Pull Andreas Metzler's fix for gnutls_certificate_verify_peers (bug 1095)
[exim.git] / src / src / tls-gnu.c
1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
4
5 /* Copyright (c) University of Cambridge 1995 - 2009 */
6 /* See the file NOTICE for conditions of use and distribution. */
7
8 /* This module provides TLS (aka SSL) support for Exim using the GnuTLS
9 library. It is #included into tls.c when that library is used. The code herein
10 is based on a patch that was contributed by Nikos Mavroyanopoulos.
11
12 No cryptographic code is included in Exim. All this module does is to call
13 functions from the GnuTLS library. */
14
15 /* Note: This appears to be using an old API from compat.h; it is likely that
16 someone familiary with GnuTLS programming could rework a lot of this to a
17 modern API and perhaps remove the explicit knowledge of crypto algorithms from
18 Exim. Such a re-work would be most welcome and we'd sacrifice support for
19 older GnuTLS releases without too many qualms -- maturity and experience
20 in crypto libraries tends to improve their robustness against attack.
21 Frankly, if you maintain it, you decide what's supported and what isn't. */
22
23 /* Heading stuff for GnuTLS */
24
25 #include <gnutls/gnutls.h>
26 #include <gnutls/x509.h>
27
28
29 #define UNKNOWN_NAME "unknown"
30 #define DH_BITS 1024
31 #define PARAM_SIZE 2*1024
32
33
34 /* Values for verify_requirment */
35
36 enum { VERIFY_NONE, VERIFY_OPTIONAL, VERIFY_REQUIRED };
37
38 /* Local static variables for GNUTLS */
39
40 static host_item *client_host;
41
42 static gnutls_dh_params dh_params = NULL;
43
44 static gnutls_certificate_server_credentials x509_cred = NULL;
45 static gnutls_session tls_session = NULL;
46
47 static char ssl_errstring[256];
48
49 static int ssl_session_timeout = 200;
50 static int verify_requirement;
51
52 /* Priorities for TLS algorithms to use. In each case there's a default table,
53 and space into which it can be copied and altered. */
54
55 static const int default_proto_priority[16] = {
56 /* These are gnutls_protocol_t enum values */
57 #if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 7
58 GNUTLS_TLS1_2,
59 #endif
60 #if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 2
61 GNUTLS_TLS1_1,
62 #endif
63 GNUTLS_TLS1,
64 GNUTLS_SSL3,
65 0 };
66
67 static int proto_priority[16];
68
69 static const int default_kx_priority[16] = {
70 GNUTLS_KX_RSA,
71 GNUTLS_KX_DHE_DSS,
72 GNUTLS_KX_DHE_RSA,
73 0 };
74
75 static int kx_priority[16];
76
77 static int default_cipher_priority[16] = {
78 GNUTLS_CIPHER_AES_256_CBC,
79 GNUTLS_CIPHER_AES_128_CBC,
80 GNUTLS_CIPHER_3DES_CBC,
81 GNUTLS_CIPHER_ARCFOUR_128,
82 0 };
83
84 static int cipher_priority[16];
85
86 static const int default_mac_priority[16] = {
87 GNUTLS_MAC_SHA,
88 GNUTLS_MAC_MD5,
89 0 };
90
91 static int mac_priority[16];
92
93 /* These two are currently not changeable. */
94
95 static const int comp_priority[16] = { GNUTLS_COMP_NULL, 0 };
96 static const int cert_type_priority[16] = { GNUTLS_CRT_X509, 0 };
97
98 /* Tables of priority names and equivalent numbers */
99
100 typedef struct pri_item {
101 uschar *name;
102 int *values;
103 } pri_item;
104
105
106 #if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 7
107 static int tls1_2_codes[] = { GNUTLS_TLS1_2, 0 };
108 #endif
109 #if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 2
110 static int tls1_1_codes[] = { GNUTLS_TLS1_1, 0 };
111 #endif
112 /* more recent libraries define this as an equivalent value to the
113 canonical GNUTLS_TLS1_0; since they're the same, we stick to the
114 older name. */
115 static int tls1_0_codes[] = { GNUTLS_TLS1, 0 };
116 static int ssl3_codes[] = { GNUTLS_SSL3, 0 };
117
118 static pri_item proto_index[] = {
119 #if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 7
120 { US"TLS1.2", tls1_2_codes },
121 #endif
122 #if GNUTLS_VERSION_MAJOR > 1 || GNUTLS_VERSION_MINOR >= 2
123 { US"TLS1.1", tls1_1_codes },
124 #endif
125 { US"TLS1.0", tls1_0_codes },
126 { US"TLS1", tls1_0_codes },
127 { US"SSL3", ssl3_codes }
128 };
129
130
131 static int kx_rsa_codes[] = { GNUTLS_KX_RSA,
132 GNUTLS_KX_DHE_RSA, 0 };
133 static int kx_dhe_codes[] = { GNUTLS_KX_DHE_DSS,
134 GNUTLS_KX_DHE_RSA, 0 };
135 static int kx_dhe_dss_codes[] = { GNUTLS_KX_DHE_DSS, 0 };
136 static int kx_dhe_rsa_codes[] = { GNUTLS_KX_DHE_RSA, 0 };
137
138 static pri_item kx_index[] = {
139 { US"DHE_DSS", kx_dhe_dss_codes },
140 { US"DHE_RSA", kx_dhe_rsa_codes },
141 { US"RSA", kx_rsa_codes },
142 { US"DHE", kx_dhe_codes }
143 };
144
145
146 static int arcfour_128_codes[] = { GNUTLS_CIPHER_ARCFOUR_128, 0 };
147 static int arcfour_40_codes[] = { GNUTLS_CIPHER_ARCFOUR_40, 0 };
148 static int arcfour_codes[] = { GNUTLS_CIPHER_ARCFOUR_128,
149 GNUTLS_CIPHER_ARCFOUR_40, 0 };
150 static int aes_256_codes[] = { GNUTLS_CIPHER_AES_256_CBC, 0 };
151 static int aes_128_codes[] = { GNUTLS_CIPHER_AES_128_CBC, 0 };
152 static int aes_codes[] = { GNUTLS_CIPHER_AES_256_CBC,
153 GNUTLS_CIPHER_AES_128_CBC, 0 };
154 static int des3_codes[] = { GNUTLS_CIPHER_3DES_CBC, 0 };
155
156 static pri_item cipher_index[] = {
157 { US"ARCFOUR_128", arcfour_128_codes },
158 { US"ARCFOUR_40", arcfour_40_codes },
159 { US"ARCFOUR", arcfour_codes },
160 { US"AES_256", aes_256_codes },
161 { US"AES_128", aes_128_codes },
162 { US"AES", aes_codes },
163 { US"3DES", des3_codes }
164 };
165
166
167 static int mac_sha_codes[] = { GNUTLS_MAC_SHA, 0 };
168 static int mac_md5_codes[] = { GNUTLS_MAC_MD5, 0 };
169
170 static pri_item mac_index[] = {
171 { US"SHA", mac_sha_codes },
172 { US"SHA1", mac_sha_codes },
173 { US"MD5", mac_md5_codes }
174 };
175
176
177
178 /*************************************************
179 * Handle TLS error *
180 *************************************************/
181
182 /* Called from lots of places when errors occur before actually starting to do
183 the TLS handshake, that is, while the session is still in clear. Always returns
184 DEFER for a server and FAIL for a client so that most calls can use "return
185 tls_error(...)" to do this processing and then give an appropriate return. A
186 single function is used for both server and client, because it is called from
187 some shared functions.
188
189 Argument:
190 prefix text to include in the logged error
191 host NULL if setting up a server;
192 the connected host if setting up a client
193 msg additional error string (may be NULL)
194 usually obtained from gnutls_strerror()
195
196 Returns: OK/DEFER/FAIL
197 */
198
199 static int
200 tls_error(uschar *prefix, host_item *host, const char *msg)
201 {
202 if (host == NULL)
203 {
204 uschar *conn_info = smtp_get_connection_info();
205 if (strncmp(conn_info, "SMTP ", 5) == 0)
206 conn_info += 5;
207 log_write(0, LOG_MAIN, "TLS error on %s (%s)%s%s",
208 conn_info, prefix, msg ? ": " : "", msg ? msg : "");
209 return DEFER;
210 }
211 else
212 {
213 log_write(0, LOG_MAIN, "TLS error on connection to %s [%s] (%s)%s%s",
214 host->name, host->address, prefix, msg ? ": " : "", msg ? msg : "");
215 return FAIL;
216 }
217 }
218
219
220
221 /*************************************************
222 * Verify certificate *
223 *************************************************/
224
225 /* Called after a successful handshake, when certificate verification is
226 required or optional, for both server and client.
227
228 Arguments:
229 session GNUTLS session
230 error where to put text giving a reason for failure
231
232 Returns: TRUE/FALSE
233 */
234
235 static BOOL
236 verify_certificate(gnutls_session session, const char **error)
237 {
238 int rc;
239 uschar *dn_string = US"";
240 const gnutls_datum *cert;
241 unsigned int verify, cert_size = 0;
242
243 *error = NULL;
244
245 /* Get the peer's certificate. If it sent one, extract it's DN, and then
246 attempt to verify the certificate. If no certificate is supplied, verification
247 is forced to fail. */
248
249 cert = gnutls_certificate_get_peers(session, &cert_size);
250 if (cert != NULL)
251 {
252 uschar buff[1024];
253 gnutls_x509_crt gcert;
254
255 gnutls_x509_crt_init(&gcert);
256 dn_string = US"unknown";
257
258 if (gnutls_x509_crt_import(gcert, cert, GNUTLS_X509_FMT_DER) == 0)
259 {
260 size_t bufsize = sizeof(buff);
261 if (gnutls_x509_crt_get_dn(gcert, CS buff, &bufsize) >= 0)
262 dn_string = string_copy_malloc(buff);
263 }
264
265 rc = gnutls_certificate_verify_peers2(session, &verify);
266 }
267 else
268 {
269 DEBUG(D_tls) debug_printf("no peer certificate supplied\n");
270 verify = GNUTLS_CERT_INVALID;
271 *error = "not supplied";
272 }
273
274 /* Handle the result of verification. INVALID seems to be set as well
275 as REVOKED, but leave the test for both. */
276
277 if ((rc < 0) || (verify & (GNUTLS_CERT_INVALID|GNUTLS_CERT_REVOKED)) != 0)
278 {
279 tls_certificate_verified = FALSE;
280 if (*error == NULL) *error = ((verify & GNUTLS_CERT_REVOKED) != 0)?
281 "revoked" : "invalid";
282 if (verify_requirement == VERIFY_REQUIRED)
283 {
284 DEBUG(D_tls) debug_printf("TLS certificate verification failed (%s): "
285 "peerdn=%s\n", *error, dn_string);
286 gnutls_alert_send(session, GNUTLS_AL_FATAL, GNUTLS_A_BAD_CERTIFICATE);
287 return FALSE; /* reject */
288 }
289 DEBUG(D_tls) debug_printf("TLS certificate verify failure (%s) overridden "
290 "(host in tls_try_verify_hosts): peerdn=%s\n", *error, dn_string);
291 }
292 else
293 {
294 tls_certificate_verified = TRUE;
295 DEBUG(D_tls) debug_printf("TLS certificate verified: peerdn=%s\n",
296 dn_string);
297 }
298
299 tls_peerdn = dn_string;
300 return TRUE; /* accept */
301 }
302
303
304
305 /*************************************************
306 * Setup up DH parameters *
307 *************************************************/
308
309 /* Generating the D-H parameters may take a long time. They only need to
310 be re-generated every so often, depending on security policy. What we do is to
311 keep these parameters in a file in the spool directory. If the file does not
312 exist, we generate them. This means that it is easy to cause a regeneration.
313
314 The new file is written as a temporary file and renamed, so that an incomplete
315 file is never present. If two processes both compute some new parameters, you
316 waste a bit of effort, but it doesn't seem worth messing around with locking to
317 prevent this.
318
319 Argument:
320 host NULL for server, server for client (for error handling)
321
322 Returns: OK/DEFER/FAIL
323 */
324
325 static int
326 init_dh(host_item *host)
327 {
328 int fd;
329 int ret;
330 gnutls_datum m;
331 uschar filename[200];
332
333 /* Initialize the data structures for holding the parameters */
334
335 ret = gnutls_dh_params_init(&dh_params);
336 if (ret < 0) return tls_error(US"init dh_params", host, gnutls_strerror(ret));
337
338 /* Set up the name of the cache file */
339
340 if (!string_format(filename, sizeof(filename), "%s/gnutls-params",
341 spool_directory))
342 return tls_error(US"overlong filename", host, NULL);
343
344 /* Open the cache file for reading and if successful, read it and set up the
345 parameters. */
346
347 fd = Uopen(filename, O_RDONLY, 0);
348 if (fd >= 0)
349 {
350 struct stat statbuf;
351 if (fstat(fd, &statbuf) < 0)
352 {
353 (void)close(fd);
354 return tls_error(US"TLS cache stat failed", host, strerror(errno));
355 }
356
357 m.size = statbuf.st_size;
358 m.data = malloc(m.size);
359 if (m.data == NULL)
360 return tls_error(US"memory allocation failed", host, strerror(errno));
361 errno = 0;
362 if (read(fd, m.data, m.size) != m.size)
363 return tls_error(US"TLS cache read failed", host, strerror(errno));
364 (void)close(fd);
365
366 ret = gnutls_dh_params_import_pkcs3(dh_params, &m, GNUTLS_X509_FMT_PEM);
367 if (ret < 0)
368 return tls_error(US"DH params import", host, gnutls_strerror(ret));
369 DEBUG(D_tls) debug_printf("read D-H parameters from file\n");
370
371 free(m.data);
372 }
373
374 /* If the file does not exist, fall through to compute new data and cache it.
375 If there was any other opening error, it is serious. */
376
377 else if (errno == ENOENT)
378 {
379 ret = -1;
380 DEBUG(D_tls)
381 debug_printf("parameter cache file %s does not exist\n", filename);
382 }
383 else
384 return tls_error(string_open_failed(errno, "%s for reading", filename),
385 host, NULL);
386
387 /* If ret < 0, either the cache file does not exist, or the data it contains
388 is not useful. One particular case of this is when upgrading from an older
389 release of Exim in which the data was stored in a different format. We don't
390 try to be clever and support both formats; we just regenerate new data in this
391 case. */
392
393 if (ret < 0)
394 {
395 uschar tempfilename[sizeof(filename) + 10];
396
397 DEBUG(D_tls) debug_printf("generating %d bit Diffie-Hellman key...\n",
398 DH_BITS);
399 ret = gnutls_dh_params_generate2(dh_params, DH_BITS);
400 if (ret < 0) return tls_error(US"D-H key generation", host, gnutls_strerror(ret));
401
402 /* Write the parameters to a file in the spool directory so that we
403 can use them from other Exim processes. */
404
405 sprintf(CS tempfilename, "%s-%d", filename, (int)getpid());
406 fd = Uopen(tempfilename, O_WRONLY|O_CREAT, 0400);
407 if (fd < 0)
408 return tls_error(string_open_failed(errno, "%s for writing", filename),
409 host, NULL);
410 (void)fchown(fd, exim_uid, exim_gid); /* Probably not necessary */
411
412 /* export the parameters in a format that can be generated using GNUTLS'
413 * certtool or other programs.
414 *
415 * The commands for certtool are:
416 * $ certtool --generate-dh-params --bits 1024 > params
417 */
418
419 m.size = PARAM_SIZE;
420 m.data = malloc(m.size);
421 if (m.data == NULL)
422 return tls_error(US"memory allocation failed", host, strerror(errno));
423
424 m.size = PARAM_SIZE;
425 ret = gnutls_dh_params_export_pkcs3(dh_params, GNUTLS_X509_FMT_PEM, m.data,
426 &m.size);
427 if (ret < 0)
428 return tls_error(US"DH params export", host, gnutls_strerror(ret));
429
430 m.size = Ustrlen(m.data);
431 errno = 0;
432 if (write(fd, m.data, m.size) != m.size || write(fd, "\n", 1) != 1)
433 return tls_error(US"TLS cache write failed", host, strerror(errno));
434
435 free(m.data);
436 (void)close(fd);
437
438 if (rename(CS tempfilename, CS filename) < 0)
439 return tls_error(string_sprintf("failed to rename %s as %s",
440 tempfilename, filename), host, strerror(errno));
441
442 DEBUG(D_tls) debug_printf("wrote D-H parameters to file %s\n", filename);
443 }
444
445 DEBUG(D_tls) debug_printf("initialized D-H parameters\n");
446 return OK;
447 }
448
449
450
451
452 /*************************************************
453 * Initialize for GnuTLS *
454 *************************************************/
455
456 /* Called from both server and client code. In the case of a server, errors
457 before actual TLS negotiation return DEFER.
458
459 Arguments:
460 host connected host, if client; NULL if server
461 certificate certificate file
462 privatekey private key file
463 cas CA certs file
464 crl CRL file
465
466 Returns: OK/DEFER/FAIL
467 */
468
469 static int
470 tls_init(host_item *host, uschar *certificate, uschar *privatekey, uschar *cas,
471 uschar *crl)
472 {
473 int rc;
474 uschar *cert_expanded, *key_expanded, *cas_expanded, *crl_expanded;
475
476 client_host = host;
477
478 rc = gnutls_global_init();
479 if (rc < 0) return tls_error(US"tls-init", host, gnutls_strerror(rc));
480
481 /* Create D-H parameters, or read them from the cache file. This function does
482 its own SMTP error messaging. */
483
484 rc = init_dh(host);
485 if (rc != OK) return rc;
486
487 /* Create the credentials structure */
488
489 rc = gnutls_certificate_allocate_credentials(&x509_cred);
490 if (rc < 0)
491 return tls_error(US"certificate_allocate_credentials",
492 host, gnutls_strerror(rc));
493
494 /* This stuff must be done for each session, because different certificates
495 may be required for different sessions. */
496
497 if (!expand_check(certificate, US"tls_certificate", &cert_expanded))
498 return DEFER;
499
500 key_expanded = NULL;
501 if (privatekey != NULL)
502 {
503 if (!expand_check(privatekey, US"tls_privatekey", &key_expanded))
504 return DEFER;
505 }
506
507 /* If expansion was forced to fail, key_expanded will be NULL. If the result of
508 the expansion is an empty string, ignore it also, and assume that the private
509 key is in the same file as the certificate. */
510
511 if (key_expanded == NULL || *key_expanded == 0)
512 key_expanded = cert_expanded;
513
514 /* Set the certificate and private keys */
515
516 if (cert_expanded != NULL)
517 {
518 DEBUG(D_tls) debug_printf("certificate file = %s\nkey file = %s\n",
519 cert_expanded, key_expanded);
520 rc = gnutls_certificate_set_x509_key_file(x509_cred, CS cert_expanded,
521 CS key_expanded, GNUTLS_X509_FMT_PEM);
522 if (rc < 0)
523 {
524 uschar *msg = string_sprintf("cert/key setup: cert=%s key=%s",
525 cert_expanded, key_expanded);
526 return tls_error(msg, host, gnutls_strerror(rc));
527 }
528 }
529
530 /* A certificate is mandatory in a server, but not in a client */
531
532 else
533 {
534 if (host == NULL)
535 return tls_error(US"no TLS server certificate is specified", NULL, NULL);
536 DEBUG(D_tls) debug_printf("no TLS client certificate is specified\n");
537 }
538
539 /* Set the trusted CAs file if one is provided, and then add the CRL if one is
540 provided. Experiment shows that, if the certificate file is empty, an unhelpful
541 error message is provided. However, if we just refrain from setting anything up
542 in that case, certificate verification fails, which seems to be the correct
543 behaviour. */
544
545 if (cas != NULL)
546 {
547 struct stat statbuf;
548
549 if (!expand_check(cas, US"tls_verify_certificates", &cas_expanded))
550 return DEFER;
551
552 if (stat(CS cas_expanded, &statbuf) < 0)
553 {
554 log_write(0, LOG_MAIN|LOG_PANIC, "could not stat %s "
555 "(tls_verify_certificates): %s", cas_expanded, strerror(errno));
556 return DEFER;
557 }
558
559 DEBUG(D_tls) debug_printf("verify certificates = %s size=" OFF_T_FMT "\n",
560 cas_expanded, statbuf.st_size);
561
562 /* If the cert file is empty, there's no point in loading the CRL file. */
563
564 if (statbuf.st_size > 0)
565 {
566 rc = gnutls_certificate_set_x509_trust_file(x509_cred, CS cas_expanded,
567 GNUTLS_X509_FMT_PEM);
568 if (rc < 0) return tls_error(US"setup_certs", host, gnutls_strerror(rc));
569
570 if (crl != NULL && *crl != 0)
571 {
572 if (!expand_check(crl, US"tls_crl", &crl_expanded))
573 return DEFER;
574 DEBUG(D_tls) debug_printf("loading CRL file = %s\n", crl_expanded);
575 rc = gnutls_certificate_set_x509_crl_file(x509_cred, CS crl_expanded,
576 GNUTLS_X509_FMT_PEM);
577 if (rc < 0) return tls_error(US"CRL setup", host, gnutls_strerror(rc));
578 }
579 }
580 }
581
582 /* Associate the parameters with the x509 credentials structure. */
583
584 gnutls_certificate_set_dh_params(x509_cred, dh_params);
585
586 DEBUG(D_tls) debug_printf("initialized certificate stuff\n");
587 return OK;
588 }
589
590
591
592
593 /*************************************************
594 * Remove from a priority list *
595 *************************************************/
596
597 /* Cautiously written so that it will remove duplicates if present.
598
599 Arguments:
600 list a zero-terminated list
601 remove_list a zero-terminated list to be removed
602
603 Returns: nothing
604 */
605
606 static void
607 remove_priority(int *list, int *remove_list)
608 {
609 for (; *remove_list != 0; remove_list++)
610 {
611 int *p = list;
612 while (*p != 0)
613 {
614 if (*p == *remove_list)
615 {
616 int *pp = p;
617 do { pp[0] = pp[1]; pp++; } while (*pp != 0);
618 }
619 else p++;
620 }
621 }
622 }
623
624
625
626 /*************************************************
627 * Add to a priority list *
628 *************************************************/
629
630 /* Cautiously written to check the list size
631
632 Arguments:
633 list a zero-terminated list
634 list_max maximum offset in the list
635 add_list a zero-terminated list to be added
636
637 Returns: TRUE if OK; FALSE if list overflows
638 */
639
640 static BOOL
641 add_priority(int *list, int list_max, int *add_list)
642 {
643 int next = 0;
644 while (list[next] != 0) next++;
645 while (*add_list != 0)
646 {
647 if (next >= list_max) return FALSE;
648 list[next++] = *add_list++;
649 }
650 list[next] = 0;
651 return TRUE;
652 }
653
654
655
656 /*************************************************
657 * Adjust a priority list *
658 *************************************************/
659
660 /* This function is called to adjust the lists of cipher algorithms, MAC
661 algorithms, key-exchange methods, and protocols.
662
663 Arguments:
664 plist the appropriate priority list
665 psize the length of the list
666 s the configuation string
667 index the index of recognized strings
668 isize the length of the index
669
670
671 which text for an error message
672
673 Returns: FALSE if the table overflows, else TRUE
674 */
675
676 static BOOL
677 set_priority(int *plist, int psize, uschar *s, pri_item *index, int isize,
678 uschar *which)
679 {
680 int sep = 0;
681 BOOL first = TRUE;
682 uschar *t;
683
684 while ((t = string_nextinlist(&s, &sep, big_buffer, big_buffer_size)) != NULL)
685 {
686 int i;
687 BOOL exclude = t[0] == '!';
688 if (first && !exclude) plist[0] = 0;
689 first = FALSE;
690 for (i = 0; i < isize; i++)
691 {
692 uschar *ss = strstric(t, index[i].name, FALSE);
693 if (ss != NULL)
694 {
695 uschar *endss = ss + Ustrlen(index[i].name);
696 if ((ss == t || !isalnum(ss[-1])) && !isalnum(*endss))
697 {
698 if (exclude)
699 remove_priority(plist, index[i].values);
700 else
701 {
702 if (!add_priority(plist, psize, index[i].values))
703 {
704 log_write(0, LOG_MAIN|LOG_PANIC, "GnuTLS init failed: %s "
705 "priority table overflow", which);
706 return FALSE;
707 }
708 }
709 }
710 }
711 }
712 }
713
714 DEBUG(D_tls)
715 {
716 int *ptr = plist;
717 debug_printf("adjusted %s priorities:", which);
718 while (*ptr != 0) debug_printf(" %d", *ptr++);
719 debug_printf("\n");
720 }
721
722 return TRUE;
723 }
724
725
726
727
728 /*************************************************
729 * Initialize a single GNUTLS session *
730 *************************************************/
731
732 /* Set the algorithm, the db backend, whether to request certificates etc.
733
734 TLS in Exim was first implemented using OpenSSL. This has a function to which
735 you pass a list of cipher suites that are permitted/not permitted. GnuTLS works
736 differently. It operates using priority lists for the different components of
737 cipher suites.
738
739 For compatibility of configuration, we scan a list of cipher suites and set
740 priorities therefrom. However, at the moment, we pay attention only to the bulk
741 cipher.
742
743 Arguments:
744 side one of GNUTLS_SERVER, GNUTLS_CLIENT
745 expciphers expanded ciphers list or NULL
746 expmac expanded MAC list or NULL
747 expkx expanded key-exchange list or NULL
748 expproto expanded protocol list or NULL
749
750 Returns: a gnutls_session, or NULL if there is a problem
751 */
752
753 static gnutls_session
754 tls_session_init(int side, uschar *expciphers, uschar *expmac, uschar *expkx,
755 uschar *expproto)
756 {
757 gnutls_session session;
758
759 gnutls_init(&session, side);
760
761 /* Initialize the lists of permitted protocols, key-exchange methods, ciphers,
762 and MACs. */
763
764 memcpy(cipher_priority, default_cipher_priority, sizeof(cipher_priority));
765 memcpy(mac_priority, default_mac_priority, sizeof(mac_priority));
766 memcpy(kx_priority, default_kx_priority, sizeof(kx_priority));
767 memcpy(proto_priority, default_proto_priority, sizeof(proto_priority));
768
769 /* The names OpenSSL uses in tls_require_ciphers are of the form DES-CBC3-SHA,
770 using hyphen separators. GnuTLS uses underscore separators. So that I can use
771 either form for tls_require_ciphers in my tests, and also for general
772 convenience, we turn hyphens into underscores before scanning the list. */
773
774 if (expciphers != NULL)
775 {
776 uschar *s = expciphers;
777 while (*s != 0) { if (*s == '-') *s = '_'; s++; }
778 }
779
780 if ((expciphers != NULL &&
781 !set_priority(cipher_priority, sizeof(cipher_priority)/sizeof(int),
782 expciphers, cipher_index, sizeof(cipher_index)/sizeof(pri_item),
783 US"cipher")) ||
784 (expmac != NULL &&
785 !set_priority(mac_priority, sizeof(mac_priority)/sizeof(int),
786 expmac, mac_index, sizeof(mac_index)/sizeof(pri_item),
787 US"MAC")) ||
788 (expkx != NULL &&
789 !set_priority(kx_priority, sizeof(kx_priority)/sizeof(int),
790 expkx, kx_index, sizeof(kx_index)/sizeof(pri_item),
791 US"key-exchange")) ||
792 (expproto != NULL &&
793 !set_priority(proto_priority, sizeof(proto_priority)/sizeof(int),
794 expproto, proto_index, sizeof(proto_index)/sizeof(pri_item),
795 US"protocol")))
796 {
797 gnutls_deinit(session);
798 return NULL;
799 }
800
801 /* Define the various priorities */
802
803 gnutls_cipher_set_priority(session, cipher_priority);
804 gnutls_compression_set_priority(session, comp_priority);
805 gnutls_kx_set_priority(session, kx_priority);
806 gnutls_protocol_set_priority(session, proto_priority);
807 gnutls_mac_set_priority(session, mac_priority);
808
809 gnutls_cred_set(session, GNUTLS_CRD_CERTIFICATE, x509_cred);
810
811 gnutls_dh_set_prime_bits(session, DH_BITS);
812
813 /* Request or demand a certificate of the peer, as configured. This will
814 happen only in a server. */
815
816 if (verify_requirement != VERIFY_NONE)
817 gnutls_certificate_server_set_request(session,
818 (verify_requirement == VERIFY_OPTIONAL)?
819 GNUTLS_CERT_REQUEST : GNUTLS_CERT_REQUIRE);
820
821 gnutls_db_set_cache_expiration(session, ssl_session_timeout);
822
823 /* Reduce security in favour of increased compatibility, if the admin
824 decides to make that trade-off. */
825 if (gnutls_compat_mode)
826 {
827 #if LIBGNUTLS_VERSION_NUMBER >= 0x020104
828 DEBUG(D_tls) debug_printf("lowering GnuTLS security, compatibility mode\n");
829 gnutls_session_enable_compatibility_mode(session);
830 #else
831 DEBUG(D_tls) debug_printf("Unable to set gnutls_compat_mode - GnuTLS version too old\n");
832 #endif
833 }
834
835 DEBUG(D_tls) debug_printf("initialized GnuTLS session\n");
836 return session;
837 }
838
839
840
841 /*************************************************
842 * Get name of cipher in use *
843 *************************************************/
844
845 /* The answer is left in a static buffer, and tls_cipher is set to point
846 to it.
847
848 Argument: pointer to a GnuTLS session
849 Returns: nothing
850 */
851
852 static void
853 construct_cipher_name(gnutls_session session)
854 {
855 static uschar cipherbuf[256];
856 uschar *ver;
857 int bits, c, kx, mac;
858
859 ver = string_copy(
860 US gnutls_protocol_get_name(gnutls_protocol_get_version(session)));
861 if (Ustrncmp(ver, "TLS ", 4) == 0) ver[3] = '-'; /* Don't want space */
862
863 c = gnutls_cipher_get(session);
864 bits = gnutls_cipher_get_key_size(c);
865
866 mac = gnutls_mac_get(session);
867 kx = gnutls_kx_get(session);
868
869 string_format(cipherbuf, sizeof(cipherbuf), "%s:%s:%u", ver,
870 gnutls_cipher_suite_get_name(kx, c, mac), bits);
871 tls_cipher = cipherbuf;
872
873 DEBUG(D_tls) debug_printf("cipher: %s\n", cipherbuf);
874 }
875
876
877
878 /*************************************************
879 * Start a TLS session in a server *
880 *************************************************/
881
882 /* This is called when Exim is running as a server, after having received
883 the STARTTLS command. It must respond to that command, and then negotiate
884 a TLS session.
885
886 Arguments:
887 require_ciphers list of allowed ciphers or NULL
888 require_mac list of allowed MACs or NULL
889 require_kx list of allowed key_exchange methods or NULL
890 require_proto list of allowed protocols or NULL
891
892 Returns: OK on success
893 DEFER for errors before the start of the negotiation
894 FAIL for errors during the negotation; the server can't
895 continue running.
896 */
897
898 int
899 tls_server_start(uschar *require_ciphers, uschar *require_mac,
900 uschar *require_kx, uschar *require_proto)
901 {
902 int rc;
903 const char *error;
904 uschar *expciphers = NULL;
905 uschar *expmac = NULL;
906 uschar *expkx = NULL;
907 uschar *expproto = NULL;
908
909 /* Check for previous activation */
910
911 if (tls_active >= 0)
912 {
913 tls_error("STARTTLS received after TLS started", NULL, "");
914 smtp_printf("554 Already in TLS\r\n");
915 return FAIL;
916 }
917
918 /* Initialize the library. If it fails, it will already have logged the error
919 and sent an SMTP response. */
920
921 DEBUG(D_tls) debug_printf("initializing GnuTLS as a server\n");
922
923 rc = tls_init(NULL, tls_certificate, tls_privatekey, tls_verify_certificates,
924 tls_crl);
925 if (rc != OK) return rc;
926
927 if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers) ||
928 !expand_check(require_mac, US"gnutls_require_mac", &expmac) ||
929 !expand_check(require_kx, US"gnutls_require_kx", &expkx) ||
930 !expand_check(require_proto, US"gnutls_require_proto", &expproto))
931 return FAIL;
932
933 /* If this is a host for which certificate verification is mandatory or
934 optional, set up appropriately. */
935
936 tls_certificate_verified = FALSE;
937 verify_requirement = VERIFY_NONE;
938
939 if (verify_check_host(&tls_verify_hosts) == OK)
940 verify_requirement = VERIFY_REQUIRED;
941 else if (verify_check_host(&tls_try_verify_hosts) == OK)
942 verify_requirement = VERIFY_OPTIONAL;
943
944 /* Prepare for new connection */
945
946 tls_session = tls_session_init(GNUTLS_SERVER, expciphers, expmac, expkx,
947 expproto);
948 if (tls_session == NULL)
949 return tls_error(US"tls_session_init", NULL,
950 gnutls_strerror(GNUTLS_E_MEMORY_ERROR));
951
952 /* Set context and tell client to go ahead, except in the case of TLS startup
953 on connection, where outputting anything now upsets the clients and tends to
954 make them disconnect. We need to have an explicit fflush() here, to force out
955 the response. Other smtp_printf() calls do not need it, because in non-TLS
956 mode, the fflush() happens when smtp_getc() is called. */
957
958 if (!tls_on_connect)
959 {
960 smtp_printf("220 TLS go ahead\r\n");
961 fflush(smtp_out);
962 }
963
964 /* Now negotiate the TLS session. We put our own timer on it, since it seems
965 that the GnuTLS library doesn't. */
966
967 gnutls_transport_set_ptr2(tls_session, (gnutls_transport_ptr)fileno(smtp_in),
968 (gnutls_transport_ptr)fileno(smtp_out));
969
970 sigalrm_seen = FALSE;
971 if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
972 rc = gnutls_handshake(tls_session);
973 alarm(0);
974
975 if (rc < 0)
976 {
977 tls_error(US"gnutls_handshake", NULL,
978 sigalrm_seen ? "timed out" : gnutls_strerror(rc));
979
980 /* It seems that, except in the case of a timeout, we have to close the
981 connection right here; otherwise if the other end is running OpenSSL it hangs
982 until the server times out. */
983
984 if (!sigalrm_seen)
985 {
986 (void)fclose(smtp_out);
987 (void)fclose(smtp_in);
988 }
989
990 return FAIL;
991 }
992
993 DEBUG(D_tls) debug_printf("gnutls_handshake was successful\n");
994
995 if (verify_requirement != VERIFY_NONE &&
996 !verify_certificate(tls_session, &error))
997 {
998 tls_error(US"certificate verification failed", NULL, error);
999 return FAIL;
1000 }
1001
1002 construct_cipher_name(tls_session);
1003
1004 /* TLS has been set up. Adjust the input functions to read via TLS,
1005 and initialize appropriately. */
1006
1007 ssl_xfer_buffer = store_malloc(ssl_xfer_buffer_size);
1008 ssl_xfer_buffer_lwm = ssl_xfer_buffer_hwm = 0;
1009 ssl_xfer_eof = ssl_xfer_error = 0;
1010
1011 receive_getc = tls_getc;
1012 receive_ungetc = tls_ungetc;
1013 receive_feof = tls_feof;
1014 receive_ferror = tls_ferror;
1015 receive_smtp_buffered = tls_smtp_buffered;
1016
1017 tls_active = fileno(smtp_out);
1018
1019 return OK;
1020 }
1021
1022
1023
1024
1025 /*************************************************
1026 * Start a TLS session in a client *
1027 *************************************************/
1028
1029 /* Called from the smtp transport after STARTTLS has been accepted.
1030
1031 Arguments:
1032 fd the fd of the connection
1033 host connected host (for messages)
1034 addr the first address (not used)
1035 dhparam DH parameter file
1036 certificate certificate file
1037 privatekey private key file
1038 verify_certs file for certificate verify
1039 verify_crl CRL for verify
1040 require_ciphers list of allowed ciphers or NULL
1041 require_mac list of allowed MACs or NULL
1042 require_kx list of allowed key_exchange methods or NULL
1043 require_proto list of allowed protocols or NULL
1044 timeout startup timeout
1045
1046 Returns: OK/DEFER/FAIL (because using common functions),
1047 but for a client, DEFER and FAIL have the same meaning
1048 */
1049
1050 int
1051 tls_client_start(int fd, host_item *host, address_item *addr, uschar *dhparam,
1052 uschar *certificate, uschar *privatekey, uschar *verify_certs,
1053 uschar *verify_crl, uschar *require_ciphers, uschar *require_mac,
1054 uschar *require_kx, uschar *require_proto, int timeout)
1055 {
1056 const gnutls_datum *server_certs;
1057 uschar *expciphers = NULL;
1058 uschar *expmac = NULL;
1059 uschar *expkx = NULL;
1060 uschar *expproto = NULL;
1061 const char *error;
1062 unsigned int server_certs_size;
1063 int rc;
1064
1065 DEBUG(D_tls) debug_printf("initializing GnuTLS as a client\n");
1066
1067 verify_requirement = (verify_certs == NULL)? VERIFY_NONE : VERIFY_REQUIRED;
1068 rc = tls_init(host, certificate, privatekey, verify_certs, verify_crl);
1069 if (rc != OK) return rc;
1070
1071 if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers) ||
1072 !expand_check(require_mac, US"gnutls_require_mac", &expmac) ||
1073 !expand_check(require_kx, US"gnutls_require_kx", &expkx) ||
1074 !expand_check(require_proto, US"gnutls_require_proto", &expproto))
1075 return FAIL;
1076
1077 tls_session = tls_session_init(GNUTLS_CLIENT, expciphers, expmac, expkx,
1078 expproto);
1079
1080 if (tls_session == NULL)
1081 return tls_error(US "tls_session_init", host,
1082 gnutls_strerror(GNUTLS_E_MEMORY_ERROR));
1083
1084 gnutls_transport_set_ptr(tls_session, (gnutls_transport_ptr)fd);
1085
1086 /* There doesn't seem to be a built-in timeout on connection. */
1087
1088 sigalrm_seen = FALSE;
1089 alarm(timeout);
1090 rc = gnutls_handshake(tls_session);
1091 alarm(0);
1092
1093 if (rc < 0)
1094 return tls_error(US "gnutls_handshake", host,
1095 sigalrm_seen ? "timed out" : gnutls_strerror(rc));
1096
1097 server_certs = gnutls_certificate_get_peers(tls_session, &server_certs_size);
1098
1099 if (server_certs != NULL)
1100 {
1101 uschar buff[1024];
1102 gnutls_x509_crt gcert;
1103
1104 gnutls_x509_crt_init(&gcert);
1105 tls_peerdn = US"unknown";
1106
1107 if (gnutls_x509_crt_import(gcert, server_certs, GNUTLS_X509_FMT_DER) == 0)
1108 {
1109 size_t bufsize = sizeof(buff);
1110 if (gnutls_x509_crt_get_dn(gcert, CS buff, &bufsize) >= 0)
1111 tls_peerdn = string_copy_malloc(buff);
1112 }
1113 }
1114
1115 /* Should we also verify the hostname here? */
1116
1117 if (verify_requirement != VERIFY_NONE &&
1118 !verify_certificate(tls_session, &error))
1119 return tls_error(US"certificate verification failed", host, error);
1120
1121 construct_cipher_name(tls_session); /* Sets tls_cipher */
1122 tls_active = fd;
1123 return OK;
1124 }
1125
1126
1127
1128 /*************************************************
1129 * Deal with logging errors during I/O *
1130 *************************************************/
1131
1132 /* We have to get the identity of the peer from saved data.
1133
1134 Argument:
1135 ec the GnuTLS error code, or 0 if it's a local error
1136 when text identifying read or write
1137 text local error text when ec is 0
1138
1139 Returns: nothing
1140 */
1141
1142 static void
1143 record_io_error(int ec, uschar *when, uschar *text)
1144 {
1145 const char *msg;
1146
1147 if (ec == GNUTLS_E_FATAL_ALERT_RECEIVED)
1148 msg = string_sprintf("%s: %s", gnutls_strerror(ec),
1149 gnutls_alert_get_name(gnutls_alert_get(tls_session)));
1150 else
1151 msg = gnutls_strerror(ec);
1152
1153 tls_error(when, client_host, msg);
1154 }
1155
1156
1157
1158 /*************************************************
1159 * TLS version of getc *
1160 *************************************************/
1161
1162 /* This gets the next byte from the TLS input buffer. If the buffer is empty,
1163 it refills the buffer via the GnuTLS reading function.
1164
1165 Arguments: none
1166 Returns: the next character or EOF
1167 */
1168
1169 int
1170 tls_getc(void)
1171 {
1172 if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm)
1173 {
1174 int inbytes;
1175
1176 DEBUG(D_tls) debug_printf("Calling gnutls_record_recv(%lx, %lx, %u)\n",
1177 (long) tls_session, (long) ssl_xfer_buffer, ssl_xfer_buffer_size);
1178
1179 if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
1180 inbytes = gnutls_record_recv(tls_session, CS ssl_xfer_buffer,
1181 ssl_xfer_buffer_size);
1182 alarm(0);
1183
1184 /* A zero-byte return appears to mean that the TLS session has been
1185 closed down, not that the socket itself has been closed down. Revert to
1186 non-TLS handling. */
1187
1188 if (inbytes == 0)
1189 {
1190 DEBUG(D_tls) debug_printf("Got TLS_EOF\n");
1191
1192 receive_getc = smtp_getc;
1193 receive_ungetc = smtp_ungetc;
1194 receive_feof = smtp_feof;
1195 receive_ferror = smtp_ferror;
1196 receive_smtp_buffered = smtp_buffered;
1197
1198 gnutls_deinit(tls_session);
1199 tls_session = NULL;
1200 tls_active = -1;
1201 tls_cipher = NULL;
1202 tls_peerdn = NULL;
1203
1204 return smtp_getc();
1205 }
1206
1207 /* Handle genuine errors */
1208
1209 else if (inbytes < 0)
1210 {
1211 record_io_error(inbytes, US"recv", NULL);
1212 ssl_xfer_error = 1;
1213 return EOF;
1214 }
1215 #ifndef DISABLE_DKIM
1216 dkim_exim_verify_feed(ssl_xfer_buffer, inbytes);
1217 #endif
1218 ssl_xfer_buffer_hwm = inbytes;
1219 ssl_xfer_buffer_lwm = 0;
1220 }
1221
1222
1223 /* Something in the buffer; return next uschar */
1224
1225 return ssl_xfer_buffer[ssl_xfer_buffer_lwm++];
1226 }
1227
1228
1229
1230 /*************************************************
1231 * Read bytes from TLS channel *
1232 *************************************************/
1233
1234 /*
1235 Arguments:
1236 buff buffer of data
1237 len size of buffer
1238
1239 Returns: the number of bytes read
1240 -1 after a failed read
1241 */
1242
1243 int
1244 tls_read(uschar *buff, size_t len)
1245 {
1246 int inbytes;
1247
1248 DEBUG(D_tls) debug_printf("Calling gnutls_record_recv(%lx, %lx, %u)\n",
1249 (long) tls_session, (long) buff, len);
1250
1251 inbytes = gnutls_record_recv(tls_session, CS buff, len);
1252 if (inbytes > 0) return inbytes;
1253 if (inbytes == 0)
1254 {
1255 DEBUG(D_tls) debug_printf("Got TLS_EOF\n");
1256 }
1257 else record_io_error(inbytes, US"recv", NULL);
1258
1259 return -1;
1260 }
1261
1262
1263
1264 /*************************************************
1265 * Write bytes down TLS channel *
1266 *************************************************/
1267
1268 /*
1269 Arguments:
1270 buff buffer of data
1271 len number of bytes
1272
1273 Returns: the number of bytes after a successful write,
1274 -1 after a failed write
1275 */
1276
1277 int
1278 tls_write(const uschar *buff, size_t len)
1279 {
1280 int outbytes;
1281 int left = len;
1282
1283 DEBUG(D_tls) debug_printf("tls_do_write(%lx, %d)\n", (long) buff, left);
1284 while (left > 0)
1285 {
1286 DEBUG(D_tls) debug_printf("gnutls_record_send(SSL, %lx, %d)\n", (long)buff,
1287 left);
1288 outbytes = gnutls_record_send(tls_session, CS buff, left);
1289
1290 DEBUG(D_tls) debug_printf("outbytes=%d\n", outbytes);
1291 if (outbytes < 0)
1292 {
1293 record_io_error(outbytes, US"send", NULL);
1294 return -1;
1295 }
1296 if (outbytes == 0)
1297 {
1298 record_io_error(0, US"send", US"TLS channel closed on write");
1299 return -1;
1300 }
1301
1302 left -= outbytes;
1303 buff += outbytes;
1304 }
1305
1306 return len;
1307 }
1308
1309
1310
1311 /*************************************************
1312 * Close down a TLS session *
1313 *************************************************/
1314
1315 /* This is also called from within a delivery subprocess forked from the
1316 daemon, to shut down the TLS library, without actually doing a shutdown (which
1317 would tamper with the TLS session in the parent process).
1318
1319 Arguments: TRUE if gnutls_bye is to be called
1320 Returns: nothing
1321 */
1322
1323 void
1324 tls_close(BOOL shutdown)
1325 {
1326 if (tls_active < 0) return; /* TLS was not active */
1327
1328 if (shutdown)
1329 {
1330 DEBUG(D_tls) debug_printf("tls_close(): shutting down TLS\n");
1331 gnutls_bye(tls_session, GNUTLS_SHUT_WR);
1332 }
1333
1334 gnutls_deinit(tls_session);
1335 tls_session = NULL;
1336 gnutls_global_deinit();
1337
1338 tls_active = -1;
1339 }
1340
1341
1342
1343
1344 /*************************************************
1345 * Report the library versions. *
1346 *************************************************/
1347
1348 /* See a description in tls-openssl.c for an explanation of why this exists.
1349
1350 Arguments: a FILE* to print the results to
1351 Returns: nothing
1352 */
1353
1354 void
1355 tls_version_report(FILE *f)
1356 {
1357 fprintf(f, "Library version: GnuTLS: Compile: %s\n"
1358 " Runtime: %s\n",
1359 LIBGNUTLS_VERSION,
1360 gnutls_check_version(NULL));
1361 }
1362
1363 /* End of tls-gnu.c */