net/netfilter/nf_conntrack_ftp.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /* FTP extension for connection tracking. */
   3
   4 /* (C) 1999-2001 Paul `Rusty' Russell
   5  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   6  * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
   7  * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
   8  */
   9
  10 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  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 #define HELPER_NAME "ftp"
  30
  31 MODULE_LICENSE("GPL");
  32 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  33 MODULE_DESCRIPTION("ftp connection tracking helper");
  34 MODULE_ALIAS("ip_conntrack_ftp");
  35 MODULE_ALIAS_NFCT_HELPER(HELPER_NAME);
  36
  37 /* This is slow, but it's simple. --RR */
  38 static char *ftp_buffer;
  39
  40 static DEFINE_SPINLOCK(nf_ftp_lock);
  41
  42 #define MAX_PORTS 8
  43 static u_int16_t ports[MAX_PORTS];
  44 static unsigned int ports_c;
  45 module_param_array(ports, ushort, &ports_c, 0400);
  46
  47 static bool loose;
  48 module_param(loose, bool, 0600);
  49
  50 unsigned int (*nf_nat_ftp_hook)(struct sk_buff *skb,
  51                                 enum ip_conntrack_info ctinfo,
  52                                 enum nf_ct_ftp_type type,
  53                                 unsigned int protoff,
  54                                 unsigned int matchoff,
  55                                 unsigned int matchlen,
  56                                 struct nf_conntrack_expect *exp);
  57 EXPORT_SYMBOL_GPL(nf_nat_ftp_hook);
  58
  59 static int try_rfc959(const char *, size_t, struct nf_conntrack_man *,
  60                       char, unsigned int *);
  61 static int try_rfc1123(const char *, size_t, struct nf_conntrack_man *,
  62                        char, unsigned int *);
  63 static int try_eprt(const char *, size_t, struct nf_conntrack_man *,
  64                     char, unsigned int *);
  65 static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *,
  66                              char, unsigned int *);
  67
  68 static struct ftp_search {
  69         const char *pattern;
  70         size_t plen;
  71         char skip;
  72         char term;
  73         enum nf_ct_ftp_type ftptype;
  74         int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char, unsigned int *);
  75 } search[IP_CT_DIR_MAX][2] = {
  76         [IP_CT_DIR_ORIGINAL] = {
  77                 {
  78                         .pattern        = "PORT",
  79                         .plen           = sizeof("PORT") - 1,
  80                         .skip           = ' ',
  81                         .term           = '\r',
  82                         .ftptype        = NF_CT_FTP_PORT,
  83                         .getnum         = try_rfc959,
  84                 },
  85                 {
  86                         .pattern        = "EPRT",
  87                         .plen           = sizeof("EPRT") - 1,
  88                         .skip           = ' ',
  89                         .term           = '\r',
  90                         .ftptype        = NF_CT_FTP_EPRT,
  91                         .getnum         = try_eprt,
  92                 },
  93         },
  94         [IP_CT_DIR_REPLY] = {
  95                 {
  96                         .pattern        = "227 ",
  97                         .plen           = sizeof("227 ") - 1,
  98                         .ftptype        = NF_CT_FTP_PASV,
  99                         .getnum         = try_rfc1123,
 100                 },
 101                 {
 102                         .pattern        = "229 ",
 103                         .plen           = sizeof("229 ") - 1,
 104                         .skip           = '(',
 105                         .term           = ')',
 106                         .ftptype        = NF_CT_FTP_EPSV,
 107                         .getnum         = try_epsv_response,
 108                 },
 109         },
 110 };
 111
 112 static int
 113 get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term)
 114 {
 115         const char *end;
 116         int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end);
 117         if (ret > 0)
 118                 return (int)(end - src);
 119         return 0;
 120 }
 121
 122 static int try_number(const char *data, size_t dlen, u_int32_t array[],
 123                       int array_size, char sep, char term)
 124 {
 125         u_int32_t i, len;
 126
 127         memset(array, 0, sizeof(array[0])*array_size);
 128
 129         /* Keep data pointing at next char. */
 130         for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) {
 131                 if (*data >= '0' && *data <= '9') {
 132                         array[i] = array[i]*10 + *data - '0';
 133                 }
 134                 else if (*data == sep)
 135                         i++;
 136                 else {
 137                         /* Unexpected character; true if it's the
 138                            terminator (or we don't care about one)
 139                            and we're finished. */
 140                         if ((*data == term || !term) && i == array_size - 1)
 141                                 return len;
 142
 143                         pr_debug("Char %u (got %u nums) `%u' unexpected\n",
 144                                  len, i, *data);
 145                         return 0;
 146                 }
 147         }
 148         pr_debug("Failed to fill %u numbers separated by %c\n",
 149                  array_size, sep);
 150         return 0;
 151 }
 152
 153 /* Returns 0, or length of numbers: 192,168,1,1,5,6 */
 154 static int try_rfc959(const char *data, size_t dlen,
 155                       struct nf_conntrack_man *cmd, char term,
 156                       unsigned int *offset)
 157 {
 158         int length;
 159         u_int32_t array[6];
 160
 161         length = try_number(data, dlen, array, 6, ',', term);
 162         if (length == 0)
 163                 return 0;
 164
 165         cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16) |
 166                                     (array[2] << 8) | array[3]);
 167         cmd->u.tcp.port = htons((array[4] << 8) | array[5]);
 168         return length;
 169 }
 170
 171 /*
 172  * From RFC 1123:
 173  * The format of the 227 reply to a PASV command is not
 174  * well standardized.  In particular, an FTP client cannot
 175  * assume that the parentheses shown on page 40 of RFC-959
 176  * will be present (and in fact, Figure 3 on page 43 omits
 177  * them).  Therefore, a User-FTP program that interprets
 178  * the PASV reply must scan the reply for the first digit
 179  * of the host and port numbers.
 180  */
 181 static int try_rfc1123(const char *data, size_t dlen,
 182                        struct nf_conntrack_man *cmd, char term,
 183                        unsigned int *offset)
 184 {
 185         int i;
 186         for (i = 0; i < dlen; i++)
 187                 if (isdigit(data[i]))
 188                         break;
 189
 190         if (i == dlen)
 191                 return 0;
 192
 193         *offset += i;
 194
 195         return try_rfc959(data + i, dlen - i, cmd, 0, offset);
 196 }
 197
 198 /* Grab port: number up to delimiter */
 199 static int get_port(const char *data, int start, size_t dlen, char delim,
 200                     __be16 *port)
 201 {
 202         u_int16_t tmp_port = 0;
 203         int i;
 204
 205         for (i = start; i < dlen; i++) {
 206                 /* Finished? */
 207                 if (data[i] == delim) {
 208                         if (tmp_port == 0)
 209                                 break;
 210                         *port = htons(tmp_port);
 211                         pr_debug("get_port: return %d\n", tmp_port);
 212                         return i + 1;
 213                 }
 214                 else if (data[i] >= '0' && data[i] <= '9')
 215                         tmp_port = tmp_port*10 + data[i] - '0';
 216                 else { /* Some other crap */
 217                         pr_debug("get_port: invalid char.\n");
 218                         break;
 219                 }
 220         }
 221         return 0;
 222 }
 223
 224 /* Returns 0, or length of numbers: |1|132.235.1.2|6275| or |2|3ffe::1|6275| */
 225 static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd,
 226                     char term, unsigned int *offset)
 227 {
 228         char delim;
 229         int length;
 230
 231         /* First character is delimiter, then "1" for IPv4 or "2" for IPv6,
 232            then delimiter again. */
 233         if (dlen <= 3) {
 234                 pr_debug("EPRT: too short\n");
 235                 return 0;
 236         }
 237         delim = data[0];
 238         if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) {
 239                 pr_debug("try_eprt: invalid delimiter.\n");
 240                 return 0;
 241         }
 242
 243         if ((cmd->l3num == PF_INET && data[1] != '1') ||
 244             (cmd->l3num == PF_INET6 && data[1] != '2')) {
 245                 pr_debug("EPRT: invalid protocol number.\n");
 246                 return 0;
 247         }
 248
 249         pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim);
 250
 251         if (data[1] == '1') {
 252                 u_int32_t array[4];
 253
 254                 /* Now we have IP address. */
 255                 length = try_number(data + 3, dlen - 3, array, 4, '.', delim);
 256                 if (length != 0)
 257                         cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16)
 258                                            | (array[2] << 8) | array[3]);
 259         } else {
 260                 /* Now we have IPv6 address. */
 261                 length = get_ipv6_addr(data + 3, dlen - 3,
 262                                        (struct in6_addr *)cmd->u3.ip6, delim);
 263         }
 264
 265         if (length == 0)
 266                 return 0;
 267         pr_debug("EPRT: Got IP address!\n");
 268         /* Start offset includes initial "|1|", and trailing delimiter */
 269         return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port);
 270 }
 271
 272 /* Returns 0, or length of numbers: |||6446| */
 273 static int try_epsv_response(const char *data, size_t dlen,
 274                              struct nf_conntrack_man *cmd, char term,
 275                              unsigned int *offset)
 276 {
 277         char delim;
 278
 279         /* Three delimiters. */
 280         if (dlen <= 3) return 0;
 281         delim = data[0];
 282         if (isdigit(delim) || delim < 33 || delim > 126 ||
 283             data[1] != delim || data[2] != delim)
 284                 return 0;
 285
 286         return get_port(data, 3, dlen, delim, &cmd->u.tcp.port);
 287 }
 288
 289 /* Return 1 for match, 0 for accept, -1 for partial. */
 290 static int find_pattern(const char *data, size_t dlen,
 291                         const char *pattern, size_t plen,
 292                         char skip, char term,
 293                         unsigned int *numoff,
 294                         unsigned int *numlen,
 295                         struct nf_conntrack_man *cmd,
 296                         int (*getnum)(const char *, size_t,
 297                                       struct nf_conntrack_man *, char,
 298                                       unsigned int *))
 299 {
 300         size_t i = plen;
 301
 302         pr_debug("find_pattern `%s': dlen = %zu\n", pattern, dlen);
 303
 304         if (dlen <= plen) {
 305                 /* Short packet: try for partial? */
 306                 if (strncasecmp(data, pattern, dlen) == 0)
 307                         return -1;
 308                 else return 0;
 309         }
 310
 311         if (strncasecmp(data, pattern, plen) != 0)
 312                 return 0;
 313
 314         pr_debug("Pattern matches!\n");
 315         /* Now we've found the constant string, try to skip
 316            to the 'skip' character */
 317         if (skip) {
 318                 for (i = plen; data[i] != skip; i++)
 319                         if (i == dlen - 1) return -1;
 320
 321                 /* Skip over the last character */
 322                 i++;
 323         }
 324
 325         pr_debug("Skipped up to 0x%hhx delimiter!\n", skip);
 326
 327         *numoff = i;
 328         *numlen = getnum(data + i, dlen - i, cmd, term, numoff);
 329         if (!*numlen)
 330                 return -1;
 331
 332         pr_debug("Match succeeded!\n");
 333         return 1;
 334 }
 335
 336 /* Look up to see if we're just after a \n. */
 337 static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir)
 338 {
 339         unsigned int i;
 340
 341         for (i = 0; i < info->seq_aft_nl_num[dir]; i++)
 342                 if (info->seq_aft_nl[dir][i] == seq)
 343                         return 1;
 344         return 0;
 345 }
 346
 347 /* We don't update if it's older than what we have. */
 348 static void update_nl_seq(struct nf_conn *ct, u32 nl_seq,
 349                           struct nf_ct_ftp_master *info, int dir,
 350                           struct sk_buff *skb)
 351 {
 352         unsigned int i, oldest;
 353
 354         /* Look for oldest: if we find exact match, we're done. */
 355         for (i = 0; i < info->seq_aft_nl_num[dir]; i++) {
 356                 if (info->seq_aft_nl[dir][i] == nl_seq)
 357                         return;
 358         }
 359
 360         if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) {
 361                 info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq;
 362         } else {
 363                 if (before(info->seq_aft_nl[dir][0], info->seq_aft_nl[dir][1]))
 364                         oldest = 0;
 365                 else
 366                         oldest = 1;
 367
 368                 if (after(nl_seq, info->seq_aft_nl[dir][oldest]))
 369                         info->seq_aft_nl[dir][oldest] = nl_seq;
 370         }
 371 }
 372
 373 static int help(struct sk_buff *skb,
 374                 unsigned int protoff,
 375                 struct nf_conn *ct,
 376                 enum ip_conntrack_info ctinfo)
 377 {
 378         unsigned int dataoff, datalen;
 379         const struct tcphdr *th;
 380         struct tcphdr _tcph;
 381         const char *fb_ptr;
 382         int ret;
 383         u32 seq;
 384         int dir = CTINFO2DIR(ctinfo);
 385         unsigned int matchlen, matchoff;
 386         struct nf_ct_ftp_master *ct_ftp_info = nfct_help_data(ct);
 387         struct nf_conntrack_expect *exp;
 388         union nf_inet_addr *daddr;
 389         struct nf_conntrack_man cmd = {};
 390         unsigned int i;
 391         int found = 0, ends_in_nl;
 392         typeof(nf_nat_ftp_hook) nf_nat_ftp;
 393
 394         /* Until there's been traffic both ways, don't look in packets. */
 395         if (ctinfo != IP_CT_ESTABLISHED &&
 396             ctinfo != IP_CT_ESTABLISHED_REPLY) {
 397                 pr_debug("ftp: Conntrackinfo = %u\n", ctinfo);
 398                 return NF_ACCEPT;
 399         }
 400
 401         th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
 402         if (th == NULL)
 403                 return NF_ACCEPT;
 404
 405         dataoff = protoff + th->doff * 4;
 406         /* No data? */
 407         if (dataoff >= skb->len) {
 408                 pr_debug("ftp: dataoff(%u) >= skblen(%u)\n", dataoff,
 409                          skb->len);
 410                 return NF_ACCEPT;
 411         }
 412         datalen = skb->len - dataoff;
 413
 414         spin_lock_bh(&nf_ftp_lock);
 415         fb_ptr = skb_header_pointer(skb, dataoff, datalen, ftp_buffer);
 416         BUG_ON(fb_ptr == NULL);
 417
 418         ends_in_nl = (fb_ptr[datalen - 1] == '\n');
 419         seq = ntohl(th->seq) + datalen;
 420
 421         /* Look up to see if we're just after a \n. */
 422         if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) {
 423                 /* We're picking up this, clear flags and let it continue */
 424                 if (unlikely(ct_ftp_info->flags[dir] & NF_CT_FTP_SEQ_PICKUP)) {
 425                         ct_ftp_info->flags[dir] ^= NF_CT_FTP_SEQ_PICKUP;
 426                         goto skip_nl_seq;
 427                 }
 428
 429                 /* Now if this ends in \n, update ftp info. */
 430                 pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n",
 431                          ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)",
 432                          ct_ftp_info->seq_aft_nl[dir][0],
 433                          ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)",
 434                          ct_ftp_info->seq_aft_nl[dir][1]);
 435                 ret = NF_ACCEPT;
 436                 goto out_update_nl;
 437         }
 438
 439 skip_nl_seq:
 440         /* Initialize IP/IPv6 addr to expected address (it's not mentioned
 441            in EPSV responses) */
 442         cmd.l3num = nf_ct_l3num(ct);
 443         memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
 444                sizeof(cmd.u3.all));
 445
 446         for (i = 0; i < ARRAY_SIZE(search[dir]); i++) {
 447                 found = find_pattern(fb_ptr, datalen,
 448                                      search[dir][i].pattern,
 449                                      search[dir][i].plen,
 450                                      search[dir][i].skip,
 451                                      search[dir][i].term,
 452                                      &matchoff, &matchlen,
 453                                      &cmd,
 454                                      search[dir][i].getnum);
 455                 if (found) break;
 456         }
 457         if (found == -1) {
 458                 /* We don't usually drop packets.  After all, this is
 459                    connection tracking, not packet filtering.
 460                    However, it is necessary for accurate tracking in
 461                    this case. */
 462                 nf_ct_helper_log(skb, ct, "partial matching of `%s'",
 463                                  search[dir][i].pattern);
 464                 ret = NF_DROP;
 465                 goto out;
 466         } else if (found == 0) { /* No match */
 467                 ret = NF_ACCEPT;
 468                 goto out_update_nl;
 469         }
 470
 471         pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n",
 472                  matchlen, fb_ptr + matchoff,
 473                  matchlen, ntohl(th->seq) + matchoff);
 474
 475         exp = nf_ct_expect_alloc(ct);
 476         if (exp == NULL) {
 477                 nf_ct_helper_log(skb, ct, "cannot alloc expectation");
 478                 ret = NF_DROP;
 479                 goto out;
 480         }
 481
 482         /* We refer to the reverse direction ("!dir") tuples here,
 483          * because we're expecting something in the other direction.
 484          * Doesn't matter unless NAT is happening.  */
 485         daddr = &ct->tuplehash[!dir].tuple.dst.u3;
 486
 487         /* Update the ftp info */
 488         if ((cmd.l3num == nf_ct_l3num(ct)) &&
 489             memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
 490                      sizeof(cmd.u3.all))) {
 491                 /* Enrico Scholz's passive FTP to partially RNAT'd ftp
 492                    server: it really wants us to connect to a
 493                    different IP address.  Simply don't record it for
 494                    NAT. */
 495                 if (cmd.l3num == PF_INET) {
 496                         pr_debug("NOT RECORDING: %pI4 != %pI4\n",
 497                                  &cmd.u3.ip,
 498                                  &ct->tuplehash[dir].tuple.src.u3.ip);
 499                 } else {
 500                         pr_debug("NOT RECORDING: %pI6 != %pI6\n",
 501                                  cmd.u3.ip6,
 502                                  ct->tuplehash[dir].tuple.src.u3.ip6);
 503                 }
 504
 505                 /* Thanks to Cristiano Lincoln Mattos
 506                    <lincoln@cesar.org.br> for reporting this potential
 507                    problem (DMZ machines opening holes to internal
 508                    networks, or the packet filter itself). */
 509                 if (!loose) {
 510                         ret = NF_ACCEPT;
 511                         goto out_put_expect;
 512                 }
 513                 daddr = &cmd.u3;
 514         }
 515
 516         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num,
 517                           &ct->tuplehash[!dir].tuple.src.u3, daddr,
 518                           IPPROTO_TCP, NULL, &cmd.u.tcp.port);
 519
 520         /* Now, NAT might want to mangle the packet, and register the
 521          * (possibly changed) expectation itself. */
 522         nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook);
 523         if (nf_nat_ftp && ct->status & IPS_NAT_MASK)
 524                 ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype,
 525                                  protoff, matchoff, matchlen, exp);
 526         else {
 527                 /* Can't expect this?  Best to drop packet now. */
 528                 if (nf_ct_expect_related(exp, 0) != 0) {
 529                         nf_ct_helper_log(skb, ct, "cannot add expectation");
 530                         ret = NF_DROP;
 531                 } else
 532                         ret = NF_ACCEPT;
 533         }
 534
 535 out_put_expect:
 536         nf_ct_expect_put(exp);
 537
 538 out_update_nl:
 539         /* Now if this ends in \n, update ftp info.  Seq may have been
 540          * adjusted by NAT code. */
 541         if (ends_in_nl)
 542                 update_nl_seq(ct, seq, ct_ftp_info, dir, skb);
 543  out:
 544         spin_unlock_bh(&nf_ftp_lock);
 545         return ret;
 546 }
 547
 548 static int nf_ct_ftp_from_nlattr(struct nlattr *attr, struct nf_conn *ct)
 549 {
 550         struct nf_ct_ftp_master *ftp = nfct_help_data(ct);
 551
 552         /* This conntrack has been injected from user-space, always pick up
 553          * sequence tracking. Otherwise, the first FTP command after the
 554          * failover breaks.
 555          */
 556         ftp->flags[IP_CT_DIR_ORIGINAL] |= NF_CT_FTP_SEQ_PICKUP;
 557         ftp->flags[IP_CT_DIR_REPLY] |= NF_CT_FTP_SEQ_PICKUP;
 558         return 0;
 559 }
 560
 561 static struct nf_conntrack_helper ftp[MAX_PORTS * 2] __read_mostly;
 562
 563 static const struct nf_conntrack_expect_policy ftp_exp_policy = {
 564         .max_expected   = 1,
 565         .timeout        = 5 * 60,
 566 };
 567
 568 static void __exit nf_conntrack_ftp_fini(void)
 569 {
 570         nf_conntrack_helpers_unregister(ftp, ports_c * 2);
 571         kfree(ftp_buffer);
 572 }
 573
 574 static int __init nf_conntrack_ftp_init(void)
 575 {
 576         int i, ret = 0;
 577
 578         NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_ftp_master));
 579
 580         ftp_buffer = kmalloc(65536, GFP_KERNEL);
 581         if (!ftp_buffer)
 582                 return -ENOMEM;
 583
 584         if (ports_c == 0)
 585                 ports[ports_c++] = FTP_PORT;
 586
 587         /* FIXME should be configurable whether IPv4 and IPv6 FTP connections
 588                  are tracked or not - YK */
 589         for (i = 0; i < ports_c; i++) {
 590                 nf_ct_helper_init(&ftp[2 * i], AF_INET, IPPROTO_TCP,
 591                                   HELPER_NAME, FTP_PORT, ports[i], ports[i],
 592                                   &ftp_exp_policy, 0, help,
 593                                   nf_ct_ftp_from_nlattr, THIS_MODULE);
 594                 nf_ct_helper_init(&ftp[2 * i + 1], AF_INET6, IPPROTO_TCP,
 595                                   HELPER_NAME, FTP_PORT, ports[i], ports[i],
 596                                   &ftp_exp_policy, 0, help,
 597                                   nf_ct_ftp_from_nlattr, THIS_MODULE);
 598         }
 599
 600         ret = nf_conntrack_helpers_register(ftp, ports_c * 2);
 601         if (ret < 0) {
 602                 pr_err("failed to register helpers\n");
 603                 kfree(ftp_buffer);
 604                 return ret;
 605         }
 606
 607         return 0;
 608 }
 609
 610 module_init(nf_conntrack_ftp_init);
 611 module_exit(nf_conntrack_ftp_fini);