git.oblomov.eu Git - linux-2.6/blob - net/netfilter/nf_conntrack_ftp.c

   1 /* FTP extension for connection tracking. */
   2
   3 /* (C) 1999-2001 Paul `Rusty' Russell
   4  * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org>
   5  * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  */
  11
  12 #include <linux/module.h>
  13 #include <linux/moduleparam.h>
  14 #include <linux/netfilter.h>
  15 #include <linux/ip.h>
  16 #include <linux/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
  28 MODULE_LICENSE("GPL");
  29 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
  30 MODULE_DESCRIPTION("ftp connection tracking helper");
  31 MODULE_ALIAS("ip_conntrack_ftp");
  32 MODULE_ALIAS_NFCT_HELPER("ftp");
  33
  34 /* This is slow, but it's simple. --RR */
  35 static char *ftp_buffer;
  36
  37 static DEFINE_SPINLOCK(nf_ftp_lock);
  38
  39 #define MAX_PORTS 8
  40 static u_int16_t ports[MAX_PORTS];
  41 static unsigned int ports_c;
  42 module_param_array(ports, ushort, &ports_c, 0400);
  43
  44 static int loose;
  45 module_param(loose, bool, 0600);
  46
  47 unsigned 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);
  53 EXPORT_SYMBOL_GPL(nf_nat_ftp_hook);
  54
  55 static int try_rfc959(const char *, size_t, struct nf_conntrack_man *, char);
  56 static int try_eprt(const char *, size_t, struct nf_conntrack_man *, char);
  57 static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *,
  58                              char);
  59
  60 static 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
 106 static int
 107 get_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
 116 static 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 */
 147 static 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 */
 164 static 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| */
 190 static 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| */
 238 static 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. */
 254 static 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. */
 311 static 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. */
 322 static 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
 349 static 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
 502 out_put_expect:
 503         nf_ct_expect_put(exp);
 504
 505 out_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
 515 static struct nf_conntrack_helper ftp[MAX_PORTS][2] __read_mostly;
 516 static char ftp_names[MAX_PORTS][2][sizeof("ftp-65535")] __read_mostly;
 517
 518 static 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 ! */
 524 static 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
 542 static 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
 589 module_init(nf_conntrack_ftp_init);
 590 module_exit(nf_conntrack_ftp_fini);