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