ebt_arpreply.c

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/*
 *  ebt_arpreply
 *
 *  Authors:
 *  Grzegorz Borowiak <[email protected]>
 *  Bart De Schuymer <[email protected]>
 *
 *  August, 2003
 *
 */
#include <linux/if_arp.h>
#include <net/arp.h>
#include <linux/module.h>
#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_bridge/ebtables.h>
#include <linux/netfilter_bridge/ebt_arpreply.h>

static unsigned int
ebt_arpreply_tg(struct sk_buff *skb, const struct xt_action_param *par)
{
    const struct ebt_arpreply_info *info = par->targinfo;
    const __be32 *siptr, *diptr;
    __be32 _sip, _dip;
    const struct arphdr *ap;
    struct arphdr _ah;
    const unsigned char *shp;
    unsigned char _sha[ETH_ALEN];

    ap = skb_header_pointer(skb, 0, sizeof(_ah), &_ah);
    if (ap == NULL)
        return EBT_DROP;

    if (ap->ar_op != htons(ARPOP_REQUEST) ||
        ap->ar_hln != ETH_ALEN ||
        ap->ar_pro != htons(ETH_P_IP) ||
        ap->ar_pln != 4)
        return EBT_CONTINUE;

    shp = skb_header_pointer(skb, sizeof(_ah), ETH_ALEN, &_sha);
    if (shp == NULL)
        return EBT_DROP;

    siptr = skb_header_pointer(skb, sizeof(_ah) + ETH_ALEN,
                   sizeof(_sip), &_sip);
    if (siptr == NULL)
        return EBT_DROP;

    diptr = skb_header_pointer(skb,
                   sizeof(_ah) + 2 * ETH_ALEN + sizeof(_sip),
                   sizeof(_dip), &_dip);
    if (diptr == NULL)
        return EBT_DROP;

    arp_send(ARPOP_REPLY, ETH_P_ARP, *siptr, (struct net_device *)par->in,
         *diptr, shp, info->mac, shp);

    return info->target;
}

static int ebt_arpreply_tg_check(const struct xt_tgchk_param *par)
{
    const struct ebt_arpreply_info *info = par->targinfo;
    const struct ebt_entry *e = par->entryinfo;

    if (BASE_CHAIN && info->target == EBT_RETURN)
        return -EINVAL;
    if (e->ethproto != htons(ETH_P_ARP) ||
        e->invflags & EBT_IPROTO)
        return -EINVAL;
    return 0;
}

static struct xt_target ebt_arpreply_tg_reg __read_mostly = {
    .name       = "arpreply",
    .revision   = 0,
    .family     = NFPROTO_BRIDGE,
    .table      = "nat",
    .hooks      = (1 << NF_BR_NUMHOOKS) | (1 << NF_BR_PRE_ROUTING),
    .target     = ebt_arpreply_tg,
    .checkentry = ebt_arpreply_tg_check,
    .targetsize = sizeof(struct ebt_arpreply_info),
    .me     = THIS_MODULE,
};

static int __init ebt_arpreply_init(void)
{
    return xt_register_target(&ebt_arpreply_tg_reg);
}

static void __exit ebt_arpreply_fini(void)
{
    xt_unregister_target(&ebt_arpreply_tg_reg);
}

module_init(ebt_arpreply_init);
module_exit(ebt_arpreply_fini);
MODULE_DESCRIPTION("Ebtables: ARP reply target");
MODULE_LICENSE("GPL");