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/ipv6.h>
17 #include <linux/ctype.h>
18 #include <linux/inet.h>
19 #include <net/checksum.h>
20 #include <net/tcp.h>
21
22 #include <net/netfilter/nf_conntrack.h>
23 #include <net/netfilter/nf_conntrack_expect.h>
24 #include <net/netfilter/nf_conntrack_ecache.h>
25 #include <net/netfilter/nf_conntrack_helper.h>
26 #include <linux/netfilter/nf_conntrack_ftp.h>
27
28 MODULE_LICENSE("GPL");
29 MODULE_AUTHOR("Rusty Russell <rusty@rustcorp.com.au>");
30 MODULE_DESCRIPTION("ftp connection tracking helper");
31 MODULE_ALIAS("ip_conntrack_ftp");
32 MODULE_ALIAS_NFCT_HELPER("ftp");
33
34 /* This is slow, but it's simple. --RR */
35 static char *ftp_buffer;
36
37 static DEFINE_SPINLOCK(nf_ftp_lock);
38
39 #define MAX_PORTS 8
40 static u_int16_t ports[MAX_PORTS];
41 static unsigned int ports_c;
42 module_param_array(ports, ushort, &ports_c, 0400);
43
44 static int loose;
45 module_param(loose, bool, 0600);
46
47 unsigned int (*nf_nat_ftp_hook)(struct sk_buff *skb,
48 enum ip_conntrack_info ctinfo,
49 enum nf_ct_ftp_type type,
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 *, char);
56 static int try_eprt(const char *, size_t, struct nf_conntrack_man *, char);
57 static int try_epsv_response(const char *, size_t, struct nf_conntrack_man *,
58 char);
59
60 static struct ftp_search {
61 const char *pattern;
62 size_t plen;
63 char skip;
64 char term;
65 enum nf_ct_ftp_type ftptype;
66 int (*getnum)(const char *, size_t, struct nf_conntrack_man *, char);
67 } search[IP_CT_DIR_MAX][2] = {
68 [IP_CT_DIR_ORIGINAL] = {
69 {
70 .pattern = "PORT",
71 .plen = sizeof("PORT") - 1,
72 .skip = ' ',
73 .term = '\r',
74 .ftptype = NF_CT_FTP_PORT,
75 .getnum = try_rfc959,
76 },
77 {
78 .pattern = "EPRT",
79 .plen = sizeof("EPRT") - 1,
80 .skip = ' ',
81 .term = '\r',
82 .ftptype = NF_CT_FTP_EPRT,
83 .getnum = try_eprt,
84 },
85 },
86 [IP_CT_DIR_REPLY] = {
87 {
88 .pattern = "227 ",
89 .plen = sizeof("227 ") - 1,
90 .skip = '(',
91 .term = ')',
92 .ftptype = NF_CT_FTP_PASV,
93 .getnum = try_rfc959,
94 },
95 {
96 .pattern = "229 ",
97 .plen = sizeof("229 ") - 1,
98 .skip = '(',
99 .term = ')',
100 .ftptype = NF_CT_FTP_EPSV,
101 .getnum = try_epsv_response,
102 },
103 },
104 };
105
106 static int
get_ipv6_addr(const char * src,size_t dlen,struct in6_addr * dst,u_int8_t term)107 get_ipv6_addr(const char *src, size_t dlen, struct in6_addr *dst, u_int8_t term)
108 {
109 const char *end;
110 int ret = in6_pton(src, min_t(size_t, dlen, 0xffff), (u8 *)dst, term, &end);
111 if (ret > 0)
112 return (int)(end - src);
113 return 0;
114 }
115
try_number(const char * data,size_t dlen,u_int32_t array[],int array_size,char sep,char term)116 static int try_number(const char *data, size_t dlen, u_int32_t array[],
117 int array_size, char sep, char term)
118 {
119 u_int32_t i, len;
120
121 memset(array, 0, sizeof(array[0])*array_size);
122
123 /* Keep data pointing at next char. */
124 for (i = 0, len = 0; len < dlen && i < array_size; len++, data++) {
125 if (*data >= '0' && *data <= '9') {
126 array[i] = array[i]*10 + *data - '0';
127 }
128 else if (*data == sep)
129 i++;
130 else {
131 /* Unexpected character; true if it's the
132 terminator and we're finished. */
133 if (*data == term && i == array_size - 1)
134 return len;
135
136 pr_debug("Char %u (got %u nums) `%u' unexpected\n",
137 len, i, *data);
138 return 0;
139 }
140 }
141 pr_debug("Failed to fill %u numbers separated by %c\n",
142 array_size, sep);
143 return 0;
144 }
145
146 /* 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)147 static int try_rfc959(const char *data, size_t dlen,
148 struct nf_conntrack_man *cmd, char term)
149 {
150 int length;
151 u_int32_t array[6];
152
153 length = try_number(data, dlen, array, 6, ',', term);
154 if (length == 0)
155 return 0;
156
157 cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16) |
158 (array[2] << 8) | array[3]);
159 cmd->u.tcp.port = htons((array[4] << 8) | array[5]);
160 return length;
161 }
162
163 /* Grab port: number up to delimiter */
get_port(const char * data,int start,size_t dlen,char delim,__be16 * port)164 static int get_port(const char *data, int start, size_t dlen, char delim,
165 __be16 *port)
166 {
167 u_int16_t tmp_port = 0;
168 int i;
169
170 for (i = start; i < dlen; i++) {
171 /* Finished? */
172 if (data[i] == delim) {
173 if (tmp_port == 0)
174 break;
175 *port = htons(tmp_port);
176 pr_debug("get_port: return %d\n", tmp_port);
177 return i + 1;
178 }
179 else if (data[i] >= '0' && data[i] <= '9')
180 tmp_port = tmp_port*10 + data[i] - '0';
181 else { /* Some other crap */
182 pr_debug("get_port: invalid char.\n");
183 break;
184 }
185 }
186 return 0;
187 }
188
189 /* 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)190 static int try_eprt(const char *data, size_t dlen, struct nf_conntrack_man *cmd,
191 char term)
192 {
193 char delim;
194 int length;
195
196 /* First character is delimiter, then "1" for IPv4 or "2" for IPv6,
197 then delimiter again. */
198 if (dlen <= 3) {
199 pr_debug("EPRT: too short\n");
200 return 0;
201 }
202 delim = data[0];
203 if (isdigit(delim) || delim < 33 || delim > 126 || data[2] != delim) {
204 pr_debug("try_eprt: invalid delimitter.\n");
205 return 0;
206 }
207
208 if ((cmd->l3num == PF_INET && data[1] != '1') ||
209 (cmd->l3num == PF_INET6 && data[1] != '2')) {
210 pr_debug("EPRT: invalid protocol number.\n");
211 return 0;
212 }
213
214 pr_debug("EPRT: Got %c%c%c\n", delim, data[1], delim);
215
216 if (data[1] == '1') {
217 u_int32_t array[4];
218
219 /* Now we have IP address. */
220 length = try_number(data + 3, dlen - 3, array, 4, '.', delim);
221 if (length != 0)
222 cmd->u3.ip = htonl((array[0] << 24) | (array[1] << 16)
223 | (array[2] << 8) | array[3]);
224 } else {
225 /* Now we have IPv6 address. */
226 length = get_ipv6_addr(data + 3, dlen - 3,
227 (struct in6_addr *)cmd->u3.ip6, delim);
228 }
229
230 if (length == 0)
231 return 0;
232 pr_debug("EPRT: Got IP address!\n");
233 /* Start offset includes initial "|1|", and trailing delimiter */
234 return get_port(data, 3 + length + 1, dlen, delim, &cmd->u.tcp.port);
235 }
236
237 /* Returns 0, or length of numbers: |||6446| */
try_epsv_response(const char * data,size_t dlen,struct nf_conntrack_man * cmd,char term)238 static int try_epsv_response(const char *data, size_t dlen,
239 struct nf_conntrack_man *cmd, char term)
240 {
241 char delim;
242
243 /* Three delimiters. */
244 if (dlen <= 3) return 0;
245 delim = data[0];
246 if (isdigit(delim) || delim < 33 || delim > 126
247 || data[1] != delim || data[2] != delim)
248 return 0;
249
250 return get_port(data, 3, dlen, delim, &cmd->u.tcp.port);
251 }
252
253 /* 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))254 static int find_pattern(const char *data, size_t dlen,
255 const char *pattern, size_t plen,
256 char skip, char term,
257 unsigned int *numoff,
258 unsigned int *numlen,
259 struct nf_conntrack_man *cmd,
260 int (*getnum)(const char *, size_t,
261 struct nf_conntrack_man *, char))
262 {
263 size_t i;
264
265 pr_debug("find_pattern `%s': dlen = %Zu\n", pattern, dlen);
266 if (dlen == 0)
267 return 0;
268
269 if (dlen <= plen) {
270 /* Short packet: try for partial? */
271 if (strnicmp(data, pattern, dlen) == 0)
272 return -1;
273 else return 0;
274 }
275
276 if (strnicmp(data, pattern, plen) != 0) {
277 #if 0
278 size_t i;
279
280 pr_debug("ftp: string mismatch\n");
281 for (i = 0; i < plen; i++) {
282 pr_debug("ftp:char %u `%c'(%u) vs `%c'(%u)\n",
283 i, data[i], data[i],
284 pattern[i], pattern[i]);
285 }
286 #endif
287 return 0;
288 }
289
290 pr_debug("Pattern matches!\n");
291 /* Now we've found the constant string, try to skip
292 to the 'skip' character */
293 for (i = plen; data[i] != skip; i++)
294 if (i == dlen - 1) return -1;
295
296 /* Skip over the last character */
297 i++;
298
299 pr_debug("Skipped up to `%c'!\n", skip);
300
301 *numoff = i;
302 *numlen = getnum(data + i, dlen - i, cmd, term);
303 if (!*numlen)
304 return -1;
305
306 pr_debug("Match succeeded!\n");
307 return 1;
308 }
309
310 /* 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)311 static int find_nl_seq(u32 seq, const struct nf_ct_ftp_master *info, int dir)
312 {
313 unsigned int i;
314
315 for (i = 0; i < info->seq_aft_nl_num[dir]; i++)
316 if (info->seq_aft_nl[dir][i] == seq)
317 return 1;
318 return 0;
319 }
320
321 /* 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)322 static void update_nl_seq(struct nf_conn *ct, u32 nl_seq,
323 struct nf_ct_ftp_master *info, int dir,
324 struct sk_buff *skb)
325 {
326 unsigned int i, oldest = NUM_SEQ_TO_REMEMBER;
327
328 /* Look for oldest: if we find exact match, we're done. */
329 for (i = 0; i < info->seq_aft_nl_num[dir]; i++) {
330 if (info->seq_aft_nl[dir][i] == nl_seq)
331 return;
332
333 if (oldest == info->seq_aft_nl_num[dir] ||
334 before(info->seq_aft_nl[dir][i],
335 info->seq_aft_nl[dir][oldest]))
336 oldest = i;
337 }
338
339 if (info->seq_aft_nl_num[dir] < NUM_SEQ_TO_REMEMBER) {
340 info->seq_aft_nl[dir][info->seq_aft_nl_num[dir]++] = nl_seq;
341 nf_conntrack_event_cache(IPCT_HELPINFO_VOLATILE, ct);
342 } else if (oldest != NUM_SEQ_TO_REMEMBER &&
343 after(nl_seq, info->seq_aft_nl[dir][oldest])) {
344 info->seq_aft_nl[dir][oldest] = nl_seq;
345 nf_conntrack_event_cache(IPCT_HELPINFO_VOLATILE, ct);
346 }
347 }
348
help(struct sk_buff * skb,unsigned int protoff,struct nf_conn * ct,enum ip_conntrack_info ctinfo)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(ct)->help.ct_ftp_info;
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+IP_CT_IS_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 /* Now if this ends in \n, update ftp info. */
400 pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n",
401 ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)",
402 ct_ftp_info->seq_aft_nl[dir][0],
403 ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)",
404 ct_ftp_info->seq_aft_nl[dir][1]);
405 ret = NF_ACCEPT;
406 goto out_update_nl;
407 }
408
409 /* Initialize IP/IPv6 addr to expected address (it's not mentioned
410 in EPSV responses) */
411 cmd.l3num = nf_ct_l3num(ct);
412 memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
413 sizeof(cmd.u3.all));
414
415 for (i = 0; i < ARRAY_SIZE(search[dir]); i++) {
416 found = find_pattern(fb_ptr, datalen,
417 search[dir][i].pattern,
418 search[dir][i].plen,
419 search[dir][i].skip,
420 search[dir][i].term,
421 &matchoff, &matchlen,
422 &cmd,
423 search[dir][i].getnum);
424 if (found) break;
425 }
426 if (found == -1) {
427 /* We don't usually drop packets. After all, this is
428 connection tracking, not packet filtering.
429 However, it is necessary for accurate tracking in
430 this case. */
431 pr_debug("conntrack_ftp: partial %s %u+%u\n",
432 search[dir][i].pattern, ntohl(th->seq), datalen);
433 ret = NF_DROP;
434 goto out;
435 } else if (found == 0) { /* No match */
436 ret = NF_ACCEPT;
437 goto out_update_nl;
438 }
439
440 pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n",
441 matchlen, fb_ptr + matchoff,
442 matchlen, ntohl(th->seq) + matchoff);
443
444 exp = nf_ct_expect_alloc(ct);
445 if (exp == NULL) {
446 ret = NF_DROP;
447 goto out;
448 }
449
450 /* We refer to the reverse direction ("!dir") tuples here,
451 * because we're expecting something in the other direction.
452 * Doesn't matter unless NAT is happening. */
453 daddr = &ct->tuplehash[!dir].tuple.dst.u3;
454
455 /* Update the ftp info */
456 if ((cmd.l3num == nf_ct_l3num(ct)) &&
457 memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
458 sizeof(cmd.u3.all))) {
459 /* Enrico Scholz's passive FTP to partially RNAT'd ftp
460 server: it really wants us to connect to a
461 different IP address. Simply don't record it for
462 NAT. */
463 if (cmd.l3num == PF_INET) {
464 pr_debug("conntrack_ftp: NOT RECORDING: %pI4 != %pI4\n",
465 &cmd.u3.ip,
466 &ct->tuplehash[dir].tuple.src.u3.ip);
467 } else {
468 pr_debug("conntrack_ftp: NOT RECORDING: %pI6 != %pI6\n",
469 cmd.u3.ip6,
470 ct->tuplehash[dir].tuple.src.u3.ip6);
471 }
472
473 /* Thanks to Cristiano Lincoln Mattos
474 <lincoln@cesar.org.br> for reporting this potential
475 problem (DMZ machines opening holes to internal
476 networks, or the packet filter itself). */
477 if (!loose) {
478 ret = NF_ACCEPT;
479 goto out_put_expect;
480 }
481 daddr = &cmd.u3;
482 }
483
484 nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num,
485 &ct->tuplehash[!dir].tuple.src.u3, daddr,
486 IPPROTO_TCP, NULL, &cmd.u.tcp.port);
487
488 /* Now, NAT might want to mangle the packet, and register the
489 * (possibly changed) expectation itself. */
490 nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook);
491 if (nf_nat_ftp && ct->status & IPS_NAT_MASK)
492 ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype,
493 matchoff, matchlen, exp);
494 else {
495 /* Can't expect this? Best to drop packet now. */
496 if (nf_ct_expect_related(exp) != 0)
497 ret = NF_DROP;
498 else
499 ret = NF_ACCEPT;
500 }
501
502 out_put_expect:
503 nf_ct_expect_put(exp);
504
505 out_update_nl:
506 /* Now if this ends in \n, update ftp info. Seq may have been
507 * adjusted by NAT code. */
508 if (ends_in_nl)
509 update_nl_seq(ct, seq, ct_ftp_info, dir, skb);
510 out:
511 spin_unlock_bh(&nf_ftp_lock);
512 return ret;
513 }
514
515 static struct nf_conntrack_helper ftp[MAX_PORTS][2] __read_mostly;
516 static char ftp_names[MAX_PORTS][2][sizeof("ftp-65535")] __read_mostly;
517
518 static const struct nf_conntrack_expect_policy ftp_exp_policy = {
519 .max_expected = 1,
520 .timeout = 5 * 60,
521 };
522
523 /* don't make this __exit, since it's called from __init ! */
nf_conntrack_ftp_fini(void)524 static void nf_conntrack_ftp_fini(void)
525 {
526 int i, j;
527 for (i = 0; i < ports_c; i++) {
528 for (j = 0; j < 2; j++) {
529 if (ftp[i][j].me == NULL)
530 continue;
531
532 pr_debug("nf_ct_ftp: unregistering helper for pf: %d "
533 "port: %d\n",
534 ftp[i][j].tuple.src.l3num, ports[i]);
535 nf_conntrack_helper_unregister(&ftp[i][j]);
536 }
537 }
538
539 kfree(ftp_buffer);
540 }
541
nf_conntrack_ftp_init(void)542 static int __init nf_conntrack_ftp_init(void)
543 {
544 int i, j = -1, ret = 0;
545 char *tmpname;
546
547 ftp_buffer = kmalloc(65536, GFP_KERNEL);
548 if (!ftp_buffer)
549 return -ENOMEM;
550
551 if (ports_c == 0)
552 ports[ports_c++] = FTP_PORT;
553
554 /* FIXME should be configurable whether IPv4 and IPv6 FTP connections
555 are tracked or not - YK */
556 for (i = 0; i < ports_c; i++) {
557 ftp[i][0].tuple.src.l3num = PF_INET;
558 ftp[i][1].tuple.src.l3num = PF_INET6;
559 for (j = 0; j < 2; j++) {
560 ftp[i][j].tuple.src.u.tcp.port = htons(ports[i]);
561 ftp[i][j].tuple.dst.protonum = IPPROTO_TCP;
562 ftp[i][j].expect_policy = &ftp_exp_policy;
563 ftp[i][j].me = THIS_MODULE;
564 ftp[i][j].help = help;
565 tmpname = &ftp_names[i][j][0];
566 if (ports[i] == FTP_PORT)
567 sprintf(tmpname, "ftp");
568 else
569 sprintf(tmpname, "ftp-%d", ports[i]);
570 ftp[i][j].name = tmpname;
571
572 pr_debug("nf_ct_ftp: registering helper for pf: %d "
573 "port: %d\n",
574 ftp[i][j].tuple.src.l3num, ports[i]);
575 ret = nf_conntrack_helper_register(&ftp[i][j]);
576 if (ret) {
577 printk("nf_ct_ftp: failed to register helper "
578 " for pf: %d port: %d\n",
579 ftp[i][j].tuple.src.l3num, ports[i]);
580 nf_conntrack_ftp_fini();
581 return ret;
582 }
583 }
584 }
585
586 return 0;
587 }
588
589 module_init(nf_conntrack_ftp_init);
590 module_exit(nf_conntrack_ftp_fini);
591