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 #define HELPER_NAME "irc"
  46
  47 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  48 MODULE_DESCRIPTION("IRC (DCC) connection tracking helper");
  49 MODULE_LICENSE("GPL");
  50 MODULE_ALIAS("ip_conntrack_irc");
  51 MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
  52
  53 module_param_array(ports, ushort, &ports_c, 0400);
  54 MODULE_PARM_DESC(ports, "port numbers of IRC servers");
  55 module_param(max_dcc_channels, uint, 0400);
  56 MODULE_PARM_DESC(max_dcc_channels, "max number of expected DCC channels per "
  57                                    "IRC session");
  58 module_param(dcc_timeout, uint, 0400);
  59 MODULE_PARM_DESC(dcc_timeout, "timeout on for unestablished DCC channels");
  60
  61 static const char *const dccprotos[] = {
  62         "SEND ", "CHAT ", "MOVE ", "TSEND ", "SCHAT "
  63 };
  64
  65 #define MINMATCHLEN     5
  66
  67 /* tries to get the ip_addr and port out of a dcc command
  68  * return value: -1 on failure, 0 on success
  69  *      data            pointer to first byte of DCC command data
  70  *      data_end        pointer to last byte of dcc command data
  71  *      ip              returns parsed ip of dcc command
  72  *      port            returns parsed port of dcc command
  73  *      ad_beg_p        returns pointer to first byte of addr data
  74  *      ad_end_p        returns pointer to last byte of addr data
  75  */
  76 static int parse_dcc(char *data, const char *data_end, __be32 *ip,
  77                      u_int16_t *port, char **ad_beg_p, char **ad_end_p)
  78 {
  79         char *tmp;
  80
  81         /* at least 12: "AAAAAAAA P\1\n" */
  82         while (*data++ != ' ')
  83                 if (data > data_end - 12)
  84                         return -1;
  85
  86         /* Make sure we have a newline character within the packet boundaries
  87          * because simple_strtoul parses until the first invalid character. */
  88         for (tmp = data; tmp <= data_end; tmp++)
  89                 if (*tmp == '\n')
  90                         break;
  91         if (tmp > data_end || *tmp != '\n')
  92                 return -1;
  93
  94         *ad_beg_p = data;
  95         *ip = cpu_to_be32(simple_strtoul(data, &data, 10));
  96
  97         /* skip blanks between ip and port */
  98         while (*data == ' ') {
  99                 if (data >= data_end)
 100                         return -1;
 101                 data++;
 102         }
 103
 104         *port = simple_strtoul(data, &data, 10);
 105         *ad_end_p = data;
 106
 107         return 0;
 108 }
 109
 110 static int help(struct sk_buff *skb, unsigned int protoff,
 111                 struct nf_conn *ct, enum ip_conntrack_info ctinfo)
 112 {
 113         unsigned int dataoff;
 114         const struct iphdr *iph;
 115         const struct tcphdr *th;
 116         struct tcphdr _tcph;
 117         const char *data_limit;
 118         char *data, *ib_ptr;
 119         int dir = CTINFO2DIR(ctinfo);
 120         struct nf_conntrack_expect *exp;
 121         struct nf_conntrack_tuple *tuple;
 122         __be32 dcc_ip;
 123         u_int16_t dcc_port;
 124         __be16 port;
 125         int i, ret = NF_ACCEPT;
 126         char *addr_beg_p, *addr_end_p;
 127         typeof(nf_nat_irc_hook) nf_nat_irc;
 128
 129         /* If packet is coming from IRC server */
 130         if (dir == IP_CT_DIR_REPLY)
 131                 return NF_ACCEPT;
 132
 133         /* Until there's been traffic both ways, don't look in packets. */
 134         if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
 135                 return NF_ACCEPT;
 136
 137         /* Not a full tcp header? */
 138         th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
 139         if (th == NULL)
 140                 return NF_ACCEPT;
 141
 142         /* No data? */
 143         dataoff = protoff + th->doff*4;
 144         if (dataoff >= skb->len)
 145                 return NF_ACCEPT;
 146
 147         spin_lock_bh(&irc_buffer_lock);
 148         ib_ptr = skb_header_pointer(skb, dataoff, skb->len - dataoff,
 149                                     irc_buffer);
 150         BUG_ON(ib_ptr == NULL);
 151
 152         data = ib_ptr;
 153         data_limit = ib_ptr + skb->len - dataoff;
 154
 155         /* strlen("\1DCC SENT t AAAAAAAA P\1\n")=24
 156          * 5+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=14 */
 157         while (data < data_limit - (19 + MINMATCHLEN)) {
 158                 if (memcmp(data, "\1DCC ", 5)) {
 159                         data++;
 160                         continue;
 161                 }
 162                 data += 5;
 163                 /* we have at least (19+MINMATCHLEN)-5 bytes valid data left */
 164
 165                 iph = ip_hdr(skb);
 166                 pr_debug("DCC found in master %pI4:%u %pI4:%u\n",
 167                          &iph->saddr, ntohs(th->source),
 168                          &iph->daddr, ntohs(th->dest));
 169
 170                 for (i = 0; i < ARRAY_SIZE(dccprotos); i++) {
 171                         if (memcmp(data, dccprotos[i], strlen(dccprotos[i]))) {
 172                                 /* no match */
 173                                 continue;
 174                         }
 175                         data += strlen(dccprotos[i]);
 176                         pr_debug("DCC %s detected\n", dccprotos[i]);
 177
 178                         /* we have at least
 179                          * (19+MINMATCHLEN)-5-dccprotos[i].matchlen bytes valid
 180                          * data left (== 14/13 bytes) */
 181                         if (parse_dcc(data, data_limit, &dcc_ip,
 182                                        &dcc_port, &addr_beg_p, &addr_end_p)) {
 183                                 pr_debug("unable to parse dcc command\n");
 184                                 continue;
 185                         }
 186
 187                         pr_debug("DCC bound ip/port: %pI4:%u\n",
 188                                  &dcc_ip, dcc_port);
 189
 190                         /* dcc_ip can be the internal OR external (NAT'ed) IP */
 191                         tuple = &ct->tuplehash[dir].tuple;
 192                         if (tuple->src.u3.ip != dcc_ip &&
 193                             tuple->dst.u3.ip != dcc_ip) {
 194                                 net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
 195                                                      &tuple->src.u3.ip,
 196                                                      &dcc_ip, dcc_port);
 197                                 continue;
 198                         }
 199
 200                         exp = nf_ct_expect_alloc(ct);
 201                         if (exp == NULL) {
 202                                 nf_ct_helper_log(skb, ct,
 203                                                  "cannot alloc expectation");
 204                                 ret = NF_DROP;
 205                                 goto out;
 206                         }
 207                         tuple = &ct->tuplehash[!dir].tuple;
 208                         port = htons(dcc_port);
 209                         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
 210                                           tuple->src.l3num,
 211                                           NULL, &tuple->dst.u3,
 212                                           IPPROTO_TCP, NULL, &port);
 213
 214                         nf_nat_irc = rcu_dereference(nf_nat_irc_hook);
 215                         if (nf_nat_irc && ct->status & IPS_NAT_MASK)
 216                                 ret = nf_nat_irc(skb, ctinfo, protoff,
 217                                                  addr_beg_p - ib_ptr,
 218                                                  addr_end_p - addr_beg_p,
 219                                                  exp);
 220                         else if (nf_ct_expect_related(exp) != 0) {
 221                                 nf_ct_helper_log(skb, ct,
 222                                                  "cannot add expectation");
 223                                 ret = NF_DROP;
 224                         }
 225                         nf_ct_expect_put(exp);
 226                         goto out;
 227                 }
 228         }
 229  out:
 230         spin_unlock_bh(&irc_buffer_lock);
 231         return ret;
 232 }
 233
 234 static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;
 235 static struct nf_conntrack_expect_policy irc_exp_policy;
 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         if (max_dcc_channels > NF_CT_EXPECT_MAX_CNT) {
 247                 pr_err("max_dcc_channels must not be more than %u\n",
 248                        NF_CT_EXPECT_MAX_CNT);
 249                 return -EINVAL;
 250         }
 251
 252         irc_exp_policy.max_expected = max_dcc_channels;
 253         irc_exp_policy.timeout = dcc_timeout;
 254
 255         irc_buffer = kmalloc(65536, GFP_KERNEL);
 256         if (!irc_buffer)
 257                 return -ENOMEM;
 258
 259         /* If no port given, default to standard irc port */
 260         if (ports_c == 0)
 261                 ports[ports_c++] = IRC_PORT;
 262
 263         for (i = 0; i < ports_c; i++) {
 264                 nf_ct_helper_init(&irc[i], AF_INET, IPPROTO_TCP, HELPER_NAME,
 265                                   IRC_PORT, ports[i], i, &irc_exp_policy,
 266                                   0, help, NULL, THIS_MODULE);
 267         }
 268
 269         ret = nf_conntrack_helpers_register(&irc[0], ports_c);
 270         if (ret) {
 271                 pr_err("failed to register helpers\n");
 272                 kfree(irc_buffer);
 273                 return ret;
 274         }
 275
 276         return 0;
 277 }
 278
 279 static void __exit nf_conntrack_irc_fini(void)
 280 {
 281         nf_conntrack_helpers_unregister(irc, ports_c);
 282         kfree(irc_buffer);
 283 }
 284
 285 module_init(nf_conntrack_irc_init);
 286 module_exit(nf_conntrack_irc_fini);