net/ipv4/netfilter/ipt_ttl.c

   1 /* IP tables module for matching the value of the TTL
   2  *
   3  * ipt_ttl.c,v 1.5 2000/11/13 11:16:08 laforge Exp
   4  *
   5  * (C) 2000,2001 by Harald Welte <laforge@netfilter.org>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <linux/skbuff.h>
  14
  15 #include <linux/netfilter_ipv4/ipt_ttl.h>
  16 #include <linux/netfilter_ipv4/ip_tables.h>
  17
  18 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  19 MODULE_DESCRIPTION("IP tables TTL matching module");
  20 MODULE_LICENSE("GPL");
  21
  22 static int match(const struct sk_buff *skb, const struct net_device *in,
  23                  const struct net_device *out, const void *matchinfo,
  24                  int offset, int *hotdrop)
  25 {
  26         const struct ipt_ttl_info *info = matchinfo;
  27
  28         switch (info->mode) {
  29                 case IPT_TTL_EQ:
  30                         return (skb->nh.iph->ttl == info->ttl);
  31                         break;
  32                 case IPT_TTL_NE:
  33                         return (!(skb->nh.iph->ttl == info->ttl));
  34                         break;
  35                 case IPT_TTL_LT:
  36                         return (skb->nh.iph->ttl < info->ttl);
  37                         break;
  38                 case IPT_TTL_GT:
  39                         return (skb->nh.iph->ttl > info->ttl);
  40                         break;
  41                 default:
  42                         printk(KERN_WARNING "ipt_ttl: unknown mode %d\n",
  43                                 info->mode);
  44                         return 0;
  45         }
  46
  47         return 0;
  48 }
  49
  50 static int checkentry(const char *tablename, const struct ipt_ip *ip,
  51                       void *matchinfo, unsigned int matchsize,
  52                       unsigned int hook_mask)
  53 {
  54         if (matchsize != IPT_ALIGN(sizeof(struct ipt_ttl_info)))
  55                 return 0;
  56
  57         return 1;
  58 }
  59
  60 static struct ipt_match ttl_match = {
  61         .name           = "ttl",
  62         .match          = &match,
  63         .checkentry     = &checkentry,
  64         .me             = THIS_MODULE,
  65 };
  66
  67 static int __init init(void)
  68 {
  69         return ipt_register_match(&ttl_match);
  70 }
  71
  72 static void __exit fini(void)
  73 {
  74         ipt_unregister_match(&ttl_match);
  75
  76 }
  77
  78 module_init(init);
  79 module_exit(fini);