ebt_snat.c

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/*
 *  ebt_snat
 *
 *  Authors:
 *  Bart De Schuymer <[email protected]>
 *
 *  June, 2002
 *
 */
#include <linux/module.h>
#include <net/sock.h>
#include <linux/if_arp.h>
#include <net/arp.h>
#include <linux/netfilter.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_bridge/ebt_nat.h>

static unsigned int
ebt_snat_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
    const struct ebt_nat_info *info = par->targinfo;

    if (!skb_make_writable(skb, 0))
        return EBT_DROP;

    memcpy(eth_hdr(skb)->h_source, info->mac, ETH_ALEN);
    if (!(info->target & NAT_ARP_BIT) &&
        eth_hdr(skb)->h_proto == htons(ETH_P_ARP)) {
        const struct arphdr *ap;
        struct arphdr _ah;

        ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
        if (ap == NULL)
            return EBT_DROP;
        if (ap->ar_hln != ETH_ALEN)
            goto out;
        if (skb_store_bits(skb, sizeof(_ah), info->mac,ETH_ALEN))
            return EBT_DROP;
    }
out:
    return info->target | ~EBT_VERDICT_BITS;
}

static int ebt_snat_tg_check(const struct xt_tgchk_param *par)
{
    const struct ebt_nat_info *info = par->targinfo;
    int tmp;

    tmp = info->target | ~EBT_VERDICT_BITS;
    if (BASE_CHAIN && tmp == EBT_RETURN)
        return -EINVAL;

    if (tmp < -NUM_STANDARD_TARGETS || tmp >= 0)
        return -EINVAL;
    tmp = info->target | EBT_VERDICT_BITS;
    if ((tmp & ~NAT_ARP_BIT) != ~NAT_ARP_BIT)
        return -EINVAL;
    return 0;
}

static struct xt_target ebt_snat_tg_reg __read_mostly = {
    .name       = "snat",
    .revision   = 0,
    .family     = NFPROTO_BRIDGE,
    .table      = "nat",
    .hooks      = (1 << NF_BR_NUMHOOKS) | (1 << NF_BR_POST_ROUTING),
    .target     = ebt_snat_tg,
    .checkentry = ebt_snat_tg_check,
    .targetsize = sizeof(struct ebt_nat_info),
    .me     = THIS_MODULE,
};

static int __init ebt_snat_init(void)
{
    return xt_register_target(&ebt_snat_tg_reg);
}

static void __exit ebt_snat_fini(void)
{
    xt_unregister_target(&ebt_snat_tg_reg);
}

module_init(ebt_snat_init);
module_exit(ebt_snat_fini);
MODULE_DESCRIPTION("Ebtables: Source MAC address translation");
MODULE_LICENSE("GPL");