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 matchoff,
  52                                unsigned int matchlen,
  53                                struct nf_conntrack_expect *exp);
  54EXPORT_SYMBOL_GPL(nf_nat_ftp_hook);
  55
  56static int try_rfc959(const char *, size_t, struct nf_conntrack_man *, char);
  57static int try_eprt(const char *, size_t, struct nf_conntrack_man *, char);
  58static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *,
  59                             char);
  60
  61static 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
 107static int
 108get_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
 117static 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 */
 148static 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 */
 165static 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| */
 191static 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| */
 239static 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. */
 255static 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. */
 312static 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. */
 323static 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
 348static 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_data(ct);
 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
 501out_put_expect:
 502        nf_ct_expect_put(exp);
 503
 504out_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
 514static struct nf_conntrack_helper ftp[MAX_PORTS][2] __read_mostly;
 515
 516static const struct nf_conntrack_expect_policy ftp_exp_policy = {
 517        .max_expected   = 1,
 518        .timeout        = 5 * 60,
 519};
 520
 521/* don't make this __exit, since it's called from __init ! */
 522static void nf_conntrack_ftp_fini(void)
 523{
 524        int i, j;
 525        for (i = 0; i < ports_c; i++) {
 526                for (j = 0; j < 2; j++) {
 527                        if (ftp[i][j].me == NULL)
 528                                continue;
 529
 530                        pr_debug("nf_ct_ftp: unregistering helper for pf: %d "
 531                                 "port: %d\n",
 532                                 ftp[i][j].tuple.src.l3num, ports[i]);
 533                        nf_conntrack_helper_unregister(&ftp[i][j]);
 534                }
 535        }
 536
 537        kfree(ftp_buffer);
 538}
 539
 540static int __init nf_conntrack_ftp_init(void)
 541{
 542        int i, j = -1, ret = 0;
 543
 544        ftp_buffer = kmalloc(65536, GFP_KERNEL);
 545        if (!ftp_buffer)
 546                return -ENOMEM;
 547
 548        if (ports_c == 0)
 549                ports[ports_c++] = FTP_PORT;
 550
 551        /* FIXME should be configurable whether IPv4 and IPv6 FTP connections
 552                 are tracked or not - YK */
 553        for (i = 0; i < ports_c; i++) {
 554                ftp[i][0].tuple.src.l3num = PF_INET;
 555                ftp[i][1].tuple.src.l3num = PF_INET6;
 556                for (j = 0; j < 2; j++) {
 557                        ftp[i][j].data_len = sizeof(struct nf_ct_ftp_master);
 558                        ftp[i][j].tuple.src.u.tcp.port = htons(ports[i]);
 559                        ftp[i][j].tuple.dst.protonum = IPPROTO_TCP;
 560                        ftp[i][j].expect_policy = &ftp_exp_policy;
 561                        ftp[i][j].me = THIS_MODULE;
 562                        ftp[i][j].help = help;
 563                        if (ports[i] == FTP_PORT)
 564                                sprintf(ftp[i][j].name, "ftp");
 565                        else
 566                                sprintf(ftp[i][j].name, "ftp-%d", ports[i]);
 567
 568                        pr_debug("nf_ct_ftp: registering helper for pf: %d "
 569                                 "port: %d\n",
 570                                 ftp[i][j].tuple.src.l3num, ports[i]);
 571                        ret = nf_conntrack_helper_register(&ftp[i][j]);
 572                        if (ret) {
 573                                printk(KERN_ERR "nf_ct_ftp: failed to register"
 574                                       " helper for pf: %d port: %d\n",
 575                                        ftp[i][j].tuple.src.l3num, ports[i]);
 576                                nf_conntrack_ftp_fini();
 577                                return ret;
 578                        }
 579                }
 580        }
 581
 582        return 0;
 583}
 584
 585module_init(nf_conntrack_ftp_init);
 586module_exit(nf_conntrack_ftp_fini);
 587
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