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 *
   5 * This program is free software; you can redistribute it and/or
   6 * modify it under the terms of the GNU General Public License
   7 * as published by the Free Software Foundation; either version
   8 * 2 of the License, or (at your option) any later version.
   9 */
  10
  11#include <linux/module.h>
  12#include <linux/moduleparam.h>
  13#include <linux/skbuff.h>
  14#include <linux/in.h>
  15#include <linux/ip.h>
  16#include <linux/tcp.h>
  17#include <linux/netfilter.h>
  18#include <linux/slab.h>
  19
  20#include <net/netfilter/nf_conntrack.h>
  21#include <net/netfilter/nf_conntrack_expect.h>
  22#include <net/netfilter/nf_conntrack_helper.h>
  23#include <linux/netfilter/nf_conntrack_irc.h>
  24
  25#define MAX_PORTS 8
  26static unsigned short ports[MAX_PORTS];
  27static unsigned int ports_c;
  28static unsigned int max_dcc_channels = 8;
  29static unsigned int dcc_timeout __read_mostly = 300;
  30/* This is slow, but it's simple. --RR */
  31static char *irc_buffer;
  32static DEFINE_SPINLOCK(irc_buffer_lock);
  33
  34unsigned int (*nf_nat_irc_hook)(struct sk_buff *skb,
  35                                enum ip_conntrack_info ctinfo,
  36                                unsigned int matchoff,
  37                                unsigned int matchlen,
  38                                struct nf_conntrack_expect *exp) __read_mostly;
  39EXPORT_SYMBOL_GPL(nf_nat_irc_hook);
  40
  41MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  42MODULE_DESCRIPTION("IRC (DCC) connection tracking helper");
  43MODULE_LICENSE("GPL");
  44MODULE_ALIAS("ip_conntrack_irc");
  45MODULE_ALIAS_NFCT_HELPER("irc");
  46
  47module_param_array(ports, ushort, &ports_c, 0400);
  48MODULE_PARM_DESC(ports, "port numbers of IRC servers");
  49module_param(max_dcc_channels, uint, 0400);
  50MODULE_PARM_DESC(max_dcc_channels, "max number of expected DCC channels per "
  51                                   "IRC session");
  52module_param(dcc_timeout, uint, 0400);
  53MODULE_PARM_DESC(dcc_timeout, "timeout on for unestablished DCC channels");
  54
  55static const char *const dccprotos[] = {
  56        "SEND ", "CHAT ", "MOVE ", "TSEND ", "SCHAT "
  57};
  58
  59#define MINMATCHLEN     5
  60
  61/* tries to get the ip_addr and port out of a dcc command
  62 * return value: -1 on failure, 0 on success
  63 *      data            pointer to first byte of DCC command data
  64 *      data_end        pointer to last byte of dcc command data
  65 *      ip              returns parsed ip of dcc command
  66 *      port            returns parsed port of dcc command
  67 *      ad_beg_p        returns pointer to first byte of addr data
  68 *      ad_end_p        returns pointer to last byte of addr data
  69 */
  70static int parse_dcc(char *data, const char *data_end, __be32 *ip,
  71                     u_int16_t *port, char **ad_beg_p, char **ad_end_p)
  72{
  73        char *tmp;
  74
  75        /* at least 12: "AAAAAAAA P\1\n" */
  76        while (*data++ != ' ')
  77                if (data > data_end - 12)
  78                        return -1;
  79
  80        /* Make sure we have a newline character within the packet boundaries
  81         * because simple_strtoul parses until the first invalid character. */
  82        for (tmp = data; tmp <= data_end; tmp++)
  83                if (*tmp == '\n')
  84                        break;
  85        if (tmp > data_end || *tmp != '\n')
  86                return -1;
  87
  88        *ad_beg_p = data;
  89        *ip = cpu_to_be32(simple_strtoul(data, &data, 10));
  90
  91        /* skip blanks between ip and port */
  92        while (*data == ' ') {
  93                if (data >= data_end)
  94                        return -1;
  95                data++;
  96        }
  97
  98        *port = simple_strtoul(data, &data, 10);
  99        *ad_end_p = data;
 100
 101        return 0;
 102}
 103
 104static int help(struct sk_buff *skb, unsigned int protoff,
 105                struct nf_conn *ct, enum ip_conntrack_info ctinfo)
 106{
 107        unsigned int dataoff;
 108        const struct iphdr *iph;
 109        const struct tcphdr *th;
 110        struct tcphdr _tcph;
 111        const char *data_limit;
 112        char *data, *ib_ptr;
 113        int dir = CTINFO2DIR(ctinfo);
 114        struct nf_conntrack_expect *exp;
 115        struct nf_conntrack_tuple *tuple;
 116        __be32 dcc_ip;
 117        u_int16_t dcc_port;
 118        __be16 port;
 119        int i, ret = NF_ACCEPT;
 120        char *addr_beg_p, *addr_end_p;
 121        typeof(nf_nat_irc_hook) nf_nat_irc;
 122
 123        /* If packet is coming from IRC server */
 124        if (dir == IP_CT_DIR_REPLY)
 125                return NF_ACCEPT;
 126
 127        /* Until there's been traffic both ways, don't look in packets. */
 128        if (ctinfo != IP_CT_ESTABLISHED && ctinfo != IP_CT_ESTABLISHED_REPLY)
 129                return NF_ACCEPT;
 130
 131        /* Not a full tcp header? */
 132        th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
 133        if (th == NULL)
 134                return NF_ACCEPT;
 135
 136        /* No data? */
 137        dataoff = protoff + th->doff*4;
 138        if (dataoff >= skb->len)
 139                return NF_ACCEPT;
 140
 141        spin_lock_bh(&irc_buffer_lock);
 142        ib_ptr = skb_header_pointer(skb, dataoff, skb->len - dataoff,
 143                                    irc_buffer);
 144        BUG_ON(ib_ptr == NULL);
 145
 146        data = ib_ptr;
 147        data_limit = ib_ptr + skb->len - dataoff;
 148
 149        /* strlen("\1DCC SENT t AAAAAAAA P\1\n")=24
 150         * 5+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=14 */
 151        while (data < data_limit - (19 + MINMATCHLEN)) {
 152                if (memcmp(data, "\1DCC ", 5)) {
 153                        data++;
 154                        continue;
 155                }
 156                data += 5;
 157                /* we have at least (19+MINMATCHLEN)-5 bytes valid data left */
 158
 159                iph = ip_hdr(skb);
 160                pr_debug("DCC found in master %pI4:%u %pI4:%u\n",
 161                         &iph->saddr, ntohs(th->source),
 162                         &iph->daddr, ntohs(th->dest));
 163
 164                for (i = 0; i < ARRAY_SIZE(dccprotos); i++) {
 165                        if (memcmp(data, dccprotos[i], strlen(dccprotos[i]))) {
 166                                /* no match */
 167                                continue;
 168                        }
 169                        data += strlen(dccprotos[i]);
 170                        pr_debug("DCC %s detected\n", dccprotos[i]);
 171
 172                        /* we have at least
 173                         * (19+MINMATCHLEN)-5-dccprotos[i].matchlen bytes valid
 174                         * data left (== 14/13 bytes) */
 175                        if (parse_dcc(data, data_limit, &dcc_ip,
 176                                       &dcc_port, &addr_beg_p, &addr_end_p)) {
 177                                pr_debug("unable to parse dcc command\n");
 178                                continue;
 179                        }
 180
 181                        pr_debug("DCC bound ip/port: %pI4:%u\n",
 182                                 &dcc_ip, dcc_port);
 183
 184                        /* dcc_ip can be the internal OR external (NAT'ed) IP */
 185                        tuple = &ct->tuplehash[dir].tuple;
 186                        if (tuple->src.u3.ip != dcc_ip &&
 187                            tuple->dst.u3.ip != dcc_ip) {
 188                                net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
 189                                                     &tuple->src.u3.ip,
 190                                                     &dcc_ip, dcc_port);
 191                                continue;
 192                        }
 193
 194                        exp = nf_ct_expect_alloc(ct);
 195                        if (exp == NULL) {
 196                                ret = NF_DROP;
 197                                goto out;
 198                        }
 199                        tuple = &ct->tuplehash[!dir].tuple;
 200                        port = htons(dcc_port);
 201                        nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
 202                                          tuple->src.l3num,
 203                                          NULL, &tuple->dst.u3,
 204                                          IPPROTO_TCP, NULL, &port);
 205
 206                        nf_nat_irc = rcu_dereference(nf_nat_irc_hook);
 207                        if (nf_nat_irc && ct->status & IPS_NAT_MASK)
 208                                ret = nf_nat_irc(skb, ctinfo,
 209                                                 addr_beg_p - ib_ptr,
 210                                                 addr_end_p - addr_beg_p,
 211                                                 exp);
 212                        else if (nf_ct_expect_related(exp) != 0)
 213                                ret = NF_DROP;
 214                        nf_ct_expect_put(exp);
 215                        goto out;
 216                }
 217        }
 218 out:
 219        spin_unlock_bh(&irc_buffer_lock);
 220        return ret;
 221}
 222
 223static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;
 224static struct nf_conntrack_expect_policy irc_exp_policy;
 225
 226static void nf_conntrack_irc_fini(void);
 227
 228static int __init nf_conntrack_irc_init(void)
 229{
 230        int i, ret;
 231
 232        if (max_dcc_channels < 1) {
 233                printk(KERN_ERR "nf_ct_irc: max_dcc_channels must not be zero\n");
 234                return -EINVAL;
 235        }
 236
 237        irc_exp_policy.max_expected = max_dcc_channels;
 238        irc_exp_policy.timeout = dcc_timeout;
 239
 240        irc_buffer = kmalloc(65536, GFP_KERNEL);
 241        if (!irc_buffer)
 242                return -ENOMEM;
 243
 244        /* If no port given, default to standard irc port */
 245        if (ports_c == 0)
 246                ports[ports_c++] = IRC_PORT;
 247
 248        for (i = 0; i < ports_c; i++) {
 249                irc[i].tuple.src.l3num = AF_INET;
 250                irc[i].tuple.src.u.tcp.port = htons(ports[i]);
 251                irc[i].tuple.dst.protonum = IPPROTO_TCP;
 252                irc[i].expect_policy = &irc_exp_policy;
 253                irc[i].me = THIS_MODULE;
 254                irc[i].help = help;
 255
 256                if (ports[i] == IRC_PORT)
 257                        sprintf(irc[i].name, "irc");
 258                else
 259                        sprintf(irc[i].name, "irc-%u", i);
 260
 261                ret = nf_conntrack_helper_register(&irc[i]);
 262                if (ret) {
 263                        printk(KERN_ERR "nf_ct_irc: failed to register helper "
 264                               "for pf: %u port: %u\n",
 265                               irc[i].tuple.src.l3num, ports[i]);
 266                        nf_conntrack_irc_fini();
 267                        return ret;
 268                }
 269        }
 270        return 0;
 271}
 272
 273/* This function is intentionally _NOT_ defined as __exit, because
 274 * it is needed by the init function */
 275static void nf_conntrack_irc_fini(void)
 276{
 277        int i;
 278
 279        for (i = 0; i < ports_c; i++)
 280                nf_conntrack_helper_unregister(&irc[i]);
 281        kfree(irc_buffer);
 282}
 283
 284module_init(nf_conntrack_irc_init);
 285module_exit(nf_conntrack_irc_fini);
 286
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