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