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Linux/net/netfilter/nf_conntrack_irc.c

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  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 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 13 
 14 #include <linux/module.h>
 15 #include <linux/moduleparam.h>
 16 #include <linux/skbuff.h>
 17 #include <linux/in.h>
 18 #include <linux/ip.h>
 19 #include <linux/tcp.h>
 20 #include <linux/netfilter.h>
 21 #include <linux/slab.h>
 22 
 23 #include <net/netfilter/nf_conntrack.h>
 24 #include <net/netfilter/nf_conntrack_expect.h>
 25 #include <net/netfilter/nf_conntrack_helper.h>
 26 #include <linux/netfilter/nf_conntrack_irc.h>
 27 
 28 #define MAX_PORTS 8
 29 static unsigned short ports[MAX_PORTS];
 30 static unsigned int ports_c;
 31 static unsigned int max_dcc_channels = 8;
 32 static unsigned int dcc_timeout __read_mostly = 300;
 33 /* This is slow, but it's simple. --RR */
 34 static char *irc_buffer;
 35 static DEFINE_SPINLOCK(irc_buffer_lock);
 36 
 37 unsigned int (*nf_nat_irc_hook)(struct sk_buff *skb,
 38                                 enum ip_conntrack_info ctinfo,
 39                                 unsigned int protoff,
 40                                 unsigned int matchoff,
 41                                 unsigned int matchlen,
 42                                 struct nf_conntrack_expect *exp) __read_mostly;
 43 EXPORT_SYMBOL_GPL(nf_nat_irc_hook);
 44 
 45 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
 46 MODULE_DESCRIPTION("IRC (DCC) connection tracking helper");
 47 MODULE_LICENSE("GPL");
 48 MODULE_ALIAS("ip_conntrack_irc");
 49 MODULE_ALIAS_NFCT_HELPER("irc");
 50 
 51 module_param_array(ports, ushort, &ports_c, 0400);
 52 MODULE_PARM_DESC(ports, "port numbers of IRC servers");
 53 module_param(max_dcc_channels, uint, 0400);
 54 MODULE_PARM_DESC(max_dcc_channels, "max number of expected DCC channels per "
 55                                    "IRC session");
 56 module_param(dcc_timeout, uint, 0400);
 57 MODULE_PARM_DESC(dcc_timeout, "timeout on for unestablished DCC channels");
 58 
 59 static const char *const dccprotos[] = {
 60         "SEND ", "CHAT ", "MOVE ", "TSEND ", "SCHAT "
 61 };
 62 
 63 #define MINMATCHLEN     5
 64 
 65 /* tries to get the ip_addr and port out of a dcc command
 66  * return value: -1 on failure, 0 on success
 67  *      data            pointer to first byte of DCC command data
 68  *      data_end        pointer to last byte of dcc command data
 69  *      ip              returns parsed ip of dcc command
 70  *      port            returns parsed port of dcc command
 71  *      ad_beg_p        returns pointer to first byte of addr data
 72  *      ad_end_p        returns pointer to last byte of addr data
 73  */
 74 static int parse_dcc(char *data, const char *data_end, __be32 *ip,
 75                      u_int16_t *port, char **ad_beg_p, char **ad_end_p)
 76 {
 77         char *tmp;
 78 
 79         /* at least 12: "AAAAAAAA P\1\n" */
 80         while (*data++ != ' ')
 81                 if (data > data_end - 12)
 82                         return -1;
 83 
 84         /* Make sure we have a newline character within the packet boundaries
 85          * because simple_strtoul parses until the first invalid character. */
 86         for (tmp = data; tmp <= data_end; tmp++)
 87                 if (*tmp == '\n')
 88                         break;
 89         if (tmp > data_end || *tmp != '\n')
 90                 return -1;
 91 
 92         *ad_beg_p = data;
 93         *ip = cpu_to_be32(simple_strtoul(data, &data, 10));
 94 
 95         /* skip blanks between ip and port */
 96         while (*data == ' ') {
 97                 if (data >= data_end)
 98                         return -1;
 99                 data++;
100         }
101 
102         *port = simple_strtoul(data, &data, 10);
103         *ad_end_p = data;
104 
105         return 0;
106 }
107 
108 static int help(struct sk_buff *skb, unsigned int protoff,
109                 struct nf_conn *ct, enum ip_conntrack_info ctinfo)
110 {
111         unsigned int dataoff;
112         const struct iphdr *iph;
113         const struct tcphdr *th;
114         struct tcphdr _tcph;
115         const char *data_limit;
116         char *data, *ib_ptr;
117         int dir = CTINFO2DIR(ctinfo);
118         struct nf_conntrack_expect *exp;
119         struct nf_conntrack_tuple *tuple;
120         __be32 dcc_ip;
121         u_int16_t dcc_port;
122         __be16 port;
123         int i, ret = NF_ACCEPT;
124         char *addr_beg_p, *addr_end_p;
125         typeof(nf_nat_irc_hook) nf_nat_irc;
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         spin_lock_bh(&irc_buffer_lock);
146         ib_ptr = skb_header_pointer(skb, dataoff, skb->len - dataoff,
147                                     irc_buffer);
148         BUG_ON(ib_ptr == NULL);
149 
150         data = ib_ptr;
151         data_limit = ib_ptr + skb->len - dataoff;
152 
153         /* strlen("\1DCC SENT t AAAAAAAA P\1\n")=24
154          * 5+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=14 */
155         while (data < data_limit - (19 + MINMATCHLEN)) {
156                 if (memcmp(data, "\1DCC ", 5)) {
157                         data++;
158                         continue;
159                 }
160                 data += 5;
161                 /* we have at least (19+MINMATCHLEN)-5 bytes valid data left */
162 
163                 iph = ip_hdr(skb);
164                 pr_debug("DCC found in master %pI4:%u %pI4:%u\n",
165                          &iph->saddr, ntohs(th->source),
166                          &iph->daddr, ntohs(th->dest));
167 
168                 for (i = 0; i < ARRAY_SIZE(dccprotos); i++) {
169                         if (memcmp(data, dccprotos[i], strlen(dccprotos[i]))) {
170                                 /* no match */
171                                 continue;
172                         }
173                         data += strlen(dccprotos[i]);
174                         pr_debug("DCC %s detected\n", dccprotos[i]);
175 
176                         /* we have at least
177                          * (19+MINMATCHLEN)-5-dccprotos[i].matchlen bytes valid
178                          * data left (== 14/13 bytes) */
179                         if (parse_dcc(data, data_limit, &dcc_ip,
180                                        &dcc_port, &addr_beg_p, &addr_end_p)) {
181                                 pr_debug("unable to parse dcc command\n");
182                                 continue;
183                         }
184 
185                         pr_debug("DCC bound ip/port: %pI4:%u\n",
186                                  &dcc_ip, dcc_port);
187 
188                         /* dcc_ip can be the internal OR external (NAT'ed) IP */
189                         tuple = &ct->tuplehash[dir].tuple;
190                         if (tuple->src.u3.ip != dcc_ip &&
191                             tuple->dst.u3.ip != dcc_ip) {
192                                 net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
193                                                      &tuple->src.u3.ip,
194                                                      &dcc_ip, dcc_port);
195                                 continue;
196                         }
197 
198                         exp = nf_ct_expect_alloc(ct);
199                         if (exp == NULL) {
200                                 nf_ct_helper_log(skb, ct,
201                                                  "cannot alloc expectation");
202                                 ret = NF_DROP;
203                                 goto out;
204                         }
205                         tuple = &ct->tuplehash[!dir].tuple;
206                         port = htons(dcc_port);
207                         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
208                                           tuple->src.l3num,
209                                           NULL, &tuple->dst.u3,
210                                           IPPROTO_TCP, NULL, &port);
211 
212                         nf_nat_irc = rcu_dereference(nf_nat_irc_hook);
213                         if (nf_nat_irc && ct->status & IPS_NAT_MASK)
214                                 ret = nf_nat_irc(skb, ctinfo, protoff,
215                                                  addr_beg_p - ib_ptr,
216                                                  addr_end_p - addr_beg_p,
217                                                  exp);
218                         else if (nf_ct_expect_related(exp) != 0) {
219                                 nf_ct_helper_log(skb, ct,
220                                                  "cannot add expectation");
221                                 ret = NF_DROP;
222                         }
223                         nf_ct_expect_put(exp);
224                         goto out;
225                 }
226         }
227  out:
228         spin_unlock_bh(&irc_buffer_lock);
229         return ret;
230 }
231 
232 static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;
233 static struct nf_conntrack_expect_policy irc_exp_policy;
234 
235 static void nf_conntrack_irc_fini(void);
236 
237 static int __init nf_conntrack_irc_init(void)
238 {
239         int i, ret;
240 
241         if (max_dcc_channels < 1) {
242                 pr_err("max_dcc_channels must not be zero\n");
243                 return -EINVAL;
244         }
245 
246         irc_exp_policy.max_expected = max_dcc_channels;
247         irc_exp_policy.timeout = dcc_timeout;
248 
249         irc_buffer = kmalloc(65536, GFP_KERNEL);
250         if (!irc_buffer)
251                 return -ENOMEM;
252 
253         /* If no port given, default to standard irc port */
254         if (ports_c == 0)
255                 ports[ports_c++] = IRC_PORT;
256 
257         for (i = 0; i < ports_c; i++) {
258                 irc[i].tuple.src.l3num = AF_INET;
259                 irc[i].tuple.src.u.tcp.port = htons(ports[i]);
260                 irc[i].tuple.dst.protonum = IPPROTO_TCP;
261                 irc[i].expect_policy = &irc_exp_policy;
262                 irc[i].me = THIS_MODULE;
263                 irc[i].help = help;
264 
265                 if (ports[i] == IRC_PORT)
266                         sprintf(irc[i].name, "irc");
267                 else
268                         sprintf(irc[i].name, "irc-%u", i);
269 
270                 ret = nf_conntrack_helper_register(&irc[i]);
271                 if (ret) {
272                         pr_err("failed to register helper for pf: %u port: %u\n",
273                                irc[i].tuple.src.l3num, ports[i]);
274                         nf_conntrack_irc_fini();
275                         return ret;
276                 }
277         }
278         return 0;
279 }
280 
281 /* This function is intentionally _NOT_ defined as __exit, because
282  * it is needed by the init function */
283 static void nf_conntrack_irc_fini(void)
284 {
285         int i;
286 
287         for (i = 0; i < ports_c; i++)
288                 nf_conntrack_helper_unregister(&irc[i]);
289         kfree(irc_buffer);
290 }
291 
292 module_init(nf_conntrack_irc_init);
293 module_exit(nf_conntrack_irc_fini);
294 

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