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
 24MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
 25MODULE_DESCRIPTION("IRC (DCC) NAT helper");
 26MODULE_LICENSE("GPL");
 27MODULE_ALIAS_NF_NAT_HELPER(NAT_HELPER_NAME);
 28
 29static struct nf_conntrack_nat_helper nat_helper_irc =
 30	NF_CT_NAT_HELPER_INIT(NAT_HELPER_NAME);
 31
 32static 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
 86static 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
 93static 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. */
102static 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}
107module_param_call(ports, warn_set, NULL, NULL, 0);
108
109module_init(nf_nat_irc_init);
110module_exit(nf_nat_irc_fini);