net/netfilter/nf_conntrack_irc.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* IRC extension for IP connection tracking, Version 1.21
   3  * (C) 2000-2002 by Harald Welte <laforge@gnumonks.org>
   4  * based on RR's ip_conntrack_ftp.c
   5  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
   6  */
   7
   8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
   9
  10 #include <linux/module.h>
  11 #include <linux/moduleparam.h>
  12 #include <linux/skbuff.h>
  13 #include <linux/in.h>
  14 #include <linux/ip.h>
  15 #include <linux/tcp.h>
  16 #include <linux/netfilter.h>
  17 #include <linux/slab.h>
  18
  19 #include <net/netfilter/nf_conntrack.h>
  20 #include <net/netfilter/nf_conntrack_expect.h>
  21 #include <net/netfilter/nf_conntrack_helper.h>
  22 #include <linux/netfilter/nf_conntrack_irc.h>
  23
  24 #define MAX_PORTS 8
  25 static unsigned short ports[MAX_PORTS];
  26 static unsigned int ports_c;
  27 static unsigned int max_dcc_channels = 8;
  28 static unsigned int dcc_timeout __read_mostly = 300;
  29 /* This is slow, but it's simple. --RR */
  30 static char *irc_buffer;
  31 static DEFINE_SPINLOCK(irc_buffer_lock);
  32
  33 unsigned int (*nf_nat_irc_hook)(struct sk_buff *skb,
  34                                 enum ip_conntrack_info ctinfo,
  35                                 unsigned int protoff,
  36                                 unsigned int matchoff,
  37                                 unsigned int matchlen,
  38                                 struct nf_conntrack_expect *exp) __read_mostly;
  39 EXPORT_SYMBOL_GPL(nf_nat_irc_hook);
  40
  41 #define HELPER_NAME "irc"
  42
  43 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  44 MODULE_DESCRIPTION("IRC (DCC) connection tracking helper");
  45 MODULE_LICENSE("GPL");
  46 MODULE_ALIAS("ip_conntrack_irc");
  47 MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
  48
  49 module_param_array(ports, ushort, &ports_c, 0400);
  50 MODULE_PARM_DESC(ports, "port numbers of IRC servers");
  51 module_param(max_dcc_channels, uint, 0400);
  52 MODULE_PARM_DESC(max_dcc_channels, "max number of expected DCC channels per "
  53                                    "IRC session");
  54 module_param(dcc_timeout, uint, 0400);
  55 MODULE_PARM_DESC(dcc_timeout, "timeout on for unestablished DCC channels");
  56
  57 static 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  */
  72 static 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
 106 static 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         if (!ib_ptr) {
 147                 spin_unlock_bh(&irc_buffer_lock);
 148                 return NF_ACCEPT;
 149         }
 150
 151         data = ib_ptr;
 152         data_limit = ib_ptr + skb->len - dataoff;
 153
 154         /* Skip any whitespace */
 155         while (data < data_limit - 10) {
 156                 if (*data == ' ' || *data == '\r' || *data == '\n')
 157                         data++;
 158                 else
 159                         break;
 160         }
 161
 162         /* strlen("PRIVMSG x ")=10 */
 163         if (data < data_limit - 10) {
 164                 if (strncasecmp("PRIVMSG ", data, 8))
 165                         goto out;
 166                 data += 8;
 167         }
 168
 169         /* strlen(" :\1DCC SENT t AAAAAAAA P\1\n")=26
 170          * 7+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=26
 171          */
 172         while (data < data_limit - (21 + MINMATCHLEN)) {
 173                 /* Find first " :", the start of message */
 174                 if (memcmp(data, " :", 2)) {
 175                         data++;
 176                         continue;
 177                 }
 178                 data += 2;
 179
 180                 /* then check that place only for the DCC command */
 181                 if (memcmp(data, "\1DCC ", 5))
 182                         goto out;
 183                 data += 5;
 184                 /* we have at least (21+MINMATCHLEN)-(2+5) bytes valid data left */
 185
 186                 iph = ip_hdr(skb);
 187                 pr_debug("DCC found in master %pI4:%u %pI4:%u\n",
 188                          &iph->saddr, ntohs(th->source),
 189                          &iph->daddr, ntohs(th->dest));
 190
 191                 for (i = 0; i < ARRAY_SIZE(dccprotos); i++) {
 192                         if (memcmp(data, dccprotos[i], strlen(dccprotos[i]))) {
 193                                 /* no match */
 194                                 continue;
 195                         }
 196                         data += strlen(dccprotos[i]);
 197                         pr_debug("DCC %s detected\n", dccprotos[i]);
 198
 199                         /* we have at least
 200                          * (21+MINMATCHLEN)-7-dccprotos[i].matchlen bytes valid
 201                          * data left (== 14/13 bytes) */
 202                         if (parse_dcc(data, data_limit, &dcc_ip,
 203                                        &dcc_port, &addr_beg_p, &addr_end_p)) {
 204                                 pr_debug("unable to parse dcc command\n");
 205                                 continue;
 206                         }
 207
 208                         pr_debug("DCC bound ip/port: %pI4:%u\n",
 209                                  &dcc_ip, dcc_port);
 210
 211                         /* dcc_ip can be the internal OR external (NAT'ed) IP */
 212                         tuple = &ct->tuplehash[dir].tuple;
 213                         if ((tuple->src.u3.ip != dcc_ip &&
 214                              ct->tuplehash[!dir].tuple.dst.u3.ip != dcc_ip) ||
 215                             dcc_port == 0) {
 216                                 net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
 217                                                      &tuple->src.u3.ip,
 218                                                      &dcc_ip, dcc_port);
 219                                 continue;
 220                         }
 221
 222                         exp = nf_ct_expect_alloc(ct);
 223                         if (exp == NULL) {
 224                                 nf_ct_helper_log(skb, ct,
 225                                                  "cannot alloc expectation");
 226                                 ret = NF_DROP;
 227                                 goto out;
 228                         }
 229                         tuple = &ct->tuplehash[!dir].tuple;
 230                         port = htons(dcc_port);
 231                         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
 232                                           tuple->src.l3num,
 233                                           NULL, &tuple->dst.u3,
 234                                           IPPROTO_TCP, NULL, &port);
 235
 236                         nf_nat_irc = rcu_dereference(nf_nat_irc_hook);
 237                         if (nf_nat_irc && ct->status & IPS_NAT_MASK)
 238                                 ret = nf_nat_irc(skb, ctinfo, protoff,
 239                                                  addr_beg_p - ib_ptr,
 240                                                  addr_end_p - addr_beg_p,
 241                                                  exp);
 242                         else if (nf_ct_expect_related(exp, 0) != 0) {
 243                                 nf_ct_helper_log(skb, ct,
 244                                                  "cannot add expectation");
 245                                 ret = NF_DROP;
 246                         }
 247                         nf_ct_expect_put(exp);
 248                         goto out;
 249                 }
 250         }
 251  out:
 252         spin_unlock_bh(&irc_buffer_lock);
 253         return ret;
 254 }
 255
 256 static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;
 257 static struct nf_conntrack_expect_policy irc_exp_policy;
 258
 259 static int __init nf_conntrack_irc_init(void)
 260 {
 261         int i, ret;
 262
 263         if (max_dcc_channels < 1) {
 264                 pr_err("max_dcc_channels must not be zero\n");
 265                 return -EINVAL;
 266         }
 267
 268         if (max_dcc_channels > NF_CT_EXPECT_MAX_CNT) {
 269                 pr_err("max_dcc_channels must not be more than %u\n",
 270                        NF_CT_EXPECT_MAX_CNT);
 271                 return -EINVAL;
 272         }
 273
 274         irc_exp_policy.max_expected = max_dcc_channels;
 275         irc_exp_policy.timeout = dcc_timeout;
 276
 277         irc_buffer = kmalloc(65536, GFP_KERNEL);
 278         if (!irc_buffer)
 279                 return -ENOMEM;
 280
 281         /* If no port given, default to standard irc port */
 282         if (ports_c == 0)
 283                 ports[ports_c++] = IRC_PORT;
 284
 285         for (i = 0; i < ports_c; i++) {
 286                 nf_ct_helper_init(&irc[i], AF_INET, IPPROTO_TCP, HELPER_NAME,
 287                                   IRC_PORT, ports[i], i, &irc_exp_policy,
 288                                   0, help, NULL, THIS_MODULE);
 289         }
 290
 291         ret = nf_conntrack_helpers_register(&irc[0], ports_c);
 292         if (ret) {
 293                 pr_err("failed to register helpers\n");
 294                 kfree(irc_buffer);
 295                 return ret;
 296         }
 297
 298         return 0;
 299 }
 300
 301 static void __exit nf_conntrack_irc_fini(void)
 302 {
 303         nf_conntrack_helpers_unregister(irc, ports_c);
 304         kfree(irc_buffer);
 305 }
 306
 307 module_init(nf_conntrack_irc_init);
 308 module_exit(nf_conntrack_irc_fini);