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 xt_length_match[] = {
  56         {
  57                 .name           = "length",
  58                 .family         = AF_INET,
  59                 .match          = match,
  60                 .matchsize      = sizeof(struct xt_length_info),
  61                 .me             = THIS_MODULE,
  62         },
  63         {
  64                 .name           = "length",
  65                 .family         = AF_INET6,
  66                 .match          = match6,
  67                 .matchsize      = sizeof(struct xt_length_info),
  68                 .me             = THIS_MODULE,
  69         },
  70 };
  71
  72 static int __init xt_length_init(void)
  73 {
  74         return xt_register_matches(xt_length_match,
  75                                    ARRAY_SIZE(xt_length_match));
  76 }
  77
  78 static void __exit xt_length_fini(void)
  79 {
  80         xt_unregister_matches(xt_length_match, ARRAY_SIZE(xt_length_match));
  81 }
  82
  83 module_init(xt_length_init);
  84 module_exit(xt_length_fini);