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("IP tables packet length matching module");
  19 MODULE_LICENSE("GPL");
  20 MODULE_ALIAS("ipt_length");
  21 MODULE_ALIAS("ip6t_length");
  22
  23 static int
  24 match(const struct sk_buff *skb,
  25       const struct net_device *in,
  26       const struct net_device *out,
  27       const struct xt_match *match,
  28       const void *matchinfo,
  29       int offset,
  30       unsigned int protoff,
  31       int *hotdrop)
  32 {
  33         const struct xt_length_info *info = matchinfo;
  34         u_int16_t pktlen = ntohs(skb->nh.iph->tot_len);
  35
  36         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  37 }
  38
  39 static int
  40 match6(const struct sk_buff *skb,
  41        const struct net_device *in,
  42        const struct net_device *out,
  43        const struct xt_match *match,
  44        const void *matchinfo,
  45        int offset,
  46        unsigned int protoff,
  47        int *hotdrop)
  48 {
  49         const struct xt_length_info *info = matchinfo;
  50         u_int16_t pktlen = ntohs(skb->nh.ipv6h->payload_len) + sizeof(struct ipv6hdr);
  51
  52         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  53 }
  54
  55 static struct xt_match length_match = {
  56         .name           = "length",
  57         .match          = match,
  58         .matchsize      = sizeof(struct xt_length_info),
  59         .me             = THIS_MODULE,
  60 };
  61
  62 static struct xt_match length6_match = {
  63         .name           = "length",
  64         .match          = match6,
  65         .matchsize      = sizeof(struct xt_length_info),
  66         .me             = THIS_MODULE,
  67 };
  68
  69 static int __init init(void)
  70 {
  71         int ret;
  72         ret = xt_register_match(AF_INET, &length_match);
  73         if (ret)
  74                 return ret;
  75         ret = xt_register_match(AF_INET6, &length6_match);
  76         if (ret)
  77                 xt_unregister_match(AF_INET, &length_match);
  78
  79         return ret;
  80 }
  81
  82 static void __exit fini(void)
  83 {
  84         xt_unregister_match(AF_INET, &length_match);
  85         xt_unregister_match(AF_INET6, &length6_match);
  86 }
  87
  88 module_init(init);
  89 module_exit(fini);