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, const struct net_device *in,
  25           const struct net_device *out, const struct xt_match *match,
  26           const void *matchinfo, int offset, unsigned int protoff,
  27           bool *hotdrop)
  28 {
  29         const struct xt_length_info *info = matchinfo;
  30         u_int16_t pktlen = ntohs(ip_hdr(skb)->tot_len);
  31
  32         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  33 }
  34
  35 static bool
  36 length_mt6(const struct sk_buff *skb, const struct net_device *in,
  37            const struct net_device *out, const struct xt_match *match,
  38            const void *matchinfo, int offset, unsigned int protoff,
  39            bool *hotdrop)
  40 {
  41         const struct xt_length_info *info = matchinfo;
  42         const u_int16_t pktlen = ntohs(ipv6_hdr(skb)->payload_len) +
  43                                  sizeof(struct ipv6hdr);
  44
  45         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  46 }
  47
  48 static struct xt_match length_mt_reg[] __read_mostly = {
  49         {
  50                 .name           = "length",
  51                 .family         = AF_INET,
  52                 .match          = length_mt,
  53                 .matchsize      = sizeof(struct xt_length_info),
  54                 .me             = THIS_MODULE,
  55         },
  56         {
  57                 .name           = "length",
  58                 .family         = AF_INET6,
  59                 .match          = length_mt6,
  60                 .matchsize      = sizeof(struct xt_length_info),
  61                 .me             = THIS_MODULE,
  62         },
  63 };
  64
  65 static int __init length_mt_init(void)
  66 {
  67         return xt_register_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));
  68 }
  69
  70 static void __exit length_mt_exit(void)
  71 {
  72         xt_unregister_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));
  73 }
  74
  75 module_init(length_mt_init);
  76 module_exit(length_mt_exit);