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);
111