1 /* $NetBSD: tls_client.c,v 1.12 2022/10/08 16:12:50 christos Exp $ */
2
3 /*++
4 /* NAME
5 /* tls_client
6 /* SUMMARY
7 /* client-side TLS engine
8 /* SYNOPSIS
9 /* #include <tls.h>
10 /*
11 /* TLS_APPL_STATE *tls_client_init(init_props)
12 /* const TLS_CLIENT_INIT_PROPS *init_props;
13 /*
14 /* TLS_SESS_STATE *tls_client_start(start_props)
15 /* const TLS_CLIENT_START_PROPS *start_props;
16 /*
17 /* TLS_SESS_STATE *tls_client_post_connect(TLScontext, start_props)
18 /* TLS_SESS_STATE *TLScontext;
19 /* const TLS_CLIENT_START_PROPS *start_props;
20 /*
21 /* void tls_client_stop(app_ctx, stream, failure, TLScontext)
22 /* TLS_APPL_STATE *app_ctx;
23 /* VSTREAM *stream;
24 /* int failure;
25 /* TLS_SESS_STATE *TLScontext;
26 /* DESCRIPTION
27 /* This module is the interface between Postfix TLS clients,
28 /* the OpenSSL library and the TLS entropy and cache manager.
29 /*
30 /* The SMTP client will attempt to verify the server hostname
31 /* against the names listed in the server certificate. When
32 /* a hostname match is required, the verification fails
33 /* on certificate verification or hostname mis-match errors.
34 /* When no hostname match is required, hostname verification
35 /* failures are logged but they do not affect the TLS handshake
36 /* or the SMTP session.
37 /*
38 /* The rules for peer name wild-card matching differ between
39 /* RFC 2818 (HTTP over TLS) and RFC 2830 (LDAP over TLS), while
40 /* RFC RFC3207 (SMTP over TLS) does not specify a rule at all.
41 /* Postfix uses a restrictive match algorithm. One asterisk
42 /* ('*') is allowed as the left-most component of a wild-card
43 /* certificate name; it matches the left-most component of
44 /* the peer hostname.
45 /*
46 /* Another area where RFCs aren't always explicit is the
47 /* handling of dNSNames in peer certificates. RFC 3207 (SMTP
48 /* over TLS) does not mention dNSNames. Postfix follows the
49 /* strict rules in RFC 2818 (HTTP over TLS), section 3.1: The
50 /* Subject Alternative Name/dNSName has precedence over
51 /* CommonName. If at least one dNSName is provided, Postfix
52 /* verifies those against the peer hostname and ignores the
53 /* CommonName, otherwise Postfix verifies the CommonName
54 /* against the peer hostname.
55 /*
56 /* tls_client_init() is called once when the SMTP client
57 /* initializes.
58 /* Certificate details are also decided during this phase,
59 /* so peer-specific certificate selection is not possible.
60 /*
61 /* tls_client_start() activates the TLS session over an established
62 /* stream. We expect that network buffers are flushed and
63 /* the TLS handshake can begin immediately.
64 /*
65 /* tls_client_stop() sends the "close notify" alert via
66 /* SSL_shutdown() to the peer and resets all connection specific
67 /* TLS data. As RFC2487 does not specify a separate shutdown, it
68 /* is assumed that the underlying TCP connection is shut down
69 /* immediately afterwards. Any further writes to the channel will
70 /* be discarded, and any further reads will report end-of-file.
71 /* If the failure flag is set, no SSL_shutdown() handshake is performed.
72 /*
73 /* Once the TLS connection is initiated, information about the TLS
74 /* state is available via the TLScontext structure:
75 /* .IP TLScontext->protocol
76 /* the protocol name (SSLv2, SSLv3, TLSv1),
77 /* .IP TLScontext->cipher_name
78 /* the cipher name (e.g. RC4/MD5),
79 /* .IP TLScontext->cipher_usebits
80 /* the number of bits actually used (e.g. 40),
81 /* .IP TLScontext->cipher_algbits
82 /* the number of bits the algorithm is based on (e.g. 128).
83 /* .PP
84 /* The last two values may differ from each other when export-strength
85 /* encryption is used.
86 /*
87 /* If the peer offered a certificate, part of the certificate data are
88 /* available as:
89 /* .IP TLScontext->peer_status
90 /* A bitmask field that records the status of the peer certificate
91 /* verification. This consists of one or more of TLS_CERT_FLAG_PRESENT,
92 /* TLS_CERT_FLAG_TRUSTED, TLS_CERT_FLAG_MATCHED and TLS_CERT_FLAG_SECURED.
93 /* .IP TLScontext->peer_CN
94 /* Extracted CommonName of the peer, or zero-length string if the
95 /* information could not be extracted.
96 /* .IP TLScontext->issuer_CN
97 /* Extracted CommonName of the issuer, or zero-length string if the
98 /* information could not be extracted.
99 /* .IP TLScontext->peer_cert_fprint
100 /* At the fingerprint security level, if the peer presented a certificate
101 /* the fingerprint of the certificate.
102 /* .PP
103 /* If no peer certificate is presented the peer_status is set to 0.
104 /* EVENT_DRIVEN APPLICATIONS
105 /* .ad
106 /* .fi
107 /* Event-driven programs manage multiple I/O channels. Such
108 /* programs cannot use the synchronous VSTREAM-over-TLS
109 /* implementation that the TLS library historically provides,
110 /* including tls_client_stop() and the underlying tls_stream(3)
111 /* and tls_bio_ops(3) routines.
112 /*
113 /* With the current TLS library implementation, this means
114 /* that an event-driven application is responsible for calling
115 /* and retrying SSL_connect(), SSL_read(), SSL_write() and
116 /* SSL_shutdown().
117 /*
118 /* To maintain control over TLS I/O, an event-driven client
119 /* invokes tls_client_start() with a null VSTREAM argument and
120 /* with an fd argument that specifies the I/O file descriptor.
121 /* Then, tls_client_start() performs all the necessary
122 /* preparations before the TLS handshake and returns a partially
123 /* populated TLS context. The event-driven application is then
124 /* responsible for invoking SSL_connect(), and if successful,
125 /* for invoking tls_client_post_connect() to finish the work
126 /* that was started by tls_client_start(). In case of unrecoverable
127 /* failure, tls_client_post_connect() destroys the TLS context
128 /* and returns a null pointer value.
129 /* LICENSE
130 /* .ad
131 /* .fi
132 /* This software is free. You can do with it whatever you want.
133 /* The original author kindly requests that you acknowledge
134 /* the use of his software.
135 /* AUTHOR(S)
136 /* Originally written by:
137 /* Lutz Jaenicke
138 /* BTU Cottbus
139 /* Allgemeine Elektrotechnik
140 /* Universitaetsplatz 3-4
141 /* D-03044 Cottbus, Germany
142 /*
143 /* Updated by:
144 /* Wietse Venema
145 /* IBM T.J. Watson Research
146 /* P.O. Box 704
147 /* Yorktown Heights, NY 10598, USA
148 /*
149 /* Wietse Venema
150 /* Google, Inc.
151 /* 111 8th Avenue
152 /* New York, NY 10011, USA
153 /*
154 /* Victor Duchovni
155 /* Morgan Stanley
156 /*--*/
157
158 /* System library. */
159
160 #include <sys_defs.h>
161
162 #ifdef USE_TLS
163 #include <string.h>
164
165 #ifdef STRCASECMP_IN_STRINGS_H
166 #include <strings.h>
167 #endif
168
169 /* Utility library. */
170
171 #include <argv.h>
172 #include <mymalloc.h>
173 #include <vstring.h>
174 #include <vstream.h>
175 #include <stringops.h>
176 #include <msg.h>
177 #include <iostuff.h> /* non-blocking */
178 #include <midna_domain.h>
179
180 /* Global library. */
181
182 #include <mail_params.h>
183
184 /* TLS library. */
185
186 #include <tls_mgr.h>
187 #define TLS_INTERNAL
188 #include <tls.h>
189
190 /* Application-specific. */
191
192 #define STR vstring_str
193 #define LEN VSTRING_LEN
194
195 /* load_clnt_session - load session from client cache (non-callback) */
196
load_clnt_session(TLS_SESS_STATE * TLScontext)197 static SSL_SESSION *load_clnt_session(TLS_SESS_STATE *TLScontext)
198 {
199 const char *myname = "load_clnt_session";
200 SSL_SESSION *session = 0;
201 VSTRING *session_data = vstring_alloc(2048);
202
203 /*
204 * Prepare the query.
205 */
206 if (TLScontext->log_mask & TLS_LOG_CACHE)
207 /* serverid contains transport:addr:port information */
208 msg_info("looking for session %s in %s cache",
209 TLScontext->serverid, TLScontext->cache_type);
210
211 /*
212 * We only get here if the cache_type is not empty. This code is not
213 * called unless caching is enabled and the cache_type is stored in the
214 * server SSL context.
215 */
216 if (TLScontext->cache_type == 0)
217 msg_panic("%s: null client session cache type in session lookup",
218 myname);
219
220 /*
221 * Look up and activate the SSL_SESSION object. Errors are non-fatal,
222 * since caching is only an optimization.
223 */
224 if (tls_mgr_lookup(TLScontext->cache_type, TLScontext->serverid,
225 session_data) == TLS_MGR_STAT_OK) {
226 session = tls_session_activate(STR(session_data), LEN(session_data));
227 if (session) {
228 if (TLScontext->log_mask & TLS_LOG_CACHE)
229 /* serverid contains transport:addr:port information */
230 msg_info("reloaded session %s from %s cache",
231 TLScontext->serverid, TLScontext->cache_type);
232 }
233 }
234
235 /*
236 * Clean up.
237 */
238 vstring_free(session_data);
239
240 return (session);
241 }
242
243 /* new_client_session_cb - name new session and save it to client cache */
244
new_client_session_cb(SSL * ssl,SSL_SESSION * session)245 static int new_client_session_cb(SSL *ssl, SSL_SESSION *session)
246 {
247 const char *myname = "new_client_session_cb";
248 TLS_SESS_STATE *TLScontext;
249 VSTRING *session_data;
250
251 /*
252 * The cache name (if caching is enabled in tlsmgr(8)) and the cache ID
253 * string for this session are stored in the TLScontext. It cannot be
254 * null at this point.
255 */
256 if ((TLScontext = SSL_get_ex_data(ssl, TLScontext_index)) == 0)
257 msg_panic("%s: null TLScontext in new session callback", myname);
258
259 /*
260 * We only get here if the cache_type is not empty. This callback is not
261 * set unless caching is enabled and the cache_type is stored in the
262 * server SSL context.
263 */
264 if (TLScontext->cache_type == 0)
265 msg_panic("%s: null session cache type in new session callback",
266 myname);
267
268 if (TLScontext->log_mask & TLS_LOG_CACHE)
269 /* serverid contains transport:addr:port information */
270 msg_info("save session %s to %s cache",
271 TLScontext->serverid, TLScontext->cache_type);
272
273 /*
274 * Passivate and save the session object. Errors are non-fatal, since
275 * caching is only an optimization.
276 */
277 if ((session_data = tls_session_passivate(session)) != 0) {
278 tls_mgr_update(TLScontext->cache_type, TLScontext->serverid,
279 STR(session_data), LEN(session_data));
280 vstring_free(session_data);
281 }
282
283 /*
284 * Clean up.
285 */
286 SSL_SESSION_free(session); /* 200502 */
287
288 return (1);
289 }
290
291 /* uncache_session - remove session from the external cache */
292
uncache_session(SSL_CTX * ctx,TLS_SESS_STATE * TLScontext)293 static void uncache_session(SSL_CTX *ctx, TLS_SESS_STATE *TLScontext)
294 {
295 SSL_SESSION *session = SSL_get_session(TLScontext->con);
296
297 SSL_CTX_remove_session(ctx, session);
298 if (TLScontext->cache_type == 0 || TLScontext->serverid == 0)
299 return;
300
301 if (TLScontext->log_mask & TLS_LOG_CACHE)
302 /* serverid contains transport:addr:port information */
303 msg_info("remove session %s from client cache", TLScontext->serverid);
304
305 tls_mgr_delete(TLScontext->cache_type, TLScontext->serverid);
306 }
307
308 /* verify_extract_name - verify peer name and extract peer information */
309
verify_extract_name(TLS_SESS_STATE * TLScontext,X509 * peercert,const TLS_CLIENT_START_PROPS * props)310 static void verify_extract_name(TLS_SESS_STATE *TLScontext, X509 *peercert,
311 const TLS_CLIENT_START_PROPS *props)
312 {
313 int verbose;
314
315 verbose = TLScontext->log_mask &
316 (TLS_LOG_CERTMATCH | TLS_LOG_VERBOSE | TLS_LOG_PEERCERT);
317
318 /*
319 * On exit both peer_CN and issuer_CN should be set.
320 */
321 TLScontext->issuer_CN = tls_issuer_CN(peercert, TLScontext);
322 TLScontext->peer_CN = tls_peer_CN(peercert, TLScontext);
323
324 /*
325 * Is the certificate trust chain trusted and matched? Any required name
326 * checks are now performed internally in OpenSSL.
327 */
328 if (SSL_get_verify_result(TLScontext->con) == X509_V_OK) {
329 if (TLScontext->must_fail) {
330 msg_panic("%s: cert valid despite trust init failure",
331 TLScontext->namaddr);
332 } else if (TLS_MUST_MATCH(TLScontext->level)) {
333
334 /*
335 * Fully secured only if not insecure like half-dane. We use
336 * TLS_CERT_FLAG_MATCHED to satisfy policy, but
337 * TLS_CERT_FLAG_SECURED to log the effective security.
338 *
339 * Would ideally also exclude "verify" (as opposed to "secure")
340 * here, because that can be subject to insecure MX indirection,
341 * but that's rather incompatible (and not even the case with
342 * explicitly chosen non-default match patterns). Users have
343 * been warned.
344 */
345 if (!TLS_NEVER_SECURED(TLScontext->level))
346 TLScontext->peer_status |= TLS_CERT_FLAG_SECURED;
347 TLScontext->peer_status |= TLS_CERT_FLAG_MATCHED;
348
349 if (verbose) {
350 const char *peername = SSL_get0_peername(TLScontext->con);
351
352 if (peername)
353 msg_info("%s: matched peername: %s",
354 TLScontext->namaddr, peername);
355 tls_dane_log(TLScontext);
356 }
357 } else
358 TLScontext->peer_status |= TLS_CERT_FLAG_TRUSTED;
359 }
360
361 /*
362 * Give them a clue. Problems with trust chain verification are logged
363 * when the session is first negotiated, before the session is stored
364 * into the cache. We don't want mystery failures, so log the fact the
365 * real problem is to be found in the past.
366 */
367 if (!TLS_CERT_IS_MATCHED(TLScontext)
368 && (TLScontext->log_mask & TLS_LOG_UNTRUSTED)) {
369 if (TLScontext->session_reused == 0)
370 tls_log_verify_error(TLScontext);
371 else
372 msg_info("%s: re-using session with untrusted certificate, "
373 "look for details earlier in the log", props->namaddr);
374 }
375 }
376
377 /* add_namechecks - tell OpenSSL what names to check */
378
add_namechecks(TLS_SESS_STATE * TLScontext,const TLS_CLIENT_START_PROPS * props)379 static void add_namechecks(TLS_SESS_STATE *TLScontext,
380 const TLS_CLIENT_START_PROPS *props)
381 {
382 SSL *ssl = TLScontext->con;
383 int namechecks_count = 0;
384 int i;
385
386 /* RFC6125: No part-label 'foo*bar.example.com' wildcards for SMTP */
387 SSL_set_hostflags(ssl, X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS);
388
389 for (i = 0; i < props->matchargv->argc; ++i) {
390 const char *name = props->matchargv->argv[i];
391 const char *aname;
392 int match_subdomain = 0;
393
394 if (strcasecmp(name, "nexthop") == 0) {
395 name = props->nexthop;
396 } else if (strcasecmp(name, "dot-nexthop") == 0) {
397 name = props->nexthop;
398 match_subdomain = 1;
399 } else if (strcasecmp(name, "hostname") == 0) {
400 name = props->host;
401 } else {
402 if (*name == '.') {
403 if (*++name == 0) {
404 msg_warn("%s: ignoring invalid match name: \".\"",
405 TLScontext->namaddr);
406 continue;
407 }
408 match_subdomain = 1;
409 }
410 #ifndef NO_EAI
411 else {
412
413 /*
414 * Besides U+002E (full stop) IDNA2003 allows labels to be
415 * separated by any of the Unicode variants U+3002
416 * (ideographic full stop), U+FF0E (fullwidth full stop), and
417 * U+FF61 (halfwidth ideographic full stop). Their respective
418 * UTF-8 encodings are: E38082, EFBC8E and EFBDA1.
419 *
420 * IDNA2008 does not permit (upper) case and other variant
421 * differences in U-labels. The midna_domain_to_ascii()
422 * function, based on UTS46, normalizes such differences
423 * away.
424 *
425 * The IDNA to_ASCII conversion does not allow empty leading
426 * labels, so we handle these explicitly here.
427 */
428 unsigned char *cp = (unsigned char *) name;
429
430 if ((cp[0] == 0xe3 && cp[1] == 0x80 && cp[2] == 0x82)
431 || (cp[0] == 0xef && cp[1] == 0xbc && cp[2] == 0x8e)
432 || (cp[0] == 0xef && cp[1] == 0xbd && cp[2] == 0xa1)) {
433 if (name[3]) {
434 name = name + 3;
435 match_subdomain = 1;
436 }
437 }
438 }
439 #endif
440 }
441
442 /*
443 * DNS subjectAltNames are required to be ASCII.
444 *
445 * Per RFC 6125 Section 6.4.4 Matching the CN-ID, follows the same rules
446 * (6.4.1, 6.4.2 and 6.4.3) that apply to subjectAltNames. In
447 * particular, 6.4.2 says that the reference identifier is coerced to
448 * ASCII, but no conversion is stated or implied for the CN-ID, so it
449 * seems it only matches if it is all ASCII. Otherwise, it is some
450 * other sort of name.
451 */
452 #ifndef NO_EAI
453 if (!allascii(name) && (aname = midna_domain_to_ascii(name)) != 0) {
454 if (msg_verbose)
455 msg_info("%s asciified to %s", name, aname);
456 name = aname;
457 }
458 #endif
459
460 if (!match_subdomain) {
461 if (SSL_add1_host(ssl, name))
462 ++namechecks_count;
463 else
464 msg_warn("%s: error loading match name: \"%s\"",
465 TLScontext->namaddr, name);
466 } else {
467 char *dot_name = concatenate(".", name, (char *) 0);
468
469 if (SSL_add1_host(ssl, dot_name))
470 ++namechecks_count;
471 else
472 msg_warn("%s: error loading match name: \"%s\"",
473 TLScontext->namaddr, dot_name);
474 myfree(dot_name);
475 }
476 }
477
478 /*
479 * If we failed to add any names, OpenSSL will perform no namechecks, so
480 * we set the "must_fail" bit to avoid verification false-positives.
481 */
482 if (namechecks_count == 0) {
483 msg_warn("%s: could not configure peer name checks",
484 TLScontext->namaddr);
485 TLScontext->must_fail = 1;
486 }
487 }
488
489 /* tls_auth_enable - set up TLS authentication */
490
tls_auth_enable(TLS_SESS_STATE * TLScontext,const TLS_CLIENT_START_PROPS * props)491 static int tls_auth_enable(TLS_SESS_STATE *TLScontext,
492 const TLS_CLIENT_START_PROPS *props)
493 {
494 const char *sni = 0;
495
496 if (props->sni && *props->sni) {
497 #ifndef NO_EAI
498 const char *aname;
499
500 #endif
501
502 /*
503 * MTA-STS policy plugin compatibility: with servername=hostname,
504 * Postfix must send the MX hostname (not CNAME expanded).
505 */
506 if (strcmp(props->sni, "hostname") == 0)
507 sni = props->host;
508 else if (strcmp(props->sni, "nexthop") == 0)
509 sni = props->nexthop;
510 else
511 sni = props->sni;
512
513 /*
514 * The SSL_set_tlsext_host_name() documentation does not promise that
515 * every implementation will convert U-label form to A-label form.
516 */
517 #ifndef NO_EAI
518 if (!allascii(sni) && (aname = midna_domain_to_ascii(sni)) != 0) {
519 if (msg_verbose)
520 msg_info("%s asciified to %s", sni, aname);
521 sni = aname;
522 }
523 #endif
524 }
525 switch (TLScontext->level) {
526 case TLS_LEV_HALF_DANE:
527 case TLS_LEV_DANE:
528 case TLS_LEV_DANE_ONLY:
529
530 /*
531 * With DANE sessions, send an SNI hint. We don't care whether the
532 * server reports finding a matching certificate or not, so no
533 * callback is required to process the server response. Our use of
534 * SNI is limited to giving servers that make use of SNI the best
535 * opportunity to find the certificate they promised via the
536 * associated TLSA RRs.
537 *
538 * Since the hostname is DNSSEC-validated, it must be a DNS FQDN and
539 * therefore valid for use with SNI.
540 */
541 if (SSL_dane_enable(TLScontext->con, 0) <= 0) {
542 msg_warn("%s: error enabling DANE-based certificate validation",
543 TLScontext->namaddr);
544 tls_print_errors();
545 return (0);
546 }
547 /* RFC7672 Section 3.1.1 specifies no name checks for DANE-EE(3) */
548 SSL_dane_set_flags(TLScontext->con, DANE_FLAG_NO_DANE_EE_NAMECHECKS);
549
550 /* Per RFC7672 the SNI name is the TLSA base domain */
551 sni = props->dane->base_domain;
552 add_namechecks(TLScontext, props);
553 break;
554
555 case TLS_LEV_FPRINT:
556 /* Synthetic DANE for fingerprint security */
557 if (SSL_dane_enable(TLScontext->con, 0) <= 0) {
558 msg_warn("%s: error enabling fingerprint certificate validation",
559 props->namaddr);
560 tls_print_errors();
561 return (0);
562 }
563 SSL_dane_set_flags(TLScontext->con, DANE_FLAG_NO_DANE_EE_NAMECHECKS);
564 break;
565
566 case TLS_LEV_SECURE:
567 case TLS_LEV_VERIFY:
568 if (TLScontext->dane != 0 && TLScontext->dane->tlsa != 0) {
569 /* Synthetic DANE for per-destination trust-anchors */
570 if (SSL_dane_enable(TLScontext->con, NULL) <= 0) {
571 msg_warn("%s: error configuring local trust anchors",
572 props->namaddr);
573 tls_print_errors();
574 return (0);
575 }
576 }
577 add_namechecks(TLScontext, props);
578 break;
579 default:
580 break;
581 }
582
583 if (sni) {
584 if (strlen(sni) > TLSEXT_MAXLEN_host_name) {
585 msg_warn("%s: ignoring too long SNI hostname: %.100s",
586 props->namaddr, sni);
587 return (0);
588 }
589
590 /*
591 * Failure to set a valid SNI hostname is a memory allocation error,
592 * and thus transient. Since we must not cache the session if we
593 * failed to send the SNI name, we have little choice but to abort.
594 */
595 if (!SSL_set_tlsext_host_name(TLScontext->con, sni)) {
596 msg_warn("%s: error setting SNI hostname to: %s", props->namaddr,
597 sni);
598 return (0);
599 }
600
601 /*
602 * The saved value is not presently used client-side, but could later
603 * be logged if acked by the server (requires new client-side
604 * callback to detect the ack). For now this just maintains symmetry
605 * with the server code, where do record the received SNI for
606 * logging.
607 */
608 TLScontext->peer_sni = mystrdup(sni);
609 if (TLScontext->log_mask & TLS_LOG_DEBUG)
610 msg_info("%s: SNI hostname: %s", props->namaddr, sni);
611 }
612 return (1);
613 }
614
615 /* tls_client_init - initialize client-side TLS engine */
616
tls_client_init(const TLS_CLIENT_INIT_PROPS * props)617 TLS_APPL_STATE *tls_client_init(const TLS_CLIENT_INIT_PROPS *props)
618 {
619 SSL_CTX *client_ctx;
620 TLS_APPL_STATE *app_ctx;
621 const EVP_MD *fpt_alg;
622 long off = 0;
623 int cachable;
624 int scache_timeout;
625 int log_mask;
626
627 /*
628 * Convert user loglevel to internal logmask.
629 */
630 log_mask = tls_log_mask(props->log_param, props->log_level);
631
632 if (log_mask & TLS_LOG_VERBOSE)
633 msg_info("initializing the client-side TLS engine");
634
635 /*
636 * Load (mostly cipher related) TLS-library internal main.cf parameters.
637 */
638 tls_param_init();
639
640 /*
641 * Detect mismatch between compile-time headers and run-time library.
642 */
643 tls_check_version();
644
645 /*
646 * Create an application data index for SSL objects, so that we can
647 * attach TLScontext information; this information is needed inside
648 * tls_verify_certificate_callback().
649 */
650 if (TLScontext_index < 0) {
651 if ((TLScontext_index = SSL_get_ex_new_index(0, 0, 0, 0, 0)) < 0) {
652 msg_warn("Cannot allocate SSL application data index: "
653 "disabling TLS support");
654 return (0);
655 }
656 }
657
658 /*
659 * If the administrator specifies an unsupported digest algorithm, fail
660 * now, rather than in the middle of a TLS handshake.
661 */
662 if ((fpt_alg = tls_validate_digest(props->mdalg)) == 0) {
663 msg_warn("disabling TLS support");
664 return (0);
665 }
666
667 /*
668 * Initialize the PRNG (Pseudo Random Number Generator) with some seed
669 * from external and internal sources. Don't enable TLS without some real
670 * entropy.
671 */
672 if (tls_ext_seed(var_tls_daemon_rand_bytes) < 0) {
673 msg_warn("no entropy for TLS key generation: disabling TLS support");
674 return (0);
675 }
676 tls_int_seed();
677
678 /*
679 * The SSL/TLS specifications require the client to send a message in the
680 * oldest specification it understands with the highest level it
681 * understands in the message. RFC2487 is only specified for TLSv1, but
682 * we want to be as compatible as possible, so we will start off with a
683 * SSLv2 greeting allowing the best we can offer: TLSv1. We can restrict
684 * this with the options setting later, anyhow.
685 */
686 ERR_clear_error();
687 client_ctx = SSL_CTX_new(TLS_client_method());
688 if (client_ctx == 0) {
689 msg_warn("cannot allocate client SSL_CTX: disabling TLS support");
690 tls_print_errors();
691 return (0);
692 }
693 #ifdef SSL_SECOP_PEER
694 /* Backwards compatible security as a base for opportunistic TLS. */
695 SSL_CTX_set_security_level(client_ctx, 0);
696 #endif
697
698 /*
699 * See the verify callback in tls_verify.c
700 */
701 SSL_CTX_set_verify_depth(client_ctx, props->verifydepth + 1);
702
703 /*
704 * This is a prerequisite for enabling DANE support in OpenSSL, but not a
705 * commitment to use DANE, thus suitable for both DANE and non-DANE TLS
706 * connections. Indeed we need this not just for DANE, but aslo for
707 * fingerprint and "tafile" support. Since it just allocates memory, it
708 * should never fail except when we're likely to fail anyway. Rather
709 * than try to run with crippled TLS support, just give up using TLS.
710 */
711 if (SSL_CTX_dane_enable(client_ctx) <= 0) {
712 msg_warn("OpenSSL DANE initialization failed: disabling TLS support");
713 tls_print_errors();
714 return (0);
715 }
716 tls_dane_digest_init(client_ctx, fpt_alg);
717
718 /*
719 * Protocol selection is destination dependent, so we delay the protocol
720 * selection options to the per-session SSL object.
721 */
722 off |= tls_bug_bits();
723 SSL_CTX_set_options(client_ctx, off);
724
725 /*
726 * Set the call-back routine for verbose logging.
727 */
728 if (log_mask & TLS_LOG_DEBUG)
729 SSL_CTX_set_info_callback(client_ctx, tls_info_callback);
730
731 /*
732 * Load the CA public key certificates for both the client cert and for
733 * the verification of server certificates. As provided by OpenSSL we
734 * support two types of CA certificate handling: One possibility is to
735 * add all CA certificates to one large CAfile, the other possibility is
736 * a directory pointed to by CApath, containing separate files for each
737 * CA with softlinks named after the hash values of the certificate. The
738 * first alternative has the advantage that the file is opened and read
739 * at startup time, so that you don't have the hassle to maintain another
740 * copy of the CApath directory for chroot-jail.
741 */
742 if (tls_set_ca_certificate_info(client_ctx,
743 props->CAfile, props->CApath) < 0) {
744 /* tls_set_ca_certificate_info() already logs a warning. */
745 SSL_CTX_free(client_ctx); /* 200411 */
746 return (0);
747 }
748
749 /*
750 * We do not need a client certificate, so the certificates are only
751 * loaded (and checked) if supplied. A clever client would handle
752 * multiple client certificates and decide based on the list of
753 * acceptable CAs, sent by the server, which certificate to submit.
754 * OpenSSL does however not do this and also has no call-back hooks to
755 * easily implement it.
756 *
757 * Load the client public key certificate and private key from file and
758 * check whether the cert matches the key. We can use RSA certificates
759 * ("cert") DSA certificates ("dcert") or ECDSA certificates ("eccert").
760 * All three can be made available at the same time. The CA certificates
761 * for all three are handled in the same setup already finished. Which
762 * one is used depends on the cipher negotiated (that is: the first
763 * cipher listed by the client which does match the server). The client
764 * certificate is presented after the server chooses the session cipher,
765 * so we will just present the right cert for the chosen cipher (if it
766 * uses certificates).
767 */
768 if (tls_set_my_certificate_key_info(client_ctx,
769 props->chain_files,
770 props->cert_file,
771 props->key_file,
772 props->dcert_file,
773 props->dkey_file,
774 props->eccert_file,
775 props->eckey_file) < 0) {
776 /* tls_set_my_certificate_key_info() already logs a warning. */
777 SSL_CTX_free(client_ctx); /* 200411 */
778 return (0);
779 }
780
781 /*
782 * With OpenSSL 1.0.2 and later the client EECDH curve list becomes
783 * configurable with the preferred curve negotiated via the supported
784 * curves extension.
785 */
786 tls_auto_eecdh_curves(client_ctx, var_tls_eecdh_auto);
787
788 /*
789 * Finally, the setup for the server certificate checking, done "by the
790 * book".
791 */
792 SSL_CTX_set_verify(client_ctx, SSL_VERIFY_NONE,
793 tls_verify_certificate_callback);
794
795 /*
796 * Initialize the session cache.
797 *
798 * Since the client does not search an internal cache, we simply disable it.
799 * It is only useful for expiring old sessions, but we do that in the
800 * tlsmgr(8).
801 *
802 * This makes SSL_CTX_remove_session() not useful for flushing broken
803 * sessions from the external cache, so we must delete them directly (not
804 * via a callback).
805 */
806 if (tls_mgr_policy(props->cache_type, &cachable,
807 &scache_timeout) != TLS_MGR_STAT_OK)
808 scache_timeout = 0;
809 if (scache_timeout <= 0)
810 cachable = 0;
811
812 /*
813 * Allocate an application context, and populate with mandatory protocol
814 * and cipher data.
815 */
816 app_ctx = tls_alloc_app_context(client_ctx, 0, log_mask);
817
818 /*
819 * The external session cache is implemented by the tlsmgr(8) process.
820 */
821 if (cachable) {
822
823 app_ctx->cache_type = mystrdup(props->cache_type);
824
825 /*
826 * OpenSSL does not use callbacks to load sessions from a client
827 * cache, so we must invoke that function directly. Apparently,
828 * OpenSSL does not provide a way to pass session names from here to
829 * call-back routines that do session lookup.
830 *
831 * OpenSSL can, however, automatically save newly created sessions for
832 * us by callback (we create the session name in the call-back
833 * function).
834 *
835 * XXX gcc 2.95 can't compile #ifdef .. #endif in the expansion of
836 * SSL_SESS_CACHE_CLIENT | SSL_SESS_CACHE_NO_INTERNAL_STORE |
837 * SSL_SESS_CACHE_NO_AUTO_CLEAR.
838 */
839 #ifndef SSL_SESS_CACHE_NO_INTERNAL_STORE
840 #define SSL_SESS_CACHE_NO_INTERNAL_STORE 0
841 #endif
842
843 SSL_CTX_set_session_cache_mode(client_ctx,
844 SSL_SESS_CACHE_CLIENT |
845 SSL_SESS_CACHE_NO_INTERNAL_STORE |
846 SSL_SESS_CACHE_NO_AUTO_CLEAR);
847 SSL_CTX_sess_set_new_cb(client_ctx, new_client_session_cb);
848
849 /*
850 * OpenSSL ignores timed-out sessions. We need to set the internal
851 * cache timeout at least as high as the external cache timeout. This
852 * applies even if no internal cache is used. We set the session to
853 * twice the cache lifetime. This way a session always lasts longer
854 * than its lifetime in the cache.
855 */
856 SSL_CTX_set_timeout(client_ctx, 2 * scache_timeout);
857 }
858 return (app_ctx);
859 }
860
861 /*
862 * This is the actual startup routine for the connection. We expect that the
863 * buffers are flushed and the "220 Ready to start TLS" was received by us,
864 * so that we can immediately start the TLS handshake process.
865 */
tls_client_start(const TLS_CLIENT_START_PROPS * props)866 TLS_SESS_STATE *tls_client_start(const TLS_CLIENT_START_PROPS *props)
867 {
868 int sts;
869 int protomask;
870 int min_proto;
871 int max_proto;
872 const char *cipher_list;
873 SSL_SESSION *session = 0;
874 TLS_SESS_STATE *TLScontext;
875 TLS_APPL_STATE *app_ctx = props->ctx;
876 int log_mask = app_ctx->log_mask;
877
878 /*
879 * When certificate verification is required, log trust chain validation
880 * errors even when disabled by default for opportunistic sessions. For
881 * DANE this only applies when using trust-anchor associations.
882 */
883 if (TLS_MUST_MATCH(props->tls_level))
884 log_mask |= TLS_LOG_UNTRUSTED;
885
886 if (log_mask & TLS_LOG_VERBOSE)
887 msg_info("setting up TLS connection to %s", props->namaddr);
888
889 /*
890 * First make sure we have valid protocol and cipher parameters
891 *
892 * Per-session protocol restrictions must be applied to the SSL connection,
893 * as restrictions in the global context cannot be cleared.
894 */
895 protomask = tls_proto_mask_lims(props->protocols, &min_proto, &max_proto);
896 if (protomask == TLS_PROTOCOL_INVALID) {
897 /* tls_protocol_mask() logs no warning. */
898 msg_warn("%s: Invalid TLS protocol list \"%s\": aborting TLS session",
899 props->namaddr, props->protocols);
900 return (0);
901 }
902
903 /*
904 * Though RFC7672 set the floor at SSLv3, we really can and should
905 * require TLS 1.0, since e.g. we send SNI, which is a TLS 1.0 extension.
906 * No DANE domains have been observed to support only SSLv3.
907 *
908 * XXX: Would be nice to make that TLS 1.2 at some point. Users can choose
909 * to exclude TLS 1.0 and TLS 1.1 if they find they don't run into any
910 * problems doing that.
911 */
912 if (TLS_DANE_BASED(props->tls_level))
913 protomask |= TLS_PROTOCOL_SSLv2 | TLS_PROTOCOL_SSLv3;
914
915 /*
916 * Allocate a new TLScontext for the new connection and get an SSL
917 * structure. Add the location of TLScontext to the SSL to later retrieve
918 * the information inside the tls_verify_certificate_callback().
919 *
920 * If session caching was enabled when TLS was initialized, the cache type
921 * is stored in the client SSL context.
922 */
923 TLScontext = tls_alloc_sess_context(log_mask, props->namaddr);
924 TLScontext->cache_type = app_ctx->cache_type;
925 TLScontext->level = props->tls_level;
926
927 if ((TLScontext->con = SSL_new(app_ctx->ssl_ctx)) == NULL) {
928 msg_warn("Could not allocate 'TLScontext->con' with SSL_new()");
929 tls_print_errors();
930 tls_free_context(TLScontext);
931 return (0);
932 }
933
934 /*
935 * Per session cipher selection for sessions with mandatory encryption
936 *
937 * The cipherlist is applied to the global SSL context, since it is likely
938 * to stay the same between connections, so we make use of a 1-element
939 * cache to return the same result for identical inputs.
940 */
941 cipher_list = tls_set_ciphers(TLScontext, props->cipher_grade,
942 props->cipher_exclusions);
943 if (cipher_list == 0) {
944 /* already warned */
945 tls_free_context(TLScontext);
946 return (0);
947 }
948 if (log_mask & TLS_LOG_VERBOSE)
949 msg_info("%s: TLS cipher list \"%s\"", props->namaddr, cipher_list);
950
951 TLScontext->stream = props->stream;
952 TLScontext->mdalg = props->mdalg;
953
954 /* Alias DANE digest info from props */
955 TLScontext->dane = props->dane;
956
957 if (!SSL_set_ex_data(TLScontext->con, TLScontext_index, TLScontext)) {
958 msg_warn("Could not set application data for 'TLScontext->con'");
959 tls_print_errors();
960 tls_free_context(TLScontext);
961 return (0);
962 }
963 #define CARP_VERSION(which) do { \
964 if (which##_proto != 0) \
965 msg_warn("%s: error setting %simum TLS version to: 0x%04x", \
966 TLScontext->namaddr, #which, which##_proto); \
967 else \
968 msg_warn("%s: error clearing %simum TLS version", \
969 TLScontext->namaddr, #which); \
970 } while (0)
971
972 /*
973 * Apply session protocol restrictions.
974 */
975 if (protomask != 0)
976 SSL_set_options(TLScontext->con, TLS_SSL_OP_PROTOMASK(protomask));
977 if (!SSL_set_min_proto_version(TLScontext->con, min_proto))
978 CARP_VERSION(min);
979 if (!SSL_set_max_proto_version(TLScontext->con, max_proto))
980 CARP_VERSION(max);
981
982 /*
983 * When applicable, configure DNS-based or synthetic (fingerprint or
984 * local trust anchor) DANE authentication, enable an appropriate SNI
985 * name and peer name matching.
986 *
987 * NOTE, this can change the effective security level, and needs to happen
988 * early.
989 */
990 if (!tls_auth_enable(TLScontext, props)) {
991 tls_free_context(TLScontext);
992 return (0);
993 }
994
995 /*
996 * Try to convey the configured TLSA records for this connection to the
997 * OpenSSL library. If none are "usable", we'll fall back to "encrypt"
998 * when authentication is not mandatory, otherwise we must arrange to
999 * ensure authentication failure.
1000 */
1001 if (TLScontext->dane && TLScontext->dane->tlsa) {
1002 int usable = tls_dane_enable(TLScontext);
1003 int must_fail = usable <= 0;
1004
1005 if (usable == 0) {
1006 switch (TLScontext->level) {
1007 case TLS_LEV_HALF_DANE:
1008 case TLS_LEV_DANE:
1009 msg_warn("%s: all TLSA records unusable, fallback to "
1010 "unauthenticated TLS", TLScontext->namaddr);
1011 must_fail = 0;
1012 TLScontext->level = TLS_LEV_ENCRYPT;
1013 break;
1014
1015 case TLS_LEV_FPRINT:
1016 msg_warn("%s: all fingerprints unusable", TLScontext->namaddr);
1017 break;
1018 case TLS_LEV_DANE_ONLY:
1019 msg_warn("%s: all TLSA records unusable", TLScontext->namaddr);
1020 break;
1021 case TLS_LEV_SECURE:
1022 case TLS_LEV_VERIFY:
1023 msg_warn("%s: all trust anchors unusable", TLScontext->namaddr);
1024 break;
1025 }
1026 }
1027 TLScontext->must_fail |= must_fail;
1028 }
1029
1030 /*
1031 * We compute the policy digest after we compute the SNI name in
1032 * tls_auth_enable() and possibly update the TLScontext security level.
1033 *
1034 * OpenSSL will ignore cached sessions that use the wrong protocol. So we do
1035 * not need to filter out cached sessions with the "wrong" protocol,
1036 * rather OpenSSL will simply negotiate a new session.
1037 *
1038 * We salt the session lookup key with the protocol list, so that sessions
1039 * found in the cache are plausibly acceptable.
1040 *
1041 * By the time a TLS client is negotiating ciphers it has already offered to
1042 * re-use a session, it is too late to renege on the offer. So we must
1043 * not attempt to re-use sessions whose ciphers are too weak. We salt the
1044 * session lookup key with the cipher list, so that sessions found in the
1045 * cache are always acceptable.
1046 *
1047 * With DANE, (more generally any TLScontext where we specified explicit
1048 * trust-anchor or end-entity certificates) the verification status of
1049 * the SSL session depends on the specified list. Since we verify the
1050 * certificate only during the initial handshake, we must segregate
1051 * sessions with different TA lists. Note, that TA re-verification is
1052 * not possible with cached sessions, since these don't hold the complete
1053 * peer trust chain. Therefore, we compute a digest of the sorted TA
1054 * parameters and append it to the serverid.
1055 */
1056 TLScontext->serverid =
1057 tls_serverid_digest(TLScontext, props, cipher_list);
1058
1059 /*
1060 * When authenticating the peer, use 80-bit plus OpenSSL security level
1061 *
1062 * XXX: We should perhaps use security level 1 also for mandatory
1063 * encryption, with only "may" tolerating weaker algorithms. But that
1064 * could mean no TLS 1.0 with OpenSSL >= 3.0 and encrypt, unless I get my
1065 * patch in on time to conditionally re-enable SHA1 at security level 1,
1066 * and we add code to make it so.
1067 *
1068 * That said, with "encrypt", we could reasonably require TLS 1.2?
1069 */
1070 if (TLS_MUST_MATCH(TLScontext->level))
1071 SSL_set_security_level(TLScontext->con, 1);
1072
1073 /*
1074 * XXX To avoid memory leaks we must always call SSL_SESSION_free() after
1075 * calling SSL_set_session(), regardless of whether or not the session
1076 * will be reused.
1077 */
1078 if (TLScontext->cache_type) {
1079 session = load_clnt_session(TLScontext);
1080 if (session) {
1081 SSL_set_session(TLScontext->con, session);
1082 SSL_SESSION_free(session); /* 200411 */
1083 }
1084 }
1085
1086 /*
1087 * Before really starting anything, try to seed the PRNG a little bit
1088 * more.
1089 */
1090 tls_int_seed();
1091 (void) tls_ext_seed(var_tls_daemon_rand_bytes);
1092
1093 /*
1094 * Connect the SSL connection with the network socket.
1095 */
1096 if (SSL_set_fd(TLScontext->con, props->stream == 0 ? props->fd :
1097 vstream_fileno(props->stream)) != 1) {
1098 msg_info("SSL_set_fd error to %s", props->namaddr);
1099 tls_print_errors();
1100 uncache_session(app_ctx->ssl_ctx, TLScontext);
1101 tls_free_context(TLScontext);
1102 return (0);
1103 }
1104
1105 /*
1106 * If the debug level selected is high enough, all of the data is dumped:
1107 * TLS_LOG_TLSPKTS will dump the SSL negotiation, TLS_LOG_ALLPKTS will
1108 * dump everything.
1109 *
1110 * We do have an SSL_set_fd() and now suddenly a BIO_ routine is called?
1111 * Well there is a BIO below the SSL routines that is automatically
1112 * created for us, so we can use it for debugging purposes.
1113 */
1114 if (log_mask & TLS_LOG_TLSPKTS)
1115 tls_set_bio_callback(SSL_get_rbio(TLScontext->con), tls_bio_dump_cb);
1116
1117 /*
1118 * If we don't trigger the handshake in the library, leave control over
1119 * SSL_connect/read/write/etc with the application.
1120 */
1121 if (props->stream == 0)
1122 return (TLScontext);
1123
1124 /*
1125 * Turn on non-blocking I/O so that we can enforce timeouts on network
1126 * I/O.
1127 */
1128 non_blocking(vstream_fileno(props->stream), NON_BLOCKING);
1129
1130 /*
1131 * Start TLS negotiations. This process is a black box that invokes our
1132 * call-backs for certificate verification.
1133 *
1134 * Error handling: If the SSL handshake fails, we print out an error message
1135 * and remove all TLS state concerning this session.
1136 */
1137 sts = tls_bio_connect(vstream_fileno(props->stream), props->timeout,
1138 TLScontext);
1139 if (sts <= 0) {
1140 if (ERR_peek_error() != 0) {
1141 msg_info("SSL_connect error to %s: %d", props->namaddr, sts);
1142 tls_print_errors();
1143 } else if (errno != 0) {
1144 msg_info("SSL_connect error to %s: %m", props->namaddr);
1145 } else {
1146 msg_info("SSL_connect error to %s: lost connection",
1147 props->namaddr);
1148 }
1149 uncache_session(app_ctx->ssl_ctx, TLScontext);
1150 tls_free_context(TLScontext);
1151 return (0);
1152 }
1153 return (tls_client_post_connect(TLScontext, props));
1154 }
1155
1156 /* tls_client_post_connect - post-handshake processing */
1157
tls_client_post_connect(TLS_SESS_STATE * TLScontext,const TLS_CLIENT_START_PROPS * props)1158 TLS_SESS_STATE *tls_client_post_connect(TLS_SESS_STATE *TLScontext,
1159 const TLS_CLIENT_START_PROPS *props)
1160 {
1161 const SSL_CIPHER *cipher;
1162 X509 *peercert;
1163
1164 /* Turn off packet dump if only dumping the handshake */
1165 if ((TLScontext->log_mask & TLS_LOG_ALLPKTS) == 0)
1166 tls_set_bio_callback(SSL_get_rbio(TLScontext->con), 0);
1167
1168 /*
1169 * The caller may want to know if this session was reused or if a new
1170 * session was negotiated.
1171 */
1172 TLScontext->session_reused = SSL_session_reused(TLScontext->con);
1173 if ((TLScontext->log_mask & TLS_LOG_CACHE) && TLScontext->session_reused)
1174 msg_info("%s: Reusing old session", TLScontext->namaddr);
1175
1176 /*
1177 * Do peername verification if requested and extract useful information
1178 * from the certificate for later use.
1179 */
1180 if ((peercert = TLS_PEEK_PEER_CERT(TLScontext->con)) != 0) {
1181 TLScontext->peer_status |= TLS_CERT_FLAG_PRESENT;
1182
1183 /*
1184 * Peer name or fingerprint verification as requested.
1185 * Unconditionally set peer_CN, issuer_CN and peer_cert_fprint. Check
1186 * fingerprint first, and avoid logging verified as untrusted in the
1187 * call to verify_extract_name().
1188 */
1189 TLScontext->peer_cert_fprint = tls_cert_fprint(peercert, props->mdalg);
1190 TLScontext->peer_pkey_fprint = tls_pkey_fprint(peercert, props->mdalg);
1191 verify_extract_name(TLScontext, peercert, props);
1192
1193 if (TLScontext->log_mask &
1194 (TLS_LOG_CERTMATCH | TLS_LOG_VERBOSE | TLS_LOG_PEERCERT))
1195 msg_info("%s: subject_CN=%s, issuer_CN=%s, "
1196 "fingerprint=%s, pkey_fingerprint=%s", props->namaddr,
1197 TLScontext->peer_CN, TLScontext->issuer_CN,
1198 TLScontext->peer_cert_fprint,
1199 TLScontext->peer_pkey_fprint);
1200 } else {
1201 TLScontext->issuer_CN = mystrdup("");
1202 TLScontext->peer_CN = mystrdup("");
1203 TLScontext->peer_cert_fprint = mystrdup("");
1204 TLScontext->peer_pkey_fprint = mystrdup("");
1205 }
1206
1207 /*
1208 * Finally, collect information about protocol and cipher for logging
1209 */
1210 TLScontext->protocol = SSL_get_version(TLScontext->con);
1211 cipher = SSL_get_current_cipher(TLScontext->con);
1212 TLScontext->cipher_name = SSL_CIPHER_get_name(cipher);
1213 TLScontext->cipher_usebits = SSL_CIPHER_get_bits(cipher,
1214 &(TLScontext->cipher_algbits));
1215
1216 /*
1217 * The TLS engine is active. Switch to the tls_timed_read/write()
1218 * functions and make the TLScontext available to those functions.
1219 */
1220 if (TLScontext->stream != 0)
1221 tls_stream_start(props->stream, TLScontext);
1222
1223 /*
1224 * With the handshake done, extract TLS 1.3 signature metadata.
1225 */
1226 tls_get_signature_params(TLScontext);
1227
1228 if (TLScontext->log_mask & TLS_LOG_SUMMARY)
1229 tls_log_summary(TLS_ROLE_CLIENT, TLS_USAGE_NEW, TLScontext);
1230
1231 tls_int_seed();
1232
1233 return (TLScontext);
1234 }
1235
1236 #endif /* USE_TLS */
1237