src/src/tls-openssl.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2016 */
   6 /* See the file NOTICE for conditions of use and distribution. */
   7
   8 /* Portions Copyright (c) The OpenSSL Project 1999 */
   9
  10 /* This module provides the TLS (aka SSL) support for Exim using the OpenSSL
  11 library. It is #included into the tls.c file when that library is used. The
  12 code herein is based on a patch that was originally contributed by Steve
  13 Haslam. It was adapted from stunnel, a GPL program by Michal Trojnara.
  14
  15 No cryptographic code is included in Exim. All this module does is to call
  16 functions from the OpenSSL library. */
  17
  18
  19 /* Heading stuff */
  20
  21 #include <openssl/lhash.h>
  22 #include <openssl/ssl.h>
  23 #include <openssl/err.h>
  24 #include <openssl/rand.h>
  25 #ifndef OPENSSL_NO_ECDH
  26 # include <openssl/ec.h>
  27 #endif
  28 #ifndef DISABLE_OCSP
  29 # include <openssl/ocsp.h>
  30 #endif
  31 #ifdef EXPERIMENTAL_DANE
  32 # include <danessl.h>
  33 #endif
  34
  35
  36 #ifndef DISABLE_OCSP
  37 # define EXIM_OCSP_SKEW_SECONDS (300L)
  38 # define EXIM_OCSP_MAX_AGE (-1L)
  39 #endif
  40
  41 #if OPENSSL_VERSION_NUMBER >= 0x0090806fL && !defined(OPENSSL_NO_TLSEXT)
  42 # define EXIM_HAVE_OPENSSL_TLSEXT
  43 #endif
  44 #if OPENSSL_VERSION_NUMBER >= 0x00908000L
  45 # define EXIM_HAVE_RSA_GENKEY_EX
  46 #endif
  47 #if OPENSSL_VERSION_NUMBER >= 0x10100000L
  48 # define EXIM_HAVE_OCSP_RESP_COUNT
  49 #else
  50 # define EXIM_HAVE_EPHEM_RSA_KEX
  51 # define EXIM_HAVE_RAND_PSEUDO
  52 #endif
  53 #if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_SHA256)
  54 # define EXIM_HAVE_SHA256
  55 #endif
  56
  57 /*
  58  * X509_check_host provides sane certificate hostname checking, but was added
  59  * to OpenSSL late, after other projects forked off the code-base.  So in
  60  * addition to guarding against the base version number, beware that LibreSSL
  61  * does not (at this time) support this function.
  62  *
  63  * If LibreSSL gains a different API, perhaps via libtls, then we'll probably
  64  * opt to disentangle and ask a LibreSSL user to provide glue for a third
  65  * crypto provider for libtls instead of continuing to tie the OpenSSL glue
  66  * into even twistier knots.  If LibreSSL gains the same API, we can just
  67  * change this guard and punt the issue for a while longer.
  68  */
  69 #ifndef LIBRESSL_VERSION_NUMBER
  70 # if OPENSSL_VERSION_NUMBER >= 0x010100000L
  71 #  define EXIM_HAVE_OPENSSL_CHECKHOST
  72 # endif
  73 # if OPENSSL_VERSION_NUMBER >= 0x010000000L \
  74     && (OPENSSL_VERSION_NUMBER & 0x0000ff000L) >= 0x000002000L
  75 #  define EXIM_HAVE_OPENSSL_CHECKHOST
  76 # endif
  77 #endif
  78
  79 #if !defined(LIBRESSL_VERSION_NUMBER) \
  80     || LIBRESSL_VERSION_NUMBER >= 0x20010000L
  81 # if !defined(OPENSSL_NO_ECDH)
  82 #  if OPENSSL_VERSION_NUMBER >= 0x0090800fL
  83 #   define EXIM_HAVE_ECDH
  84 #  endif
  85 #  if OPENSSL_VERSION_NUMBER >= 0x10002000L
  86 #   define EXIM_HAVE_OPENSSL_EC_NIST2NID
  87 #  endif
  88 # endif
  89 #endif
  90
  91 #if !defined(EXIM_HAVE_OPENSSL_TLSEXT) && !defined(DISABLE_OCSP)
  92 # warning "OpenSSL library version too old; define DISABLE_OCSP in Makefile"
  93 # define DISABLE_OCSP
  94 #endif
  95
  96 /* Structure for collecting random data for seeding. */
  97
  98 typedef struct randstuff {
  99   struct timeval tv;
 100   pid_t          p;
 101 } randstuff;
 102
 103 /* Local static variables */
 104
 105 static BOOL client_verify_callback_called = FALSE;
 106 static BOOL server_verify_callback_called = FALSE;
 107 static const uschar *sid_ctx = US"exim";
 108
 109 /* We have three different contexts to care about.
 110
 111 Simple case: client, `client_ctx`
 112  As a client, we can be doing a callout or cut-through delivery while receiving
 113  a message.  So we have a client context, which should have options initialised
 114  from the SMTP Transport.
 115
 116 Server:
 117  There are two cases: with and without ServerNameIndication from the client.
 118  Given TLS SNI, we can be using different keys, certs and various other
 119  configuration settings, because they're re-expanded with $tls_sni set.  This
 120  allows vhosting with TLS.  This SNI is sent in the handshake.
 121  A client might not send SNI, so we need a fallback, and an initial setup too.
 122  So as a server, we start out using `server_ctx`.
 123  If SNI is sent by the client, then we as server, mid-negotiation, try to clone
 124  `server_sni` from `server_ctx` and then initialise settings by re-expanding
 125  configuration.
 126 */
 127
 128 static SSL_CTX *client_ctx = NULL;
 129 static SSL_CTX *server_ctx = NULL;
 130 static SSL     *client_ssl = NULL;
 131 static SSL     *server_ssl = NULL;
 132
 133 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
 134 static SSL_CTX *server_sni = NULL;
 135 #endif
 136
 137 static char ssl_errstring[256];
 138
 139 static int  ssl_session_timeout = 200;
 140 static BOOL client_verify_optional = FALSE;
 141 static BOOL server_verify_optional = FALSE;
 142
 143 static BOOL reexpand_tls_files_for_sni = FALSE;
 144
 145
 146 typedef struct tls_ext_ctx_cb {
 147   uschar *certificate;
 148   uschar *privatekey;
 149 #ifndef DISABLE_OCSP
 150   BOOL is_server;
 151   STACK_OF(X509) *verify_stack;         /* chain for verifying the proof */
 152   union {
 153     struct {
 154       uschar        *file;
 155       uschar        *file_expanded;
 156       OCSP_RESPONSE *response;
 157     } server;
 158     struct {
 159       X509_STORE    *verify_store;      /* non-null if status requested */
 160       BOOL          verify_required;
 161     } client;
 162   } u_ocsp;
 163 #endif
 164   uschar *dhparam;
 165   /* these are cached from first expand */
 166   uschar *server_cipher_list;
 167   /* only passed down to tls_error: */
 168   host_item *host;
 169   const uschar * verify_cert_hostnames;
 170 #ifndef DISABLE_EVENT
 171   uschar * event_action;
 172 #endif
 173 } tls_ext_ctx_cb;
 174
 175 /* should figure out a cleanup of API to handle state preserved per
 176 implementation, for various reasons, which can be void * in the APIs.
 177 For now, we hack around it. */
 178 tls_ext_ctx_cb *client_static_cbinfo = NULL;
 179 tls_ext_ctx_cb *server_static_cbinfo = NULL;
 180
 181 static int
 182 setup_certs(SSL_CTX *sctx, uschar *certs, uschar *crl, host_item *host, BOOL optional,
 183     int (*cert_vfy_cb)(int, X509_STORE_CTX *) );
 184
 185 /* Callbacks */
 186 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
 187 static int tls_servername_cb(SSL *s, int *ad ARG_UNUSED, void *arg);
 188 #endif
 189 #ifndef DISABLE_OCSP
 190 static int tls_server_stapling_cb(SSL *s, void *arg);
 191 #endif
 192
 193
 194 /*************************************************
 195 *               Handle TLS error                 *
 196 *************************************************/
 197
 198 /* Called from lots of places when errors occur before actually starting to do
 199 the TLS handshake, that is, while the session is still in clear. Always returns
 200 DEFER for a server and FAIL for a client so that most calls can use "return
 201 tls_error(...)" to do this processing and then give an appropriate return. A
 202 single function is used for both server and client, because it is called from
 203 some shared functions.
 204
 205 Argument:
 206   prefix    text to include in the logged error
 207   host      NULL if setting up a server;
 208             the connected host if setting up a client
 209   msg       error message or NULL if we should ask OpenSSL
 210
 211 Returns:    OK/DEFER/FAIL
 212 */
 213
 214 static int
 215 tls_error(uschar * prefix, const host_item * host, uschar * msg)
 216 {
 217 if (!msg)
 218   {
 219   ERR_error_string(ERR_get_error(), ssl_errstring);
 220   msg = (uschar *)ssl_errstring;
 221   }
 222
 223 if (host)
 224   {
 225   log_write(0, LOG_MAIN, "H=%s [%s] TLS error on connection (%s): %s",
 226     host->name, host->address, prefix, msg);
 227   return FAIL;
 228   }
 229 else
 230   {
 231   uschar *conn_info = smtp_get_connection_info();
 232   if (Ustrncmp(conn_info, US"SMTP ", 5) == 0)
 233     conn_info += 5;
 234   /* I'd like to get separated H= here, but too hard for now */
 235   log_write(0, LOG_MAIN, "TLS error on %s (%s): %s",
 236     conn_info, prefix, msg);
 237   return DEFER;
 238   }
 239 }
 240
 241
 242
 243 #ifdef EXIM_HAVE_EPHEM_RSA_KEX
 244 /*************************************************
 245 *        Callback to generate RSA key            *
 246 *************************************************/
 247
 248 /*
 249 Arguments:
 250   s          SSL connection
 251   export     not used
 252   keylength  keylength
 253
 254 Returns:     pointer to generated key
 255 */
 256
 257 static RSA *
 258 rsa_callback(SSL *s, int export, int keylength)
 259 {
 260 RSA *rsa_key;
 261 #ifdef EXIM_HAVE_RSA_GENKEY_EX
 262 BIGNUM *bn = BN_new();
 263 #endif
 264
 265 export = export;     /* Shut picky compilers up */
 266 DEBUG(D_tls) debug_printf("Generating %d bit RSA key...\n", keylength);
 267
 268 #ifdef EXIM_HAVE_RSA_GENKEY_EX
 269 if (  !BN_set_word(bn, (unsigned long)RSA_F4)
 270    || !(rsa_key = RSA_new())
 271    || !RSA_generate_key_ex(rsa_key, keylength, bn, NULL)
 272    )
 273 #else
 274 if (!(rsa_key = RSA_generate_key(keylength, RSA_F4, NULL, NULL)))
 275 #endif
 276
 277   {
 278   ERR_error_string(ERR_get_error(), ssl_errstring);
 279   log_write(0, LOG_MAIN|LOG_PANIC, "TLS error (RSA_generate_key): %s",
 280     ssl_errstring);
 281   return NULL;
 282   }
 283 return rsa_key;
 284 }
 285 #endif
 286
 287
 288
 289 /* Extreme debug
 290 #ifndef DISABLE_OCSP
 291 void
 292 x509_store_dump_cert_s_names(X509_STORE * store)
 293 {
 294 STACK_OF(X509_OBJECT) * roots= store->objs;
 295 int i;
 296 static uschar name[256];
 297
 298 for(i= 0; i<sk_X509_OBJECT_num(roots); i++)
 299   {
 300   X509_OBJECT * tmp_obj= sk_X509_OBJECT_value(roots, i);
 301   if(tmp_obj->type == X509_LU_X509)
 302     {
 303     X509 * current_cert= tmp_obj->data.x509;
 304     X509_NAME_oneline(X509_get_subject_name(current_cert), CS name, sizeof(name));
 305         name[sizeof(name)-1] = '\0';
 306     debug_printf(" %s\n", name);
 307     }
 308   }
 309 }
 310 #endif
 311 */
 312
 313
 314 #ifndef DISABLE_EVENT
 315 static int
 316 verify_event(tls_support * tlsp, X509 * cert, int depth, const uschar * dn,
 317   BOOL *calledp, const BOOL *optionalp, const uschar * what)
 318 {
 319 uschar * ev;
 320 uschar * yield;
 321 X509 * old_cert;
 322
 323 ev = tlsp == &tls_out ? client_static_cbinfo->event_action : event_action;
 324 if (ev)
 325   {
 326   DEBUG(D_tls) debug_printf("verify_event: %s %d\n", what, depth);
 327   old_cert = tlsp->peercert;
 328   tlsp->peercert = X509_dup(cert);
 329   /* NB we do not bother setting peerdn */
 330   if ((yield = event_raise(ev, US"tls:cert", string_sprintf("%d", depth))))
 331     {
 332     log_write(0, LOG_MAIN, "[%s] %s verify denied by event-action: "
 333                 "depth=%d cert=%s: %s",
 334               tlsp == &tls_out ? deliver_host_address : sender_host_address,
 335               what, depth, dn, yield);
 336     *calledp = TRUE;
 337     if (!*optionalp)
 338       {
 339       if (old_cert) tlsp->peercert = old_cert;  /* restore 1st failing cert */
 340       return 1;                     /* reject (leaving peercert set) */
 341       }
 342     DEBUG(D_tls) debug_printf("Event-action verify failure overridden "
 343       "(host in tls_try_verify_hosts)\n");
 344     }
 345   X509_free(tlsp->peercert);
 346   tlsp->peercert = old_cert;
 347   }
 348 return 0;
 349 }
 350 #endif
 351
 352 /*************************************************
 353 *        Callback for verification               *
 354 *************************************************/
 355
 356 /* The SSL library does certificate verification if set up to do so. This
 357 callback has the current yes/no state is in "state". If verification succeeded,
 358 we set the certificate-verified flag. If verification failed, what happens
 359 depends on whether the client is required to present a verifiable certificate
 360 or not.
 361
 362 If verification is optional, we change the state to yes, but still log the
 363 verification error. For some reason (it really would help to have proper
 364 documentation of OpenSSL), this callback function then gets called again, this
 365 time with state = 1.  We must take care not to set the private verified flag on
 366 the second time through.
 367
 368 Note: this function is not called if the client fails to present a certificate
 369 when asked. We get here only if a certificate has been received. Handling of
 370 optional verification for this case is done when requesting SSL to verify, by
 371 setting SSL_VERIFY_FAIL_IF_NO_PEER_CERT in the non-optional case.
 372
 373 May be called multiple times for different issues with a certificate, even
 374 for a given "depth" in the certificate chain.
 375
 376 Arguments:
 377   preverify_ok current yes/no state as 1/0
 378   x509ctx      certificate information.
 379   tlsp         per-direction (client vs. server) support data
 380   calledp      has-been-called flag
 381   optionalp    verification-is-optional flag
 382
 383 Returns:     0 if verification should fail, otherwise 1
 384 */
 385
 386 static int
 387 verify_callback(int preverify_ok, X509_STORE_CTX *x509ctx,
 388   tls_support *tlsp, BOOL *calledp, BOOL *optionalp)
 389 {
 390 X509 * cert = X509_STORE_CTX_get_current_cert(x509ctx);
 391 int depth = X509_STORE_CTX_get_error_depth(x509ctx);
 392 uschar dn[256];
 393
 394 X509_NAME_oneline(X509_get_subject_name(cert), CS dn, sizeof(dn));
 395 dn[sizeof(dn)-1] = '\0';
 396
 397 if (preverify_ok == 0)
 398   {
 399   log_write(0, LOG_MAIN, "[%s] SSL verify error: depth=%d error=%s cert=%s",
 400         tlsp == &tls_out ? deliver_host_address : sender_host_address,
 401     depth,
 402     X509_verify_cert_error_string(X509_STORE_CTX_get_error(x509ctx)),
 403     dn);
 404   *calledp = TRUE;
 405   if (!*optionalp)
 406     {
 407     if (!tlsp->peercert)
 408       tlsp->peercert = X509_dup(cert);  /* record failing cert */
 409     return 0;                           /* reject */
 410     }
 411   DEBUG(D_tls) debug_printf("SSL verify failure overridden (host in "
 412     "tls_try_verify_hosts)\n");
 413   }
 414
 415 else if (depth != 0)
 416   {
 417   DEBUG(D_tls) debug_printf("SSL verify ok: depth=%d SN=%s\n", depth, dn);
 418 #ifndef DISABLE_OCSP
 419   if (tlsp == &tls_out && client_static_cbinfo->u_ocsp.client.verify_store)
 420     {   /* client, wanting stapling  */
 421     /* Add the server cert's signing chain as the one
 422     for the verification of the OCSP stapled information. */
 423
 424     if (!X509_STORE_add_cert(client_static_cbinfo->u_ocsp.client.verify_store,
 425                              cert))
 426       ERR_clear_error();
 427     sk_X509_push(client_static_cbinfo->verify_stack, cert);
 428     }
 429 #endif
 430 #ifndef DISABLE_EVENT
 431     if (verify_event(tlsp, cert, depth, dn, calledp, optionalp, US"SSL"))
 432       return 0;                         /* reject, with peercert set */
 433 #endif
 434   }
 435 else
 436   {
 437   const uschar * verify_cert_hostnames;
 438
 439   if (  tlsp == &tls_out
 440      && ((verify_cert_hostnames = client_static_cbinfo->verify_cert_hostnames)))
 441         /* client, wanting hostname check */
 442     {
 443
 444 #ifdef EXIM_HAVE_OPENSSL_CHECKHOST
 445 # ifndef X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
 446 #  define X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS 0
 447 # endif
 448 # ifndef X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS
 449 #  define X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS 0
 450 # endif
 451     int sep = 0;
 452     const uschar * list = verify_cert_hostnames;
 453     uschar * name;
 454     int rc;
 455     while ((name = string_nextinlist(&list, &sep, NULL, 0)))
 456       if ((rc = X509_check_host(cert, CCS name, 0,
 457                   X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
 458                   | X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS,
 459                   NULL)))
 460         {
 461         if (rc < 0)
 462           {
 463           log_write(0, LOG_MAIN, "[%s] SSL verify error: internal error",
 464                 deliver_host_address);
 465           name = NULL;
 466           }
 467         break;
 468         }
 469     if (!name)
 470 #else
 471     if (!tls_is_name_for_cert(verify_cert_hostnames, cert))
 472 #endif
 473       {
 474       log_write(0, LOG_MAIN,
 475                 "[%s] SSL verify error: certificate name mismatch: "
 476                 "DN=\"%s\" H=\"%s\"",
 477                 deliver_host_address, dn, verify_cert_hostnames);
 478       *calledp = TRUE;
 479       if (!*optionalp)
 480         {
 481         if (!tlsp->peercert)
 482           tlsp->peercert = X509_dup(cert);      /* record failing cert */
 483         return 0;                               /* reject */
 484         }
 485       DEBUG(D_tls) debug_printf("SSL verify failure overridden (host in "
 486         "tls_try_verify_hosts)\n");
 487       }
 488     }
 489
 490 #ifndef DISABLE_EVENT
 491   if (verify_event(tlsp, cert, depth, dn, calledp, optionalp, US"SSL"))
 492     return 0;                           /* reject, with peercert set */
 493 #endif
 494
 495   DEBUG(D_tls) debug_printf("SSL%s verify ok: depth=0 SN=%s\n",
 496     *calledp ? "" : " authenticated", dn);
 497   if (!*calledp) tlsp->certificate_verified = TRUE;
 498   *calledp = TRUE;
 499   }
 500
 501 return 1;   /* accept, at least for this level */
 502 }
 503
 504 static int
 505 verify_callback_client(int preverify_ok, X509_STORE_CTX *x509ctx)
 506 {
 507 return verify_callback(preverify_ok, x509ctx, &tls_out,
 508   &client_verify_callback_called, &client_verify_optional);
 509 }
 510
 511 static int
 512 verify_callback_server(int preverify_ok, X509_STORE_CTX *x509ctx)
 513 {
 514 return verify_callback(preverify_ok, x509ctx, &tls_in,
 515   &server_verify_callback_called, &server_verify_optional);
 516 }
 517
 518
 519 #ifdef EXPERIMENTAL_DANE
 520
 521 /* This gets called *by* the dane library verify callback, which interposes
 522 itself.
 523 */
 524 static int
 525 verify_callback_client_dane(int preverify_ok, X509_STORE_CTX * x509ctx)
 526 {
 527 X509 * cert = X509_STORE_CTX_get_current_cert(x509ctx);
 528 uschar dn[256];
 529 #ifndef DISABLE_EVENT
 530 int depth = X509_STORE_CTX_get_error_depth(x509ctx);
 531 BOOL dummy_called, optional = FALSE;
 532 #endif
 533
 534 X509_NAME_oneline(X509_get_subject_name(cert), CS dn, sizeof(dn));
 535 dn[sizeof(dn)-1] = '\0';
 536
 537 DEBUG(D_tls) debug_printf("verify_callback_client_dane: %s depth %d %s\n",
 538   preverify_ok ? "ok":"BAD", depth, dn);
 539
 540 #ifndef DISABLE_EVENT
 541   if (verify_event(&tls_out, cert, depth, dn,
 542           &dummy_called, &optional, US"DANE"))
 543     return 0;                           /* reject, with peercert set */
 544 #endif
 545
 546 if (preverify_ok == 1)
 547   tls_out.dane_verified =
 548   tls_out.certificate_verified = TRUE;
 549 else
 550   {
 551   int err = X509_STORE_CTX_get_error(x509ctx);
 552   DEBUG(D_tls)
 553     debug_printf(" - err %d '%s'\n", err, X509_verify_cert_error_string(err));
 554   if (err == X509_V_ERR_APPLICATION_VERIFICATION)
 555     preverify_ok = 1;
 556   }
 557 return preverify_ok;
 558 }
 559
 560 #endif  /*EXPERIMENTAL_DANE*/
 561
 562
 563 /*************************************************
 564 *           Information callback                 *
 565 *************************************************/
 566
 567 /* The SSL library functions call this from time to time to indicate what they
 568 are doing. We copy the string to the debugging output when TLS debugging has
 569 been requested.
 570
 571 Arguments:
 572   s         the SSL connection
 573   where
 574   ret
 575
 576 Returns:    nothing
 577 */
 578
 579 static void
 580 info_callback(SSL *s, int where, int ret)
 581 {
 582 where = where;
 583 ret = ret;
 584 DEBUG(D_tls) debug_printf("SSL info: %s\n", SSL_state_string_long(s));
 585 }
 586
 587
 588
 589 /*************************************************
 590 *                Initialize for DH               *
 591 *************************************************/
 592
 593 /* If dhparam is set, expand it, and load up the parameters for DH encryption.
 594
 595 Arguments:
 596   sctx      The current SSL CTX (inbound or outbound)
 597   dhparam   DH parameter file or fixed parameter identity string
 598   host      connected host, if client; NULL if server
 599
 600 Returns:    TRUE if OK (nothing to set up, or setup worked)
 601 */
 602
 603 static BOOL
 604 init_dh(SSL_CTX *sctx, uschar *dhparam, const host_item *host)
 605 {
 606 BIO *bio;
 607 DH *dh;
 608 uschar *dhexpanded;
 609 const char *pem;
 610
 611 if (!expand_check(dhparam, US"tls_dhparam", &dhexpanded))
 612   return FALSE;
 613
 614 if (!dhexpanded || !*dhexpanded)
 615   bio = BIO_new_mem_buf(CS std_dh_prime_default(), -1);
 616 else if (dhexpanded[0] == '/')
 617   {
 618   if (!(bio = BIO_new_file(CS dhexpanded, "r")))
 619     {
 620     tls_error(string_sprintf("could not read dhparams file %s", dhexpanded),
 621           host, US strerror(errno));
 622     return FALSE;
 623     }
 624   }
 625 else
 626   {
 627   if (Ustrcmp(dhexpanded, "none") == 0)
 628     {
 629     DEBUG(D_tls) debug_printf("Requested no DH parameters.\n");
 630     return TRUE;
 631     }
 632
 633   if (!(pem = std_dh_prime_named(dhexpanded)))
 634     {
 635     tls_error(string_sprintf("Unknown standard DH prime \"%s\"", dhexpanded),
 636         host, US strerror(errno));
 637     return FALSE;
 638     }
 639   bio = BIO_new_mem_buf(CS pem, -1);
 640   }
 641
 642 if (!(dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL)))
 643   {
 644   BIO_free(bio);
 645   tls_error(string_sprintf("Could not read tls_dhparams \"%s\"", dhexpanded),
 646       host, NULL);
 647   return FALSE;
 648   }
 649
 650 /* Even if it is larger, we silently return success rather than cause things
 651  * to fail out, so that a too-large DH will not knock out all TLS; it's a
 652  * debatable choice. */
 653 if ((8*DH_size(dh)) > tls_dh_max_bits)
 654   {
 655   DEBUG(D_tls)
 656     debug_printf("dhparams file %d bits, is > tls_dh_max_bits limit of %d",
 657         8*DH_size(dh), tls_dh_max_bits);
 658   }
 659 else
 660   {
 661   SSL_CTX_set_tmp_dh(sctx, dh);
 662   DEBUG(D_tls)
 663     debug_printf("Diffie-Hellman initialized from %s with %d-bit prime\n",
 664       dhexpanded ? dhexpanded : US"default", 8*DH_size(dh));
 665   }
 666
 667 DH_free(dh);
 668 BIO_free(bio);
 669
 670 return TRUE;
 671 }
 672
 673
 674
 675
 676 /*************************************************
 677 *               Initialize for ECDH              *
 678 *************************************************/
 679
 680 /* Load parameters for ECDH encryption.
 681
 682 For now, we stick to NIST P-256 because: it's simple and easy to configure;
 683 it avoids any patent issues that might bite redistributors; despite events in
 684 the news and concerns over curve choices, we're not cryptographers, we're not
 685 pretending to be, and this is "good enough" to be better than no support,
 686 protecting against most adversaries.  Given another year or two, there might
 687 be sufficient clarity about a "right" way forward to let us make an informed
 688 decision, instead of a knee-jerk reaction.
 689
 690 Longer-term, we should look at supporting both various named curves and
 691 external files generated with "openssl ecparam", much as we do for init_dh().
 692 We should also support "none" as a value, to explicitly avoid initialisation.
 693
 694 Patches welcome.
 695
 696 Arguments:
 697   sctx      The current SSL CTX (inbound or outbound)
 698   host      connected host, if client; NULL if server
 699
 700 Returns:    TRUE if OK (nothing to set up, or setup worked)
 701 */
 702
 703 static BOOL
 704 init_ecdh(SSL_CTX * sctx, host_item * host)
 705 {
 706 #ifdef OPENSSL_NO_ECDH
 707 return TRUE;
 708 #else
 709
 710 EC_KEY * ecdh;
 711 uschar * exp_curve;
 712 int nid;
 713 BOOL rv;
 714
 715 if (host)       /* No ECDH setup for clients, only for servers */
 716   return TRUE;
 717
 718 # ifndef EXIM_HAVE_ECDH
 719 DEBUG(D_tls)
 720   debug_printf("No OpenSSL API to define ECDH parameters, skipping\n");
 721 return TRUE;
 722 # else
 723
 724 if (!expand_check(tls_eccurve, US"tls_eccurve", &exp_curve))
 725   return FALSE;
 726 if (!exp_curve || !*exp_curve)
 727   return TRUE;
 728
 729 /* "auto" needs to be handled carefully.
 730  * OpenSSL <  1.0.2: we do not select anything, but fallback to primve256v1
 731  * OpenSSL <  1.1.0: we have to call SSL_CTX_set_ecdh_auto
 732  *                   (openss/ssl.h defines SSL_CTRL_SET_ECDH_AUTO)
 733  * OpenSSL >= 1.1.0: we do not set anything, the libray does autoselection
 734  *                   https://github.com/openssl/openssl/commit/fe6ef2472db933f01b59cad82aa925736935984b
 735  */
 736 if (Ustrcmp(exp_curve, "auto") == 0)
 737   {
 738 #if OPENSSL_VERSION_NUMBER < 0x10002000L
 739   DEBUG(D_tls) debug_printf(
 740     "ECDH OpenSSL < 1.0.2: temp key parameter settings: overriding \"auto\" with \"prime256v1\"\n");
 741   exp_curve = "prime256v1";
 742 #else
 743 # if defined SSL_CTRL_SET_ECDH_AUTO
 744   DEBUG(D_tls) debug_printf(
 745     "ECDH OpenSSL 1.0.2+ temp key parameter settings: autoselection\n");
 746   SSL_CTX_set_ecdh_auto(sctx, 1);
 747   return TRUE;
 748 # else
 749   DEBUG(D_tls) debug_printf(
 750     "ECDH OpenSSL 1.1.0+ temp key parameter settings: default selection\n");
 751   return TRUE;
 752 # endif
 753 #endif
 754   }
 755
 756 DEBUG(D_tls) debug_printf("ECDH: curve '%s'\n", exp_curve);
 757 if (  (nid = OBJ_sn2nid       (CCS exp_curve)) == NID_undef
 758 #   ifdef EXIM_HAVE_OPENSSL_EC_NIST2NID
 759    && (nid = EC_curve_nist2nid(CCS exp_curve)) == NID_undef
 760 #   endif
 761    )
 762   {
 763   tls_error(string_sprintf("Unknown curve name tls_eccurve '%s'",
 764       exp_curve),
 765     host, NULL);
 766   return FALSE;
 767   }
 768
 769 if (!(ecdh = EC_KEY_new_by_curve_name(nid)))
 770   {
 771   tls_error(US"Unable to create ec curve", host, NULL);
 772   return FALSE;
 773   }
 774
 775 /* The "tmp" in the name here refers to setting a temporary key
 776 not to the stability of the interface. */
 777
 778 if ((rv = SSL_CTX_set_tmp_ecdh(sctx, ecdh) == 0))
 779   tls_error(string_sprintf("Error enabling '%s' curve", exp_curve), host, NULL);
 780 else
 781   DEBUG(D_tls) debug_printf("ECDH: enabled '%s' curve\n", exp_curve);
 782
 783 EC_KEY_free(ecdh);
 784 return !rv;
 785
 786 # endif /*EXIM_HAVE_ECDH*/
 787 #endif /*OPENSSL_NO_ECDH*/
 788 }
 789
 790
 791
 792
 793 #ifndef DISABLE_OCSP
 794 /*************************************************
 795 *       Load OCSP information into state         *
 796 *************************************************/
 797 /* Called to load the server OCSP response from the given file into memory, once
 798 caller has determined this is needed.  Checks validity.  Debugs a message
 799 if invalid.
 800
 801 ASSUMES: single response, for single cert.
 802
 803 Arguments:
 804   sctx            the SSL_CTX* to update
 805   cbinfo          various parts of session state
 806   expanded        the filename putatively holding an OCSP response
 807
 808 */
 809
 810 static void
 811 ocsp_load_response(SSL_CTX *sctx, tls_ext_ctx_cb *cbinfo, const uschar *expanded)
 812 {
 813 BIO * bio;
 814 OCSP_RESPONSE * resp;
 815 OCSP_BASICRESP * basic_response;
 816 OCSP_SINGLERESP * single_response;
 817 ASN1_GENERALIZEDTIME * rev, * thisupd, * nextupd;
 818 STACK_OF(X509) * sk;
 819 unsigned long verify_flags;
 820 int status, reason, i;
 821
 822 cbinfo->u_ocsp.server.file_expanded = string_copy(expanded);
 823 if (cbinfo->u_ocsp.server.response)
 824   {
 825   OCSP_RESPONSE_free(cbinfo->u_ocsp.server.response);
 826   cbinfo->u_ocsp.server.response = NULL;
 827   }
 828
 829 if (!(bio = BIO_new_file(CS cbinfo->u_ocsp.server.file_expanded, "rb")))
 830   {
 831   DEBUG(D_tls) debug_printf("Failed to open OCSP response file \"%s\"\n",
 832       cbinfo->u_ocsp.server.file_expanded);
 833   return;
 834   }
 835
 836 resp = d2i_OCSP_RESPONSE_bio(bio, NULL);
 837 BIO_free(bio);
 838 if (!resp)
 839   {
 840   DEBUG(D_tls) debug_printf("Error reading OCSP response.\n");
 841   return;
 842   }
 843
 844 if ((status = OCSP_response_status(resp)) != OCSP_RESPONSE_STATUS_SUCCESSFUL)
 845   {
 846   DEBUG(D_tls) debug_printf("OCSP response not valid: %s (%d)\n",
 847       OCSP_response_status_str(status), status);
 848   goto bad;
 849   }
 850
 851 if (!(basic_response = OCSP_response_get1_basic(resp)))
 852   {
 853   DEBUG(D_tls)
 854     debug_printf("OCSP response parse error: unable to extract basic response.\n");
 855   goto bad;
 856   }
 857
 858 sk = cbinfo->verify_stack;
 859 verify_flags = OCSP_NOVERIFY; /* check sigs, but not purpose */
 860
 861 /* May need to expose ability to adjust those flags?
 862 OCSP_NOSIGS OCSP_NOVERIFY OCSP_NOCHAIN OCSP_NOCHECKS OCSP_NOEXPLICIT
 863 OCSP_TRUSTOTHER OCSP_NOINTERN */
 864
 865 /* This does a full verify on the OCSP proof before we load it for serviing
 866 up; possibly overkill - just date-checks might be nice enough.
 867
 868 OCSP_basic_verify takes a "store" arg, but does not
 869 use it for the chain verification, which is all we do
 870 when OCSP_NOVERIFY is set.  The content from the wire
 871 "basic_response" and a cert-stack "sk" are all that is used.
 872
 873 We have a stack, loaded in setup_certs() if tls_verify_certificates
 874 was a file (not a directory, or "system").  It is unfortunate we
 875 cannot used the connection context store, as that would neatly
 876 handle the "system" case too, but there seems to be no library
 877 function for getting a stack from a store.
 878 [ In OpenSSL 1.1 - ?  X509_STORE_CTX_get0_chain(ctx) ? ]
 879 We do not free the stack since it could be needed a second time for
 880 SNI handling.
 881
 882 Seperately we might try to replace using OCSP_basic_verify() - which seems to not
 883 be a public interface into the OpenSSL library (there's no manual entry) -
 884 But what with?  We also use OCSP_basic_verify in the client stapling callback.
 885 And there we NEED it; we miust verify that status... unless the
 886 library does it for us anyway?  */
 887
 888 if ((i = OCSP_basic_verify(basic_response, sk, NULL, verify_flags)) < 0)
 889   {
 890   DEBUG(D_tls)
 891     {
 892     ERR_error_string(ERR_get_error(), ssl_errstring);
 893     debug_printf("OCSP response verify failure: %s\n", US ssl_errstring);
 894     }
 895   goto bad;
 896   }
 897
 898 /* Here's the simplifying assumption: there's only one response, for the
 899 one certificate we use, and nothing for anything else in a chain.  If this
 900 proves false, we need to extract a cert id from our issued cert
 901 (tls_certificate) and use that for OCSP_resp_find_status() (which finds the
 902 right cert in the stack and then calls OCSP_single_get0_status()).
 903
 904 I'm hoping to avoid reworking a bunch more of how we handle state here. */
 905
 906 if (!(single_response = OCSP_resp_get0(basic_response, 0)))
 907   {
 908   DEBUG(D_tls)
 909     debug_printf("Unable to get first response from OCSP basic response.\n");
 910   goto bad;
 911   }
 912
 913 status = OCSP_single_get0_status(single_response, &reason, &rev, &thisupd, &nextupd);
 914 if (status != V_OCSP_CERTSTATUS_GOOD)
 915   {
 916   DEBUG(D_tls) debug_printf("OCSP response bad cert status: %s (%d) %s (%d)\n",
 917       OCSP_cert_status_str(status), status,
 918       OCSP_crl_reason_str(reason), reason);
 919   goto bad;
 920   }
 921
 922 if (!OCSP_check_validity(thisupd, nextupd, EXIM_OCSP_SKEW_SECONDS, EXIM_OCSP_MAX_AGE))
 923   {
 924   DEBUG(D_tls) debug_printf("OCSP status invalid times.\n");
 925   goto bad;
 926   }
 927
 928 supply_response:
 929   cbinfo->u_ocsp.server.response = resp;
 930 return;
 931
 932 bad:
 933   if (running_in_test_harness)
 934     {
 935     extern char ** environ;
 936     uschar ** p;
 937     if (environ) for (p = USS environ; *p != NULL; p++)
 938       if (Ustrncmp(*p, "EXIM_TESTHARNESS_DISABLE_OCSPVALIDITYCHECK", 42) == 0)
 939         {
 940         DEBUG(D_tls) debug_printf("Supplying known bad OCSP response\n");
 941         goto supply_response;
 942         }
 943     }
 944 return;
 945 }
 946 #endif  /*!DISABLE_OCSP*/
 947
 948
 949
 950
 951 /* Create and install a selfsigned certificate, for use in server mode */
 952
 953 static int
 954 tls_install_selfsign(SSL_CTX * sctx)
 955 {
 956 X509 * x509 = NULL;
 957 EVP_PKEY * pkey;
 958 RSA * rsa;
 959 X509_NAME * name;
 960 uschar * where;
 961
 962 where = US"allocating pkey";
 963 if (!(pkey = EVP_PKEY_new()))
 964   goto err;
 965
 966 where = US"allocating cert";
 967 if (!(x509 = X509_new()))
 968   goto err;
 969
 970 where = US"generating pkey";
 971                 /* deprecated, use RSA_generate_key_ex() */
 972 if (!(rsa = RSA_generate_key(1024, RSA_F4, NULL, NULL)))
 973   goto err;
 974
 975 where = US"assiging pkey";
 976 if (!EVP_PKEY_assign_RSA(pkey, rsa))
 977   goto err;
 978
 979 X509_set_version(x509, 2);                              /* N+1 - version 3 */
 980 ASN1_INTEGER_set(X509_get_serialNumber(x509), 0);
 981 X509_gmtime_adj(X509_get_notBefore(x509), 0);
 982 X509_gmtime_adj(X509_get_notAfter(x509), (long)60 * 60);        /* 1 hour */
 983 X509_set_pubkey(x509, pkey);
 984
 985 name = X509_get_subject_name(x509);
 986 X509_NAME_add_entry_by_txt(name, "C",
 987                           MBSTRING_ASC, CUS "UK", -1, -1, 0);
 988 X509_NAME_add_entry_by_txt(name, "O",
 989                           MBSTRING_ASC, CUS "Exim Developers", -1, -1, 0);
 990 X509_NAME_add_entry_by_txt(name, "CN",
 991                           MBSTRING_ASC, CUS smtp_active_hostname, -1, -1, 0);
 992 X509_set_issuer_name(x509, name);
 993
 994 where = US"signing cert";
 995 if (!X509_sign(x509, pkey, EVP_md5()))
 996   goto err;
 997
 998 where = US"installing selfsign cert";
 999 if (!SSL_CTX_use_certificate(sctx, x509))
1000   goto err;
1001
1002 where = US"installing selfsign key";
1003 if (!SSL_CTX_use_PrivateKey(sctx, pkey))
1004   goto err;
1005
1006 return OK;
1007
1008 err:
1009   (void) tls_error(where, NULL, NULL);
1010   if (x509) X509_free(x509);
1011   if (pkey) EVP_PKEY_free(pkey);
1012   return DEFER;
1013 }
1014
1015
1016
1017
1018 /*************************************************
1019 *        Expand key and cert file specs          *
1020 *************************************************/
1021
1022 /* Called once during tls_init and possibly again during TLS setup, for a
1023 new context, if Server Name Indication was used and tls_sni was seen in
1024 the certificate string.
1025
1026 Arguments:
1027   sctx            the SSL_CTX* to update
1028   cbinfo          various parts of session state
1029
1030 Returns:          OK/DEFER/FAIL
1031 */
1032
1033 static int
1034 tls_expand_session_files(SSL_CTX *sctx, tls_ext_ctx_cb *cbinfo)
1035 {
1036 uschar *expanded;
1037
1038 if (!cbinfo->certificate)
1039   {
1040   if (cbinfo->host)                     /* client */
1041     return OK;
1042                                         /* server */
1043   if (tls_install_selfsign(sctx) != OK)
1044     return DEFER;
1045   }
1046 else
1047   {
1048   if (Ustrstr(cbinfo->certificate, US"tls_sni") ||
1049       Ustrstr(cbinfo->certificate, US"tls_in_sni") ||
1050       Ustrstr(cbinfo->certificate, US"tls_out_sni")
1051      )
1052     reexpand_tls_files_for_sni = TRUE;
1053
1054   if (!expand_check(cbinfo->certificate, US"tls_certificate", &expanded))
1055     return DEFER;
1056
1057   if (expanded != NULL)
1058     {
1059     DEBUG(D_tls) debug_printf("tls_certificate file %s\n", expanded);
1060     if (!SSL_CTX_use_certificate_chain_file(sctx, CS expanded))
1061       return tls_error(string_sprintf(
1062         "SSL_CTX_use_certificate_chain_file file=%s", expanded),
1063           cbinfo->host, NULL);
1064     }
1065
1066   if (cbinfo->privatekey != NULL &&
1067       !expand_check(cbinfo->privatekey, US"tls_privatekey", &expanded))
1068     return DEFER;
1069
1070   /* If expansion was forced to fail, key_expanded will be NULL. If the result
1071   of the expansion is an empty string, ignore it also, and assume the private
1072   key is in the same file as the certificate. */
1073
1074   if (expanded && *expanded)
1075     {
1076     DEBUG(D_tls) debug_printf("tls_privatekey file %s\n", expanded);
1077     if (!SSL_CTX_use_PrivateKey_file(sctx, CS expanded, SSL_FILETYPE_PEM))
1078       return tls_error(string_sprintf(
1079         "SSL_CTX_use_PrivateKey_file file=%s", expanded), cbinfo->host, NULL);
1080     }
1081   }
1082
1083 #ifndef DISABLE_OCSP
1084 if (cbinfo->is_server && cbinfo->u_ocsp.server.file)
1085   {
1086   if (!expand_check(cbinfo->u_ocsp.server.file, US"tls_ocsp_file", &expanded))
1087     return DEFER;
1088
1089   if (expanded && *expanded)
1090     {
1091     DEBUG(D_tls) debug_printf("tls_ocsp_file %s\n", expanded);
1092     if (  cbinfo->u_ocsp.server.file_expanded
1093        && (Ustrcmp(expanded, cbinfo->u_ocsp.server.file_expanded) == 0))
1094       {
1095       DEBUG(D_tls) debug_printf(" - value unchanged, using existing values\n");
1096       }
1097     else
1098       ocsp_load_response(sctx, cbinfo, expanded);
1099     }
1100   }
1101 #endif
1102
1103 return OK;
1104 }
1105
1106
1107
1108
1109 /*************************************************
1110 *            Callback to handle SNI              *
1111 *************************************************/
1112
1113 /* Called when acting as server during the TLS session setup if a Server Name
1114 Indication extension was sent by the client.
1115
1116 API documentation is OpenSSL s_server.c implementation.
1117
1118 Arguments:
1119   s               SSL* of the current session
1120   ad              unknown (part of OpenSSL API) (unused)
1121   arg             Callback of "our" registered data
1122
1123 Returns:          SSL_TLSEXT_ERR_{OK,ALERT_WARNING,ALERT_FATAL,NOACK}
1124 */
1125
1126 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
1127 static int
1128 tls_servername_cb(SSL *s, int *ad ARG_UNUSED, void *arg)
1129 {
1130 const char *servername = SSL_get_servername(s, TLSEXT_NAMETYPE_host_name);
1131 tls_ext_ctx_cb *cbinfo = (tls_ext_ctx_cb *) arg;
1132 int rc;
1133 int old_pool = store_pool;
1134
1135 if (!servername)
1136   return SSL_TLSEXT_ERR_OK;
1137
1138 DEBUG(D_tls) debug_printf("Received TLS SNI \"%s\"%s\n", servername,
1139     reexpand_tls_files_for_sni ? "" : " (unused for certificate selection)");
1140
1141 /* Make the extension value available for expansion */
1142 store_pool = POOL_PERM;
1143 tls_in.sni = string_copy(US servername);
1144 store_pool = old_pool;
1145
1146 if (!reexpand_tls_files_for_sni)
1147   return SSL_TLSEXT_ERR_OK;
1148
1149 /* Can't find an SSL_CTX_clone() or equivalent, so we do it manually;
1150 not confident that memcpy wouldn't break some internal reference counting.
1151 Especially since there's a references struct member, which would be off. */
1152
1153 if (!(server_sni = SSL_CTX_new(SSLv23_server_method())))
1154   {
1155   ERR_error_string(ERR_get_error(), ssl_errstring);
1156   DEBUG(D_tls) debug_printf("SSL_CTX_new() failed: %s\n", ssl_errstring);
1157   return SSL_TLSEXT_ERR_NOACK;
1158   }
1159
1160 /* Not sure how many of these are actually needed, since SSL object
1161 already exists.  Might even need this selfsame callback, for reneg? */
1162
1163 SSL_CTX_set_info_callback(server_sni, SSL_CTX_get_info_callback(server_ctx));
1164 SSL_CTX_set_mode(server_sni, SSL_CTX_get_mode(server_ctx));
1165 SSL_CTX_set_options(server_sni, SSL_CTX_get_options(server_ctx));
1166 SSL_CTX_set_timeout(server_sni, SSL_CTX_get_timeout(server_ctx));
1167 SSL_CTX_set_tlsext_servername_callback(server_sni, tls_servername_cb);
1168 SSL_CTX_set_tlsext_servername_arg(server_sni, cbinfo);
1169
1170 if (  !init_dh(server_sni, cbinfo->dhparam, NULL)
1171    || !init_ecdh(server_sni, NULL)
1172    )
1173   return SSL_TLSEXT_ERR_NOACK;
1174
1175 if (cbinfo->server_cipher_list)
1176   SSL_CTX_set_cipher_list(server_sni, CS cbinfo->server_cipher_list);
1177 #ifndef DISABLE_OCSP
1178 if (cbinfo->u_ocsp.server.file)
1179   {
1180   SSL_CTX_set_tlsext_status_cb(server_sni, tls_server_stapling_cb);
1181   SSL_CTX_set_tlsext_status_arg(server_sni, cbinfo);
1182   }
1183 #endif
1184
1185 if ((rc = setup_certs(server_sni, tls_verify_certificates, tls_crl, NULL, FALSE,
1186                       verify_callback_server)) != OK)
1187   return SSL_TLSEXT_ERR_NOACK;
1188
1189 /* do this after setup_certs, because this can require the certs for verifying
1190 OCSP information. */
1191 if ((rc = tls_expand_session_files(server_sni, cbinfo)) != OK)
1192   return SSL_TLSEXT_ERR_NOACK;
1193
1194 DEBUG(D_tls) debug_printf("Switching SSL context.\n");
1195 SSL_set_SSL_CTX(s, server_sni);
1196
1197 return SSL_TLSEXT_ERR_OK;
1198 }
1199 #endif /* EXIM_HAVE_OPENSSL_TLSEXT */
1200
1201
1202
1203
1204 #ifndef DISABLE_OCSP
1205
1206 /*************************************************
1207 *        Callback to handle OCSP Stapling        *
1208 *************************************************/
1209
1210 /* Called when acting as server during the TLS session setup if the client
1211 requests OCSP information with a Certificate Status Request.
1212
1213 Documentation via openssl s_server.c and the Apache patch from the OpenSSL
1214 project.
1215
1216 */
1217
1218 static int
1219 tls_server_stapling_cb(SSL *s, void *arg)
1220 {
1221 const tls_ext_ctx_cb *cbinfo = (tls_ext_ctx_cb *) arg;
1222 uschar *response_der;
1223 int response_der_len;
1224
1225 DEBUG(D_tls)
1226   debug_printf("Received TLS status request (OCSP stapling); %s response\n",
1227     cbinfo->u_ocsp.server.response ? "have" : "lack");
1228
1229 tls_in.ocsp = OCSP_NOT_RESP;
1230 if (!cbinfo->u_ocsp.server.response)
1231   return SSL_TLSEXT_ERR_NOACK;
1232
1233 response_der = NULL;
1234 response_der_len = i2d_OCSP_RESPONSE(cbinfo->u_ocsp.server.response,
1235                       &response_der);
1236 if (response_der_len <= 0)
1237   return SSL_TLSEXT_ERR_NOACK;
1238
1239 SSL_set_tlsext_status_ocsp_resp(server_ssl, response_der, response_der_len);
1240 tls_in.ocsp = OCSP_VFIED;
1241 return SSL_TLSEXT_ERR_OK;
1242 }
1243
1244
1245 static void
1246 time_print(BIO * bp, const char * str, ASN1_GENERALIZEDTIME * time)
1247 {
1248 BIO_printf(bp, "\t%s: ", str);
1249 ASN1_GENERALIZEDTIME_print(bp, time);
1250 BIO_puts(bp, "\n");
1251 }
1252
1253 static int
1254 tls_client_stapling_cb(SSL *s, void *arg)
1255 {
1256 tls_ext_ctx_cb * cbinfo = arg;
1257 const unsigned char * p;
1258 int len;
1259 OCSP_RESPONSE * rsp;
1260 OCSP_BASICRESP * bs;
1261 int i;
1262
1263 DEBUG(D_tls) debug_printf("Received TLS status response (OCSP stapling):");
1264 len = SSL_get_tlsext_status_ocsp_resp(s, &p);
1265 if(!p)
1266  {
1267   /* Expect this when we requested ocsp but got none */
1268   if (cbinfo->u_ocsp.client.verify_required && LOGGING(tls_cipher))
1269     log_write(0, LOG_MAIN, "Received TLS status callback, null content");
1270   else
1271     DEBUG(D_tls) debug_printf(" null\n");
1272   return cbinfo->u_ocsp.client.verify_required ? 0 : 1;
1273  }
1274
1275 if(!(rsp = d2i_OCSP_RESPONSE(NULL, &p, len)))
1276  {
1277   tls_out.ocsp = OCSP_FAILED;
1278   if (LOGGING(tls_cipher))
1279     log_write(0, LOG_MAIN, "Received TLS cert status response, parse error");
1280   else
1281     DEBUG(D_tls) debug_printf(" parse error\n");
1282   return 0;
1283  }
1284
1285 if(!(bs = OCSP_response_get1_basic(rsp)))
1286   {
1287   tls_out.ocsp = OCSP_FAILED;
1288   if (LOGGING(tls_cipher))
1289     log_write(0, LOG_MAIN, "Received TLS cert status response, error parsing response");
1290   else
1291     DEBUG(D_tls) debug_printf(" error parsing response\n");
1292   OCSP_RESPONSE_free(rsp);
1293   return 0;
1294   }
1295
1296 /* We'd check the nonce here if we'd put one in the request. */
1297 /* However that would defeat cacheability on the server so we don't. */
1298
1299 /* This section of code reworked from OpenSSL apps source;
1300    The OpenSSL Project retains copyright:
1301    Copyright (c) 1999 The OpenSSL Project.  All rights reserved.
1302 */
1303   {
1304     BIO * bp = NULL;
1305     int status, reason;
1306     ASN1_GENERALIZEDTIME *rev, *thisupd, *nextupd;
1307
1308     DEBUG(D_tls) bp = BIO_new_fp(stderr, BIO_NOCLOSE);
1309
1310     /*OCSP_RESPONSE_print(bp, rsp, 0);   extreme debug: stapling content */
1311
1312     /* Use the chain that verified the server cert to verify the stapled info */
1313     /* DEBUG(D_tls) x509_store_dump_cert_s_names(cbinfo->u_ocsp.client.verify_store); */
1314
1315     if ((i = OCSP_basic_verify(bs, cbinfo->verify_stack,
1316               cbinfo->u_ocsp.client.verify_store, 0)) <= 0)
1317       {
1318       tls_out.ocsp = OCSP_FAILED;
1319       if (LOGGING(tls_cipher))
1320         log_write(0, LOG_MAIN, "Received TLS cert status response, itself unverifiable");
1321       BIO_printf(bp, "OCSP response verify failure\n");
1322       ERR_print_errors(bp);
1323       goto failed;
1324       }
1325
1326     BIO_printf(bp, "OCSP response well-formed and signed OK\n");
1327
1328     /*XXX So we have a good stapled OCSP status.  How do we know
1329     it is for the cert of interest?  OpenSSL 1.1.0 has a routine
1330     OCSP_resp_find_status() which matches on a cert id, which presumably
1331     we should use. Making an id needs OCSP_cert_id_new(), which takes
1332     issuerName, issuerKey, serialNumber.  Are they all in the cert?
1333
1334     For now, carry on blindly accepting the resp. */
1335
1336       {
1337       OCSP_SINGLERESP * single;
1338
1339 #ifdef EXIM_HAVE_OCSP_RESP_COUNT
1340       if (OCSP_resp_count(bs) != 1)
1341 #else
1342       STACK_OF(OCSP_SINGLERESP) * sresp = bs->tbsResponseData->responses;
1343       if (sk_OCSP_SINGLERESP_num(sresp) != 1)
1344 #endif
1345         {
1346         tls_out.ocsp = OCSP_FAILED;
1347         log_write(0, LOG_MAIN, "OCSP stapling "
1348             "with multiple responses not handled");
1349         goto failed;
1350         }
1351       single = OCSP_resp_get0(bs, 0);
1352       status = OCSP_single_get0_status(single, &reason, &rev,
1353                   &thisupd, &nextupd);
1354       }
1355
1356     DEBUG(D_tls) time_print(bp, "This OCSP Update", thisupd);
1357     DEBUG(D_tls) if(nextupd) time_print(bp, "Next OCSP Update", nextupd);
1358     if (!OCSP_check_validity(thisupd, nextupd,
1359           EXIM_OCSP_SKEW_SECONDS, EXIM_OCSP_MAX_AGE))
1360       {
1361       tls_out.ocsp = OCSP_FAILED;
1362       DEBUG(D_tls) ERR_print_errors(bp);
1363       log_write(0, LOG_MAIN, "Server OSCP dates invalid");
1364       }
1365     else
1366       {
1367       DEBUG(D_tls) BIO_printf(bp, "Certificate status: %s\n",
1368                     OCSP_cert_status_str(status));
1369       switch(status)
1370         {
1371         case V_OCSP_CERTSTATUS_GOOD:
1372           tls_out.ocsp = OCSP_VFIED;
1373           i = 1;
1374           goto good;
1375         case V_OCSP_CERTSTATUS_REVOKED:
1376           tls_out.ocsp = OCSP_FAILED;
1377           log_write(0, LOG_MAIN, "Server certificate revoked%s%s",
1378               reason != -1 ? "; reason: " : "",
1379               reason != -1 ? OCSP_crl_reason_str(reason) : "");
1380           DEBUG(D_tls) time_print(bp, "Revocation Time", rev);
1381           break;
1382         default:
1383           tls_out.ocsp = OCSP_FAILED;
1384           log_write(0, LOG_MAIN,
1385               "Server certificate status unknown, in OCSP stapling");
1386           break;
1387         }
1388       }
1389   failed:
1390     i = cbinfo->u_ocsp.client.verify_required ? 0 : 1;
1391   good:
1392     BIO_free(bp);
1393   }
1394
1395 OCSP_RESPONSE_free(rsp);
1396 return i;
1397 }
1398 #endif  /*!DISABLE_OCSP*/
1399
1400
1401 /*************************************************
1402 *            Initialize for TLS                  *
1403 *************************************************/
1404
1405 /* Called from both server and client code, to do preliminary initialization
1406 of the library.  We allocate and return a context structure.
1407
1408 Arguments:
1409   ctxp            returned SSL context
1410   host            connected host, if client; NULL if server
1411   dhparam         DH parameter file
1412   certificate     certificate file
1413   privatekey      private key
1414   ocsp_file       file of stapling info (server); flag for require ocsp (client)
1415   addr            address if client; NULL if server (for some randomness)
1416   cbp             place to put allocated callback context
1417
1418 Returns:          OK/DEFER/FAIL
1419 */
1420
1421 static int
1422 tls_init(SSL_CTX **ctxp, host_item *host, uschar *dhparam, uschar *certificate,
1423   uschar *privatekey,
1424 #ifndef DISABLE_OCSP
1425   uschar *ocsp_file,
1426 #endif
1427   address_item *addr, tls_ext_ctx_cb ** cbp)
1428 {
1429 long init_options;
1430 int rc;
1431 BOOL okay;
1432 tls_ext_ctx_cb * cbinfo;
1433
1434 cbinfo = store_malloc(sizeof(tls_ext_ctx_cb));
1435 cbinfo->certificate = certificate;
1436 cbinfo->privatekey = privatekey;
1437 #ifndef DISABLE_OCSP
1438 cbinfo->verify_stack = NULL;
1439 if ((cbinfo->is_server = host==NULL))
1440   {
1441   cbinfo->u_ocsp.server.file = ocsp_file;
1442   cbinfo->u_ocsp.server.file_expanded = NULL;
1443   cbinfo->u_ocsp.server.response = NULL;
1444   }
1445 else
1446   cbinfo->u_ocsp.client.verify_store = NULL;
1447 #endif
1448 cbinfo->dhparam = dhparam;
1449 cbinfo->server_cipher_list = NULL;
1450 cbinfo->host = host;
1451 #ifndef DISABLE_EVENT
1452 cbinfo->event_action = NULL;
1453 #endif
1454
1455 SSL_load_error_strings();          /* basic set up */
1456 OpenSSL_add_ssl_algorithms();
1457
1458 #ifdef EXIM_HAVE_SHA256
1459 /* SHA256 is becoming ever more popular. This makes sure it gets added to the
1460 list of available digests. */
1461 EVP_add_digest(EVP_sha256());
1462 #endif
1463
1464 /* Create a context.
1465 The OpenSSL docs in 1.0.1b have not been updated to clarify TLS variant
1466 negotiation in the different methods; as far as I can tell, the only
1467 *_{server,client}_method which allows negotiation is SSLv23, which exists even
1468 when OpenSSL is built without SSLv2 support.
1469 By disabling with openssl_options, we can let admins re-enable with the
1470 existing knob. */
1471
1472 *ctxp = SSL_CTX_new(host ? SSLv23_client_method() : SSLv23_server_method());
1473
1474 if (!*ctxp) return tls_error(US"SSL_CTX_new", host, NULL);
1475
1476 /* It turns out that we need to seed the random number generator this early in
1477 order to get the full complement of ciphers to work. It took me roughly a day
1478 of work to discover this by experiment.
1479
1480 On systems that have /dev/urandom, SSL may automatically seed itself from
1481 there. Otherwise, we have to make something up as best we can. Double check
1482 afterwards. */
1483
1484 if (!RAND_status())
1485   {
1486   randstuff r;
1487   gettimeofday(&r.tv, NULL);
1488   r.p = getpid();
1489
1490   RAND_seed((uschar *)(&r), sizeof(r));
1491   RAND_seed((uschar *)big_buffer, big_buffer_size);
1492   if (addr != NULL) RAND_seed((uschar *)addr, sizeof(addr));
1493
1494   if (!RAND_status())
1495     return tls_error(US"RAND_status", host,
1496       US"unable to seed random number generator");
1497   }
1498
1499 /* Set up the information callback, which outputs if debugging is at a suitable
1500 level. */
1501
1502 DEBUG(D_tls) SSL_CTX_set_info_callback(*ctxp, (void (*)())info_callback);
1503
1504 /* Automatically re-try reads/writes after renegotiation. */
1505 (void) SSL_CTX_set_mode(*ctxp, SSL_MODE_AUTO_RETRY);
1506
1507 /* Apply administrator-supplied work-arounds.
1508 Historically we applied just one requested option,
1509 SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS, but when bug 994 requested a second, we
1510 moved to an administrator-controlled list of options to specify and
1511 grandfathered in the first one as the default value for "openssl_options".
1512
1513 No OpenSSL version number checks: the options we accept depend upon the
1514 availability of the option value macros from OpenSSL.  */
1515
1516 okay = tls_openssl_options_parse(openssl_options, &init_options);
1517 if (!okay)
1518   return tls_error(US"openssl_options parsing failed", host, NULL);
1519
1520 if (init_options)
1521   {
1522   DEBUG(D_tls) debug_printf("setting SSL CTX options: %#lx\n", init_options);
1523   if (!(SSL_CTX_set_options(*ctxp, init_options)))
1524     return tls_error(string_sprintf(
1525           "SSL_CTX_set_option(%#lx)", init_options), host, NULL);
1526   }
1527 else
1528   DEBUG(D_tls) debug_printf("no SSL CTX options to set\n");
1529
1530 /* Initialize with DH parameters if supplied */
1531 /* Initialize ECDH temp key parameter selection */
1532
1533 if (  !init_dh(*ctxp, dhparam, host)
1534    || !init_ecdh(*ctxp, host)
1535    )
1536   return DEFER;
1537
1538 /* Set up certificate and key (and perhaps OCSP info) */
1539
1540 if ((rc = tls_expand_session_files(*ctxp, cbinfo)) != OK)
1541   return rc;
1542
1543 /* If we need to handle SNI or OCSP, do so */
1544
1545 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
1546 # ifndef DISABLE_OCSP
1547   if (!(cbinfo->verify_stack = sk_X509_new_null()))
1548     {
1549     DEBUG(D_tls) debug_printf("failed to create stack for stapling verify\n");
1550     return FAIL;
1551     }
1552 # endif
1553
1554 if (host == NULL)               /* server */
1555   {
1556 # ifndef DISABLE_OCSP
1557   /* We check u_ocsp.server.file, not server.response, because we care about if
1558   the option exists, not what the current expansion might be, as SNI might
1559   change the certificate and OCSP file in use between now and the time the
1560   callback is invoked. */
1561   if (cbinfo->u_ocsp.server.file)
1562     {
1563     SSL_CTX_set_tlsext_status_cb(server_ctx, tls_server_stapling_cb);
1564     SSL_CTX_set_tlsext_status_arg(server_ctx, cbinfo);
1565     }
1566 # endif
1567   /* We always do this, so that $tls_sni is available even if not used in
1568   tls_certificate */
1569   SSL_CTX_set_tlsext_servername_callback(*ctxp, tls_servername_cb);
1570   SSL_CTX_set_tlsext_servername_arg(*ctxp, cbinfo);
1571   }
1572 # ifndef DISABLE_OCSP
1573 else                    /* client */
1574   if(ocsp_file)         /* wanting stapling */
1575     {
1576     if (!(cbinfo->u_ocsp.client.verify_store = X509_STORE_new()))
1577       {
1578       DEBUG(D_tls) debug_printf("failed to create store for stapling verify\n");
1579       return FAIL;
1580       }
1581     SSL_CTX_set_tlsext_status_cb(*ctxp, tls_client_stapling_cb);
1582     SSL_CTX_set_tlsext_status_arg(*ctxp, cbinfo);
1583     }
1584 # endif
1585 #endif
1586
1587 cbinfo->verify_cert_hostnames = NULL;
1588
1589 #ifdef EXIM_HAVE_EPHEM_RSA_KEX
1590 /* Set up the RSA callback */
1591 SSL_CTX_set_tmp_rsa_callback(*ctxp, rsa_callback);
1592 #endif
1593
1594 /* Finally, set the timeout, and we are done */
1595
1596 SSL_CTX_set_timeout(*ctxp, ssl_session_timeout);
1597 DEBUG(D_tls) debug_printf("Initialized TLS\n");
1598
1599 *cbp = cbinfo;
1600
1601 return OK;
1602 }
1603
1604
1605
1606
1607 /*************************************************
1608 *           Get name of cipher in use            *
1609 *************************************************/
1610
1611 /*
1612 Argument:   pointer to an SSL structure for the connection
1613             buffer to use for answer
1614             size of buffer
1615             pointer to number of bits for cipher
1616 Returns:    nothing
1617 */
1618
1619 static void
1620 construct_cipher_name(SSL *ssl, uschar *cipherbuf, int bsize, int *bits)
1621 {
1622 /* With OpenSSL 1.0.0a, this needs to be const but the documentation doesn't
1623 yet reflect that.  It should be a safe change anyway, even 0.9.8 versions have
1624 the accessor functions use const in the prototype. */
1625 const SSL_CIPHER *c;
1626 const uschar *ver;
1627
1628 ver = (const uschar *)SSL_get_version(ssl);
1629
1630 c = (const SSL_CIPHER *) SSL_get_current_cipher(ssl);
1631 SSL_CIPHER_get_bits(c, bits);
1632
1633 string_format(cipherbuf, bsize, "%s:%s:%u", ver,
1634   SSL_CIPHER_get_name(c), *bits);
1635
1636 DEBUG(D_tls) debug_printf("Cipher: %s\n", cipherbuf);
1637 }
1638
1639
1640 static void
1641 peer_cert(SSL * ssl, tls_support * tlsp, uschar * peerdn, unsigned bsize)
1642 {
1643 /*XXX we might consider a list-of-certs variable for the cert chain.
1644 SSL_get_peer_cert_chain(SSL*).  We'd need a new variable type and support
1645 in list-handling functions, also consider the difference between the entire
1646 chain and the elements sent by the peer. */
1647
1648 /* Will have already noted peercert on a verify fail; possibly not the leaf */
1649 if (!tlsp->peercert)
1650   tlsp->peercert = SSL_get_peer_certificate(ssl);
1651 /* Beware anonymous ciphers which lead to server_cert being NULL */
1652 if (tlsp->peercert)
1653   {
1654   X509_NAME_oneline(X509_get_subject_name(tlsp->peercert), CS peerdn, bsize);
1655   peerdn[bsize-1] = '\0';
1656   tlsp->peerdn = peerdn;                /*XXX a static buffer... */
1657   }
1658 else
1659   tlsp->peerdn = NULL;
1660 }
1661
1662
1663
1664
1665
1666 /*************************************************
1667 *        Set up for verifying certificates       *
1668 *************************************************/
1669
1670 /* Load certs from file, return TRUE on success */
1671
1672 static BOOL
1673 chain_from_pem_file(const uschar * file, STACK_OF(X509) * verify_stack)
1674 {
1675 BIO * bp;
1676 X509 * x;
1677
1678 if (!(bp = BIO_new_file(CS file, "r"))) return FALSE;
1679 while ((x = PEM_read_bio_X509(bp, NULL, 0, NULL)))
1680   sk_X509_push(verify_stack, x);
1681 BIO_free(bp);
1682 return TRUE;
1683 }
1684
1685
1686
1687 /* Called by both client and server startup
1688
1689 Arguments:
1690   sctx          SSL_CTX* to initialise
1691   certs         certs file or NULL
1692   crl           CRL file or NULL
1693   host          NULL in a server; the remote host in a client
1694   optional      TRUE if called from a server for a host in tls_try_verify_hosts;
1695                 otherwise passed as FALSE
1696   cert_vfy_cb   Callback function for certificate verification
1697
1698 Returns:        OK/DEFER/FAIL
1699 */
1700
1701 static int
1702 setup_certs(SSL_CTX *sctx, uschar *certs, uschar *crl, host_item *host, BOOL optional,
1703     int (*cert_vfy_cb)(int, X509_STORE_CTX *) )
1704 {
1705 uschar *expcerts, *expcrl;
1706
1707 if (!expand_check(certs, US"tls_verify_certificates", &expcerts))
1708   return DEFER;
1709
1710 if (expcerts && *expcerts)
1711   {
1712   /* Tell the library to use its compiled-in location for the system default
1713   CA bundle. Then add the ones specified in the config, if any. */
1714
1715   if (!SSL_CTX_set_default_verify_paths(sctx))
1716     return tls_error(US"SSL_CTX_set_default_verify_paths", host, NULL);
1717
1718   if (Ustrcmp(expcerts, "system") != 0)
1719     {
1720     struct stat statbuf;
1721
1722     if (Ustat(expcerts, &statbuf) < 0)
1723       {
1724       log_write(0, LOG_MAIN|LOG_PANIC,
1725         "failed to stat %s for certificates", expcerts);
1726       return DEFER;
1727       }
1728     else
1729       {
1730       uschar *file, *dir;
1731       if ((statbuf.st_mode & S_IFMT) == S_IFDIR)
1732         { file = NULL; dir = expcerts; }
1733       else
1734         {
1735         file = expcerts; dir = NULL;
1736 #ifndef DISABLE_OCSP
1737         /* In the server if we will be offering an OCSP proof, load chain from
1738         file for verifying the OCSP proof at load time. */
1739
1740         if (  !host
1741            && statbuf.st_size > 0
1742            && server_static_cbinfo->u_ocsp.server.file
1743            && !chain_from_pem_file(file, server_static_cbinfo->verify_stack)
1744            )
1745           {
1746           log_write(0, LOG_MAIN|LOG_PANIC,
1747             "failed to load cert hain from %s", file);
1748           return DEFER;
1749           }
1750 #endif
1751         }
1752
1753       /* If a certificate file is empty, the next function fails with an
1754       unhelpful error message. If we skip it, we get the correct behaviour (no
1755       certificates are recognized, but the error message is still misleading (it
1756       says no certificate was supplied).  But this is better. */
1757
1758       if (  (!file || statbuf.st_size > 0)
1759          && !SSL_CTX_load_verify_locations(sctx, CS file, CS dir))
1760         return tls_error(US"SSL_CTX_load_verify_locations", host, NULL);
1761
1762       /* Load the list of CAs for which we will accept certs, for sending
1763       to the client.  This is only for the one-file tls_verify_certificates
1764       variant.
1765       If a list isn't loaded into the server, but
1766       some verify locations are set, the server end appears to make
1767       a wildcard reqest for client certs.
1768       Meanwhile, the client library as default behaviour *ignores* the list
1769       we send over the wire - see man SSL_CTX_set_client_cert_cb.
1770       Because of this, and that the dir variant is likely only used for
1771       the public-CA bundle (not for a private CA), not worth fixing.
1772       */
1773       if (file)
1774         {
1775         STACK_OF(X509_NAME) * names = SSL_load_client_CA_file(CS file);
1776
1777         DEBUG(D_tls) debug_printf("Added %d certificate authorities.\n",
1778                                     sk_X509_NAME_num(names));
1779         SSL_CTX_set_client_CA_list(sctx, names);
1780         }
1781       }
1782     }
1783
1784   /* Handle a certificate revocation list. */
1785
1786 #if OPENSSL_VERSION_NUMBER > 0x00907000L
1787
1788   /* This bit of code is now the version supplied by Lars Mainka. (I have
1789   merely reformatted it into the Exim code style.)
1790
1791   "From here I changed the code to add support for multiple crl's
1792   in pem format in one file or to support hashed directory entries in
1793   pem format instead of a file. This method now uses the library function
1794   X509_STORE_load_locations to add the CRL location to the SSL context.
1795   OpenSSL will then handle the verify against CA certs and CRLs by
1796   itself in the verify callback." */
1797
1798   if (!expand_check(crl, US"tls_crl", &expcrl)) return DEFER;
1799   if (expcrl && *expcrl)
1800     {
1801     struct stat statbufcrl;
1802     if (Ustat(expcrl, &statbufcrl) < 0)
1803       {
1804       log_write(0, LOG_MAIN|LOG_PANIC,
1805         "failed to stat %s for certificates revocation lists", expcrl);
1806       return DEFER;
1807       }
1808     else
1809       {
1810       /* is it a file or directory? */
1811       uschar *file, *dir;
1812       X509_STORE *cvstore = SSL_CTX_get_cert_store(sctx);
1813       if ((statbufcrl.st_mode & S_IFMT) == S_IFDIR)
1814         {
1815         file = NULL;
1816         dir = expcrl;
1817         DEBUG(D_tls) debug_printf("SSL CRL value is a directory %s\n", dir);
1818         }
1819       else
1820         {
1821         file = expcrl;
1822         dir = NULL;
1823         DEBUG(D_tls) debug_printf("SSL CRL value is a file %s\n", file);
1824         }
1825       if (X509_STORE_load_locations(cvstore, CS file, CS dir) == 0)
1826         return tls_error(US"X509_STORE_load_locations", host, NULL);
1827
1828       /* setting the flags to check against the complete crl chain */
1829
1830       X509_STORE_set_flags(cvstore,
1831         X509_V_FLAG_CRL_CHECK|X509_V_FLAG_CRL_CHECK_ALL);
1832       }
1833     }
1834
1835 #endif  /* OPENSSL_VERSION_NUMBER > 0x00907000L */
1836
1837   /* If verification is optional, don't fail if no certificate */
1838
1839   SSL_CTX_set_verify(sctx,
1840     SSL_VERIFY_PEER | (optional? 0 : SSL_VERIFY_FAIL_IF_NO_PEER_CERT),
1841     cert_vfy_cb);
1842   }
1843
1844 return OK;
1845 }
1846
1847
1848
1849 /*************************************************
1850 *       Start a TLS session in a server          *
1851 *************************************************/
1852
1853 /* This is called when Exim is running as a server, after having received
1854 the STARTTLS command. It must respond to that command, and then negotiate
1855 a TLS session.
1856
1857 Arguments:
1858   require_ciphers   allowed ciphers
1859
1860 Returns:            OK on success
1861                     DEFER for errors before the start of the negotiation
1862                     FAIL for errors during the negotation; the server can't
1863                       continue running.
1864 */
1865
1866 int
1867 tls_server_start(const uschar *require_ciphers)
1868 {
1869 int rc;
1870 uschar *expciphers;
1871 tls_ext_ctx_cb *cbinfo;
1872 static uschar peerdn[256];
1873 static uschar cipherbuf[256];
1874
1875 /* Check for previous activation */
1876
1877 if (tls_in.active >= 0)
1878   {
1879   tls_error(US"STARTTLS received after TLS started", NULL, US"");
1880   smtp_printf("554 Already in TLS\r\n");
1881   return FAIL;
1882   }
1883
1884 /* Initialize the SSL library. If it fails, it will already have logged
1885 the error. */
1886
1887 rc = tls_init(&server_ctx, NULL, tls_dhparam, tls_certificate, tls_privatekey,
1888 #ifndef DISABLE_OCSP
1889     tls_ocsp_file,
1890 #endif
1891     NULL, &server_static_cbinfo);
1892 if (rc != OK) return rc;
1893 cbinfo = server_static_cbinfo;
1894
1895 if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers))
1896   return FAIL;
1897
1898 /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they
1899 were historically separated by underscores. So that I can use either form in my
1900 tests, and also for general convenience, we turn underscores into hyphens here.
1901 */
1902
1903 if (expciphers)
1904   {
1905   uschar * s = expciphers;
1906   while (*s != 0) { if (*s == '_') *s = '-'; s++; }
1907   DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers);
1908   if (!SSL_CTX_set_cipher_list(server_ctx, CS expciphers))
1909     return tls_error(US"SSL_CTX_set_cipher_list", NULL, NULL);
1910   cbinfo->server_cipher_list = expciphers;
1911   }
1912
1913 /* If this is a host for which certificate verification is mandatory or
1914 optional, set up appropriately. */
1915
1916 tls_in.certificate_verified = FALSE;
1917 #ifdef EXPERIMENTAL_DANE
1918 tls_in.dane_verified = FALSE;
1919 #endif
1920 server_verify_callback_called = FALSE;
1921
1922 if (verify_check_host(&tls_verify_hosts) == OK)
1923   {
1924   rc = setup_certs(server_ctx, tls_verify_certificates, tls_crl, NULL,
1925                         FALSE, verify_callback_server);
1926   if (rc != OK) return rc;
1927   server_verify_optional = FALSE;
1928   }
1929 else if (verify_check_host(&tls_try_verify_hosts) == OK)
1930   {
1931   rc = setup_certs(server_ctx, tls_verify_certificates, tls_crl, NULL,
1932                         TRUE, verify_callback_server);
1933   if (rc != OK) return rc;
1934   server_verify_optional = TRUE;
1935   }
1936
1937 /* Prepare for new connection */
1938
1939 if (!(server_ssl = SSL_new(server_ctx))) return tls_error(US"SSL_new", NULL, NULL);
1940
1941 /* Warning: we used to SSL_clear(ssl) here, it was removed.
1942  *
1943  * With the SSL_clear(), we get strange interoperability bugs with
1944  * OpenSSL 1.0.1b and TLS1.1/1.2.  It looks as though this may be a bug in
1945  * OpenSSL itself, as a clear should not lead to inability to follow protocols.
1946  *
1947  * The SSL_clear() call is to let an existing SSL* be reused, typically after
1948  * session shutdown.  In this case, we have a brand new object and there's no
1949  * obvious reason to immediately clear it.  I'm guessing that this was
1950  * originally added because of incomplete initialisation which the clear fixed,
1951  * in some historic release.
1952  */
1953
1954 /* Set context and tell client to go ahead, except in the case of TLS startup
1955 on connection, where outputting anything now upsets the clients and tends to
1956 make them disconnect. We need to have an explicit fflush() here, to force out
1957 the response. Other smtp_printf() calls do not need it, because in non-TLS
1958 mode, the fflush() happens when smtp_getc() is called. */
1959
1960 SSL_set_session_id_context(server_ssl, sid_ctx, Ustrlen(sid_ctx));
1961 if (!tls_in.on_connect)
1962   {
1963   smtp_printf("220 TLS go ahead\r\n");
1964   fflush(smtp_out);
1965   }
1966
1967 /* Now negotiate the TLS session. We put our own timer on it, since it seems
1968 that the OpenSSL library doesn't. */
1969
1970 SSL_set_wfd(server_ssl, fileno(smtp_out));
1971 SSL_set_rfd(server_ssl, fileno(smtp_in));
1972 SSL_set_accept_state(server_ssl);
1973
1974 DEBUG(D_tls) debug_printf("Calling SSL_accept\n");
1975
1976 sigalrm_seen = FALSE;
1977 if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
1978 rc = SSL_accept(server_ssl);
1979 alarm(0);
1980
1981 if (rc <= 0)
1982   {
1983   tls_error(US"SSL_accept", NULL, sigalrm_seen ? US"timed out" : NULL);
1984   if (ERR_get_error() == 0)
1985     log_write(0, LOG_MAIN,
1986         "TLS client disconnected cleanly (rejected our certificate?)");
1987   return FAIL;
1988   }
1989
1990 DEBUG(D_tls) debug_printf("SSL_accept was successful\n");
1991
1992 /* TLS has been set up. Adjust the input functions to read via TLS,
1993 and initialize things. */
1994
1995 peer_cert(server_ssl, &tls_in, peerdn, sizeof(peerdn));
1996
1997 construct_cipher_name(server_ssl, cipherbuf, sizeof(cipherbuf), &tls_in.bits);
1998 tls_in.cipher = cipherbuf;
1999
2000 DEBUG(D_tls)
2001   {
2002   uschar buf[2048];
2003   if (SSL_get_shared_ciphers(server_ssl, CS buf, sizeof(buf)) != NULL)
2004     debug_printf("Shared ciphers: %s\n", buf);
2005   }
2006
2007 /* Record the certificate we presented */
2008   {
2009   X509 * crt = SSL_get_certificate(server_ssl);
2010   tls_in.ourcert = crt ? X509_dup(crt) : NULL;
2011   }
2012
2013 /* Only used by the server-side tls (tls_in), including tls_getc.
2014    Client-side (tls_out) reads (seem to?) go via
2015    smtp_read_response()/ip_recv().
2016    Hence no need to duplicate for _in and _out.
2017  */
2018 ssl_xfer_buffer = store_malloc(ssl_xfer_buffer_size);
2019 ssl_xfer_buffer_lwm = ssl_xfer_buffer_hwm = 0;
2020 ssl_xfer_eof = ssl_xfer_error = 0;
2021
2022 receive_getc = tls_getc;
2023 receive_get_cache = tls_get_cache;
2024 receive_ungetc = tls_ungetc;
2025 receive_feof = tls_feof;
2026 receive_ferror = tls_ferror;
2027 receive_smtp_buffered = tls_smtp_buffered;
2028
2029 tls_in.active = fileno(smtp_out);
2030 return OK;
2031 }
2032
2033
2034
2035
2036 static int
2037 tls_client_basic_ctx_init(SSL_CTX * ctx,
2038     host_item * host, smtp_transport_options_block * ob, tls_ext_ctx_cb * cbinfo
2039                           )
2040 {
2041 int rc;
2042 /* stick to the old behaviour for compatibility if tls_verify_certificates is
2043    set but both tls_verify_hosts and tls_try_verify_hosts is not set. Check only
2044    the specified host patterns if one of them is defined */
2045
2046 if (  (  !ob->tls_verify_hosts
2047       && (!ob->tls_try_verify_hosts || !*ob->tls_try_verify_hosts)
2048       )
2049    || (verify_check_given_host(&ob->tls_verify_hosts, host) == OK)
2050    )
2051   client_verify_optional = FALSE;
2052 else if (verify_check_given_host(&ob->tls_try_verify_hosts, host) == OK)
2053   client_verify_optional = TRUE;
2054 else
2055   return OK;
2056
2057 if ((rc = setup_certs(ctx, ob->tls_verify_certificates,
2058       ob->tls_crl, host, client_verify_optional, verify_callback_client)) != OK)
2059   return rc;
2060
2061 if (verify_check_given_host(&ob->tls_verify_cert_hostnames, host) == OK)
2062   {
2063   cbinfo->verify_cert_hostnames =
2064 #ifdef SUPPORT_I18N
2065     string_domain_utf8_to_alabel(host->name, NULL);
2066 #else
2067     host->name;
2068 #endif
2069   DEBUG(D_tls) debug_printf("Cert hostname to check: \"%s\"\n",
2070                     cbinfo->verify_cert_hostnames);
2071   }
2072 return OK;
2073 }
2074
2075
2076 #ifdef EXPERIMENTAL_DANE
2077 static int
2078 dane_tlsa_load(SSL * ssl, host_item * host, dns_answer * dnsa)
2079 {
2080 dns_record * rr;
2081 dns_scan dnss;
2082 const char * hostnames[2] = { CS host->name, NULL };
2083 int found = 0;
2084
2085 if (DANESSL_init(ssl, NULL, hostnames) != 1)
2086   return tls_error(US"hostnames load", host, NULL);
2087
2088 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
2089      rr;
2090      rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)
2091     ) if (rr->type == T_TLSA)
2092   {
2093   const uschar * p = rr->data;
2094   uint8_t usage, selector, mtype;
2095   const char * mdname;
2096
2097   usage = *p++;
2098
2099   /* Only DANE-TA(2) and DANE-EE(3) are supported */
2100   if (usage != 2 && usage != 3) continue;
2101
2102   selector = *p++;
2103   mtype = *p++;
2104
2105   switch (mtype)
2106     {
2107     default: continue;  /* Only match-types 0, 1, 2 are supported */
2108     case 0:  mdname = NULL; break;
2109     case 1:  mdname = "sha256"; break;
2110     case 2:  mdname = "sha512"; break;
2111     }
2112
2113   found++;
2114   switch (DANESSL_add_tlsa(ssl, usage, selector, mdname, p, rr->size - 3))
2115     {
2116     default:
2117       return tls_error(US"tlsa load", host, NULL);
2118     case 0:     /* action not taken */
2119     case 1:     break;
2120     }
2121
2122   tls_out.tlsa_usage |= 1<<usage;
2123   }
2124
2125 if (found)
2126   return OK;
2127
2128 log_write(0, LOG_MAIN, "DANE error: No usable TLSA records");
2129 return DEFER;
2130 }
2131 #endif  /*EXPERIMENTAL_DANE*/
2132
2133
2134
2135 /*************************************************
2136 *    Start a TLS session in a client             *
2137 *************************************************/
2138
2139 /* Called from the smtp transport after STARTTLS has been accepted.
2140
2141 Argument:
2142   fd               the fd of the connection
2143   host             connected host (for messages)
2144   addr             the first address
2145   tb               transport (always smtp)
2146   tlsa_dnsa        tlsa lookup, if DANE, else null
2147
2148 Returns:           OK on success
2149                    FAIL otherwise - note that tls_error() will not give DEFER
2150                      because this is not a server
2151 */
2152
2153 int
2154 tls_client_start(int fd, host_item *host, address_item *addr,
2155   transport_instance *tb
2156 #ifdef EXPERIMENTAL_DANE
2157   , dns_answer * tlsa_dnsa
2158 #endif
2159   )
2160 {
2161 smtp_transport_options_block * ob =
2162   (smtp_transport_options_block *)tb->options_block;
2163 static uschar peerdn[256];
2164 uschar * expciphers;
2165 int rc;
2166 static uschar cipherbuf[256];
2167
2168 #ifndef DISABLE_OCSP
2169 BOOL request_ocsp = FALSE;
2170 BOOL require_ocsp = FALSE;
2171 #endif
2172
2173 #ifdef EXPERIMENTAL_DANE
2174 tls_out.tlsa_usage = 0;
2175 #endif
2176
2177 #ifndef DISABLE_OCSP
2178   {
2179 # ifdef EXPERIMENTAL_DANE
2180   if (  tlsa_dnsa
2181      && ob->hosts_request_ocsp[0] == '*'
2182      && ob->hosts_request_ocsp[1] == '\0'
2183      )
2184     {
2185     /* Unchanged from default.  Use a safer one under DANE */
2186     request_ocsp = TRUE;
2187     ob->hosts_request_ocsp = US"${if or { {= {0}{$tls_out_tlsa_usage}} "
2188                                       "   {= {4}{$tls_out_tlsa_usage}} } "
2189                                  " {*}{}}";
2190     }
2191 # endif
2192
2193   if ((require_ocsp =
2194         verify_check_given_host(&ob->hosts_require_ocsp, host) == OK))
2195     request_ocsp = TRUE;
2196   else
2197 # ifdef EXPERIMENTAL_DANE
2198     if (!request_ocsp)
2199 # endif
2200       request_ocsp =
2201         verify_check_given_host(&ob->hosts_request_ocsp, host) == OK;
2202   }
2203 #endif
2204
2205 rc = tls_init(&client_ctx, host, NULL,
2206     ob->tls_certificate, ob->tls_privatekey,
2207 #ifndef DISABLE_OCSP
2208     (void *)(long)request_ocsp,
2209 #endif
2210     addr, &client_static_cbinfo);
2211 if (rc != OK) return rc;
2212
2213 tls_out.certificate_verified = FALSE;
2214 client_verify_callback_called = FALSE;
2215
2216 if (!expand_check(ob->tls_require_ciphers, US"tls_require_ciphers",
2217     &expciphers))
2218   return FAIL;
2219
2220 /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they
2221 are separated by underscores. So that I can use either form in my tests, and
2222 also for general convenience, we turn underscores into hyphens here. */
2223
2224 if (expciphers != NULL)
2225   {
2226   uschar *s = expciphers;
2227   while (*s != 0) { if (*s == '_') *s = '-'; s++; }
2228   DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers);
2229   if (!SSL_CTX_set_cipher_list(client_ctx, CS expciphers))
2230     return tls_error(US"SSL_CTX_set_cipher_list", host, NULL);
2231   }
2232
2233 #ifdef EXPERIMENTAL_DANE
2234 if (tlsa_dnsa)
2235   {
2236   SSL_CTX_set_verify(client_ctx,
2237     SSL_VERIFY_PEER | SSL_VERIFY_FAIL_IF_NO_PEER_CERT,
2238     verify_callback_client_dane);
2239
2240   if (!DANESSL_library_init())
2241     return tls_error(US"library init", host, NULL);
2242   if (DANESSL_CTX_init(client_ctx) <= 0)
2243     return tls_error(US"context init", host, NULL);
2244   }
2245 else
2246
2247 #endif
2248
2249   if ((rc = tls_client_basic_ctx_init(client_ctx, host, ob, client_static_cbinfo))
2250       != OK)
2251     return rc;
2252
2253 if ((client_ssl = SSL_new(client_ctx)) == NULL)
2254   return tls_error(US"SSL_new", host, NULL);
2255 SSL_set_session_id_context(client_ssl, sid_ctx, Ustrlen(sid_ctx));
2256 SSL_set_fd(client_ssl, fd);
2257 SSL_set_connect_state(client_ssl);
2258
2259 if (ob->tls_sni)
2260   {
2261   if (!expand_check(ob->tls_sni, US"tls_sni", &tls_out.sni))
2262     return FAIL;
2263   if (tls_out.sni == NULL)
2264     {
2265     DEBUG(D_tls) debug_printf("Setting TLS SNI forced to fail, not sending\n");
2266     }
2267   else if (!Ustrlen(tls_out.sni))
2268     tls_out.sni = NULL;
2269   else
2270     {
2271 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
2272     DEBUG(D_tls) debug_printf("Setting TLS SNI \"%s\"\n", tls_out.sni);
2273     SSL_set_tlsext_host_name(client_ssl, tls_out.sni);
2274 #else
2275     log_write(0, LOG_MAIN, "SNI unusable with this OpenSSL library version; ignoring \"%s\"\n",
2276           tls_out.sni);
2277 #endif
2278     }
2279   }
2280
2281 #ifdef EXPERIMENTAL_DANE
2282 if (tlsa_dnsa)
2283   if ((rc = dane_tlsa_load(client_ssl, host, tlsa_dnsa)) != OK)
2284     return rc;
2285 #endif
2286
2287 #ifndef DISABLE_OCSP
2288 /* Request certificate status at connection-time.  If the server
2289 does OCSP stapling we will get the callback (set in tls_init()) */
2290 # ifdef EXPERIMENTAL_DANE
2291 if (request_ocsp)
2292   {
2293   const uschar * s;
2294   if (  ((s = ob->hosts_require_ocsp) && Ustrstr(s, US"tls_out_tlsa_usage"))
2295      || ((s = ob->hosts_request_ocsp) && Ustrstr(s, US"tls_out_tlsa_usage"))
2296      )
2297     {   /* Re-eval now $tls_out_tlsa_usage is populated.  If
2298         this means we avoid the OCSP request, we wasted the setup
2299         cost in tls_init(). */
2300     require_ocsp = verify_check_given_host(&ob->hosts_require_ocsp, host) == OK;
2301     request_ocsp = require_ocsp
2302       || verify_check_given_host(&ob->hosts_request_ocsp, host) == OK;
2303     }
2304   }
2305 # endif
2306
2307 if (request_ocsp)
2308   {
2309   SSL_set_tlsext_status_type(client_ssl, TLSEXT_STATUSTYPE_ocsp);
2310   client_static_cbinfo->u_ocsp.client.verify_required = require_ocsp;
2311   tls_out.ocsp = OCSP_NOT_RESP;
2312   }
2313 #endif
2314
2315 #ifndef DISABLE_EVENT
2316 client_static_cbinfo->event_action = tb->event_action;
2317 #endif
2318
2319 /* There doesn't seem to be a built-in timeout on connection. */
2320
2321 DEBUG(D_tls) debug_printf("Calling SSL_connect\n");
2322 sigalrm_seen = FALSE;
2323 alarm(ob->command_timeout);
2324 rc = SSL_connect(client_ssl);
2325 alarm(0);
2326
2327 #ifdef EXPERIMENTAL_DANE
2328 if (tlsa_dnsa)
2329   DANESSL_cleanup(client_ssl);
2330 #endif
2331
2332 if (rc <= 0)
2333   return tls_error(US"SSL_connect", host, sigalrm_seen ? US"timed out" : NULL);
2334
2335 DEBUG(D_tls) debug_printf("SSL_connect succeeded\n");
2336
2337 peer_cert(client_ssl, &tls_out, peerdn, sizeof(peerdn));
2338
2339 construct_cipher_name(client_ssl, cipherbuf, sizeof(cipherbuf), &tls_out.bits);
2340 tls_out.cipher = cipherbuf;
2341
2342 /* Record the certificate we presented */
2343   {
2344   X509 * crt = SSL_get_certificate(client_ssl);
2345   tls_out.ourcert = crt ? X509_dup(crt) : NULL;
2346   }
2347
2348 tls_out.active = fd;
2349 return OK;
2350 }
2351
2352
2353
2354
2355
2356 /*************************************************
2357 *            TLS version of getc                 *
2358 *************************************************/
2359
2360 /* This gets the next byte from the TLS input buffer. If the buffer is empty,
2361 it refills the buffer via the SSL reading function.
2362
2363 Arguments:  none
2364 Returns:    the next character or EOF
2365
2366 Only used by the server-side TLS.
2367 */
2368
2369 int
2370 tls_getc(void)
2371 {
2372 if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm)
2373   {
2374   int error;
2375   int inbytes;
2376
2377   DEBUG(D_tls) debug_printf("Calling SSL_read(%p, %p, %u)\n", server_ssl,
2378     ssl_xfer_buffer, ssl_xfer_buffer_size);
2379
2380   if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
2381   inbytes = SSL_read(server_ssl, CS ssl_xfer_buffer, ssl_xfer_buffer_size);
2382   error = SSL_get_error(server_ssl, inbytes);
2383   alarm(0);
2384
2385   /* SSL_ERROR_ZERO_RETURN appears to mean that the SSL session has been
2386   closed down, not that the socket itself has been closed down. Revert to
2387   non-SSL handling. */
2388
2389   if (error == SSL_ERROR_ZERO_RETURN)
2390     {
2391     DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n");
2392
2393     receive_getc = smtp_getc;
2394     receive_get_cache = smtp_get_cache;
2395     receive_ungetc = smtp_ungetc;
2396     receive_feof = smtp_feof;
2397     receive_ferror = smtp_ferror;
2398     receive_smtp_buffered = smtp_buffered;
2399
2400     SSL_free(server_ssl);
2401     server_ssl = NULL;
2402     tls_in.active = -1;
2403     tls_in.bits = 0;
2404     tls_in.cipher = NULL;
2405     tls_in.peerdn = NULL;
2406     tls_in.sni = NULL;
2407
2408     return smtp_getc();
2409     }
2410
2411   /* Handle genuine errors */
2412
2413   else if (error == SSL_ERROR_SSL)
2414     {
2415     ERR_error_string(ERR_get_error(), ssl_errstring);
2416     log_write(0, LOG_MAIN, "TLS error (SSL_read): %s", ssl_errstring);
2417     ssl_xfer_error = 1;
2418     return EOF;
2419     }
2420
2421   else if (error != SSL_ERROR_NONE)
2422     {
2423     DEBUG(D_tls) debug_printf("Got SSL error %d\n", error);
2424     ssl_xfer_error = 1;
2425     return EOF;
2426     }
2427
2428 #ifndef DISABLE_DKIM
2429   dkim_exim_verify_feed(ssl_xfer_buffer, inbytes);
2430 #endif
2431   ssl_xfer_buffer_hwm = inbytes;
2432   ssl_xfer_buffer_lwm = 0;
2433   }
2434
2435 /* Something in the buffer; return next uschar */
2436
2437 return ssl_xfer_buffer[ssl_xfer_buffer_lwm++];
2438 }
2439
2440 void
2441 tls_get_cache()
2442 {
2443 #ifndef DISABLE_DKIM
2444 int n = ssl_xfer_buffer_hwm - ssl_xfer_buffer_lwm;
2445 if (n > 0)
2446   dkim_exim_verify_feed(ssl_xfer_buffer+ssl_xfer_buffer_lwm, n);
2447 #endif
2448 }
2449
2450
2451
2452 /*************************************************
2453 *          Read bytes from TLS channel           *
2454 *************************************************/
2455
2456 /*
2457 Arguments:
2458   buff      buffer of data
2459   len       size of buffer
2460
2461 Returns:    the number of bytes read
2462             -1 after a failed read
2463
2464 Only used by the client-side TLS.
2465 */
2466
2467 int
2468 tls_read(BOOL is_server, uschar *buff, size_t len)
2469 {
2470 SSL *ssl = is_server ? server_ssl : client_ssl;
2471 int inbytes;
2472 int error;
2473
2474 DEBUG(D_tls) debug_printf("Calling SSL_read(%p, %p, %u)\n", ssl,
2475   buff, (unsigned int)len);
2476
2477 inbytes = SSL_read(ssl, CS buff, len);
2478 error = SSL_get_error(ssl, inbytes);
2479
2480 if (error == SSL_ERROR_ZERO_RETURN)
2481   {
2482   DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n");
2483   return -1;
2484   }
2485 else if (error != SSL_ERROR_NONE)
2486   {
2487   return -1;
2488   }
2489
2490 return inbytes;
2491 }
2492
2493
2494
2495
2496
2497 /*************************************************
2498 *         Write bytes down TLS channel           *
2499 *************************************************/
2500
2501 /*
2502 Arguments:
2503   is_server channel specifier
2504   buff      buffer of data
2505   len       number of bytes
2506
2507 Returns:    the number of bytes after a successful write,
2508             -1 after a failed write
2509
2510 Used by both server-side and client-side TLS.
2511 */
2512
2513 int
2514 tls_write(BOOL is_server, const uschar *buff, size_t len)
2515 {
2516 int outbytes;
2517 int error;
2518 int left = len;
2519 SSL *ssl = is_server ? server_ssl : client_ssl;
2520
2521 DEBUG(D_tls) debug_printf("tls_do_write(%p, %d)\n", buff, left);
2522 while (left > 0)
2523   {
2524   DEBUG(D_tls) debug_printf("SSL_write(SSL, %p, %d)\n", buff, left);
2525   outbytes = SSL_write(ssl, CS buff, left);
2526   error = SSL_get_error(ssl, outbytes);
2527   DEBUG(D_tls) debug_printf("outbytes=%d error=%d\n", outbytes, error);
2528   switch (error)
2529     {
2530     case SSL_ERROR_SSL:
2531       ERR_error_string(ERR_get_error(), ssl_errstring);
2532       log_write(0, LOG_MAIN, "TLS error (SSL_write): %s", ssl_errstring);
2533       return -1;
2534
2535     case SSL_ERROR_NONE:
2536       left -= outbytes;
2537       buff += outbytes;
2538       break;
2539
2540     case SSL_ERROR_ZERO_RETURN:
2541       log_write(0, LOG_MAIN, "SSL channel closed on write");
2542       return -1;
2543
2544     case SSL_ERROR_SYSCALL:
2545       log_write(0, LOG_MAIN, "SSL_write: (from %s) syscall: %s",
2546         sender_fullhost ? sender_fullhost : US"<unknown>",
2547         strerror(errno));
2548       return -1;
2549
2550     default:
2551       log_write(0, LOG_MAIN, "SSL_write error %d", error);
2552       return -1;
2553     }
2554   }
2555 return len;
2556 }
2557
2558
2559
2560 /*************************************************
2561 *         Close down a TLS session               *
2562 *************************************************/
2563
2564 /* This is also called from within a delivery subprocess forked from the
2565 daemon, to shut down the TLS library, without actually doing a shutdown (which
2566 would tamper with the SSL session in the parent process).
2567
2568 Arguments:   TRUE if SSL_shutdown is to be called
2569 Returns:     nothing
2570
2571 Used by both server-side and client-side TLS.
2572 */
2573
2574 void
2575 tls_close(BOOL is_server, BOOL shutdown)
2576 {
2577 SSL **sslp = is_server ? &server_ssl : &client_ssl;
2578 int *fdp = is_server ? &tls_in.active : &tls_out.active;
2579
2580 if (*fdp < 0) return;  /* TLS was not active */
2581
2582 if (shutdown)
2583   {
2584   DEBUG(D_tls) debug_printf("tls_close(): shutting down SSL\n");
2585   SSL_shutdown(*sslp);
2586   }
2587
2588 SSL_free(*sslp);
2589 *sslp = NULL;
2590
2591 *fdp = -1;
2592 }
2593
2594
2595
2596
2597 /*************************************************
2598 *  Let tls_require_ciphers be checked at startup *
2599 *************************************************/
2600
2601 /* The tls_require_ciphers option, if set, must be something which the
2602 library can parse.
2603
2604 Returns:     NULL on success, or error message
2605 */
2606
2607 uschar *
2608 tls_validate_require_cipher(void)
2609 {
2610 SSL_CTX *ctx;
2611 uschar *s, *expciphers, *err;
2612
2613 /* this duplicates from tls_init(), we need a better "init just global
2614 state, for no specific purpose" singleton function of our own */
2615
2616 SSL_load_error_strings();
2617 OpenSSL_add_ssl_algorithms();
2618 #if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_SHA256)
2619 /* SHA256 is becoming ever more popular. This makes sure it gets added to the
2620 list of available digests. */
2621 EVP_add_digest(EVP_sha256());
2622 #endif
2623
2624 if (!(tls_require_ciphers && *tls_require_ciphers))
2625   return NULL;
2626
2627 if (!expand_check(tls_require_ciphers, US"tls_require_ciphers", &expciphers))
2628   return US"failed to expand tls_require_ciphers";
2629
2630 if (!(expciphers && *expciphers))
2631   return NULL;
2632
2633 /* normalisation ripped from above */
2634 s = expciphers;
2635 while (*s != 0) { if (*s == '_') *s = '-'; s++; }
2636
2637 err = NULL;
2638
2639 ctx = SSL_CTX_new(SSLv23_server_method());
2640 if (!ctx)
2641   {
2642   ERR_error_string(ERR_get_error(), ssl_errstring);
2643   return string_sprintf("SSL_CTX_new() failed: %s", ssl_errstring);
2644   }
2645
2646 DEBUG(D_tls)
2647   debug_printf("tls_require_ciphers expands to \"%s\"\n", expciphers);
2648
2649 if (!SSL_CTX_set_cipher_list(ctx, CS expciphers))
2650   {
2651   ERR_error_string(ERR_get_error(), ssl_errstring);
2652   err = string_sprintf("SSL_CTX_set_cipher_list(%s) failed", expciphers);
2653   }
2654
2655 SSL_CTX_free(ctx);
2656
2657 return err;
2658 }
2659
2660
2661
2662
2663 /*************************************************
2664 *         Report the library versions.           *
2665 *************************************************/
2666
2667 /* There have historically been some issues with binary compatibility in
2668 OpenSSL libraries; if Exim (like many other applications) is built against
2669 one version of OpenSSL but the run-time linker picks up another version,
2670 it can result in serious failures, including crashing with a SIGSEGV.  So
2671 report the version found by the compiler and the run-time version.
2672
2673 Note: some OS vendors backport security fixes without changing the version
2674 number/string, and the version date remains unchanged.  The _build_ date
2675 will change, so we can more usefully assist with version diagnosis by also
2676 reporting the build date.
2677
2678 Arguments:   a FILE* to print the results to
2679 Returns:     nothing
2680 */
2681
2682 void
2683 tls_version_report(FILE *f)
2684 {
2685 fprintf(f, "Library version: OpenSSL: Compile: %s\n"
2686            "                          Runtime: %s\n"
2687            "                                 : %s\n",
2688            OPENSSL_VERSION_TEXT,
2689            SSLeay_version(SSLEAY_VERSION),
2690            SSLeay_version(SSLEAY_BUILT_ON));
2691 /* third line is 38 characters for the %s and the line is 73 chars long;
2692 the OpenSSL output includes a "built on: " prefix already. */
2693 }
2694
2695
2696
2697
2698 /*************************************************
2699 *            Random number generation            *
2700 *************************************************/
2701
2702 /* Pseudo-random number generation.  The result is not expected to be
2703 cryptographically strong but not so weak that someone will shoot themselves
2704 in the foot using it as a nonce in input in some email header scheme or
2705 whatever weirdness they'll twist this into.  The result should handle fork()
2706 and avoid repeating sequences.  OpenSSL handles that for us.
2707
2708 Arguments:
2709   max       range maximum
2710 Returns     a random number in range [0, max-1]
2711 */
2712
2713 int
2714 vaguely_random_number(int max)
2715 {
2716 unsigned int r;
2717 int i, needed_len;
2718 static pid_t pidlast = 0;
2719 pid_t pidnow;
2720 uschar *p;
2721 uschar smallbuf[sizeof(r)];
2722
2723 if (max <= 1)
2724   return 0;
2725
2726 pidnow = getpid();
2727 if (pidnow != pidlast)
2728   {
2729   /* Although OpenSSL documents that "OpenSSL makes sure that the PRNG state
2730   is unique for each thread", this doesn't apparently apply across processes,
2731   so our own warning from vaguely_random_number_fallback() applies here too.
2732   Fix per PostgreSQL. */
2733   if (pidlast != 0)
2734     RAND_cleanup();
2735   pidlast = pidnow;
2736   }
2737
2738 /* OpenSSL auto-seeds from /dev/random, etc, but this a double-check. */
2739 if (!RAND_status())
2740   {
2741   randstuff r;
2742   gettimeofday(&r.tv, NULL);
2743   r.p = getpid();
2744
2745   RAND_seed((uschar *)(&r), sizeof(r));
2746   }
2747 /* We're after pseudo-random, not random; if we still don't have enough data
2748 in the internal PRNG then our options are limited.  We could sleep and hope
2749 for entropy to come along (prayer technique) but if the system is so depleted
2750 in the first place then something is likely to just keep taking it.  Instead,
2751 we'll just take whatever little bit of pseudo-random we can still manage to
2752 get. */
2753
2754 needed_len = sizeof(r);
2755 /* Don't take 8 times more entropy than needed if int is 8 octets and we were
2756 asked for a number less than 10. */
2757 for (r = max, i = 0; r; ++i)
2758   r >>= 1;
2759 i = (i + 7) / 8;
2760 if (i < needed_len)
2761   needed_len = i;
2762
2763 #ifdef EXIM_HAVE_RAND_PSEUDO
2764 /* We do not care if crypto-strong */
2765 i = RAND_pseudo_bytes(smallbuf, needed_len);
2766 #else
2767 i = RAND_bytes(smallbuf, needed_len);
2768 #endif
2769
2770 if (i < 0)
2771   {
2772   DEBUG(D_all)
2773     debug_printf("OpenSSL RAND_pseudo_bytes() not supported by RAND method, using fallback.\n");
2774   return vaguely_random_number_fallback(max);
2775   }
2776
2777 r = 0;
2778 for (p = smallbuf; needed_len; --needed_len, ++p)
2779   {
2780   r *= 256;
2781   r += *p;
2782   }
2783
2784 /* We don't particularly care about weighted results; if someone wants
2785 smooth distribution and cares enough then they should submit a patch then. */
2786 return r % max;
2787 }
2788
2789
2790
2791
2792 /*************************************************
2793 *        OpenSSL option parse                    *
2794 *************************************************/
2795
2796 /* Parse one option for tls_openssl_options_parse below
2797
2798 Arguments:
2799   name    one option name
2800   value   place to store a value for it
2801 Returns   success or failure in parsing
2802 */
2803
2804 struct exim_openssl_option {
2805   uschar *name;
2806   long    value;
2807 };
2808 /* We could use a macro to expand, but we need the ifdef and not all the
2809 options document which version they were introduced in.  Policylet: include
2810 all options unless explicitly for DTLS, let the administrator choose which
2811 to apply.
2812
2813 This list is current as of:
2814   ==>  1.0.1b  <==
2815 Plus SSL_OP_SAFARI_ECDHE_ECDSA_BUG from 2013-June patch/discussion on openssl-dev
2816 */
2817 static struct exim_openssl_option exim_openssl_options[] = {
2818 /* KEEP SORTED ALPHABETICALLY! */
2819 #ifdef SSL_OP_ALL
2820   { US"all", SSL_OP_ALL },
2821 #endif
2822 #ifdef SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
2823   { US"allow_unsafe_legacy_renegotiation", SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION },
2824 #endif
2825 #ifdef SSL_OP_CIPHER_SERVER_PREFERENCE
2826   { US"cipher_server_preference", SSL_OP_CIPHER_SERVER_PREFERENCE },
2827 #endif
2828 #ifdef SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
2829   { US"dont_insert_empty_fragments", SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS },
2830 #endif
2831 #ifdef SSL_OP_EPHEMERAL_RSA
2832   { US"ephemeral_rsa", SSL_OP_EPHEMERAL_RSA },
2833 #endif
2834 #ifdef SSL_OP_LEGACY_SERVER_CONNECT
2835   { US"legacy_server_connect", SSL_OP_LEGACY_SERVER_CONNECT },
2836 #endif
2837 #ifdef SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
2838   { US"microsoft_big_sslv3_buffer", SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER },
2839 #endif
2840 #ifdef SSL_OP_MICROSOFT_SESS_ID_BUG
2841   { US"microsoft_sess_id_bug", SSL_OP_MICROSOFT_SESS_ID_BUG },
2842 #endif
2843 #ifdef SSL_OP_MSIE_SSLV2_RSA_PADDING
2844   { US"msie_sslv2_rsa_padding", SSL_OP_MSIE_SSLV2_RSA_PADDING },
2845 #endif
2846 #ifdef SSL_OP_NETSCAPE_CHALLENGE_BUG
2847   { US"netscape_challenge_bug", SSL_OP_NETSCAPE_CHALLENGE_BUG },
2848 #endif
2849 #ifdef SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
2850   { US"netscape_reuse_cipher_change_bug", SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG },
2851 #endif
2852 #ifdef SSL_OP_NO_COMPRESSION
2853   { US"no_compression", SSL_OP_NO_COMPRESSION },
2854 #endif
2855 #ifdef SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
2856   { US"no_session_resumption_on_renegotiation", SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION },
2857 #endif
2858 #ifdef SSL_OP_NO_SSLv2
2859   { US"no_sslv2", SSL_OP_NO_SSLv2 },
2860 #endif
2861 #ifdef SSL_OP_NO_SSLv3
2862   { US"no_sslv3", SSL_OP_NO_SSLv3 },
2863 #endif
2864 #ifdef SSL_OP_NO_TICKET
2865   { US"no_ticket", SSL_OP_NO_TICKET },
2866 #endif
2867 #ifdef SSL_OP_NO_TLSv1
2868   { US"no_tlsv1", SSL_OP_NO_TLSv1 },
2869 #endif
2870 #ifdef SSL_OP_NO_TLSv1_1
2871 #if SSL_OP_NO_TLSv1_1 == 0x00000400L
2872   /* Error in chosen value in 1.0.1a; see first item in CHANGES for 1.0.1b */
2873 #warning OpenSSL 1.0.1a uses a bad value for SSL_OP_NO_TLSv1_1, ignoring
2874 #else
2875   { US"no_tlsv1_1", SSL_OP_NO_TLSv1_1 },
2876 #endif
2877 #endif
2878 #ifdef SSL_OP_NO_TLSv1_2
2879   { US"no_tlsv1_2", SSL_OP_NO_TLSv1_2 },
2880 #endif
2881 #ifdef SSL_OP_SAFARI_ECDHE_ECDSA_BUG
2882   { US"safari_ecdhe_ecdsa_bug", SSL_OP_SAFARI_ECDHE_ECDSA_BUG },
2883 #endif
2884 #ifdef SSL_OP_SINGLE_DH_USE
2885   { US"single_dh_use", SSL_OP_SINGLE_DH_USE },
2886 #endif
2887 #ifdef SSL_OP_SINGLE_ECDH_USE
2888   { US"single_ecdh_use", SSL_OP_SINGLE_ECDH_USE },
2889 #endif
2890 #ifdef SSL_OP_SSLEAY_080_CLIENT_DH_BUG
2891   { US"ssleay_080_client_dh_bug", SSL_OP_SSLEAY_080_CLIENT_DH_BUG },
2892 #endif
2893 #ifdef SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
2894   { US"sslref2_reuse_cert_type_bug", SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG },
2895 #endif
2896 #ifdef SSL_OP_TLS_BLOCK_PADDING_BUG
2897   { US"tls_block_padding_bug", SSL_OP_TLS_BLOCK_PADDING_BUG },
2898 #endif
2899 #ifdef SSL_OP_TLS_D5_BUG
2900   { US"tls_d5_bug", SSL_OP_TLS_D5_BUG },
2901 #endif
2902 #ifdef SSL_OP_TLS_ROLLBACK_BUG
2903   { US"tls_rollback_bug", SSL_OP_TLS_ROLLBACK_BUG },
2904 #endif
2905 };
2906 static int exim_openssl_options_size =
2907   sizeof(exim_openssl_options)/sizeof(struct exim_openssl_option);
2908
2909
2910 static BOOL
2911 tls_openssl_one_option_parse(uschar *name, long *value)
2912 {
2913 int first = 0;
2914 int last = exim_openssl_options_size;
2915 while (last > first)
2916   {
2917   int middle = (first + last)/2;
2918   int c = Ustrcmp(name, exim_openssl_options[middle].name);
2919   if (c == 0)
2920     {
2921     *value = exim_openssl_options[middle].value;
2922     return TRUE;
2923     }
2924   else if (c > 0)
2925     first = middle + 1;
2926   else
2927     last = middle;
2928   }
2929 return FALSE;
2930 }
2931
2932
2933
2934
2935 /*************************************************
2936 *        OpenSSL option parsing logic            *
2937 *************************************************/
2938
2939 /* OpenSSL has a number of compatibility options which an administrator might
2940 reasonably wish to set.  Interpret a list similarly to decode_bits(), so that
2941 we look like log_selector.
2942
2943 Arguments:
2944   option_spec  the administrator-supplied string of options
2945   results      ptr to long storage for the options bitmap
2946 Returns        success or failure
2947 */
2948
2949 BOOL
2950 tls_openssl_options_parse(uschar *option_spec, long *results)
2951 {
2952 long result, item;
2953 uschar *s, *end;
2954 uschar keep_c;
2955 BOOL adding, item_parsed;
2956
2957 result = 0L;
2958 /* Prior to 4.80 we or'd in SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS; removed
2959  * from default because it increases BEAST susceptibility. */
2960 #ifdef SSL_OP_NO_SSLv2
2961 result |= SSL_OP_NO_SSLv2;
2962 #endif
2963 #ifdef SSL_OP_SINGLE_DH_USE
2964 result |= SSL_OP_SINGLE_DH_USE;
2965 #endif
2966
2967 if (option_spec == NULL)
2968   {
2969   *results = result;
2970   return TRUE;
2971   }
2972
2973 for (s=option_spec; *s != '\0'; /**/)
2974   {
2975   while (isspace(*s)) ++s;
2976   if (*s == '\0')
2977     break;
2978   if (*s != '+' && *s != '-')
2979     {
2980     DEBUG(D_tls) debug_printf("malformed openssl option setting: "
2981         "+ or - expected but found \"%s\"\n", s);
2982     return FALSE;
2983     }
2984   adding = *s++ == '+';
2985   for (end = s; (*end != '\0') && !isspace(*end); ++end) /**/ ;
2986   keep_c = *end;
2987   *end = '\0';
2988   item_parsed = tls_openssl_one_option_parse(s, &item);
2989   *end = keep_c;
2990   if (!item_parsed)
2991     {
2992     DEBUG(D_tls) debug_printf("openssl option setting unrecognised: \"%s\"\n", s);
2993     return FALSE;
2994     }
2995   DEBUG(D_tls) debug_printf("openssl option, %s from %lx: %lx (%s)\n",
2996       adding ? "adding" : "removing", result, item, s);
2997   if (adding)
2998     result |= item;
2999   else
3000     result &= ~item;
3001   s = end;
3002   }
3003
3004 *results = result;
3005 return TRUE;
3006 }
3007
3008 /* vi: aw ai sw=2
3009 */
3010 /* End of tls-openssl.c */