net/netfilter/xt_helper.c

   1 /* iptables module to match on related connections */
   2 /*
   3  * (C) 2001 Martin Josefsson <gandalf@wlug.westbo.se>
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License version 2 as
   7  * published by the Free Software Foundation.
   8  */
   9
  10 #include <linux/module.h>
  11 #include <linux/skbuff.h>
  12 #include <linux/netfilter.h>
  13 #include <net/netfilter/nf_conntrack.h>
  14 #include <net/netfilter/nf_conntrack_core.h>
  15 #include <net/netfilter/nf_conntrack_helper.h>
  16 #include <linux/netfilter/x_tables.h>
  17 #include <linux/netfilter/xt_helper.h>
  18
  19 MODULE_LICENSE("GPL");
  20 MODULE_AUTHOR("Martin Josefsson <gandalf@netfilter.org>");
  21 MODULE_DESCRIPTION("Xtables: Related connection matching");
  22 MODULE_ALIAS("ipt_helper");
  23 MODULE_ALIAS("ip6t_helper");
  24
  25
  26 static bool
  27 helper_mt(const struct sk_buff *skb, const struct net_device *in,
  28           const struct net_device *out, const struct xt_match *match,
  29           const void *matchinfo, int offset, unsigned int protoff,
  30           bool *hotdrop)
  31 {
  32         const struct xt_helper_info *info = matchinfo;
  33         const struct nf_conn *ct;
  34         const struct nf_conn_help *master_help;
  35         const struct nf_conntrack_helper *helper;
  36         enum ip_conntrack_info ctinfo;
  37         bool ret = info->invert;
  38
  39         ct = nf_ct_get(skb, &ctinfo);
  40         if (!ct || !ct->master)
  41                 return ret;
  42
  43         master_help = nfct_help(ct->master);
  44         if (!master_help)
  45                 return ret;
  46
  47         /* rcu_read_lock()ed by nf_hook_slow */
  48         helper = rcu_dereference(master_help->helper);
  49         if (!helper)
  50                 return ret;
  51
  52         if (info->name[0] == '\0')
  53                 ret = !ret;
  54         else
  55                 ret ^= !strncmp(helper->name, info->name,
  56                                 strlen(helper->name));
  57         return ret;
  58 }
  59
  60 static bool
  61 helper_mt_check(const char *tablename, const void *inf,
  62                 const struct xt_match *match, void *matchinfo,
  63                 unsigned int hook_mask)
  64 {
  65         struct xt_helper_info *info = matchinfo;
  66
  67         if (nf_ct_l3proto_try_module_get(match->family) < 0) {
  68                 printk(KERN_WARNING "can't load conntrack support for "
  69                                     "proto=%u\n", match->family);
  70                 return false;
  71         }
  72         info->name[29] = '\0';
  73         return true;
  74 }
  75
  76 static void helper_mt_destroy(const struct xt_match *match, void *matchinfo)
  77 {
  78         nf_ct_l3proto_module_put(match->family);
  79 }
  80
  81 static struct xt_match helper_mt_reg[] __read_mostly = {
  82         {
  83                 .name           = "helper",
  84                 .family         = AF_INET,
  85                 .checkentry     = helper_mt_check,
  86                 .match          = helper_mt,
  87                 .destroy        = helper_mt_destroy,
  88                 .matchsize      = sizeof(struct xt_helper_info),
  89                 .me             = THIS_MODULE,
  90         },
  91         {
  92                 .name           = "helper",
  93                 .family         = AF_INET6,
  94                 .checkentry     = helper_mt_check,
  95                 .match          = helper_mt,
  96                 .destroy        = helper_mt_destroy,
  97                 .matchsize      = sizeof(struct xt_helper_info),
  98                 .me             = THIS_MODULE,
  99         },
 100 };
 101
 102 static int __init helper_mt_init(void)
 103 {
 104         return xt_register_matches(helper_mt_reg, ARRAY_SIZE(helper_mt_reg));
 105 }
 106
 107 static void __exit helper_mt_exit(void)
 108 {
 109         xt_unregister_matches(helper_mt_reg, ARRAY_SIZE(helper_mt_reg));
 110 }
 111
 112 module_init(helper_mt_init);
 113 module_exit(helper_mt_exit);