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