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/ipv6.h>
  17#include <linux/ctype.h>
  18#include <linux/inet.h>
  19#include <net/checksum.h>
  20#include <net/tcp.h>
  21
  22#include <net/netfilter/nf_conntrack.h>
  23#include <net/netfilter/nf_conntrack_expect.h>
  24#include <net/netfilter/nf_conntrack_ecache.h>
  25#include <net/netfilter/nf_conntrack_helper.h>
  26#include <linux/netfilter/nf_conntrack_ftp.h>
  27
  28MODULE_LICENSE("GPL");
  29MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  30MODULE_DESCRIPTION("ftp connection tracking helper");
  31MODULE_ALIAS("ip_conntrack_ftp");
  32MODULE_ALIAS_NFCT_HELPER("ftp");
  33
  34/* This is slow, but it's simple. --RR */
  35static char *ftp_buffer;
  36
  37static DEFINE_SPINLOCK(nf_ftp_lock);
  38
  39#define MAX_PORTS 8
  40static u_int16_t ports[MAX_PORTS];
  41static unsigned int ports_c;
  42module_param_array(ports, ushort, &ports_c, 0400);
  43
  44static int loose;
  45module_param(loose, bool, 0600);
  46
  47unsigned int (*nf_nat_ftp_hook)(struct sk_buff *skb,
  48                                enum ip_conntrack_info ctinfo,
  49                                enum nf_ct_ftp_type type,
  50                                unsigned int matchoff,
  51                                unsigned int matchlen,
  52                                struct nf_conntrack_expect *exp);
  53EXPORT_SYMBOL_GPL(nf_nat_ftp_hook);
  54
  55static int try_rfc959(const char *, size_t, struct nf_conntrack_man *, char);
  56static int try_eprt(const char *, size_t, struct nf_conntrack_man *, char);
  57static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *,
  58                             char);
  59
  60static struct ftp_search {
  61        const char *pattern;
  62        size_t plen;
  63        char skip;
  64        char term;
  65        enum nf_ct_ftp_type ftptype;
  66        int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char);
  67} search[IP_CT_DIR_MAX][2] = {
  68        [IP_CT_DIR_ORIGINAL] = {
  69                {
  70                        .pattern        = "PORT",
  71                        .plen           = sizeof("PORT") - 1,
  72                        .skip           = ' ',
  73                        .term           = '\r',
  74                        .ftptype        = NF_CT_FTP_PORT,
  75                        .getnum         = try_rfc959,
  76                },
  77                {
  78                        .pattern        = "EPRT",
  79                        .plen           = sizeof("EPRT") - 1,
  80                        .skip           = ' ',
  81                        .term           = '\r',
  82                        .ftptype        = NF_CT_FTP_EPRT,
  83                        .getnum         = try_eprt,
  84                },
  85        },
  86        [IP_CT_DIR_REPLY] = {
  87                {
  88                        .pattern        = "227 ",
  89                        .plen           = sizeof("227 ") - 1,
  90                        .skip           = '(',
  91                        .term           = ')',
  92                        .ftptype        = NF_CT_FTP_PASV,
  93                        .getnum         = try_rfc959,
  94                },
  95                {
  96                        .pattern        = "229 ",
  97                        .plen           = sizeof("229 ") - 1,
  98                        .skip           = '(',
  99                        .term           = ')',
 100                        .ftptype        = NF_CT_FTP_EPSV,
 101                        .getnum         = try_epsv_response,
 102                },
 103        },
 104};
 105
 106static int
 107get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term)
 108{
 109        const char *end;
 110        int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end);
 111        if (ret > 0)
 112                return (int)(end - src);
 113        return 0;
 114}
 115
 116static int try_number(const char *data, size_t dlen, u_int32_t array[],
 117                      int array_size, char sep, char term)
 118{
 119        u_int32_t i, len;
 120
 121        memset(array, 0, sizeof(array[0])*array_size);
 122
 123        /* Keep data pointing at next char. */
 124        for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) {
 125                if (*data >= '0' && *data <= '9') {
 126                        array[i] = array[i]*10 + *data - '0';
 127                }
 128                else if (*data == sep)
 129                        i++;
 130                else {
 131                        /* Unexpected character; true if it's the
 132                           terminator and we're finished. */
 133                        if (*data == term && i == array_size - 1)
 134                                return len;
 135
 136                        pr_debug("Char %u (got %u nums) `%u' unexpected\n",
 137                                 len, i, *data);
 138                        return 0;
 139                }
 140        }
 141        pr_debug("Failed to fill %u numbers separated by %c\n",
 142                 array_size, sep);
 143        return 0;
 144}
 145
 146/* Returns 0, or length of numbers: 192,168,1,1,5,6 */
 147static int try_rfc959(const char *data, size_t dlen,
 148                      struct nf_conntrack_man *cmd, char term)
 149{
 150        int length;
 151        u_int32_t array[6];
 152
 153        length = try_number(data, dlen, array, 6, ',', term);
 154        if (length == 0)
 155                return 0;
 156
 157        cmd->u3.ip =  htonl((array[0] << 24) | (array[1] << 16) |
 158                                    (array[2] << 8) | array[3]);
 159        cmd->u.tcp.port = htons((array[4] << 8) | array[5]);
 160        return length;
 161}
 162
 163/* Grab port: number up to delimiter */
 164static int get_port(const char *data, int start, size_t dlen, char delim,
 165                    __be16 *port)
 166{
 167        u_int16_t tmp_port = 0;
 168        int i;
 169
 170        for (i = start; i < dlen; i++) {
 171                /* Finished? */
 172                if (data[i] == delim) {
 173                        if (tmp_port == 0)
 174                                break;
 175                        *port = htons(tmp_port);
 176                        pr_debug("get_port: return %d\n", tmp_port);
 177                        return i + 1;
 178                }
 179                else if (data[i] >= '0' && data[i] <= '9')
 180                        tmp_port = tmp_port*10 + data[i] - '0';
 181                else { /* Some other crap */
 182                        pr_debug("get_port: invalid char.\n");
 183                        break;
 184                }
 185        }
 186        return 0;
 187}
 188
 189/* Returns 0, or length of numbers: |1|132.235.1.2|6275| or |2|3ffe::1|6275| */
 190static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd,
 191                    char term)
 192{
 193        char delim;
 194        int length;
 195
 196        /* First character is delimiter, then "1" for IPv4 or "2" for IPv6,
 197           then delimiter again. */
 198        if (dlen <= 3) {
 199                pr_debug("EPRT: too short\n");
 200                return 0;
 201        }
 202        delim = data[0];
 203        if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) {
 204                pr_debug("try_eprt: invalid delimitter.\n");
 205                return 0;
 206        }
 207
 208        if ((cmd->l3num == PF_INET && data[1] != '1') ||
 209            (cmd->l3num == PF_INET6 && data[1] != '2')) {
 210                pr_debug("EPRT: invalid protocol number.\n");
 211                return 0;
 212        }
 213
 214        pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim);
 215
 216        if (data[1] == '1') {
 217                u_int32_t array[4];
 218
 219                /* Now we have IP address. */
 220                length = try_number(data + 3, dlen - 3, array, 4, '.', delim);
 221                if (length != 0)
 222                        cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16)
 223                                           | (array[2] << 8) | array[3]);
 224        } else {
 225                /* Now we have IPv6 address. */
 226                length = get_ipv6_addr(data + 3, dlen - 3,
 227                                       (struct in6_addr *)cmd->u3.ip6, delim);
 228        }
 229
 230        if (length == 0)
 231                return 0;
 232        pr_debug("EPRT: Got IP address!\n");
 233        /* Start offset includes initial "|1|", and trailing delimiter */
 234        return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port);
 235}
 236
 237/* Returns 0, or length of numbers: |||6446| */
 238static int try_epsv_response(const char *data, size_t dlen,
 239                             struct nf_conntrack_man *cmd, char term)
 240{
 241        char delim;
 242
 243        /* Three delimiters. */
 244        if (dlen <= 3) return 0;
 245        delim = data[0];
 246        if (isdigit(delim) || delim < 33 || delim > 126
 247            || data[1] != delim || data[2] != delim)
 248                return 0;
 249
 250        return get_port(data, 3, dlen, delim, &cmd->u.tcp.port);
 251}
 252
 253/* Return 1 for match, 0 for accept, -1 for partial. */
 254static int find_pattern(const char *data, size_t dlen,
 255                        const char *pattern, size_t plen,
 256                        char skip, char term,
 257                        unsigned int *numoff,
 258                        unsigned int *numlen,
 259                        struct nf_conntrack_man *cmd,
 260                        int (*getnum)(const char *, size_t,
 261                                      struct nf_conntrack_man *, char))
 262{
 263        size_t i;
 264
 265        pr_debug("find_pattern `%s': dlen = %Zu\n", pattern, dlen);
 266        if (dlen == 0)
 267                return 0;
 268
 269        if (dlen <= plen) {
 270                /* Short packet: try for partial? */
 271                if (strnicmp(data, pattern, dlen) == 0)
 272                        return -1;
 273                else return 0;
 274        }
 275
 276        if (strnicmp(data, pattern, plen) != 0) {
 277#if 0
 278                size_t i;
 279
 280                pr_debug("ftp: string mismatch\n");
 281                for (i = 0; i < plen; i++) {
 282                        pr_debug("ftp:char %u `%c'(%u) vs `%c'(%u)\n",
 283                                 i, data[i], data[i],
 284                                 pattern[i], pattern[i]);
 285                }
 286#endif
 287                return 0;
 288        }
 289
 290        pr_debug("Pattern matches!\n");
 291        /* Now we've found the constant string, try to skip
 292           to the 'skip' character */
 293        for (i = plen; data[i] != skip; i++)
 294                if (i == dlen - 1) return -1;
 295
 296        /* Skip over the last character */
 297        i++;
 298
 299        pr_debug("Skipped up to `%c'!\n", skip);
 300
 301        *numoff = i;
 302        *numlen = getnum(data + i, dlen - i, cmd, term);
 303        if (!*numlen)
 304                return -1;
 305
 306        pr_debug("Match succeeded!\n");
 307        return 1;
 308}
 309
 310/* Look up to see if we're just after a \n. */
 311static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir)
 312{
 313        unsigned int i;
 314
 315        for (i = 0; i < info->seq_aft_nl_num[dir]; i++)
 316                if (info->seq_aft_nl[dir][i] == seq)
 317                        return 1;
 318        return 0;
 319}
 320
 321/* We don't update if it's older than what we have. */
 322static void update_nl_seq(struct nf_conn *ct, u32 nl_seq,
 323                          struct nf_ct_ftp_master *info, int dir,
 324                          struct sk_buff *skb)
 325{
 326        unsigned int i, oldest = NUM_SEQ_TO_REMEMBER;
 327
 328        /* Look for oldest: if we find exact match, we're done. */
 329        for (i = 0; i < info->seq_aft_nl_num[dir]; i++) {
 330                if (info->seq_aft_nl[dir][i] == nl_seq)
 331                        return;
 332
 333                if (oldest == info->seq_aft_nl_num[dir] ||
 334                    before(info->seq_aft_nl[dir][i],
 335                           info->seq_aft_nl[dir][oldest]))
 336                        oldest = i;
 337        }
 338
 339        if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) {
 340                info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq;
 341                nf_conntrack_event_cache(IPCT_HELPINFO_VOLATILE, ct);
 342        } else if (oldest != NUM_SEQ_TO_REMEMBER &&
 343                   after(nl_seq, info->seq_aft_nl[dir][oldest])) {
 344                info->seq_aft_nl[dir][oldest] = nl_seq;
 345                nf_conntrack_event_cache(IPCT_HELPINFO_VOLATILE, ct);
 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(ct)->help.ct_ftp_info;
 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+IP_CT_IS_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                /* Now if this ends in \n, update ftp info. */
 400                pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n",
 401                         ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)",
 402                         ct_ftp_info->seq_aft_nl[dir][0],
 403                         ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)",
 404                         ct_ftp_info->seq_aft_nl[dir][1]);
 405                ret = NF_ACCEPT;
 406                goto out_update_nl;
 407        }
 408
 409        /* Initialize IP/IPv6 addr to expected address (it's not mentioned
 410           in EPSV responses) */
 411        cmd.l3num = nf_ct_l3num(ct);
 412        memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
 413               sizeof(cmd.u3.all));
 414
 415        for (i = 0; i < ARRAY_SIZE(search[dir]); i++) {
 416                found = find_pattern(fb_ptr, datalen,
 417                                     search[dir][i].pattern,
 418                                     search[dir][i].plen,
 419                                     search[dir][i].skip,
 420                                     search[dir][i].term,
 421                                     &matchoff, &matchlen,
 422                                     &cmd,
 423                                     search[dir][i].getnum);
 424                if (found) break;
 425        }
 426        if (found == -1) {
 427                /* We don't usually drop packets.  After all, this is
 428                   connection tracking, not packet filtering.
 429                   However, it is necessary for accurate tracking in
 430                   this case. */
 431                pr_debug("conntrack_ftp: partial %s %u+%u\n",
 432                         search[dir][i].pattern,  ntohl(th->seq), datalen);
 433                ret = NF_DROP;
 434                goto out;
 435        } else if (found == 0) { /* No match */
 436                ret = NF_ACCEPT;
 437                goto out_update_nl;
 438        }
 439
 440        pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n",
 441                 matchlen, fb_ptr + matchoff,
 442                 matchlen, ntohl(th->seq) + matchoff);
 443
 444        exp = nf_ct_expect_alloc(ct);
 445        if (exp == NULL) {
 446                ret = NF_DROP;
 447                goto out;
 448        }
 449
 450        /* We refer to the reverse direction ("!dir") tuples here,
 451         * because we're expecting something in the other direction.
 452         * Doesn't matter unless NAT is happening.  */
 453        daddr = &ct->tuplehash[!dir].tuple.dst.u3;
 454
 455        /* Update the ftp info */
 456        if ((cmd.l3num == nf_ct_l3num(ct)) &&
 457            memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
 458                     sizeof(cmd.u3.all))) {
 459                /* Enrico Scholz's passive FTP to partially RNAT'd ftp
 460                   server: it really wants us to connect to a
 461                   different IP address.  Simply don't record it for
 462                   NAT. */
 463                if (cmd.l3num == PF_INET) {
 464                        pr_debug("conntrack_ftp: NOT RECORDING: %pI4 != %pI4\n",
 465                                 &cmd.u3.ip,
 466                                 &ct->tuplehash[dir].tuple.src.u3.ip);
 467                } else {
 468                        pr_debug("conntrack_ftp: NOT RECORDING: %pI6 != %pI6\n",
 469                                 cmd.u3.ip6,
 470                                 ct->tuplehash[dir].tuple.src.u3.ip6);
 471                }
 472
 473                /* Thanks to Cristiano Lincoln Mattos
 474                   <lincoln@cesar.org.br> for reporting this potential
 475                   problem (DMZ machines opening holes to internal
 476                   networks, or the packet filter itself). */
 477                if (!loose) {
 478                        ret = NF_ACCEPT;
 479                        goto out_put_expect;
 480                }
 481                daddr = &cmd.u3;
 482        }
 483
 484        nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num,
 485                          &ct->tuplehash[!dir].tuple.src.u3, daddr,
 486                          IPPROTO_TCP, NULL, &cmd.u.tcp.port);
 487
 488        /* Now, NAT might want to mangle the packet, and register the
 489         * (possibly changed) expectation itself. */
 490        nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook);
 491        if (nf_nat_ftp && ct->status & IPS_NAT_MASK)
 492                ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype,
 493                                 matchoff, matchlen, exp);
 494        else {
 495                /* Can't expect this?  Best to drop packet now. */
 496                if (nf_ct_expect_related(exp) != 0)
 497                        ret = NF_DROP;
 498                else
 499                        ret = NF_ACCEPT;
 500        }
 501
 502out_put_expect:
 503        nf_ct_expect_put(exp);
 504
 505out_update_nl:
 506        /* Now if this ends in \n, update ftp info.  Seq may have been
 507         * adjusted by NAT code. */
 508        if (ends_in_nl)
 509                update_nl_seq(ct, seq, ct_ftp_info, dir, skb);
 510 out:
 511        spin_unlock_bh(&nf_ftp_lock);
 512        return ret;
 513}
 514
 515static struct nf_conntrack_helper ftp[MAX_PORTS][2] __read_mostly;
 516static char ftp_names[MAX_PORTS][2][sizeof("ftp-65535")] __read_mostly;
 517
 518static const struct nf_conntrack_expect_policy ftp_exp_policy = {
 519        .max_expected   = 1,
 520        .timeout        = 5 * 60,
 521};
 522
 523/* don't make this __exit, since it's called from __init ! */
 524static void nf_conntrack_ftp_fini(void)
 525{
 526        int i, j;
 527        for (i = 0; i < ports_c; i++) {
 528                for (j = 0; j < 2; j++) {
 529                        if (ftp[i][j].me == NULL)
 530                                continue;
 531
 532                        pr_debug("nf_ct_ftp: unregistering helper for pf: %d "
 533                                 "port: %d\n",
 534                                 ftp[i][j].tuple.src.l3num, ports[i]);
 535                        nf_conntrack_helper_unregister(&ftp[i][j]);
 536                }
 537        }
 538
 539        kfree(ftp_buffer);
 540}
 541
 542static int __init nf_conntrack_ftp_init(void)
 543{
 544        int i, j = -1, ret = 0;
 545        char *tmpname;
 546
 547        ftp_buffer = kmalloc(65536, GFP_KERNEL);
 548        if (!ftp_buffer)
 549                return -ENOMEM;
 550
 551        if (ports_c == 0)
 552                ports[ports_c++] = FTP_PORT;
 553
 554        /* FIXME should be configurable whether IPv4 and IPv6 FTP connections
 555                 are tracked or not - YK */
 556        for (i = 0; i < ports_c; i++) {
 557                ftp[i][0].tuple.src.l3num = PF_INET;
 558                ftp[i][1].tuple.src.l3num = PF_INET6;
 559                for (j = 0; j < 2; j++) {
 560                        ftp[i][j].tuple.src.u.tcp.port = htons(ports[i]);
 561                        ftp[i][j].tuple.dst.protonum = IPPROTO_TCP;
 562                        ftp[i][j].expect_policy = &ftp_exp_policy;
 563                        ftp[i][j].me = THIS_MODULE;
 564                        ftp[i][j].help = help;
 565                        tmpname = &ftp_names[i][j][0];
 566                        if (ports[i] == FTP_PORT)
 567                                sprintf(tmpname, "ftp");
 568                        else
 569                                sprintf(tmpname, "ftp-%d", ports[i]);
 570                        ftp[i][j].name = tmpname;
 571
 572                        pr_debug("nf_ct_ftp: registering helper for pf: %d "
 573                                 "port: %d\n",
 574                                 ftp[i][j].tuple.src.l3num, ports[i]);
 575                        ret = nf_conntrack_helper_register(&ftp[i][j]);
 576                        if (ret) {
 577                                printk("nf_ct_ftp: failed to register helper "
 578                                       " for pf: %d port: %d\n",
 579                                        ftp[i][j].tuple.src.l3num, ports[i]);
 580                                nf_conntrack_ftp_fini();
 581                                return ret;
 582                        }
 583                }
 584        }
 585
 586        return 0;
 587}
 588
 589module_init(nf_conntrack_ftp_init);
 590module_exit(nf_conntrack_ftp_fini);
 591