net/ipv4/netfilter/ipt_ttl.c

   1 /* IP tables module for matching the value of the TTL
   2  *
   3  * (C) 2000,2001 by Harald Welte <laforge@netfilter.org>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License version 2 as
   7  * published by the Free Software Foundation.
   8  */
   9
  10 #include <linux/ip.h>
  11 #include <linux/module.h>
  12 #include <linux/skbuff.h>
  13
  14 #include <linux/netfilter_ipv4/ipt_ttl.h>
  15 #include <linux/netfilter/x_tables.h>
  16
  17 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  18 MODULE_DESCRIPTION("Xtables: IPv4 TTL field match");
  19 MODULE_LICENSE("GPL");
  20
  21 static bool ttl_mt(const struct sk_buff *skb, const struct xt_match_param *par)
  22 {
  23         const struct ipt_ttl_info *info = par->matchinfo;
  24         const u8 ttl = ip_hdr(skb)->ttl;
  25
  26         switch (info->mode) {
  27                 case IPT_TTL_EQ:
  28                         return ttl == info->ttl;
  29                 case IPT_TTL_NE:
  30                         return ttl != info->ttl;
  31                 case IPT_TTL_LT:
  32                         return ttl < info->ttl;
  33                 case IPT_TTL_GT:
  34                         return ttl > info->ttl;
  35                 default:
  36                         printk(KERN_WARNING "ipt_ttl: unknown mode %d\n",
  37                                 info->mode);
  38                         return false;
  39         }
  40
  41         return false;
  42 }
  43
  44 static struct xt_match ttl_mt_reg __read_mostly = {
  45         .name           = "ttl",
  46         .family         = NFPROTO_IPV4,
  47         .match          = ttl_mt,
  48         .matchsize      = sizeof(struct ipt_ttl_info),
  49         .me             = THIS_MODULE,
  50 };
  51
  52 static int __init ttl_mt_init(void)
  53 {
  54         return xt_register_match(&ttl_mt_reg);
  55 }
  56
  57 static void __exit ttl_mt_exit(void)
  58 {
  59         xt_unregister_match(&ttl_mt_reg);
  60 }
  61
  62 module_init(ttl_mt_init);
  63 module_exit(ttl_mt_exit);