1/* IRC extension for IP connection tracking, Version 1.21
2 * (C) 2000-2002 by Harald Welte <laforge@gnumonks.org>
3 * based on RR's ip_conntrack_ftp.c
4 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
5 *
6 * This program is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU General Public License
8 * as published by the Free Software Foundation; either version
9 * 2 of the License, or (at your option) any later version.
10 */
11
12#include <linux/module.h>
13#include <linux/moduleparam.h>
14#include <linux/skbuff.h>
15#include <linux/in.h>
16#include <linux/ip.h>
17#include <linux/tcp.h>
18#include <linux/netfilter.h>
19#include <linux/slab.h>
20
21#include <net/netfilter/nf_conntrack.h>
22#include <net/netfilter/nf_conntrack_expect.h>
23#include <net/netfilter/nf_conntrack_helper.h>
24#include <linux/netfilter/nf_conntrack_irc.h>
25
26#define MAX_PORTS 8
27static unsigned short ports[MAX_PORTS];
28static unsigned int ports_c;
29static unsigned int max_dcc_channels = 8;
30static unsigned int dcc_timeout __read_mostly = 300;
31/* This is slow, but it's simple. --RR */
32static char *irc_buffer;
33static DEFINE_SPINLOCK(irc_buffer_lock);
34
35unsigned int (*nf_nat_irc_hook)(struct sk_buff *skb,
36				enum ip_conntrack_info ctinfo,
37				unsigned int protoff,
38				unsigned int matchoff,
39				unsigned int matchlen,
40				struct nf_conntrack_expect *exp) __read_mostly;
41EXPORT_SYMBOL_GPL(nf_nat_irc_hook);
42
43MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
44MODULE_DESCRIPTION("IRC (DCC) connection tracking helper");
45MODULE_LICENSE("GPL");
46MODULE_ALIAS("ip_conntrack_irc");
47MODULE_ALIAS_NFCT_HELPER("irc");
48
49module_param_array(ports, ushort, &ports_c, 0400);
50MODULE_PARM_DESC(ports, "port numbers of IRC servers");
51module_param(max_dcc_channels, uint, 0400);
52MODULE_PARM_DESC(max_dcc_channels, "max number of expected DCC channels per "
53				   "IRC session");
54module_param(dcc_timeout, uint, 0400);
55MODULE_PARM_DESC(dcc_timeout, "timeout on for unestablished DCC channels");
56
57static const char *const dccprotos[] = {
58	"SEND ", "CHAT ", "MOVE ", "TSEND ", "SCHAT "
59};
60
61#define MINMATCHLEN	5
62
63/* tries to get the ip_addr and port out of a dcc command
64 * return value: -1 on failure, 0 on success
65 *	data		pointer to first byte of DCC command data
66 *	data_end	pointer to last byte of dcc command data
67 *	ip		returns parsed ip of dcc command
68 *	port		returns parsed port of dcc command
69 *	ad_beg_p	returns pointer to first byte of addr data
70 *	ad_end_p	returns pointer to last byte of addr data
71 */
72static int parse_dcc(char *data, const char *data_end, __be32 *ip,
73		     u_int16_t *port, char **ad_beg_p, char **ad_end_p)
74{
75	char *tmp;
76
77	/* at least 12: "AAAAAAAA P\1\n" */
78	while (*data++ != ' ')
79		if (data > data_end - 12)
80			return -1;
81
82	/* Make sure we have a newline character within the packet boundaries
83	 * because simple_strtoul parses until the first invalid character. */
84	for (tmp = data; tmp <= data_end; tmp++)
85		if (*tmp == '\n')
86			break;
87	if (tmp > data_end || *tmp != '\n')
88		return -1;
89
90	*ad_beg_p = data;
91	*ip = cpu_to_be32(simple_strtoul(data, &data, 10));
92
93	/* skip blanks between ip and port */
94	while (*data == ' ') {
95		if (data >= data_end)
96			return -1;
97		data++;
98	}
99
100	*port = simple_strtoul(data, &data, 10);
101	*ad_end_p = data;
102
103	return 0;
104}
105
106static int help(struct sk_buff *skb, unsigned int protoff,
107		struct nf_conn *ct, enum ip_conntrack_info ctinfo)
108{
109	unsigned int dataoff;
110	const struct iphdr *iph;
111	const struct tcphdr *th;
112	struct tcphdr _tcph;
113	const char *data_limit;
114	char *data, *ib_ptr;
115	int dir = CTINFO2DIR(ctinfo);
116	struct nf_conntrack_expect *exp;
117	struct nf_conntrack_tuple *tuple;
118	__be32 dcc_ip;
119	u_int16_t dcc_port;
120	__be16 port;
121	int i, ret = NF_ACCEPT;
122	char *addr_beg_p, *addr_end_p;
123	typeof(nf_nat_irc_hook) nf_nat_irc;
124
125	/* If packet is coming from IRC server */
126	if (dir == IP_CT_DIR_REPLY)
127		return NF_ACCEPT;
128
129	/* Until there's been traffic both ways, don't look in packets. */
130	if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
131		return NF_ACCEPT;
132
133	/* Not a full tcp header? */
134	th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
135	if (th == NULL)
136		return NF_ACCEPT;
137
138	/* No data? */
139	dataoff = protoff + th->doff*4;
140	if (dataoff >= skb->len)
141		return NF_ACCEPT;
142
143	spin_lock_bh(&irc_buffer_lock);
144	ib_ptr = skb_header_pointer(skb, dataoff, skb->len - dataoff,
145				    irc_buffer);
146	BUG_ON(ib_ptr == NULL);
147
148	data = ib_ptr;
149	data_limit = ib_ptr + skb->len - dataoff;
150
151	/* strlen("\1DCC SENT t AAAAAAAA P\1\n")=24
152	 * 5+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=14 */
153	while (data < data_limit - (19 + MINMATCHLEN)) {
154		if (memcmp(data, "\1DCC ", 5)) {
155			data++;
156			continue;
157		}
158		data += 5;
159		/* we have at least (19+MINMATCHLEN)-5 bytes valid data left */
160
161		iph = ip_hdr(skb);
162		pr_debug("DCC found in master %pI4:%u %pI4:%u\n",
163			 &iph->saddr, ntohs(th->source),
164			 &iph->daddr, ntohs(th->dest));
165
166		for (i = 0; i < ARRAY_SIZE(dccprotos); i++) {
167			if (memcmp(data, dccprotos[i], strlen(dccprotos[i]))) {
168				/* no match */
169				continue;
170			}
171			data += strlen(dccprotos[i]);
172			pr_debug("DCC %s detected\n", dccprotos[i]);
173
174			/* we have at least
175			 * (19+MINMATCHLEN)-5-dccprotos[i].matchlen bytes valid
176			 * data left (== 14/13 bytes) */
177			if (parse_dcc(data, data_limit, &dcc_ip,
178				       &dcc_port, &addr_beg_p, &addr_end_p)) {
179				pr_debug("unable to parse dcc command\n");
180				continue;
181			}
182
183			pr_debug("DCC bound ip/port: %pI4:%u\n",
184				 &dcc_ip, dcc_port);
185
186			/* dcc_ip can be the internal OR external (NAT'ed) IP */
187			tuple = &ct->tuplehash[dir].tuple;
188			if (tuple->src.u3.ip != dcc_ip &&
189			    tuple->dst.u3.ip != dcc_ip) {
190				net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
191						     &tuple->src.u3.ip,
192						     &dcc_ip, dcc_port);
193				continue;
194			}
195
196			exp = nf_ct_expect_alloc(ct);
197			if (exp == NULL) {
198				nf_ct_helper_log(skb, ct,
199						 "cannot alloc expectation");
200				ret = NF_DROP;
201				goto out;
202			}
203			tuple = &ct->tuplehash[!dir].tuple;
204			port = htons(dcc_port);
205			nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
206					  tuple->src.l3num,
207					  NULL, &tuple->dst.u3,
208					  IPPROTO_TCP, NULL, &port);
209
210			nf_nat_irc = rcu_dereference(nf_nat_irc_hook);
211			if (nf_nat_irc && ct->status & IPS_NAT_MASK)
212				ret = nf_nat_irc(skb, ctinfo, protoff,
213						 addr_beg_p - ib_ptr,
214						 addr_end_p - addr_beg_p,
215						 exp);
216			else if (nf_ct_expect_related(exp) != 0) {
217				nf_ct_helper_log(skb, ct,
218						 "cannot add expectation");
219				ret = NF_DROP;
220			}
221			nf_ct_expect_put(exp);
222			goto out;
223		}
224	}
225 out:
226	spin_unlock_bh(&irc_buffer_lock);
227	return ret;
228}
229
230static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;
231static struct nf_conntrack_expect_policy irc_exp_policy;
232
233static void nf_conntrack_irc_fini(void);
234
235static int __init nf_conntrack_irc_init(void)
236{
237	int i, ret;
238
239	if (max_dcc_channels < 1) {
240		printk(KERN_ERR "nf_ct_irc: max_dcc_channels must not be zero\n");
241		return -EINVAL;
242	}
243
244	irc_exp_policy.max_expected = max_dcc_channels;
245	irc_exp_policy.timeout = dcc_timeout;
246
247	irc_buffer = kmalloc(65536, GFP_KERNEL);
248	if (!irc_buffer)
249		return -ENOMEM;
250
251	/* If no port given, default to standard irc port */
252	if (ports_c == 0)
253		ports[ports_c++] = IRC_PORT;
254
255	for (i = 0; i < ports_c; i++) {
256		irc[i].tuple.src.l3num = AF_INET;
257		irc[i].tuple.src.u.tcp.port = htons(ports[i]);
258		irc[i].tuple.dst.protonum = IPPROTO_TCP;
259		irc[i].expect_policy = &irc_exp_policy;
260		irc[i].me = THIS_MODULE;
261		irc[i].help = help;
262
263		if (ports[i] == IRC_PORT)
264			sprintf(irc[i].name, "irc");
265		else
266			sprintf(irc[i].name, "irc-%u", i);
267
268		ret = nf_conntrack_helper_register(&irc[i]);
269		if (ret) {
270			printk(KERN_ERR "nf_ct_irc: failed to register helper "
271			       "for pf: %u port: %u\n",
272			       irc[i].tuple.src.l3num, ports[i]);
273			nf_conntrack_irc_fini();
274			return ret;
275		}
276	}
277	return 0;
278}
279
280/* This function is intentionally _NOT_ defined as __exit, because
281 * it is needed by the init function */
282static void nf_conntrack_irc_fini(void)
283{
284	int i;
285
286	for (i = 0; i < ports_c; i++)
287		nf_conntrack_helper_unregister(&irc[i]);
288	kfree(irc_buffer);
289}
290
291module_init(nf_conntrack_irc_init);
292module_exit(nf_conntrack_irc_fini);
293