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 void *matchinfo,
  28       int offset,
  29       unsigned int protoff,
  30       int *hotdrop)
  31 {
  32         const struct xt_length_info *info = matchinfo;
  33         u_int16_t pktlen = ntohs(skb->nh.iph->tot_len);
  34
  35         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  36 }
  37
  38 static int
  39 match6(const struct sk_buff *skb,
  40        const struct net_device *in,
  41        const struct net_device *out,
  42        const void *matchinfo,
  43        int offset,
  44        unsigned int protoff,
  45        int *hotdrop)
  46 {
  47         const struct xt_length_info *info = matchinfo;
  48         u_int16_t pktlen = ntohs(skb->nh.ipv6h->payload_len) + sizeof(struct ipv6hdr);
  49
  50         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  51 }
  52
  53 static int
  54 checkentry(const char *tablename,
  55            const void *ip,
  56            void *matchinfo,
  57            unsigned int matchsize,
  58            unsigned int hook_mask)
  59 {
  60         if (matchsize != XT_ALIGN(sizeof(struct xt_length_info)))
  61                 return 0;
  62
  63         return 1;
  64 }
  65
  66 static struct xt_match length_match = {
  67         .name           = "length",
  68         .match          = &match,
  69         .checkentry     = &checkentry,
  70         .me             = THIS_MODULE,
  71 };
  72 static struct xt_match length6_match = {
  73         .name           = "length",
  74         .match          = &match6,
  75         .checkentry     = &checkentry,
  76         .me             = THIS_MODULE,
  77 };
  78
  79 static int __init init(void)
  80 {
  81         int ret;
  82         ret = xt_register_match(AF_INET, &length_match);
  83         if (ret)
  84                 return ret;
  85         ret = xt_register_match(AF_INET6, &length6_match);
  86         if (ret)
  87                 xt_unregister_match(AF_INET, &length_match);
  88
  89         return ret;
  90 }
  91
  92 static void __exit fini(void)
  93 {
  94         xt_unregister_match(AF_INET, &length_match);
  95         xt_unregister_match(AF_INET6, &length6_match);
  96 }
  97
  98 module_init(init);
  99 module_exit(fini);