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 * (C) 2006-2012 Patrick McHardy <kaber@trash.net> 7 * 8 * This program is free software; you can redistribute it and/or modify 9 * it under the terms of the GNU General Public License version 2 as 10 * published by the Free Software Foundation. 11 */ 12 13 #include <linux/module.h> 14 #include <linux/moduleparam.h> 15 #include <linux/netfilter.h> 16 #include <linux/ip.h> 17 #include <linux/slab.h> 18 #include <linux/ipv6.h> 19 #include <linux/ctype.h> 20 #include <linux/inet.h> 21 #include <net/checksum.h> 22 #include <net/tcp.h> 23 24 #include <net/netfilter/nf_conntrack.h> 25 #include <net/netfilter/nf_conntrack_expect.h> 26 #include <net/netfilter/nf_conntrack_ecache.h> 27 #include <net/netfilter/nf_conntrack_helper.h> 28 #include <linux/netfilter/nf_conntrack_ftp.h> 29 30 MODULE_LICENSE("GPL"); 31 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>"); 32 MODULE_DESCRIPTION("ftp connection tracking helper"); 33 MODULE_ALIAS("ip_conntrack_ftp"); 34 MODULE_ALIAS_NFCT_HELPER("ftp"); 35 36 /* This is slow, but it's simple. --RR */ 37 static char *ftp_buffer; 38 39 static DEFINE_SPINLOCK(nf_ftp_lock); 40 41 #define MAX_PORTS 8 42 static u_int16_t ports[MAX_PORTS]; 43 static unsigned int ports_c; 44 module_param_array(ports, ushort, &ports_c, 0400); 45 46 static bool loose; 47 module_param(loose, bool, 0600); 48 49 unsigned int (*nf_nat_ftp_hook)(struct sk_buff *skb, 50 enum ip_conntrack_info ctinfo, 51 enum nf_ct_ftp_type type, 52 unsigned int protoff, 53 unsigned int matchoff, 54 unsigned int matchlen, 55 struct nf_conntrack_expect *exp); 56 EXPORT_SYMBOL_GPL(nf_nat_ftp_hook); 57 58 static int try_rfc959(const char *, size_t, struct nf_conntrack_man *, 59 char, unsigned int *); 60 static int try_rfc1123(const char *, size_t, struct nf_conntrack_man *, 61 char, unsigned int *); 62 static int try_eprt(const char *, size_t, struct nf_conntrack_man *, 63 char, unsigned int *); 64 static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *, 65 char, unsigned int *); 66 67 static struct ftp_search { 68 const char *pattern; 69 size_t plen; 70 char skip; 71 char term; 72 enum nf_ct_ftp_type ftptype; 73 int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char, unsigned int *); 74 } search[IP_CT_DIR_MAX][2] = { 75 [IP_CT_DIR_ORIGINAL] = { 76 { 77 .pattern = "PORT", 78 .plen = sizeof("PORT") - 1, 79 .skip = ' ', 80 .term = '\r', 81 .ftptype = NF_CT_FTP_PORT, 82 .getnum = try_rfc959, 83 }, 84 { 85 .pattern = "EPRT", 86 .plen = sizeof("EPRT") - 1, 87 .skip = ' ', 88 .term = '\r', 89 .ftptype = NF_CT_FTP_EPRT, 90 .getnum = try_eprt, 91 }, 92 }, 93 [IP_CT_DIR_REPLY] = { 94 { 95 .pattern = "227 ", 96 .plen = sizeof("227 ") - 1, 97 .ftptype = NF_CT_FTP_PASV, 98 .getnum = try_rfc1123, 99 }, 100 { 101 .pattern = "229 ", 102 .plen = sizeof("229 ") - 1, 103 .skip = '(', 104 .term = ')', 105 .ftptype = NF_CT_FTP_EPSV, 106 .getnum = try_epsv_response, 107 }, 108 }, 109 }; 110 111 static int 112 get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term) 113 { 114 const char *end; 115 int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end); 116 if (ret > 0) 117 return (int)(end - src); 118 return 0; 119 } 120 121 static int try_number(const char *data, size_t dlen, u_int32_t array[], 122 int array_size, char sep, char term) 123 { 124 u_int32_t i, len; 125 126 memset(array, 0, sizeof(array[0])*array_size); 127 128 /* Keep data pointing at next char. */ 129 for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) { 130 if (*data >= '0' && *data <= '9') { 131 array[i] = array[i]*10 + *data - '0'; 132 } 133 else if (*data == sep) 134 i++; 135 else { 136 /* Unexpected character; true if it's the 137 terminator (or we don't care about one) 138 and we're finished. */ 139 if ((*data == term || !term) && i == array_size - 1) 140 return len; 141 142 pr_debug("Char %u (got %u nums) `%u' unexpected\n", 143 len, i, *data); 144 return 0; 145 } 146 } 147 pr_debug("Failed to fill %u numbers separated by %c\n", 148 array_size, sep); 149 return 0; 150 } 151 152 /* Returns 0, or length of numbers: 192,168,1,1,5,6 */ 153 static int try_rfc959(const char *data, size_t dlen, 154 struct nf_conntrack_man *cmd, char term, 155 unsigned int *offset) 156 { 157 int length; 158 u_int32_t array[6]; 159 160 length = try_number(data, dlen, array, 6, ',', term); 161 if (length == 0) 162 return 0; 163 164 cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16) | 165 (array[2] << 8) | array[3]); 166 cmd->u.tcp.port = htons((array[4] << 8) | array[5]); 167 return length; 168 } 169 170 /* 171 * From RFC 1123: 172 * The format of the 227 reply to a PASV command is not 173 * well standardized. In particular, an FTP client cannot 174 * assume that the parentheses shown on page 40 of RFC-959 175 * will be present (and in fact, Figure 3 on page 43 omits 176 * them). Therefore, a User-FTP program that interprets 177 * the PASV reply must scan the reply for the first digit 178 * of the host and port numbers. 179 */ 180 static int try_rfc1123(const char *data, size_t dlen, 181 struct nf_conntrack_man *cmd, char term, 182 unsigned int *offset) 183 { 184 int i; 185 for (i = 0; i < dlen; i++) 186 if (isdigit(data[i])) 187 break; 188 189 if (i == dlen) 190 return 0; 191 192 *offset += i; 193 194 return try_rfc959(data + i, dlen - i, cmd, 0, offset); 195 } 196 197 /* Grab port: number up to delimiter */ 198 static int get_port(const char *data, int start, size_t dlen, char delim, 199 __be16 *port) 200 { 201 u_int16_t tmp_port = 0; 202 int i; 203 204 for (i = start; i < dlen; i++) { 205 /* Finished? */ 206 if (data[i] == delim) { 207 if (tmp_port == 0) 208 break; 209 *port = htons(tmp_port); 210 pr_debug("get_port: return %d\n", tmp_port); 211 return i + 1; 212 } 213 else if (data[i] >= '0' && data[i] <= '9') 214 tmp_port = tmp_port*10 + data[i] - '0'; 215 else { /* Some other crap */ 216 pr_debug("get_port: invalid char.\n"); 217 break; 218 } 219 } 220 return 0; 221 } 222 223 /* Returns 0, or length of numbers: |1|132.235.1.2|6275| or |2|3ffe::1|6275| */ 224 static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd, 225 char term, unsigned int *offset) 226 { 227 char delim; 228 int length; 229 230 /* First character is delimiter, then "1" for IPv4 or "2" for IPv6, 231 then delimiter again. */ 232 if (dlen <= 3) { 233 pr_debug("EPRT: too short\n"); 234 return 0; 235 } 236 delim = data[0]; 237 if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) { 238 pr_debug("try_eprt: invalid delimitter.\n"); 239 return 0; 240 } 241 242 if ((cmd->l3num == PF_INET && data[1] != '1') || 243 (cmd->l3num == PF_INET6 && data[1] != '2')) { 244 pr_debug("EPRT: invalid protocol number.\n"); 245 return 0; 246 } 247 248 pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim); 249 250 if (data[1] == '1') { 251 u_int32_t array[4]; 252 253 /* Now we have IP address. */ 254 length = try_number(data + 3, dlen - 3, array, 4, '.', delim); 255 if (length != 0) 256 cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16) 257 | (array[2] << 8) | array[3]); 258 } else { 259 /* Now we have IPv6 address. */ 260 length = get_ipv6_addr(data + 3, dlen - 3, 261 (struct in6_addr *)cmd->u3.ip6, delim); 262 } 263 264 if (length == 0) 265 return 0; 266 pr_debug("EPRT: Got IP address!\n"); 267 /* Start offset includes initial "|1|", and trailing delimiter */ 268 return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port); 269 } 270 271 /* Returns 0, or length of numbers: |||6446| */ 272 static int try_epsv_response(const char *data, size_t dlen, 273 struct nf_conntrack_man *cmd, char term, 274 unsigned int *offset) 275 { 276 char delim; 277 278 /* Three delimiters. */ 279 if (dlen <= 3) return 0; 280 delim = data[0]; 281 if (isdigit(delim) || delim < 33 || delim > 126 || 282 data[1] != delim || data[2] != delim) 283 return 0; 284 285 return get_port(data, 3, dlen, delim, &cmd->u.tcp.port); 286 } 287 288 /* Return 1 for match, 0 for accept, -1 for partial. */ 289 static int find_pattern(const char *data, size_t dlen, 290 const char *pattern, size_t plen, 291 char skip, char term, 292 unsigned int *numoff, 293 unsigned int *numlen, 294 struct nf_conntrack_man *cmd, 295 int (*getnum)(const char *, size_t, 296 struct nf_conntrack_man *, char, 297 unsigned int *)) 298 { 299 size_t i = plen; 300 301 pr_debug("find_pattern `%s': dlen = %Zu\n", pattern, dlen); 302 if (dlen == 0) 303 return 0; 304 305 if (dlen <= plen) { 306 /* Short packet: try for partial? */ 307 if (strncasecmp(data, pattern, dlen) == 0) 308 return -1; 309 else return 0; 310 } 311 312 if (strncasecmp(data, pattern, plen) != 0) { 313 #if 0 314 size_t i; 315 316 pr_debug("ftp: string mismatch\n"); 317 for (i = 0; i < plen; i++) { 318 pr_debug("ftp:char %u `%c'(%u) vs `%c'(%u)\n", 319 i, data[i], data[i], 320 pattern[i], pattern[i]); 321 } 322 #endif 323 return 0; 324 } 325 326 pr_debug("Pattern matches!\n"); 327 /* Now we've found the constant string, try to skip 328 to the 'skip' character */ 329 if (skip) { 330 for (i = plen; data[i] != skip; i++) 331 if (i == dlen - 1) return -1; 332 333 /* Skip over the last character */ 334 i++; 335 } 336 337 pr_debug("Skipped up to `%c'!\n", skip); 338 339 *numoff = i; 340 *numlen = getnum(data + i, dlen - i, cmd, term, numoff); 341 if (!*numlen) 342 return -1; 343 344 pr_debug("Match succeeded!\n"); 345 return 1; 346 } 347 348 /* Look up to see if we're just after a \n. */ 349 static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir) 350 { 351 unsigned int i; 352 353 for (i = 0; i < info->seq_aft_nl_num[dir]; i++) 354 if (info->seq_aft_nl[dir][i] == seq) 355 return 1; 356 return 0; 357 } 358 359 /* We don't update if it's older than what we have. */ 360 static void update_nl_seq(struct nf_conn *ct, u32 nl_seq, 361 struct nf_ct_ftp_master *info, int dir, 362 struct sk_buff *skb) 363 { 364 unsigned int i, oldest; 365 366 /* Look for oldest: if we find exact match, we're done. */ 367 for (i = 0; i < info->seq_aft_nl_num[dir]; i++) { 368 if (info->seq_aft_nl[dir][i] == nl_seq) 369 return; 370 } 371 372 if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) { 373 info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq; 374 } else { 375 if (before(info->seq_aft_nl[dir][0], info->seq_aft_nl[dir][1])) 376 oldest = 0; 377 else 378 oldest = 1; 379 380 if (after(nl_seq, info->seq_aft_nl[dir][oldest])) 381 info->seq_aft_nl[dir][oldest] = nl_seq; 382 } 383 } 384 385 static int help(struct sk_buff *skb, 386 unsigned int protoff, 387 struct nf_conn *ct, 388 enum ip_conntrack_info ctinfo) 389 { 390 unsigned int dataoff, datalen; 391 const struct tcphdr *th; 392 struct tcphdr _tcph; 393 const char *fb_ptr; 394 int ret; 395 u32 seq; 396 int dir = CTINFO2DIR(ctinfo); 397 unsigned int uninitialized_var(matchlen), uninitialized_var(matchoff); 398 struct nf_ct_ftp_master *ct_ftp_info = nfct_help_data(ct); 399 struct nf_conntrack_expect *exp; 400 union nf_inet_addr *daddr; 401 struct nf_conntrack_man cmd = {}; 402 unsigned int i; 403 int found = 0, ends_in_nl; 404 typeof(nf_nat_ftp_hook) nf_nat_ftp; 405 406 /* Until there's been traffic both ways, don't look in packets. */ 407 if (ctinfo != IP_CT_ESTABLISHED && 408 ctinfo != IP_CT_ESTABLISHED_REPLY) { 409 pr_debug("ftp: Conntrackinfo = %u\n", ctinfo); 410 return NF_ACCEPT; 411 } 412 413 th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph); 414 if (th == NULL) 415 return NF_ACCEPT; 416 417 dataoff = protoff + th->doff * 4; 418 /* No data? */ 419 if (dataoff >= skb->len) { 420 pr_debug("ftp: dataoff(%u) >= skblen(%u)\n", dataoff, 421 skb->len); 422 return NF_ACCEPT; 423 } 424 datalen = skb->len - dataoff; 425 426 spin_lock_bh(&nf_ftp_lock); 427 fb_ptr = skb_header_pointer(skb, dataoff, datalen, ftp_buffer); 428 BUG_ON(fb_ptr == NULL); 429 430 ends_in_nl = (fb_ptr[datalen - 1] == '\n'); 431 seq = ntohl(th->seq) + datalen; 432 433 /* Look up to see if we're just after a \n. */ 434 if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) { 435 /* We're picking up this, clear flags and let it continue */ 436 if (unlikely(ct_ftp_info->flags[dir] & NF_CT_FTP_SEQ_PICKUP)) { 437 ct_ftp_info->flags[dir] ^= NF_CT_FTP_SEQ_PICKUP; 438 goto skip_nl_seq; 439 } 440 441 /* Now if this ends in \n, update ftp info. */ 442 pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n", 443 ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)", 444 ct_ftp_info->seq_aft_nl[dir][0], 445 ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)", 446 ct_ftp_info->seq_aft_nl[dir][1]); 447 ret = NF_ACCEPT; 448 goto out_update_nl; 449 } 450 451 skip_nl_seq: 452 /* Initialize IP/IPv6 addr to expected address (it's not mentioned 453 in EPSV responses) */ 454 cmd.l3num = nf_ct_l3num(ct); 455 memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all, 456 sizeof(cmd.u3.all)); 457 458 for (i = 0; i < ARRAY_SIZE(search[dir]); i++) { 459 found = find_pattern(fb_ptr, datalen, 460 search[dir][i].pattern, 461 search[dir][i].plen, 462 search[dir][i].skip, 463 search[dir][i].term, 464 &matchoff, &matchlen, 465 &cmd, 466 search[dir][i].getnum); 467 if (found) break; 468 } 469 if (found == -1) { 470 /* We don't usually drop packets. After all, this is 471 connection tracking, not packet filtering. 472 However, it is necessary for accurate tracking in 473 this case. */ 474 nf_ct_helper_log(skb, ct, "partial matching of `%s'", 475 search[dir][i].pattern); 476 ret = NF_DROP; 477 goto out; 478 } else if (found == 0) { /* No match */ 479 ret = NF_ACCEPT; 480 goto out_update_nl; 481 } 482 483 pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n", 484 matchlen, fb_ptr + matchoff, 485 matchlen, ntohl(th->seq) + matchoff); 486 487 exp = nf_ct_expect_alloc(ct); 488 if (exp == NULL) { 489 nf_ct_helper_log(skb, ct, "cannot alloc expectation"); 490 ret = NF_DROP; 491 goto out; 492 } 493 494 /* We refer to the reverse direction ("!dir") tuples here, 495 * because we're expecting something in the other direction. 496 * Doesn't matter unless NAT is happening. */ 497 daddr = &ct->tuplehash[!dir].tuple.dst.u3; 498 499 /* Update the ftp info */ 500 if ((cmd.l3num == nf_ct_l3num(ct)) && 501 memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all, 502 sizeof(cmd.u3.all))) { 503 /* Enrico Scholz's passive FTP to partially RNAT'd ftp 504 server: it really wants us to connect to a 505 different IP address. Simply don't record it for 506 NAT. */ 507 if (cmd.l3num == PF_INET) { 508 pr_debug("conntrack_ftp: NOT RECORDING: %pI4 != %pI4\n", 509 &cmd.u3.ip, 510 &ct->tuplehash[dir].tuple.src.u3.ip); 511 } else { 512 pr_debug("conntrack_ftp: NOT RECORDING: %pI6 != %pI6\n", 513 cmd.u3.ip6, 514 ct->tuplehash[dir].tuple.src.u3.ip6); 515 } 516 517 /* Thanks to Cristiano Lincoln Mattos 518 <lincoln@cesar.org.br> for reporting this potential 519 problem (DMZ machines opening holes to internal 520 networks, or the packet filter itself). */ 521 if (!loose) { 522 ret = NF_ACCEPT; 523 goto out_put_expect; 524 } 525 daddr = &cmd.u3; 526 } 527 528 nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num, 529 &ct->tuplehash[!dir].tuple.src.u3, daddr, 530 IPPROTO_TCP, NULL, &cmd.u.tcp.port); 531 532 /* Now, NAT might want to mangle the packet, and register the 533 * (possibly changed) expectation itself. */ 534 nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook); 535 if (nf_nat_ftp && ct->status & IPS_NAT_MASK) 536 ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype, 537 protoff, matchoff, matchlen, exp); 538 else { 539 /* Can't expect this? Best to drop packet now. */ 540 if (nf_ct_expect_related(exp) != 0) { 541 nf_ct_helper_log(skb, ct, "cannot add expectation"); 542 ret = NF_DROP; 543 } else 544 ret = NF_ACCEPT; 545 } 546 547 out_put_expect: 548 nf_ct_expect_put(exp); 549 550 out_update_nl: 551 /* Now if this ends in \n, update ftp info. Seq may have been 552 * adjusted by NAT code. */ 553 if (ends_in_nl) 554 update_nl_seq(ct, seq, ct_ftp_info, dir, skb); 555 out: 556 spin_unlock_bh(&nf_ftp_lock); 557 return ret; 558 } 559 560 static int nf_ct_ftp_from_nlattr(struct nlattr *attr, struct nf_conn *ct) 561 { 562 struct nf_ct_ftp_master *ftp = nfct_help_data(ct); 563 564 /* This conntrack has been injected from user-space, always pick up 565 * sequence tracking. Otherwise, the first FTP command after the 566 * failover breaks. 567 */ 568 ftp->flags[IP_CT_DIR_ORIGINAL] |= NF_CT_FTP_SEQ_PICKUP; 569 ftp->flags[IP_CT_DIR_REPLY] |= NF_CT_FTP_SEQ_PICKUP; 570 return 0; 571 } 572 573 static struct nf_conntrack_helper ftp[MAX_PORTS][2] __read_mostly; 574 575 static const struct nf_conntrack_expect_policy ftp_exp_policy = { 576 .max_expected = 1, 577 .timeout = 5 * 60, 578 }; 579 580 /* don't make this __exit, since it's called from __init ! */ 581 static void nf_conntrack_ftp_fini(void) 582 { 583 int i, j; 584 for (i = 0; i < ports_c; i++) { 585 for (j = 0; j < 2; j++) { 586 if (ftp[i][j].me == NULL) 587 continue; 588 589 pr_debug("nf_ct_ftp: unregistering helper for pf: %d " 590 "port: %d\n", 591 ftp[i][j].tuple.src.l3num, ports[i]); 592 nf_conntrack_helper_unregister(&ftp[i][j]); 593 } 594 } 595 596 kfree(ftp_buffer); 597 } 598 599 static int __init nf_conntrack_ftp_init(void) 600 { 601 int i, j = -1, ret = 0; 602 603 ftp_buffer = kmalloc(65536, GFP_KERNEL); 604 if (!ftp_buffer) 605 return -ENOMEM; 606 607 if (ports_c == 0) 608 ports[ports_c++] = FTP_PORT; 609 610 /* FIXME should be configurable whether IPv4 and IPv6 FTP connections 611 are tracked or not - YK */ 612 for (i = 0; i < ports_c; i++) { 613 ftp[i][0].tuple.src.l3num = PF_INET; 614 ftp[i][1].tuple.src.l3num = PF_INET6; 615 for (j = 0; j < 2; j++) { 616 ftp[i][j].data_len = sizeof(struct nf_ct_ftp_master); 617 ftp[i][j].tuple.src.u.tcp.port = htons(ports[i]); 618 ftp[i][j].tuple.dst.protonum = IPPROTO_TCP; 619 ftp[i][j].expect_policy = &ftp_exp_policy; 620 ftp[i][j].me = THIS_MODULE; 621 ftp[i][j].help = help; 622 ftp[i][j].from_nlattr = nf_ct_ftp_from_nlattr; 623 if (ports[i] == FTP_PORT) 624 sprintf(ftp[i][j].name, "ftp"); 625 else 626 sprintf(ftp[i][j].name, "ftp-%d", ports[i]); 627 628 pr_debug("nf_ct_ftp: registering helper for pf: %d " 629 "port: %d\n", 630 ftp[i][j].tuple.src.l3num, ports[i]); 631 ret = nf_conntrack_helper_register(&ftp[i][j]); 632 if (ret) { 633 printk(KERN_ERR "nf_ct_ftp: failed to register" 634 " helper for pf: %d port: %d\n", 635 ftp[i][j].tuple.src.l3num, ports[i]); 636 nf_conntrack_ftp_fini(); 637 return ret; 638 } 639 } 640 } 641 642 return 0; 643 } 644 645 module_init(nf_conntrack_ftp_init); 646 module_exit(nf_conntrack_ftp_fini); 647