nf_conntrack_irc.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/* IRC extension for IP connection tracking, Version 1.21
  3 * (C) 2000-2002 by Harald Welte <laforge@gnumonks.org>
  4 * based on RR's ip_conntrack_ftp.c
  5 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
  6 */
  7
  8#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  9
 10#include <linux/module.h>
 11#include <linux/moduleparam.h>
 12#include <linux/skbuff.h>
 13#include <linux/in.h>
 14#include <linux/ip.h>
 15#include <linux/tcp.h>
 16#include <linux/netfilter.h>
 17#include <linux/slab.h>
 18
 19#include <net/netfilter/nf_conntrack.h>
 20#include <net/netfilter/nf_conntrack_expect.h>
 21#include <net/netfilter/nf_conntrack_helper.h>
 22#include <linux/netfilter/nf_conntrack_irc.h>
 23
 24#define MAX_PORTS 8
 25static unsigned short ports[MAX_PORTS];
 26static unsigned int ports_c;
 27static unsigned int max_dcc_channels = 8;
 28static unsigned int dcc_timeout __read_mostly = 300;
 29/* This is slow, but it's simple. --RR */
 30static char *irc_buffer;
 31static DEFINE_SPINLOCK(irc_buffer_lock);
 32
 33unsigned int (*nf_nat_irc_hook)(struct sk_buff *skb,
 34				enum ip_conntrack_info ctinfo,
 35				unsigned int protoff,
 36				unsigned int matchoff,
 37				unsigned int matchlen,
 38				struct nf_conntrack_expect *exp) __read_mostly;
 39EXPORT_SYMBOL_GPL(nf_nat_irc_hook);
 40
 41#define HELPER_NAME "irc"
 42#define MAX_SEARCH_SIZE	4095
 43
 44MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
 45MODULE_DESCRIPTION("IRC (DCC) connection tracking helper");
 46MODULE_LICENSE("GPL");
 47MODULE_ALIAS("ip_conntrack_irc");
 48MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
 49
 50module_param_array(ports, ushort, &ports_c, 0400);
 51MODULE_PARM_DESC(ports, "port numbers of IRC servers");
 52module_param(max_dcc_channels, uint, 0400);
 53MODULE_PARM_DESC(max_dcc_channels, "max number of expected DCC channels per "
 54				   "IRC session");
 55module_param(dcc_timeout, uint, 0400);
 56MODULE_PARM_DESC(dcc_timeout, "timeout on for unestablished DCC channels");
 57
 58static const char *const dccprotos[] = {
 59	"SEND ", "CHAT ", "MOVE ", "TSEND ", "SCHAT "
 60};
 61
 62#define MINMATCHLEN	5
 63
 64/* tries to get the ip_addr and port out of a dcc command
 65 * return value: -1 on failure, 0 on success
 66 *	data		pointer to first byte of DCC command data
 67 *	data_end	pointer to last byte of dcc command data
 68 *	ip		returns parsed ip of dcc command
 69 *	port		returns parsed port of dcc command
 70 *	ad_beg_p	returns pointer to first byte of addr data
 71 *	ad_end_p	returns pointer to last byte of addr data
 72 */
 73static int parse_dcc(char *data, const char *data_end, __be32 *ip,
 74		     u_int16_t *port, char **ad_beg_p, char **ad_end_p)
 75{
 76	char *tmp;
 77
 78	/* at least 12: "AAAAAAAA P\1\n" */
 79	while (*data++ != ' ')
 80		if (data > data_end - 12)
 81			return -1;
 82
 83	/* Make sure we have a newline character within the packet boundaries
 84	 * because simple_strtoul parses until the first invalid character. */
 85	for (tmp = data; tmp <= data_end; tmp++)
 86		if (*tmp == '\n')
 87			break;
 88	if (tmp > data_end || *tmp != '\n')
 89		return -1;
 90
 91	*ad_beg_p = data;
 92	*ip = cpu_to_be32(simple_strtoul(data, &data, 10));
 93
 94	/* skip blanks between ip and port */
 95	while (*data == ' ') {
 96		if (data >= data_end)
 97			return -1;
 98		data++;
 99	}
100
101	*port = simple_strtoul(data, &data, 10);
102	*ad_end_p = data;
103
104	return 0;
105}
106
107static int help(struct sk_buff *skb, unsigned int protoff,
108		struct nf_conn *ct, enum ip_conntrack_info ctinfo)
109{
110	unsigned int dataoff;
111	const struct iphdr *iph;
112	const struct tcphdr *th;
113	struct tcphdr _tcph;
114	const char *data_limit;
115	char *data, *ib_ptr;
116	int dir = CTINFO2DIR(ctinfo);
117	struct nf_conntrack_expect *exp;
118	struct nf_conntrack_tuple *tuple;
119	__be32 dcc_ip;
120	u_int16_t dcc_port;
121	__be16 port;
122	int i, ret = NF_ACCEPT;
123	char *addr_beg_p, *addr_end_p;
124	typeof(nf_nat_irc_hook) nf_nat_irc;
125	unsigned int datalen;
126
127	/* If packet is coming from IRC server */
128	if (dir == IP_CT_DIR_REPLY)
129		return NF_ACCEPT;
130
131	/* Until there's been traffic both ways, don't look in packets. */
132	if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
133		return NF_ACCEPT;
134
135	/* Not a full tcp header? */
136	th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
137	if (th == NULL)
138		return NF_ACCEPT;
139
140	/* No data? */
141	dataoff = protoff + th->doff*4;
142	if (dataoff >= skb->len)
143		return NF_ACCEPT;
144
145	datalen = skb->len - dataoff;
146	if (datalen > MAX_SEARCH_SIZE)
147		datalen = MAX_SEARCH_SIZE;
148
149	spin_lock_bh(&irc_buffer_lock);
150	ib_ptr = skb_header_pointer(skb, dataoff, datalen,
151				    irc_buffer);
152	if (!ib_ptr) {
153		spin_unlock_bh(&irc_buffer_lock);
154		return NF_ACCEPT;
155	}
156
157	data = ib_ptr;
158	data_limit = ib_ptr + datalen;
159
160	/* Skip any whitespace */
161	while (data < data_limit - 10) {
162		if (*data == ' ' || *data == '\r' || *data == '\n')
163			data++;
164		else
165			break;
166	}
167
168	/* strlen("PRIVMSG x ")=10 */
169	if (data < data_limit - 10) {
170		if (strncasecmp("PRIVMSG ", data, 8))
171			goto out;
172		data += 8;
173	}
174
175	/* strlen(" :\1DCC SENT t AAAAAAAA P\1\n")=26
176	 * 7+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=26
177	 */
178	while (data < data_limit - (21 + MINMATCHLEN)) {
179		/* Find first " :", the start of message */
180		if (memcmp(data, " :", 2)) {
181			data++;
182			continue;
183		}
184		data += 2;
185
186		/* then check that place only for the DCC command */
187		if (memcmp(data, "\1DCC ", 5))
188			goto out;
189		data += 5;
190		/* we have at least (21+MINMATCHLEN)-(2+5) bytes valid data left */
191
192		iph = ip_hdr(skb);
193		pr_debug("DCC found in master %pI4:%u %pI4:%u\n",
194			 &iph->saddr, ntohs(th->source),
195			 &iph->daddr, ntohs(th->dest));
196
197		for (i = 0; i < ARRAY_SIZE(dccprotos); i++) {
198			if (memcmp(data, dccprotos[i], strlen(dccprotos[i]))) {
199				/* no match */
200				continue;
201			}
202			data += strlen(dccprotos[i]);
203			pr_debug("DCC %s detected\n", dccprotos[i]);
204
205			/* we have at least
206			 * (21+MINMATCHLEN)-7-dccprotos[i].matchlen bytes valid
207			 * data left (== 14/13 bytes) */
208			if (parse_dcc(data, data_limit, &dcc_ip,
209				       &dcc_port, &addr_beg_p, &addr_end_p)) {
210				pr_debug("unable to parse dcc command\n");
211				continue;
212			}
213
214			pr_debug("DCC bound ip/port: %pI4:%u\n",
215				 &dcc_ip, dcc_port);
216
217			/* dcc_ip can be the internal OR external (NAT'ed) IP */
218			tuple = &ct->tuplehash[dir].tuple;
219			if ((tuple->src.u3.ip != dcc_ip &&
220			     ct->tuplehash[!dir].tuple.dst.u3.ip != dcc_ip) ||
221			    dcc_port == 0) {
222				net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
223						     &tuple->src.u3.ip,
224						     &dcc_ip, dcc_port);
225				continue;
226			}
227
228			exp = nf_ct_expect_alloc(ct);
229			if (exp == NULL) {
230				nf_ct_helper_log(skb, ct,
231						 "cannot alloc expectation");
232				ret = NF_DROP;
233				goto out;
234			}
235			tuple = &ct->tuplehash[!dir].tuple;
236			port = htons(dcc_port);
237			nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
238					  tuple->src.l3num,
239					  NULL, &tuple->dst.u3,
240					  IPPROTO_TCP, NULL, &port);
241
242			nf_nat_irc = rcu_dereference(nf_nat_irc_hook);
243			if (nf_nat_irc && ct->status & IPS_NAT_MASK)
244				ret = nf_nat_irc(skb, ctinfo, protoff,
245						 addr_beg_p - ib_ptr,
246						 addr_end_p - addr_beg_p,
247						 exp);
248			else if (nf_ct_expect_related(exp, 0) != 0) {
249				nf_ct_helper_log(skb, ct,
250						 "cannot add expectation");
251				ret = NF_DROP;
252			}
253			nf_ct_expect_put(exp);
254			goto out;
255		}
256	}
257 out:
258	spin_unlock_bh(&irc_buffer_lock);
259	return ret;
260}
261
262static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;
263static struct nf_conntrack_expect_policy irc_exp_policy;
264
265static int __init nf_conntrack_irc_init(void)
266{
267	int i, ret;
268
269	if (max_dcc_channels < 1) {
270		pr_err("max_dcc_channels must not be zero\n");
271		return -EINVAL;
272	}
273
274	if (max_dcc_channels > NF_CT_EXPECT_MAX_CNT) {
275		pr_err("max_dcc_channels must not be more than %u\n",
276		       NF_CT_EXPECT_MAX_CNT);
277		return -EINVAL;
278	}
279
280	irc_exp_policy.max_expected = max_dcc_channels;
281	irc_exp_policy.timeout = dcc_timeout;
282
283	irc_buffer = kmalloc(MAX_SEARCH_SIZE + 1, GFP_KERNEL);
284	if (!irc_buffer)
285		return -ENOMEM;
286
287	/* If no port given, default to standard irc port */
288	if (ports_c == 0)
289		ports[ports_c++] = IRC_PORT;
290
291	for (i = 0; i < ports_c; i++) {
292		nf_ct_helper_init(&irc[i], AF_INET, IPPROTO_TCP, HELPER_NAME,
293				  IRC_PORT, ports[i], i, &irc_exp_policy,
294				  0, help, NULL, THIS_MODULE);
295	}
296
297	ret = nf_conntrack_helpers_register(&irc[0], ports_c);
298	if (ret) {
299		pr_err("failed to register helpers\n");
300		kfree(irc_buffer);
301		return ret;
302	}
303
304	return 0;
305}
306
307static void __exit nf_conntrack_irc_fini(void)
308{
309	nf_conntrack_helpers_unregister(irc, ports_c);
310	kfree(irc_buffer);
311}
312
313module_init(nf_conntrack_irc_init);
314module_exit(nf_conntrack_irc_fini);