src/src/tls-openssl.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2014 */
   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 DISABLE_OCSP
  26 # include <openssl/ocsp.h>
  27 #endif
  28
  29 #ifndef DISABLE_OCSP
  30 # define EXIM_OCSP_SKEW_SECONDS (300L)
  31 # define EXIM_OCSP_MAX_AGE (-1L)
  32 #endif
  33
  34 #if OPENSSL_VERSION_NUMBER >= 0x0090806fL && !defined(OPENSSL_NO_TLSEXT)
  35 # define EXIM_HAVE_OPENSSL_TLSEXT
  36 #endif
  37
  38 #if !defined(EXIM_HAVE_OPENSSL_TLSEXT) && !defined(DISABLE_OCSP)
  39 # warning "OpenSSL library version too old; define DISABLE_OCSP in Makefile"
  40 # define DISABLE_OCSP
  41 #endif
  42
  43 /* Structure for collecting random data for seeding. */
  44
  45 typedef struct randstuff {
  46   struct timeval tv;
  47   pid_t          p;
  48 } randstuff;
  49
  50 /* Local static variables */
  51
  52 static BOOL client_verify_callback_called = FALSE;
  53 static BOOL server_verify_callback_called = FALSE;
  54 static const uschar *sid_ctx = US"exim";
  55
  56 /* We have three different contexts to care about.
  57
  58 Simple case: client, `client_ctx`
  59  As a client, we can be doing a callout or cut-through delivery while receiving
  60  a message.  So we have a client context, which should have options initialised
  61  from the SMTP Transport.
  62
  63 Server:
  64  There are two cases: with and without ServerNameIndication from the client.
  65  Given TLS SNI, we can be using different keys, certs and various other
  66  configuration settings, because they're re-expanded with $tls_sni set.  This
  67  allows vhosting with TLS.  This SNI is sent in the handshake.
  68  A client might not send SNI, so we need a fallback, and an initial setup too.
  69  So as a server, we start out using `server_ctx`.
  70  If SNI is sent by the client, then we as server, mid-negotiation, try to clone
  71  `server_sni` from `server_ctx` and then initialise settings by re-expanding
  72  configuration.
  73 */
  74
  75 static SSL_CTX *client_ctx = NULL;
  76 static SSL_CTX *server_ctx = NULL;
  77 static SSL     *client_ssl = NULL;
  78 static SSL     *server_ssl = NULL;
  79
  80 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
  81 static SSL_CTX *server_sni = NULL;
  82 #endif
  83
  84 static char ssl_errstring[256];
  85
  86 static int  ssl_session_timeout = 200;
  87 static BOOL client_verify_optional = FALSE;
  88 static BOOL server_verify_optional = FALSE;
  89
  90 static BOOL reexpand_tls_files_for_sni = FALSE;
  91
  92
  93 typedef struct tls_ext_ctx_cb {
  94   uschar *certificate;
  95   uschar *privatekey;
  96 #ifndef DISABLE_OCSP
  97   BOOL is_server;
  98   union {
  99     struct {
 100       uschar        *file;
 101       uschar        *file_expanded;
 102       OCSP_RESPONSE *response;
 103     } server;
 104     struct {
 105       X509_STORE    *verify_store;      /* non-null if status requested */
 106       BOOL          verify_required;
 107     } client;
 108   } u_ocsp;
 109 #endif
 110   uschar *dhparam;
 111   /* these are cached from first expand */
 112   uschar *server_cipher_list;
 113   /* only passed down to tls_error: */
 114   host_item *host;
 115
 116 #ifdef EXPERIMENTAL_CERTNAMES
 117   uschar * verify_cert_hostnames;
 118 #endif
 119 } tls_ext_ctx_cb;
 120
 121 /* should figure out a cleanup of API to handle state preserved per
 122 implementation, for various reasons, which can be void * in the APIs.
 123 For now, we hack around it. */
 124 tls_ext_ctx_cb *client_static_cbinfo = NULL;
 125 tls_ext_ctx_cb *server_static_cbinfo = NULL;
 126
 127 static int
 128 setup_certs(SSL_CTX *sctx, uschar *certs, uschar *crl, host_item *host, BOOL optional,
 129     int (*cert_vfy_cb)(int, X509_STORE_CTX *) );
 130
 131 /* Callbacks */
 132 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
 133 static int tls_servername_cb(SSL *s, int *ad ARG_UNUSED, void *arg);
 134 #endif
 135 #ifndef DISABLE_OCSP
 136 static int tls_server_stapling_cb(SSL *s, void *arg);
 137 #endif
 138
 139
 140 /*************************************************
 141 *               Handle TLS error                 *
 142 *************************************************/
 143
 144 /* Called from lots of places when errors occur before actually starting to do
 145 the TLS handshake, that is, while the session is still in clear. Always returns
 146 DEFER for a server and FAIL for a client so that most calls can use "return
 147 tls_error(...)" to do this processing and then give an appropriate return. A
 148 single function is used for both server and client, because it is called from
 149 some shared functions.
 150
 151 Argument:
 152   prefix    text to include in the logged error
 153   host      NULL if setting up a server;
 154             the connected host if setting up a client
 155   msg       error message or NULL if we should ask OpenSSL
 156
 157 Returns:    OK/DEFER/FAIL
 158 */
 159
 160 static int
 161 tls_error(uschar *prefix, host_item *host, uschar *msg)
 162 {
 163 if (msg == NULL)
 164   {
 165   ERR_error_string(ERR_get_error(), ssl_errstring);
 166   msg = (uschar *)ssl_errstring;
 167   }
 168
 169 if (host == NULL)
 170   {
 171   uschar *conn_info = smtp_get_connection_info();
 172   if (Ustrncmp(conn_info, US"SMTP ", 5) == 0)
 173     conn_info += 5;
 174   log_write(0, LOG_MAIN, "TLS error on %s (%s): %s",
 175     conn_info, prefix, msg);
 176   return DEFER;
 177   }
 178 else
 179   {
 180   log_write(0, LOG_MAIN, "TLS error on connection to %s [%s] (%s): %s",
 181     host->name, host->address, prefix, msg);
 182   return FAIL;
 183   }
 184 }
 185
 186
 187
 188 /*************************************************
 189 *        Callback to generate RSA key            *
 190 *************************************************/
 191
 192 /*
 193 Arguments:
 194   s          SSL connection
 195   export     not used
 196   keylength  keylength
 197
 198 Returns:     pointer to generated key
 199 */
 200
 201 static RSA *
 202 rsa_callback(SSL *s, int export, int keylength)
 203 {
 204 RSA *rsa_key;
 205 export = export;     /* Shut picky compilers up */
 206 DEBUG(D_tls) debug_printf("Generating %d bit RSA key...\n", keylength);
 207 rsa_key = RSA_generate_key(keylength, RSA_F4, NULL, NULL);
 208 if (rsa_key == NULL)
 209   {
 210   ERR_error_string(ERR_get_error(), ssl_errstring);
 211   log_write(0, LOG_MAIN|LOG_PANIC, "TLS error (RSA_generate_key): %s",
 212     ssl_errstring);
 213   return NULL;
 214   }
 215 return rsa_key;
 216 }
 217
 218
 219
 220 /* Extreme debug
 221 #ifndef DISABLE_OCSP
 222 void
 223 x509_store_dump_cert_s_names(X509_STORE * store)
 224 {
 225 STACK_OF(X509_OBJECT) * roots= store->objs;
 226 int i;
 227 static uschar name[256];
 228
 229 for(i= 0; i<sk_X509_OBJECT_num(roots); i++)
 230   {
 231   X509_OBJECT * tmp_obj= sk_X509_OBJECT_value(roots, i);
 232   if(tmp_obj->type == X509_LU_X509)
 233     {
 234     X509 * current_cert= tmp_obj->data.x509;
 235     X509_NAME_oneline(X509_get_subject_name(current_cert), CS name, sizeof(name));
 236     debug_printf(" %s\n", name);
 237     }
 238   }
 239 }
 240 #endif
 241 */
 242
 243
 244 /*************************************************
 245 *        Callback for verification               *
 246 *************************************************/
 247
 248 /* The SSL library does certificate verification if set up to do so. This
 249 callback has the current yes/no state is in "state". If verification succeeded,
 250 we set up the tls_peerdn string. If verification failed, what happens depends
 251 on whether the client is required to present a verifiable certificate or not.
 252
 253 If verification is optional, we change the state to yes, but still log the
 254 verification error. For some reason (it really would help to have proper
 255 documentation of OpenSSL), this callback function then gets called again, this
 256 time with state = 1. In fact, that's useful, because we can set up the peerdn
 257 value, but we must take care not to set the private verified flag on the second
 258 time through.
 259
 260 Note: this function is not called if the client fails to present a certificate
 261 when asked. We get here only if a certificate has been received. Handling of
 262 optional verification for this case is done when requesting SSL to verify, by
 263 setting SSL_VERIFY_FAIL_IF_NO_PEER_CERT in the non-optional case.
 264
 265 Arguments:
 266   state      current yes/no state as 1/0
 267   x509ctx    certificate information.
 268   client     TRUE for client startup, FALSE for server startup
 269
 270 Returns:     1 if verified, 0 if not
 271 */
 272
 273 static int
 274 verify_callback(int state, X509_STORE_CTX *x509ctx,
 275   tls_support *tlsp, BOOL *calledp, BOOL *optionalp)
 276 {
 277 X509 * cert = X509_STORE_CTX_get_current_cert(x509ctx);
 278 static uschar txt[256];
 279
 280 X509_NAME_oneline(X509_get_subject_name(cert), CS txt, sizeof(txt));
 281
 282 if (state == 0)
 283   {
 284   log_write(0, LOG_MAIN, "SSL verify error: depth=%d error=%s cert=%s",
 285     X509_STORE_CTX_get_error_depth(x509ctx),
 286     X509_verify_cert_error_string(X509_STORE_CTX_get_error(x509ctx)),
 287     txt);
 288   tlsp->certificate_verified = FALSE;
 289   *calledp = TRUE;
 290   if (!*optionalp)
 291     {
 292     tlsp->peercert = X509_dup(cert);
 293     return 0;                       /* reject */
 294     }
 295   DEBUG(D_tls) debug_printf("SSL verify failure overridden (host in "
 296     "tls_try_verify_hosts)\n");
 297   }
 298
 299 else if (X509_STORE_CTX_get_error_depth(x509ctx) != 0)
 300   {
 301   DEBUG(D_tls) debug_printf("SSL verify ok: depth=%d SN=%s\n",
 302      X509_STORE_CTX_get_error_depth(x509ctx), txt);
 303 #ifndef DISABLE_OCSP
 304   if (tlsp == &tls_out && client_static_cbinfo->u_ocsp.client.verify_store)
 305     {   /* client, wanting stapling  */
 306     /* Add the server cert's signing chain as the one
 307     for the verification of the OCSP stapled information. */
 308
 309     if (!X509_STORE_add_cert(client_static_cbinfo->u_ocsp.client.verify_store,
 310                              cert))
 311       ERR_clear_error();
 312     }
 313 #endif
 314   }
 315 else
 316   {
 317 #ifdef EXPERIMENTAL_CERTNAMES
 318   uschar * verify_cert_hostnames;
 319 #endif
 320
 321   tlsp->peerdn = txt;
 322   tlsp->peercert = X509_dup(cert);
 323
 324 #ifdef EXPERIMENTAL_CERTNAMES
 325   if (  tlsp == &tls_out
 326      && ((verify_cert_hostnames = client_static_cbinfo->verify_cert_hostnames)))
 327         /* client, wanting hostname check */
 328
 329 # if OPENSSL_VERSION_NUMBER >= 0x010100000L || OPENSSL_VERSION_NUMBER >= 0x010002000L
 330 #  ifndef X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
 331 #   define X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS 0
 332 #  endif
 333     {
 334     int sep = 0;
 335     uschar * list = verify_cert_hostnames;
 336     uschar * name;
 337     int rc;
 338     while ((name = string_nextinlist(&list, &sep, NULL, 0)))
 339       if ((rc = X509_check_host(cert, name, 0,
 340                   X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS)))
 341         {
 342         if (rc < 0)
 343           {
 344           log_write(0, LOG_MAIN, "SSL verify error: internal error\n");
 345           name = NULL;
 346           }
 347         break;
 348         }
 349     if (!name)
 350       {
 351       log_write(0, LOG_MAIN,
 352         "SSL verify error: certificate name mismatch: \"%s\"\n", txt);
 353       return 0;                         /* reject */
 354       }
 355     }
 356 # else
 357     if (!tls_is_name_for_cert(verify_cert_hostnames, cert))
 358       {
 359       log_write(0, LOG_MAIN,
 360         "SSL verify error: certificate name mismatch: \"%s\"\n", txt);
 361       return 0;                         /* reject */
 362       }
 363 # endif
 364 #endif  /*EXPERIMENTAL_CERTNAMES*/
 365
 366   DEBUG(D_tls) debug_printf("SSL%s verify ok: depth=0 SN=%s\n",
 367     *calledp ? "" : " authenticated", txt);
 368   if (!*calledp) tlsp->certificate_verified = TRUE;
 369   *calledp = TRUE;
 370   }
 371
 372 return 1;   /* accept */
 373 }
 374
 375 static int
 376 verify_callback_client(int state, X509_STORE_CTX *x509ctx)
 377 {
 378 return verify_callback(state, x509ctx, &tls_out, &client_verify_callback_called, &client_verify_optional);
 379 }
 380
 381 static int
 382 verify_callback_server(int state, X509_STORE_CTX *x509ctx)
 383 {
 384 return verify_callback(state, x509ctx, &tls_in, &server_verify_callback_called, &server_verify_optional);
 385 }
 386
 387
 388 #ifdef EXPERIMENTAL_DANE
 389
 390 /* This gets called *by* the dane library verify callback, which interposes
 391 itself.
 392 */
 393 static int
 394 verify_callback_client_dane(int state, X509_STORE_CTX * x509ctx)
 395 {
 396 X509 * cert = X509_STORE_CTX_get_current_cert(x509ctx);
 397 static uschar txt[256];
 398
 399 X509_NAME_oneline(X509_get_subject_name(cert), CS txt, sizeof(txt));
 400
 401 DEBUG(D_tls) debug_printf("verify_callback_client_dane: %s\n", txt);
 402 tls_out.peerdn = txt;
 403 tls_out.peercert = X509_dup(cert);
 404
 405 if (state == 1)
 406   tls_out.dane_verified =
 407   tls_out.certificate_verified = TRUE;
 408 return 1;
 409 }
 410
 411 #endif  /*EXPERIMENTAL_DANE*/
 412
 413
 414 /*************************************************
 415 *           Information callback                 *
 416 *************************************************/
 417
 418 /* The SSL library functions call this from time to time to indicate what they
 419 are doing. We copy the string to the debugging output when TLS debugging has
 420 been requested.
 421
 422 Arguments:
 423   s         the SSL connection
 424   where
 425   ret
 426
 427 Returns:    nothing
 428 */
 429
 430 static void
 431 info_callback(SSL *s, int where, int ret)
 432 {
 433 where = where;
 434 ret = ret;
 435 DEBUG(D_tls) debug_printf("SSL info: %s\n", SSL_state_string_long(s));
 436 }
 437
 438
 439
 440 /*************************************************
 441 *                Initialize for DH               *
 442 *************************************************/
 443
 444 /* If dhparam is set, expand it, and load up the parameters for DH encryption.
 445
 446 Arguments:
 447   dhparam   DH parameter file or fixed parameter identity string
 448   host      connected host, if client; NULL if server
 449
 450 Returns:    TRUE if OK (nothing to set up, or setup worked)
 451 */
 452
 453 static BOOL
 454 init_dh(SSL_CTX *sctx, uschar *dhparam, host_item *host)
 455 {
 456 BIO *bio;
 457 DH *dh;
 458 uschar *dhexpanded;
 459 const char *pem;
 460
 461 if (!expand_check(dhparam, US"tls_dhparam", &dhexpanded))
 462   return FALSE;
 463
 464 if (!dhexpanded || !*dhexpanded)
 465   bio = BIO_new_mem_buf(CS std_dh_prime_default(), -1);
 466 else if (dhexpanded[0] == '/')
 467   {
 468   if (!(bio = BIO_new_file(CS dhexpanded, "r")))
 469     {
 470     tls_error(string_sprintf("could not read dhparams file %s", dhexpanded),
 471           host, US strerror(errno));
 472     return FALSE;
 473     }
 474   }
 475 else
 476   {
 477   if (Ustrcmp(dhexpanded, "none") == 0)
 478     {
 479     DEBUG(D_tls) debug_printf("Requested no DH parameters.\n");
 480     return TRUE;
 481     }
 482
 483   if (!(pem = std_dh_prime_named(dhexpanded)))
 484     {
 485     tls_error(string_sprintf("Unknown standard DH prime \"%s\"", dhexpanded),
 486         host, US strerror(errno));
 487     return FALSE;
 488     }
 489   bio = BIO_new_mem_buf(CS pem, -1);
 490   }
 491
 492 if (!(dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL)))
 493   {
 494   BIO_free(bio);
 495   tls_error(string_sprintf("Could not read tls_dhparams \"%s\"", dhexpanded),
 496       host, NULL);
 497   return FALSE;
 498   }
 499
 500 /* Even if it is larger, we silently return success rather than cause things
 501  * to fail out, so that a too-large DH will not knock out all TLS; it's a
 502  * debatable choice. */
 503 if ((8*DH_size(dh)) > tls_dh_max_bits)
 504   {
 505   DEBUG(D_tls)
 506     debug_printf("dhparams file %d bits, is > tls_dh_max_bits limit of %d",
 507         8*DH_size(dh), tls_dh_max_bits);
 508   }
 509 else
 510   {
 511   SSL_CTX_set_tmp_dh(sctx, dh);
 512   DEBUG(D_tls)
 513     debug_printf("Diffie-Hellman initialized from %s with %d-bit prime\n",
 514       dhexpanded ? dhexpanded : US"default", 8*DH_size(dh));
 515   }
 516
 517 DH_free(dh);
 518 BIO_free(bio);
 519
 520 return TRUE;
 521 }
 522
 523
 524
 525
 526 #ifndef DISABLE_OCSP
 527 /*************************************************
 528 *       Load OCSP information into state         *
 529 *************************************************/
 530
 531 /* Called to load the server OCSP response from the given file into memory, once
 532 caller has determined this is needed.  Checks validity.  Debugs a message
 533 if invalid.
 534
 535 ASSUMES: single response, for single cert.
 536
 537 Arguments:
 538   sctx            the SSL_CTX* to update
 539   cbinfo          various parts of session state
 540   expanded        the filename putatively holding an OCSP response
 541
 542 */
 543
 544 static void
 545 ocsp_load_response(SSL_CTX *sctx, tls_ext_ctx_cb *cbinfo, const uschar *expanded)
 546 {
 547 BIO *bio;
 548 OCSP_RESPONSE *resp;
 549 OCSP_BASICRESP *basic_response;
 550 OCSP_SINGLERESP *single_response;
 551 ASN1_GENERALIZEDTIME *rev, *thisupd, *nextupd;
 552 X509_STORE *store;
 553 unsigned long verify_flags;
 554 int status, reason, i;
 555
 556 cbinfo->u_ocsp.server.file_expanded = string_copy(expanded);
 557 if (cbinfo->u_ocsp.server.response)
 558   {
 559   OCSP_RESPONSE_free(cbinfo->u_ocsp.server.response);
 560   cbinfo->u_ocsp.server.response = NULL;
 561   }
 562
 563 bio = BIO_new_file(CS cbinfo->u_ocsp.server.file_expanded, "rb");
 564 if (!bio)
 565   {
 566   DEBUG(D_tls) debug_printf("Failed to open OCSP response file \"%s\"\n",
 567       cbinfo->u_ocsp.server.file_expanded);
 568   return;
 569   }
 570
 571 resp = d2i_OCSP_RESPONSE_bio(bio, NULL);
 572 BIO_free(bio);
 573 if (!resp)
 574   {
 575   DEBUG(D_tls) debug_printf("Error reading OCSP response.\n");
 576   return;
 577   }
 578
 579 status = OCSP_response_status(resp);
 580 if (status != OCSP_RESPONSE_STATUS_SUCCESSFUL)
 581   {
 582   DEBUG(D_tls) debug_printf("OCSP response not valid: %s (%d)\n",
 583       OCSP_response_status_str(status), status);
 584   goto bad;
 585   }
 586
 587 basic_response = OCSP_response_get1_basic(resp);
 588 if (!basic_response)
 589   {
 590   DEBUG(D_tls)
 591     debug_printf("OCSP response parse error: unable to extract basic response.\n");
 592   goto bad;
 593   }
 594
 595 store = SSL_CTX_get_cert_store(sctx);
 596 verify_flags = OCSP_NOVERIFY; /* check sigs, but not purpose */
 597
 598 /* May need to expose ability to adjust those flags?
 599 OCSP_NOSIGS OCSP_NOVERIFY OCSP_NOCHAIN OCSP_NOCHECKS OCSP_NOEXPLICIT
 600 OCSP_TRUSTOTHER OCSP_NOINTERN */
 601
 602 i = OCSP_basic_verify(basic_response, NULL, store, verify_flags);
 603 if (i <= 0)
 604   {
 605   DEBUG(D_tls) {
 606     ERR_error_string(ERR_get_error(), ssl_errstring);
 607     debug_printf("OCSP response verify failure: %s\n", US ssl_errstring);
 608     }
 609   goto bad;
 610   }
 611
 612 /* Here's the simplifying assumption: there's only one response, for the
 613 one certificate we use, and nothing for anything else in a chain.  If this
 614 proves false, we need to extract a cert id from our issued cert
 615 (tls_certificate) and use that for OCSP_resp_find_status() (which finds the
 616 right cert in the stack and then calls OCSP_single_get0_status()).
 617
 618 I'm hoping to avoid reworking a bunch more of how we handle state here. */
 619 single_response = OCSP_resp_get0(basic_response, 0);
 620 if (!single_response)
 621   {
 622   DEBUG(D_tls)
 623     debug_printf("Unable to get first response from OCSP basic response.\n");
 624   goto bad;
 625   }
 626
 627 status = OCSP_single_get0_status(single_response, &reason, &rev, &thisupd, &nextupd);
 628 if (status != V_OCSP_CERTSTATUS_GOOD)
 629   {
 630   DEBUG(D_tls) debug_printf("OCSP response bad cert status: %s (%d) %s (%d)\n",
 631       OCSP_cert_status_str(status), status,
 632       OCSP_crl_reason_str(reason), reason);
 633   goto bad;
 634   }
 635
 636 if (!OCSP_check_validity(thisupd, nextupd, EXIM_OCSP_SKEW_SECONDS, EXIM_OCSP_MAX_AGE))
 637   {
 638   DEBUG(D_tls) debug_printf("OCSP status invalid times.\n");
 639   goto bad;
 640   }
 641
 642 supply_response:
 643   cbinfo->u_ocsp.server.response = resp;
 644 return;
 645
 646 bad:
 647   if (running_in_test_harness)
 648     {
 649     extern char ** environ;
 650     uschar ** p;
 651     for (p = USS environ; *p != NULL; p++)
 652       if (Ustrncmp(*p, "EXIM_TESTHARNESS_DISABLE_OCSPVALIDITYCHECK", 42) == 0)
 653         {
 654         DEBUG(D_tls) debug_printf("Supplying known bad OCSP response\n");
 655         goto supply_response;
 656         }
 657     }
 658 return;
 659 }
 660 #endif  /*!DISABLE_OCSP*/
 661
 662
 663
 664
 665 /*************************************************
 666 *        Expand key and cert file specs          *
 667 *************************************************/
 668
 669 /* Called once during tls_init and possibly again during TLS setup, for a
 670 new context, if Server Name Indication was used and tls_sni was seen in
 671 the certificate string.
 672
 673 Arguments:
 674   sctx            the SSL_CTX* to update
 675   cbinfo          various parts of session state
 676
 677 Returns:          OK/DEFER/FAIL
 678 */
 679
 680 static int
 681 tls_expand_session_files(SSL_CTX *sctx, tls_ext_ctx_cb *cbinfo)
 682 {
 683 uschar *expanded;
 684
 685 if (cbinfo->certificate == NULL)
 686   return OK;
 687
 688 if (Ustrstr(cbinfo->certificate, US"tls_sni") ||
 689     Ustrstr(cbinfo->certificate, US"tls_in_sni") ||
 690     Ustrstr(cbinfo->certificate, US"tls_out_sni")
 691    )
 692   reexpand_tls_files_for_sni = TRUE;
 693
 694 if (!expand_check(cbinfo->certificate, US"tls_certificate", &expanded))
 695   return DEFER;
 696
 697 if (expanded != NULL)
 698   {
 699   DEBUG(D_tls) debug_printf("tls_certificate file %s\n", expanded);
 700   if (!SSL_CTX_use_certificate_chain_file(sctx, CS expanded))
 701     return tls_error(string_sprintf(
 702       "SSL_CTX_use_certificate_chain_file file=%s", expanded),
 703         cbinfo->host, NULL);
 704   }
 705
 706 if (cbinfo->privatekey != NULL &&
 707     !expand_check(cbinfo->privatekey, US"tls_privatekey", &expanded))
 708   return DEFER;
 709
 710 /* If expansion was forced to fail, key_expanded will be NULL. If the result
 711 of the expansion is an empty string, ignore it also, and assume the private
 712 key is in the same file as the certificate. */
 713
 714 if (expanded != NULL && *expanded != 0)
 715   {
 716   DEBUG(D_tls) debug_printf("tls_privatekey file %s\n", expanded);
 717   if (!SSL_CTX_use_PrivateKey_file(sctx, CS expanded, SSL_FILETYPE_PEM))
 718     return tls_error(string_sprintf(
 719       "SSL_CTX_use_PrivateKey_file file=%s", expanded), cbinfo->host, NULL);
 720   }
 721
 722 #ifndef DISABLE_OCSP
 723 if (cbinfo->is_server &&  cbinfo->u_ocsp.server.file != NULL)
 724   {
 725   if (!expand_check(cbinfo->u_ocsp.server.file, US"tls_ocsp_file", &expanded))
 726     return DEFER;
 727
 728   if (expanded != NULL && *expanded != 0)
 729     {
 730     DEBUG(D_tls) debug_printf("tls_ocsp_file %s\n", expanded);
 731     if (cbinfo->u_ocsp.server.file_expanded &&
 732         (Ustrcmp(expanded, cbinfo->u_ocsp.server.file_expanded) == 0))
 733       {
 734       DEBUG(D_tls)
 735         debug_printf("tls_ocsp_file value unchanged, using existing values.\n");
 736       } else {
 737         ocsp_load_response(sctx, cbinfo, expanded);
 738       }
 739     }
 740   }
 741 #endif
 742
 743 return OK;
 744 }
 745
 746
 747
 748
 749 /*************************************************
 750 *            Callback to handle SNI              *
 751 *************************************************/
 752
 753 /* Called when acting as server during the TLS session setup if a Server Name
 754 Indication extension was sent by the client.
 755
 756 API documentation is OpenSSL s_server.c implementation.
 757
 758 Arguments:
 759   s               SSL* of the current session
 760   ad              unknown (part of OpenSSL API) (unused)
 761   arg             Callback of "our" registered data
 762
 763 Returns:          SSL_TLSEXT_ERR_{OK,ALERT_WARNING,ALERT_FATAL,NOACK}
 764 */
 765
 766 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
 767 static int
 768 tls_servername_cb(SSL *s, int *ad ARG_UNUSED, void *arg)
 769 {
 770 const char *servername = SSL_get_servername(s, TLSEXT_NAMETYPE_host_name);
 771 tls_ext_ctx_cb *cbinfo = (tls_ext_ctx_cb *) arg;
 772 int rc;
 773 int old_pool = store_pool;
 774
 775 if (!servername)
 776   return SSL_TLSEXT_ERR_OK;
 777
 778 DEBUG(D_tls) debug_printf("Received TLS SNI \"%s\"%s\n", servername,
 779     reexpand_tls_files_for_sni ? "" : " (unused for certificate selection)");
 780
 781 /* Make the extension value available for expansion */
 782 store_pool = POOL_PERM;
 783 tls_in.sni = string_copy(US servername);
 784 store_pool = old_pool;
 785
 786 if (!reexpand_tls_files_for_sni)
 787   return SSL_TLSEXT_ERR_OK;
 788
 789 /* Can't find an SSL_CTX_clone() or equivalent, so we do it manually;
 790 not confident that memcpy wouldn't break some internal reference counting.
 791 Especially since there's a references struct member, which would be off. */
 792
 793 if (!(server_sni = SSL_CTX_new(SSLv23_server_method())))
 794   {
 795   ERR_error_string(ERR_get_error(), ssl_errstring);
 796   DEBUG(D_tls) debug_printf("SSL_CTX_new() failed: %s\n", ssl_errstring);
 797   return SSL_TLSEXT_ERR_NOACK;
 798   }
 799
 800 /* Not sure how many of these are actually needed, since SSL object
 801 already exists.  Might even need this selfsame callback, for reneg? */
 802
 803 SSL_CTX_set_info_callback(server_sni, SSL_CTX_get_info_callback(server_ctx));
 804 SSL_CTX_set_mode(server_sni, SSL_CTX_get_mode(server_ctx));
 805 SSL_CTX_set_options(server_sni, SSL_CTX_get_options(server_ctx));
 806 SSL_CTX_set_timeout(server_sni, SSL_CTX_get_timeout(server_ctx));
 807 SSL_CTX_set_tlsext_servername_callback(server_sni, tls_servername_cb);
 808 SSL_CTX_set_tlsext_servername_arg(server_sni, cbinfo);
 809 if (cbinfo->server_cipher_list)
 810   SSL_CTX_set_cipher_list(server_sni, CS cbinfo->server_cipher_list);
 811 #ifndef DISABLE_OCSP
 812 if (cbinfo->u_ocsp.server.file)
 813   {
 814   SSL_CTX_set_tlsext_status_cb(server_sni, tls_server_stapling_cb);
 815   SSL_CTX_set_tlsext_status_arg(server_sni, cbinfo);
 816   }
 817 #endif
 818
 819 rc = setup_certs(server_sni, tls_verify_certificates, tls_crl, NULL, FALSE, verify_callback_server);
 820 if (rc != OK) return SSL_TLSEXT_ERR_NOACK;
 821
 822 /* do this after setup_certs, because this can require the certs for verifying
 823 OCSP information. */
 824 rc = tls_expand_session_files(server_sni, cbinfo);
 825 if (rc != OK) return SSL_TLSEXT_ERR_NOACK;
 826
 827 if (!init_dh(server_sni, cbinfo->dhparam, NULL))
 828   return SSL_TLSEXT_ERR_NOACK;
 829
 830 DEBUG(D_tls) debug_printf("Switching SSL context.\n");
 831 SSL_set_SSL_CTX(s, server_sni);
 832
 833 return SSL_TLSEXT_ERR_OK;
 834 }
 835 #endif /* EXIM_HAVE_OPENSSL_TLSEXT */
 836
 837
 838
 839
 840 #ifndef DISABLE_OCSP
 841
 842 /*************************************************
 843 *        Callback to handle OCSP Stapling        *
 844 *************************************************/
 845
 846 /* Called when acting as server during the TLS session setup if the client
 847 requests OCSP information with a Certificate Status Request.
 848
 849 Documentation via openssl s_server.c and the Apache patch from the OpenSSL
 850 project.
 851
 852 */
 853
 854 static int
 855 tls_server_stapling_cb(SSL *s, void *arg)
 856 {
 857 const tls_ext_ctx_cb *cbinfo = (tls_ext_ctx_cb *) arg;
 858 uschar *response_der;
 859 int response_der_len;
 860
 861 DEBUG(D_tls)
 862   debug_printf("Received TLS status request (OCSP stapling); %s response.",
 863     cbinfo->u_ocsp.server.response ? "have" : "lack");
 864
 865 tls_in.ocsp = OCSP_NOT_RESP;
 866 if (!cbinfo->u_ocsp.server.response)
 867   return SSL_TLSEXT_ERR_NOACK;
 868
 869 response_der = NULL;
 870 response_der_len = i2d_OCSP_RESPONSE(cbinfo->u_ocsp.server.response,
 871                       &response_der);
 872 if (response_der_len <= 0)
 873   return SSL_TLSEXT_ERR_NOACK;
 874
 875 SSL_set_tlsext_status_ocsp_resp(server_ssl, response_der, response_der_len);
 876 tls_in.ocsp = OCSP_VFIED;
 877 return SSL_TLSEXT_ERR_OK;
 878 }
 879
 880
 881 static void
 882 time_print(BIO * bp, const char * str, ASN1_GENERALIZEDTIME * time)
 883 {
 884 BIO_printf(bp, "\t%s: ", str);
 885 ASN1_GENERALIZEDTIME_print(bp, time);
 886 BIO_puts(bp, "\n");
 887 }
 888
 889 static int
 890 tls_client_stapling_cb(SSL *s, void *arg)
 891 {
 892 tls_ext_ctx_cb * cbinfo = arg;
 893 const unsigned char * p;
 894 int len;
 895 OCSP_RESPONSE * rsp;
 896 OCSP_BASICRESP * bs;
 897 int i;
 898
 899 DEBUG(D_tls) debug_printf("Received TLS status response (OCSP stapling):");
 900 len = SSL_get_tlsext_status_ocsp_resp(s, &p);
 901 if(!p)
 902  {
 903   /* Expect this when we requested ocsp but got none */
 904   if (  cbinfo->u_ocsp.client.verify_required
 905      && log_extra_selector & LX_tls_cipher)
 906     log_write(0, LOG_MAIN, "Received TLS status callback, null content");
 907   else
 908     DEBUG(D_tls) debug_printf(" null\n");
 909   return cbinfo->u_ocsp.client.verify_required ? 0 : 1;
 910  }
 911
 912 if(!(rsp = d2i_OCSP_RESPONSE(NULL, &p, len)))
 913  {
 914   tls_out.ocsp = OCSP_FAILED;
 915   if (log_extra_selector & LX_tls_cipher)
 916     log_write(0, LOG_MAIN, "Received TLS status response, parse error");
 917   else
 918     DEBUG(D_tls) debug_printf(" parse error\n");
 919   return 0;
 920  }
 921
 922 if(!(bs = OCSP_response_get1_basic(rsp)))
 923   {
 924   tls_out.ocsp = OCSP_FAILED;
 925   if (log_extra_selector & LX_tls_cipher)
 926     log_write(0, LOG_MAIN, "Received TLS status response, error parsing response");
 927   else
 928     DEBUG(D_tls) debug_printf(" error parsing response\n");
 929   OCSP_RESPONSE_free(rsp);
 930   return 0;
 931   }
 932
 933 /* We'd check the nonce here if we'd put one in the request. */
 934 /* However that would defeat cacheability on the server so we don't. */
 935
 936 /* This section of code reworked from OpenSSL apps source;
 937    The OpenSSL Project retains copyright:
 938    Copyright (c) 1999 The OpenSSL Project.  All rights reserved.
 939 */
 940   {
 941     BIO * bp = NULL;
 942     int status, reason;
 943     ASN1_GENERALIZEDTIME *rev, *thisupd, *nextupd;
 944
 945     DEBUG(D_tls) bp = BIO_new_fp(stderr, BIO_NOCLOSE);
 946
 947     /*OCSP_RESPONSE_print(bp, rsp, 0);   extreme debug: stapling content */
 948
 949     /* Use the chain that verified the server cert to verify the stapled info */
 950     /* DEBUG(D_tls) x509_store_dump_cert_s_names(cbinfo->u_ocsp.client.verify_store); */
 951
 952     if ((i = OCSP_basic_verify(bs, NULL,
 953               cbinfo->u_ocsp.client.verify_store, 0)) <= 0)
 954       {
 955       tls_out.ocsp = OCSP_FAILED;
 956       BIO_printf(bp, "OCSP response verify failure\n");
 957       ERR_print_errors(bp);
 958       i = cbinfo->u_ocsp.client.verify_required ? 0 : 1;
 959       goto out;
 960       }
 961
 962     BIO_printf(bp, "OCSP response well-formed and signed OK\n");
 963
 964       {
 965       STACK_OF(OCSP_SINGLERESP) * sresp = bs->tbsResponseData->responses;
 966       OCSP_SINGLERESP * single;
 967
 968       if (sk_OCSP_SINGLERESP_num(sresp) != 1)
 969         {
 970         tls_out.ocsp = OCSP_FAILED;
 971         log_write(0, LOG_MAIN, "OCSP stapling "
 972             "with multiple responses not handled");
 973         i = cbinfo->u_ocsp.client.verify_required ? 0 : 1;
 974         goto out;
 975         }
 976       single = OCSP_resp_get0(bs, 0);
 977       status = OCSP_single_get0_status(single, &reason, &rev,
 978                   &thisupd, &nextupd);
 979       }
 980
 981     DEBUG(D_tls) time_print(bp, "This OCSP Update", thisupd);
 982     DEBUG(D_tls) if(nextupd) time_print(bp, "Next OCSP Update", nextupd);
 983     if (!OCSP_check_validity(thisupd, nextupd,
 984           EXIM_OCSP_SKEW_SECONDS, EXIM_OCSP_MAX_AGE))
 985       {
 986       tls_out.ocsp = OCSP_FAILED;
 987       DEBUG(D_tls) ERR_print_errors(bp);
 988       log_write(0, LOG_MAIN, "Server OSCP dates invalid");
 989       i = cbinfo->u_ocsp.client.verify_required ? 0 : 1;
 990       }
 991     else
 992       {
 993       DEBUG(D_tls) BIO_printf(bp, "Certificate status: %s\n",
 994                     OCSP_cert_status_str(status));
 995       switch(status)
 996         {
 997         case V_OCSP_CERTSTATUS_GOOD:
 998           tls_out.ocsp = OCSP_VFIED;
 999           i = 1;
1000           break;
1001         case V_OCSP_CERTSTATUS_REVOKED:
1002           tls_out.ocsp = OCSP_FAILED;
1003           log_write(0, LOG_MAIN, "Server certificate revoked%s%s",
1004               reason != -1 ? "; reason: " : "",
1005               reason != -1 ? OCSP_crl_reason_str(reason) : "");
1006           DEBUG(D_tls) time_print(bp, "Revocation Time", rev);
1007           i = cbinfo->u_ocsp.client.verify_required ? 0 : 1;
1008           break;
1009         default:
1010           tls_out.ocsp = OCSP_FAILED;
1011           log_write(0, LOG_MAIN,
1012               "Server certificate status unknown, in OCSP stapling");
1013           i = cbinfo->u_ocsp.client.verify_required ? 0 : 1;
1014           break;
1015         }
1016       }
1017   out:
1018     BIO_free(bp);
1019   }
1020
1021 OCSP_RESPONSE_free(rsp);
1022 return i;
1023 }
1024 #endif  /*!DISABLE_OCSP*/
1025
1026
1027 /*************************************************
1028 *            Initialize for TLS                  *
1029 *************************************************/
1030
1031 /* Called from both server and client code, to do preliminary initialization
1032 of the library.  We allocate and return a context structure.
1033
1034 Arguments:
1035   ctxp            returned SSL context
1036   host            connected host, if client; NULL if server
1037   dhparam         DH parameter file
1038   certificate     certificate file
1039   privatekey      private key
1040   ocsp_file       file of stapling info (server); flag for require ocsp (client)
1041   addr            address if client; NULL if server (for some randomness)
1042   cbp             place to put allocated callback context
1043
1044 Returns:          OK/DEFER/FAIL
1045 */
1046
1047 static int
1048 tls_init(SSL_CTX **ctxp, host_item *host, uschar *dhparam, uschar *certificate,
1049   uschar *privatekey,
1050 #ifndef DISABLE_OCSP
1051   uschar *ocsp_file,
1052 #endif
1053   address_item *addr, tls_ext_ctx_cb ** cbp)
1054 {
1055 long init_options;
1056 int rc;
1057 BOOL okay;
1058 tls_ext_ctx_cb *cbinfo;
1059
1060 cbinfo = store_malloc(sizeof(tls_ext_ctx_cb));
1061 cbinfo->certificate = certificate;
1062 cbinfo->privatekey = privatekey;
1063 #ifndef DISABLE_OCSP
1064 if ((cbinfo->is_server = host==NULL))
1065   {
1066   cbinfo->u_ocsp.server.file = ocsp_file;
1067   cbinfo->u_ocsp.server.file_expanded = NULL;
1068   cbinfo->u_ocsp.server.response = NULL;
1069   }
1070 else
1071   cbinfo->u_ocsp.client.verify_store = NULL;
1072 #endif
1073 cbinfo->dhparam = dhparam;
1074 cbinfo->server_cipher_list = NULL;
1075 cbinfo->host = host;
1076
1077 SSL_load_error_strings();          /* basic set up */
1078 OpenSSL_add_ssl_algorithms();
1079
1080 #if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_SHA256)
1081 /* SHA256 is becoming ever more popular. This makes sure it gets added to the
1082 list of available digests. */
1083 EVP_add_digest(EVP_sha256());
1084 #endif
1085
1086 /* Create a context.
1087 The OpenSSL docs in 1.0.1b have not been updated to clarify TLS variant
1088 negotiation in the different methods; as far as I can tell, the only
1089 *_{server,client}_method which allows negotiation is SSLv23, which exists even
1090 when OpenSSL is built without SSLv2 support.
1091 By disabling with openssl_options, we can let admins re-enable with the
1092 existing knob. */
1093
1094 *ctxp = SSL_CTX_new((host == NULL)?
1095   SSLv23_server_method() : SSLv23_client_method());
1096
1097 if (*ctxp == NULL) return tls_error(US"SSL_CTX_new", host, NULL);
1098
1099 /* It turns out that we need to seed the random number generator this early in
1100 order to get the full complement of ciphers to work. It took me roughly a day
1101 of work to discover this by experiment.
1102
1103 On systems that have /dev/urandom, SSL may automatically seed itself from
1104 there. Otherwise, we have to make something up as best we can. Double check
1105 afterwards. */
1106
1107 if (!RAND_status())
1108   {
1109   randstuff r;
1110   gettimeofday(&r.tv, NULL);
1111   r.p = getpid();
1112
1113   RAND_seed((uschar *)(&r), sizeof(r));
1114   RAND_seed((uschar *)big_buffer, big_buffer_size);
1115   if (addr != NULL) RAND_seed((uschar *)addr, sizeof(addr));
1116
1117   if (!RAND_status())
1118     return tls_error(US"RAND_status", host,
1119       US"unable to seed random number generator");
1120   }
1121
1122 /* Set up the information callback, which outputs if debugging is at a suitable
1123 level. */
1124
1125 SSL_CTX_set_info_callback(*ctxp, (void (*)())info_callback);
1126
1127 /* Automatically re-try reads/writes after renegotiation. */
1128 (void) SSL_CTX_set_mode(*ctxp, SSL_MODE_AUTO_RETRY);
1129
1130 /* Apply administrator-supplied work-arounds.
1131 Historically we applied just one requested option,
1132 SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS, but when bug 994 requested a second, we
1133 moved to an administrator-controlled list of options to specify and
1134 grandfathered in the first one as the default value for "openssl_options".
1135
1136 No OpenSSL version number checks: the options we accept depend upon the
1137 availability of the option value macros from OpenSSL.  */
1138
1139 okay = tls_openssl_options_parse(openssl_options, &init_options);
1140 if (!okay)
1141   return tls_error(US"openssl_options parsing failed", host, NULL);
1142
1143 if (init_options)
1144   {
1145   DEBUG(D_tls) debug_printf("setting SSL CTX options: %#lx\n", init_options);
1146   if (!(SSL_CTX_set_options(*ctxp, init_options)))
1147     return tls_error(string_sprintf(
1148           "SSL_CTX_set_option(%#lx)", init_options), host, NULL);
1149   }
1150 else
1151   DEBUG(D_tls) debug_printf("no SSL CTX options to set\n");
1152
1153 /* Initialize with DH parameters if supplied */
1154
1155 if (!init_dh(*ctxp, dhparam, host)) return DEFER;
1156
1157 /* Set up certificate and key (and perhaps OCSP info) */
1158
1159 rc = tls_expand_session_files(*ctxp, cbinfo);
1160 if (rc != OK) return rc;
1161
1162 /* If we need to handle SNI, do so */
1163 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
1164 if (host == NULL)               /* server */
1165   {
1166 # ifndef DISABLE_OCSP
1167   /* We check u_ocsp.server.file, not server.response, because we care about if
1168   the option exists, not what the current expansion might be, as SNI might
1169   change the certificate and OCSP file in use between now and the time the
1170   callback is invoked. */
1171   if (cbinfo->u_ocsp.server.file)
1172     {
1173     SSL_CTX_set_tlsext_status_cb(server_ctx, tls_server_stapling_cb);
1174     SSL_CTX_set_tlsext_status_arg(server_ctx, cbinfo);
1175     }
1176 # endif
1177   /* We always do this, so that $tls_sni is available even if not used in
1178   tls_certificate */
1179   SSL_CTX_set_tlsext_servername_callback(*ctxp, tls_servername_cb);
1180   SSL_CTX_set_tlsext_servername_arg(*ctxp, cbinfo);
1181   }
1182 # ifndef DISABLE_OCSP
1183 else                    /* client */
1184   if(ocsp_file)         /* wanting stapling */
1185     {
1186     if (!(cbinfo->u_ocsp.client.verify_store = X509_STORE_new()))
1187       {
1188       DEBUG(D_tls) debug_printf("failed to create store for stapling verify\n");
1189       return FAIL;
1190       }
1191     SSL_CTX_set_tlsext_status_cb(*ctxp, tls_client_stapling_cb);
1192     SSL_CTX_set_tlsext_status_arg(*ctxp, cbinfo);
1193     }
1194 # endif
1195 #endif
1196
1197 #ifdef EXPERIMENTAL_CERTNAMES
1198 cbinfo->verify_cert_hostnames = NULL;
1199 #endif
1200
1201 /* Set up the RSA callback */
1202
1203 SSL_CTX_set_tmp_rsa_callback(*ctxp, rsa_callback);
1204
1205 /* Finally, set the timeout, and we are done */
1206
1207 SSL_CTX_set_timeout(*ctxp, ssl_session_timeout);
1208 DEBUG(D_tls) debug_printf("Initialized TLS\n");
1209
1210 *cbp = cbinfo;
1211
1212 return OK;
1213 }
1214
1215
1216
1217
1218 /*************************************************
1219 *           Get name of cipher in use            *
1220 *************************************************/
1221
1222 /*
1223 Argument:   pointer to an SSL structure for the connection
1224             buffer to use for answer
1225             size of buffer
1226             pointer to number of bits for cipher
1227 Returns:    nothing
1228 */
1229
1230 static void
1231 construct_cipher_name(SSL *ssl, uschar *cipherbuf, int bsize, int *bits)
1232 {
1233 /* With OpenSSL 1.0.0a, this needs to be const but the documentation doesn't
1234 yet reflect that.  It should be a safe change anyway, even 0.9.8 versions have
1235 the accessor functions use const in the prototype. */
1236 const SSL_CIPHER *c;
1237 const uschar *ver;
1238
1239 ver = (const uschar *)SSL_get_version(ssl);
1240
1241 c = (const SSL_CIPHER *) SSL_get_current_cipher(ssl);
1242 SSL_CIPHER_get_bits(c, bits);
1243
1244 string_format(cipherbuf, bsize, "%s:%s:%u", ver,
1245   SSL_CIPHER_get_name(c), *bits);
1246
1247 DEBUG(D_tls) debug_printf("Cipher: %s\n", cipherbuf);
1248 }
1249
1250
1251
1252
1253
1254 /*************************************************
1255 *        Set up for verifying certificates       *
1256 *************************************************/
1257
1258 /* Called by both client and server startup
1259
1260 Arguments:
1261   sctx          SSL_CTX* to initialise
1262   certs         certs file or NULL
1263   crl           CRL file or NULL
1264   host          NULL in a server; the remote host in a client
1265   optional      TRUE if called from a server for a host in tls_try_verify_hosts;
1266                 otherwise passed as FALSE
1267   cert_vfy_cb   Callback function for certificate verification
1268
1269 Returns:        OK/DEFER/FAIL
1270 */
1271
1272 static int
1273 setup_certs(SSL_CTX *sctx, uschar *certs, uschar *crl, host_item *host, BOOL optional,
1274     int (*cert_vfy_cb)(int, X509_STORE_CTX *) )
1275 {
1276 uschar *expcerts, *expcrl;
1277
1278 if (!expand_check(certs, US"tls_verify_certificates", &expcerts))
1279   return DEFER;
1280
1281 if (expcerts != NULL && *expcerts != '\0')
1282   {
1283   struct stat statbuf;
1284   if (!SSL_CTX_set_default_verify_paths(sctx))
1285     return tls_error(US"SSL_CTX_set_default_verify_paths", host, NULL);
1286
1287   if (Ustat(expcerts, &statbuf) < 0)
1288     {
1289     log_write(0, LOG_MAIN|LOG_PANIC,
1290       "failed to stat %s for certificates", expcerts);
1291     return DEFER;
1292     }
1293   else
1294     {
1295     uschar *file, *dir;
1296     if ((statbuf.st_mode & S_IFMT) == S_IFDIR)
1297       { file = NULL; dir = expcerts; }
1298     else
1299       { file = expcerts; dir = NULL; }
1300
1301     /* If a certificate file is empty, the next function fails with an
1302     unhelpful error message. If we skip it, we get the correct behaviour (no
1303     certificates are recognized, but the error message is still misleading (it
1304     says no certificate was supplied.) But this is better. */
1305
1306     if ((file == NULL || statbuf.st_size > 0) &&
1307           !SSL_CTX_load_verify_locations(sctx, CS file, CS dir))
1308       return tls_error(US"SSL_CTX_load_verify_locations", host, NULL);
1309
1310     if (file != NULL)
1311       {
1312       SSL_CTX_set_client_CA_list(sctx, SSL_load_client_CA_file(CS file));
1313       }
1314     }
1315
1316   /* Handle a certificate revocation list. */
1317
1318   #if OPENSSL_VERSION_NUMBER > 0x00907000L
1319
1320   /* This bit of code is now the version supplied by Lars Mainka. (I have
1321    * merely reformatted it into the Exim code style.)
1322
1323    * "From here I changed the code to add support for multiple crl's
1324    * in pem format in one file or to support hashed directory entries in
1325    * pem format instead of a file. This method now uses the library function
1326    * X509_STORE_load_locations to add the CRL location to the SSL context.
1327    * OpenSSL will then handle the verify against CA certs and CRLs by
1328    * itself in the verify callback." */
1329
1330   if (!expand_check(crl, US"tls_crl", &expcrl)) return DEFER;
1331   if (expcrl != NULL && *expcrl != 0)
1332     {
1333     struct stat statbufcrl;
1334     if (Ustat(expcrl, &statbufcrl) < 0)
1335       {
1336       log_write(0, LOG_MAIN|LOG_PANIC,
1337         "failed to stat %s for certificates revocation lists", expcrl);
1338       return DEFER;
1339       }
1340     else
1341       {
1342       /* is it a file or directory? */
1343       uschar *file, *dir;
1344       X509_STORE *cvstore = SSL_CTX_get_cert_store(sctx);
1345       if ((statbufcrl.st_mode & S_IFMT) == S_IFDIR)
1346         {
1347         file = NULL;
1348         dir = expcrl;
1349         DEBUG(D_tls) debug_printf("SSL CRL value is a directory %s\n", dir);
1350         }
1351       else
1352         {
1353         file = expcrl;
1354         dir = NULL;
1355         DEBUG(D_tls) debug_printf("SSL CRL value is a file %s\n", file);
1356         }
1357       if (X509_STORE_load_locations(cvstore, CS file, CS dir) == 0)
1358         return tls_error(US"X509_STORE_load_locations", host, NULL);
1359
1360       /* setting the flags to check against the complete crl chain */
1361
1362       X509_STORE_set_flags(cvstore,
1363         X509_V_FLAG_CRL_CHECK|X509_V_FLAG_CRL_CHECK_ALL);
1364       }
1365     }
1366
1367   #endif  /* OPENSSL_VERSION_NUMBER > 0x00907000L */
1368
1369   /* If verification is optional, don't fail if no certificate */
1370
1371   SSL_CTX_set_verify(sctx,
1372     SSL_VERIFY_PEER | (optional? 0 : SSL_VERIFY_FAIL_IF_NO_PEER_CERT),
1373     cert_vfy_cb);
1374   }
1375
1376 return OK;
1377 }
1378
1379
1380
1381 /*************************************************
1382 *       Start a TLS session in a server          *
1383 *************************************************/
1384
1385 /* This is called when Exim is running as a server, after having received
1386 the STARTTLS command. It must respond to that command, and then negotiate
1387 a TLS session.
1388
1389 Arguments:
1390   require_ciphers   allowed ciphers
1391
1392 Returns:            OK on success
1393                     DEFER for errors before the start of the negotiation
1394                     FAIL for errors during the negotation; the server can't
1395                       continue running.
1396 */
1397
1398 int
1399 tls_server_start(const uschar *require_ciphers)
1400 {
1401 int rc;
1402 uschar *expciphers;
1403 tls_ext_ctx_cb *cbinfo;
1404 static uschar cipherbuf[256];
1405
1406 /* Check for previous activation */
1407
1408 if (tls_in.active >= 0)
1409   {
1410   tls_error(US"STARTTLS received after TLS started", NULL, US"");
1411   smtp_printf("554 Already in TLS\r\n");
1412   return FAIL;
1413   }
1414
1415 /* Initialize the SSL library. If it fails, it will already have logged
1416 the error. */
1417
1418 rc = tls_init(&server_ctx, NULL, tls_dhparam, tls_certificate, tls_privatekey,
1419 #ifndef DISABLE_OCSP
1420     tls_ocsp_file,
1421 #endif
1422     NULL, &server_static_cbinfo);
1423 if (rc != OK) return rc;
1424 cbinfo = server_static_cbinfo;
1425
1426 if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers))
1427   return FAIL;
1428
1429 /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they
1430 were historically separated by underscores. So that I can use either form in my
1431 tests, and also for general convenience, we turn underscores into hyphens here.
1432 */
1433
1434 if (expciphers != NULL)
1435   {
1436   uschar *s = expciphers;
1437   while (*s != 0) { if (*s == '_') *s = '-'; s++; }
1438   DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers);
1439   if (!SSL_CTX_set_cipher_list(server_ctx, CS expciphers))
1440     return tls_error(US"SSL_CTX_set_cipher_list", NULL, NULL);
1441   cbinfo->server_cipher_list = expciphers;
1442   }
1443
1444 /* If this is a host for which certificate verification is mandatory or
1445 optional, set up appropriately. */
1446
1447 tls_in.certificate_verified = FALSE;
1448 #ifdef EXPERIMENTAL_DANE
1449 tls_in.dane_verified = FALSE;
1450 #endif
1451 server_verify_callback_called = FALSE;
1452
1453 if (verify_check_host(&tls_verify_hosts) == OK)
1454   {
1455   rc = setup_certs(server_ctx, tls_verify_certificates, tls_crl, NULL,
1456                         FALSE, verify_callback_server);
1457   if (rc != OK) return rc;
1458   server_verify_optional = FALSE;
1459   }
1460 else if (verify_check_host(&tls_try_verify_hosts) == OK)
1461   {
1462   rc = setup_certs(server_ctx, tls_verify_certificates, tls_crl, NULL,
1463                         TRUE, verify_callback_server);
1464   if (rc != OK) return rc;
1465   server_verify_optional = TRUE;
1466   }
1467
1468 /* Prepare for new connection */
1469
1470 if ((server_ssl = SSL_new(server_ctx)) == NULL) return tls_error(US"SSL_new", NULL, NULL);
1471
1472 /* Warning: we used to SSL_clear(ssl) here, it was removed.
1473  *
1474  * With the SSL_clear(), we get strange interoperability bugs with
1475  * OpenSSL 1.0.1b and TLS1.1/1.2.  It looks as though this may be a bug in
1476  * OpenSSL itself, as a clear should not lead to inability to follow protocols.
1477  *
1478  * The SSL_clear() call is to let an existing SSL* be reused, typically after
1479  * session shutdown.  In this case, we have a brand new object and there's no
1480  * obvious reason to immediately clear it.  I'm guessing that this was
1481  * originally added because of incomplete initialisation which the clear fixed,
1482  * in some historic release.
1483  */
1484
1485 /* Set context and tell client to go ahead, except in the case of TLS startup
1486 on connection, where outputting anything now upsets the clients and tends to
1487 make them disconnect. We need to have an explicit fflush() here, to force out
1488 the response. Other smtp_printf() calls do not need it, because in non-TLS
1489 mode, the fflush() happens when smtp_getc() is called. */
1490
1491 SSL_set_session_id_context(server_ssl, sid_ctx, Ustrlen(sid_ctx));
1492 if (!tls_in.on_connect)
1493   {
1494   smtp_printf("220 TLS go ahead\r\n");
1495   fflush(smtp_out);
1496   }
1497
1498 /* Now negotiate the TLS session. We put our own timer on it, since it seems
1499 that the OpenSSL library doesn't. */
1500
1501 SSL_set_wfd(server_ssl, fileno(smtp_out));
1502 SSL_set_rfd(server_ssl, fileno(smtp_in));
1503 SSL_set_accept_state(server_ssl);
1504
1505 DEBUG(D_tls) debug_printf("Calling SSL_accept\n");
1506
1507 sigalrm_seen = FALSE;
1508 if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
1509 rc = SSL_accept(server_ssl);
1510 alarm(0);
1511
1512 if (rc <= 0)
1513   {
1514   tls_error(US"SSL_accept", NULL, sigalrm_seen ? US"timed out" : NULL);
1515   if (ERR_get_error() == 0)
1516     log_write(0, LOG_MAIN,
1517         "TLS client disconnected cleanly (rejected our certificate?)");
1518   return FAIL;
1519   }
1520
1521 DEBUG(D_tls) debug_printf("SSL_accept was successful\n");
1522
1523 /* TLS has been set up. Adjust the input functions to read via TLS,
1524 and initialize things. */
1525
1526 construct_cipher_name(server_ssl, cipherbuf, sizeof(cipherbuf), &tls_in.bits);
1527 tls_in.cipher = cipherbuf;
1528
1529 DEBUG(D_tls)
1530   {
1531   uschar buf[2048];
1532   if (SSL_get_shared_ciphers(server_ssl, CS buf, sizeof(buf)) != NULL)
1533     debug_printf("Shared ciphers: %s\n", buf);
1534   }
1535
1536 /* Record the certificate we presented */
1537   {
1538   X509 * crt = SSL_get_certificate(server_ssl);
1539   tls_in.ourcert = crt ? X509_dup(crt) : NULL;
1540   }
1541
1542 /* Only used by the server-side tls (tls_in), including tls_getc.
1543    Client-side (tls_out) reads (seem to?) go via
1544    smtp_read_response()/ip_recv().
1545    Hence no need to duplicate for _in and _out.
1546  */
1547 ssl_xfer_buffer = store_malloc(ssl_xfer_buffer_size);
1548 ssl_xfer_buffer_lwm = ssl_xfer_buffer_hwm = 0;
1549 ssl_xfer_eof = ssl_xfer_error = 0;
1550
1551 receive_getc = tls_getc;
1552 receive_ungetc = tls_ungetc;
1553 receive_feof = tls_feof;
1554 receive_ferror = tls_ferror;
1555 receive_smtp_buffered = tls_smtp_buffered;
1556
1557 tls_in.active = fileno(smtp_out);
1558 return OK;
1559 }
1560
1561
1562
1563
1564 static int
1565 tls_client_basic_ctx_init(SSL_CTX * ctx,
1566     host_item * host, smtp_transport_options_block * ob
1567 #ifdef EXPERIMENTAL_CERTNAMES
1568     , tls_ext_ctx_cb * cbinfo
1569 #endif
1570                           )
1571 {
1572 int rc;
1573 /* stick to the old behaviour for compatibility if tls_verify_certificates is
1574    set but both tls_verify_hosts and tls_try_verify_hosts is not set. Check only
1575    the specified host patterns if one of them is defined */
1576
1577 if ((!ob->tls_verify_hosts && !ob->tls_try_verify_hosts) ||
1578     (verify_check_host(&ob->tls_verify_hosts) == OK))
1579   {
1580   if ((rc = setup_certs(ctx, ob->tls_verify_certificates,
1581         ob->tls_crl, host, FALSE, verify_callback_client)) != OK)
1582     return rc;
1583   client_verify_optional = FALSE;
1584
1585 #ifdef EXPERIMENTAL_CERTNAMES
1586   if (ob->tls_verify_cert_hostnames)
1587     {
1588     if (!expand_check(ob->tls_verify_cert_hostnames,
1589                       US"tls_verify_cert_hostnames",
1590                       &cbinfo->verify_cert_hostnames))
1591       return FAIL;
1592     if (cbinfo->verify_cert_hostnames)
1593       DEBUG(D_tls) debug_printf("Cert hostname to check: \"%s\"\n",
1594                       cbinfo->verify_cert_hostnames);
1595     }
1596 #endif
1597   }
1598 else if (verify_check_host(&ob->tls_try_verify_hosts) == OK)
1599   {
1600   if ((rc = setup_certs(ctx, ob->tls_verify_certificates,
1601         ob->tls_crl, host, TRUE, verify_callback_client)) != OK)
1602     return rc;
1603   client_verify_optional = TRUE;
1604   }
1605
1606 return OK;
1607 }
1608
1609 /*************************************************
1610 *    Start a TLS session in a client             *
1611 *************************************************/
1612
1613 /* Called from the smtp transport after STARTTLS has been accepted.
1614
1615 Argument:
1616   fd               the fd of the connection
1617   host             connected host (for messages)
1618   addr             the first address
1619   ob               smtp transport options
1620
1621 Returns:           OK on success
1622                    FAIL otherwise - note that tls_error() will not give DEFER
1623                      because this is not a server
1624 */
1625
1626 int
1627 tls_client_start(int fd, host_item *host, address_item *addr,
1628   void *v_ob)
1629 {
1630 smtp_transport_options_block * ob = v_ob;
1631 static uschar txt[256];
1632 uschar * expciphers;
1633 X509 * server_cert;
1634 int rc;
1635 static uschar cipherbuf[256];
1636
1637 #ifndef DISABLE_OCSP
1638 BOOL request_ocsp = FALSE;
1639 BOOL require_ocsp = FALSE;
1640 #endif
1641 #ifdef EXPERIMENTAL_DANE
1642 dns_answer tlsa_dnsa;
1643 BOOL dane = FALSE;
1644 BOOL dane_required;
1645 #endif
1646
1647 #ifdef EXPERIMENTAL_DANE
1648 dane_required = verify_check_this_host(&ob->hosts_require_dane, NULL,
1649                           host->name, host->address, NULL) == OK;
1650
1651 if (host->dnssec == DS_YES)
1652   {
1653   if(  dane_required
1654     || verify_check_this_host(&ob->hosts_try_dane, NULL,
1655                           host->name, host->address, NULL) == OK
1656     )
1657     {
1658     /* move this out to host.c given the similarity to dns_lookup() ? */
1659     uschar buffer[300];
1660     uschar * fullname = buffer;
1661
1662     /* TLSA lookup string */
1663     (void)sprintf(CS buffer, "_%d._tcp.%.256s", host->port,
1664       host->name);
1665
1666     switch (rc = dns_lookup(&tlsa_dnsa, buffer, T_TLSA, &fullname))
1667       {
1668       case DNS_AGAIN:
1669         return DEFER; /* just defer this TLS'd conn */
1670
1671       default:
1672       case DNS_FAIL:
1673         if (dane_required)
1674           {
1675           log_write(0, LOG_MAIN, "DANE error: TLSA lookup failed");
1676           return FAIL;
1677           }
1678         break;
1679
1680       case DNS_SUCCEED:
1681         if (!dns_is_secure(&tlsa_dnsa))
1682           {
1683           log_write(0, LOG_MAIN, "DANE error: TLSA lookup not DNSSEC");
1684           return DEFER;
1685           }
1686         dane = TRUE;
1687         break;
1688       }
1689     }
1690   }
1691 else if (dane_required)
1692   {
1693   /*XXX a shame we only find this after making tcp & smtp connection */
1694   /* move the test earlier? */
1695   log_write(0, LOG_MAIN, "DANE error: previous lookup not DNSSEC");
1696   return FAIL;
1697   }
1698
1699 #endif
1700
1701 #ifndef DISABLE_OCSP
1702   {
1703   require_ocsp = verify_check_this_host(&ob->hosts_require_ocsp,
1704     NULL, host->name, host->address, NULL) == OK;
1705   request_ocsp = require_ocsp ? TRUE
1706     : verify_check_this_host(&ob->hosts_request_ocsp,
1707         NULL, host->name, host->address, NULL) == OK;
1708   }
1709 #endif
1710
1711 rc = tls_init(&client_ctx, host, NULL,
1712     ob->tls_certificate, ob->tls_privatekey,
1713 #ifndef DISABLE_OCSP
1714     (void *)(long)request_ocsp,
1715 #endif
1716     addr, &client_static_cbinfo);
1717 if (rc != OK) return rc;
1718
1719 tls_out.certificate_verified = FALSE;
1720 #ifdef EXPERIMENTAL_DANE
1721 tls_out.dane_verified = FALSE;
1722 #endif
1723 client_verify_callback_called = FALSE;
1724
1725 if (!expand_check(ob->tls_require_ciphers, US"tls_require_ciphers",
1726     &expciphers))
1727   return FAIL;
1728
1729 /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they
1730 are separated by underscores. So that I can use either form in my tests, and
1731 also for general convenience, we turn underscores into hyphens here. */
1732
1733 if (expciphers != NULL)
1734   {
1735   uschar *s = expciphers;
1736   while (*s != 0) { if (*s == '_') *s = '-'; s++; }
1737   DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers);
1738   if (!SSL_CTX_set_cipher_list(client_ctx, CS expciphers))
1739     return tls_error(US"SSL_CTX_set_cipher_list", host, NULL);
1740   }
1741
1742 #ifdef EXPERIMENTAL_DANE
1743 if (dane)
1744   {
1745   SSL_CTX_set_verify(client_ctx, SSL_VERIFY_PEER, verify_callback_client_dane);
1746
1747   if (!DANESSL_library_init())
1748     return tls_error(US"library init", host, NULL);
1749   if (DANESSL_CTX_init(client_ctx) <= 0)
1750     return tls_error(US"context init", host, NULL);
1751   }
1752 else
1753
1754 #endif
1755
1756   if ((rc = tls_client_basic_ctx_init(client_ctx, host, ob
1757 #ifdef EXPERIMENTAL_CERTNAMES
1758                                 , client_static_cbinfo
1759 #endif
1760                                 )) != OK)
1761     return rc;
1762
1763 if ((client_ssl = SSL_new(client_ctx)) == NULL)
1764   return tls_error(US"SSL_new", host, NULL);
1765 SSL_set_session_id_context(client_ssl, sid_ctx, Ustrlen(sid_ctx));
1766 SSL_set_fd(client_ssl, fd);
1767 SSL_set_connect_state(client_ssl);
1768
1769 if (ob->tls_sni)
1770   {
1771   if (!expand_check(ob->tls_sni, US"tls_sni", &tls_out.sni))
1772     return FAIL;
1773   if (tls_out.sni == NULL)
1774     {
1775     DEBUG(D_tls) debug_printf("Setting TLS SNI forced to fail, not sending\n");
1776     }
1777   else if (!Ustrlen(tls_out.sni))
1778     tls_out.sni = NULL;
1779   else
1780     {
1781 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
1782     DEBUG(D_tls) debug_printf("Setting TLS SNI \"%s\"\n", tls_out.sni);
1783     SSL_set_tlsext_host_name(client_ssl, tls_out.sni);
1784 #else
1785     DEBUG(D_tls)
1786       debug_printf("OpenSSL at build-time lacked SNI support, ignoring \"%s\"\n",
1787           tls_out.sni);
1788 #endif
1789     }
1790   }
1791
1792 #ifndef DISABLE_OCSP
1793 /* Request certificate status at connection-time.  If the server
1794 does OCSP stapling we will get the callback (set in tls_init()) */
1795 if (request_ocsp)
1796   {
1797   SSL_set_tlsext_status_type(client_ssl, TLSEXT_STATUSTYPE_ocsp);
1798   client_static_cbinfo->u_ocsp.client.verify_required = require_ocsp;
1799   tls_out.ocsp = OCSP_NOT_RESP;
1800   }
1801 #endif
1802
1803 #ifdef EXPERIMENTAL_DANE
1804 if (dane)
1805   {
1806   dns_record * rr;
1807   dns_scan dnss;
1808   uschar * hostnames[2] = { host->name, NULL };
1809   int found = 0;
1810
1811   if (DANESSL_init(client_ssl, NULL, hostnames) != 1)
1812     return tls_error(US"hostnames load", host, NULL);
1813
1814   for (rr = dns_next_rr(&tlsa_dnsa, &dnss, RESET_ANSWERS);
1815        rr;
1816        rr = dns_next_rr(&tlsa_dnsa, &dnss, RESET_NEXT)
1817       ) if (rr->type == T_TLSA)
1818     {
1819     uschar * p = rr->data;
1820     int usage, selector, mtype;
1821     const char * mdname;
1822
1823     found++;
1824     usage = *p++;
1825     selector = *p++;
1826     mtype = *p++;
1827
1828     switch (mtype)
1829       {
1830       default:
1831         log_write(0, LOG_MAIN, "DANE error: TLSA record w/bad mtype 0x%x", mtype);
1832         return FAIL;
1833       case 0:   mdname = NULL; break;
1834       case 1:   mdname = "sha256"; break;
1835       case 2:   mdname = "sha512"; break;
1836       }
1837
1838     switch (DANESSL_add_tlsa(client_ssl,
1839                 (uint8_t) usage, (uint8_t) selector,
1840                 mdname, p, rr->size - (p - rr->data)))
1841       {
1842       default:
1843       case 0:   /* action not taken */
1844         return tls_error(US"tlsa load", host, NULL);
1845       case 1:   break;
1846       }
1847     }
1848
1849   if (!found)
1850     {
1851     log_write(0, LOG_MAIN, "DANE error: No TLSA records");
1852     return FAIL;
1853     }
1854   }
1855 #endif
1856
1857
1858 /* There doesn't seem to be a built-in timeout on connection. */
1859
1860 DEBUG(D_tls) debug_printf("Calling SSL_connect\n");
1861 sigalrm_seen = FALSE;
1862 alarm(ob->command_timeout);
1863 rc = SSL_connect(client_ssl);
1864 alarm(0);
1865
1866 #ifdef EXPERIMENTAL_DANE
1867 if (dane)
1868   DANESSL_cleanup(client_ssl);  /*XXX earliest possible callpoint. Too early? */
1869 #endif
1870
1871 if (rc <= 0)
1872   return tls_error(US"SSL_connect", host, sigalrm_seen ? US"timed out" : NULL);
1873
1874 DEBUG(D_tls) debug_printf("SSL_connect succeeded\n");
1875
1876 /* Beware anonymous ciphers which lead to server_cert being NULL */
1877 /*XXX server_cert is never freed... use X509_free() */
1878 server_cert = SSL_get_peer_certificate (client_ssl);
1879 if (server_cert)
1880   {
1881   tls_out.peerdn = US X509_NAME_oneline(X509_get_subject_name(server_cert),
1882     CS txt, sizeof(txt));
1883   tls_out.peerdn = txt;         /*XXX a static buffer... */
1884   }
1885 else
1886   tls_out.peerdn = NULL;
1887
1888 construct_cipher_name(client_ssl, cipherbuf, sizeof(cipherbuf), &tls_out.bits);
1889 tls_out.cipher = cipherbuf;
1890
1891 /* Record the certificate we presented */
1892   {
1893   X509 * crt = SSL_get_certificate(client_ssl);
1894   tls_out.ourcert = crt ? X509_dup(crt) : NULL;
1895   }
1896
1897 tls_out.active = fd;
1898 return OK;
1899 }
1900
1901
1902
1903
1904
1905 /*************************************************
1906 *            TLS version of getc                 *
1907 *************************************************/
1908
1909 /* This gets the next byte from the TLS input buffer. If the buffer is empty,
1910 it refills the buffer via the SSL reading function.
1911
1912 Arguments:  none
1913 Returns:    the next character or EOF
1914
1915 Only used by the server-side TLS.
1916 */
1917
1918 int
1919 tls_getc(void)
1920 {
1921 if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm)
1922   {
1923   int error;
1924   int inbytes;
1925
1926   DEBUG(D_tls) debug_printf("Calling SSL_read(%p, %p, %u)\n", server_ssl,
1927     ssl_xfer_buffer, ssl_xfer_buffer_size);
1928
1929   if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
1930   inbytes = SSL_read(server_ssl, CS ssl_xfer_buffer, ssl_xfer_buffer_size);
1931   error = SSL_get_error(server_ssl, inbytes);
1932   alarm(0);
1933
1934   /* SSL_ERROR_ZERO_RETURN appears to mean that the SSL session has been
1935   closed down, not that the socket itself has been closed down. Revert to
1936   non-SSL handling. */
1937
1938   if (error == SSL_ERROR_ZERO_RETURN)
1939     {
1940     DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n");
1941
1942     receive_getc = smtp_getc;
1943     receive_ungetc = smtp_ungetc;
1944     receive_feof = smtp_feof;
1945     receive_ferror = smtp_ferror;
1946     receive_smtp_buffered = smtp_buffered;
1947
1948     SSL_free(server_ssl);
1949     server_ssl = NULL;
1950     tls_in.active = -1;
1951     tls_in.bits = 0;
1952     tls_in.cipher = NULL;
1953     tls_in.peerdn = NULL;
1954     tls_in.sni = NULL;
1955
1956     return smtp_getc();
1957     }
1958
1959   /* Handle genuine errors */
1960
1961   else if (error == SSL_ERROR_SSL)
1962     {
1963     ERR_error_string(ERR_get_error(), ssl_errstring);
1964     log_write(0, LOG_MAIN, "TLS error (SSL_read): %s", ssl_errstring);
1965     ssl_xfer_error = 1;
1966     return EOF;
1967     }
1968
1969   else if (error != SSL_ERROR_NONE)
1970     {
1971     DEBUG(D_tls) debug_printf("Got SSL error %d\n", error);
1972     ssl_xfer_error = 1;
1973     return EOF;
1974     }
1975
1976 #ifndef DISABLE_DKIM
1977   dkim_exim_verify_feed(ssl_xfer_buffer, inbytes);
1978 #endif
1979   ssl_xfer_buffer_hwm = inbytes;
1980   ssl_xfer_buffer_lwm = 0;
1981   }
1982
1983 /* Something in the buffer; return next uschar */
1984
1985 return ssl_xfer_buffer[ssl_xfer_buffer_lwm++];
1986 }
1987
1988
1989
1990 /*************************************************
1991 *          Read bytes from TLS channel           *
1992 *************************************************/
1993
1994 /*
1995 Arguments:
1996   buff      buffer of data
1997   len       size of buffer
1998
1999 Returns:    the number of bytes read
2000             -1 after a failed read
2001
2002 Only used by the client-side TLS.
2003 */
2004
2005 int
2006 tls_read(BOOL is_server, uschar *buff, size_t len)
2007 {
2008 SSL *ssl = is_server ? server_ssl : client_ssl;
2009 int inbytes;
2010 int error;
2011
2012 DEBUG(D_tls) debug_printf("Calling SSL_read(%p, %p, %u)\n", ssl,
2013   buff, (unsigned int)len);
2014
2015 inbytes = SSL_read(ssl, CS buff, len);
2016 error = SSL_get_error(ssl, inbytes);
2017
2018 if (error == SSL_ERROR_ZERO_RETURN)
2019   {
2020   DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n");
2021   return -1;
2022   }
2023 else if (error != SSL_ERROR_NONE)
2024   {
2025   return -1;
2026   }
2027
2028 return inbytes;
2029 }
2030
2031
2032
2033
2034
2035 /*************************************************
2036 *         Write bytes down TLS channel           *
2037 *************************************************/
2038
2039 /*
2040 Arguments:
2041   is_server channel specifier
2042   buff      buffer of data
2043   len       number of bytes
2044
2045 Returns:    the number of bytes after a successful write,
2046             -1 after a failed write
2047
2048 Used by both server-side and client-side TLS.
2049 */
2050
2051 int
2052 tls_write(BOOL is_server, const uschar *buff, size_t len)
2053 {
2054 int outbytes;
2055 int error;
2056 int left = len;
2057 SSL *ssl = is_server ? server_ssl : client_ssl;
2058
2059 DEBUG(D_tls) debug_printf("tls_do_write(%p, %d)\n", buff, left);
2060 while (left > 0)
2061   {
2062   DEBUG(D_tls) debug_printf("SSL_write(SSL, %p, %d)\n", buff, left);
2063   outbytes = SSL_write(ssl, CS buff, left);
2064   error = SSL_get_error(ssl, outbytes);
2065   DEBUG(D_tls) debug_printf("outbytes=%d error=%d\n", outbytes, error);
2066   switch (error)
2067     {
2068     case SSL_ERROR_SSL:
2069     ERR_error_string(ERR_get_error(), ssl_errstring);
2070     log_write(0, LOG_MAIN, "TLS error (SSL_write): %s", ssl_errstring);
2071     return -1;
2072
2073     case SSL_ERROR_NONE:
2074     left -= outbytes;
2075     buff += outbytes;
2076     break;
2077
2078     case SSL_ERROR_ZERO_RETURN:
2079     log_write(0, LOG_MAIN, "SSL channel closed on write");
2080     return -1;
2081
2082     case SSL_ERROR_SYSCALL:
2083     log_write(0, LOG_MAIN, "SSL_write: (from %s) syscall: %s",
2084       sender_fullhost ? sender_fullhost : US"<unknown>",
2085       strerror(errno));
2086
2087     default:
2088     log_write(0, LOG_MAIN, "SSL_write error %d", error);
2089     return -1;
2090     }
2091   }
2092 return len;
2093 }
2094
2095
2096
2097 /*************************************************
2098 *         Close down a TLS session               *
2099 *************************************************/
2100
2101 /* This is also called from within a delivery subprocess forked from the
2102 daemon, to shut down the TLS library, without actually doing a shutdown (which
2103 would tamper with the SSL session in the parent process).
2104
2105 Arguments:   TRUE if SSL_shutdown is to be called
2106 Returns:     nothing
2107
2108 Used by both server-side and client-side TLS.
2109 */
2110
2111 void
2112 tls_close(BOOL is_server, BOOL shutdown)
2113 {
2114 SSL **sslp = is_server ? &server_ssl : &client_ssl;
2115 int *fdp = is_server ? &tls_in.active : &tls_out.active;
2116
2117 if (*fdp < 0) return;  /* TLS was not active */
2118
2119 if (shutdown)
2120   {
2121   DEBUG(D_tls) debug_printf("tls_close(): shutting down SSL\n");
2122   SSL_shutdown(*sslp);
2123   }
2124
2125 SSL_free(*sslp);
2126 *sslp = NULL;
2127
2128 *fdp = -1;
2129 }
2130
2131
2132
2133
2134 /*************************************************
2135 *  Let tls_require_ciphers be checked at startup *
2136 *************************************************/
2137
2138 /* The tls_require_ciphers option, if set, must be something which the
2139 library can parse.
2140
2141 Returns:     NULL on success, or error message
2142 */
2143
2144 uschar *
2145 tls_validate_require_cipher(void)
2146 {
2147 SSL_CTX *ctx;
2148 uschar *s, *expciphers, *err;
2149
2150 /* this duplicates from tls_init(), we need a better "init just global
2151 state, for no specific purpose" singleton function of our own */
2152
2153 SSL_load_error_strings();
2154 OpenSSL_add_ssl_algorithms();
2155 #if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_SHA256)
2156 /* SHA256 is becoming ever more popular. This makes sure it gets added to the
2157 list of available digests. */
2158 EVP_add_digest(EVP_sha256());
2159 #endif
2160
2161 if (!(tls_require_ciphers && *tls_require_ciphers))
2162   return NULL;
2163
2164 if (!expand_check(tls_require_ciphers, US"tls_require_ciphers", &expciphers))
2165   return US"failed to expand tls_require_ciphers";
2166
2167 if (!(expciphers && *expciphers))
2168   return NULL;
2169
2170 /* normalisation ripped from above */
2171 s = expciphers;
2172 while (*s != 0) { if (*s == '_') *s = '-'; s++; }
2173
2174 err = NULL;
2175
2176 ctx = SSL_CTX_new(SSLv23_server_method());
2177 if (!ctx)
2178   {
2179   ERR_error_string(ERR_get_error(), ssl_errstring);
2180   return string_sprintf("SSL_CTX_new() failed: %s", ssl_errstring);
2181   }
2182
2183 DEBUG(D_tls)
2184   debug_printf("tls_require_ciphers expands to \"%s\"\n", expciphers);
2185
2186 if (!SSL_CTX_set_cipher_list(ctx, CS expciphers))
2187   {
2188   ERR_error_string(ERR_get_error(), ssl_errstring);
2189   err = string_sprintf("SSL_CTX_set_cipher_list(%s) failed", expciphers);
2190   }
2191
2192 SSL_CTX_free(ctx);
2193
2194 return err;
2195 }
2196
2197
2198
2199
2200 /*************************************************
2201 *         Report the library versions.           *
2202 *************************************************/
2203
2204 /* There have historically been some issues with binary compatibility in
2205 OpenSSL libraries; if Exim (like many other applications) is built against
2206 one version of OpenSSL but the run-time linker picks up another version,
2207 it can result in serious failures, including crashing with a SIGSEGV.  So
2208 report the version found by the compiler and the run-time version.
2209
2210 Note: some OS vendors backport security fixes without changing the version
2211 number/string, and the version date remains unchanged.  The _build_ date
2212 will change, so we can more usefully assist with version diagnosis by also
2213 reporting the build date.
2214
2215 Arguments:   a FILE* to print the results to
2216 Returns:     nothing
2217 */
2218
2219 void
2220 tls_version_report(FILE *f)
2221 {
2222 fprintf(f, "Library version: OpenSSL: Compile: %s\n"
2223            "                          Runtime: %s\n"
2224            "                                 : %s\n",
2225            OPENSSL_VERSION_TEXT,
2226            SSLeay_version(SSLEAY_VERSION),
2227            SSLeay_version(SSLEAY_BUILT_ON));
2228 /* third line is 38 characters for the %s and the line is 73 chars long;
2229 the OpenSSL output includes a "built on: " prefix already. */
2230 }
2231
2232
2233
2234
2235 /*************************************************
2236 *            Random number generation            *
2237 *************************************************/
2238
2239 /* Pseudo-random number generation.  The result is not expected to be
2240 cryptographically strong but not so weak that someone will shoot themselves
2241 in the foot using it as a nonce in input in some email header scheme or
2242 whatever weirdness they'll twist this into.  The result should handle fork()
2243 and avoid repeating sequences.  OpenSSL handles that for us.
2244
2245 Arguments:
2246   max       range maximum
2247 Returns     a random number in range [0, max-1]
2248 */
2249
2250 int
2251 vaguely_random_number(int max)
2252 {
2253 unsigned int r;
2254 int i, needed_len;
2255 static pid_t pidlast = 0;
2256 pid_t pidnow;
2257 uschar *p;
2258 uschar smallbuf[sizeof(r)];
2259
2260 if (max <= 1)
2261   return 0;
2262
2263 pidnow = getpid();
2264 if (pidnow != pidlast)
2265   {
2266   /* Although OpenSSL documents that "OpenSSL makes sure that the PRNG state
2267   is unique for each thread", this doesn't apparently apply across processes,
2268   so our own warning from vaguely_random_number_fallback() applies here too.
2269   Fix per PostgreSQL. */
2270   if (pidlast != 0)
2271     RAND_cleanup();
2272   pidlast = pidnow;
2273   }
2274
2275 /* OpenSSL auto-seeds from /dev/random, etc, but this a double-check. */
2276 if (!RAND_status())
2277   {
2278   randstuff r;
2279   gettimeofday(&r.tv, NULL);
2280   r.p = getpid();
2281
2282   RAND_seed((uschar *)(&r), sizeof(r));
2283   }
2284 /* We're after pseudo-random, not random; if we still don't have enough data
2285 in the internal PRNG then our options are limited.  We could sleep and hope
2286 for entropy to come along (prayer technique) but if the system is so depleted
2287 in the first place then something is likely to just keep taking it.  Instead,
2288 we'll just take whatever little bit of pseudo-random we can still manage to
2289 get. */
2290
2291 needed_len = sizeof(r);
2292 /* Don't take 8 times more entropy than needed if int is 8 octets and we were
2293 asked for a number less than 10. */
2294 for (r = max, i = 0; r; ++i)
2295   r >>= 1;
2296 i = (i + 7) / 8;
2297 if (i < needed_len)
2298   needed_len = i;
2299
2300 /* We do not care if crypto-strong */
2301 i = RAND_pseudo_bytes(smallbuf, needed_len);
2302 if (i < 0)
2303   {
2304   DEBUG(D_all)
2305     debug_printf("OpenSSL RAND_pseudo_bytes() not supported by RAND method, using fallback.\n");
2306   return vaguely_random_number_fallback(max);
2307   }
2308
2309 r = 0;
2310 for (p = smallbuf; needed_len; --needed_len, ++p)
2311   {
2312   r *= 256;
2313   r += *p;
2314   }
2315
2316 /* We don't particularly care about weighted results; if someone wants
2317 smooth distribution and cares enough then they should submit a patch then. */
2318 return r % max;
2319 }
2320
2321
2322
2323
2324 /*************************************************
2325 *        OpenSSL option parse                    *
2326 *************************************************/
2327
2328 /* Parse one option for tls_openssl_options_parse below
2329
2330 Arguments:
2331   name    one option name
2332   value   place to store a value for it
2333 Returns   success or failure in parsing
2334 */
2335
2336 struct exim_openssl_option {
2337   uschar *name;
2338   long    value;
2339 };
2340 /* We could use a macro to expand, but we need the ifdef and not all the
2341 options document which version they were introduced in.  Policylet: include
2342 all options unless explicitly for DTLS, let the administrator choose which
2343 to apply.
2344
2345 This list is current as of:
2346   ==>  1.0.1b  <==
2347 Plus SSL_OP_SAFARI_ECDHE_ECDSA_BUG from 2013-June patch/discussion on openssl-dev
2348 */
2349 static struct exim_openssl_option exim_openssl_options[] = {
2350 /* KEEP SORTED ALPHABETICALLY! */
2351 #ifdef SSL_OP_ALL
2352   { US"all", SSL_OP_ALL },
2353 #endif
2354 #ifdef SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
2355   { US"allow_unsafe_legacy_renegotiation", SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION },
2356 #endif
2357 #ifdef SSL_OP_CIPHER_SERVER_PREFERENCE
2358   { US"cipher_server_preference", SSL_OP_CIPHER_SERVER_PREFERENCE },
2359 #endif
2360 #ifdef SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
2361   { US"dont_insert_empty_fragments", SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS },
2362 #endif
2363 #ifdef SSL_OP_EPHEMERAL_RSA
2364   { US"ephemeral_rsa", SSL_OP_EPHEMERAL_RSA },
2365 #endif
2366 #ifdef SSL_OP_LEGACY_SERVER_CONNECT
2367   { US"legacy_server_connect", SSL_OP_LEGACY_SERVER_CONNECT },
2368 #endif
2369 #ifdef SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
2370   { US"microsoft_big_sslv3_buffer", SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER },
2371 #endif
2372 #ifdef SSL_OP_MICROSOFT_SESS_ID_BUG
2373   { US"microsoft_sess_id_bug", SSL_OP_MICROSOFT_SESS_ID_BUG },
2374 #endif
2375 #ifdef SSL_OP_MSIE_SSLV2_RSA_PADDING
2376   { US"msie_sslv2_rsa_padding", SSL_OP_MSIE_SSLV2_RSA_PADDING },
2377 #endif
2378 #ifdef SSL_OP_NETSCAPE_CHALLENGE_BUG
2379   { US"netscape_challenge_bug", SSL_OP_NETSCAPE_CHALLENGE_BUG },
2380 #endif
2381 #ifdef SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
2382   { US"netscape_reuse_cipher_change_bug", SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG },
2383 #endif
2384 #ifdef SSL_OP_NO_COMPRESSION
2385   { US"no_compression", SSL_OP_NO_COMPRESSION },
2386 #endif
2387 #ifdef SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
2388   { US"no_session_resumption_on_renegotiation", SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION },
2389 #endif
2390 #ifdef SSL_OP_NO_SSLv2
2391   { US"no_sslv2", SSL_OP_NO_SSLv2 },
2392 #endif
2393 #ifdef SSL_OP_NO_SSLv3
2394   { US"no_sslv3", SSL_OP_NO_SSLv3 },
2395 #endif
2396 #ifdef SSL_OP_NO_TICKET
2397   { US"no_ticket", SSL_OP_NO_TICKET },
2398 #endif
2399 #ifdef SSL_OP_NO_TLSv1
2400   { US"no_tlsv1", SSL_OP_NO_TLSv1 },
2401 #endif
2402 #ifdef SSL_OP_NO_TLSv1_1
2403 #if SSL_OP_NO_TLSv1_1 == 0x00000400L
2404   /* Error in chosen value in 1.0.1a; see first item in CHANGES for 1.0.1b */
2405 #warning OpenSSL 1.0.1a uses a bad value for SSL_OP_NO_TLSv1_1, ignoring
2406 #else
2407   { US"no_tlsv1_1", SSL_OP_NO_TLSv1_1 },
2408 #endif
2409 #endif
2410 #ifdef SSL_OP_NO_TLSv1_2
2411   { US"no_tlsv1_2", SSL_OP_NO_TLSv1_2 },
2412 #endif
2413 #ifdef SSL_OP_SAFARI_ECDHE_ECDSA_BUG
2414   { US"safari_ecdhe_ecdsa_bug", SSL_OP_SAFARI_ECDHE_ECDSA_BUG },
2415 #endif
2416 #ifdef SSL_OP_SINGLE_DH_USE
2417   { US"single_dh_use", SSL_OP_SINGLE_DH_USE },
2418 #endif
2419 #ifdef SSL_OP_SINGLE_ECDH_USE
2420   { US"single_ecdh_use", SSL_OP_SINGLE_ECDH_USE },
2421 #endif
2422 #ifdef SSL_OP_SSLEAY_080_CLIENT_DH_BUG
2423   { US"ssleay_080_client_dh_bug", SSL_OP_SSLEAY_080_CLIENT_DH_BUG },
2424 #endif
2425 #ifdef SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
2426   { US"sslref2_reuse_cert_type_bug", SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG },
2427 #endif
2428 #ifdef SSL_OP_TLS_BLOCK_PADDING_BUG
2429   { US"tls_block_padding_bug", SSL_OP_TLS_BLOCK_PADDING_BUG },
2430 #endif
2431 #ifdef SSL_OP_TLS_D5_BUG
2432   { US"tls_d5_bug", SSL_OP_TLS_D5_BUG },
2433 #endif
2434 #ifdef SSL_OP_TLS_ROLLBACK_BUG
2435   { US"tls_rollback_bug", SSL_OP_TLS_ROLLBACK_BUG },
2436 #endif
2437 };
2438 static int exim_openssl_options_size =
2439   sizeof(exim_openssl_options)/sizeof(struct exim_openssl_option);
2440
2441
2442 static BOOL
2443 tls_openssl_one_option_parse(uschar *name, long *value)
2444 {
2445 int first = 0;
2446 int last = exim_openssl_options_size;
2447 while (last > first)
2448   {
2449   int middle = (first + last)/2;
2450   int c = Ustrcmp(name, exim_openssl_options[middle].name);
2451   if (c == 0)
2452     {
2453     *value = exim_openssl_options[middle].value;
2454     return TRUE;
2455     }
2456   else if (c > 0)
2457     first = middle + 1;
2458   else
2459     last = middle;
2460   }
2461 return FALSE;
2462 }
2463
2464
2465
2466
2467 /*************************************************
2468 *        OpenSSL option parsing logic            *
2469 *************************************************/
2470
2471 /* OpenSSL has a number of compatibility options which an administrator might
2472 reasonably wish to set.  Interpret a list similarly to decode_bits(), so that
2473 we look like log_selector.
2474
2475 Arguments:
2476   option_spec  the administrator-supplied string of options
2477   results      ptr to long storage for the options bitmap
2478 Returns        success or failure
2479 */
2480
2481 BOOL
2482 tls_openssl_options_parse(uschar *option_spec, long *results)
2483 {
2484 long result, item;
2485 uschar *s, *end;
2486 uschar keep_c;
2487 BOOL adding, item_parsed;
2488
2489 result = 0L;
2490 /* Prior to 4.80 we or'd in SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS; removed
2491  * from default because it increases BEAST susceptibility. */
2492 #ifdef SSL_OP_NO_SSLv2
2493 result |= SSL_OP_NO_SSLv2;
2494 #endif
2495
2496 if (option_spec == NULL)
2497   {
2498   *results = result;
2499   return TRUE;
2500   }
2501
2502 for (s=option_spec; *s != '\0'; /**/)
2503   {
2504   while (isspace(*s)) ++s;
2505   if (*s == '\0')
2506     break;
2507   if (*s != '+' && *s != '-')
2508     {
2509     DEBUG(D_tls) debug_printf("malformed openssl option setting: "
2510         "+ or - expected but found \"%s\"\n", s);
2511     return FALSE;
2512     }
2513   adding = *s++ == '+';
2514   for (end = s; (*end != '\0') && !isspace(*end); ++end) /**/ ;
2515   keep_c = *end;
2516   *end = '\0';
2517   item_parsed = tls_openssl_one_option_parse(s, &item);
2518   if (!item_parsed)
2519     {
2520     DEBUG(D_tls) debug_printf("openssl option setting unrecognised: \"%s\"\n", s);
2521     return FALSE;
2522     }
2523   DEBUG(D_tls) debug_printf("openssl option, %s from %lx: %lx (%s)\n",
2524       adding ? "adding" : "removing", result, item, s);
2525   if (adding)
2526     result |= item;
2527   else
2528     result &= ~item;
2529   *end = keep_c;
2530   s = end;
2531   }
2532
2533 *results = result;
2534 return TRUE;
2535 }
2536
2537 /* vi: aw ai sw=2
2538 */
2539 /* End of tls-openssl.c */