net/ipv4/netfilter/ipt_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
  12 #include <linux/netfilter_ipv4/ipt_length.h>
  13 #include <linux/netfilter_ipv4/ip_tables.h>
  14
  15 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
  16 MODULE_DESCRIPTION("IP tables packet length matching module");
  17 MODULE_LICENSE("GPL");
  18
  19 static int
  20 match(const struct sk_buff *skb,
  21       const struct net_device *in,
  22       const struct net_device *out,
  23       const void *matchinfo,
  24       int offset,
  25       int *hotdrop)
  26 {
  27         const struct ipt_length_info *info = matchinfo;
  28         u_int16_t pktlen = ntohs(skb->nh.iph->tot_len);
  29
  30         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  31 }
  32
  33 static int
  34 checkentry(const char *tablename,
  35            const struct ipt_ip *ip,
  36            void *matchinfo,
  37            unsigned int matchsize,
  38            unsigned int hook_mask)
  39 {
  40         if (matchsize != IPT_ALIGN(sizeof(struct ipt_length_info)))
  41                 return 0;
  42
  43         return 1;
  44 }
  45
  46 static struct ipt_match length_match = {
  47         .name           = "length",
  48         .match          = &match,
  49         .checkentry     = &checkentry,
  50         .me             = THIS_MODULE,
  51 };
  52
  53 static int __init init(void)
  54 {
  55         return ipt_register_match(&length_match);
  56 }
  57
  58 static void __exit fini(void)
  59 {
  60         ipt_unregister_match(&length_match);
  61 }
  62
  63 module_init(init);
  64 module_exit(fini);