net/netfilter/nf_conntrack_irc.c

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