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
  22 ttl_mt(const struct sk_buff *skb, const struct net_device *in,
  23        const struct net_device *out, const struct xt_match *match,
  24        const void *matchinfo, int offset, unsigned int protoff, bool *hotdrop)
  25 {
  26         const struct ipt_ttl_info *info = matchinfo;
  27         const u8 ttl = ip_hdr(skb)->ttl;
  28
  29         switch (info->mode) {
  30                 case IPT_TTL_EQ:
  31                         return ttl == info->ttl;
  32                 case IPT_TTL_NE:
  33                         return ttl != info->ttl;
  34                 case IPT_TTL_LT:
  35                         return ttl < info->ttl;
  36                 case IPT_TTL_GT:
  37                         return ttl > info->ttl;
  38                 default:
  39                         printk(KERN_WARNING "ipt_ttl: unknown mode %d\n",
  40                                 info->mode);
  41                         return false;
  42         }
  43
  44         return false;
  45 }
  46
  47 static struct xt_match ttl_mt_reg __read_mostly = {
  48         .name           = "ttl",
  49         .family         = AF_INET,
  50         .match          = ttl_mt,
  51         .matchsize      = sizeof(struct ipt_ttl_info),
  52         .me             = THIS_MODULE,
  53 };
  54
  55 static int __init ttl_mt_init(void)
  56 {
  57         return xt_register_match(&ttl_mt_reg);
  58 }
  59
  60 static void __exit ttl_mt_exit(void)
  61 {
  62         xt_unregister_match(&ttl_mt_reg);
  63 }
  64
  65 module_init(ttl_mt_init);
  66 module_exit(ttl_mt_exit);