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
  33 /* This is slow, but it's simple. --RR */
  34 static char *ftp_buffer;
  35
  36 static DEFINE_SPINLOCK(nf_ftp_lock);
  37
  38 #define MAX_PORTS 8
  39 static u_int16_t ports[MAX_PORTS];
  40 static unsigned int ports_c;
  41 module_param_array(ports, ushort, &ports_c, 0400);
  42
  43 static int loose;
  44 module_param(loose, bool, 0600);
  45
  46 unsigned int (*nf_nat_ftp_hook)(struct sk_buff *skb,
  47                                 enum ip_conntrack_info ctinfo,
  48                                 enum nf_ct_ftp_type type,
  49                                 unsigned int matchoff,
  50                                 unsigned int matchlen,
  51                                 struct nf_conntrack_expect *exp);
  52 EXPORT_SYMBOL_GPL(nf_nat_ftp_hook);
  53
  54 static int try_rfc959(const char *, size_t, struct nf_conntrack_man *, char);
  55 static int try_eprt(const char *, size_t, struct nf_conntrack_man *, char);
  56 static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *,
  57                              char);
  58
  59 static struct ftp_search {
  60         const char *pattern;
  61         size_t plen;
  62         char skip;
  63         char term;
  64         enum nf_ct_ftp_type ftptype;
  65         int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char);
  66 } search[IP_CT_DIR_MAX][2] = {
  67         [IP_CT_DIR_ORIGINAL] = {
  68                 {
  69                         .pattern        = "PORT",
  70                         .plen           = sizeof("PORT") - 1,
  71                         .skip           = ' ',
  72                         .term           = '\r',
  73                         .ftptype        = NF_CT_FTP_PORT,
  74                         .getnum         = try_rfc959,
  75                 },
  76                 {
  77                         .pattern        = "EPRT",
  78                         .plen           = sizeof("EPRT") - 1,
  79                         .skip           = ' ',
  80                         .term           = '\r',
  81                         .ftptype        = NF_CT_FTP_EPRT,
  82                         .getnum         = try_eprt,
  83                 },
  84         },
  85         [IP_CT_DIR_REPLY] = {
  86                 {
  87                         .pattern        = "227 ",
  88                         .plen           = sizeof("227 ") - 1,
  89                         .skip           = '(',
  90                         .term           = ')',
  91                         .ftptype        = NF_CT_FTP_PASV,
  92                         .getnum         = try_rfc959,
  93                 },
  94                 {
  95                         .pattern        = "229 ",
  96                         .plen           = sizeof("229 ") - 1,
  97                         .skip           = '(',
  98                         .term           = ')',
  99                         .ftptype        = NF_CT_FTP_EPSV,
 100                         .getnum         = try_epsv_response,
 101                 },
 102         },
 103 };
 104
 105 static int
 106 get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term)
 107 {
 108         const char *end;
 109         int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end);
 110         if (ret > 0)
 111                 return (int)(end - src);
 112         return 0;
 113 }
 114
 115 static int try_number(const char *data, size_t dlen, u_int32_t array[],
 116                       int array_size, char sep, char term)
 117 {
 118         u_int32_t i, len;
 119
 120         memset(array, 0, sizeof(array[0])*array_size);
 121
 122         /* Keep data pointing at next char. */
 123         for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) {
 124                 if (*data >= '0' && *data <= '9') {
 125                         array[i] = array[i]*10 + *data - '0';
 126                 }
 127                 else if (*data == sep)
 128                         i++;
 129                 else {
 130                         /* Unexpected character; true if it's the
 131                            terminator and we're finished. */
 132                         if (*data == term && i == array_size - 1)
 133                                 return len;
 134
 135                         pr_debug("Char %u (got %u nums) `%u' unexpected\n",
 136                                  len, i, *data);
 137                         return 0;
 138                 }
 139         }
 140         pr_debug("Failed to fill %u numbers separated by %c\n",
 141                  array_size, sep);
 142         return 0;
 143 }
 144
 145 /* Returns 0, or length of numbers: 192,168,1,1,5,6 */
 146 static int try_rfc959(const char *data, size_t dlen,
 147                       struct nf_conntrack_man *cmd, char term)
 148 {
 149         int length;
 150         u_int32_t array[6];
 151
 152         length = try_number(data, dlen, array, 6, ',', term);
 153         if (length == 0)
 154                 return 0;
 155
 156         cmd->u3.ip =  htonl((array[0] << 24) | (array[1] << 16) |
 157                                     (array[2] << 8) | array[3]);
 158         cmd->u.tcp.port = htons((array[4] << 8) | array[5]);
 159         return length;
 160 }
 161
 162 /* Grab port: number up to delimiter */
 163 static int get_port(const char *data, int start, size_t dlen, char delim,
 164                     __be16 *port)
 165 {
 166         u_int16_t tmp_port = 0;
 167         int i;
 168
 169         for (i = start; i < dlen; i++) {
 170                 /* Finished? */
 171                 if (data[i] == delim) {
 172                         if (tmp_port == 0)
 173                                 break;
 174                         *port = htons(tmp_port);
 175                         pr_debug("get_port: return %d\n", tmp_port);
 176                         return i + 1;
 177                 }
 178                 else if (data[i] >= '0' && data[i] <= '9')
 179                         tmp_port = tmp_port*10 + data[i] - '0';
 180                 else { /* Some other crap */
 181                         pr_debug("get_port: invalid char.\n");
 182                         break;
 183                 }
 184         }
 185         return 0;
 186 }
 187
 188 /* Returns 0, or length of numbers: |1|132.235.1.2|6275| or |2|3ffe::1|6275| */
 189 static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd,
 190                     char term)
 191 {
 192         char delim;
 193         int length;
 194
 195         /* First character is delimiter, then "1" for IPv4 or "2" for IPv6,
 196            then delimiter again. */
 197         if (dlen <= 3) {
 198                 pr_debug("EPRT: too short\n");
 199                 return 0;
 200         }
 201         delim = data[0];
 202         if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) {
 203                 pr_debug("try_eprt: invalid delimitter.\n");
 204                 return 0;
 205         }
 206
 207         if ((cmd->l3num == PF_INET && data[1] != '1') ||
 208             (cmd->l3num == PF_INET6 && data[1] != '2')) {
 209                 pr_debug("EPRT: invalid protocol number.\n");
 210                 return 0;
 211         }
 212
 213         pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim);
 214
 215         if (data[1] == '1') {
 216                 u_int32_t array[4];
 217
 218                 /* Now we have IP address. */
 219                 length = try_number(data + 3, dlen - 3, array, 4, '.', delim);
 220                 if (length != 0)
 221                         cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16)
 222                                            | (array[2] << 8) | array[3]);
 223         } else {
 224                 /* Now we have IPv6 address. */
 225                 length = get_ipv6_addr(data + 3, dlen - 3,
 226                                        (struct in6_addr *)cmd->u3.ip6, delim);
 227         }
 228
 229         if (length == 0)
 230                 return 0;
 231         pr_debug("EPRT: Got IP address!\n");
 232         /* Start offset includes initial "|1|", and trailing delimiter */
 233         return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port);
 234 }
 235
 236 /* Returns 0, or length of numbers: |||6446| */
 237 static int try_epsv_response(const char *data, size_t dlen,
 238                              struct nf_conntrack_man *cmd, char term)
 239 {
 240         char delim;
 241
 242         /* Three delimiters. */
 243         if (dlen <= 3) return 0;
 244         delim = data[0];
 245         if (isdigit(delim) || delim < 33 || delim > 126
 246             || data[1] != delim || data[2] != delim)
 247                 return 0;
 248
 249         return get_port(data, 3, dlen, delim, &cmd->u.tcp.port);
 250 }
 251
 252 /* Return 1 for match, 0 for accept, -1 for partial. */
 253 static int find_pattern(const char *data, size_t dlen,
 254                         const char *pattern, size_t plen,
 255                         char skip, char term,
 256                         unsigned int *numoff,
 257                         unsigned int *numlen,
 258                         struct nf_conntrack_man *cmd,
 259                         int (*getnum)(const char *, size_t,
 260                                       struct nf_conntrack_man *, char))
 261 {
 262         size_t i;
 263
 264         pr_debug("find_pattern `%s': dlen = %Zu\n", pattern, dlen);
 265         if (dlen == 0)
 266                 return 0;
 267
 268         if (dlen <= plen) {
 269                 /* Short packet: try for partial? */
 270                 if (strnicmp(data, pattern, dlen) == 0)
 271                         return -1;
 272                 else return 0;
 273         }
 274
 275         if (strnicmp(data, pattern, plen) != 0) {
 276 #if 0
 277                 size_t i;
 278
 279                 pr_debug("ftp: string mismatch\n");
 280                 for (i = 0; i < plen; i++) {
 281                         pr_debug("ftp:char %u `%c'(%u) vs `%c'(%u)\n",
 282                                  i, data[i], data[i],
 283                                  pattern[i], pattern[i]);
 284                 }
 285 #endif
 286                 return 0;
 287         }
 288
 289         pr_debug("Pattern matches!\n");
 290         /* Now we've found the constant string, try to skip
 291            to the 'skip' character */
 292         for (i = plen; data[i] != skip; i++)
 293                 if (i == dlen - 1) return -1;
 294
 295         /* Skip over the last character */
 296         i++;
 297
 298         pr_debug("Skipped up to `%c'!\n", skip);
 299
 300         *numoff = i;
 301         *numlen = getnum(data + i, dlen - i, cmd, term);
 302         if (!*numlen)
 303                 return -1;
 304
 305         pr_debug("Match succeeded!\n");
 306         return 1;
 307 }
 308
 309 /* Look up to see if we're just after a \n. */
 310 static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir)
 311 {
 312         unsigned int i;
 313
 314         for (i = 0; i < info->seq_aft_nl_num[dir]; i++)
 315                 if (info->seq_aft_nl[dir][i] == seq)
 316                         return 1;
 317         return 0;
 318 }
 319
 320 /* We don't update if it's older than what we have. */
 321 static void update_nl_seq(u32 nl_seq, struct nf_ct_ftp_master *info, int dir,
 322                           struct sk_buff *skb)
 323 {
 324         unsigned int i, oldest = NUM_SEQ_TO_REMEMBER;
 325
 326         /* Look for oldest: if we find exact match, we're done. */
 327         for (i = 0; i < info->seq_aft_nl_num[dir]; i++) {
 328                 if (info->seq_aft_nl[dir][i] == nl_seq)
 329                         return;
 330
 331                 if (oldest == info->seq_aft_nl_num[dir] ||
 332                     before(info->seq_aft_nl[dir][i],
 333                            info->seq_aft_nl[dir][oldest]))
 334                         oldest = i;
 335         }
 336
 337         if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) {
 338                 info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq;
 339                 nf_conntrack_event_cache(IPCT_HELPINFO_VOLATILE, skb);
 340         } else if (oldest != NUM_SEQ_TO_REMEMBER &&
 341                    after(nl_seq, info->seq_aft_nl[dir][oldest])) {
 342                 info->seq_aft_nl[dir][oldest] = nl_seq;
 343                 nf_conntrack_event_cache(IPCT_HELPINFO_VOLATILE, skb);
 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 matchlen, 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                 if (net_ratelimit())
 430                         printk("conntrack_ftp: partial %s %u+%u\n",
 431                                search[dir][i].pattern,
 432                                ntohl(th->seq), datalen);
 433                 ret = NF_DROP;
 434                 goto out;
 435         } else if (found == 0) { /* No match */
 436                 ret = NF_ACCEPT;
 437                 goto out_update_nl;
 438         }
 439
 440         pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n",
 441                  matchlen, fb_ptr + matchoff,
 442                  matchlen, ntohl(th->seq) + matchoff);
 443
 444         exp = nf_ct_expect_alloc(ct);
 445         if (exp == NULL) {
 446                 ret = NF_DROP;
 447                 goto out;
 448         }
 449
 450         /* We refer to the reverse direction ("!dir") tuples here,
 451          * because we're expecting something in the other direction.
 452          * Doesn't matter unless NAT is happening.  */
 453         daddr = &ct->tuplehash[!dir].tuple.dst.u3;
 454
 455         /* Update the ftp info */
 456         if ((cmd.l3num == nf_ct_l3num(ct)) &&
 457             memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
 458                      sizeof(cmd.u3.all))) {
 459                 /* Enrico Scholz's passive FTP to partially RNAT'd ftp
 460                    server: it really wants us to connect to a
 461                    different IP address.  Simply don't record it for
 462                    NAT. */
 463                 if (cmd.l3num == PF_INET) {
 464                         pr_debug("conntrack_ftp: NOT RECORDING: " NIPQUAD_FMT
 465                                  " != " NIPQUAD_FMT "\n",
 466                                  NIPQUAD(cmd.u3.ip),
 467                                  NIPQUAD(ct->tuplehash[dir].tuple.src.u3.ip));
 468                 } else {
 469                         pr_debug("conntrack_ftp: NOT RECORDING: " NIP6_FMT
 470                                  " != " NIP6_FMT "\n",
 471                                  NIP6(*((struct in6_addr *)cmd.u3.ip6)),
 472                                  NIP6(*((struct in6_addr *)
 473                                         ct->tuplehash[dir].tuple.src.u3.ip6)));
 474                 }
 475
 476                 /* Thanks to Cristiano Lincoln Mattos
 477                    <lincoln@cesar.org.br> for reporting this potential
 478                    problem (DMZ machines opening holes to internal
 479                    networks, or the packet filter itself). */
 480                 if (!loose) {
 481                         ret = NF_ACCEPT;
 482                         goto out_put_expect;
 483                 }
 484                 daddr = &cmd.u3;
 485         }
 486
 487         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num,
 488                           &ct->tuplehash[!dir].tuple.src.u3, daddr,
 489                           IPPROTO_TCP, NULL, &cmd.u.tcp.port);
 490
 491         /* Now, NAT might want to mangle the packet, and register the
 492          * (possibly changed) expectation itself. */
 493         nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook);
 494         if (nf_nat_ftp && ct->status & IPS_NAT_MASK)
 495                 ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype,
 496                                  matchoff, matchlen, exp);
 497         else {
 498                 /* Can't expect this?  Best to drop packet now. */
 499                 if (nf_ct_expect_related(exp) != 0)
 500                         ret = NF_DROP;
 501                 else
 502                         ret = NF_ACCEPT;
 503         }
 504
 505 out_put_expect:
 506         nf_ct_expect_put(exp);
 507
 508 out_update_nl:
 509         /* Now if this ends in \n, update ftp info.  Seq may have been
 510          * adjusted by NAT code. */
 511         if (ends_in_nl)
 512                 update_nl_seq(seq, ct_ftp_info, dir, skb);
 513  out:
 514         spin_unlock_bh(&nf_ftp_lock);
 515         return ret;
 516 }
 517
 518 static struct nf_conntrack_helper ftp[MAX_PORTS][2] __read_mostly;
 519 static char ftp_names[MAX_PORTS][2][sizeof("ftp-65535")] __read_mostly;
 520
 521 static const struct nf_conntrack_expect_policy ftp_exp_policy = {
 522         .max_expected   = 1,
 523         .timeout        = 5 * 60,
 524 };
 525
 526 /* don't make this __exit, since it's called from __init ! */
 527 static void nf_conntrack_ftp_fini(void)
 528 {
 529         int i, j;
 530         for (i = 0; i < ports_c; i++) {
 531                 for (j = 0; j < 2; j++) {
 532                         if (ftp[i][j].me == NULL)
 533                                 continue;
 534
 535                         pr_debug("nf_ct_ftp: unregistering helper for pf: %d "
 536                                  "port: %d\n",
 537                                  ftp[i][j].tuple.src.l3num, ports[i]);
 538                         nf_conntrack_helper_unregister(&ftp[i][j]);
 539                 }
 540         }
 541
 542         kfree(ftp_buffer);
 543 }
 544
 545 static int __init nf_conntrack_ftp_init(void)
 546 {
 547         int i, j = -1, ret = 0;
 548         char *tmpname;
 549
 550         ftp_buffer = kmalloc(65536, GFP_KERNEL);
 551         if (!ftp_buffer)
 552                 return -ENOMEM;
 553
 554         if (ports_c == 0)
 555                 ports[ports_c++] = FTP_PORT;
 556
 557         /* FIXME should be configurable whether IPv4 and IPv6 FTP connections
 558                  are tracked or not - YK */
 559         for (i = 0; i < ports_c; i++) {
 560                 ftp[i][0].tuple.src.l3num = PF_INET;
 561                 ftp[i][1].tuple.src.l3num = PF_INET6;
 562                 for (j = 0; j < 2; j++) {
 563                         ftp[i][j].tuple.src.u.tcp.port = htons(ports[i]);
 564                         ftp[i][j].tuple.dst.protonum = IPPROTO_TCP;
 565                         ftp[i][j].expect_policy = &ftp_exp_policy;
 566                         ftp[i][j].me = THIS_MODULE;
 567                         ftp[i][j].help = help;
 568                         tmpname = &ftp_names[i][j][0];
 569                         if (ports[i] == FTP_PORT)
 570                                 sprintf(tmpname, "ftp");
 571                         else
 572                                 sprintf(tmpname, "ftp-%d", ports[i]);
 573                         ftp[i][j].name = tmpname;
 574
 575                         pr_debug("nf_ct_ftp: registering helper for pf: %d "
 576                                  "port: %d\n",
 577                                  ftp[i][j].tuple.src.l3num, ports[i]);
 578                         ret = nf_conntrack_helper_register(&ftp[i][j]);
 579                         if (ret) {
 580                                 printk("nf_ct_ftp: failed to register helper "
 581                                        " for pf: %d port: %d\n",
 582                                         ftp[i][j].tuple.src.l3num, ports[i]);
 583                                 nf_conntrack_ftp_fini();
 584                                 return ret;
 585                         }
 586                 }
 587         }
 588
 589         return 0;
 590 }
 591
 592 module_init(nf_conntrack_ftp_init);
 593 module_exit(nf_conntrack_ftp_fini);