linux/net/netfilter/xt_length.c
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   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
  17MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
  18MODULE_DESCRIPTION("Xtables: Packet length (Layer3,4,5) match");
  19MODULE_LICENSE("GPL");
  20MODULE_ALIAS("ipt_length");
  21MODULE_ALIAS("ip6t_length");
  22
  23static bool
  24length_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
  32static bool
  33length_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
  42static 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
  59static int __init length_mt_init(void)
  60{
  61        return xt_register_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));
  62}
  63
  64static void __exit length_mt_exit(void)
  65{
  66        xt_unregister_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));
  67}
  68
  69module_init(length_mt_init);
  70module_exit(length_mt_exit);
  71
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