net/netfilter/xt_length.c

   1 /* Kernel module to match packet length. */
   2 /* (C) 1999-2001 James Morris <jmorros@intercode.com.au>
   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 #include <linux/module.h>
  10 #include <linux/skbuff.h>
  11 #include <linux/ipv6.h>
  12 #include <net/ip.h>
  13
  14 #include <linux/netfilter/xt_length.h>
  15 #include <linux/netfilter/x_tables.h>
  16
  17 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
  18 MODULE_DESCRIPTION("Xtables: Packet length (Layer3,4,5) match");
  19 MODULE_LICENSE("GPL");
  20 MODULE_ALIAS("ipt_length");
  21 MODULE_ALIAS("ip6t_length");
  22
  23 static bool
  24 length_mt(const struct sk_buff *skb, struct xt_action_param *par)
  25 {
  26         const struct xt_length_info *info = par->matchinfo;
  27         u_int16_t pktlen = ntohs(ip_hdr(skb)->tot_len);
  28
  29         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  30 }
  31
  32 static bool
  33 length_mt6(const struct sk_buff *skb, struct xt_action_param *par)
  34 {
  35         const struct xt_length_info *info = par->matchinfo;
  36         const u_int16_t pktlen = ntohs(ipv6_hdr(skb)->payload_len) +
  37                                  sizeof(struct ipv6hdr);
  38
  39         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  40 }
  41
  42 static struct xt_match length_mt_reg[] __read_mostly = {
  43         {
  44                 .name           = "length",
  45                 .family         = NFPROTO_IPV4,
  46                 .match          = length_mt,
  47                 .matchsize      = sizeof(struct xt_length_info),
  48                 .me             = THIS_MODULE,
  49         },
  50         {
  51                 .name           = "length",
  52                 .family         = NFPROTO_IPV6,
  53                 .match          = length_mt6,
  54                 .matchsize      = sizeof(struct xt_length_info),
  55                 .me             = THIS_MODULE,
  56         },
  57 };
  58
  59 static int __init length_mt_init(void)
  60 {
  61         return xt_register_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));
  62 }
  63
  64 static void __exit length_mt_exit(void)
  65 {
  66         xt_unregister_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));
  67 }
  68
  69 module_init(length_mt_init);
  70 module_exit(length_mt_exit);