linux/net/netfilter/nf_conntrack_ftp.c
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   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
  29MODULE_LICENSE("GPL");
  30MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  31MODULE_DESCRIPTION("ftp connection tracking helper");
  32MODULE_ALIAS("ip_conntrack_ftp");
  33MODULE_ALIAS_NFCT_HELPER("ftp");
  34
  35/* This is slow, but it's simple. --RR */
  36static char *ftp_buffer;
  37
  38static DEFINE_SPINLOCK(nf_ftp_lock);
  39
  40#define MAX_PORTS 8
  41static u_int16_t ports[MAX_PORTS];
  42static unsigned int ports_c;
  43module_param_array(ports, ushort, &ports_c, 0400);
  44
  45static bool loose;
  46module_param(loose, bool, 0600);
  47
  48unsigned 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 protoff,
  52                                unsigned int matchoff,
  53                                unsigned int matchlen,
  54                                struct nf_conntrack_expect *exp);
  55EXPORT_SYMBOL_GPL(nf_nat_ftp_hook);
  56
  57static int try_rfc959(const char *, size_t, struct nf_conntrack_man *, char);
  58static int try_eprt(const char *, size_t, struct nf_conntrack_man *, char);
  59static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *,
  60                             char);
  61
  62static struct ftp_search {
  63        const char *pattern;
  64        size_t plen;
  65        char skip;
  66        char term;
  67        enum nf_ct_ftp_type ftptype;
  68        int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char);
  69} search[IP_CT_DIR_MAX][2] = {
  70        [IP_CT_DIR_ORIGINAL] = {
  71                {
  72                        .pattern        = "PORT",
  73                        .plen           = sizeof("PORT") - 1,
  74                        .skip           = ' ',
  75                        .term           = '\r',
  76                        .ftptype        = NF_CT_FTP_PORT,
  77                        .getnum         = try_rfc959,
  78                },
  79                {
  80                        .pattern        = "EPRT",
  81                        .plen           = sizeof("EPRT") - 1,
  82                        .skip           = ' ',
  83                        .term           = '\r',
  84                        .ftptype        = NF_CT_FTP_EPRT,
  85                        .getnum         = try_eprt,
  86                },
  87        },
  88        [IP_CT_DIR_REPLY] = {
  89                {
  90                        .pattern        = "227 ",
  91                        .plen           = sizeof("227 ") - 1,
  92                        .skip           = '(',
  93                        .term           = ')',
  94                        .ftptype        = NF_CT_FTP_PASV,
  95                        .getnum         = try_rfc959,
  96                },
  97                {
  98                        .pattern        = "229 ",
  99                        .plen           = sizeof("229 ") - 1,
 100                        .skip           = '(',
 101                        .term           = ')',
 102                        .ftptype        = NF_CT_FTP_EPSV,
 103                        .getnum         = try_epsv_response,
 104                },
 105        },
 106};
 107
 108static int
 109get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term)
 110{
 111        const char *end;
 112        int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end);
 113        if (ret > 0)
 114                return (int)(end - src);
 115        return 0;
 116}
 117
 118static int try_number(const char *data, size_t dlen, u_int32_t array[],
 119                      int array_size, char sep, char term)
 120{
 121        u_int32_t i, len;
 122
 123        memset(array, 0, sizeof(array[0])*array_size);
 124
 125        /* Keep data pointing at next char. */
 126        for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) {
 127                if (*data >= '0' && *data <= '9') {
 128                        array[i] = array[i]*10 + *data - '0';
 129                }
 130                else if (*data == sep)
 131                        i++;
 132                else {
 133                        /* Unexpected character; true if it's the
 134                           terminator and we're finished. */
 135                        if (*data == term && i == array_size - 1)
 136                                return len;
 137
 138                        pr_debug("Char %u (got %u nums) `%u' unexpected\n",
 139                                 len, i, *data);
 140                        return 0;
 141                }
 142        }
 143        pr_debug("Failed to fill %u numbers separated by %c\n",
 144                 array_size, sep);
 145        return 0;
 146}
 147
 148/* Returns 0, or length of numbers: 192,168,1,1,5,6 */
 149static int try_rfc959(const char *data, size_t dlen,
 150                      struct nf_conntrack_man *cmd, char term)
 151{
 152        int length;
 153        u_int32_t array[6];
 154
 155        length = try_number(data, dlen, array, 6, ',', term);
 156        if (length == 0)
 157                return 0;
 158
 159        cmd->u3.ip =  htonl((array[0] << 24) | (array[1] << 16) |
 160                                    (array[2] << 8) | array[3]);
 161        cmd->u.tcp.port = htons((array[4] << 8) | array[5]);
 162        return length;
 163}
 164
 165/* Grab port: number up to delimiter */
 166static int get_port(const char *data, int start, size_t dlen, char delim,
 167                    __be16 *port)
 168{
 169        u_int16_t tmp_port = 0;
 170        int i;
 171
 172        for (i = start; i < dlen; i++) {
 173                /* Finished? */
 174                if (data[i] == delim) {
 175                        if (tmp_port == 0)
 176                                break;
 177                        *port = htons(tmp_port);
 178                        pr_debug("get_port: return %d\n", tmp_port);
 179                        return i + 1;
 180                }
 181                else if (data[i] >= '0' && data[i] <= '9')
 182                        tmp_port = tmp_port*10 + data[i] - '0';
 183                else { /* Some other crap */
 184                        pr_debug("get_port: invalid char.\n");
 185                        break;
 186                }
 187        }
 188        return 0;
 189}
 190
 191/* Returns 0, or length of numbers: |1|132.235.1.2|6275| or |2|3ffe::1|6275| */
 192static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd,
 193                    char term)
 194{
 195        char delim;
 196        int length;
 197
 198        /* First character is delimiter, then "1" for IPv4 or "2" for IPv6,
 199           then delimiter again. */
 200        if (dlen <= 3) {
 201                pr_debug("EPRT: too short\n");
 202                return 0;
 203        }
 204        delim = data[0];
 205        if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) {
 206                pr_debug("try_eprt: invalid delimitter.\n");
 207                return 0;
 208        }
 209
 210        if ((cmd->l3num == PF_INET && data[1] != '1') ||
 211            (cmd->l3num == PF_INET6 && data[1] != '2')) {
 212                pr_debug("EPRT: invalid protocol number.\n");
 213                return 0;
 214        }
 215
 216        pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim);
 217
 218        if (data[1] == '1') {
 219                u_int32_t array[4];
 220
 221                /* Now we have IP address. */
 222                length = try_number(data + 3, dlen - 3, array, 4, '.', delim);
 223                if (length != 0)
 224                        cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16)
 225                                           | (array[2] << 8) | array[3]);
 226        } else {
 227                /* Now we have IPv6 address. */
 228                length = get_ipv6_addr(data + 3, dlen - 3,
 229                                       (struct in6_addr *)cmd->u3.ip6, delim);
 230        }
 231
 232        if (length == 0)
 233                return 0;
 234        pr_debug("EPRT: Got IP address!\n");
 235        /* Start offset includes initial "|1|", and trailing delimiter */
 236        return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port);
 237}
 238
 239/* Returns 0, or length of numbers: |||6446| */
 240static int try_epsv_response(const char *data, size_t dlen,
 241                             struct nf_conntrack_man *cmd, char term)
 242{
 243        char delim;
 244
 245        /* Three delimiters. */
 246        if (dlen <= 3) return 0;
 247        delim = data[0];
 248        if (isdigit(delim) || delim < 33 || delim > 126 ||
 249            data[1] != delim || data[2] != delim)
 250                return 0;
 251
 252        return get_port(data, 3, dlen, delim, &cmd->u.tcp.port);
 253}
 254
 255/* Return 1 for match, 0 for accept, -1 for partial. */
 256static int find_pattern(const char *data, size_t dlen,
 257                        const char *pattern, size_t plen,
 258                        char skip, char term,
 259                        unsigned int *numoff,
 260                        unsigned int *numlen,
 261                        struct nf_conntrack_man *cmd,
 262                        int (*getnum)(const char *, size_t,
 263                                      struct nf_conntrack_man *, char))
 264{
 265        size_t i;
 266
 267        pr_debug("find_pattern `%s': dlen = %Zu\n", pattern, dlen);
 268        if (dlen == 0)
 269                return 0;
 270
 271        if (dlen <= plen) {
 272                /* Short packet: try for partial? */
 273                if (strnicmp(data, pattern, dlen) == 0)
 274                        return -1;
 275                else return 0;
 276        }
 277
 278        if (strnicmp(data, pattern, plen) != 0) {
 279#if 0
 280                size_t i;
 281
 282                pr_debug("ftp: string mismatch\n");
 283                for (i = 0; i < plen; i++) {
 284                        pr_debug("ftp:char %u `%c'(%u) vs `%c'(%u)\n",
 285                                 i, data[i], data[i],
 286                                 pattern[i], pattern[i]);
 287                }
 288#endif
 289                return 0;
 290        }
 291
 292        pr_debug("Pattern matches!\n");
 293        /* Now we've found the constant string, try to skip
 294           to the 'skip' character */
 295        for (i = plen; data[i] != skip; i++)
 296                if (i == dlen - 1) return -1;
 297
 298        /* Skip over the last character */
 299        i++;
 300
 301        pr_debug("Skipped up to `%c'!\n", skip);
 302
 303        *numoff = i;
 304        *numlen = getnum(data + i, dlen - i, cmd, term);
 305        if (!*numlen)
 306                return -1;
 307
 308        pr_debug("Match succeeded!\n");
 309        return 1;
 310}
 311
 312/* Look up to see if we're just after a \n. */
 313static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir)
 314{
 315        unsigned int i;
 316
 317        for (i = 0; i < info->seq_aft_nl_num[dir]; i++)
 318                if (info->seq_aft_nl[dir][i] == seq)
 319                        return 1;
 320        return 0;
 321}
 322
 323/* We don't update if it's older than what we have. */
 324static void update_nl_seq(struct nf_conn *ct, u32 nl_seq,
 325                          struct nf_ct_ftp_master *info, int dir,
 326                          struct sk_buff *skb)
 327{
 328        unsigned int i, oldest;
 329
 330        /* Look for oldest: if we find exact match, we're done. */
 331        for (i = 0; i < info->seq_aft_nl_num[dir]; i++) {
 332                if (info->seq_aft_nl[dir][i] == nl_seq)
 333                        return;
 334        }
 335
 336        if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) {
 337                info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq;
 338        } else {
 339                if (before(info->seq_aft_nl[dir][0], info->seq_aft_nl[dir][1]))
 340                        oldest = 0;
 341                else
 342                        oldest = 1;
 343
 344                if (after(nl_seq, info->seq_aft_nl[dir][oldest]))
 345                        info->seq_aft_nl[dir][oldest] = nl_seq;
 346        }
 347}
 348
 349static int help(struct sk_buff *skb,
 350                unsigned int protoff,
 351                struct nf_conn *ct,
 352                enum ip_conntrack_info ctinfo)
 353{
 354        unsigned int dataoff, datalen;
 355        const struct tcphdr *th;
 356        struct tcphdr _tcph;
 357        const char *fb_ptr;
 358        int ret;
 359        u32 seq;
 360        int dir = CTINFO2DIR(ctinfo);
 361        unsigned int uninitialized_var(matchlen), uninitialized_var(matchoff);
 362        struct nf_ct_ftp_master *ct_ftp_info = nfct_help_data(ct);
 363        struct nf_conntrack_expect *exp;
 364        union nf_inet_addr *daddr;
 365        struct nf_conntrack_man cmd = {};
 366        unsigned int i;
 367        int found = 0, ends_in_nl;
 368        typeof(nf_nat_ftp_hook) nf_nat_ftp;
 369
 370        /* Until there's been traffic both ways, don't look in packets. */
 371        if (ctinfo != IP_CT_ESTABLISHED &&
 372            ctinfo != IP_CT_ESTABLISHED_REPLY) {
 373                pr_debug("ftp: Conntrackinfo = %u\n", ctinfo);
 374                return NF_ACCEPT;
 375        }
 376
 377        th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
 378        if (th == NULL)
 379                return NF_ACCEPT;
 380
 381        dataoff = protoff + th->doff * 4;
 382        /* No data? */
 383        if (dataoff >= skb->len) {
 384                pr_debug("ftp: dataoff(%u) >= skblen(%u)\n", dataoff,
 385                         skb->len);
 386                return NF_ACCEPT;
 387        }
 388        datalen = skb->len - dataoff;
 389
 390        spin_lock_bh(&nf_ftp_lock);
 391        fb_ptr = skb_header_pointer(skb, dataoff, datalen, ftp_buffer);
 392        BUG_ON(fb_ptr == NULL);
 393
 394        ends_in_nl = (fb_ptr[datalen - 1] == '\n');
 395        seq = ntohl(th->seq) + datalen;
 396
 397        /* Look up to see if we're just after a \n. */
 398        if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) {
 399                /* We're picking up this, clear flags and let it continue */
 400                if (unlikely(ct_ftp_info->flags[dir] & NF_CT_FTP_SEQ_PICKUP)) {
 401                        ct_ftp_info->flags[dir] ^= NF_CT_FTP_SEQ_PICKUP;
 402                        goto skip_nl_seq;
 403                }
 404
 405                /* Now if this ends in \n, update ftp info. */
 406                pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n",
 407                         ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)",
 408                         ct_ftp_info->seq_aft_nl[dir][0],
 409                         ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)",
 410                         ct_ftp_info->seq_aft_nl[dir][1]);
 411                ret = NF_ACCEPT;
 412                goto out_update_nl;
 413        }
 414
 415skip_nl_seq:
 416        /* Initialize IP/IPv6 addr to expected address (it's not mentioned
 417           in EPSV responses) */
 418        cmd.l3num = nf_ct_l3num(ct);
 419        memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
 420               sizeof(cmd.u3.all));
 421
 422        for (i = 0; i < ARRAY_SIZE(search[dir]); i++) {
 423                found = find_pattern(fb_ptr, datalen,
 424                                     search[dir][i].pattern,
 425                                     search[dir][i].plen,
 426                                     search[dir][i].skip,
 427                                     search[dir][i].term,
 428                                     &matchoff, &matchlen,
 429                                     &cmd,
 430                                     search[dir][i].getnum);
 431                if (found) break;
 432        }
 433        if (found == -1) {
 434                /* We don't usually drop packets.  After all, this is
 435                   connection tracking, not packet filtering.
 436                   However, it is necessary for accurate tracking in
 437                   this case. */
 438                pr_debug("conntrack_ftp: partial %s %u+%u\n",
 439                         search[dir][i].pattern,  ntohl(th->seq), datalen);
 440                ret = NF_DROP;
 441                goto out;
 442        } else if (found == 0) { /* No match */
 443                ret = NF_ACCEPT;
 444                goto out_update_nl;
 445        }
 446
 447        pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n",
 448                 matchlen, fb_ptr + matchoff,
 449                 matchlen, ntohl(th->seq) + matchoff);
 450
 451        exp = nf_ct_expect_alloc(ct);
 452        if (exp == NULL) {
 453                ret = NF_DROP;
 454                goto out;
 455        }
 456
 457        /* We refer to the reverse direction ("!dir") tuples here,
 458         * because we're expecting something in the other direction.
 459         * Doesn't matter unless NAT is happening.  */
 460        daddr = &ct->tuplehash[!dir].tuple.dst.u3;
 461
 462        /* Update the ftp info */
 463        if ((cmd.l3num == nf_ct_l3num(ct)) &&
 464            memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
 465                     sizeof(cmd.u3.all))) {
 466                /* Enrico Scholz's passive FTP to partially RNAT'd ftp
 467                   server: it really wants us to connect to a
 468                   different IP address.  Simply don't record it for
 469                   NAT. */
 470                if (cmd.l3num == PF_INET) {
 471                        pr_debug("conntrack_ftp: NOT RECORDING: %pI4 != %pI4\n",
 472                                 &cmd.u3.ip,
 473                                 &ct->tuplehash[dir].tuple.src.u3.ip);
 474                } else {
 475                        pr_debug("conntrack_ftp: NOT RECORDING: %pI6 != %pI6\n",
 476                                 cmd.u3.ip6,
 477                                 ct->tuplehash[dir].tuple.src.u3.ip6);
 478                }
 479
 480                /* Thanks to Cristiano Lincoln Mattos
 481                   <lincoln@cesar.org.br> for reporting this potential
 482                   problem (DMZ machines opening holes to internal
 483                   networks, or the packet filter itself). */
 484                if (!loose) {
 485                        ret = NF_ACCEPT;
 486                        goto out_put_expect;
 487                }
 488                daddr = &cmd.u3;
 489        }
 490
 491        nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num,
 492                          &ct->tuplehash[!dir].tuple.src.u3, daddr,
 493                          IPPROTO_TCP, NULL, &cmd.u.tcp.port);
 494
 495        /* Now, NAT might want to mangle the packet, and register the
 496         * (possibly changed) expectation itself. */
 497        nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook);
 498        if (nf_nat_ftp && ct->status & IPS_NAT_MASK)
 499                ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype,
 500                                 protoff, matchoff, matchlen, exp);
 501        else {
 502                /* Can't expect this?  Best to drop packet now. */
 503                if (nf_ct_expect_related(exp) != 0)
 504                        ret = NF_DROP;
 505                else
 506                        ret = NF_ACCEPT;
 507        }
 508
 509out_put_expect:
 510        nf_ct_expect_put(exp);
 511
 512out_update_nl:
 513        /* Now if this ends in \n, update ftp info.  Seq may have been
 514         * adjusted by NAT code. */
 515        if (ends_in_nl)
 516                update_nl_seq(ct, seq, ct_ftp_info, dir, skb);
 517 out:
 518        spin_unlock_bh(&nf_ftp_lock);
 519        return ret;
 520}
 521
 522static int nf_ct_ftp_from_nlattr(struct nlattr *attr, struct nf_conn *ct)
 523{
 524        struct nf_ct_ftp_master *ftp = nfct_help_data(ct);
 525
 526        /* This conntrack has been injected from user-space, always pick up
 527         * sequence tracking. Otherwise, the first FTP command after the
 528         * failover breaks.
 529         */
 530        ftp->flags[IP_CT_DIR_ORIGINAL] |= NF_CT_FTP_SEQ_PICKUP;
 531        ftp->flags[IP_CT_DIR_REPLY] |= NF_CT_FTP_SEQ_PICKUP;
 532        return 0;
 533}
 534
 535static struct nf_conntrack_helper ftp[MAX_PORTS][2] __read_mostly;
 536
 537static const struct nf_conntrack_expect_policy ftp_exp_policy = {
 538        .max_expected   = 1,
 539        .timeout        = 5 * 60,
 540};
 541
 542/* don't make this __exit, since it's called from __init ! */
 543static void nf_conntrack_ftp_fini(void)
 544{
 545        int i, j;
 546        for (i = 0; i < ports_c; i++) {
 547                for (j = 0; j < 2; j++) {
 548                        if (ftp[i][j].me == NULL)
 549                                continue;
 550
 551                        pr_debug("nf_ct_ftp: unregistering helper for pf: %d "
 552                                 "port: %d\n",
 553                                 ftp[i][j].tuple.src.l3num, ports[i]);
 554                        nf_conntrack_helper_unregister(&ftp[i][j]);
 555                }
 556        }
 557
 558        kfree(ftp_buffer);
 559}
 560
 561static int __init nf_conntrack_ftp_init(void)
 562{
 563        int i, j = -1, ret = 0;
 564
 565        ftp_buffer = kmalloc(65536, GFP_KERNEL);
 566        if (!ftp_buffer)
 567                return -ENOMEM;
 568
 569        if (ports_c == 0)
 570                ports[ports_c++] = FTP_PORT;
 571
 572        /* FIXME should be configurable whether IPv4 and IPv6 FTP connections
 573                 are tracked or not - YK */
 574        for (i = 0; i < ports_c; i++) {
 575                ftp[i][0].tuple.src.l3num = PF_INET;
 576                ftp[i][1].tuple.src.l3num = PF_INET6;
 577                for (j = 0; j < 2; j++) {
 578                        ftp[i][j].data_len = sizeof(struct nf_ct_ftp_master);
 579                        ftp[i][j].tuple.src.u.tcp.port = htons(ports[i]);
 580                        ftp[i][j].tuple.dst.protonum = IPPROTO_TCP;
 581                        ftp[i][j].expect_policy = &ftp_exp_policy;
 582                        ftp[i][j].me = THIS_MODULE;
 583                        ftp[i][j].help = help;
 584                        ftp[i][j].from_nlattr = nf_ct_ftp_from_nlattr;
 585                        if (ports[i] == FTP_PORT)
 586                                sprintf(ftp[i][j].name, "ftp");
 587                        else
 588                                sprintf(ftp[i][j].name, "ftp-%d", ports[i]);
 589
 590                        pr_debug("nf_ct_ftp: registering helper for pf: %d "
 591                                 "port: %d\n",
 592                                 ftp[i][j].tuple.src.l3num, ports[i]);
 593                        ret = nf_conntrack_helper_register(&ftp[i][j]);
 594                        if (ret) {
 595                                printk(KERN_ERR "nf_ct_ftp: failed to register"
 596                                       " helper for pf: %d port: %d\n",
 597                                        ftp[i][j].tuple.src.l3num, ports[i]);
 598                                nf_conntrack_ftp_fini();
 599                                return ret;
 600                        }
 601                }
 602        }
 603
 604        return 0;
 605}
 606
 607module_init(nf_conntrack_ftp_init);
 608module_exit(nf_conntrack_ftp_fini);
 609
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