linux/net/netfilter/xt_HL.c
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   1/*
   2 * TTL modification target for IP tables
   3 * (C) 2000,2005 by Harald Welte <laforge@netfilter.org>
   4 *
   5 * Hop Limit modification target for ip6tables
   6 * Maciej Soltysiak <solt@dns.toxicfilms.tv>
   7 *
   8 * This program is free software; you can redistribute it and/or modify
   9 * it under the terms of the GNU General Public License version 2 as
  10 * published by the Free Software Foundation.
  11 */
  12#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  13#include <linux/module.h>
  14#include <linux/skbuff.h>
  15#include <linux/ip.h>
  16#include <linux/ipv6.h>
  17#include <net/checksum.h>
  18
  19#include <linux/netfilter/x_tables.h>
  20#include <linux/netfilter_ipv4/ipt_TTL.h>
  21#include <linux/netfilter_ipv6/ip6t_HL.h>
  22
  23MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  24MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
  25MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target");
  26MODULE_LICENSE("GPL");
  27
  28static unsigned int
  29ttl_tg(struct sk_buff *skb, const struct xt_action_param *par)
  30{
  31        struct iphdr *iph;
  32        const struct ipt_TTL_info *info = par->targinfo;
  33        int new_ttl;
  34
  35        if (!skb_make_writable(skb, skb->len))
  36                return NF_DROP;
  37
  38        iph = ip_hdr(skb);
  39
  40        switch (info->mode) {
  41        case IPT_TTL_SET:
  42                new_ttl = info->ttl;
  43                break;
  44        case IPT_TTL_INC:
  45                new_ttl = iph->ttl + info->ttl;
  46                if (new_ttl > 255)
  47                        new_ttl = 255;
  48                break;
  49        case IPT_TTL_DEC:
  50                new_ttl = iph->ttl - info->ttl;
  51                if (new_ttl < 0)
  52                        new_ttl = 0;
  53                break;
  54        default:
  55                new_ttl = iph->ttl;
  56                break;
  57        }
  58
  59        if (new_ttl != iph->ttl) {
  60                csum_replace2(&iph->check, htons(iph->ttl << 8),
  61                                           htons(new_ttl << 8));
  62                iph->ttl = new_ttl;
  63        }
  64
  65        return XT_CONTINUE;
  66}
  67
  68static unsigned int
  69hl_tg6(struct sk_buff *skb, const struct xt_action_param *par)
  70{
  71        struct ipv6hdr *ip6h;
  72        const struct ip6t_HL_info *info = par->targinfo;
  73        int new_hl;
  74
  75        if (!skb_make_writable(skb, skb->len))
  76                return NF_DROP;
  77
  78        ip6h = ipv6_hdr(skb);
  79
  80        switch (info->mode) {
  81        case IP6T_HL_SET:
  82                new_hl = info->hop_limit;
  83                break;
  84        case IP6T_HL_INC:
  85                new_hl = ip6h->hop_limit + info->hop_limit;
  86                if (new_hl > 255)
  87                        new_hl = 255;
  88                break;
  89        case IP6T_HL_DEC:
  90                new_hl = ip6h->hop_limit - info->hop_limit;
  91                if (new_hl < 0)
  92                        new_hl = 0;
  93                break;
  94        default:
  95                new_hl = ip6h->hop_limit;
  96                break;
  97        }
  98
  99        ip6h->hop_limit = new_hl;
 100
 101        return XT_CONTINUE;
 102}
 103
 104static int ttl_tg_check(const struct xt_tgchk_param *par)
 105{
 106        const struct ipt_TTL_info *info = par->targinfo;
 107
 108        if (info->mode > IPT_TTL_MAXMODE) {
 109                pr_info("TTL: invalid or unknown mode %u\n", info->mode);
 110                return -EINVAL;
 111        }
 112        if (info->mode != IPT_TTL_SET && info->ttl == 0)
 113                return -EINVAL;
 114        return 0;
 115}
 116
 117static int hl_tg6_check(const struct xt_tgchk_param *par)
 118{
 119        const struct ip6t_HL_info *info = par->targinfo;
 120
 121        if (info->mode > IP6T_HL_MAXMODE) {
 122                pr_info("invalid or unknown mode %u\n", info->mode);
 123                return -EINVAL;
 124        }
 125        if (info->mode != IP6T_HL_SET && info->hop_limit == 0) {
 126                pr_info("increment/decrement does not "
 127                        "make sense with value 0\n");
 128                return -EINVAL;
 129        }
 130        return 0;
 131}
 132
 133static struct xt_target hl_tg_reg[] __read_mostly = {
 134        {
 135                .name       = "TTL",
 136                .revision   = 0,
 137                .family     = NFPROTO_IPV4,
 138                .target     = ttl_tg,
 139                .targetsize = sizeof(struct ipt_TTL_info),
 140                .table      = "mangle",
 141                .checkentry = ttl_tg_check,
 142                .me         = THIS_MODULE,
 143        },
 144        {
 145                .name       = "HL",
 146                .revision   = 0,
 147                .family     = NFPROTO_IPV6,
 148                .target     = hl_tg6,
 149                .targetsize = sizeof(struct ip6t_HL_info),
 150                .table      = "mangle",
 151                .checkentry = hl_tg6_check,
 152                .me         = THIS_MODULE,
 153        },
 154};
 155
 156static int __init hl_tg_init(void)
 157{
 158        return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
 159}
 160
 161static void __exit hl_tg_exit(void)
 162{
 163        xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
 164}
 165
 166module_init(hl_tg_init);
 167module_exit(hl_tg_exit);
 168MODULE_ALIAS("ipt_TTL");
 169MODULE_ALIAS("ip6t_HL");
 170
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