net/netfilter/nf_nat_irc.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* IRC extension for TCP NAT alteration.
   3  *
   4  * (C) 2000-2001 by Harald Welte <laforge@gnumonks.org>
   5  * (C) 2004 Rusty Russell <rusty@rustcorp.com.au> IBM Corporation
   6  * based on a copy of RR's ip_nat_ftp.c
   7  */
   8
   9 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  10
  11 #include <linux/module.h>
  12 #include <linux/moduleparam.h>
  13 #include <linux/tcp.h>
  14 #include <linux/kernel.h>
  15
  16 #include <net/netfilter/nf_nat.h>
  17 #include <net/netfilter/nf_nat_helper.h>
  18 #include <net/netfilter/nf_conntrack_helper.h>
  19 #include <net/netfilter/nf_conntrack_expect.h>
  20 #include <linux/netfilter/nf_conntrack_irc.h>
  21
  22 #define NAT_HELPER_NAME "irc"
  23
  24 MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
  25 MODULE_DESCRIPTION("IRC (DCC) NAT helper");
  26 MODULE_LICENSE("GPL");
  27 MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
  28
  29 static struct nf_conntrack_nat_helper nat_helper_irc =
  30         NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
  31
  32 static unsigned int help(struct sk_buff *skb,
  33                          enum ip_conntrack_info ctinfo,
  34                          unsigned int protoff,
  35                          unsigned int matchoff,
  36                          unsigned int matchlen,
  37                          struct nf_conntrack_expect *exp)
  38 {
  39         char buffer[sizeof("4294967296 65635")];
  40         struct nf_conn *ct = exp->master;
  41         union nf_inet_addr newaddr;
  42         u_int16_t port;
  43
  44         /* Reply comes from server. */
  45         newaddr = ct->tuplehash[IP_CT_DIR_REPLY].tuple.dst.u3;
  46
  47         exp->saved_proto.tcp.port = exp->tuple.dst.u.tcp.port;
  48         exp->dir = IP_CT_DIR_REPLY;
  49         exp->expectfn = nf_nat_follow_master;
  50
  51         port = nf_nat_exp_find_port(exp,
  52                                     ntohs(exp->saved_proto.tcp.port));
  53         if (port == 0) {
  54                 nf_ct_helper_log(skb, ct, "all ports in use");
  55                 return NF_DROP;
  56         }
  57
  58         /* strlen("\1DCC CHAT chat AAAAAAAA P\1\n")=27
  59          * strlen("\1DCC SCHAT chat AAAAAAAA P\1\n")=28
  60          * strlen("\1DCC SEND F AAAAAAAA P S\1\n")=26
  61          * strlen("\1DCC MOVE F AAAAAAAA P S\1\n")=26
  62          * strlen("\1DCC TSEND F AAAAAAAA P S\1\n")=27
  63          *
  64          * AAAAAAAAA: bound addr (1.0.0.0==16777216, min 8 digits,
  65          *                        255.255.255.255==4294967296, 10 digits)
  66          * P:         bound port (min 1 d, max 5d (65635))
  67          * F:         filename   (min 1 d )
  68          * S:         size       (min 1 d )
  69          * 0x01, \n:  terminators
  70          */
  71         /* AAA = "us", ie. where server normally talks to. */
  72         snprintf(buffer, sizeof(buffer), "%u %u", ntohl(newaddr.ip), port);
  73         pr_debug("inserting '%s' == %pI4, port %u\n",
  74                  buffer, &newaddr.ip, port);
  75
  76         if (!nf_nat_mangle_tcp_packet(skb, ct, ctinfo, protoff, matchoff,
  77                                       matchlen, buffer, strlen(buffer))) {
  78                 nf_ct_helper_log(skb, ct, "cannot mangle packet");
  79                 nf_ct_unexpect_related(exp);
  80                 return NF_DROP;
  81         }
  82
  83         return NF_ACCEPT;
  84 }
  85
  86 static void __exit nf_nat_irc_fini(void)
  87 {
  88         nf_nat_helper_unregister(&nat_helper_irc);
  89         RCU_INIT_POINTER(nf_nat_irc_hook, NULL);
  90         synchronize_rcu();
  91 }
  92
  93 static int __init nf_nat_irc_init(void)
  94 {
  95         BUG_ON(nf_nat_irc_hook != NULL);
  96         nf_nat_helper_register(&nat_helper_irc);
  97         RCU_INIT_POINTER(nf_nat_irc_hook, help);
  98         return 0;
  99 }
 100
 101 /* Prior to 2.6.11, we had a ports param.  No longer, but don't break users. */
 102 static int warn_set(const char *val, const struct kernel_param *kp)
 103 {
 104         pr_info("kernel >= 2.6.10 only uses 'ports' for conntrack modules\n");
 105         return 0;
 106 }
 107 module_param_call(ports, warn_set, NULL, NULL, 0);
 108
 109 module_init(nf_nat_irc_init);
 110 module_exit(nf_nat_irc_fini);