net/netfilter/nf_nat_irc.c

   1 /* IRC extension for TCP NAT alteration.
   2  *
   3  * (C) 2000-2001 by Harald Welte <laforge@gnumonks.org>
   4  * (C) 2004 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
   5  * based on a copy of RR's ip_nat_ftp.c
   6  *
   7  * This program is free software; you can redistribute it and/or
   8  * modify it under the terms of the GNU General Public License
   9  * as published by the Free Software Foundation; either version
  10  * 2 of the License, or (at your option) any later version.
  11  */
  12
  13 #include <linux/module.h>
  14 #include <linux/moduleparam.h>
  15 #include <linux/tcp.h>
  16 #include <linux/kernel.h>
  17
  18 #include <net/netfilter/nf_nat.h>
  19 #include <net/netfilter/nf_nat_helper.h>
  20 #include <net/netfilter/nf_conntrack_helper.h>
  21 #include <net/netfilter/nf_conntrack_expect.h>
  22 #include <linux/netfilter/nf_conntrack_irc.h>
  23
  24 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  25 MODULE_DESCRIPTION("IRC (DCC) NAT helper");
  26 MODULE_LICENSE("GPL");
  27 MODULE_ALIAS("ip_nat_irc");
  28
  29 static unsigned int help(struct sk_buff *skb,
  30                          enum ip_conntrack_info ctinfo,
  31                          unsigned int protoff,
  32                          unsigned int matchoff,
  33                          unsigned int matchlen,
  34                          struct nf_conntrack_expect *exp)
  35 {
  36         char buffer[sizeof("4294967296 65635")];
  37         struct nf_conn *ct = exp->master;
  38         union nf_inet_addr newaddr;
  39         u_int16_t port;
  40         unsigned int ret;
  41
  42         /* Reply comes from server. */
  43         newaddr = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3;
  44
  45         exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  46         exp->dir = IP_CT_DIR_REPLY;
  47         exp->expectfn = nf_nat_follow_master;
  48
  49         /* Try to get same port: if not, try to change it. */
  50         for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
  51                 int ret;
  52
  53                 exp->tuple.dst.u.tcp.port = htons(port);
  54                 ret = nf_ct_expect_related(exp);
  55                 if (ret == 0)
  56                         break;
  57                 else if (ret != -EBUSY) {
  58                         port = 0;
  59                         break;
  60                 }
  61         }
  62
  63         if (port == 0) {
  64                 nf_ct_helper_log(skb, ct, "all ports in use");
  65                 return NF_DROP;
  66         }
  67
  68         /* strlen("\1DCC CHAT chat AAAAAAAA P\1\n")=27
  69          * strlen("\1DCC SCHAT chat AAAAAAAA P\1\n")=28
  70          * strlen("\1DCC SEND F AAAAAAAA P S\1\n")=26
  71          * strlen("\1DCC MOVE F AAAAAAAA P S\1\n")=26
  72          * strlen("\1DCC TSEND F AAAAAAAA P S\1\n")=27
  73          *
  74          * AAAAAAAAA: bound addr (1.0.0.0==16777216, min 8 digits,
  75          *                        255.255.255.255==4294967296, 10 digits)
  76          * P:         bound port (min 1 d, max 5d (65635))
  77          * F:         filename   (min 1 d )
  78          * S:         size       (min 1 d )
  79          * 0x01, \n:  terminators
  80          */
  81         /* AAA = "us", ie. where server normally talks to. */
  82         snprintf(buffer, sizeof(buffer), "%u %u", ntohl(newaddr.ip), port);
  83         pr_debug("nf_nat_irc: inserting '%s' == %pI4, port %u\n",
  84                  buffer, &newaddr.ip, port);
  85
  86         ret = nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
  87                                        matchlen, buffer, strlen(buffer));
  88         if (ret != NF_ACCEPT) {
  89                 nf_ct_helper_log(skb, ct, "cannot mangle packet");
  90                 nf_ct_unexpect_related(exp);
  91         }
  92
  93         return ret;
  94 }
  95
  96 static void __exit nf_nat_irc_fini(void)
  97 {
  98         RCU_INIT_POINTER(nf_nat_irc_hook, NULL);
  99         synchronize_rcu();
 100 }
 101
 102 static int __init nf_nat_irc_init(void)
 103 {
 104         BUG_ON(nf_nat_irc_hook != NULL);
 105         RCU_INIT_POINTER(nf_nat_irc_hook, help);
 106         return 0;
 107 }
 108
 109 /* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
 110 static int warn_set(const char *val, struct kernel_param *kp)
 111 {
 112         printk(KERN_INFO KBUILD_MODNAME
 113                ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
 114         return 0;
 115 }
 116 module_param_call(ports, warn_set, NULL, NULL, 0);
 117
 118 module_init(nf_nat_irc_init);
 119 module_exit(nf_nat_irc_fini);