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("iptables helper match module");
  22 MODULE_ALIAS("ipt_helper");
  23 MODULE_ALIAS("ip6t_helper");
  24
  25 #if 0
  26 #define DEBUGP printk
  27 #else
  28 #define DEBUGP(format, args...)
  29 #endif
  30
  31 static int
  32 match(const struct sk_buff *skb,
  33       const struct net_device *in,
  34       const struct net_device *out,
  35       const struct xt_match *match,
  36       const void *matchinfo,
  37       int offset,
  38       unsigned int protoff,
  39       int *hotdrop)
  40 {
  41         const struct xt_helper_info *info = matchinfo;
  42         struct nf_conn *ct;
  43         struct nf_conn_help *master_help;
  44         enum ip_conntrack_info ctinfo;
  45         int ret = info->invert;
  46
  47         ct = nf_ct_get((struct sk_buff *)skb, &ctinfo);
  48         if (!ct) {
  49                 DEBUGP("xt_helper: Eek! invalid conntrack?\n");
  50                 return ret;
  51         }
  52
  53         if (!ct->master) {
  54                 DEBUGP("xt_helper: conntrack %p has no master\n", ct);
  55                 return ret;
  56         }
  57
  58         read_lock_bh(&nf_conntrack_lock);
  59         master_help = nfct_help(ct->master);
  60         if (!master_help || !master_help->helper) {
  61                 DEBUGP("xt_helper: master ct %p has no helper\n",
  62                         exp->expectant);
  63                 goto out_unlock;
  64         }
  65
  66         DEBUGP("master's name = %s , info->name = %s\n",
  67                 ct->master->helper->name, info->name);
  68
  69         if (info->name[0] == '\0')
  70                 ret ^= 1;
  71         else
  72                 ret ^= !strncmp(master_help->helper->name, info->name,
  73                                 strlen(master_help->helper->name));
  74 out_unlock:
  75         read_unlock_bh(&nf_conntrack_lock);
  76         return ret;
  77 }
  78
  79 static int check(const char *tablename,
  80                  const void *inf,
  81                  const struct xt_match *match,
  82                  void *matchinfo,
  83                  unsigned int hook_mask)
  84 {
  85         struct xt_helper_info *info = matchinfo;
  86
  87         if (nf_ct_l3proto_try_module_get(match->family) < 0) {
  88                 printk(KERN_WARNING "can't load conntrack support for "
  89                                     "proto=%d\n", match->family);
  90                 return 0;
  91         }
  92         info->name[29] = '\0';
  93         return 1;
  94 }
  95
  96 static void
  97 destroy(const struct xt_match *match, void *matchinfo)
  98 {
  99         nf_ct_l3proto_module_put(match->family);
 100 }
 101
 102 static struct xt_match xt_helper_match[] = {
 103         {
 104                 .name           = "helper",
 105                 .family         = AF_INET,
 106                 .checkentry     = check,
 107                 .match          = match,
 108                 .destroy        = destroy,
 109                 .matchsize      = sizeof(struct xt_helper_info),
 110                 .me             = THIS_MODULE,
 111         },
 112         {
 113                 .name           = "helper",
 114                 .family         = AF_INET6,
 115                 .checkentry     = check,
 116                 .match          = match,
 117                 .destroy        = destroy,
 118                 .matchsize      = sizeof(struct xt_helper_info),
 119                 .me             = THIS_MODULE,
 120         },
 121 };
 122
 123 static int __init xt_helper_init(void)
 124 {
 125         return xt_register_matches(xt_helper_match,
 126                                    ARRAY_SIZE(xt_helper_match));
 127 }
 128
 129 static void __exit xt_helper_fini(void)
 130 {
 131         xt_unregister_matches(xt_helper_match, ARRAY_SIZE(xt_helper_match));
 132 }
 133
 134 module_init(xt_helper_init);
 135 module_exit(xt_helper_fini);
 136