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