BUGFIX: forced-fail smtp option tls_sni would dereference NULL
[exim.git] / src / src / tls-openssl.c
1 /*************************************************
2 * Exim - an Internet mail transport agent *
3 *************************************************/
4
5 /* Copyright (c) University of Cambridge 1995 - 2012 */
6 /* See the file NOTICE for conditions of use and distribution. */
7
8 /* This module provides the TLS (aka SSL) support for Exim using the OpenSSL
9 library. It is #included into the tls.c file when that library is used. The
10 code herein is based on a patch that was originally contributed by Steve
11 Haslam. It was adapted from stunnel, a GPL program by Michal Trojnara.
12
13 No cryptographic code is included in Exim. All this module does is to call
14 functions from the OpenSSL library. */
15
16
17 /* Heading stuff */
18
19 #include <openssl/lhash.h>
20 #include <openssl/ssl.h>
21 #include <openssl/err.h>
22 #include <openssl/rand.h>
23 #ifdef EXPERIMENTAL_OCSP
24 #include <openssl/ocsp.h>
25 #endif
26
27 #ifdef EXPERIMENTAL_OCSP
28 #define EXIM_OCSP_SKEW_SECONDS (300L)
29 #define EXIM_OCSP_MAX_AGE (-1L)
30 #endif
31
32 #if OPENSSL_VERSION_NUMBER >= 0x0090806fL && !defined(OPENSSL_NO_TLSEXT)
33 #define EXIM_HAVE_OPENSSL_TLSEXT
34 #endif
35
36 /* Structure for collecting random data for seeding. */
37
38 typedef struct randstuff {
39 struct timeval tv;
40 pid_t p;
41 } randstuff;
42
43 /* Local static variables */
44
45 static BOOL client_verify_callback_called = FALSE;
46 static BOOL server_verify_callback_called = FALSE;
47 static const uschar *sid_ctx = US"exim";
48
49 static SSL_CTX *client_ctx = NULL;
50 static SSL_CTX *server_ctx = NULL;
51 static SSL *client_ssl = NULL;
52 static SSL *server_ssl = NULL;
53
54 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
55 static SSL_CTX *client_sni = NULL;
56 static SSL_CTX *server_sni = NULL;
57 #endif
58
59 static char ssl_errstring[256];
60
61 static int ssl_session_timeout = 200;
62 static BOOL client_verify_optional = FALSE;
63 static BOOL server_verify_optional = FALSE;
64
65 static BOOL reexpand_tls_files_for_sni = FALSE;
66
67
68 typedef struct tls_ext_ctx_cb {
69 uschar *certificate;
70 uschar *privatekey;
71 #ifdef EXPERIMENTAL_OCSP
72 uschar *ocsp_file;
73 uschar *ocsp_file_expanded;
74 OCSP_RESPONSE *ocsp_response;
75 #endif
76 uschar *dhparam;
77 /* these are cached from first expand */
78 uschar *server_cipher_list;
79 /* only passed down to tls_error: */
80 host_item *host;
81 } tls_ext_ctx_cb;
82
83 /* should figure out a cleanup of API to handle state preserved per
84 implementation, for various reasons, which can be void * in the APIs.
85 For now, we hack around it. */
86 tls_ext_ctx_cb *client_static_cbinfo = NULL;
87 tls_ext_ctx_cb *server_static_cbinfo = NULL;
88
89 static int
90 setup_certs(SSL_CTX *sctx, uschar *certs, uschar *crl, host_item *host, BOOL optional, BOOL client);
91
92 /* Callbacks */
93 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
94 static int tls_servername_cb(SSL *s, int *ad ARG_UNUSED, void *arg);
95 #endif
96 #ifdef EXPERIMENTAL_OCSP
97 static int tls_stapling_cb(SSL *s, void *arg);
98 #endif
99
100
101 /*************************************************
102 * Handle TLS error *
103 *************************************************/
104
105 /* Called from lots of places when errors occur before actually starting to do
106 the TLS handshake, that is, while the session is still in clear. Always returns
107 DEFER for a server and FAIL for a client so that most calls can use "return
108 tls_error(...)" to do this processing and then give an appropriate return. A
109 single function is used for both server and client, because it is called from
110 some shared functions.
111
112 Argument:
113 prefix text to include in the logged error
114 host NULL if setting up a server;
115 the connected host if setting up a client
116 msg error message or NULL if we should ask OpenSSL
117
118 Returns: OK/DEFER/FAIL
119 */
120
121 static int
122 tls_error(uschar *prefix, host_item *host, uschar *msg)
123 {
124 if (msg == NULL)
125 {
126 ERR_error_string(ERR_get_error(), ssl_errstring);
127 msg = (uschar *)ssl_errstring;
128 }
129
130 if (host == NULL)
131 {
132 uschar *conn_info = smtp_get_connection_info();
133 if (Ustrncmp(conn_info, US"SMTP ", 5) == 0)
134 conn_info += 5;
135 log_write(0, LOG_MAIN, "TLS error on %s (%s): %s",
136 conn_info, prefix, msg);
137 return DEFER;
138 }
139 else
140 {
141 log_write(0, LOG_MAIN, "TLS error on connection to %s [%s] (%s): %s",
142 host->name, host->address, prefix, msg);
143 return FAIL;
144 }
145 }
146
147
148
149 /*************************************************
150 * Callback to generate RSA key *
151 *************************************************/
152
153 /*
154 Arguments:
155 s SSL connection
156 export not used
157 keylength keylength
158
159 Returns: pointer to generated key
160 */
161
162 static RSA *
163 rsa_callback(SSL *s, int export, int keylength)
164 {
165 RSA *rsa_key;
166 export = export; /* Shut picky compilers up */
167 DEBUG(D_tls) debug_printf("Generating %d bit RSA key...\n", keylength);
168 rsa_key = RSA_generate_key(keylength, RSA_F4, NULL, NULL);
169 if (rsa_key == NULL)
170 {
171 ERR_error_string(ERR_get_error(), ssl_errstring);
172 log_write(0, LOG_MAIN|LOG_PANIC, "TLS error (RSA_generate_key): %s",
173 ssl_errstring);
174 return NULL;
175 }
176 return rsa_key;
177 }
178
179
180
181
182 /*************************************************
183 * Callback for verification *
184 *************************************************/
185
186 /* The SSL library does certificate verification if set up to do so. This
187 callback has the current yes/no state is in "state". If verification succeeded,
188 we set up the tls_peerdn string. If verification failed, what happens depends
189 on whether the client is required to present a verifiable certificate or not.
190
191 If verification is optional, we change the state to yes, but still log the
192 verification error. For some reason (it really would help to have proper
193 documentation of OpenSSL), this callback function then gets called again, this
194 time with state = 1. In fact, that's useful, because we can set up the peerdn
195 value, but we must take care not to set the private verified flag on the second
196 time through.
197
198 Note: this function is not called if the client fails to present a certificate
199 when asked. We get here only if a certificate has been received. Handling of
200 optional verification for this case is done when requesting SSL to verify, by
201 setting SSL_VERIFY_FAIL_IF_NO_PEER_CERT in the non-optional case.
202
203 Arguments:
204 state current yes/no state as 1/0
205 x509ctx certificate information.
206 client TRUE for client startup, FALSE for server startup
207
208 Returns: 1 if verified, 0 if not
209 */
210
211 static int
212 verify_callback(int state, X509_STORE_CTX *x509ctx, BOOL client)
213 {
214 static uschar txt[256];
215 tls_support * tlsp;
216 BOOL * calledp;
217 BOOL * optionalp;
218
219 if (client)
220 {
221 tlsp= &tls_out;
222 calledp= &client_verify_callback_called;
223 optionalp= &client_verify_optional;
224 }
225 else
226 {
227 tlsp= &tls_in;
228 calledp= &server_verify_callback_called;
229 optionalp= &server_verify_optional;
230 }
231
232 X509_NAME_oneline(X509_get_subject_name(x509ctx->current_cert),
233 CS txt, sizeof(txt));
234
235 if (state == 0)
236 {
237 log_write(0, LOG_MAIN, "SSL verify error: depth=%d error=%s cert=%s",
238 x509ctx->error_depth,
239 X509_verify_cert_error_string(x509ctx->error),
240 txt);
241 tlsp->certificate_verified = FALSE;
242 *calledp = TRUE;
243 if (!*optionalp) return 0; /* reject */
244 DEBUG(D_tls) debug_printf("SSL verify failure overridden (host in "
245 "tls_try_verify_hosts)\n");
246 return 1; /* accept */
247 }
248
249 if (x509ctx->error_depth != 0)
250 {
251 DEBUG(D_tls) debug_printf("SSL verify ok: depth=%d cert=%s\n",
252 x509ctx->error_depth, txt);
253 }
254 else
255 {
256 DEBUG(D_tls) debug_printf("SSL%s peer: %s\n",
257 *calledp ? "" : " authenticated", txt);
258 tlsp->peerdn = txt;
259 }
260
261 if (!*calledp) tlsp->certificate_verified = TRUE;
262 *calledp = TRUE;
263
264 return 1; /* accept */
265 }
266
267 static int
268 verify_callback_client(int state, X509_STORE_CTX *x509ctx)
269 {
270 return verify_callback(state, x509ctx, TRUE);
271 }
272
273 static int
274 verify_callback_server(int state, X509_STORE_CTX *x509ctx)
275 {
276 return verify_callback(state, x509ctx, FALSE);
277 }
278
279
280
281 /*************************************************
282 * Information callback *
283 *************************************************/
284
285 /* The SSL library functions call this from time to time to indicate what they
286 are doing. We copy the string to the debugging output when TLS debugging has
287 been requested.
288
289 Arguments:
290 s the SSL connection
291 where
292 ret
293
294 Returns: nothing
295 */
296
297 static void
298 info_callback(SSL *s, int where, int ret)
299 {
300 where = where;
301 ret = ret;
302 DEBUG(D_tls) debug_printf("SSL info: %s\n", SSL_state_string_long(s));
303 }
304
305
306
307 /*************************************************
308 * Initialize for DH *
309 *************************************************/
310
311 /* If dhparam is set, expand it, and load up the parameters for DH encryption.
312
313 Arguments:
314 dhparam DH parameter file or fixed parameter identity string
315 host connected host, if client; NULL if server
316
317 Returns: TRUE if OK (nothing to set up, or setup worked)
318 */
319
320 static BOOL
321 init_dh(SSL_CTX *sctx, uschar *dhparam, host_item *host)
322 {
323 BIO *bio;
324 DH *dh;
325 uschar *dhexpanded;
326 const char *pem;
327
328 if (!expand_check(dhparam, US"tls_dhparam", &dhexpanded))
329 return FALSE;
330
331 if (dhexpanded == NULL || *dhexpanded == '\0')
332 {
333 bio = BIO_new_mem_buf(CS std_dh_prime_default(), -1);
334 }
335 else if (dhexpanded[0] == '/')
336 {
337 bio = BIO_new_file(CS dhexpanded, "r");
338 if (bio == NULL)
339 {
340 tls_error(string_sprintf("could not read dhparams file %s", dhexpanded),
341 host, US strerror(errno));
342 return FALSE;
343 }
344 }
345 else
346 {
347 if (Ustrcmp(dhexpanded, "none") == 0)
348 {
349 DEBUG(D_tls) debug_printf("Requested no DH parameters.\n");
350 return TRUE;
351 }
352
353 pem = std_dh_prime_named(dhexpanded);
354 if (!pem)
355 {
356 tls_error(string_sprintf("Unknown standard DH prime \"%s\"", dhexpanded),
357 host, US strerror(errno));
358 return FALSE;
359 }
360 bio = BIO_new_mem_buf(CS pem, -1);
361 }
362
363 dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL);
364 if (dh == NULL)
365 {
366 BIO_free(bio);
367 tls_error(string_sprintf("Could not read tls_dhparams \"%s\"", dhexpanded),
368 host, NULL);
369 return FALSE;
370 }
371
372 /* Even if it is larger, we silently return success rather than cause things
373 * to fail out, so that a too-large DH will not knock out all TLS; it's a
374 * debatable choice. */
375 if ((8*DH_size(dh)) > tls_dh_max_bits)
376 {
377 DEBUG(D_tls)
378 debug_printf("dhparams file %d bits, is > tls_dh_max_bits limit of %d",
379 8*DH_size(dh), tls_dh_max_bits);
380 }
381 else
382 {
383 SSL_CTX_set_tmp_dh(sctx, dh);
384 DEBUG(D_tls)
385 debug_printf("Diffie-Hellman initialized from %s with %d-bit prime\n",
386 dhexpanded ? dhexpanded : US"default", 8*DH_size(dh));
387 }
388
389 DH_free(dh);
390 BIO_free(bio);
391
392 return TRUE;
393 }
394
395
396
397
398 #ifdef EXPERIMENTAL_OCSP
399 /*************************************************
400 * Load OCSP information into state *
401 *************************************************/
402
403 /* Called to load the OCSP response from the given file into memory, once
404 caller has determined this is needed. Checks validity. Debugs a message
405 if invalid.
406
407 ASSUMES: single response, for single cert.
408
409 Arguments:
410 sctx the SSL_CTX* to update
411 cbinfo various parts of session state
412 expanded the filename putatively holding an OCSP response
413
414 */
415
416 static void
417 ocsp_load_response(SSL_CTX *sctx,
418 tls_ext_ctx_cb *cbinfo,
419 const uschar *expanded)
420 {
421 BIO *bio;
422 OCSP_RESPONSE *resp;
423 OCSP_BASICRESP *basic_response;
424 OCSP_SINGLERESP *single_response;
425 ASN1_GENERALIZEDTIME *rev, *thisupd, *nextupd;
426 X509_STORE *store;
427 unsigned long verify_flags;
428 int status, reason, i;
429
430 cbinfo->ocsp_file_expanded = string_copy(expanded);
431 if (cbinfo->ocsp_response)
432 {
433 OCSP_RESPONSE_free(cbinfo->ocsp_response);
434 cbinfo->ocsp_response = NULL;
435 }
436
437 bio = BIO_new_file(CS cbinfo->ocsp_file_expanded, "rb");
438 if (!bio)
439 {
440 DEBUG(D_tls) debug_printf("Failed to open OCSP response file \"%s\"\n",
441 cbinfo->ocsp_file_expanded);
442 return;
443 }
444
445 resp = d2i_OCSP_RESPONSE_bio(bio, NULL);
446 BIO_free(bio);
447 if (!resp)
448 {
449 DEBUG(D_tls) debug_printf("Error reading OCSP response.\n");
450 return;
451 }
452
453 status = OCSP_response_status(resp);
454 if (status != OCSP_RESPONSE_STATUS_SUCCESSFUL)
455 {
456 DEBUG(D_tls) debug_printf("OCSP response not valid: %s (%d)\n",
457 OCSP_response_status_str(status), status);
458 return;
459 }
460
461 basic_response = OCSP_response_get1_basic(resp);
462 if (!basic_response)
463 {
464 DEBUG(D_tls)
465 debug_printf("OCSP response parse error: unable to extract basic response.\n");
466 return;
467 }
468
469 store = SSL_CTX_get_cert_store(sctx);
470 verify_flags = OCSP_NOVERIFY; /* check sigs, but not purpose */
471
472 /* May need to expose ability to adjust those flags?
473 OCSP_NOSIGS OCSP_NOVERIFY OCSP_NOCHAIN OCSP_NOCHECKS OCSP_NOEXPLICIT
474 OCSP_TRUSTOTHER OCSP_NOINTERN */
475
476 i = OCSP_basic_verify(basic_response, NULL, store, verify_flags);
477 if (i <= 0)
478 {
479 DEBUG(D_tls) {
480 ERR_error_string(ERR_get_error(), ssl_errstring);
481 debug_printf("OCSP response verify failure: %s\n", US ssl_errstring);
482 }
483 return;
484 }
485
486 /* Here's the simplifying assumption: there's only one response, for the
487 one certificate we use, and nothing for anything else in a chain. If this
488 proves false, we need to extract a cert id from our issued cert
489 (tls_certificate) and use that for OCSP_resp_find_status() (which finds the
490 right cert in the stack and then calls OCSP_single_get0_status()).
491
492 I'm hoping to avoid reworking a bunch more of how we handle state here. */
493 single_response = OCSP_resp_get0(basic_response, 0);
494 if (!single_response)
495 {
496 DEBUG(D_tls)
497 debug_printf("Unable to get first response from OCSP basic response.\n");
498 return;
499 }
500
501 status = OCSP_single_get0_status(single_response, &reason, &rev, &thisupd, &nextupd);
502 /* how does this status differ from the one above? */
503 if (status != OCSP_RESPONSE_STATUS_SUCCESSFUL)
504 {
505 DEBUG(D_tls) debug_printf("OCSP response not valid (take 2): %s (%d)\n",
506 OCSP_response_status_str(status), status);
507 return;
508 }
509
510 if (!OCSP_check_validity(thisupd, nextupd, EXIM_OCSP_SKEW_SECONDS, EXIM_OCSP_MAX_AGE))
511 {
512 DEBUG(D_tls) debug_printf("OCSP status invalid times.\n");
513 return;
514 }
515
516 cbinfo->ocsp_response = resp;
517 }
518 #endif
519
520
521
522
523 /*************************************************
524 * Expand key and cert file specs *
525 *************************************************/
526
527 /* Called once during tls_init and possibly againt during TLS setup, for a
528 new context, if Server Name Indication was used and tls_sni was seen in
529 the certificate string.
530
531 Arguments:
532 sctx the SSL_CTX* to update
533 cbinfo various parts of session state
534
535 Returns: OK/DEFER/FAIL
536 */
537
538 static int
539 tls_expand_session_files(SSL_CTX *sctx, tls_ext_ctx_cb *cbinfo)
540 {
541 uschar *expanded;
542
543 if (cbinfo->certificate == NULL)
544 return OK;
545
546 if (Ustrstr(cbinfo->certificate, US"tls_sni") ||
547 Ustrstr(cbinfo->certificate, US"tls_in_sni") ||
548 Ustrstr(cbinfo->certificate, US"tls_out_sni")
549 )
550 reexpand_tls_files_for_sni = TRUE;
551
552 if (!expand_check(cbinfo->certificate, US"tls_certificate", &expanded))
553 return DEFER;
554
555 if (expanded != NULL)
556 {
557 DEBUG(D_tls) debug_printf("tls_certificate file %s\n", expanded);
558 if (!SSL_CTX_use_certificate_chain_file(sctx, CS expanded))
559 return tls_error(string_sprintf(
560 "SSL_CTX_use_certificate_chain_file file=%s", expanded),
561 cbinfo->host, NULL);
562 }
563
564 if (cbinfo->privatekey != NULL &&
565 !expand_check(cbinfo->privatekey, US"tls_privatekey", &expanded))
566 return DEFER;
567
568 /* If expansion was forced to fail, key_expanded will be NULL. If the result
569 of the expansion is an empty string, ignore it also, and assume the private
570 key is in the same file as the certificate. */
571
572 if (expanded != NULL && *expanded != 0)
573 {
574 DEBUG(D_tls) debug_printf("tls_privatekey file %s\n", expanded);
575 if (!SSL_CTX_use_PrivateKey_file(sctx, CS expanded, SSL_FILETYPE_PEM))
576 return tls_error(string_sprintf(
577 "SSL_CTX_use_PrivateKey_file file=%s", expanded), cbinfo->host, NULL);
578 }
579
580 #ifdef EXPERIMENTAL_OCSP
581 if (cbinfo->ocsp_file != NULL)
582 {
583 if (!expand_check(cbinfo->ocsp_file, US"tls_ocsp_file", &expanded))
584 return DEFER;
585
586 if (expanded != NULL && *expanded != 0)
587 {
588 DEBUG(D_tls) debug_printf("tls_ocsp_file %s\n", expanded);
589 if (cbinfo->ocsp_file_expanded &&
590 (Ustrcmp(expanded, cbinfo->ocsp_file_expanded) == 0))
591 {
592 DEBUG(D_tls)
593 debug_printf("tls_ocsp_file value unchanged, using existing values.\n");
594 } else {
595 ocsp_load_response(sctx, cbinfo, expanded);
596 }
597 }
598 }
599 #endif
600
601 return OK;
602 }
603
604
605
606
607 /*************************************************
608 * Callback to handle SNI *
609 *************************************************/
610
611 /* Called when acting as server during the TLS session setup if a Server Name
612 Indication extension was sent by the client.
613
614 API documentation is OpenSSL s_server.c implementation.
615
616 Arguments:
617 s SSL* of the current session
618 ad unknown (part of OpenSSL API) (unused)
619 arg Callback of "our" registered data
620
621 Returns: SSL_TLSEXT_ERR_{OK,ALERT_WARNING,ALERT_FATAL,NOACK}
622 */
623
624 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
625 static int
626 tls_servername_cb(SSL *s, int *ad ARG_UNUSED, void *arg)
627 {
628 const char *servername = SSL_get_servername(s, TLSEXT_NAMETYPE_host_name);
629 tls_ext_ctx_cb *cbinfo = (tls_ext_ctx_cb *) arg;
630 int rc;
631 int old_pool = store_pool;
632
633 if (!servername)
634 return SSL_TLSEXT_ERR_OK;
635
636 DEBUG(D_tls) debug_printf("Received TLS SNI \"%s\"%s\n", servername,
637 reexpand_tls_files_for_sni ? "" : " (unused for certificate selection)");
638
639 /* Make the extension value available for expansion */
640 store_pool = POOL_PERM;
641 tls_in.sni = string_copy(US servername);
642 store_pool = old_pool;
643
644 if (!reexpand_tls_files_for_sni)
645 return SSL_TLSEXT_ERR_OK;
646
647 /* Can't find an SSL_CTX_clone() or equivalent, so we do it manually;
648 not confident that memcpy wouldn't break some internal reference counting.
649 Especially since there's a references struct member, which would be off. */
650
651 server_sni = SSL_CTX_new(SSLv23_server_method());
652 if (!server_sni)
653 {
654 ERR_error_string(ERR_get_error(), ssl_errstring);
655 DEBUG(D_tls) debug_printf("SSL_CTX_new() failed: %s\n", ssl_errstring);
656 return SSL_TLSEXT_ERR_NOACK;
657 }
658
659 /* Not sure how many of these are actually needed, since SSL object
660 already exists. Might even need this selfsame callback, for reneg? */
661
662 SSL_CTX_set_info_callback(server_sni, SSL_CTX_get_info_callback(server_ctx));
663 SSL_CTX_set_mode(server_sni, SSL_CTX_get_mode(server_ctx));
664 SSL_CTX_set_options(server_sni, SSL_CTX_get_options(server_ctx));
665 SSL_CTX_set_timeout(server_sni, SSL_CTX_get_timeout(server_ctx));
666 SSL_CTX_set_tlsext_servername_callback(server_sni, tls_servername_cb);
667 SSL_CTX_set_tlsext_servername_arg(server_sni, cbinfo);
668 if (cbinfo->server_cipher_list)
669 SSL_CTX_set_cipher_list(server_sni, CS cbinfo->server_cipher_list);
670 #ifdef EXPERIMENTAL_OCSP
671 if (cbinfo->ocsp_file)
672 {
673 SSL_CTX_set_tlsext_status_cb(server_sni, tls_stapling_cb);
674 SSL_CTX_set_tlsext_status_arg(ctx, cbinfo);
675 }
676 #endif
677
678 rc = setup_certs(server_sni, tls_verify_certificates, tls_crl, NULL, FALSE, FALSE);
679 if (rc != OK) return SSL_TLSEXT_ERR_NOACK;
680
681 /* do this after setup_certs, because this can require the certs for verifying
682 OCSP information. */
683 rc = tls_expand_session_files(server_sni, cbinfo);
684 if (rc != OK) return SSL_TLSEXT_ERR_NOACK;
685
686 rc = init_dh(server_sni, cbinfo->dhparam, NULL);
687 if (rc != OK) return SSL_TLSEXT_ERR_NOACK;
688
689 DEBUG(D_tls) debug_printf("Switching SSL context.\n");
690 SSL_set_SSL_CTX(s, server_sni);
691
692 return SSL_TLSEXT_ERR_OK;
693 }
694 #endif /* EXIM_HAVE_OPENSSL_TLSEXT */
695
696
697
698
699 #ifdef EXPERIMENTAL_OCSP
700 /*************************************************
701 * Callback to handle OCSP Stapling *
702 *************************************************/
703
704 /* Called when acting as server during the TLS session setup if the client
705 requests OCSP information with a Certificate Status Request.
706
707 Documentation via openssl s_server.c and the Apache patch from the OpenSSL
708 project.
709
710 */
711
712 static int
713 tls_stapling_cb(SSL *s, void *arg)
714 {
715 const tls_ext_ctx_cb *cbinfo = (tls_ext_ctx_cb *) arg;
716 uschar *response_der;
717 int response_der_len;
718
719 DEBUG(D_tls) debug_printf("Received TLS status request (OCSP stapling); %s response.\n",
720 cbinfo->ocsp_response ? "have" : "lack");
721 if (!cbinfo->ocsp_response)
722 return SSL_TLSEXT_ERR_NOACK;
723
724 response_der = NULL;
725 response_der_len = i2d_OCSP_RESPONSE(cbinfo->ocsp_response, &response_der);
726 if (response_der_len <= 0)
727 return SSL_TLSEXT_ERR_NOACK;
728
729 SSL_set_tlsext_status_ocsp_resp(ssl, response_der, response_der_len);
730 return SSL_TLSEXT_ERR_OK;
731 }
732
733 #endif /* EXPERIMENTAL_OCSP */
734
735
736
737
738 /*************************************************
739 * Initialize for TLS *
740 *************************************************/
741
742 /* Called from both server and client code, to do preliminary initialization of
743 the library.
744
745 Arguments:
746 host connected host, if client; NULL if server
747 dhparam DH parameter file
748 certificate certificate file
749 privatekey private key
750 addr address if client; NULL if server (for some randomness)
751
752 Returns: OK/DEFER/FAIL
753 */
754
755 static int
756 tls_init(SSL_CTX **ctxp, host_item *host, uschar *dhparam, uschar *certificate,
757 uschar *privatekey,
758 #ifdef EXPERIMENTAL_OCSP
759 uschar *ocsp_file,
760 #endif
761 address_item *addr, tls_ext_ctx_cb ** cbp)
762 {
763 long init_options;
764 int rc;
765 BOOL okay;
766 tls_ext_ctx_cb *cbinfo;
767
768 cbinfo = store_malloc(sizeof(tls_ext_ctx_cb));
769 cbinfo->certificate = certificate;
770 cbinfo->privatekey = privatekey;
771 #ifdef EXPERIMENTAL_OCSP
772 cbinfo->ocsp_file = ocsp_file;
773 #endif
774 cbinfo->dhparam = dhparam;
775 cbinfo->host = host;
776
777 SSL_load_error_strings(); /* basic set up */
778 OpenSSL_add_ssl_algorithms();
779
780 #if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_SHA256)
781 /* SHA256 is becoming ever more popular. This makes sure it gets added to the
782 list of available digests. */
783 EVP_add_digest(EVP_sha256());
784 #endif
785
786 /* Create a context.
787 The OpenSSL docs in 1.0.1b have not been updated to clarify TLS variant
788 negotiation in the different methods; as far as I can tell, the only
789 *_{server,client}_method which allows negotiation is SSLv23, which exists even
790 when OpenSSL is built without SSLv2 support.
791 By disabling with openssl_options, we can let admins re-enable with the
792 existing knob. */
793
794 *ctxp = SSL_CTX_new((host == NULL)?
795 SSLv23_server_method() : SSLv23_client_method());
796
797 if (*ctxp == NULL) return tls_error(US"SSL_CTX_new", host, NULL);
798
799 /* It turns out that we need to seed the random number generator this early in
800 order to get the full complement of ciphers to work. It took me roughly a day
801 of work to discover this by experiment.
802
803 On systems that have /dev/urandom, SSL may automatically seed itself from
804 there. Otherwise, we have to make something up as best we can. Double check
805 afterwards. */
806
807 if (!RAND_status())
808 {
809 randstuff r;
810 gettimeofday(&r.tv, NULL);
811 r.p = getpid();
812
813 RAND_seed((uschar *)(&r), sizeof(r));
814 RAND_seed((uschar *)big_buffer, big_buffer_size);
815 if (addr != NULL) RAND_seed((uschar *)addr, sizeof(addr));
816
817 if (!RAND_status())
818 return tls_error(US"RAND_status", host,
819 US"unable to seed random number generator");
820 }
821
822 /* Set up the information callback, which outputs if debugging is at a suitable
823 level. */
824
825 SSL_CTX_set_info_callback(*ctxp, (void (*)())info_callback);
826
827 /* Automatically re-try reads/writes after renegotiation. */
828 (void) SSL_CTX_set_mode(*ctxp, SSL_MODE_AUTO_RETRY);
829
830 /* Apply administrator-supplied work-arounds.
831 Historically we applied just one requested option,
832 SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS, but when bug 994 requested a second, we
833 moved to an administrator-controlled list of options to specify and
834 grandfathered in the first one as the default value for "openssl_options".
835
836 No OpenSSL version number checks: the options we accept depend upon the
837 availability of the option value macros from OpenSSL. */
838
839 okay = tls_openssl_options_parse(openssl_options, &init_options);
840 if (!okay)
841 return tls_error(US"openssl_options parsing failed", host, NULL);
842
843 if (init_options)
844 {
845 DEBUG(D_tls) debug_printf("setting SSL CTX options: %#lx\n", init_options);
846 if (!(SSL_CTX_set_options(*ctxp, init_options)))
847 return tls_error(string_sprintf(
848 "SSL_CTX_set_option(%#lx)", init_options), host, NULL);
849 }
850 else
851 DEBUG(D_tls) debug_printf("no SSL CTX options to set\n");
852
853 /* Initialize with DH parameters if supplied */
854
855 if (!init_dh(*ctxp, dhparam, host)) return DEFER;
856
857 /* Set up certificate and key (and perhaps OCSP info) */
858
859 rc = tls_expand_session_files(*ctxp, cbinfo);
860 if (rc != OK) return rc;
861
862 /* If we need to handle SNI, do so */
863 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
864 if (host == NULL)
865 {
866 #ifdef EXPERIMENTAL_OCSP
867 /* We check ocsp_file, not ocsp_response, because we care about if
868 the option exists, not what the current expansion might be, as SNI might
869 change the certificate and OCSP file in use between now and the time the
870 callback is invoked. */
871 if (cbinfo->ocsp_file)
872 {
873 SSL_CTX_set_tlsext_status_cb(ctx, tls_stapling_cb);
874 SSL_CTX_set_tlsext_status_arg(ctx, cbinfo);
875 }
876 #endif
877 /* We always do this, so that $tls_sni is available even if not used in
878 tls_certificate */
879 SSL_CTX_set_tlsext_servername_callback(*ctxp, tls_servername_cb);
880 SSL_CTX_set_tlsext_servername_arg(*ctxp, cbinfo);
881 }
882 #endif
883
884 /* Set up the RSA callback */
885
886 SSL_CTX_set_tmp_rsa_callback(*ctxp, rsa_callback);
887
888 /* Finally, set the timeout, and we are done */
889
890 SSL_CTX_set_timeout(*ctxp, ssl_session_timeout);
891 DEBUG(D_tls) debug_printf("Initialized TLS\n");
892
893 *cbp = cbinfo;
894
895 return OK;
896 }
897
898
899
900
901 /*************************************************
902 * Get name of cipher in use *
903 *************************************************/
904
905 /*
906 Argument: pointer to an SSL structure for the connection
907 buffer to use for answer
908 size of buffer
909 pointer to number of bits for cipher
910 Returns: nothing
911 */
912
913 static void
914 construct_cipher_name(SSL *ssl, uschar *cipherbuf, int bsize, int *bits)
915 {
916 /* With OpenSSL 1.0.0a, this needs to be const but the documentation doesn't
917 yet reflect that. It should be a safe change anyway, even 0.9.8 versions have
918 the accessor functions use const in the prototype. */
919 const SSL_CIPHER *c;
920 uschar *ver;
921
922 switch (ssl->session->ssl_version)
923 {
924 case SSL2_VERSION:
925 ver = US"SSLv2";
926 break;
927
928 case SSL3_VERSION:
929 ver = US"SSLv3";
930 break;
931
932 case TLS1_VERSION:
933 ver = US"TLSv1";
934 break;
935
936 #ifdef TLS1_1_VERSION
937 case TLS1_1_VERSION:
938 ver = US"TLSv1.1";
939 break;
940 #endif
941
942 #ifdef TLS1_2_VERSION
943 case TLS1_2_VERSION:
944 ver = US"TLSv1.2";
945 break;
946 #endif
947
948 default:
949 ver = US"UNKNOWN";
950 }
951
952 c = (const SSL_CIPHER *) SSL_get_current_cipher(ssl);
953 SSL_CIPHER_get_bits(c, bits);
954
955 string_format(cipherbuf, bsize, "%s:%s:%u", ver,
956 SSL_CIPHER_get_name(c), *bits);
957
958 DEBUG(D_tls) debug_printf("Cipher: %s\n", cipherbuf);
959 }
960
961
962
963
964
965 /*************************************************
966 * Set up for verifying certificates *
967 *************************************************/
968
969 /* Called by both client and server startup
970
971 Arguments:
972 sctx SSL_CTX* to initialise
973 certs certs file or NULL
974 crl CRL file or NULL
975 host NULL in a server; the remote host in a client
976 optional TRUE if called from a server for a host in tls_try_verify_hosts;
977 otherwise passed as FALSE
978 client TRUE if called for client startup, FALSE for server startup
979
980 Returns: OK/DEFER/FAIL
981 */
982
983 static int
984 setup_certs(SSL_CTX *sctx, uschar *certs, uschar *crl, host_item *host, BOOL optional, BOOL client)
985 {
986 uschar *expcerts, *expcrl;
987
988 if (!expand_check(certs, US"tls_verify_certificates", &expcerts))
989 return DEFER;
990
991 if (expcerts != NULL)
992 {
993 struct stat statbuf;
994 if (!SSL_CTX_set_default_verify_paths(sctx))
995 return tls_error(US"SSL_CTX_set_default_verify_paths", host, NULL);
996
997 if (Ustat(expcerts, &statbuf) < 0)
998 {
999 log_write(0, LOG_MAIN|LOG_PANIC,
1000 "failed to stat %s for certificates", expcerts);
1001 return DEFER;
1002 }
1003 else
1004 {
1005 uschar *file, *dir;
1006 if ((statbuf.st_mode & S_IFMT) == S_IFDIR)
1007 { file = NULL; dir = expcerts; }
1008 else
1009 { file = expcerts; dir = NULL; }
1010
1011 /* If a certificate file is empty, the next function fails with an
1012 unhelpful error message. If we skip it, we get the correct behaviour (no
1013 certificates are recognized, but the error message is still misleading (it
1014 says no certificate was supplied.) But this is better. */
1015
1016 if ((file == NULL || statbuf.st_size > 0) &&
1017 !SSL_CTX_load_verify_locations(sctx, CS file, CS dir))
1018 return tls_error(US"SSL_CTX_load_verify_locations", host, NULL);
1019
1020 if (file != NULL)
1021 {
1022 SSL_CTX_set_client_CA_list(sctx, SSL_load_client_CA_file(CS file));
1023 }
1024 }
1025
1026 /* Handle a certificate revocation list. */
1027
1028 #if OPENSSL_VERSION_NUMBER > 0x00907000L
1029
1030 /* This bit of code is now the version supplied by Lars Mainka. (I have
1031 * merely reformatted it into the Exim code style.)
1032
1033 * "From here I changed the code to add support for multiple crl's
1034 * in pem format in one file or to support hashed directory entries in
1035 * pem format instead of a file. This method now uses the library function
1036 * X509_STORE_load_locations to add the CRL location to the SSL context.
1037 * OpenSSL will then handle the verify against CA certs and CRLs by
1038 * itself in the verify callback." */
1039
1040 if (!expand_check(crl, US"tls_crl", &expcrl)) return DEFER;
1041 if (expcrl != NULL && *expcrl != 0)
1042 {
1043 struct stat statbufcrl;
1044 if (Ustat(expcrl, &statbufcrl) < 0)
1045 {
1046 log_write(0, LOG_MAIN|LOG_PANIC,
1047 "failed to stat %s for certificates revocation lists", expcrl);
1048 return DEFER;
1049 }
1050 else
1051 {
1052 /* is it a file or directory? */
1053 uschar *file, *dir;
1054 X509_STORE *cvstore = SSL_CTX_get_cert_store(sctx);
1055 if ((statbufcrl.st_mode & S_IFMT) == S_IFDIR)
1056 {
1057 file = NULL;
1058 dir = expcrl;
1059 DEBUG(D_tls) debug_printf("SSL CRL value is a directory %s\n", dir);
1060 }
1061 else
1062 {
1063 file = expcrl;
1064 dir = NULL;
1065 DEBUG(D_tls) debug_printf("SSL CRL value is a file %s\n", file);
1066 }
1067 if (X509_STORE_load_locations(cvstore, CS file, CS dir) == 0)
1068 return tls_error(US"X509_STORE_load_locations", host, NULL);
1069
1070 /* setting the flags to check against the complete crl chain */
1071
1072 X509_STORE_set_flags(cvstore,
1073 X509_V_FLAG_CRL_CHECK|X509_V_FLAG_CRL_CHECK_ALL);
1074 }
1075 }
1076
1077 #endif /* OPENSSL_VERSION_NUMBER > 0x00907000L */
1078
1079 /* If verification is optional, don't fail if no certificate */
1080
1081 SSL_CTX_set_verify(sctx,
1082 SSL_VERIFY_PEER | (optional? 0 : SSL_VERIFY_FAIL_IF_NO_PEER_CERT),
1083 client ? verify_callback_client : verify_callback_server);
1084 }
1085
1086 return OK;
1087 }
1088
1089
1090
1091 /*************************************************
1092 * Start a TLS session in a server *
1093 *************************************************/
1094
1095 /* This is called when Exim is running as a server, after having received
1096 the STARTTLS command. It must respond to that command, and then negotiate
1097 a TLS session.
1098
1099 Arguments:
1100 require_ciphers allowed ciphers
1101
1102 Returns: OK on success
1103 DEFER for errors before the start of the negotiation
1104 FAIL for errors during the negotation; the server can't
1105 continue running.
1106 */
1107
1108 int
1109 tls_server_start(const uschar *require_ciphers)
1110 {
1111 int rc;
1112 uschar *expciphers;
1113 tls_ext_ctx_cb *cbinfo;
1114 static uschar cipherbuf[256];
1115
1116 /* Check for previous activation */
1117
1118 if (tls_in.active >= 0)
1119 {
1120 tls_error(US"STARTTLS received after TLS started", NULL, US"");
1121 smtp_printf("554 Already in TLS\r\n");
1122 return FAIL;
1123 }
1124
1125 /* Initialize the SSL library. If it fails, it will already have logged
1126 the error. */
1127
1128 rc = tls_init(&server_ctx, NULL, tls_dhparam, tls_certificate, tls_privatekey,
1129 #ifdef EXPERIMENTAL_OCSP
1130 tls_ocsp_file,
1131 #endif
1132 NULL, &server_static_cbinfo);
1133 if (rc != OK) return rc;
1134 cbinfo = server_static_cbinfo;
1135
1136 if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers))
1137 return FAIL;
1138
1139 /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they
1140 were historically separated by underscores. So that I can use either form in my
1141 tests, and also for general convenience, we turn underscores into hyphens here.
1142 */
1143
1144 if (expciphers != NULL)
1145 {
1146 uschar *s = expciphers;
1147 while (*s != 0) { if (*s == '_') *s = '-'; s++; }
1148 DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers);
1149 if (!SSL_CTX_set_cipher_list(server_ctx, CS expciphers))
1150 return tls_error(US"SSL_CTX_set_cipher_list", NULL, NULL);
1151 cbinfo->server_cipher_list = expciphers;
1152 }
1153
1154 /* If this is a host for which certificate verification is mandatory or
1155 optional, set up appropriately. */
1156
1157 tls_in.certificate_verified = FALSE;
1158 server_verify_callback_called = FALSE;
1159
1160 if (verify_check_host(&tls_verify_hosts) == OK)
1161 {
1162 rc = setup_certs(server_ctx, tls_verify_certificates, tls_crl, NULL, FALSE, FALSE);
1163 if (rc != OK) return rc;
1164 server_verify_optional = FALSE;
1165 }
1166 else if (verify_check_host(&tls_try_verify_hosts) == OK)
1167 {
1168 rc = setup_certs(server_ctx, tls_verify_certificates, tls_crl, NULL, TRUE, FALSE);
1169 if (rc != OK) return rc;
1170 server_verify_optional = TRUE;
1171 }
1172
1173 /* Prepare for new connection */
1174
1175 if ((server_ssl = SSL_new(server_ctx)) == NULL) return tls_error(US"SSL_new", NULL, NULL);
1176
1177 /* Warning: we used to SSL_clear(ssl) here, it was removed.
1178 *
1179 * With the SSL_clear(), we get strange interoperability bugs with
1180 * OpenSSL 1.0.1b and TLS1.1/1.2. It looks as though this may be a bug in
1181 * OpenSSL itself, as a clear should not lead to inability to follow protocols.
1182 *
1183 * The SSL_clear() call is to let an existing SSL* be reused, typically after
1184 * session shutdown. In this case, we have a brand new object and there's no
1185 * obvious reason to immediately clear it. I'm guessing that this was
1186 * originally added because of incomplete initialisation which the clear fixed,
1187 * in some historic release.
1188 */
1189
1190 /* Set context and tell client to go ahead, except in the case of TLS startup
1191 on connection, where outputting anything now upsets the clients and tends to
1192 make them disconnect. We need to have an explicit fflush() here, to force out
1193 the response. Other smtp_printf() calls do not need it, because in non-TLS
1194 mode, the fflush() happens when smtp_getc() is called. */
1195
1196 SSL_set_session_id_context(server_ssl, sid_ctx, Ustrlen(sid_ctx));
1197 if (!tls_in.on_connect)
1198 {
1199 smtp_printf("220 TLS go ahead\r\n");
1200 fflush(smtp_out);
1201 }
1202
1203 /* Now negotiate the TLS session. We put our own timer on it, since it seems
1204 that the OpenSSL library doesn't. */
1205
1206 SSL_set_wfd(server_ssl, fileno(smtp_out));
1207 SSL_set_rfd(server_ssl, fileno(smtp_in));
1208 SSL_set_accept_state(server_ssl);
1209
1210 DEBUG(D_tls) debug_printf("Calling SSL_accept\n");
1211
1212 sigalrm_seen = FALSE;
1213 if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
1214 rc = SSL_accept(server_ssl);
1215 alarm(0);
1216
1217 if (rc <= 0)
1218 {
1219 tls_error(US"SSL_accept", NULL, sigalrm_seen ? US"timed out" : NULL);
1220 if (ERR_get_error() == 0)
1221 log_write(0, LOG_MAIN,
1222 "TLS client disconnected cleanly (rejected our certificate?)");
1223 return FAIL;
1224 }
1225
1226 DEBUG(D_tls) debug_printf("SSL_accept was successful\n");
1227
1228 /* TLS has been set up. Adjust the input functions to read via TLS,
1229 and initialize things. */
1230
1231 construct_cipher_name(server_ssl, cipherbuf, sizeof(cipherbuf), &tls_in.bits);
1232 tls_in.cipher = cipherbuf;
1233
1234 DEBUG(D_tls)
1235 {
1236 uschar buf[2048];
1237 if (SSL_get_shared_ciphers(server_ssl, CS buf, sizeof(buf)) != NULL)
1238 debug_printf("Shared ciphers: %s\n", buf);
1239 }
1240
1241
1242 /* Only used by the server-side tls (tls_in), including tls_getc.
1243 Client-side (tls_out) reads (seem to?) go via
1244 smtp_read_response()/ip_recv().
1245 Hence no need to duplicate for _in and _out.
1246 */
1247 ssl_xfer_buffer = store_malloc(ssl_xfer_buffer_size);
1248 ssl_xfer_buffer_lwm = ssl_xfer_buffer_hwm = 0;
1249 ssl_xfer_eof = ssl_xfer_error = 0;
1250
1251 receive_getc = tls_getc;
1252 receive_ungetc = tls_ungetc;
1253 receive_feof = tls_feof;
1254 receive_ferror = tls_ferror;
1255 receive_smtp_buffered = tls_smtp_buffered;
1256
1257 tls_in.active = fileno(smtp_out);
1258 return OK;
1259 }
1260
1261
1262
1263
1264
1265 /*************************************************
1266 * Start a TLS session in a client *
1267 *************************************************/
1268
1269 /* Called from the smtp transport after STARTTLS has been accepted.
1270
1271 Argument:
1272 fd the fd of the connection
1273 host connected host (for messages)
1274 addr the first address
1275 dhparam DH parameter file
1276 certificate certificate file
1277 privatekey private key file
1278 sni TLS SNI to send to remote host
1279 verify_certs file for certificate verify
1280 crl file containing CRL
1281 require_ciphers list of allowed ciphers
1282 dh_min_bits minimum number of bits acceptable in server's DH prime
1283 (unused in OpenSSL)
1284 timeout startup timeout
1285
1286 Returns: OK on success
1287 FAIL otherwise - note that tls_error() will not give DEFER
1288 because this is not a server
1289 */
1290
1291 int
1292 tls_client_start(int fd, host_item *host, address_item *addr, uschar *dhparam,
1293 uschar *certificate, uschar *privatekey, uschar *sni,
1294 uschar *verify_certs, uschar *crl,
1295 uschar *require_ciphers, int dh_min_bits ARG_UNUSED, int timeout)
1296 {
1297 static uschar txt[256];
1298 uschar *expciphers;
1299 X509* server_cert;
1300 int rc;
1301 static uschar cipherbuf[256];
1302
1303 rc = tls_init(&client_ctx, host, dhparam, certificate, privatekey,
1304 #ifdef EXPERIMENTAL_OCSP
1305 NULL,
1306 #endif
1307 addr, &client_static_cbinfo);
1308 if (rc != OK) return rc;
1309
1310 tls_out.certificate_verified = FALSE;
1311 client_verify_callback_called = FALSE;
1312
1313 if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers))
1314 return FAIL;
1315
1316 /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they
1317 are separated by underscores. So that I can use either form in my tests, and
1318 also for general convenience, we turn underscores into hyphens here. */
1319
1320 if (expciphers != NULL)
1321 {
1322 uschar *s = expciphers;
1323 while (*s != 0) { if (*s == '_') *s = '-'; s++; }
1324 DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers);
1325 if (!SSL_CTX_set_cipher_list(client_ctx, CS expciphers))
1326 return tls_error(US"SSL_CTX_set_cipher_list", host, NULL);
1327 }
1328
1329 rc = setup_certs(client_ctx, verify_certs, crl, host, FALSE, TRUE);
1330 if (rc != OK) return rc;
1331
1332 if ((client_ssl = SSL_new(client_ctx)) == NULL) return tls_error(US"SSL_new", host, NULL);
1333 SSL_set_session_id_context(client_ssl, sid_ctx, Ustrlen(sid_ctx));
1334 SSL_set_fd(client_ssl, fd);
1335 SSL_set_connect_state(client_ssl);
1336
1337 if (sni)
1338 {
1339 if (!expand_check(sni, US"tls_sni", &tls_out.sni))
1340 return FAIL;
1341 if (tls_out.sni == NULL)
1342 {
1343 DEBUG(D_tls) debug_printf("Setting TLS SNI forced to fail, not sending\n");
1344 }
1345 else if (!Ustrlen(tls_out.sni))
1346 tls_out.sni = NULL;
1347 else
1348 {
1349 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
1350 DEBUG(D_tls) debug_printf("Setting TLS SNI \"%s\"\n", tls_out.sni);
1351 SSL_set_tlsext_host_name(client_ssl, tls_out.sni);
1352 #else
1353 DEBUG(D_tls)
1354 debug_printf("OpenSSL at build-time lacked SNI support, ignoring \"%s\"\n",
1355 tls_sni);
1356 #endif
1357 }
1358 }
1359
1360 /* There doesn't seem to be a built-in timeout on connection. */
1361
1362 DEBUG(D_tls) debug_printf("Calling SSL_connect\n");
1363 sigalrm_seen = FALSE;
1364 alarm(timeout);
1365 rc = SSL_connect(client_ssl);
1366 alarm(0);
1367
1368 if (rc <= 0)
1369 return tls_error(US"SSL_connect", host, sigalrm_seen ? US"timed out" : NULL);
1370
1371 DEBUG(D_tls) debug_printf("SSL_connect succeeded\n");
1372
1373 /* Beware anonymous ciphers which lead to server_cert being NULL */
1374 server_cert = SSL_get_peer_certificate (client_ssl);
1375 if (server_cert)
1376 {
1377 tls_out.peerdn = US X509_NAME_oneline(X509_get_subject_name(server_cert),
1378 CS txt, sizeof(txt));
1379 tls_out.peerdn = txt;
1380 }
1381 else
1382 tls_out.peerdn = NULL;
1383
1384 construct_cipher_name(client_ssl, cipherbuf, sizeof(cipherbuf), &tls_out.bits);
1385 tls_out.cipher = cipherbuf;
1386
1387 tls_out.active = fd;
1388 return OK;
1389 }
1390
1391
1392
1393
1394
1395 /*************************************************
1396 * TLS version of getc *
1397 *************************************************/
1398
1399 /* This gets the next byte from the TLS input buffer. If the buffer is empty,
1400 it refills the buffer via the SSL reading function.
1401
1402 Arguments: none
1403 Returns: the next character or EOF
1404
1405 Only used by the server-side TLS.
1406 */
1407
1408 int
1409 tls_getc(void)
1410 {
1411 if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm)
1412 {
1413 int error;
1414 int inbytes;
1415
1416 DEBUG(D_tls) debug_printf("Calling SSL_read(%p, %p, %u)\n", server_ssl,
1417 ssl_xfer_buffer, ssl_xfer_buffer_size);
1418
1419 if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
1420 inbytes = SSL_read(server_ssl, CS ssl_xfer_buffer, ssl_xfer_buffer_size);
1421 error = SSL_get_error(server_ssl, inbytes);
1422 alarm(0);
1423
1424 /* SSL_ERROR_ZERO_RETURN appears to mean that the SSL session has been
1425 closed down, not that the socket itself has been closed down. Revert to
1426 non-SSL handling. */
1427
1428 if (error == SSL_ERROR_ZERO_RETURN)
1429 {
1430 DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n");
1431
1432 receive_getc = smtp_getc;
1433 receive_ungetc = smtp_ungetc;
1434 receive_feof = smtp_feof;
1435 receive_ferror = smtp_ferror;
1436 receive_smtp_buffered = smtp_buffered;
1437
1438 SSL_free(server_ssl);
1439 server_ssl = NULL;
1440 tls_in.active = -1;
1441 tls_in.bits = 0;
1442 tls_in.cipher = NULL;
1443 tls_in.peerdn = NULL;
1444 tls_in.sni = NULL;
1445
1446 return smtp_getc();
1447 }
1448
1449 /* Handle genuine errors */
1450
1451 else if (error == SSL_ERROR_SSL)
1452 {
1453 ERR_error_string(ERR_get_error(), ssl_errstring);
1454 log_write(0, LOG_MAIN, "TLS error (SSL_read): %s", ssl_errstring);
1455 ssl_xfer_error = 1;
1456 return EOF;
1457 }
1458
1459 else if (error != SSL_ERROR_NONE)
1460 {
1461 DEBUG(D_tls) debug_printf("Got SSL error %d\n", error);
1462 ssl_xfer_error = 1;
1463 return EOF;
1464 }
1465
1466 #ifndef DISABLE_DKIM
1467 dkim_exim_verify_feed(ssl_xfer_buffer, inbytes);
1468 #endif
1469 ssl_xfer_buffer_hwm = inbytes;
1470 ssl_xfer_buffer_lwm = 0;
1471 }
1472
1473 /* Something in the buffer; return next uschar */
1474
1475 return ssl_xfer_buffer[ssl_xfer_buffer_lwm++];
1476 }
1477
1478
1479
1480 /*************************************************
1481 * Read bytes from TLS channel *
1482 *************************************************/
1483
1484 /*
1485 Arguments:
1486 buff buffer of data
1487 len size of buffer
1488
1489 Returns: the number of bytes read
1490 -1 after a failed read
1491
1492 Only used by the client-side TLS.
1493 */
1494
1495 int
1496 tls_read(BOOL is_server, uschar *buff, size_t len)
1497 {
1498 SSL *ssl = is_server ? server_ssl : client_ssl;
1499 int inbytes;
1500 int error;
1501
1502 DEBUG(D_tls) debug_printf("Calling SSL_read(%p, %p, %u)\n", ssl,
1503 buff, (unsigned int)len);
1504
1505 inbytes = SSL_read(ssl, CS buff, len);
1506 error = SSL_get_error(ssl, inbytes);
1507
1508 if (error == SSL_ERROR_ZERO_RETURN)
1509 {
1510 DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n");
1511 return -1;
1512 }
1513 else if (error != SSL_ERROR_NONE)
1514 {
1515 return -1;
1516 }
1517
1518 return inbytes;
1519 }
1520
1521
1522
1523
1524
1525 /*************************************************
1526 * Write bytes down TLS channel *
1527 *************************************************/
1528
1529 /*
1530 Arguments:
1531 is_server channel specifier
1532 buff buffer of data
1533 len number of bytes
1534
1535 Returns: the number of bytes after a successful write,
1536 -1 after a failed write
1537
1538 Used by both server-side and client-side TLS.
1539 */
1540
1541 int
1542 tls_write(BOOL is_server, const uschar *buff, size_t len)
1543 {
1544 int outbytes;
1545 int error;
1546 int left = len;
1547 SSL *ssl = is_server ? server_ssl : client_ssl;
1548
1549 DEBUG(D_tls) debug_printf("tls_do_write(%p, %d)\n", buff, left);
1550 while (left > 0)
1551 {
1552 DEBUG(D_tls) debug_printf("SSL_write(SSL, %p, %d)\n", buff, left);
1553 outbytes = SSL_write(ssl, CS buff, left);
1554 error = SSL_get_error(ssl, outbytes);
1555 DEBUG(D_tls) debug_printf("outbytes=%d error=%d\n", outbytes, error);
1556 switch (error)
1557 {
1558 case SSL_ERROR_SSL:
1559 ERR_error_string(ERR_get_error(), ssl_errstring);
1560 log_write(0, LOG_MAIN, "TLS error (SSL_write): %s", ssl_errstring);
1561 return -1;
1562
1563 case SSL_ERROR_NONE:
1564 left -= outbytes;
1565 buff += outbytes;
1566 break;
1567
1568 case SSL_ERROR_ZERO_RETURN:
1569 log_write(0, LOG_MAIN, "SSL channel closed on write");
1570 return -1;
1571
1572 case SSL_ERROR_SYSCALL:
1573 log_write(0, LOG_MAIN, "SSL_write: (from %s) syscall: %s",
1574 sender_fullhost ? sender_fullhost : US"<unknown>",
1575 strerror(errno));
1576
1577 default:
1578 log_write(0, LOG_MAIN, "SSL_write error %d", error);
1579 return -1;
1580 }
1581 }
1582 return len;
1583 }
1584
1585
1586
1587 /*************************************************
1588 * Close down a TLS session *
1589 *************************************************/
1590
1591 /* This is also called from within a delivery subprocess forked from the
1592 daemon, to shut down the TLS library, without actually doing a shutdown (which
1593 would tamper with the SSL session in the parent process).
1594
1595 Arguments: TRUE if SSL_shutdown is to be called
1596 Returns: nothing
1597
1598 Used by both server-side and client-side TLS.
1599 */
1600
1601 void
1602 tls_close(BOOL is_server, BOOL shutdown)
1603 {
1604 SSL **sslp = is_server ? &server_ssl : &client_ssl;
1605 int *fdp = is_server ? &tls_in.active : &tls_out.active;
1606
1607 if (*fdp < 0) return; /* TLS was not active */
1608
1609 if (shutdown)
1610 {
1611 DEBUG(D_tls) debug_printf("tls_close(): shutting down SSL\n");
1612 SSL_shutdown(*sslp);
1613 }
1614
1615 SSL_free(*sslp);
1616 *sslp = NULL;
1617
1618 *fdp = -1;
1619 }
1620
1621
1622
1623
1624 /*************************************************
1625 * Let tls_require_ciphers be checked at startup *
1626 *************************************************/
1627
1628 /* The tls_require_ciphers option, if set, must be something which the
1629 library can parse.
1630
1631 Returns: NULL on success, or error message
1632 */
1633
1634 uschar *
1635 tls_validate_require_cipher(void)
1636 {
1637 SSL_CTX *ctx;
1638 uschar *s, *expciphers, *err;
1639
1640 /* this duplicates from tls_init(), we need a better "init just global
1641 state, for no specific purpose" singleton function of our own */
1642
1643 SSL_load_error_strings();
1644 OpenSSL_add_ssl_algorithms();
1645 #if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_SHA256)
1646 /* SHA256 is becoming ever more popular. This makes sure it gets added to the
1647 list of available digests. */
1648 EVP_add_digest(EVP_sha256());
1649 #endif
1650
1651 if (!(tls_require_ciphers && *tls_require_ciphers))
1652 return NULL;
1653
1654 if (!expand_check(tls_require_ciphers, US"tls_require_ciphers", &expciphers))
1655 return US"failed to expand tls_require_ciphers";
1656
1657 if (!(expciphers && *expciphers))
1658 return NULL;
1659
1660 /* normalisation ripped from above */
1661 s = expciphers;
1662 while (*s != 0) { if (*s == '_') *s = '-'; s++; }
1663
1664 err = NULL;
1665
1666 ctx = SSL_CTX_new(SSLv23_server_method());
1667 if (!ctx)
1668 {
1669 ERR_error_string(ERR_get_error(), ssl_errstring);
1670 return string_sprintf("SSL_CTX_new() failed: %s", ssl_errstring);
1671 }
1672
1673 DEBUG(D_tls)
1674 debug_printf("tls_require_ciphers expands to \"%s\"\n", expciphers);
1675
1676 if (!SSL_CTX_set_cipher_list(ctx, CS expciphers))
1677 {
1678 ERR_error_string(ERR_get_error(), ssl_errstring);
1679 err = string_sprintf("SSL_CTX_set_cipher_list(%s) failed", expciphers);
1680 }
1681
1682 SSL_CTX_free(ctx);
1683
1684 return err;
1685 }
1686
1687
1688
1689
1690 /*************************************************
1691 * Report the library versions. *
1692 *************************************************/
1693
1694 /* There have historically been some issues with binary compatibility in
1695 OpenSSL libraries; if Exim (like many other applications) is built against
1696 one version of OpenSSL but the run-time linker picks up another version,
1697 it can result in serious failures, including crashing with a SIGSEGV. So
1698 report the version found by the compiler and the run-time version.
1699
1700 Arguments: a FILE* to print the results to
1701 Returns: nothing
1702 */
1703
1704 void
1705 tls_version_report(FILE *f)
1706 {
1707 fprintf(f, "Library version: OpenSSL: Compile: %s\n"
1708 " Runtime: %s\n",
1709 OPENSSL_VERSION_TEXT,
1710 SSLeay_version(SSLEAY_VERSION));
1711 }
1712
1713
1714
1715
1716 /*************************************************
1717 * Random number generation *
1718 *************************************************/
1719
1720 /* Pseudo-random number generation. The result is not expected to be
1721 cryptographically strong but not so weak that someone will shoot themselves
1722 in the foot using it as a nonce in input in some email header scheme or
1723 whatever weirdness they'll twist this into. The result should handle fork()
1724 and avoid repeating sequences. OpenSSL handles that for us.
1725
1726 Arguments:
1727 max range maximum
1728 Returns a random number in range [0, max-1]
1729 */
1730
1731 int
1732 vaguely_random_number(int max)
1733 {
1734 unsigned int r;
1735 int i, needed_len;
1736 uschar *p;
1737 uschar smallbuf[sizeof(r)];
1738
1739 if (max <= 1)
1740 return 0;
1741
1742 /* OpenSSL auto-seeds from /dev/random, etc, but this a double-check. */
1743 if (!RAND_status())
1744 {
1745 randstuff r;
1746 gettimeofday(&r.tv, NULL);
1747 r.p = getpid();
1748
1749 RAND_seed((uschar *)(&r), sizeof(r));
1750 }
1751 /* We're after pseudo-random, not random; if we still don't have enough data
1752 in the internal PRNG then our options are limited. We could sleep and hope
1753 for entropy to come along (prayer technique) but if the system is so depleted
1754 in the first place then something is likely to just keep taking it. Instead,
1755 we'll just take whatever little bit of pseudo-random we can still manage to
1756 get. */
1757
1758 needed_len = sizeof(r);
1759 /* Don't take 8 times more entropy than needed if int is 8 octets and we were
1760 asked for a number less than 10. */
1761 for (r = max, i = 0; r; ++i)
1762 r >>= 1;
1763 i = (i + 7) / 8;
1764 if (i < needed_len)
1765 needed_len = i;
1766
1767 /* We do not care if crypto-strong */
1768 i = RAND_pseudo_bytes(smallbuf, needed_len);
1769 if (i < 0)
1770 {
1771 DEBUG(D_all)
1772 debug_printf("OpenSSL RAND_pseudo_bytes() not supported by RAND method, using fallback.\n");
1773 return vaguely_random_number_fallback(max);
1774 }
1775
1776 r = 0;
1777 for (p = smallbuf; needed_len; --needed_len, ++p)
1778 {
1779 r *= 256;
1780 r += *p;
1781 }
1782
1783 /* We don't particularly care about weighted results; if someone wants
1784 smooth distribution and cares enough then they should submit a patch then. */
1785 return r % max;
1786 }
1787
1788
1789
1790
1791 /*************************************************
1792 * OpenSSL option parse *
1793 *************************************************/
1794
1795 /* Parse one option for tls_openssl_options_parse below
1796
1797 Arguments:
1798 name one option name
1799 value place to store a value for it
1800 Returns success or failure in parsing
1801 */
1802
1803 struct exim_openssl_option {
1804 uschar *name;
1805 long value;
1806 };
1807 /* We could use a macro to expand, but we need the ifdef and not all the
1808 options document which version they were introduced in. Policylet: include
1809 all options unless explicitly for DTLS, let the administrator choose which
1810 to apply.
1811
1812 This list is current as of:
1813 ==> 1.0.1b <== */
1814 static struct exim_openssl_option exim_openssl_options[] = {
1815 /* KEEP SORTED ALPHABETICALLY! */
1816 #ifdef SSL_OP_ALL
1817 { US"all", SSL_OP_ALL },
1818 #endif
1819 #ifdef SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
1820 { US"allow_unsafe_legacy_renegotiation", SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION },
1821 #endif
1822 #ifdef SSL_OP_CIPHER_SERVER_PREFERENCE
1823 { US"cipher_server_preference", SSL_OP_CIPHER_SERVER_PREFERENCE },
1824 #endif
1825 #ifdef SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
1826 { US"dont_insert_empty_fragments", SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS },
1827 #endif
1828 #ifdef SSL_OP_EPHEMERAL_RSA
1829 { US"ephemeral_rsa", SSL_OP_EPHEMERAL_RSA },
1830 #endif
1831 #ifdef SSL_OP_LEGACY_SERVER_CONNECT
1832 { US"legacy_server_connect", SSL_OP_LEGACY_SERVER_CONNECT },
1833 #endif
1834 #ifdef SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
1835 { US"microsoft_big_sslv3_buffer", SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER },
1836 #endif
1837 #ifdef SSL_OP_MICROSOFT_SESS_ID_BUG
1838 { US"microsoft_sess_id_bug", SSL_OP_MICROSOFT_SESS_ID_BUG },
1839 #endif
1840 #ifdef SSL_OP_MSIE_SSLV2_RSA_PADDING
1841 { US"msie_sslv2_rsa_padding", SSL_OP_MSIE_SSLV2_RSA_PADDING },
1842 #endif
1843 #ifdef SSL_OP_NETSCAPE_CHALLENGE_BUG
1844 { US"netscape_challenge_bug", SSL_OP_NETSCAPE_CHALLENGE_BUG },
1845 #endif
1846 #ifdef SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
1847 { US"netscape_reuse_cipher_change_bug", SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG },
1848 #endif
1849 #ifdef SSL_OP_NO_COMPRESSION
1850 { US"no_compression", SSL_OP_NO_COMPRESSION },
1851 #endif
1852 #ifdef SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
1853 { US"no_session_resumption_on_renegotiation", SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION },
1854 #endif
1855 #ifdef SSL_OP_NO_SSLv2
1856 { US"no_sslv2", SSL_OP_NO_SSLv2 },
1857 #endif
1858 #ifdef SSL_OP_NO_SSLv3
1859 { US"no_sslv3", SSL_OP_NO_SSLv3 },
1860 #endif
1861 #ifdef SSL_OP_NO_TICKET
1862 { US"no_ticket", SSL_OP_NO_TICKET },
1863 #endif
1864 #ifdef SSL_OP_NO_TLSv1
1865 { US"no_tlsv1", SSL_OP_NO_TLSv1 },
1866 #endif
1867 #ifdef SSL_OP_NO_TLSv1_1
1868 #if SSL_OP_NO_TLSv1_1 == 0x00000400L
1869 /* Error in chosen value in 1.0.1a; see first item in CHANGES for 1.0.1b */
1870 #warning OpenSSL 1.0.1a uses a bad value for SSL_OP_NO_TLSv1_1, ignoring
1871 #else
1872 { US"no_tlsv1_1", SSL_OP_NO_TLSv1_1 },
1873 #endif
1874 #endif
1875 #ifdef SSL_OP_NO_TLSv1_2
1876 { US"no_tlsv1_2", SSL_OP_NO_TLSv1_2 },
1877 #endif
1878 #ifdef SSL_OP_SINGLE_DH_USE
1879 { US"single_dh_use", SSL_OP_SINGLE_DH_USE },
1880 #endif
1881 #ifdef SSL_OP_SINGLE_ECDH_USE
1882 { US"single_ecdh_use", SSL_OP_SINGLE_ECDH_USE },
1883 #endif
1884 #ifdef SSL_OP_SSLEAY_080_CLIENT_DH_BUG
1885 { US"ssleay_080_client_dh_bug", SSL_OP_SSLEAY_080_CLIENT_DH_BUG },
1886 #endif
1887 #ifdef SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
1888 { US"sslref2_reuse_cert_type_bug", SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG },
1889 #endif
1890 #ifdef SSL_OP_TLS_BLOCK_PADDING_BUG
1891 { US"tls_block_padding_bug", SSL_OP_TLS_BLOCK_PADDING_BUG },
1892 #endif
1893 #ifdef SSL_OP_TLS_D5_BUG
1894 { US"tls_d5_bug", SSL_OP_TLS_D5_BUG },
1895 #endif
1896 #ifdef SSL_OP_TLS_ROLLBACK_BUG
1897 { US"tls_rollback_bug", SSL_OP_TLS_ROLLBACK_BUG },
1898 #endif
1899 };
1900 static int exim_openssl_options_size =
1901 sizeof(exim_openssl_options)/sizeof(struct exim_openssl_option);
1902
1903
1904 static BOOL
1905 tls_openssl_one_option_parse(uschar *name, long *value)
1906 {
1907 int first = 0;
1908 int last = exim_openssl_options_size;
1909 while (last > first)
1910 {
1911 int middle = (first + last)/2;
1912 int c = Ustrcmp(name, exim_openssl_options[middle].name);
1913 if (c == 0)
1914 {
1915 *value = exim_openssl_options[middle].value;
1916 return TRUE;
1917 }
1918 else if (c > 0)
1919 first = middle + 1;
1920 else
1921 last = middle;
1922 }
1923 return FALSE;
1924 }
1925
1926
1927
1928
1929 /*************************************************
1930 * OpenSSL option parsing logic *
1931 *************************************************/
1932
1933 /* OpenSSL has a number of compatibility options which an administrator might
1934 reasonably wish to set. Interpret a list similarly to decode_bits(), so that
1935 we look like log_selector.
1936
1937 Arguments:
1938 option_spec the administrator-supplied string of options
1939 results ptr to long storage for the options bitmap
1940 Returns success or failure
1941 */
1942
1943 BOOL
1944 tls_openssl_options_parse(uschar *option_spec, long *results)
1945 {
1946 long result, item;
1947 uschar *s, *end;
1948 uschar keep_c;
1949 BOOL adding, item_parsed;
1950
1951 result = 0L;
1952 /* Prior to 4.80 we or'd in SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS; removed
1953 * from default because it increases BEAST susceptibility. */
1954 #ifdef SSL_OP_NO_SSLv2
1955 result |= SSL_OP_NO_SSLv2;
1956 #endif
1957
1958 if (option_spec == NULL)
1959 {
1960 *results = result;
1961 return TRUE;
1962 }
1963
1964 for (s=option_spec; *s != '\0'; /**/)
1965 {
1966 while (isspace(*s)) ++s;
1967 if (*s == '\0')
1968 break;
1969 if (*s != '+' && *s != '-')
1970 {
1971 DEBUG(D_tls) debug_printf("malformed openssl option setting: "
1972 "+ or - expected but found \"%s\"\n", s);
1973 return FALSE;
1974 }
1975 adding = *s++ == '+';
1976 for (end = s; (*end != '\0') && !isspace(*end); ++end) /**/ ;
1977 keep_c = *end;
1978 *end = '\0';
1979 item_parsed = tls_openssl_one_option_parse(s, &item);
1980 if (!item_parsed)
1981 {
1982 DEBUG(D_tls) debug_printf("openssl option setting unrecognised: \"%s\"\n", s);
1983 return FALSE;
1984 }
1985 DEBUG(D_tls) debug_printf("openssl option, %s from %lx: %lx (%s)\n",
1986 adding ? "adding" : "removing", result, item, s);
1987 if (adding)
1988 result |= item;
1989 else
1990 result &= ~item;
1991 *end = keep_c;
1992 s = end;
1993 }
1994
1995 *results = result;
1996 return TRUE;
1997 }
1998
1999 /* End of tls-openssl.c */