xt_hl.c

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/*
 * IP tables module for matching the value of the TTL
 * (C) 2000,2001 by Harald Welte <[email protected]>
 *
 * Hop Limit matching module
 * (C) 2001-2002 Maciej Soltysiak <[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.
 */

#include <linux/ip.h>
#include <linux/ipv6.h>
#include <linux/module.h>
#include <linux/skbuff.h>

#include <linux/netfilter/x_tables.h>
#include <linux/netfilter_ipv4/ipt_ttl.h>
#include <linux/netfilter_ipv6/ip6t_hl.h>

MODULE_AUTHOR("Maciej Soltysiak <[email protected]>");
MODULE_DESCRIPTION("Xtables: Hoplimit/TTL field match");
MODULE_LICENSE("GPL");
MODULE_ALIAS("ipt_ttl");
MODULE_ALIAS("ip6t_hl");

static bool ttl_mt(const struct sk_buff *skb, struct xt_action_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;
    }

    return false;
}

static bool hl_mt6(const struct sk_buff *skb, struct xt_action_param *par)
{
    const struct ip6t_hl_info *info = par->matchinfo;
    const struct ipv6hdr *ip6h = ipv6_hdr(skb);

    switch (info->mode) {
    case IP6T_HL_EQ:
        return ip6h->hop_limit == info->hop_limit;
    case IP6T_HL_NE:
        return ip6h->hop_limit != info->hop_limit;
    case IP6T_HL_LT:
        return ip6h->hop_limit < info->hop_limit;
    case IP6T_HL_GT:
        return ip6h->hop_limit > info->hop_limit;
    }

    return false;
}

static struct xt_match hl_mt_reg[] __read_mostly = {
    {
        .name       = "ttl",
        .revision   = 0,
        .family     = NFPROTO_IPV4,
        .match      = ttl_mt,
        .matchsize  = sizeof(struct ipt_ttl_info),
        .me         = THIS_MODULE,
    },
    {
        .name       = "hl",
        .revision   = 0,
        .family     = NFPROTO_IPV6,
        .match      = hl_mt6,
        .matchsize  = sizeof(struct ip6t_hl_info),
        .me         = THIS_MODULE,
    },
};

static int __init hl_mt_init(void)
{
    return xt_register_matches(hl_mt_reg, ARRAY_SIZE(hl_mt_reg));
}

static void __exit hl_mt_exit(void)
{
    xt_unregister_matches(hl_mt_reg, ARRAY_SIZE(hl_mt_reg));
}

module_init(hl_mt_init);
module_exit(hl_mt_exit);