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
get_ipv6_addr(const char * src,size_t dlen,struct in6_addr * dst,u_int8_t term)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
try_number(const char * data,size_t dlen,u_int32_t array[],int array_size,char sep,char term)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 */
try_rfc959(const char * data,size_t dlen,struct nf_conntrack_man * cmd,char term,unsigned int * offset)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 */
try_rfc1123(const char * data,size_t dlen,struct nf_conntrack_man * cmd,char term,unsigned int * offset)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 */
get_port(const char * data,int start,size_t dlen,char delim,__be16 * port)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| */
try_eprt(const char * data,size_t dlen,struct nf_conntrack_man * cmd,char term,unsigned int * offset)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| */
try_epsv_response(const char * data,size_t dlen,struct nf_conntrack_man * cmd,char term,unsigned int * offset)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. */
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 *))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. */
find_nl_seq(u32 seq,const struct nf_ct_ftp_master * info,int dir)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. */
update_nl_seq(struct nf_conn * ct,u32 nl_seq,struct nf_ct_ftp_master * info,int dir,struct sk_buff * skb)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
help(struct sk_buff * skb,unsigned int protoff,struct nf_conn * ct,enum ip_conntrack_info ctinfo)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
nf_ct_ftp_from_nlattr(struct nlattr * attr,struct nf_conn * ct)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
nf_conntrack_ftp_fini(void)567 static void __exit nf_conntrack_ftp_fini(void)
568 {
569 nf_conntrack_helpers_unregister(ftp, ports_c * 2);
570 }
571
nf_conntrack_ftp_init(void)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