root/net/ipv4/netfilter/ipt_ttl.c

DEFINITIONS

1. ttl_mt
2. ttl_mt_init
3. ttl_mt_exit

/* IP tables module for matching the value of the TTL
 *
 * (C) 2000,2001 by Harald Welte <laforge@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/ip.h>
#include <linux/module.h>
#include <linux/skbuff.h>

#include <linux/netfilter_ipv4/ipt_ttl.h>
#include <linux/netfilter/x_tables.h>

MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
MODULE_DESCRIPTION("Xtables: IPv4 TTL field match");
MODULE_LICENSE("GPL");

static bool ttl_mt(const struct sk_buff *skb, const struct xt_match_param *par)
{
        const struct ipt_ttl_info *info = par->matchinfo;
        const u8 ttl = ip_hdr(skb)->ttl;

        switch (info->mode) {
                case IPT_TTL_EQ:
                        return ttl == info->ttl;
                case IPT_TTL_NE:
                        return ttl != info->ttl;
                case IPT_TTL_LT:
                        return ttl < info->ttl;
                case IPT_TTL_GT:
                        return ttl > info->ttl;
                default:
                        printk(KERN_WARNING "ipt_ttl: unknown mode %d\n",
                                info->mode);
                        return false;
        }

        return false;
}

static struct xt_match ttl_mt_reg __read_mostly = {
        .name           = "ttl",
        .family         = NFPROTO_IPV4,
        .match          = ttl_mt,
        .matchsize      = sizeof(struct ipt_ttl_info),
        .me             = THIS_MODULE,
};

static int __init ttl_mt_init(void)
{
        return xt_register_match(&ttl_mt_reg);
}

static void __exit ttl_mt_exit(void)
{
        xt_unregister_match(&ttl_mt_reg);
}

module_init(ttl_mt_init);
module_exit(ttl_mt_exit);