
        .target         = masquerade_tg,
        .targetsize     = sizeof(struct nf_nat_multi_range_compat),
        .table          = "nat",
        .hooks          = 1 << NF_INET_POST_ROUTING,
        .checkentry     = masquerade_tg_check,
        .me             = THIS_MODULE,
};

static int __init masquerade_tg_init(void)
{
        int ret;

        ret = xt_register_target(&masquerade_tg_reg);

        if (ret == 0) {
                /* Register for device down reports */
                register_netdevice_notifier(&masq_dev_notifier);
                /* Register IP address change reports */
                register_inetaddr_notifier(&masq_inet_notifier);
        }

        return ret;
}

static void __exit masquerade_tg_exit(void)
{
        xt_unregister_target(&masquerade_tg_reg);
        unregister_netdevice_notifier(&masq_dev_notifier);
        unregister_inetaddr_notifier(&masq_inet_notifier);
}

module_init(masquerade_tg_init);
module_exit(masquerade_tg_exit);