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
24MODULE_AUTHOR("Harald Welte <laforge@gnumonks.org>");
25MODULE_DESCRIPTION("IRC (DCC) NAT helper");
26MODULE_LICENSE("GPL");
27MODULE_ALIAS("ip_nat_irc");
28
29static 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
96static void __exit nf_nat_irc_fini(void)
97{
98	RCU_INIT_POINTER(nf_nat_irc_hook, NULL);
99	synchronize_rcu();
100}
101
102static 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. */
110static 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}
116module_param_call(ports, warn_set, NULL, NULL, 0);
117
118module_init(nf_nat_irc_init);
119module_exit(nf_nat_irc_fini);
120