root/net/netfilter/nf_conntrack_irc.c

DEFINITIONS

1. parse_dcc
2. help
3. nf_conntrack_irc_init
4. nf_conntrack_irc_fini

   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         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) != 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 
 230 static struct nf_conntrack_helper irc[MAX_PORTS] __read_mostly;
 231 static struct nf_conntrack_expect_policy irc_exp_policy;
 232 
 233 static int __init nf_conntrack_irc_init(void)
 234 {
 235         int i, ret;
 236 
 237         if (max_dcc_channels < 1) {
 238                 pr_err("max_dcc_channels must not be zero\n");
 239                 return -EINVAL;
 240         }
 241 
 242         if (max_dcc_channels > NF_CT_EXPECT_MAX_CNT) {
 243                 pr_err("max_dcc_channels must not be more than %u\n",
 244                        NF_CT_EXPECT_MAX_CNT);
 245                 return -EINVAL;
 246         }
 247 
 248         irc_exp_policy.max_expected = max_dcc_channels;
 249         irc_exp_policy.timeout = dcc_timeout;
 250 
 251         irc_buffer = kmalloc(65536, GFP_KERNEL);
 252         if (!irc_buffer)
 253                 return -ENOMEM;
 254 
 255         /* If no port given, default to standard irc port */
 256         if (ports_c == 0)
 257                 ports[ports_c++] = IRC_PORT;
 258 
 259         for (i = 0; i < ports_c; i++) {
 260                 nf_ct_helper_init(&irc[i], AF_INET, IPPROTO_TCP, HELPER_NAME,
 261                                   IRC_PORT, ports[i], i, &irc_exp_policy,
 262                                   0, help, NULL, THIS_MODULE);
 263         }
 264 
 265         ret = nf_conntrack_helpers_register(&irc[0], ports_c);
 266         if (ret) {
 267                 pr_err("failed to register helpers\n");
 268                 kfree(irc_buffer);
 269                 return ret;
 270         }
 271 
 272         return 0;
 273 }
 274 
 275 static void __exit nf_conntrack_irc_fini(void)
 276 {
 277         nf_conntrack_helpers_unregister(irc, ports_c);
 278         kfree(irc_buffer);
 279 }
 280 
 281 module_init(nf_conntrack_irc_init);
 282 module_exit(nf_conntrack_irc_fini);