ipt_MASQUERADE.c

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/* 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 <[email protected]>
 *
 * 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.
 */
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#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 <linux/netfilter_ipv4.h>
#include <linux/netfilter/x_tables.h>
#include <net/netfilter/nf_nat.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Netfilter Core Team <[email protected]>");
MODULE_DESCRIPTION("Xtables: automatic-address SNAT");

/* FIXME: Multiple targets. --RR */
static int masquerade_tg_check(const struct xt_tgchk_param *par)
{
    const struct nf_nat_ipv4_multi_range_compat *mr = par->targinfo;

    if (mr->range[0].flags & NF_NAT_RANGE_MAP_IPS) {
        pr_debug("bad MAP_IPS.\n");
        return -EINVAL;
    }
    if (mr->rangesize != 1) {
        pr_debug("bad rangesize %u\n", mr->rangesize);
        return -EINVAL;
    }
    return 0;
}

static unsigned int
masquerade_tg(struct sk_buff *skb, const struct xt_action_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_ipv4_multi_range_compat *mr;
    const struct rtable *rt;
    __be32 newsrc, nh;

    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_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(skb);
    nh = rt_nexthop(rt, ip_hdr(skb)->daddr);
    newsrc = inet_select_addr(par->out, nh, RT_SCOPE_UNIVERSE);
    if (!newsrc) {
        pr_info("%s ate my IP address\n", par->out->name);
        return NF_DROP;
    }

    nat->masq_index = par->out->ifindex;

    /* Transfer from original range. */
    memset(&newrange.min_addr, 0, sizeof(newrange.min_addr));
    memset(&newrange.max_addr, 0, sizeof(newrange.max_addr));
    newrange.flags       = mr->range[0].flags | NF_NAT_RANGE_MAP_IPS;
    newrange.min_addr.ip = newsrc;
    newrange.max_addr.ip = newsrc;
    newrange.min_proto   = mr->range[0].min;
    newrange.max_proto   = mr->range[0].max;

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

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

    if (!nat)
        return 0;
    if (nf_ct_l3num(i) != NFPROTO_IPV4)
        return 0;
    return nat->masq_index == (int)(long)ifindex;
}

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_ipv4_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);