net/netfilter/xt_length.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* Kernel module to match packet length. */
   3 /* (C) 1999-2001 James Morris <jmorros@intercode.com.au>
   4  */
   5
   6 #include <linux/module.h>
   7 #include <linux/skbuff.h>
   8 #include <linux/ipv6.h>
   9 #include <net/ip.h>
  10
  11 #include <linux/netfilter/xt_length.h>
  12 #include <linux/netfilter/x_tables.h>
  13
  14 MODULE_AUTHOR("James Morris <jmorris@intercode.com.au>");
  15 MODULE_DESCRIPTION("Xtables: Packet length (Layer3,4,5) match");
  16 MODULE_LICENSE("GPL");
  17 MODULE_ALIAS("ipt_length");
  18 MODULE_ALIAS("ip6t_length");
  19
  20 static bool
  21 length_mt(const struct sk_buff *skb, struct xt_action_param *par)
  22 {
  23         const struct xt_length_info *info = par->matchinfo;
  24         u_int16_t pktlen = ntohs(ip_hdr(skb)->tot_len);
  25
  26         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  27 }
  28
  29 static bool
  30 length_mt6(const struct sk_buff *skb, struct xt_action_param *par)
  31 {
  32         const struct xt_length_info *info = par->matchinfo;
  33         const u_int16_t pktlen = ntohs(ipv6_hdr(skb)->payload_len) +
  34                                  sizeof(struct ipv6hdr);
  35
  36         return (pktlen >= info->min && pktlen <= info->max) ^ info->invert;
  37 }
  38
  39 static struct xt_match length_mt_reg[] __read_mostly = {
  40         {
  41                 .name           = "length",
  42                 .family         = NFPROTO_IPV4,
  43                 .match          = length_mt,
  44                 .matchsize      = sizeof(struct xt_length_info),
  45                 .me             = THIS_MODULE,
  46         },
  47         {
  48                 .name           = "length",
  49                 .family         = NFPROTO_IPV6,
  50                 .match          = length_mt6,
  51                 .matchsize      = sizeof(struct xt_length_info),
  52                 .me             = THIS_MODULE,
  53         },
  54 };
  55
  56 static int __init length_mt_init(void)
  57 {
  58         return xt_register_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));
  59 }
  60
  61 static void __exit length_mt_exit(void)
  62 {
  63         xt_unregister_matches(length_mt_reg, ARRAY_SIZE(length_mt_reg));
  64 }
  65
  66 module_init(length_mt_init);
  67 module_exit(length_mt_exit);