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 29MODULE_LICENSE("GPL"); 30MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>"); 31MODULE_DESCRIPTION("ftp connection tracking helper"); 32MODULE_ALIAS("ip_conntrack_ftp"); 33MODULE_ALIAS_NFCT_HELPER("ftp"); 34 35/* This is slow, but it's simple. --RR */ 36static char *ftp_buffer; 37 38static DEFINE_SPINLOCK(nf_ftp_lock); 39 40#define MAX_PORTS 8 41static u_int16_t ports[MAX_PORTS]; 42static unsigned int ports_c; 43module_param_array(ports, ushort, &ports_c, 0400); 44 45static int loose; 46module_param(loose, bool, 0600); 47 48unsigned 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 matchoff, 52 unsigned int matchlen, 53 struct nf_conntrack_expect *exp); 54EXPORT_SYMBOL_GPL(nf_nat_ftp_hook); 55 56static int try_rfc959(const char *, size_t, struct nf_conntrack_man *, char); 57static int try_eprt(const char *, size_t, struct nf_conntrack_man *, char); 58static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *, 59 char); 60 61static struct ftp_search { 62 const char *pattern; 63 size_t plen; 64 char skip; 65 char term; 66 enum nf_ct_ftp_type ftptype; 67 int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char); 68} search[IP_CT_DIR_MAX][2] = { 69 [IP_CT_DIR_ORIGINAL] = { 70 { 71 .pattern = "PORT", 72 .plen = sizeof("PORT") - 1, 73 .skip = ' ', 74 .term = '\r', 75 .ftptype = NF_CT_FTP_PORT, 76 .getnum = try_rfc959, 77 }, 78 { 79 .pattern = "EPRT", 80 .plen = sizeof("EPRT") - 1, 81 .skip = ' ', 82 .term = '\r', 83 .ftptype = NF_CT_FTP_EPRT, 84 .getnum = try_eprt, 85 }, 86 }, 87 [IP_CT_DIR_REPLY] = { 88 { 89 .pattern = "227 ", 90 .plen = sizeof("227 ") - 1, 91 .skip = '(', 92 .term = ')', 93 .ftptype = NF_CT_FTP_PASV, 94 .getnum = try_rfc959, 95 }, 96 { 97 .pattern = "229 ", 98 .plen = sizeof("229 ") - 1, 99 .skip = '(', 100 .term = ')', 101 .ftptype = NF_CT_FTP_EPSV, 102 .getnum = try_epsv_response, 103 }, 104 }, 105}; 106 107static int 108get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term) 109{ 110 const char *end; 111 int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end); 112 if (ret > 0) 113 return (int)(end - src); 114 return 0; 115} 116 117static int try_number(const char *data, size_t dlen, u_int32_t array[], 118 int array_size, char sep, char term) 119{ 120 u_int32_t i, len; 121 122 memset(array, 0, sizeof(array[0])*array_size); 123 124 /* Keep data pointing at next char. */ 125 for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) { 126 if (*data >= '0' && *data <= '9') { 127 array[i] = array[i]*10 + *data - '0'; 128 } 129 else if (*data == sep) 130 i++; 131 else { 132 /* Unexpected character; true if it's the 133 terminator and we're finished. */ 134 if (*data == term && i == array_size - 1) 135 return len; 136 137 pr_debug("Char %u (got %u nums) `%u' unexpected\n", 138 len, i, *data); 139 return 0; 140 } 141 } 142 pr_debug("Failed to fill %u numbers separated by %c\n", 143 array_size, sep); 144 return 0; 145} 146 147/* Returns 0, or length of numbers: 192,168,1,1,5,6 */ 148static int try_rfc959(const char *data, size_t dlen, 149 struct nf_conntrack_man *cmd, char term) 150{ 151 int length; 152 u_int32_t array[6]; 153 154 length = try_number(data, dlen, array, 6, ',', term); 155 if (length == 0) 156 return 0; 157 158 cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16) | 159 (array[2] << 8) | array[3]); 160 cmd->u.tcp.port = htons((array[4] << 8) | array[5]); 161 return length; 162} 163 164/* Grab port: number up to delimiter */ 165static int get_port(const char *data, int start, size_t dlen, char delim, 166 __be16 *port) 167{ 168 u_int16_t tmp_port = 0; 169 int i; 170 171 for (i = start; i < dlen; i++) { 172 /* Finished? */ 173 if (data[i] == delim) { 174 if (tmp_port == 0) 175 break; 176 *port = htons(tmp_port); 177 pr_debug("get_port: return %d\n", tmp_port); 178 return i + 1; 179 } 180 else if (data[i] >= '0' && data[i] <= '9') 181 tmp_port = tmp_port*10 + data[i] - '0'; 182 else { /* Some other crap */ 183 pr_debug("get_port: invalid char.\n"); 184 break; 185 } 186 } 187 return 0; 188} 189 190/* Returns 0, or length of numbers: |1|132.235.1.2|6275| or |2|3ffe::1|6275| */ 191static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd, 192 char term) 193{ 194 char delim; 195 int length; 196 197 /* First character is delimiter, then "1" for IPv4 or "2" for IPv6, 198 then delimiter again. */ 199 if (dlen <= 3) { 200 pr_debug("EPRT: too short\n"); 201 return 0; 202 } 203 delim = data[0]; 204 if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) { 205 pr_debug("try_eprt: invalid delimitter.\n"); 206 return 0; 207 } 208 209 if ((cmd->l3num == PF_INET && data[1] != '1') || 210 (cmd->l3num == PF_INET6 && data[1] != '2')) { 211 pr_debug("EPRT: invalid protocol number.\n"); 212 return 0; 213 } 214 215 pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim); 216 217 if (data[1] == '1') { 218 u_int32_t array[4]; 219 220 /* Now we have IP address. */ 221 length = try_number(data + 3, dlen - 3, array, 4, '.', delim); 222 if (length != 0) 223 cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16) 224 | (array[2] << 8) | array[3]); 225 } else { 226 /* Now we have IPv6 address. */ 227 length = get_ipv6_addr(data + 3, dlen - 3, 228 (struct in6_addr *)cmd->u3.ip6, delim); 229 } 230 231 if (length == 0) 232 return 0; 233 pr_debug("EPRT: Got IP address!\n"); 234 /* Start offset includes initial "|1|", and trailing delimiter */ 235 return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port); 236} 237 238/* Returns 0, or length of numbers: |||6446| */ 239static int try_epsv_response(const char *data, size_t dlen, 240 struct nf_conntrack_man *cmd, char term) 241{ 242 char delim; 243 244 /* Three delimiters. */ 245 if (dlen <= 3) return 0; 246 delim = data[0]; 247 if (isdigit(delim) || delim < 33 || delim > 126 || 248 data[1] != delim || data[2] != delim) 249 return 0; 250 251 return get_port(data, 3, dlen, delim, &cmd->u.tcp.port); 252} 253 254/* Return 1 for match, 0 for accept, -1 for partial. */ 255static int find_pattern(const char *data, size_t dlen, 256 const char *pattern, size_t plen, 257 char skip, char term, 258 unsigned int *numoff, 259 unsigned int *numlen, 260 struct nf_conntrack_man *cmd, 261 int (*getnum)(const char *, size_t, 262 struct nf_conntrack_man *, char)) 263{ 264 size_t i; 265 266 pr_debug("find_pattern `%s': dlen = %Zu\n", pattern, dlen); 267 if (dlen == 0) 268 return 0; 269 270 if (dlen <= plen) { 271 /* Short packet: try for partial? */ 272 if (strnicmp(data, pattern, dlen) == 0) 273 return -1; 274 else return 0; 275 } 276 277 if (strnicmp(data, pattern, plen) != 0) { 278 return 0; 279 } 280 281 pr_debug("Pattern matches!\n"); 282 /* Now we've found the constant string, try to skip 283 to the 'skip' character */ 284 for (i = plen; data[i] != skip; i++) 285 if (i == dlen - 1) return -1; 286 287 /* Skip over the last character */ 288 i++; 289 290 pr_debug("Skipped up to `%c'!\n", skip); 291 292 *numoff = i; 293 *numlen = getnum(data + i, dlen - i, cmd, term); 294 if (!*numlen) 295 return -1; 296 297 pr_debug("Match succeeded!\n"); 298 return 1; 299} 300 301/* Look up to see if we're just after a \n. */ 302static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir) 303{ 304 unsigned int i; 305 306 for (i = 0; i < info->seq_aft_nl_num[dir]; i++) 307 if (info->seq_aft_nl[dir][i] == seq) 308 return 1; 309 return 0; 310} 311 312/* We don't update if it's older than what we have. */ 313static void update_nl_seq(struct nf_conn *ct, u32 nl_seq, 314 struct nf_ct_ftp_master *info, int dir, 315 struct sk_buff *skb) 316{ 317 unsigned int i, oldest; 318 319 /* Look for oldest: if we find exact match, we're done. */ 320 for (i = 0; i < info->seq_aft_nl_num[dir]; i++) { 321 if (info->seq_aft_nl[dir][i] == nl_seq) 322 return; 323 } 324 325 if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) { 326 info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq; 327 } else { 328 if (before(info->seq_aft_nl[dir][0], info->seq_aft_nl[dir][1])) 329 oldest = 0; 330 else 331 oldest = 1; 332 333 if (after(nl_seq, info->seq_aft_nl[dir][oldest])) 334 info->seq_aft_nl[dir][oldest] = nl_seq; 335 } 336} 337 338static int help(struct sk_buff *skb, 339 unsigned int protoff, 340 struct nf_conn *ct, 341 enum ip_conntrack_info ctinfo) 342{ 343 unsigned int dataoff, datalen; 344 const struct tcphdr *th; 345 struct tcphdr _tcph; 346 const char *fb_ptr; 347 int ret; 348 u32 seq; 349 int dir = CTINFO2DIR(ctinfo); 350 unsigned int uninitialized_var(matchlen), uninitialized_var(matchoff); 351 struct nf_ct_ftp_master *ct_ftp_info = &nfct_help(ct)->help.ct_ftp_info; 352 struct nf_conntrack_expect *exp; 353 union nf_inet_addr *daddr; 354 struct nf_conntrack_man cmd = {}; 355 unsigned int i; 356 int found = 0, ends_in_nl; 357 typeof(nf_nat_ftp_hook) nf_nat_ftp; 358 359 /* Until there's been traffic both ways, don't look in packets. */ 360 if (ctinfo != IP_CT_ESTABLISHED && 361 ctinfo != IP_CT_ESTABLISHED + IP_CT_IS_REPLY) { 362 pr_debug("ftp: Conntrackinfo = %u\n", ctinfo); 363 return NF_ACCEPT; 364 } 365 366 th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph); 367 if (th == NULL) 368 return NF_ACCEPT; 369 370 dataoff = protoff + th->doff * 4; 371 /* No data? */ 372 if (dataoff >= skb->len) { 373 pr_debug("ftp: dataoff(%u) >= skblen(%u)\n", dataoff, 374 skb->len); 375 return NF_ACCEPT; 376 } 377 datalen = skb->len - dataoff; 378 379 spin_lock_bh(&nf_ftp_lock); 380 fb_ptr = skb_header_pointer(skb, dataoff, datalen, ftp_buffer); 381 BUG_ON(fb_ptr == NULL); 382 383 ends_in_nl = (fb_ptr[datalen - 1] == '\n'); 384 seq = ntohl(th->seq) + datalen; 385 386 /* Look up to see if we're just after a \n. */ 387 if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) { 388 /* Now if this ends in \n, update ftp info. */ 389 pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n", 390 ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)", 391 ct_ftp_info->seq_aft_nl[dir][0], 392 ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)", 393 ct_ftp_info->seq_aft_nl[dir][1]); 394 ret = NF_ACCEPT; 395 goto out_update_nl; 396 } 397 398 /* Initialize IP/IPv6 addr to expected address (it's not mentioned 399 in EPSV responses) */ 400 cmd.l3num = nf_ct_l3num(ct); 401 memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all, 402 sizeof(cmd.u3.all)); 403 404 for (i = 0; i < ARRAY_SIZE(search[dir]); i++) { 405 found = find_pattern(fb_ptr, datalen, 406 search[dir][i].pattern, 407 search[dir][i].plen, 408 search[dir][i].skip, 409 search[dir][i].term, 410 &matchoff, &matchlen, 411 &cmd, 412 search[dir][i].getnum); 413 if (found) break; 414 } 415 if (found == -1) { 416 /* We don't usually drop packets. After all, this is 417 connection tracking, not packet filtering. 418 However, it is necessary for accurate tracking in 419 this case. */ 420 pr_debug("conntrack_ftp: partial %s %u+%u\n", 421 search[dir][i].pattern, ntohl(th->seq), datalen); 422 ret = NF_DROP; 423 goto out; 424 } else if (found == 0) { /* No match */ 425 ret = NF_ACCEPT; 426 goto out_update_nl; 427 } 428 429 pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n", 430 matchlen, fb_ptr + matchoff, 431 matchlen, ntohl(th->seq) + matchoff); 432 433 exp = nf_ct_expect_alloc(ct); 434 if (exp == NULL) { 435 ret = NF_DROP; 436 goto out; 437 } 438 439 /* We refer to the reverse direction ("!dir") tuples here, 440 * because we're expecting something in the other direction. 441 * Doesn't matter unless NAT is happening. */ 442 daddr = &ct->tuplehash[!dir].tuple.dst.u3; 443 444 /* Update the ftp info */ 445 if ((cmd.l3num == nf_ct_l3num(ct)) && 446 memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all, 447 sizeof(cmd.u3.all))) { 448 /* Enrico Scholz's passive FTP to partially RNAT'd ftp 449 server: it really wants us to connect to a 450 different IP address. Simply don't record it for 451 NAT. */ 452 if (cmd.l3num == PF_INET) { 453 pr_debug("conntrack_ftp: NOT RECORDING: %pI4 != %pI4\n", 454 &cmd.u3.ip, 455 &ct->tuplehash[dir].tuple.src.u3.ip); 456 } else { 457 pr_debug("conntrack_ftp: NOT RECORDING: %pI6 != %pI6\n", 458 cmd.u3.ip6, 459 ct->tuplehash[dir].tuple.src.u3.ip6); 460 } 461 462 /* Thanks to Cristiano Lincoln Mattos 463 <lincoln@cesar.org.br> for reporting this potential 464 problem (DMZ machines opening holes to internal 465 networks, or the packet filter itself). */ 466 if (!loose) { 467 ret = NF_ACCEPT; 468 goto out_put_expect; 469 } 470 daddr = &cmd.u3; 471 } 472 473 nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num, 474 &ct->tuplehash[!dir].tuple.src.u3, daddr, 475 IPPROTO_TCP, NULL, &cmd.u.tcp.port); 476 477 /* Now, NAT might want to mangle the packet, and register the 478 * (possibly changed) expectation itself. */ 479 nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook); 480 if (nf_nat_ftp && ct->status & IPS_NAT_MASK) 481 ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype, 482 matchoff, matchlen, exp); 483 else { 484 /* Can't expect this? Best to drop packet now. */ 485 if (nf_ct_expect_related(exp) != 0) 486 ret = NF_DROP; 487 else 488 ret = NF_ACCEPT; 489 } 490 491out_put_expect: 492 nf_ct_expect_put(exp); 493 494out_update_nl: 495 /* Now if this ends in \n, update ftp info. Seq may have been 496 * adjusted by NAT code. */ 497 if (ends_in_nl) 498 update_nl_seq(ct, seq, ct_ftp_info, dir, skb); 499 out: 500 spin_unlock_bh(&nf_ftp_lock); 501 return ret; 502} 503 504static struct nf_conntrack_helper ftp[MAX_PORTS][2] __read_mostly; 505static char ftp_names[MAX_PORTS][2][sizeof("ftp-65535")] __read_mostly; 506 507static const struct nf_conntrack_expect_policy ftp_exp_policy = { 508 .max_expected = 1, 509 .timeout = 5 * 60, 510}; 511 512/* don't make this __exit, since it's called from __init ! */ 513static void nf_conntrack_ftp_fini(void) 514{ 515 int i, j; 516 for (i = 0; i < ports_c; i++) { 517 for (j = 0; j < 2; j++) { 518 if (ftp[i][j].me == NULL) 519 continue; 520 521 pr_debug("nf_ct_ftp: unregistering helper for pf: %d " 522 "port: %d\n", 523 ftp[i][j].tuple.src.l3num, ports[i]); 524 nf_conntrack_helper_unregister(&ftp[i][j]); 525 } 526 } 527 528 kfree(ftp_buffer); 529} 530 531static int __init nf_conntrack_ftp_init(void) 532{ 533 int i, j = -1, ret = 0; 534 char *tmpname; 535 536 ftp_buffer = kmalloc(65536, GFP_KERNEL); 537 if (!ftp_buffer) 538 return -ENOMEM; 539 540 if (ports_c == 0) 541 ports[ports_c++] = FTP_PORT; 542 543 for (i = 0; i < ports_c; i++) { 544 ftp[i][0].tuple.src.l3num = PF_INET; 545 ftp[i][1].tuple.src.l3num = PF_INET6; 546 for (j = 0; j < 2; j++) { 547 ftp[i][j].tuple.src.u.tcp.port = htons(ports[i]); 548 ftp[i][j].tuple.dst.protonum = IPPROTO_TCP; 549 ftp[i][j].expect_policy = &ftp_exp_policy; 550 ftp[i][j].me = THIS_MODULE; 551 ftp[i][j].help = help; 552 tmpname = &ftp_names[i][j][0]; 553 if (ports[i] == FTP_PORT) 554 sprintf(tmpname, "ftp"); 555 else 556 sprintf(tmpname, "ftp-%d", ports[i]); 557 ftp[i][j].name = tmpname; 558 559 pr_debug("nf_ct_ftp: registering helper for pf: %d " 560 "port: %d\n", 561 ftp[i][j].tuple.src.l3num, ports[i]); 562 ret = nf_conntrack_helper_register(&ftp[i][j]); 563 if (ret) { 564 printk(KERN_ERR "nf_ct_ftp: failed to register" 565 " helper for pf: %d port: %d\n", 566 ftp[i][j].tuple.src.l3num, ports[i]); 567 nf_conntrack_ftp_fini(); 568 return ret; 569 } 570 } 571 } 572 573 return 0; 574} 575 576module_init(nf_conntrack_ftp_init); 577module_exit(nf_conntrack_ftp_fini); 578