git.oblomov.eu Git - linux-2.6/blob - net/ipv4/netfilter/ipt_TTL.c

   1 /* TTL modification target for IP tables
   2  * (C) 2000,2005 by Harald Welte <laforge@netfilter.org>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  *
   8  */
   9
  10 #include <linux/module.h>
  11 #include <linux/skbuff.h>
  12 #include <linux/ip.h>
  13 #include <net/checksum.h>
  14
  15 #include <linux/netfilter_ipv4/ip_tables.h>
  16 #include <linux/netfilter_ipv4/ipt_TTL.h>
  17
  18 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  19 MODULE_DESCRIPTION("IP tables TTL modification module");
  20 MODULE_LICENSE("GPL");
  21
  22 static unsigned int
  23 ipt_ttl_target(struct sk_buff **pskb,
  24                const struct net_device *in, const struct net_device *out,
  25                unsigned int hooknum, const struct xt_target *target,
  26                const void *targinfo, void *userinfo)
  27 {
  28         struct iphdr *iph;
  29         const struct ipt_TTL_info *info = targinfo;
  30         u_int16_t diffs[2];
  31         int new_ttl;
  32
  33         if (!skb_make_writable(pskb, (*pskb)->len))
  34                 return NF_DROP;
  35
  36         iph = (*pskb)->nh.iph;
  37
  38         switch (info->mode) {
  39                 case IPT_TTL_SET:
  40                         new_ttl = info->ttl;
  41                         break;
  42                 case IPT_TTL_INC:
  43                         new_ttl = iph->ttl + info->ttl;
  44                         if (new_ttl > 255)
  45                                 new_ttl = 255;
  46                         break;
  47                 case IPT_TTL_DEC:
  48                         new_ttl = iph->ttl - info->ttl;
  49                         if (new_ttl < 0)
  50                                 new_ttl = 0;
  51                         break;
  52                 default:
  53                         new_ttl = iph->ttl;
  54                         break;
  55         }
  56
  57         if (new_ttl != iph->ttl) {
  58                 diffs[0] = htons(((unsigned)iph->ttl) << 8) ^ 0xFFFF;
  59                 iph->ttl = new_ttl;
  60                 diffs[1] = htons(((unsigned)iph->ttl) << 8);
  61                 iph->check = csum_fold(csum_partial((char *)diffs,
  62                                                     sizeof(diffs),
  63                                                     iph->check^0xFFFF));
  64         }
  65
  66         return IPT_CONTINUE;
  67 }
  68
  69 static int ipt_ttl_checkentry(const char *tablename,
  70                 const void *e,
  71                 const struct xt_target *target,
  72                 void *targinfo,
  73                 unsigned int targinfosize,
  74                 unsigned int hook_mask)
  75 {
  76         struct ipt_TTL_info *info = targinfo;
  77
  78         if (info->mode > IPT_TTL_MAXMODE) {
  79                 printk(KERN_WARNING "ipt_TTL: invalid or unknown Mode %u\n",
  80                         info->mode);
  81                 return 0;
  82         }
  83         if ((info->mode != IPT_TTL_SET) && (info->ttl == 0))
  84                 return 0;
  85         return 1;
  86 }
  87
  88 static struct ipt_target ipt_TTL = {
  89         .name           = "TTL",
  90         .target         = ipt_ttl_target,
  91         .targetsize     = sizeof(struct ipt_TTL_info),
  92         .table          = "mangle",
  93         .checkentry     = ipt_ttl_checkentry,
  94         .me             = THIS_MODULE,
  95 };
  96
  97 static int __init ipt_ttl_init(void)
  98 {
  99         return ipt_register_target(&ipt_TTL);
 100 }
 101
 102 static void __exit ipt_ttl_fini(void)
 103 {
 104         ipt_unregister_target(&ipt_TTL);
 105 }
 106
 107 module_init(ipt_ttl_init);
 108 module_exit(ipt_ttl_fini);