1 // SPDX-License-Identifier: GPL-2.0-only 2 /* FTP extension for connection tracking. */ 3 4 /* (C) 1999-2001 Paul `Rusty' Russell 5 * (C) 2002-2004 Netfilter Core Team <coreteam@netfilter.org> 6 * (C) 2003,2004 USAGI/WIDE Project <http://www.linux-ipv6.org> 7 * (C) 2006-2012 Patrick McHardy <kaber@trash.net> 8 */ 9 10 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 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 29 #define HELPER_NAME "ftp" 30 31 MODULE_LICENSE("GPL"); 32 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>"); 33 MODULE_DESCRIPTION("ftp connection tracking helper"); 34 MODULE_ALIAS("ip_conntrack_ftp"); 35 MODULE_ALIAS_NFCT_HELPER(HELPER_NAME); 36 37 /* This is slow, but it's simple. --RR */ 38 static char *ftp_buffer; 39 40 static DEFINE_SPINLOCK(nf_ftp_lock); 41 42 #define MAX_PORTS 8 43 static u_int16_t ports[MAX_PORTS]; 44 static unsigned int ports_c; 45 module_param_array(ports, ushort, &ports_c, 0400); 46 47 static bool loose; 48 module_param(loose, bool, 0600); 49 50 unsigned int (*nf_nat_ftp_hook)(struct sk_buff *skb, 51 enum ip_conntrack_info ctinfo, 52 enum nf_ct_ftp_type type, 53 unsigned int protoff, 54 unsigned int matchoff, 55 unsigned int matchlen, 56 struct nf_conntrack_expect *exp); 57 EXPORT_SYMBOL_GPL(nf_nat_ftp_hook); 58 59 static int try_rfc959(const char *, size_t, struct nf_conntrack_man *, 60 char, unsigned int *); 61 static int try_rfc1123(const char *, size_t, struct nf_conntrack_man *, 62 char, unsigned int *); 63 static int try_eprt(const char *, size_t, struct nf_conntrack_man *, 64 char, unsigned int *); 65 static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *, 66 char, unsigned int *); 67 68 static struct ftp_search { 69 const char *pattern; 70 size_t plen; 71 char skip; 72 char term; 73 enum nf_ct_ftp_type ftptype; 74 int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char, unsigned int *); 75 } search[IP_CT_DIR_MAX][2] = { 76 [IP_CT_DIR_ORIGINAL] = { 77 { 78 .pattern = "PORT", 79 .plen = sizeof("PORT") - 1, 80 .skip = ' ', 81 .term = '\r', 82 .ftptype = NF_CT_FTP_PORT, 83 .getnum = try_rfc959, 84 }, 85 { 86 .pattern = "EPRT", 87 .plen = sizeof("EPRT") - 1, 88 .skip = ' ', 89 .term = '\r', 90 .ftptype = NF_CT_FTP_EPRT, 91 .getnum = try_eprt, 92 }, 93 }, 94 [IP_CT_DIR_REPLY] = { 95 { 96 .pattern = "227 ", 97 .plen = sizeof("227 ") - 1, 98 .ftptype = NF_CT_FTP_PASV, 99 .getnum = try_rfc1123, 100 }, 101 { 102 .pattern = "229 ", 103 .plen = sizeof("229 ") - 1, 104 .skip = '(', 105 .term = ')', 106 .ftptype = NF_CT_FTP_EPSV, 107 .getnum = try_epsv_response, 108 }, 109 }, 110 }; 111 112 static int 113 get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term) 114 { 115 const char *end; 116 int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end); 117 if (ret > 0) 118 return (int)(end - src); 119 return 0; 120 } 121 122 static int try_number(const char *data, size_t dlen, u_int32_t array[], 123 int array_size, char sep, char term) 124 { 125 u_int32_t i, len; 126 127 memset(array, 0, sizeof(array[0])*array_size); 128 129 /* Keep data pointing at next char. */ 130 for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) { 131 if (*data >= '0' && *data <= '9') { 132 array[i] = array[i]*10 + *data - '0'; 133 } 134 else if (*data == sep) 135 i++; 136 else { 137 /* Unexpected character; true if it's the 138 terminator (or we don't care about one) 139 and we're finished. */ 140 if ((*data == term || !term) && i == array_size - 1) 141 return len; 142 143 pr_debug("Char %u (got %u nums) `%u' unexpected\n", 144 len, i, *data); 145 return 0; 146 } 147 } 148 pr_debug("Failed to fill %u numbers separated by %c\n", 149 array_size, sep); 150 return 0; 151 } 152 153 /* Returns 0, or length of numbers: 192,168,1,1,5,6 */ 154 static int try_rfc959(const char *data, size_t dlen, 155 struct nf_conntrack_man *cmd, char term, 156 unsigned int *offset) 157 { 158 int length; 159 u_int32_t array[6]; 160 161 length = try_number(data, dlen, array, 6, ',', term); 162 if (length == 0) 163 return 0; 164 165 cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16) | 166 (array[2] << 8) | array[3]); 167 cmd->u.tcp.port = htons((array[4] << 8) | array[5]); 168 return length; 169 } 170 171 /* 172 * From RFC 1123: 173 * The format of the 227 reply to a PASV command is not 174 * well standardized. In particular, an FTP client cannot 175 * assume that the parentheses shown on page 40 of RFC-959 176 * will be present (and in fact, Figure 3 on page 43 omits 177 * them). Therefore, a User-FTP program that interprets 178 * the PASV reply must scan the reply for the first digit 179 * of the host and port numbers. 180 */ 181 static int try_rfc1123(const char *data, size_t dlen, 182 struct nf_conntrack_man *cmd, char term, 183 unsigned int *offset) 184 { 185 int i; 186 for (i = 0; i < dlen; i++) 187 if (isdigit(data[i])) 188 break; 189 190 if (i == dlen) 191 return 0; 192 193 *offset += i; 194 195 return try_rfc959(data + i, dlen - i, cmd, 0, offset); 196 } 197 198 /* Grab port: number up to delimiter */ 199 static int get_port(const char *data, int start, size_t dlen, char delim, 200 __be16 *port) 201 { 202 u_int16_t tmp_port = 0; 203 int i; 204 205 for (i = start; i < dlen; i++) { 206 /* Finished? */ 207 if (data[i] == delim) { 208 if (tmp_port == 0) 209 break; 210 *port = htons(tmp_port); 211 pr_debug("get_port: return %d\n", tmp_port); 212 return i + 1; 213 } 214 else if (data[i] >= '0' && data[i] <= '9') 215 tmp_port = tmp_port*10 + data[i] - '0'; 216 else { /* Some other crap */ 217 pr_debug("get_port: invalid char.\n"); 218 break; 219 } 220 } 221 return 0; 222 } 223 224 /* Returns 0, or length of numbers: |1|132.235.1.2|6275| or |2|3ffe::1|6275| */ 225 static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd, 226 char term, unsigned int *offset) 227 { 228 char delim; 229 int length; 230 231 /* First character is delimiter, then "1" for IPv4 or "2" for IPv6, 232 then delimiter again. */ 233 if (dlen <= 3) { 234 pr_debug("EPRT: too short\n"); 235 return 0; 236 } 237 delim = data[0]; 238 if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) { 239 pr_debug("try_eprt: invalid delimiter.\n"); 240 return 0; 241 } 242 243 if ((cmd->l3num == PF_INET && data[1] != '1') || 244 (cmd->l3num == PF_INET6 && data[1] != '2')) { 245 pr_debug("EPRT: invalid protocol number.\n"); 246 return 0; 247 } 248 249 pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim); 250 251 if (data[1] == '1') { 252 u_int32_t array[4]; 253 254 /* Now we have IP address. */ 255 length = try_number(data + 3, dlen - 3, array, 4, '.', delim); 256 if (length != 0) 257 cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16) 258 | (array[2] << 8) | array[3]); 259 } else { 260 /* Now we have IPv6 address. */ 261 length = get_ipv6_addr(data + 3, dlen - 3, 262 (struct in6_addr *)cmd->u3.ip6, delim); 263 } 264 265 if (length == 0) 266 return 0; 267 pr_debug("EPRT: Got IP address!\n"); 268 /* Start offset includes initial "|1|", and trailing delimiter */ 269 return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port); 270 } 271 272 /* Returns 0, or length of numbers: |||6446| */ 273 static int try_epsv_response(const char *data, size_t dlen, 274 struct nf_conntrack_man *cmd, char term, 275 unsigned int *offset) 276 { 277 char delim; 278 279 /* Three delimiters. */ 280 if (dlen <= 3) return 0; 281 delim = data[0]; 282 if (isdigit(delim) || delim < 33 || delim > 126 || 283 data[1] != delim || data[2] != delim) 284 return 0; 285 286 return get_port(data, 3, dlen, delim, &cmd->u.tcp.port); 287 } 288 289 /* Return 1 for match, 0 for accept, -1 for partial. */ 290 static int find_pattern(const char *data, size_t dlen, 291 const char *pattern, size_t plen, 292 char skip, char term, 293 unsigned int *numoff, 294 unsigned int *numlen, 295 struct nf_conntrack_man *cmd, 296 int (*getnum)(const char *, size_t, 297 struct nf_conntrack_man *, char, 298 unsigned int *)) 299 { 300 size_t i = plen; 301 302 pr_debug("find_pattern `%s': dlen = %zu\n", pattern, dlen); 303 304 if (dlen <= plen) { 305 /* Short packet: try for partial? */ 306 if (strncasecmp(data, pattern, dlen) == 0) 307 return -1; 308 else return 0; 309 } 310 311 if (strncasecmp(data, pattern, plen) != 0) 312 return 0; 313 314 pr_debug("Pattern matches!\n"); 315 /* Now we've found the constant string, try to skip 316 to the 'skip' character */ 317 if (skip) { 318 for (i = plen; data[i] != skip; i++) 319 if (i == dlen - 1) return -1; 320 321 /* Skip over the last character */ 322 i++; 323 } 324 325 pr_debug("Skipped up to 0x%hhx delimiter!\n", skip); 326 327 *numoff = i; 328 *numlen = getnum(data + i, dlen - i, cmd, term, numoff); 329 if (!*numlen) 330 return -1; 331 332 pr_debug("Match succeeded!\n"); 333 return 1; 334 } 335 336 /* Look up to see if we're just after a \n. */ 337 static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir) 338 { 339 unsigned int i; 340 341 for (i = 0; i < info->seq_aft_nl_num[dir]; i++) 342 if (info->seq_aft_nl[dir][i] == seq) 343 return 1; 344 return 0; 345 } 346 347 /* We don't update if it's older than what we have. */ 348 static void update_nl_seq(struct nf_conn *ct, u32 nl_seq, 349 struct nf_ct_ftp_master *info, int dir, 350 struct sk_buff *skb) 351 { 352 unsigned int i, oldest; 353 354 /* Look for oldest: if we find exact match, we're done. */ 355 for (i = 0; i < info->seq_aft_nl_num[dir]; i++) { 356 if (info->seq_aft_nl[dir][i] == nl_seq) 357 return; 358 } 359 360 if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) { 361 info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq; 362 } else { 363 if (before(info->seq_aft_nl[dir][0], info->seq_aft_nl[dir][1])) 364 oldest = 0; 365 else 366 oldest = 1; 367 368 if (after(nl_seq, info->seq_aft_nl[dir][oldest])) 369 info->seq_aft_nl[dir][oldest] = nl_seq; 370 } 371 } 372 373 static int help(struct sk_buff *skb, 374 unsigned int protoff, 375 struct nf_conn *ct, 376 enum ip_conntrack_info ctinfo) 377 { 378 unsigned int dataoff, datalen; 379 const struct tcphdr *th; 380 struct tcphdr _tcph; 381 const char *fb_ptr; 382 int ret; 383 u32 seq; 384 int dir = CTINFO2DIR(ctinfo); 385 unsigned int matchlen, matchoff; 386 struct nf_ct_ftp_master *ct_ftp_info = nfct_help_data(ct); 387 struct nf_conntrack_expect *exp; 388 union nf_inet_addr *daddr; 389 struct nf_conntrack_man cmd = {}; 390 unsigned int i; 391 int found = 0, ends_in_nl; 392 typeof(nf_nat_ftp_hook) nf_nat_ftp; 393 394 /* Until there's been traffic both ways, don't look in packets. */ 395 if (ctinfo != IP_CT_ESTABLISHED && 396 ctinfo != IP_CT_ESTABLISHED_REPLY) { 397 pr_debug("ftp: Conntrackinfo = %u\n", ctinfo); 398 return NF_ACCEPT; 399 } 400 401 th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph); 402 if (th == NULL) 403 return NF_ACCEPT; 404 405 dataoff = protoff + th->doff * 4; 406 /* No data? */ 407 if (dataoff >= skb->len) { 408 pr_debug("ftp: dataoff(%u) >= skblen(%u)\n", dataoff, 409 skb->len); 410 return NF_ACCEPT; 411 } 412 datalen = skb->len - dataoff; 413 414 spin_lock_bh(&nf_ftp_lock); 415 fb_ptr = skb_header_pointer(skb, dataoff, datalen, ftp_buffer); 416 BUG_ON(fb_ptr == NULL); 417 418 ends_in_nl = (fb_ptr[datalen - 1] == '\n'); 419 seq = ntohl(th->seq) + datalen; 420 421 /* Look up to see if we're just after a \n. */ 422 if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) { 423 /* We're picking up this, clear flags and let it continue */ 424 if (unlikely(ct_ftp_info->flags[dir] & NF_CT_FTP_SEQ_PICKUP)) { 425 ct_ftp_info->flags[dir] ^= NF_CT_FTP_SEQ_PICKUP; 426 goto skip_nl_seq; 427 } 428 429 /* Now if this ends in \n, update ftp info. */ 430 pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n", 431 ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)", 432 ct_ftp_info->seq_aft_nl[dir][0], 433 ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)", 434 ct_ftp_info->seq_aft_nl[dir][1]); 435 ret = NF_ACCEPT; 436 goto out_update_nl; 437 } 438 439 skip_nl_seq: 440 /* Initialize IP/IPv6 addr to expected address (it's not mentioned 441 in EPSV responses) */ 442 cmd.l3num = nf_ct_l3num(ct); 443 memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all, 444 sizeof(cmd.u3.all)); 445 446 for (i = 0; i < ARRAY_SIZE(search[dir]); i++) { 447 found = find_pattern(fb_ptr, datalen, 448 search[dir][i].pattern, 449 search[dir][i].plen, 450 search[dir][i].skip, 451 search[dir][i].term, 452 &matchoff, &matchlen, 453 &cmd, 454 search[dir][i].getnum); 455 if (found) break; 456 } 457 if (found == -1) { 458 /* We don't usually drop packets. After all, this is 459 connection tracking, not packet filtering. 460 However, it is necessary for accurate tracking in 461 this case. */ 462 nf_ct_helper_log(skb, ct, "partial matching of `%s'", 463 search[dir][i].pattern); 464 ret = NF_DROP; 465 goto out; 466 } else if (found == 0) { /* No match */ 467 ret = NF_ACCEPT; 468 goto out_update_nl; 469 } 470 471 pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n", 472 matchlen, fb_ptr + matchoff, 473 matchlen, ntohl(th->seq) + matchoff); 474 475 exp = nf_ct_expect_alloc(ct); 476 if (exp == NULL) { 477 nf_ct_helper_log(skb, ct, "cannot alloc expectation"); 478 ret = NF_DROP; 479 goto out; 480 } 481 482 /* We refer to the reverse direction ("!dir") tuples here, 483 * because we're expecting something in the other direction. 484 * Doesn't matter unless NAT is happening. */ 485 daddr = &ct->tuplehash[!dir].tuple.dst.u3; 486 487 /* Update the ftp info */ 488 if ((cmd.l3num == nf_ct_l3num(ct)) && 489 memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all, 490 sizeof(cmd.u3.all))) { 491 /* Enrico Scholz's passive FTP to partially RNAT'd ftp 492 server: it really wants us to connect to a 493 different IP address. Simply don't record it for 494 NAT. */ 495 if (cmd.l3num == PF_INET) { 496 pr_debug("NOT RECORDING: %pI4 != %pI4\n", 497 &cmd.u3.ip, 498 &ct->tuplehash[dir].tuple.src.u3.ip); 499 } else { 500 pr_debug("NOT RECORDING: %pI6 != %pI6\n", 501 cmd.u3.ip6, 502 ct->tuplehash[dir].tuple.src.u3.ip6); 503 } 504 505 /* Thanks to Cristiano Lincoln Mattos 506 <lincoln@cesar.org.br> for reporting this potential 507 problem (DMZ machines opening holes to internal 508 networks, or the packet filter itself). */ 509 if (!loose) { 510 ret = NF_ACCEPT; 511 goto out_put_expect; 512 } 513 daddr = &cmd.u3; 514 } 515 516 nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num, 517 &ct->tuplehash[!dir].tuple.src.u3, daddr, 518 IPPROTO_TCP, NULL, &cmd.u.tcp.port); 519 520 /* Now, NAT might want to mangle the packet, and register the 521 * (possibly changed) expectation itself. */ 522 nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook); 523 if (nf_nat_ftp && ct->status & IPS_NAT_MASK) 524 ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype, 525 protoff, matchoff, matchlen, exp); 526 else { 527 /* Can't expect this? Best to drop packet now. */ 528 if (nf_ct_expect_related(exp, 0) != 0) { 529 nf_ct_helper_log(skb, ct, "cannot add expectation"); 530 ret = NF_DROP; 531 } else 532 ret = NF_ACCEPT; 533 } 534 535 out_put_expect: 536 nf_ct_expect_put(exp); 537 538 out_update_nl: 539 /* Now if this ends in \n, update ftp info. Seq may have been 540 * adjusted by NAT code. */ 541 if (ends_in_nl) 542 update_nl_seq(ct, seq, ct_ftp_info, dir, skb); 543 out: 544 spin_unlock_bh(&nf_ftp_lock); 545 return ret; 546 } 547 548 static int nf_ct_ftp_from_nlattr(struct nlattr *attr, struct nf_conn *ct) 549 { 550 struct nf_ct_ftp_master *ftp = nfct_help_data(ct); 551 552 /* This conntrack has been injected from user-space, always pick up 553 * sequence tracking. Otherwise, the first FTP command after the 554 * failover breaks. 555 */ 556 ftp->flags[IP_CT_DIR_ORIGINAL] |= NF_CT_FTP_SEQ_PICKUP; 557 ftp->flags[IP_CT_DIR_REPLY] |= NF_CT_FTP_SEQ_PICKUP; 558 return 0; 559 } 560 561 static struct nf_conntrack_helper ftp[MAX_PORTS * 2] __read_mostly; 562 563 static const struct nf_conntrack_expect_policy ftp_exp_policy = { 564 .max_expected = 1, 565 .timeout = 5 * 60, 566 }; 567 568 static void __exit nf_conntrack_ftp_fini(void) 569 { 570 nf_conntrack_helpers_unregister(ftp, ports_c * 2); 571 kfree(ftp_buffer); 572 } 573 574 static int __init nf_conntrack_ftp_init(void) 575 { 576 int i, ret = 0; 577 578 NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_ftp_master)); 579 580 ftp_buffer = kmalloc(65536, GFP_KERNEL); 581 if (!ftp_buffer) 582 return -ENOMEM; 583 584 if (ports_c == 0) 585 ports[ports_c++] = FTP_PORT; 586 587 /* FIXME should be configurable whether IPv4 and IPv6 FTP connections 588 are tracked or not - YK */ 589 for (i = 0; i < ports_c; i++) { 590 nf_ct_helper_init(&ftp[2 * i], AF_INET, IPPROTO_TCP, 591 HELPER_NAME, FTP_PORT, ports[i], ports[i], 592 &ftp_exp_policy, 0, help, 593 nf_ct_ftp_from_nlattr, THIS_MODULE); 594 nf_ct_helper_init(&ftp[2 * i + 1], AF_INET6, IPPROTO_TCP, 595 HELPER_NAME, FTP_PORT, ports[i], ports[i], 596 &ftp_exp_policy, 0, help, 597 nf_ct_ftp_from_nlattr, THIS_MODULE); 598 } 599 600 ret = nf_conntrack_helpers_register(ftp, ports_c * 2); 601 if (ret < 0) { 602 pr_err("failed to register helpers\n"); 603 kfree(ftp_buffer); 604 return ret; 605 } 606 607 return 0; 608 } 609 610 module_init(nf_conntrack_ftp_init); 611 module_exit(nf_conntrack_ftp_fini); 612