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 #define MAX_SEARCH_SIZE 4095
  43
  44 MODULE_AUTHOR("Harald Welte <laforge@netfilter.org>");
  45 MODULE_DESCRIPTION("IRC (DCC) connection tracking helper");
  46 MODULE_LICENSE("GPL");
  47 MODULE_ALIAS("ip_conntrack_irc");
  48 MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
  49
  50 module_param_array(ports, ushort, &ports_c, 0400);
  51 MODULE_PARM_DESC(ports, "port numbers of IRC servers");
  52 module_param(max_dcc_channels, uint, 0400);
  53 MODULE_PARM_DESC(max_dcc_channels, "max number of expected DCC channels per "
  54                                    "IRC session");
  55 module_param(dcc_timeout, uint, 0400);
  56 MODULE_PARM_DESC(dcc_timeout, "timeout on for unestablished DCC channels");
  57
  58 static const char *const dccprotos[] = {
  59         "SEND ", "CHAT ", "MOVE ", "TSEND ", "SCHAT "
  60 };
  61
  62 #define MINMATCHLEN     5
  63
  64 /* tries to get the ip_addr and port out of a dcc command
  65  * return value: -1 on failure, 0 on success
  66  *      data            pointer to first byte of DCC command data
  67  *      data_end        pointer to last byte of dcc command data
  68  *      ip              returns parsed ip of dcc command
  69  *      port            returns parsed port of dcc command
  70  *      ad_beg_p        returns pointer to first byte of addr data
  71  *      ad_end_p        returns pointer to last byte of addr data
  72  */
  73 static int parse_dcc(char *data, const char *data_end, __be32 *ip,
  74                      u_int16_t *port, char **ad_beg_p, char **ad_end_p)
  75 {
  76         char *tmp;
  77
  78         /* at least 12: "AAAAAAAA P\1\n" */
  79         while (*data++ != ' ')
  80                 if (data > data_end - 12)
  81                         return -1;
  82
  83         /* Make sure we have a newline character within the packet boundaries
  84          * because simple_strtoul parses until the first invalid character. */
  85         for (tmp = data; tmp <= data_end; tmp++)
  86                 if (*tmp == '\n')
  87                         break;
  88         if (tmp > data_end || *tmp != '\n')
  89                 return -1;
  90
  91         *ad_beg_p = data;
  92         *ip = cpu_to_be32(simple_strtoul(data, &data, 10));
  93
  94         /* skip blanks between ip and port */
  95         while (*data == ' ') {
  96                 if (data >= data_end)
  97                         return -1;
  98                 data++;
  99         }
 100
 101         *port = simple_strtoul(data, &data, 10);
 102         *ad_end_p = data;
 103
 104         return 0;
 105 }
 106
 107 static int help(struct sk_buff *skb, unsigned int protoff,
 108                 struct nf_conn *ct, enum ip_conntrack_info ctinfo)
 109 {
 110         unsigned int dataoff;
 111         const struct iphdr *iph;
 112         const struct tcphdr *th;
 113         struct tcphdr _tcph;
 114         const char *data_limit;
 115         char *data, *ib_ptr;
 116         int dir = CTINFO2DIR(ctinfo);
 117         struct nf_conntrack_expect *exp;
 118         struct nf_conntrack_tuple *tuple;
 119         __be32 dcc_ip;
 120         u_int16_t dcc_port;
 121         __be16 port;
 122         int i, ret = NF_ACCEPT;
 123         char *addr_beg_p, *addr_end_p;
 124         typeof(nf_nat_irc_hook) nf_nat_irc;
 125         unsigned int datalen;
 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         datalen = skb->len - dataoff;
 146         if (datalen > MAX_SEARCH_SIZE)
 147                 datalen = MAX_SEARCH_SIZE;
 148
 149         spin_lock_bh(&irc_buffer_lock);
 150         ib_ptr = skb_header_pointer(skb, dataoff, datalen,
 151                                     irc_buffer);
 152         if (!ib_ptr) {
 153                 spin_unlock_bh(&irc_buffer_lock);
 154                 return NF_ACCEPT;
 155         }
 156
 157         data = ib_ptr;
 158         data_limit = ib_ptr + datalen;
 159
 160         /* strlen("\1DCC SENT t AAAAAAAA P\1\n")=24
 161          * 5+MINMATCHLEN+strlen("t AAAAAAAA P\1\n")=14 */
 162         while (data < data_limit - (19 + MINMATCHLEN)) {
 163                 if (memcmp(data, "\1DCC ", 5)) {
 164                         data++;
 165                         continue;
 166                 }
 167                 data += 5;
 168                 /* we have at least (19+MINMATCHLEN)-5 bytes valid data left */
 169
 170                 iph = ip_hdr(skb);
 171                 pr_debug("DCC found in master %pI4:%u %pI4:%u\n",
 172                          &iph->saddr, ntohs(th->source),
 173                          &iph->daddr, ntohs(th->dest));
 174
 175                 for (i = 0; i < ARRAY_SIZE(dccprotos); i++) {
 176                         if (memcmp(data, dccprotos[i], strlen(dccprotos[i]))) {
 177                                 /* no match */
 178                                 continue;
 179                         }
 180                         data += strlen(dccprotos[i]);
 181                         pr_debug("DCC %s detected\n", dccprotos[i]);
 182
 183                         /* we have at least
 184                          * (19+MINMATCHLEN)-5-dccprotos[i].matchlen bytes valid
 185                          * data left (== 14/13 bytes) */
 186                         if (parse_dcc(data, data_limit, &dcc_ip,
 187                                        &dcc_port, &addr_beg_p, &addr_end_p)) {
 188                                 pr_debug("unable to parse dcc command\n");
 189                                 continue;
 190                         }
 191
 192                         pr_debug("DCC bound ip/port: %pI4:%u\n",
 193                                  &dcc_ip, dcc_port);
 194
 195                         /* dcc_ip can be the internal OR external (NAT'ed) IP */
 196                         tuple = &ct->tuplehash[dir].tuple;
 197                         if ((tuple->src.u3.ip != dcc_ip &&
 198                              ct->tuplehash[!dir].tuple.dst.u3.ip != dcc_ip) ||
 199                             dcc_port == 0) {
 200                                 net_warn_ratelimited("Forged DCC command from %pI4: %pI4:%u\n",
 201                                                      &tuple->src.u3.ip,
 202                                                      &dcc_ip, dcc_port);
 203                                 continue;
 204                         }
 205
 206                         exp = nf_ct_expect_alloc(ct);
 207                         if (exp == NULL) {
 208                                 nf_ct_helper_log(skb, ct,
 209                                                  "cannot alloc expectation");
 210                                 ret = NF_DROP;
 211                                 goto out;
 212                         }
 213                         tuple = &ct->tuplehash[!dir].tuple;
 214                         port = htons(dcc_port);
 215                         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT,
 216                                           tuple->src.l3num,
 217                                           NULL, &tuple->dst.u3,
 218                                           IPPROTO_TCP, NULL, &port);
 219
 220                         nf_nat_irc = rcu_dereference(nf_nat_irc_hook);
 221                         if (nf_nat_irc && ct->status & IPS_NAT_MASK)
 222                                 ret = nf_nat_irc(skb, ctinfo, protoff,
 223                                                  addr_beg_p - ib_ptr,
 224                                                  addr_end_p - addr_beg_p,
 225                                                  exp);
 226                         else if (nf_ct_expect_related(exp, 0) != 0) {
 227                                 nf_ct_helper_log(skb, ct,
 228                                                  "cannot add expectation");
 229                                 ret = NF_DROP;
 230                         }
 231                         nf_ct_expect_put(exp);
 232                         goto out;
 233                 }
 234         }
 235  out:
 236         spin_unlock_bh(&irc_buffer_lock);
 237         return ret;
 238 }
 239
 240 static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;
 241 static struct nf_conntrack_expect_policy irc_exp_policy;
 242
 243 static int __init nf_conntrack_irc_init(void)
 244 {
 245         int i, ret;
 246
 247         if (max_dcc_channels < 1) {
 248                 pr_err("max_dcc_channels must not be zero\n");
 249                 return -EINVAL;
 250         }
 251
 252         if (max_dcc_channels > NF_CT_EXPECT_MAX_CNT) {
 253                 pr_err("max_dcc_channels must not be more than %u\n",
 254                        NF_CT_EXPECT_MAX_CNT);
 255                 return -EINVAL;
 256         }
 257
 258         irc_exp_policy.max_expected = max_dcc_channels;
 259         irc_exp_policy.timeout = dcc_timeout;
 260
 261         irc_buffer = kmalloc(MAX_SEARCH_SIZE + 1, GFP_KERNEL);
 262         if (!irc_buffer)
 263                 return -ENOMEM;
 264
 265         /* If no port given, default to standard irc port */
 266         if (ports_c == 0)
 267                 ports[ports_c++] = IRC_PORT;
 268
 269         for (i = 0; i < ports_c; i++) {
 270                 nf_ct_helper_init(&irc[i], AF_INET, IPPROTO_TCP, HELPER_NAME,
 271                                   IRC_PORT, ports[i], i, &irc_exp_policy,
 272                                   0, help, NULL, THIS_MODULE);
 273         }
 274
 275         ret = nf_conntrack_helpers_register(&irc[0], ports_c);
 276         if (ret) {
 277                 pr_err("failed to register helpers\n");
 278                 kfree(irc_buffer);
 279                 return ret;
 280         }
 281
 282         return 0;
 283 }
 284
 285 static void __exit nf_conntrack_irc_fini(void)
 286 {
 287         nf_conntrack_helpers_unregister(irc, ports_c);
 288         kfree(irc_buffer);
 289 }
 290
 291 module_init(nf_conntrack_irc_init);
 292 module_exit(nf_conntrack_irc_fini);