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