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
43 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
44 MODULE_DESCRIPTION("IRC (DCC) connection tracking helper");
45 MODULE_LICENSE("GPL");
46 MODULE_ALIAS("ip_conntrack_irc");
47 MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
48
49 module_param_array(ports, ushort, &ports_c, 0400);
50 MODULE_PARM_DESC(ports, "port numbers of IRC servers");
51 module_param(max_dcc_channels, uint, 0400);
52 MODULE_PARM_DESC(max_dcc_channels, "max number of expected DCC channels per "
53 "IRC session");
54 module_param(dcc_timeout, uint, 0400);
55 MODULE_PARM_DESC(dcc_timeout, "timeout on for unestablished DCC channels");
56
57 static 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 */
parse_dcc(char * data,const char * data_end,__be32 * ip,u_int16_t * port,char ** ad_beg_p,char ** ad_end_p)72 static 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
help(struct sk_buff * skb,unsigned int protoff,struct nf_conn * ct,enum ip_conntrack_info ctinfo)106 static 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 /* Skip any whitespace */
152 while (data < data_limit - 10) {
153 if (*data == ' ' || *data == '\r' || *data == '\n')
154 data++;
155 else
156 break;
157 }
158
159 /* strlen("PRIVMSG x ")=10 */
160 if (data < data_limit - 10) {
161 if (strncasecmp("PRIVMSG ", data, 8))
162 goto out;
163 data += 8;
164 }
165
166 /* strlen(" :\1DCC SENT t AAAAAAAA P\1\n")=26
167 * 7+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=26
168 */
169 while (data < data_limit - (21 + MINMATCHLEN)) {
170 /* Find first " :", the start of message */
171 if (memcmp(data, " :", 2)) {
172 data++;
173 continue;
174 }
175 data += 2;
176
177 /* then check that place only for the DCC command */
178 if (memcmp(data, "\1DCC ", 5))
179 goto out;
180 data += 5;
181 /* we have at least (21+MINMATCHLEN)-(2+5) bytes valid data left */
182
183 iph = ip_hdr(skb);
184 pr_debug("DCC found in master %pI4:%u %pI4:%u\n",
185 &iph->saddr, ntohs(th->source),
186 &iph->daddr, ntohs(th->dest));
187
188 for (i = 0; i < ARRAY_SIZE(dccprotos); i++) {
189 if (memcmp(data, dccprotos[i], strlen(dccprotos[i]))) {
190 /* no match */
191 continue;
192 }
193 data += strlen(dccprotos[i]);
194 pr_debug("DCC %s detected\n", dccprotos[i]);
195
196 /* we have at least
197 * (21+MINMATCHLEN)-7-dccprotos[i].matchlen bytes valid
198 * data left (== 14/13 bytes) */
199 if (parse_dcc(data, data_limit, &dcc_ip,
200 &dcc_port, &addr_beg_p, &addr_end_p)) {
201 pr_debug("unable to parse dcc command\n");
202 continue;
203 }
204
205 pr_debug("DCC bound ip/port: %pI4:%u\n",
206 &dcc_ip, dcc_port);
207
208 /* dcc_ip can be the internal OR external (NAT'ed) IP */
209 tuple = &ct->tuplehash[dir].tuple;
210 if ((tuple->src.u3.ip != dcc_ip &&
211 ct->tuplehash[!dir].tuple.dst.u3.ip != dcc_ip) ||
212 dcc_port == 0) {
213 net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
214 &tuple->src.u3.ip,
215 &dcc_ip, dcc_port);
216 continue;
217 }
218
219 exp = nf_ct_expect_alloc(ct);
220 if (exp == NULL) {
221 nf_ct_helper_log(skb, ct,
222 "cannot alloc expectation");
223 ret = NF_DROP;
224 goto out;
225 }
226 tuple = &ct->tuplehash[!dir].tuple;
227 port = htons(dcc_port);
228 nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
229 tuple->src.l3num,
230 NULL, &tuple->dst.u3,
231 IPPROTO_TCP, NULL, &port);
232
233 nf_nat_irc = rcu_dereference(nf_nat_irc_hook);
234 if (nf_nat_irc && ct->status & IPS_NAT_MASK)
235 ret = nf_nat_irc(skb, ctinfo, protoff,
236 addr_beg_p - ib_ptr,
237 addr_end_p - addr_beg_p,
238 exp);
239 else if (nf_ct_expect_related(exp, 0) != 0) {
240 nf_ct_helper_log(skb, ct,
241 "cannot add expectation");
242 ret = NF_DROP;
243 }
244 nf_ct_expect_put(exp);
245 goto out;
246 }
247 }
248 out:
249 spin_unlock_bh(&irc_buffer_lock);
250 return ret;
251 }
252
253 static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;
254 static struct nf_conntrack_expect_policy irc_exp_policy;
255
nf_conntrack_irc_init(void)256 static int __init nf_conntrack_irc_init(void)
257 {
258 int i, ret;
259
260 if (max_dcc_channels < 1) {
261 pr_err("max_dcc_channels must not be zero\n");
262 return -EINVAL;
263 }
264
265 if (max_dcc_channels > NF_CT_EXPECT_MAX_CNT) {
266 pr_err("max_dcc_channels must not be more than %u\n",
267 NF_CT_EXPECT_MAX_CNT);
268 return -EINVAL;
269 }
270
271 irc_exp_policy.max_expected = max_dcc_channels;
272 irc_exp_policy.timeout = dcc_timeout;
273
274 irc_buffer = kmalloc(65536, GFP_KERNEL);
275 if (!irc_buffer)
276 return -ENOMEM;
277
278 /* If no port given, default to standard irc port */
279 if (ports_c == 0)
280 ports[ports_c++] = IRC_PORT;
281
282 for (i = 0; i < ports_c; i++) {
283 nf_ct_helper_init(&irc[i], AF_INET, IPPROTO_TCP, HELPER_NAME,
284 IRC_PORT, ports[i], i, &irc_exp_policy,
285 0, help, NULL, THIS_MODULE);
286 }
287
288 ret = nf_conntrack_helpers_register(&irc[0], ports_c);
289 if (ret) {
290 pr_err("failed to register helpers\n");
291 kfree(irc_buffer);
292 return ret;
293 }
294
295 return 0;
296 }
297
nf_conntrack_irc_fini(void)298 static void __exit nf_conntrack_irc_fini(void)
299 {
300 nf_conntrack_helpers_unregister(irc, ports_c);
301 kfree(irc_buffer);
302 }
303
304 module_init(nf_conntrack_irc_init);
305 module_exit(nf_conntrack_irc_fini);
306