net/netfilter/xt_HL.c

   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
  23 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  24 MODULE_AUTHOR("Maciej Soltysiak <solt@dns.toxicfilms.tv>");
  25 MODULE_DESCRIPTION("Xtables: Hoplimit/TTL Limit field modification target");
  26 MODULE_LICENSE("GPL");
  27
  28 static unsigned int
  29 ttl_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
  68 static unsigned int
  69 hl_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
 104 static 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
 117 static 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
 133 static 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
 156 static int __init hl_tg_init(void)
 157 {
 158         return xt_register_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
 159 }
 160
 161 static void __exit hl_tg_exit(void)
 162 {
 163         xt_unregister_targets(hl_tg_reg, ARRAY_SIZE(hl_tg_reg));
 164 }
 165
 166 module_init(hl_tg_init);
 167 module_exit(hl_tg_exit);
 168 MODULE_ALIAS("ipt_TTL");
 169 MODULE_ALIAS("ip6t_HL");