xref: /linux/net/netfilter/nf_conntrack_irc.c (revision 4f2c0a4acffbec01079c28f839422e64ddeff004)
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
25 static unsigned short ports[MAX_PORTS];
26 static unsigned int ports_c;
27 static unsigned int max_dcc_channels = 8;
28 static unsigned int dcc_timeout __read_mostly = 300;
29 /* This is slow, but it's simple. --RR */
30 static char *irc_buffer;
31 static DEFINE_SPINLOCK(irc_buffer_lock);
32 
33 unsigned 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;
39 EXPORT_SYMBOL_GPL(nf_nat_irc_hook);
40 
41 #define HELPER_NAME "irc"
42 #define MAX_SEARCH_SIZE	4095
43 
44 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
45 MODULE_DESCRIPTION("IRC (DCC) connection tracking helper");
46 MODULE_LICENSE("GPL");
47 MODULE_ALIAS("ip_conntrack_irc");
48 MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
49 
50 module_param_array(ports, ushort, &ports_c, 0400);
51 MODULE_PARM_DESC(ports, "port numbers of IRC servers");
52 module_param(max_dcc_channels, uint, 0400);
53 MODULE_PARM_DESC(max_dcc_channels, "max number of expected DCC channels per "
54 				   "IRC session");
55 module_param(dcc_timeout, uint, 0400);
56 MODULE_PARM_DESC(dcc_timeout, "timeout on for unestablished DCC channels");
57 
58 static 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  */
parse_dcc(char * data,const char * data_end,__be32 * ip,u_int16_t * port,char ** ad_beg_p,char ** ad_end_p)73 static 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 
help(struct sk_buff * skb,unsigned int protoff,struct nf_conn * ct,enum ip_conntrack_info ctinfo)107 static 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 
262 static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;
263 static struct nf_conntrack_expect_policy irc_exp_policy;
264 
nf_conntrack_irc_init(void)265 static 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 
nf_conntrack_irc_fini(void)307 static void __exit nf_conntrack_irc_fini(void)
308 {
309 	nf_conntrack_helpers_unregister(irc, ports_c);
310 	kfree(irc_buffer);
311 }
312 
313 module_init(nf_conntrack_irc_init);
314 module_exit(nf_conntrack_irc_fini);
315