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 bool
  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       bool *hotdrop)
  32 {
  33         const struct xt_length_info *info = matchinfo;
  34         u_int16_t pktlen = ntohs(ip_hdr(skb)->tot_len);
  35
  36         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  37 }
  38
  39 static bool
  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        bool *hotdrop)
  48 {
  49         const struct xt_length_info *info = matchinfo;
  50         const u_int16_t pktlen = ntohs(ipv6_hdr(skb)->payload_len) +
  51                                  sizeof(struct ipv6hdr);
  52
  53         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  54 }
  55
  56 static struct xt_match xt_length_match[] = {
  57         {
  58                 .name           = "length",
  59                 .family         = AF_INET,
  60                 .match          = match,
  61                 .matchsize      = sizeof(struct xt_length_info),
  62                 .me             = THIS_MODULE,
  63         },
  64         {
  65                 .name           = "length",
  66                 .family         = AF_INET6,
  67                 .match          = match6,
  68                 .matchsize      = sizeof(struct xt_length_info),
  69                 .me             = THIS_MODULE,
  70         },
  71 };
  72
  73 static int __init xt_length_init(void)
  74 {
  75         return xt_register_matches(xt_length_match,
  76                                    ARRAY_SIZE(xt_length_match));
  77 }
  78
  79 static void __exit xt_length_fini(void)
  80 {
  81         xt_unregister_matches(xt_length_match, ARRAY_SIZE(xt_length_match));
  82 }
  83
  84 module_init(xt_length_init);
  85 module_exit(xt_length_fini);