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