net/netfilter/nf_conntrack_ftp.c

   1 /* FTP extension for connection tracking. */
   2
   3 /* (C) 1999-2001 Paul `Rusty' Russell
   4  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   5  * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <linux/moduleparam.h>
  14 #include <linux/netfilter.h>
  15 #include <linux/ip.h>
  16 #include <linux/ipv6.h>
  17 #include <linux/ctype.h>
  18 #include <linux/inet.h>
  19 #include <net/checksum.h>
  20 #include <net/tcp.h>
  21
  22 #include <net/netfilter/nf_conntrack.h>
  23 #include <net/netfilter/nf_conntrack_expect.h>
  24 #include <net/netfilter/nf_conntrack_ecache.h>
  25 #include <net/netfilter/nf_conntrack_helper.h>
  26 #include <linux/netfilter/nf_conntrack_ftp.h>
  27
  28 MODULE_LICENSE("GPL");
  29 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  30 MODULE_DESCRIPTION("ftp connection tracking helper");
  31 MODULE_ALIAS("ip_conntrack_ftp");
  32 MODULE_ALIAS_NFCT_HELPER("ftp");
  33
  34 /* This is slow, but it's simple. --RR */
  35 static char *ftp_buffer;
  36
  37 static DEFINE_SPINLOCK(nf_ftp_lock);
  38
  39 #define MAX_PORTS 8
  40 static u_int16_t ports[MAX_PORTS];
  41 static unsigned int ports_c;
  42 module_param_array(ports, ushort, &ports_c, 0400);
  43
  44 static int loose;
  45 module_param(loose, bool, 0600);
  46
  47 unsigned int (*nf_nat_ftp_hook)(struct sk_buff *skb,
  48                                 enum ip_conntrack_info ctinfo,
  49                                 enum nf_ct_ftp_type type,
  50                                 unsigned int matchoff,
  51                                 unsigned int matchlen,
  52                                 struct nf_conntrack_expect *exp);
  53 EXPORT_SYMBOL_GPL(nf_nat_ftp_hook);
  54
  55 static int try_rfc959(const char *, size_t, struct nf_conntrack_man *, char);
  56 static int try_eprt(const char *, size_t, struct nf_conntrack_man *, char);
  57 static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *,
  58                              char);
  59
  60 static struct ftp_search {
  61         const char *pattern;
  62         size_t plen;
  63         char skip;
  64         char term;
  65         enum nf_ct_ftp_type ftptype;
  66         int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char);
  67 } search[IP_CT_DIR_MAX][2] = {
  68         [IP_CT_DIR_ORIGINAL] = {
  69                 {
  70                         .pattern        = "PORT",
  71                         .plen           = sizeof("PORT") - 1,
  72                         .skip           = ' ',
  73                         .term           = '\r',
  74                         .ftptype        = NF_CT_FTP_PORT,
  75                         .getnum         = try_rfc959,
  76                 },
  77                 {
  78                         .pattern        = "EPRT",
  79                         .plen           = sizeof("EPRT") - 1,
  80                         .skip           = ' ',
  81                         .term           = '\r',
  82                         .ftptype        = NF_CT_FTP_EPRT,
  83                         .getnum         = try_eprt,
  84                 },
  85         },
  86         [IP_CT_DIR_REPLY] = {
  87                 {
  88                         .pattern        = "227 ",
  89                         .plen           = sizeof("227 ") - 1,
  90                         .skip           = '(',
  91                         .term           = ')',
  92                         .ftptype        = NF_CT_FTP_PASV,
  93                         .getnum         = try_rfc959,
  94                 },
  95                 {
  96                         .pattern        = "229 ",
  97                         .plen           = sizeof("229 ") - 1,
  98                         .skip           = '(',
  99                         .term           = ')',
 100                         .ftptype        = NF_CT_FTP_EPSV,
 101                         .getnum         = try_epsv_response,
 102                 },
 103         },
 104 };
 105
 106 static int
 107 get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term)
 108 {
 109         const char *end;
 110         int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end);
 111         if (ret > 0)
 112                 return (int)(end - src);
 113         return 0;
 114 }
 115
 116 static int try_number(const char *data, size_t dlen, u_int32_t array[],
 117                       int array_size, char sep, char term)
 118 {
 119         u_int32_t i, len;
 120
 121         memset(array, 0, sizeof(array[0])*array_size);
 122
 123         /* Keep data pointing at next char. */
 124         for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) {
 125                 if (*data >= '0' && *data <= '9') {
 126                         array[i] = array[i]*10 + *data - '0';
 127                 }
 128                 else if (*data == sep)
 129                         i++;
 130                 else {
 131                         /* Unexpected character; true if it's the
 132                            terminator and we're finished. */
 133                         if (*data == term && i == array_size - 1)
 134                                 return len;
 135
 136                         pr_debug("Char %u (got %u nums) `%u' unexpected\n",
 137                                  len, i, *data);
 138                         return 0;
 139                 }
 140         }
 141         pr_debug("Failed to fill %u numbers separated by %c\n",
 142                  array_size, sep);
 143         return 0;
 144 }
 145
 146 /* Returns 0, or length of numbers: 192,168,1,1,5,6 */
 147 static int try_rfc959(const char *data, size_t dlen,
 148                       struct nf_conntrack_man *cmd, char term)
 149 {
 150         int length;
 151         u_int32_t array[6];
 152
 153         length = try_number(data, dlen, array, 6, ',', term);
 154         if (length == 0)
 155                 return 0;
 156
 157         cmd->u3.ip =  htonl((array[0] << 24) | (array[1] << 16) |
 158                                     (array[2] << 8) | array[3]);
 159         cmd->u.tcp.port = htons((array[4] << 8) | array[5]);
 160         return length;
 161 }
 162
 163 /* Grab port: number up to delimiter */
 164 static int get_port(const char *data, int start, size_t dlen, char delim,
 165                     __be16 *port)
 166 {
 167         u_int16_t tmp_port = 0;
 168         int i;
 169
 170         for (i = start; i < dlen; i++) {
 171                 /* Finished? */
 172                 if (data[i] == delim) {
 173                         if (tmp_port == 0)
 174                                 break;
 175                         *port = htons(tmp_port);
 176                         pr_debug("get_port: return %d\n", tmp_port);
 177                         return i + 1;
 178                 }
 179                 else if (data[i] >= '0' && data[i] <= '9')
 180                         tmp_port = tmp_port*10 + data[i] - '0';
 181                 else { /* Some other crap */
 182                         pr_debug("get_port: invalid char.\n");
 183                         break;
 184                 }
 185         }
 186         return 0;
 187 }
 188
 189 /* Returns 0, or length of numbers: |1|132.235.1.2|6275| or |2|3ffe::1|6275| */
 190 static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd,
 191                     char term)
 192 {
 193         char delim;
 194         int length;
 195
 196         /* First character is delimiter, then "1" for IPv4 or "2" for IPv6,
 197            then delimiter again. */
 198         if (dlen <= 3) {
 199                 pr_debug("EPRT: too short\n");
 200                 return 0;
 201         }
 202         delim = data[0];
 203         if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) {
 204                 pr_debug("try_eprt: invalid delimitter.\n");
 205                 return 0;
 206         }
 207
 208         if ((cmd->l3num == PF_INET && data[1] != '1') ||
 209             (cmd->l3num == PF_INET6 && data[1] != '2')) {
 210                 pr_debug("EPRT: invalid protocol number.\n");
 211                 return 0;
 212         }
 213
 214         pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim);
 215
 216         if (data[1] == '1') {
 217                 u_int32_t array[4];
 218
 219                 /* Now we have IP address. */
 220                 length = try_number(data + 3, dlen - 3, array, 4, '.', delim);
 221                 if (length != 0)
 222                         cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16)
 223                                            | (array[2] << 8) | array[3]);
 224         } else {
 225                 /* Now we have IPv6 address. */
 226                 length = get_ipv6_addr(data + 3, dlen - 3,
 227                                        (struct in6_addr *)cmd->u3.ip6, delim);
 228         }
 229
 230         if (length == 0)
 231                 return 0;
 232         pr_debug("EPRT: Got IP address!\n");
 233         /* Start offset includes initial "|1|", and trailing delimiter */
 234         return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port);
 235 }
 236
 237 /* Returns 0, or length of numbers: |||6446| */
 238 static int try_epsv_response(const char *data, size_t dlen,
 239                              struct nf_conntrack_man *cmd, char term)
 240 {
 241         char delim;
 242
 243         /* Three delimiters. */
 244         if (dlen <= 3) return 0;
 245         delim = data[0];
 246         if (isdigit(delim) || delim < 33 || delim > 126 ||
 247             data[1] != delim || data[2] != delim)
 248                 return 0;
 249
 250         return get_port(data, 3, dlen, delim, &cmd->u.tcp.port);
 251 }
 252
 253 /* Return 1 for match, 0 for accept, -1 for partial. */
 254 static int find_pattern(const char *data, size_t dlen,
 255                         const char *pattern, size_t plen,
 256                         char skip, char term,
 257                         unsigned int *numoff,
 258                         unsigned int *numlen,
 259                         struct nf_conntrack_man *cmd,
 260                         int (*getnum)(const char *, size_t,
 261                                       struct nf_conntrack_man *, char))
 262 {
 263         size_t i;
 264
 265         pr_debug("find_pattern `%s': dlen = %Zu\n", pattern, dlen);
 266         if (dlen == 0)
 267                 return 0;
 268
 269         if (dlen <= plen) {
 270                 /* Short packet: try for partial? */
 271                 if (strnicmp(data, pattern, dlen) == 0)
 272                         return -1;
 273                 else return 0;
 274         }
 275
 276         if (strnicmp(data, pattern, plen) != 0) {
 277 #if 0
 278                 size_t i;
 279
 280                 pr_debug("ftp: string mismatch\n");
 281                 for (i = 0; i < plen; i++) {
 282                         pr_debug("ftp:char %u `%c'(%u) vs `%c'(%u)\n",
 283                                  i, data[i], data[i],
 284                                  pattern[i], pattern[i]);
 285                 }
 286 #endif
 287                 return 0;
 288         }
 289
 290         pr_debug("Pattern matches!\n");
 291         /* Now we've found the constant string, try to skip
 292            to the 'skip' character */
 293         for (i = plen; data[i] != skip; i++)
 294                 if (i == dlen - 1) return -1;
 295
 296         /* Skip over the last character */
 297         i++;
 298
 299         pr_debug("Skipped up to `%c'!\n", skip);
 300
 301         *numoff = i;
 302         *numlen = getnum(data + i, dlen - i, cmd, term);
 303         if (!*numlen)
 304                 return -1;
 305
 306         pr_debug("Match succeeded!\n");
 307         return 1;
 308 }
 309
 310 /* Look up to see if we're just after a \n. */
 311 static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir)
 312 {
 313         unsigned int i;
 314
 315         for (i = 0; i < info->seq_aft_nl_num[dir]; i++)
 316                 if (info->seq_aft_nl[dir][i] == seq)
 317                         return 1;
 318         return 0;
 319 }
 320
 321 /* We don't update if it's older than what we have. */
 322 static void update_nl_seq(struct nf_conn *ct, u32 nl_seq,
 323                           struct nf_ct_ftp_master *info, int dir,
 324                           struct sk_buff *skb)
 325 {
 326         unsigned int i, oldest = NUM_SEQ_TO_REMEMBER;
 327
 328         /* Look for oldest: if we find exact match, we're done. */
 329         for (i = 0; i < info->seq_aft_nl_num[dir]; i++) {
 330                 if (info->seq_aft_nl[dir][i] == nl_seq)
 331                         return;
 332
 333                 if (oldest == info->seq_aft_nl_num[dir] ||
 334                     before(info->seq_aft_nl[dir][i],
 335                            info->seq_aft_nl[dir][oldest]))
 336                         oldest = i;
 337         }
 338
 339         if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) {
 340                 info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq;
 341         } else if (oldest != NUM_SEQ_TO_REMEMBER &&
 342                    after(nl_seq, info->seq_aft_nl[dir][oldest])) {
 343                 info->seq_aft_nl[dir][oldest] = nl_seq;
 344         }
 345 }
 346
 347 static int help(struct sk_buff *skb,
 348                 unsigned int protoff,
 349                 struct nf_conn *ct,
 350                 enum ip_conntrack_info ctinfo)
 351 {
 352         unsigned int dataoff, datalen;
 353         const struct tcphdr *th;
 354         struct tcphdr _tcph;
 355         const char *fb_ptr;
 356         int ret;
 357         u32 seq;
 358         int dir = CTINFO2DIR(ctinfo);
 359         unsigned int uninitialized_var(matchlen), uninitialized_var(matchoff);
 360         struct nf_ct_ftp_master *ct_ftp_info = &nfct_help(ct)->help.ct_ftp_info;
 361         struct nf_conntrack_expect *exp;
 362         union nf_inet_addr *daddr;
 363         struct nf_conntrack_man cmd = {};
 364         unsigned int i;
 365         int found = 0, ends_in_nl;
 366         typeof(nf_nat_ftp_hook) nf_nat_ftp;
 367
 368         /* Until there's been traffic both ways, don't look in packets. */
 369         if (ctinfo != IP_CT_ESTABLISHED &&
 370             ctinfo != IP_CT_ESTABLISHED + IP_CT_IS_REPLY) {
 371                 pr_debug("ftp: Conntrackinfo = %u\n", ctinfo);
 372                 return NF_ACCEPT;
 373         }
 374
 375         th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
 376         if (th == NULL)
 377                 return NF_ACCEPT;
 378
 379         dataoff = protoff + th->doff * 4;
 380         /* No data? */
 381         if (dataoff >= skb->len) {
 382                 pr_debug("ftp: dataoff(%u) >= skblen(%u)\n", dataoff,
 383                          skb->len);
 384                 return NF_ACCEPT;
 385         }
 386         datalen = skb->len - dataoff;
 387
 388         spin_lock_bh(&nf_ftp_lock);
 389         fb_ptr = skb_header_pointer(skb, dataoff, datalen, ftp_buffer);
 390         BUG_ON(fb_ptr == NULL);
 391
 392         ends_in_nl = (fb_ptr[datalen - 1] == '\n');
 393         seq = ntohl(th->seq) + datalen;
 394
 395         /* Look up to see if we're just after a \n. */
 396         if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) {
 397                 /* Now if this ends in \n, update ftp info. */
 398                 pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n",
 399                          ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)",
 400                          ct_ftp_info->seq_aft_nl[dir][0],
 401                          ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)",
 402                          ct_ftp_info->seq_aft_nl[dir][1]);
 403                 ret = NF_ACCEPT;
 404                 goto out_update_nl;
 405         }
 406
 407         /* Initialize IP/IPv6 addr to expected address (it's not mentioned
 408            in EPSV responses) */
 409         cmd.l3num = nf_ct_l3num(ct);
 410         memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
 411                sizeof(cmd.u3.all));
 412
 413         for (i = 0; i < ARRAY_SIZE(search[dir]); i++) {
 414                 found = find_pattern(fb_ptr, datalen,
 415                                      search[dir][i].pattern,
 416                                      search[dir][i].plen,
 417                                      search[dir][i].skip,
 418                                      search[dir][i].term,
 419                                      &matchoff, &matchlen,
 420                                      &cmd,
 421                                      search[dir][i].getnum);
 422                 if (found) break;
 423         }
 424         if (found == -1) {
 425                 /* We don't usually drop packets.  After all, this is
 426                    connection tracking, not packet filtering.
 427                    However, it is necessary for accurate tracking in
 428                    this case. */
 429                 pr_debug("conntrack_ftp: partial %s %u+%u\n",
 430                          search[dir][i].pattern,  ntohl(th->seq), datalen);
 431                 ret = NF_DROP;
 432                 goto out;
 433         } else if (found == 0) { /* No match */
 434                 ret = NF_ACCEPT;
 435                 goto out_update_nl;
 436         }
 437
 438         pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n",
 439                  matchlen, fb_ptr + matchoff,
 440                  matchlen, ntohl(th->seq) + matchoff);
 441
 442         exp = nf_ct_expect_alloc(ct);
 443         if (exp == NULL) {
 444                 ret = NF_DROP;
 445                 goto out;
 446         }
 447
 448         /* We refer to the reverse direction ("!dir") tuples here,
 449          * because we're expecting something in the other direction.
 450          * Doesn't matter unless NAT is happening.  */
 451         daddr = &ct->tuplehash[!dir].tuple.dst.u3;
 452
 453         /* Update the ftp info */
 454         if ((cmd.l3num == nf_ct_l3num(ct)) &&
 455             memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
 456                      sizeof(cmd.u3.all))) {
 457                 /* Enrico Scholz's passive FTP to partially RNAT'd ftp
 458                    server: it really wants us to connect to a
 459                    different IP address.  Simply don't record it for
 460                    NAT. */
 461                 if (cmd.l3num == PF_INET) {
 462                         pr_debug("conntrack_ftp: NOT RECORDING: %pI4 != %pI4\n",
 463                                  &cmd.u3.ip,
 464                                  &ct->tuplehash[dir].tuple.src.u3.ip);
 465                 } else {
 466                         pr_debug("conntrack_ftp: NOT RECORDING: %pI6 != %pI6\n",
 467                                  cmd.u3.ip6,
 468                                  ct->tuplehash[dir].tuple.src.u3.ip6);
 469                 }
 470
 471                 /* Thanks to Cristiano Lincoln Mattos
 472                    <lincoln@cesar.org.br> for reporting this potential
 473                    problem (DMZ machines opening holes to internal
 474                    networks, or the packet filter itself). */
 475                 if (!loose) {
 476                         ret = NF_ACCEPT;
 477                         goto out_put_expect;
 478                 }
 479                 daddr = &cmd.u3;
 480         }
 481
 482         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num,
 483                           &ct->tuplehash[!dir].tuple.src.u3, daddr,
 484                           IPPROTO_TCP, NULL, &cmd.u.tcp.port);
 485
 486         /* Now, NAT might want to mangle the packet, and register the
 487          * (possibly changed) expectation itself. */
 488         nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook);
 489         if (nf_nat_ftp && ct->status & IPS_NAT_MASK)
 490                 ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype,
 491                                  matchoff, matchlen, exp);
 492         else {
 493                 /* Can't expect this?  Best to drop packet now. */
 494                 if (nf_ct_expect_related(exp) != 0)
 495                         ret = NF_DROP;
 496                 else
 497                         ret = NF_ACCEPT;
 498         }
 499
 500 out_put_expect:
 501         nf_ct_expect_put(exp);
 502
 503 out_update_nl:
 504         /* Now if this ends in \n, update ftp info.  Seq may have been
 505          * adjusted by NAT code. */
 506         if (ends_in_nl)
 507                 update_nl_seq(ct, seq, ct_ftp_info, dir, skb);
 508  out:
 509         spin_unlock_bh(&nf_ftp_lock);
 510         return ret;
 511 }
 512
 513 static struct nf_conntrack_helper ftp[MAX_PORTS][2] __read_mostly;
 514 static char ftp_names[MAX_PORTS][2][sizeof("ftp-65535")] __read_mostly;
 515
 516 static const struct nf_conntrack_expect_policy ftp_exp_policy = {
 517         .max_expected   = 1,
 518         .timeout        = 5 * 60,
 519 };
 520
 521 /* don't make this __exit, since it's called from __init ! */
 522 static void nf_conntrack_ftp_fini(void)
 523 {
 524         int i, j;
 525         for (i = 0; i < ports_c; i++) {
 526                 for (j = 0; j < 2; j++) {
 527                         if (ftp[i][j].me == NULL)
 528                                 continue;
 529
 530                         pr_debug("nf_ct_ftp: unregistering helper for pf: %d "
 531                                  "port: %d\n",
 532                                  ftp[i][j].tuple.src.l3num, ports[i]);
 533                         nf_conntrack_helper_unregister(&ftp[i][j]);
 534                 }
 535         }
 536
 537         kfree(ftp_buffer);
 538 }
 539
 540 static int __init nf_conntrack_ftp_init(void)
 541 {
 542         int i, j = -1, ret = 0;
 543         char *tmpname;
 544
 545         ftp_buffer = kmalloc(65536, GFP_KERNEL);
 546         if (!ftp_buffer)
 547                 return -ENOMEM;
 548
 549         if (ports_c == 0)
 550                 ports[ports_c++] = FTP_PORT;
 551
 552         /* FIXME should be configurable whether IPv4 and IPv6 FTP connections
 553                  are tracked or not - YK */
 554         for (i = 0; i < ports_c; i++) {
 555                 ftp[i][0].tuple.src.l3num = PF_INET;
 556                 ftp[i][1].tuple.src.l3num = PF_INET6;
 557                 for (j = 0; j < 2; j++) {
 558                         ftp[i][j].tuple.src.u.tcp.port = htons(ports[i]);
 559                         ftp[i][j].tuple.dst.protonum = IPPROTO_TCP;
 560                         ftp[i][j].expect_policy = &ftp_exp_policy;
 561                         ftp[i][j].me = THIS_MODULE;
 562                         ftp[i][j].help = help;
 563                         tmpname = &ftp_names[i][j][0];
 564                         if (ports[i] == FTP_PORT)
 565                                 sprintf(tmpname, "ftp");
 566                         else
 567                                 sprintf(tmpname, "ftp-%d", ports[i]);
 568                         ftp[i][j].name = tmpname;
 569
 570                         pr_debug("nf_ct_ftp: registering helper for pf: %d "
 571                                  "port: %d\n",
 572                                  ftp[i][j].tuple.src.l3num, ports[i]);
 573                         ret = nf_conntrack_helper_register(&ftp[i][j]);
 574                         if (ret) {
 575                                 printk("nf_ct_ftp: failed to register helper "
 576                                        " for pf: %d port: %d\n",
 577                                         ftp[i][j].tuple.src.l3num, ports[i]);
 578                                 nf_conntrack_ftp_fini();
 579                                 return ret;
 580                         }
 581                 }
 582         }
 583
 584         return 0;
 585 }
 586
 587 module_init(nf_conntrack_ftp_init);
 588 module_exit(nf_conntrack_ftp_fini);