net/netfilter/xt_helper.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* iptables module to match on related connections */
   3 /*
   4  * (C) 2001 Martin Josefsson <gandalf@wlug.westbo.se>
   5  */
   6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   7 #include <linux/module.h>
   8 #include <linux/skbuff.h>
   9 #include <linux/netfilter.h>
  10 #include <net/netfilter/nf_conntrack.h>
  11 #include <net/netfilter/nf_conntrack_core.h>
  12 #include <net/netfilter/nf_conntrack_helper.h>
  13 #include <linux/netfilter/x_tables.h>
  14 #include <linux/netfilter/xt_helper.h>
  15
  16 MODULE_LICENSE("GPL");
  17 MODULE_AUTHOR("Martin Josefsson <gandalf@netfilter.org>");
  18 MODULE_DESCRIPTION("Xtables: Related connection matching");
  19 MODULE_ALIAS("ipt_helper");
  20 MODULE_ALIAS("ip6t_helper");
  21
  22
  23 static bool
  24 helper_mt(const struct sk_buff *skb, struct xt_action_param *par)
  25 {
  26         const struct xt_helper_info *info = par->matchinfo;
  27         const struct nf_conn *ct;
  28         const struct nf_conn_help *master_help;
  29         const struct nf_conntrack_helper *helper;
  30         enum ip_conntrack_info ctinfo;
  31         bool ret = info->invert;
  32
  33         ct = nf_ct_get(skb, &ctinfo);
  34         if (!ct || !ct->master)
  35                 return ret;
  36
  37         master_help = nfct_help(ct->master);
  38         if (!master_help)
  39                 return ret;
  40
  41         /* rcu_read_lock()ed by nf_hook_thresh */
  42         helper = rcu_dereference(master_help->helper);
  43         if (!helper)
  44                 return ret;
  45
  46         if (info->name[0] == '\0')
  47                 ret = !ret;
  48         else
  49                 ret ^= !strncmp(helper->name, info->name,
  50                                 strlen(helper->name));
  51         return ret;
  52 }
  53
  54 static int helper_mt_check(const struct xt_mtchk_param *par)
  55 {
  56         struct xt_helper_info *info = par->matchinfo;
  57         int ret;
  58
  59         ret = nf_ct_netns_get(par->net, par->family);
  60         if (ret < 0) {
  61                 pr_info_ratelimited("cannot load conntrack support for proto=%u\n",
  62                                     par->family);
  63                 return ret;
  64         }
  65         info->name[sizeof(info->name) - 1] = '\0';
  66         return 0;
  67 }
  68
  69 static void helper_mt_destroy(const struct xt_mtdtor_param *par)
  70 {
  71         nf_ct_netns_put(par->net, par->family);
  72 }
  73
  74 static struct xt_match helper_mt_reg __read_mostly = {
  75         .name       = "helper",
  76         .revision   = 0,
  77         .family     = NFPROTO_UNSPEC,
  78         .checkentry = helper_mt_check,
  79         .match      = helper_mt,
  80         .destroy    = helper_mt_destroy,
  81         .matchsize  = sizeof(struct xt_helper_info),
  82         .me         = THIS_MODULE,
  83 };
  84
  85 static int __init helper_mt_init(void)
  86 {
  87         return xt_register_match(&helper_mt_reg);
  88 }
  89
  90 static void __exit helper_mt_exit(void)
  91 {
  92         xt_unregister_match(&helper_mt_reg);
  93 }
  94
  95 module_init(helper_mt_init);
  96 module_exit(helper_mt_exit);