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Linux/net/netfilter/nf_conntrack_ftp.c

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  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
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 
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 >= '' && *data <= '9') {
132                         array[i] = array[i]*10 + *data - '';
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 */
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  */
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 */
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] >= '' && data[i] <= '9')
215                         tmp_port = tmp_port*10 + data[i] - '';
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| */
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| */
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. */
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. */
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. */
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 
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 matchlen, 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         if (!fb_ptr) {
417                 spin_unlock_bh(&nf_ftp_lock);
418                 return NF_ACCEPT;
419         }
420 
421         ends_in_nl = (fb_ptr[datalen - 1] == '\n');
422         seq = ntohl(th->seq) + datalen;
423 
424         /* Look up to see if we're just after a \n. */
425         if (!find_nl_seq(ntohl(th->seq), ct_ftp_info, dir)) {
426                 /* We're picking up this, clear flags and let it continue */
427                 if (unlikely(ct_ftp_info->flags[dir] & NF_CT_FTP_SEQ_PICKUP)) {
428                         ct_ftp_info->flags[dir] ^= NF_CT_FTP_SEQ_PICKUP;
429                         goto skip_nl_seq;
430                 }
431 
432                 /* Now if this ends in \n, update ftp info. */
433                 pr_debug("nf_conntrack_ftp: wrong seq pos %s(%u) or %s(%u)\n",
434                          ct_ftp_info->seq_aft_nl_num[dir] > 0 ? "" : "(UNSET)",
435                          ct_ftp_info->seq_aft_nl[dir][0],
436                          ct_ftp_info->seq_aft_nl_num[dir] > 1 ? "" : "(UNSET)",
437                          ct_ftp_info->seq_aft_nl[dir][1]);
438                 ret = NF_ACCEPT;
439                 goto out_update_nl;
440         }
441 
442 skip_nl_seq:
443         /* Initialize IP/IPv6 addr to expected address (it's not mentioned
444            in EPSV responses) */
445         cmd.l3num = nf_ct_l3num(ct);
446         memcpy(cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
447                sizeof(cmd.u3.all));
448 
449         for (i = 0; i < ARRAY_SIZE(search[dir]); i++) {
450                 found = find_pattern(fb_ptr, datalen,
451                                      search[dir][i].pattern,
452                                      search[dir][i].plen,
453                                      search[dir][i].skip,
454                                      search[dir][i].term,
455                                      &matchoff, &matchlen,
456                                      &cmd,
457                                      search[dir][i].getnum);
458                 if (found) break;
459         }
460         if (found == -1) {
461                 /* We don't usually drop packets.  After all, this is
462                    connection tracking, not packet filtering.
463                    However, it is necessary for accurate tracking in
464                    this case. */
465                 nf_ct_helper_log(skb, ct, "partial matching of `%s'",
466                                  search[dir][i].pattern);
467                 ret = NF_DROP;
468                 goto out;
469         } else if (found == 0) { /* No match */
470                 ret = NF_ACCEPT;
471                 goto out_update_nl;
472         }
473 
474         pr_debug("conntrack_ftp: match `%.*s' (%u bytes at %u)\n",
475                  matchlen, fb_ptr + matchoff,
476                  matchlen, ntohl(th->seq) + matchoff);
477 
478         exp = nf_ct_expect_alloc(ct);
479         if (exp == NULL) {
480                 nf_ct_helper_log(skb, ct, "cannot alloc expectation");
481                 ret = NF_DROP;
482                 goto out;
483         }
484 
485         /* We refer to the reverse direction ("!dir") tuples here,
486          * because we're expecting something in the other direction.
487          * Doesn't matter unless NAT is happening.  */
488         daddr = &ct->tuplehash[!dir].tuple.dst.u3;
489 
490         /* Update the ftp info */
491         if ((cmd.l3num == nf_ct_l3num(ct)) &&
492             memcmp(&cmd.u3.all, &ct->tuplehash[dir].tuple.src.u3.all,
493                      sizeof(cmd.u3.all))) {
494                 /* Enrico Scholz's passive FTP to partially RNAT'd ftp
495                    server: it really wants us to connect to a
496                    different IP address.  Simply don't record it for
497                    NAT. */
498                 if (cmd.l3num == PF_INET) {
499                         pr_debug("NOT RECORDING: %pI4 != %pI4\n",
500                                  &cmd.u3.ip,
501                                  &ct->tuplehash[dir].tuple.src.u3.ip);
502                 } else {
503                         pr_debug("NOT RECORDING: %pI6 != %pI6\n",
504                                  cmd.u3.ip6,
505                                  ct->tuplehash[dir].tuple.src.u3.ip6);
506                 }
507 
508                 /* Thanks to Cristiano Lincoln Mattos
509                    <lincoln@cesar.org.br> for reporting this potential
510                    problem (DMZ machines opening holes to internal
511                    networks, or the packet filter itself). */
512                 if (!loose) {
513                         ret = NF_ACCEPT;
514                         goto out_put_expect;
515                 }
516                 daddr = &cmd.u3;
517         }
518 
519         nf_ct_expect_init(exp, NF_CT_EXPECT_CLASS_DEFAULT, cmd.l3num,
520                           &ct->tuplehash[!dir].tuple.src.u3, daddr,
521                           IPPROTO_TCP, NULL, &cmd.u.tcp.port);
522 
523         /* Now, NAT might want to mangle the packet, and register the
524          * (possibly changed) expectation itself. */
525         nf_nat_ftp = rcu_dereference(nf_nat_ftp_hook);
526         if (nf_nat_ftp && ct->status & IPS_NAT_MASK)
527                 ret = nf_nat_ftp(skb, ctinfo, search[dir][i].ftptype,
528                                  protoff, matchoff, matchlen, exp);
529         else {
530                 /* Can't expect this?  Best to drop packet now. */
531                 if (nf_ct_expect_related(exp, 0) != 0) {
532                         nf_ct_helper_log(skb, ct, "cannot add expectation");
533                         ret = NF_DROP;
534                 } else
535                         ret = NF_ACCEPT;
536         }
537 
538 out_put_expect:
539         nf_ct_expect_put(exp);
540 
541 out_update_nl:
542         /* Now if this ends in \n, update ftp info.  Seq may have been
543          * adjusted by NAT code. */
544         if (ends_in_nl)
545                 update_nl_seq(ct, seq, ct_ftp_info, dir, skb);
546  out:
547         spin_unlock_bh(&nf_ftp_lock);
548         return ret;
549 }
550 
551 static int nf_ct_ftp_from_nlattr(struct nlattr *attr, struct nf_conn *ct)
552 {
553         struct nf_ct_ftp_master *ftp = nfct_help_data(ct);
554 
555         /* This conntrack has been injected from user-space, always pick up
556          * sequence tracking. Otherwise, the first FTP command after the
557          * failover breaks.
558          */
559         ftp->flags[IP_CT_DIR_ORIGINAL] |= NF_CT_FTP_SEQ_PICKUP;
560         ftp->flags[IP_CT_DIR_REPLY] |= NF_CT_FTP_SEQ_PICKUP;
561         return 0;
562 }
563 
564 static struct nf_conntrack_helper ftp[MAX_PORTS * 2] __read_mostly;
565 
566 static const struct nf_conntrack_expect_policy ftp_exp_policy = {
567         .max_expected   = 1,
568         .timeout        = 5 * 60,
569 };
570 
571 static void __exit nf_conntrack_ftp_fini(void)
572 {
573         nf_conntrack_helpers_unregister(ftp, ports_c * 2);
574         kfree(ftp_buffer);
575 }
576 
577 static int __init nf_conntrack_ftp_init(void)
578 {
579         int i, ret = 0;
580 
581         NF_CT_HELPER_BUILD_BUG_ON(sizeof(struct nf_ct_ftp_master));
582 
583         ftp_buffer = kmalloc(65536, GFP_KERNEL);
584         if (!ftp_buffer)
585                 return -ENOMEM;
586 
587         if (ports_c == 0)
588                 ports[ports_c++] = FTP_PORT;
589 
590         /* FIXME should be configurable whether IPv4 and IPv6 FTP connections
591                  are tracked or not - YK */
592         for (i = 0; i < ports_c; i++) {
593                 nf_ct_helper_init(&ftp[2 * i], AF_INET, IPPROTO_TCP,
594                                   HELPER_NAME, FTP_PORT, ports[i], ports[i],
595                                   &ftp_exp_policy, 0, help,
596                                   nf_ct_ftp_from_nlattr, THIS_MODULE);
597                 nf_ct_helper_init(&ftp[2 * i + 1], AF_INET6, IPPROTO_TCP,
598                                   HELPER_NAME, FTP_PORT, ports[i], ports[i],
599                                   &ftp_exp_policy, 0, help,
600                                   nf_ct_ftp_from_nlattr, THIS_MODULE);
601         }
602 
603         ret = nf_conntrack_helpers_register(ftp, ports_c * 2);
604         if (ret < 0) {
605                 pr_err("failed to register helpers\n");
606                 kfree(ftp_buffer);
607                 return ret;
608         }
609 
610         return 0;
611 }
612 
613 module_init(nf_conntrack_ftp_init);
614 module_exit(nf_conntrack_ftp_fini);
615 

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