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TOMOYO Linux Cross Reference
Linux/net/netfilter/nf_conntrack_ftp.c

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  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         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, "ftp",
591                                   FTP_PORT, ports[i], ports[i], &ftp_exp_policy,
592                                   0, sizeof(struct nf_ct_ftp_master), help,
593                                   nf_ct_ftp_from_nlattr, THIS_MODULE);
594                 nf_ct_helper_init(&ftp[2 * i + 1], AF_INET6, IPPROTO_TCP, "ftp",
595                                   FTP_PORT, ports[i], ports[i], &ftp_exp_policy,
596                                   0, sizeof(struct nf_ct_ftp_master), 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 

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