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#include <linux/module.h>
  13#include <linux/moduleparam.h>
  14#include <linux/skbuff.h>
  15#include <linux/in.h>
  16#include <linux/ip.h>
  17#include <linux/tcp.h>
  18#include <linux/netfilter.h>
  19#include <linux/slab.h>
  20
  21#include <net/netfilter/nf_conntrack.h>
  22#include <net/netfilter/nf_conntrack_expect.h>
  23#include <net/netfilter/nf_conntrack_helper.h>
  24#include <linux/netfilter/nf_conntrack_irc.h>
  25
  26#define MAX_PORTS 8
  27static unsigned short ports[MAX_PORTS];
  28static unsigned int ports_c;
  29static unsigned int max_dcc_channels = 8;
  30static unsigned int dcc_timeout __read_mostly = 300;
  31/* This is slow, but it's simple. --RR */
  32static char *irc_buffer;
  33static DEFINE_SPINLOCK(irc_buffer_lock);
  34
  35unsigned int (*nf_nat_irc_hook)(struct sk_buff *skb,
  36                                enum ip_conntrack_info ctinfo,
  37                                unsigned int protoff,
  38                                unsigned int matchoff,
  39                                unsigned int matchlen,
  40                                struct nf_conntrack_expect *exp) __read_mostly;
  41EXPORT_SYMBOL_GPL(nf_nat_irc_hook);
  42
  43MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  44MODULE_DESCRIPTION("IRC (DCC) connection tracking helper");
  45MODULE_LICENSE("GPL");
  46MODULE_ALIAS("ip_conntrack_irc");
  47MODULE_ALIAS_NFCT_HELPER("irc");
  48
  49module_param_array(ports, ushort, &ports_c, 0400);
  50MODULE_PARM_DESC(ports, "port numbers of IRC servers");
  51module_param(max_dcc_channels, uint, 0400);
  52MODULE_PARM_DESC(max_dcc_channels, "max number of expected DCC channels per "
  53                                   "IRC session");
  54module_param(dcc_timeout, uint, 0400);
  55MODULE_PARM_DESC(dcc_timeout, "timeout on for unestablished DCC channels");
  56
  57static 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 */
  72static 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
 106static 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        /* strlen("\1DCC SENT t AAAAAAAA P\1\n")=24
 152         * 5+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=14 */
 153        while (data < data_limit - (19 + MINMATCHLEN)) {
 154                if (memcmp(data, "\1DCC ", 5)) {
 155                        data++;
 156                        continue;
 157                }
 158                data += 5;
 159                /* we have at least (19+MINMATCHLEN)-5 bytes valid data left */
 160
 161                iph = ip_hdr(skb);
 162                pr_debug("DCC found in master %pI4:%u %pI4:%u\n",
 163                         &iph->saddr, ntohs(th->source),
 164                         &iph->daddr, ntohs(th->dest));
 165
 166                for (i = 0; i < ARRAY_SIZE(dccprotos); i++) {
 167                        if (memcmp(data, dccprotos[i], strlen(dccprotos[i]))) {
 168                                /* no match */
 169                                continue;
 170                        }
 171                        data += strlen(dccprotos[i]);
 172                        pr_debug("DCC %s detected\n", dccprotos[i]);
 173
 174                        /* we have at least
 175                         * (19+MINMATCHLEN)-5-dccprotos[i].matchlen bytes valid
 176                         * data left (== 14/13 bytes) */
 177                        if (parse_dcc(data, data_limit, &dcc_ip,
 178                                       &dcc_port, &addr_beg_p, &addr_end_p)) {
 179                                pr_debug("unable to parse dcc command\n");
 180                                continue;
 181                        }
 182
 183                        pr_debug("DCC bound ip/port: %pI4:%u\n",
 184                                 &dcc_ip, dcc_port);
 185
 186                        /* dcc_ip can be the internal OR external (NAT'ed) IP */
 187                        tuple = &ct->tuplehash[dir].tuple;
 188                        if (tuple->src.u3.ip != dcc_ip &&
 189                            tuple->dst.u3.ip != dcc_ip) {
 190                                net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
 191                                                     &tuple->src.u3.ip,
 192                                                     &dcc_ip, dcc_port);
 193                                continue;
 194                        }
 195
 196                        exp = nf_ct_expect_alloc(ct);
 197                        if (exp == NULL) {
 198                                nf_ct_helper_log(skb, ct,
 199                                                 "cannot alloc expectation");
 200                                ret = NF_DROP;
 201                                goto out;
 202                        }
 203                        tuple = &ct->tuplehash[!dir].tuple;
 204                        port = htons(dcc_port);
 205                        nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
 206                                          tuple->src.l3num,
 207                                          NULL, &tuple->dst.u3,
 208                                          IPPROTO_TCP, NULL, &port);
 209
 210                        nf_nat_irc = rcu_dereference(nf_nat_irc_hook);
 211                        if (nf_nat_irc && ct->status & IPS_NAT_MASK)
 212                                ret = nf_nat_irc(skb, ctinfo, protoff,
 213                                                 addr_beg_p - ib_ptr,
 214                                                 addr_end_p - addr_beg_p,
 215                                                 exp);
 216                        else if (nf_ct_expect_related(exp) != 0) {
 217                                nf_ct_helper_log(skb, ct,
 218                                                 "cannot add expectation");
 219                                ret = NF_DROP;
 220                        }
 221                        nf_ct_expect_put(exp);
 222                        goto out;
 223                }
 224        }
 225 out:
 226        spin_unlock_bh(&irc_buffer_lock);
 227        return ret;
 228}
 229
 230static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;
 231static struct nf_conntrack_expect_policy irc_exp_policy;
 232
 233static void nf_conntrack_irc_fini(void);
 234
 235static int __init nf_conntrack_irc_init(void)
 236{
 237        int i, ret;
 238
 239        if (max_dcc_channels < 1) {
 240                printk(KERN_ERR "nf_ct_irc: max_dcc_channels must not be zero\n");
 241                return -EINVAL;
 242        }
 243
 244        irc_exp_policy.max_expected = max_dcc_channels;
 245        irc_exp_policy.timeout = dcc_timeout;
 246
 247        irc_buffer = kmalloc(65536, GFP_KERNEL);
 248        if (!irc_buffer)
 249                return -ENOMEM;
 250
 251        /* If no port given, default to standard irc port */
 252        if (ports_c == 0)
 253                ports[ports_c++] = IRC_PORT;
 254
 255        for (i = 0; i < ports_c; i++) {
 256                irc[i].tuple.src.l3num = AF_INET;
 257                irc[i].tuple.src.u.tcp.port = htons(ports[i]);
 258                irc[i].tuple.dst.protonum = IPPROTO_TCP;
 259                irc[i].expect_policy = &irc_exp_policy;
 260                irc[i].me = THIS_MODULE;
 261                irc[i].help = help;
 262
 263                if (ports[i] == IRC_PORT)
 264                        sprintf(irc[i].name, "irc");
 265                else
 266                        sprintf(irc[i].name, "irc-%u", i);
 267
 268                ret = nf_conntrack_helper_register(&irc[i]);
 269                if (ret) {
 270                        printk(KERN_ERR "nf_ct_irc: failed to register helper "
 271                               "for pf: %u port: %u\n",
 272                               irc[i].tuple.src.l3num, ports[i]);
 273                        nf_conntrack_irc_fini();
 274                        return ret;
 275                }
 276        }
 277        return 0;
 278}
 279
 280/* This function is intentionally _NOT_ defined as __exit, because
 281 * it is needed by the init function */
 282static void nf_conntrack_irc_fini(void)
 283{
 284        int i;
 285
 286        for (i = 0; i < ports_c; i++)
 287                nf_conntrack_helper_unregister(&irc[i]);
 288        kfree(irc_buffer);
 289}
 290
 291module_init(nf_conntrack_irc_init);
 292module_exit(nf_conntrack_irc_fini);
 293
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