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
  41         /* Reply comes from server. */
  42         newaddr = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3;
  43
  44         exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  45         exp->dir = IP_CT_DIR_REPLY;
  46         exp->expectfn = nf_nat_follow_master;
  47
  48         /* Try to get same port: if not, try to change it. */
  49         for (port = ntohs(exp->saved_proto.tcp.port); port != 0; port++) {
  50                 int ret;
  51
  52                 exp->tuple.dst.u.tcp.port = htons(port);
  53                 ret = nf_ct_expect_related(exp);
  54                 if (ret == 0)
  55                         break;
  56                 else if (ret != -EBUSY) {
  57                         port = 0;
  58                         break;
  59                 }
  60         }
  61
  62         if (port == 0) {
  63                 nf_ct_helper_log(skb, ct, "all ports in use");
  64                 return NF_DROP;
  65         }
  66
  67         /* strlen("\1DCC CHAT chat AAAAAAAA P\1\n")=27
  68          * strlen("\1DCC SCHAT chat AAAAAAAA P\1\n")=28
  69          * strlen("\1DCC SEND F AAAAAAAA P S\1\n")=26
  70          * strlen("\1DCC MOVE F AAAAAAAA P S\1\n")=26
  71          * strlen("\1DCC TSEND F AAAAAAAA P S\1\n")=27
  72          *
  73          * AAAAAAAAA: bound addr (1.0.0.0==16777216, min 8 digits,
  74          *                        255.255.255.255==4294967296, 10 digits)
  75          * P:         bound port (min 1 d, max 5d (65635))
  76          * F:         filename   (min 1 d )
  77          * S:         size       (min 1 d )
  78          * 0x01, \n:  terminators
  79          */
  80         /* AAA = "us", ie. where server normally talks to. */
  81         snprintf(buffer, sizeof(buffer), "%u %u", ntohl(newaddr.ip), port);
  82         pr_debug("nf_nat_irc: inserting '%s' == %pI4, port %u\n",
  83                  buffer, &newaddr.ip, port);
  84
  85         if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
  86                                       matchlen, buffer, strlen(buffer))) {
  87                 nf_ct_helper_log(skb, ct, "cannot mangle packet");
  88                 nf_ct_unexpect_related(exp);
  89                 return NF_DROP;
  90         }
  91
  92         return NF_ACCEPT;
  93 }
  94
  95 static void __exit nf_nat_irc_fini(void)
  96 {
  97         RCU_INIT_POINTER(nf_nat_irc_hook, NULL);
  98         synchronize_rcu();
  99 }
 100
 101 static int __init nf_nat_irc_init(void)
 102 {
 103         BUG_ON(nf_nat_irc_hook != NULL);
 104         RCU_INIT_POINTER(nf_nat_irc_hook, help);
 105         return 0;
 106 }
 107
 108 /* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
 109 static int warn_set(const char *val, struct kernel_param *kp)
 110 {
 111         printk(KERN_INFO KBUILD_MODNAME
 112                ": kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
 113         return 0;
 114 }
 115 module_param_call(ports, warn_set, NULL, NULL, 0);
 116
 117 module_init(nf_nat_irc_init);
 118 module_exit(nf_nat_irc_fini);