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Linux/net/netfilter/xt_helper.c

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  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_netns_get(par->net, par->family);
 63         if (ret < 0) {
 64                 pr_info_ratelimited("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_netns_put(par->net, 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);
100 

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