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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  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, struct xt_action_param *par)
  28 {
  29         const struct xt_helper_info *info = par->matchinfo;
  30         const struct nf_conn *ct;
  31         const struct nf_conn_help *master_help;
  32         const struct nf_conntrack_helper *helper;
  33         enum ip_conntrack_info ctinfo;
  34         bool ret = info->invert;
  35
  36         ct = nf_ct_get(skb, &ctinfo);
  37         if (!ct || !ct->master)
  38                 return ret;
  39
  40         master_help = nfct_help(ct->master);
  41         if (!master_help)
  42                 return ret;
  43
  44         /* rcu_read_lock()ed by nf_hook_thresh */
  45         helper = rcu_dereference(master_help->helper);
  46         if (!helper)
  47                 return ret;
  48
  49         if (info->name[0] == '\0')
  50                 ret = !ret;
  51         else
  52                 ret ^= !strncmp(helper->name, info->name,
  53                                 strlen(helper->name));
  54         return ret;
  55 }
  56
  57 static int helper_mt_check(const struct xt_mtchk_param *par)
  58 {
  59         struct xt_helper_info *info = par->matchinfo;
  60         int ret;
  61
  62         ret = nf_ct_l3proto_try_module_get(par->family);
  63         if (ret < 0) {
  64                 pr_info("cannot load conntrack support for proto=%u\n",
  65                         par->family);
  66                 return ret;
  67         }
  68         info->name[sizeof(info->name) - 1] = '\0';
  69         return 0;
  70 }
  71
  72 static void helper_mt_destroy(const struct xt_mtdtor_param *par)
  73 {
  74         nf_ct_l3proto_module_put(par->family);
  75 }
  76
  77 static struct xt_match helper_mt_reg __read_mostly = {
  78         .name       = "helper",
  79         .revision   = 0,
  80         .family     = NFPROTO_UNSPEC,
  81         .checkentry = helper_mt_check,
  82         .match      = helper_mt,
  83         .destroy    = helper_mt_destroy,
  84         .matchsize  = sizeof(struct xt_helper_info),
  85         .me         = THIS_MODULE,
  86 };
  87
  88 static int __init helper_mt_init(void)
  89 {
  90         return xt_register_match(&helper_mt_reg);
  91 }
  92
  93 static void __exit helper_mt_exit(void)
  94 {
  95         xt_unregister_match(&helper_mt_reg);
  96 }
  97
  98 module_init(helper_mt_init);
  99 module_exit(helper_mt_exit);