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 * (C) 2006-2012 Patrick McHardy <kaber@trash.net>
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License version 2 as
10 * published by the Free Software Foundation.
11 */
12
13 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
14
15 #include <linux/module.h>
16 #include <linux/moduleparam.h>
17 #include <linux/netfilter.h>
18 #include <linux/ip.h>
19 #include <linux/slab.h>
20 #include <linux/ipv6.h>
21 #include <linux/ctype.h>
22 #include <linux/inet.h>
23 #include <net/checksum.h>
24 #include <net/tcp.h>
25
26 #include <net/netfilter/nf_conntrack.h>
27 #include <net/netfilter/nf_conntrack_expect.h>
28 #include <net/netfilter/nf_conntrack_ecache.h>
29 #include <net/netfilter/nf_conntrack_helper.h>
30 #include <linux/netfilter/nf_conntrack_ftp.h>
31
32 MODULE_LICENSE("GPL");
33 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
34 MODULE_DESCRIPTION("ftp connection tracking helper");
35 MODULE_ALIAS("ip_conntrack_ftp");
36 MODULE_ALIAS_NFCT_HELPER("ftp");
37
38 /* This is slow, but it's simple. --RR */
39 static char *ftp_buffer;
40
41 static DEFINE_SPINLOCK(nf_ftp_lock);
42
43 #define MAX_PORTS 8
44 static u_int16_t ports[MAX_PORTS];
45 static unsigned int ports_c;
46 module_param_array(ports, ushort, &ports_c, 0400);
47
48 static bool loose;
49 module_param(loose, bool, 0600);
50
51 unsigned int (*nf_nat_ftp_hook)(struct sk_buff *skb,
52 enum ip_conntrack_info ctinfo,
53 enum nf_ct_ftp_type type,
54 unsigned int protoff,
55 unsigned int matchoff,
56 unsigned int matchlen,
57 struct nf_conntrack_expect *exp);
58 EXPORT_SYMBOL_GPL(nf_nat_ftp_hook);
59
60 static int try_rfc959(const char *, size_t, struct nf_conntrack_man *,
61 char, unsigned int *);
62 static int try_rfc1123(const char *, size_t, struct nf_conntrack_man *,
63 char, unsigned int *);
64 static int try_eprt(const char *, size_t, struct nf_conntrack_man *,
65 char, unsigned int *);
66 static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *,
67 char, unsigned int *);
68
69 static struct ftp_search {
70 const char *pattern;
71 size_t plen;
72 char skip;
73 char term;
74 enum nf_ct_ftp_type ftptype;
75 int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char, unsigned int *);
76 } search[IP_CT_DIR_MAX][2] = {
77 [IP_CT_DIR_ORIGINAL] = {
78 {
79 .pattern = "PORT",
80 .plen = sizeof("PORT") - 1,
81 .skip = ' ',
82 .term = '\r',
83 .ftptype = NF_CT_FTP_PORT,
84 .getnum = try_rfc959,
85 },
86 {
87 .pattern = "EPRT",
88 .plen = sizeof("EPRT") - 1,
89 .skip = ' ',
90 .term = '\r',
91 .ftptype = NF_CT_FTP_EPRT,
92 .getnum = try_eprt,
93 },
94 },
95 [IP_CT_DIR_REPLY] = {
96 {
97 .pattern = "227 ",
98 .plen = sizeof("227 ") - 1,
99 .ftptype = NF_CT_FTP_PASV,
100 .getnum = try_rfc1123,
101 },
102 {
103 .pattern = "229 ",
104 .plen = sizeof("229 ") - 1,
105 .skip = '(',
106 .term = ')',
107 .ftptype = NF_CT_FTP_EPSV,
108 .getnum = try_epsv_response,
109 },
110 },
111 };
112
113 static int
114 get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term)
115 {
116 const char *end;
117 int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end);
118 if (ret > 0)
119 return (int)(end - src);
120 return 0;
121 }
122
123 static int try_number(const char *data, size_t dlen, u_int32_t array[],
124 int array_size, char sep, char term)
125 {
126 u_int32_t i, len;
127
128 memset(array, 0, sizeof(array[0])*array_size);
129
130 /* Keep data pointing at next char. */
131 for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) {
132 if (*data >= '' && *data <= '9') {
133 array[i] = array[i]*10 + *data - '';
134 }
135 else if (*data == sep)
136 i++;
137 else {
138 /* Unexpected character; true if it's the
139 terminator (or we don't care about one)
140 and we're finished. */
141 if ((*data == term || !term) && i == array_size - 1)
142 return len;
143
144 pr_debug("Char %u (got %u nums) `%u' unexpected\n",
145 len, i, *data);
146 return 0;
147 }
148 }
149 pr_debug("Failed to fill %u numbers separated by %c\n",
150 array_size, sep);
151 return 0;
152 }
153
154 /* Returns 0, or length of numbers: 192,168,1,1,5,6 */
155 static int try_rfc959(const char *data, size_t dlen,
156 struct nf_conntrack_man *cmd, char term,
157 unsigned int *offset)
158 {
159 int length;
160 u_int32_t array[6];
161
162 length = try_number(data, dlen, array, 6, ',', term);
163 if (length == 0)
164 return 0;
165
166 cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16) |
167 (array[2] << 8) | array[3]);
168 cmd->u.tcp.port = htons((array[4] << 8) | array[5]);
169 return length;
170 }
171
172 /*
173 * From RFC 1123:
174 * The format of the 227 reply to a PASV command is not
175 * well standardized. In particular, an FTP client cannot
176 * assume that the parentheses shown on page 40 of RFC-959
177 * will be present (and in fact, Figure 3 on page 43 omits
178 * them). Therefore, a User-FTP program that interprets
179 * the PASV reply must scan the reply for the first digit
180 * of the host and port numbers.
181 */
182 static int try_rfc1123(const char *data, size_t dlen,
183 struct nf_conntrack_man *cmd, char term,
184 unsigned int *offset)
185 {
186 int i;
187 for (i = 0; i < dlen; i++)
188 if (isdigit(data[i]))
189 break;
190
191 if (i == dlen)
192 return 0;
193
194 *offset += i;
195
196 return try_rfc959(data + i, dlen - i, cmd, 0, offset);
197 }
198
199 /* Grab port: number up to delimiter */
200 static int get_port(const char *data, int start, size_t dlen, char delim,
201 __be16 *port)
202 {
203 u_int16_t tmp_port = 0;
204 int i;
205
206 for (i = start; i < dlen; i++) {
207 /* Finished? */
208 if (data[i] == delim) {
209 if (tmp_port == 0)
210 break;
211 *port = htons(tmp_port);
212 pr_debug("get_port: return %d\n", tmp_port);
213 return i + 1;
214 }
215 else if (data[i] >= '' && data[i] <= '9')
216 tmp_port = tmp_port*10 + data[i] - '';
217 else { /* Some other crap */
218 pr_debug("get_port: invalid char.\n");
219 break;
220 }
221 }
222 return 0;
223 }
224
225 /* Returns 0, or length of numbers: |1|132.235.1.2|6275| or |2|3ffe::1|6275| */
226 static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd,
227 char term, unsigned int *offset)
228 {
229 char delim;
230 int length;
231
232 /* First character is delimiter, then "1" for IPv4 or "2" for IPv6,
233 then delimiter again. */
234 if (dlen <= 3) {
235 pr_debug("EPRT: too short\n");
236 return 0;
237 }
238 delim = data[0];
239 if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) {
240 pr_debug("try_eprt: invalid delimiter.\n");
241 return 0;
242 }
243
244 if ((cmd->l3num == PF_INET && data[1] != '1') ||
245 (cmd->l3num == PF_INET6 && data[1] != '2')) {
246 pr_debug("EPRT: invalid protocol number.\n");
247 return 0;
248 }
249
250 pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim);
251
252 if (data[1] == '1') {
253 u_int32_t array[4];
254
255 /* Now we have IP address. */
256 length = try_number(data + 3, dlen - 3, array, 4, '.', delim);
257 if (length != 0)
258 cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16)
259 | (array[2] << 8) | array[3]);
260 } else {
261 /* Now we have IPv6 address. */
262 length = get_ipv6_addr(data + 3, dlen - 3,
263 (struct in6_addr *)cmd->u3.ip6, delim);
264 }
265
266 if (length == 0)
267 return 0;
268 pr_debug("EPRT: Got IP address!\n");
269 /* Start offset includes initial "|1|", and trailing delimiter */
270 return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port);
271 }
272
273 /* Returns 0, or length of numbers: |||6446| */
274 static int try_epsv_response(const char *data, size_t dlen,
275 struct nf_conntrack_man *cmd, char term,
276 unsigned int *offset)
277 {
278 char delim;
279
280 /* Three delimiters. */
281 if (dlen <= 3) return 0;
282 delim = data[0];
283 if (isdigit(delim) || delim < 33 || delim > 126 ||
284 data[1] != delim || data[2] != delim)
285 return 0;
286
287 return get_port(data, 3, dlen, delim, &cmd->u.tcp.port);
288 }
289
290 /* Return 1 for match, 0 for accept, -1 for partial. */
291 static int find_pattern(const char *data, size_t dlen,
292 const char *pattern, size_t plen,
293 char skip, char term,
294 unsigned int *numoff,
295 unsigned int *numlen,
296 struct nf_conntrack_man *cmd,
297 int (*getnum)(const char *, size_t,
298 struct nf_conntrack_man *, char,
299 unsigned int *))
300 {
301 size_t i = plen;
302
303 pr_debug("find_pattern `%s': dlen = %zu\n", pattern, dlen);
304
305 if (dlen <= plen) {
306 /* Short packet: try for partial? */
307 if (strncasecmp(data, pattern, dlen) == 0)
308 return -1;
309 else return 0;
310 }
311
312 if (strncasecmp(data, pattern, plen) != 0)
313 return 0;
314
315 pr_debug("Pattern matches!\n");
316 /* Now we've found the constant string, try to skip
317 to the 'skip' character */
318 if (skip) {
319 for (i = plen; data[i] != skip; i++)
320 if (i == dlen - 1) return -1;
321
322 /* Skip over the last character */
323 i++;
324 }
325
326 pr_debug("Skipped up to `%c'!\n", skip);
327
328 *numoff = i;
329 *numlen = getnum(data + i, dlen - i, cmd, term, numoff);
330 if (!*numlen)
331 return -1;
332
333 pr_debug("Match succeeded!\n");
334 return 1;
335 }
336
337 /* Look up to see if we're just after a \n. */
338 static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir)
339 {
340 unsigned int i;
341
342 for (i = 0; i < info->seq_aft_nl_num[dir]; i++)
343 if (info->seq_aft_nl[dir][i] == seq)
344 return 1;
345 return 0;
346 }
347
348 /* We don't update if it's older than what we have. */
349 static void update_nl_seq(struct nf_conn *ct, u32 nl_seq,
350 struct nf_ct_ftp_master *info, int dir,
351 struct sk_buff *skb)
352 {
353 unsigned int i, oldest;
354
355 /* Look for oldest: if we find exact match, we're done. */
356 for (i = 0; i < info->seq_aft_nl_num[dir]; i++) {
357 if (info->seq_aft_nl[dir][i] == nl_seq)
358 return;
359 }
360
361 if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) {
362 info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq;
363 } else {
364 if (before(info->seq_aft_nl[dir][0], info->seq_aft_nl[dir][1]))
365 oldest = 0;
366 else
367 oldest = 1;
368
369 if (after(nl_seq, info->seq_aft_nl[dir][oldest]))
370 info->seq_aft_nl[dir][oldest] = nl_seq;
371 }
372 }
373
374 static int help(struct sk_buff *skb,
375 unsigned int protoff,
376 struct nf_conn *ct,
377 enum ip_conntrack_info ctinfo)
378 {
379 unsigned int dataoff, datalen;
380 const struct tcphdr *th;
381 struct tcphdr _tcph;
382 const char *fb_ptr;
383 int ret;
384 u32 seq;
385 int dir = CTINFO2DIR(ctinfo);
386 unsigned int uninitialized_var(matchlen), uninitialized_var(matchoff);
387 struct nf_ct_ftp_master *ct_ftp_info = nfct_help_data(ct);
388 struct nf_conntrack_expect *exp;
389 union nf_inet_addr *daddr;
390 struct nf_conntrack_man cmd = {};
391 unsigned int i;
392 int found = 0, ends_in_nl;
393 typeof(nf_nat_ftp_hook) nf_nat_ftp;
394
395 /* Until there's been traffic both ways, don't look in packets. */
396 if (ctinfo != IP_CT_ESTABLISHED &&
397 ctinfo != IP_CT_ESTABLISHED_REPLY) {
398 pr_debug("ftp: Conntrackinfo = %u\n", ctinfo);
399 return NF_ACCEPT;
400 }
401
402 th = skb_header_pointer(skb, protoff, sizeof(_tcph), &_tcph);
403 if (th == NULL)
404 return NF_ACCEPT;
405
406 dataoff = protoff + th->doff * 4;
407 /* No data? */
408 if (dataoff >= skb->len) {
409 pr_debug("ftp: dataoff(%u) >= skblen(%u)\n", dataoff,
410 skb->len);
411 return NF_ACCEPT;
412 }
413 datalen = skb->len - dataoff;
414
415 spin_lock_bh(&nf_ftp_lock);
416 fb_ptr = skb_header_pointer(skb, dataoff, datalen, ftp_buffer);
417 BUG_ON(fb_ptr == NULL);
418
419 ends_in_nl = (fb_ptr[datalen - 1] == '\n');
420 seq = ntohl(th->seq) + datalen;
421
422 /* Look up to see if we're just after a \n. */
423 if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) {
424 /* We're picking up this, clear flags and let it continue */
425 if (unlikely(ct_ftp_info->flags[dir] & NF_CT_FTP_SEQ_PICKUP)) {
426 ct_ftp_info->flags[dir] ^= NF_CT_FTP_SEQ_PICKUP;
427 goto skip_nl_seq;
428 }
429
430 /* Now if this ends in \n, update ftp info. */
431 pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n",
432 ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)",
433 ct_ftp_info->seq_aft_nl[dir][0],
434 ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)",
435 ct_ftp_info->seq_aft_nl[dir][1]);
436 ret = NF_ACCEPT;
437 goto out_update_nl;
438 }
439
440 skip_nl_seq:
441 /* Initialize IP/IPv6 addr to expected address (it's not mentioned
442 in EPSV responses) */
443 cmd.l3num = nf_ct_l3num(ct);
444 memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
445 sizeof(cmd.u3.all));
446
447 for (i = 0; i < ARRAY_SIZE(search[dir]); i++) {
448 found = find_pattern(fb_ptr, datalen,
449 search[dir][i].pattern,
450 search[dir][i].plen,
451 search[dir][i].skip,
452 search[dir][i].term,
453 &matchoff, &matchlen,
454 &cmd,
455 search[dir][i].getnum);
456 if (found) break;
457 }
458 if (found == -1) {
459 /* We don't usually drop packets. After all, this is
460 connection tracking, not packet filtering.
461 However, it is necessary for accurate tracking in
462 this case. */
463 nf_ct_helper_log(skb, ct, "partial matching of `%s'",
464 search[dir][i].pattern);
465 ret = NF_DROP;
466 goto out;
467 } else if (found == 0) { /* No match */
468 ret = NF_ACCEPT;
469 goto out_update_nl;
470 }
471
472 pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n",
473 matchlen, fb_ptr + matchoff,
474 matchlen, ntohl(th->seq) + matchoff);
475
476 exp = nf_ct_expect_alloc(ct);
477 if (exp == NULL) {
478 nf_ct_helper_log(skb, ct, "cannot alloc expectation");
479 ret = NF_DROP;
480 goto out;
481 }
482
483 /* We refer to the reverse direction ("!dir") tuples here,
484 * because we're expecting something in the other direction.
485 * Doesn't matter unless NAT is happening. */
486 daddr = &ct->tuplehash[!dir].tuple.dst.u3;
487
488 /* Update the ftp info */
489 if ((cmd.l3num == nf_ct_l3num(ct)) &&
490 memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
491 sizeof(cmd.u3.all))) {
492 /* Enrico Scholz's passive FTP to partially RNAT'd ftp
493 server: it really wants us to connect to a
494 different IP address. Simply don't record it for
495 NAT. */
496 if (cmd.l3num == PF_INET) {
497 pr_debug("NOT RECORDING: %pI4 != %pI4\n",
498 &cmd.u3.ip,
499 &ct->tuplehash[dir].tuple.src.u3.ip);
500 } else {
501 pr_debug("NOT RECORDING: %pI6 != %pI6\n",
502 cmd.u3.ip6,
503 ct->tuplehash[dir].tuple.src.u3.ip6);
504 }
505
506 /* Thanks to Cristiano Lincoln Mattos
507 <lincoln@cesar.org.br> for reporting this potential
508 problem (DMZ machines opening holes to internal
509 networks, or the packet filter itself). */
510 if (!loose) {
511 ret = NF_ACCEPT;
512 goto out_put_expect;
513 }
514 daddr = &cmd.u3;
515 }
516
517 nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num,
518 &ct->tuplehash[!dir].tuple.src.u3, daddr,
519 IPPROTO_TCP, NULL, &cmd.u.tcp.port);
520
521 /* Now, NAT might want to mangle the packet, and register the
522 * (possibly changed) expectation itself. */
523 nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook);
524 if (nf_nat_ftp && ct->status & IPS_NAT_MASK)
525 ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype,
526 protoff, matchoff, matchlen, exp);
527 else {
528 /* Can't expect this? Best to drop packet now. */
529 if (nf_ct_expect_related(exp) != 0) {
530 nf_ct_helper_log(skb, ct, "cannot add expectation");
531 ret = NF_DROP;
532 } else
533 ret = NF_ACCEPT;
534 }
535
536 out_put_expect:
537 nf_ct_expect_put(exp);
538
539 out_update_nl:
540 /* Now if this ends in \n, update ftp info. Seq may have been
541 * adjusted by NAT code. */
542 if (ends_in_nl)
543 update_nl_seq(ct, seq, ct_ftp_info, dir, skb);
544 out:
545 spin_unlock_bh(&nf_ftp_lock);
546 return ret;
547 }
548
549 static int nf_ct_ftp_from_nlattr(struct nlattr *attr, struct nf_conn *ct)
550 {
551 struct nf_ct_ftp_master *ftp = nfct_help_data(ct);
552
553 /* This conntrack has been injected from user-space, always pick up
554 * sequence tracking. Otherwise, the first FTP command after the
555 * failover breaks.
556 */
557 ftp->flags[IP_CT_DIR_ORIGINAL] |= NF_CT_FTP_SEQ_PICKUP;
558 ftp->flags[IP_CT_DIR_REPLY] |= NF_CT_FTP_SEQ_PICKUP;
559 return 0;
560 }
561
562 static struct nf_conntrack_helper ftp[MAX_PORTS * 2] __read_mostly;
563
564 static const struct nf_conntrack_expect_policy ftp_exp_policy = {
565 .max_expected = 1,
566 .timeout = 5 * 60,
567 };
568
569 /* don't make this __exit, since it's called from __init ! */
570 static void nf_conntrack_ftp_fini(void)
571 {
572 nf_conntrack_helpers_unregister(ftp, ports_c * 2);
573 kfree(ftp_buffer);
574 }
575
576 static int __init nf_conntrack_ftp_init(void)
577 {
578 int i, ret = 0;
579
580 NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_ftp_master));
581
582 ftp_buffer = kmalloc(65536, GFP_KERNEL);
583 if (!ftp_buffer)
584 return -ENOMEM;
585
586 if (ports_c == 0)
587 ports[ports_c++] = FTP_PORT;
588
589 /* FIXME should be configurable whether IPv4 and IPv6 FTP connections
590 are tracked or not - YK */
591 for (i = 0; i < ports_c; i++) {
592 nf_ct_helper_init(&ftp[2 * i], AF_INET, IPPROTO_TCP, "ftp",
593 FTP_PORT, ports[i], ports[i], &ftp_exp_policy,
594 0, help, nf_ct_ftp_from_nlattr, THIS_MODULE);
595 nf_ct_helper_init(&ftp[2 * i + 1], AF_INET6, IPPROTO_TCP, "ftp",
596 FTP_PORT, ports[i], ports[i], &ftp_exp_policy,
597 0, help, 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
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