src/src/tls-openssl.c

   1 /* $Cambridge: exim/src/src/tls-openssl.c,v 1.25 2010/06/05 09:36:11 pdp Exp $ */
   2
   3 /*************************************************
   4 *     Exim - an Internet mail transport agent    *
   5 *************************************************/
   6
   7 /* Copyright (c) University of Cambridge 1995 - 2009 */
   8 /* See the file NOTICE for conditions of use and distribution. */
   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
  26 /* Structure for collecting random data for seeding. */
  27
  28 typedef struct randstuff {
  29   struct timeval tv;
  30   pid_t          p;
  31 } randstuff;
  32
  33 /* Local static variables */
  34
  35 static BOOL verify_callback_called = FALSE;
  36 static const uschar *sid_ctx = US"exim";
  37
  38 static SSL_CTX *ctx = NULL;
  39 static SSL *ssl = NULL;
  40
  41 static char ssl_errstring[256];
  42
  43 static int  ssl_session_timeout = 200;
  44 static BOOL verify_optional = FALSE;
  45
  46
  47
  48
  49
  50 /*************************************************
  51 *               Handle TLS error                 *
  52 *************************************************/
  53
  54 /* Called from lots of places when errors occur before actually starting to do
  55 the TLS handshake, that is, while the session is still in clear. Always returns
  56 DEFER for a server and FAIL for a client so that most calls can use "return
  57 tls_error(...)" to do this processing and then give an appropriate return. A
  58 single function is used for both server and client, because it is called from
  59 some shared functions.
  60
  61 Argument:
  62   prefix    text to include in the logged error
  63   host      NULL if setting up a server;
  64             the connected host if setting up a client
  65   msg       error message or NULL if we should ask OpenSSL
  66
  67 Returns:    OK/DEFER/FAIL
  68 */
  69
  70 static int
  71 tls_error(uschar *prefix, host_item *host, uschar *msg)
  72 {
  73 if (msg == NULL)
  74   {
  75   ERR_error_string(ERR_get_error(), ssl_errstring);
  76   msg = (uschar *)ssl_errstring;
  77   }
  78
  79 if (host == NULL)
  80   {
  81   uschar *conn_info = smtp_get_connection_info();
  82   if (Ustrncmp(conn_info, US"SMTP ", 5) == 0)
  83     conn_info += 5;
  84   log_write(0, LOG_MAIN, "TLS error on %s (%s): %s",
  85     conn_info, prefix, msg);
  86   return DEFER;
  87   }
  88 else
  89   {
  90   log_write(0, LOG_MAIN, "TLS error on connection to %s [%s] (%s): %s",
  91     host->name, host->address, prefix, msg);
  92   return FAIL;
  93   }
  94 }
  95
  96
  97
  98 /*************************************************
  99 *        Callback to generate RSA key            *
 100 *************************************************/
 101
 102 /*
 103 Arguments:
 104   s          SSL connection
 105   export     not used
 106   keylength  keylength
 107
 108 Returns:     pointer to generated key
 109 */
 110
 111 static RSA *
 112 rsa_callback(SSL *s, int export, int keylength)
 113 {
 114 RSA *rsa_key;
 115 export = export;     /* Shut picky compilers up */
 116 DEBUG(D_tls) debug_printf("Generating %d bit RSA key...\n", keylength);
 117 rsa_key = RSA_generate_key(keylength, RSA_F4, NULL, NULL);
 118 if (rsa_key == NULL)
 119   {
 120   ERR_error_string(ERR_get_error(), ssl_errstring);
 121   log_write(0, LOG_MAIN|LOG_PANIC, "TLS error (RSA_generate_key): %s",
 122     ssl_errstring);
 123   return NULL;
 124   }
 125 return rsa_key;
 126 }
 127
 128
 129
 130
 131 /*************************************************
 132 *        Callback for verification               *
 133 *************************************************/
 134
 135 /* The SSL library does certificate verification if set up to do so. This
 136 callback has the current yes/no state is in "state". If verification succeeded,
 137 we set up the tls_peerdn string. If verification failed, what happens depends
 138 on whether the client is required to present a verifiable certificate or not.
 139
 140 If verification is optional, we change the state to yes, but still log the
 141 verification error. For some reason (it really would help to have proper
 142 documentation of OpenSSL), this callback function then gets called again, this
 143 time with state = 1. In fact, that's useful, because we can set up the peerdn
 144 value, but we must take care not to set the private verified flag on the second
 145 time through.
 146
 147 Note: this function is not called if the client fails to present a certificate
 148 when asked. We get here only if a certificate has been received. Handling of
 149 optional verification for this case is done when requesting SSL to verify, by
 150 setting SSL_VERIFY_FAIL_IF_NO_PEER_CERT in the non-optional case.
 151
 152 Arguments:
 153   state      current yes/no state as 1/0
 154   x509ctx    certificate information.
 155
 156 Returns:     1 if verified, 0 if not
 157 */
 158
 159 static int
 160 verify_callback(int state, X509_STORE_CTX *x509ctx)
 161 {
 162 static uschar txt[256];
 163
 164 X509_NAME_oneline(X509_get_subject_name(x509ctx->current_cert),
 165   CS txt, sizeof(txt));
 166
 167 if (state == 0)
 168   {
 169   log_write(0, LOG_MAIN, "SSL verify error: depth=%d error=%s cert=%s",
 170     x509ctx->error_depth,
 171     X509_verify_cert_error_string(x509ctx->error),
 172     txt);
 173   tls_certificate_verified = FALSE;
 174   verify_callback_called = TRUE;
 175   if (!verify_optional) return 0;    /* reject */
 176   DEBUG(D_tls) debug_printf("SSL verify failure overridden (host in "
 177     "tls_try_verify_hosts)\n");
 178   return 1;                          /* accept */
 179   }
 180
 181 if (x509ctx->error_depth != 0)
 182   {
 183   DEBUG(D_tls) debug_printf("SSL verify ok: depth=%d cert=%s\n",
 184      x509ctx->error_depth, txt);
 185   }
 186 else
 187   {
 188   DEBUG(D_tls) debug_printf("SSL%s peer: %s\n",
 189     verify_callback_called? "" : " authenticated", txt);
 190   tls_peerdn = txt;
 191   }
 192
 193 if (!verify_callback_called) tls_certificate_verified = TRUE;
 194 verify_callback_called = TRUE;
 195
 196 return 1;   /* accept */
 197 }
 198
 199
 200
 201 /*************************************************
 202 *           Information callback                 *
 203 *************************************************/
 204
 205 /* The SSL library functions call this from time to time to indicate what they
 206 are doing. We copy the string to the debugging output when the level is high
 207 enough.
 208
 209 Arguments:
 210   s         the SSL connection
 211   where
 212   ret
 213
 214 Returns:    nothing
 215 */
 216
 217 static void
 218 info_callback(SSL *s, int where, int ret)
 219 {
 220 where = where;
 221 ret = ret;
 222 DEBUG(D_tls) debug_printf("SSL info: %s\n", SSL_state_string_long(s));
 223 }
 224
 225
 226
 227 /*************************************************
 228 *                Initialize for DH               *
 229 *************************************************/
 230
 231 /* If dhparam is set, expand it, and load up the parameters for DH encryption.
 232
 233 Arguments:
 234   dhparam   DH parameter file
 235   host      connected host, if client; NULL if server
 236
 237 Returns:    TRUE if OK (nothing to set up, or setup worked)
 238 */
 239
 240 static BOOL
 241 init_dh(uschar *dhparam, host_item *host)
 242 {
 243 BOOL yield = TRUE;
 244 BIO *bio;
 245 DH *dh;
 246 uschar *dhexpanded;
 247
 248 if (!expand_check(dhparam, US"tls_dhparam", &dhexpanded))
 249   return FALSE;
 250
 251 if (dhexpanded == NULL) return TRUE;
 252
 253 if ((bio = BIO_new_file(CS dhexpanded, "r")) == NULL)
 254   {
 255   tls_error(string_sprintf("could not read dhparams file %s", dhexpanded),
 256     host, (uschar *)strerror(errno));
 257   yield = FALSE;
 258   }
 259 else
 260   {
 261   if ((dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL)) == NULL)
 262     {
 263     tls_error(string_sprintf("could not read dhparams file %s", dhexpanded),
 264       host, NULL);
 265     yield = FALSE;
 266     }
 267   else
 268     {
 269     SSL_CTX_set_tmp_dh(ctx, dh);
 270     DEBUG(D_tls)
 271       debug_printf("Diffie-Hellman initialized from %s with %d-bit key\n",
 272         dhexpanded, 8*DH_size(dh));
 273     DH_free(dh);
 274     }
 275   BIO_free(bio);
 276   }
 277
 278 return yield;
 279 }
 280
 281
 282
 283
 284 /*************************************************
 285 *            Initialize for TLS                  *
 286 *************************************************/
 287
 288 /* Called from both server and client code, to do preliminary initialization of
 289 the library.
 290
 291 Arguments:
 292   host            connected host, if client; NULL if server
 293   dhparam         DH parameter file
 294   certificate     certificate file
 295   privatekey      private key
 296   addr            address if client; NULL if server (for some randomness)
 297
 298 Returns:          OK/DEFER/FAIL
 299 */
 300
 301 static int
 302 tls_init(host_item *host, uschar *dhparam, uschar *certificate,
 303   uschar *privatekey, address_item *addr)
 304 {
 305 long init_options;
 306 BOOL okay;
 307
 308 SSL_load_error_strings();          /* basic set up */
 309 OpenSSL_add_ssl_algorithms();
 310
 311 #if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_SHA256)
 312 /* SHA256 is becoming ever more popular. This makes sure it gets added to the
 313 list of available digests. */
 314 EVP_add_digest(EVP_sha256());
 315 #endif
 316
 317 /* Create a context */
 318
 319 ctx = SSL_CTX_new((host == NULL)?
 320   SSLv23_server_method() : SSLv23_client_method());
 321
 322 if (ctx == NULL) return tls_error(US"SSL_CTX_new", host, NULL);
 323
 324 /* It turns out that we need to seed the random number generator this early in
 325 order to get the full complement of ciphers to work. It took me roughly a day
 326 of work to discover this by experiment.
 327
 328 On systems that have /dev/urandom, SSL may automatically seed itself from
 329 there. Otherwise, we have to make something up as best we can. Double check
 330 afterwards. */
 331
 332 if (!RAND_status())
 333   {
 334   randstuff r;
 335   gettimeofday(&r.tv, NULL);
 336   r.p = getpid();
 337
 338   RAND_seed((uschar *)(&r), sizeof(r));
 339   RAND_seed((uschar *)big_buffer, big_buffer_size);
 340   if (addr != NULL) RAND_seed((uschar *)addr, sizeof(addr));
 341
 342   if (!RAND_status())
 343     return tls_error(US"RAND_status", host,
 344       US"unable to seed random number generator");
 345   }
 346
 347 /* Set up the information callback, which outputs if debugging is at a suitable
 348 level. */
 349
 350 SSL_CTX_set_info_callback(ctx, (void (*)())info_callback);
 351
 352 /* Apply administrator-supplied work-arounds.
 353 Historically we applied just one requested option,
 354 SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS, but when bug 994 requested a second, we
 355 moved to an administrator-controlled list of options to specify and
 356 grandfathered in the first one as the default value for "openssl_options".
 357
 358 No OpenSSL version number checks: the options we accept depend upon the
 359 availability of the option value macros from OpenSSL.  */
 360
 361 okay = tls_openssl_options_parse(openssl_options, &init_options);
 362 if (!okay)
 363   return tls_error("openssl_options parsing failed", host, NULL);
 364
 365 if (init_options)
 366   {
 367   DEBUG(D_tls) debug_printf("setting SSL CTX options: %#lx\n", init_options);
 368   if (!(SSL_CTX_set_options(ctx, init_options)))
 369     return tls_error(string_sprintf(
 370           "SSL_CTX_set_option(%#lx)", init_options), host, NULL);
 371   }
 372 else
 373   DEBUG(D_tls) debug_printf("no SSL CTX options to set\n");
 374
 375 /* Initialize with DH parameters if supplied */
 376
 377 if (!init_dh(dhparam, host)) return DEFER;
 378
 379 /* Set up certificate and key */
 380
 381 if (certificate != NULL)
 382   {
 383   uschar *expanded;
 384   if (!expand_check(certificate, US"tls_certificate", &expanded))
 385     return DEFER;
 386
 387   if (expanded != NULL)
 388     {
 389     DEBUG(D_tls) debug_printf("tls_certificate file %s\n", expanded);
 390     if (!SSL_CTX_use_certificate_chain_file(ctx, CS expanded))
 391       return tls_error(string_sprintf(
 392         "SSL_CTX_use_certificate_chain_file file=%s", expanded), host, NULL);
 393     }
 394
 395   if (privatekey != NULL &&
 396       !expand_check(privatekey, US"tls_privatekey", &expanded))
 397     return DEFER;
 398
 399   /* If expansion was forced to fail, key_expanded will be NULL. If the result
 400   of the expansion is an empty string, ignore it also, and assume the private
 401   key is in the same file as the certificate. */
 402
 403   if (expanded != NULL && *expanded != 0)
 404     {
 405     DEBUG(D_tls) debug_printf("tls_privatekey file %s\n", expanded);
 406     if (!SSL_CTX_use_PrivateKey_file(ctx, CS expanded, SSL_FILETYPE_PEM))
 407       return tls_error(string_sprintf(
 408         "SSL_CTX_use_PrivateKey_file file=%s", expanded), host, NULL);
 409     }
 410   }
 411
 412 /* Set up the RSA callback */
 413
 414 SSL_CTX_set_tmp_rsa_callback(ctx, rsa_callback);
 415
 416 /* Finally, set the timeout, and we are done */
 417
 418 SSL_CTX_set_timeout(ctx, ssl_session_timeout);
 419 DEBUG(D_tls) debug_printf("Initialized TLS\n");
 420 return OK;
 421 }
 422
 423
 424
 425
 426 /*************************************************
 427 *           Get name of cipher in use            *
 428 *************************************************/
 429
 430 /* The answer is left in a static buffer, and tls_cipher is set to point
 431 to it.
 432
 433 Argument:   pointer to an SSL structure for the connection
 434 Returns:    nothing
 435 */
 436
 437 static void
 438 construct_cipher_name(SSL *ssl)
 439 {
 440 static uschar cipherbuf[256];
 441 SSL_CIPHER *c;
 442 uschar *ver;
 443 int bits;
 444
 445 switch (ssl->session->ssl_version)
 446   {
 447   case SSL2_VERSION:
 448   ver = US"SSLv2";
 449   break;
 450
 451   case SSL3_VERSION:
 452   ver = US"SSLv3";
 453   break;
 454
 455   case TLS1_VERSION:
 456   ver = US"TLSv1";
 457   break;
 458
 459   default:
 460   ver = US"UNKNOWN";
 461   }
 462
 463 c = SSL_get_current_cipher(ssl);
 464 SSL_CIPHER_get_bits(c, &bits);
 465
 466 string_format(cipherbuf, sizeof(cipherbuf), "%s:%s:%u", ver,
 467   SSL_CIPHER_get_name(c), bits);
 468 tls_cipher = cipherbuf;
 469
 470 DEBUG(D_tls) debug_printf("Cipher: %s\n", cipherbuf);
 471 }
 472
 473
 474
 475
 476
 477 /*************************************************
 478 *        Set up for verifying certificates       *
 479 *************************************************/
 480
 481 /* Called by both client and server startup
 482
 483 Arguments:
 484   certs         certs file or NULL
 485   crl           CRL file or NULL
 486   host          NULL in a server; the remote host in a client
 487   optional      TRUE if called from a server for a host in tls_try_verify_hosts;
 488                 otherwise passed as FALSE
 489
 490 Returns:        OK/DEFER/FAIL
 491 */
 492
 493 static int
 494 setup_certs(uschar *certs, uschar *crl, host_item *host, BOOL optional)
 495 {
 496 uschar *expcerts, *expcrl;
 497
 498 if (!expand_check(certs, US"tls_verify_certificates", &expcerts))
 499   return DEFER;
 500
 501 if (expcerts != NULL)
 502   {
 503   struct stat statbuf;
 504   if (!SSL_CTX_set_default_verify_paths(ctx))
 505     return tls_error(US"SSL_CTX_set_default_verify_paths", host, NULL);
 506
 507   if (Ustat(expcerts, &statbuf) < 0)
 508     {
 509     log_write(0, LOG_MAIN|LOG_PANIC,
 510       "failed to stat %s for certificates", expcerts);
 511     return DEFER;
 512     }
 513   else
 514     {
 515     uschar *file, *dir;
 516     if ((statbuf.st_mode & S_IFMT) == S_IFDIR)
 517       { file = NULL; dir = expcerts; }
 518     else
 519       { file = expcerts; dir = NULL; }
 520
 521     /* If a certificate file is empty, the next function fails with an
 522     unhelpful error message. If we skip it, we get the correct behaviour (no
 523     certificates are recognized, but the error message is still misleading (it
 524     says no certificate was supplied.) But this is better. */
 525
 526     if ((file == NULL || statbuf.st_size > 0) &&
 527           !SSL_CTX_load_verify_locations(ctx, CS file, CS dir))
 528       return tls_error(US"SSL_CTX_load_verify_locations", host, NULL);
 529
 530     if (file != NULL)
 531       {
 532       SSL_CTX_set_client_CA_list(ctx, SSL_load_client_CA_file(CS file));
 533       }
 534     }
 535
 536   /* Handle a certificate revocation list. */
 537
 538   #if OPENSSL_VERSION_NUMBER > 0x00907000L
 539
 540   /* This bit of code is now the version supplied by Lars Mainka. (I have
 541    * merely reformatted it into the Exim code style.)
 542
 543    * "From here I changed the code to add support for multiple crl's
 544    * in pem format in one file or to support hashed directory entries in
 545    * pem format instead of a file. This method now uses the library function
 546    * X509_STORE_load_locations to add the CRL location to the SSL context.
 547    * OpenSSL will then handle the verify against CA certs and CRLs by
 548    * itself in the verify callback." */
 549
 550   if (!expand_check(crl, US"tls_crl", &expcrl)) return DEFER;
 551   if (expcrl != NULL && *expcrl != 0)
 552     {
 553     struct stat statbufcrl;
 554     if (Ustat(expcrl, &statbufcrl) < 0)
 555       {
 556       log_write(0, LOG_MAIN|LOG_PANIC,
 557         "failed to stat %s for certificates revocation lists", expcrl);
 558       return DEFER;
 559       }
 560     else
 561       {
 562       /* is it a file or directory? */
 563       uschar *file, *dir;
 564       X509_STORE *cvstore = SSL_CTX_get_cert_store(ctx);
 565       if ((statbufcrl.st_mode & S_IFMT) == S_IFDIR)
 566         {
 567         file = NULL;
 568         dir = expcrl;
 569         DEBUG(D_tls) debug_printf("SSL CRL value is a directory %s\n", dir);
 570         }
 571       else
 572         {
 573         file = expcrl;
 574         dir = NULL;
 575         DEBUG(D_tls) debug_printf("SSL CRL value is a file %s\n", file);
 576         }
 577       if (X509_STORE_load_locations(cvstore, CS file, CS dir) == 0)
 578         return tls_error(US"X509_STORE_load_locations", host, NULL);
 579
 580       /* setting the flags to check against the complete crl chain */
 581
 582       X509_STORE_set_flags(cvstore,
 583         X509_V_FLAG_CRL_CHECK|X509_V_FLAG_CRL_CHECK_ALL);
 584       }
 585     }
 586
 587   #endif  /* OPENSSL_VERSION_NUMBER > 0x00907000L */
 588
 589   /* If verification is optional, don't fail if no certificate */
 590
 591   SSL_CTX_set_verify(ctx,
 592     SSL_VERIFY_PEER | (optional? 0 : SSL_VERIFY_FAIL_IF_NO_PEER_CERT),
 593     verify_callback);
 594   }
 595
 596 return OK;
 597 }
 598
 599
 600
 601 /*************************************************
 602 *       Start a TLS session in a server          *
 603 *************************************************/
 604
 605 /* This is called when Exim is running as a server, after having received
 606 the STARTTLS command. It must respond to that command, and then negotiate
 607 a TLS session.
 608
 609 Arguments:
 610   require_ciphers   allowed ciphers
 611   ------------------------------------------------------
 612   require_mac      list of allowed MACs                 ) Not used
 613   require_kx       list of allowed key_exchange methods )   for
 614   require_proto    list of allowed protocols            ) OpenSSL
 615   ------------------------------------------------------
 616
 617 Returns:            OK on success
 618                     DEFER for errors before the start of the negotiation
 619                     FAIL for errors during the negotation; the server can't
 620                       continue running.
 621 */
 622
 623 int
 624 tls_server_start(uschar *require_ciphers, uschar *require_mac,
 625   uschar *require_kx, uschar *require_proto)
 626 {
 627 int rc;
 628 uschar *expciphers;
 629
 630 /* Check for previous activation */
 631
 632 if (tls_active >= 0)
 633   {
 634   tls_error(US"STARTTLS received after TLS started", NULL, US"");
 635   smtp_printf("554 Already in TLS\r\n");
 636   return FAIL;
 637   }
 638
 639 /* Initialize the SSL library. If it fails, it will already have logged
 640 the error. */
 641
 642 rc = tls_init(NULL, tls_dhparam, tls_certificate, tls_privatekey, NULL);
 643 if (rc != OK) return rc;
 644
 645 if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers))
 646   return FAIL;
 647
 648 /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they
 649 are separated by underscores. So that I can use either form in my tests, and
 650 also for general convenience, we turn underscores into hyphens here. */
 651
 652 if (expciphers != NULL)
 653   {
 654   uschar *s = expciphers;
 655   while (*s != 0) { if (*s == '_') *s = '-'; s++; }
 656   DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers);
 657   if (!SSL_CTX_set_cipher_list(ctx, CS expciphers))
 658     return tls_error(US"SSL_CTX_set_cipher_list", NULL, NULL);
 659   }
 660
 661 /* If this is a host for which certificate verification is mandatory or
 662 optional, set up appropriately. */
 663
 664 tls_certificate_verified = FALSE;
 665 verify_callback_called = FALSE;
 666
 667 if (verify_check_host(&tls_verify_hosts) == OK)
 668   {
 669   rc = setup_certs(tls_verify_certificates, tls_crl, NULL, FALSE);
 670   if (rc != OK) return rc;
 671   verify_optional = FALSE;
 672   }
 673 else if (verify_check_host(&tls_try_verify_hosts) == OK)
 674   {
 675   rc = setup_certs(tls_verify_certificates, tls_crl, NULL, TRUE);
 676   if (rc != OK) return rc;
 677   verify_optional = TRUE;
 678   }
 679
 680 /* Prepare for new connection */
 681
 682 if ((ssl = SSL_new(ctx)) == NULL) return tls_error(US"SSL_new", NULL, NULL);
 683 SSL_clear(ssl);
 684
 685 /* Set context and tell client to go ahead, except in the case of TLS startup
 686 on connection, where outputting anything now upsets the clients and tends to
 687 make them disconnect. We need to have an explicit fflush() here, to force out
 688 the response. Other smtp_printf() calls do not need it, because in non-TLS
 689 mode, the fflush() happens when smtp_getc() is called. */
 690
 691 SSL_set_session_id_context(ssl, sid_ctx, Ustrlen(sid_ctx));
 692 if (!tls_on_connect)
 693   {
 694   smtp_printf("220 TLS go ahead\r\n");
 695   fflush(smtp_out);
 696   }
 697
 698 /* Now negotiate the TLS session. We put our own timer on it, since it seems
 699 that the OpenSSL library doesn't. */
 700
 701 SSL_set_wfd(ssl, fileno(smtp_out));
 702 SSL_set_rfd(ssl, fileno(smtp_in));
 703 SSL_set_accept_state(ssl);
 704
 705 DEBUG(D_tls) debug_printf("Calling SSL_accept\n");
 706
 707 sigalrm_seen = FALSE;
 708 if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
 709 rc = SSL_accept(ssl);
 710 alarm(0);
 711
 712 if (rc <= 0)
 713   {
 714   tls_error(US"SSL_accept", NULL, sigalrm_seen ? US"timed out" : NULL);
 715   if (ERR_get_error() == 0)
 716     log_write(0, LOG_MAIN,
 717         "  => client disconnected cleanly (rejected our certificate?)\n");
 718   return FAIL;
 719   }
 720
 721 DEBUG(D_tls) debug_printf("SSL_accept was successful\n");
 722
 723 /* TLS has been set up. Adjust the input functions to read via TLS,
 724 and initialize things. */
 725
 726 construct_cipher_name(ssl);
 727
 728 DEBUG(D_tls)
 729   {
 730   uschar buf[2048];
 731   if (SSL_get_shared_ciphers(ssl, CS buf, sizeof(buf)) != NULL)
 732     debug_printf("Shared ciphers: %s\n", buf);
 733   }
 734
 735
 736 ssl_xfer_buffer = store_malloc(ssl_xfer_buffer_size);
 737 ssl_xfer_buffer_lwm = ssl_xfer_buffer_hwm = 0;
 738 ssl_xfer_eof = ssl_xfer_error = 0;
 739
 740 receive_getc = tls_getc;
 741 receive_ungetc = tls_ungetc;
 742 receive_feof = tls_feof;
 743 receive_ferror = tls_ferror;
 744 receive_smtp_buffered = tls_smtp_buffered;
 745
 746 tls_active = fileno(smtp_out);
 747 return OK;
 748 }
 749
 750
 751
 752
 753
 754 /*************************************************
 755 *    Start a TLS session in a client             *
 756 *************************************************/
 757
 758 /* Called from the smtp transport after STARTTLS has been accepted.
 759
 760 Argument:
 761   fd               the fd of the connection
 762   host             connected host (for messages)
 763   addr             the first address
 764   dhparam          DH parameter file
 765   certificate      certificate file
 766   privatekey       private key file
 767   verify_certs     file for certificate verify
 768   crl              file containing CRL
 769   require_ciphers  list of allowed ciphers
 770   ------------------------------------------------------
 771   require_mac      list of allowed MACs                 ) Not used
 772   require_kx       list of allowed key_exchange methods )   for
 773   require_proto    list of allowed protocols            ) OpenSSL
 774   ------------------------------------------------------
 775   timeout          startup timeout
 776
 777 Returns:           OK on success
 778                    FAIL otherwise - note that tls_error() will not give DEFER
 779                      because this is not a server
 780 */
 781
 782 int
 783 tls_client_start(int fd, host_item *host, address_item *addr, uschar *dhparam,
 784   uschar *certificate, uschar *privatekey, uschar *verify_certs, uschar *crl,
 785   uschar *require_ciphers, uschar *require_mac, uschar *require_kx,
 786   uschar *require_proto, int timeout)
 787 {
 788 static uschar txt[256];
 789 uschar *expciphers;
 790 X509* server_cert;
 791 int rc;
 792
 793 rc = tls_init(host, dhparam, certificate, privatekey, addr);
 794 if (rc != OK) return rc;
 795
 796 tls_certificate_verified = FALSE;
 797 verify_callback_called = FALSE;
 798
 799 if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers))
 800   return FAIL;
 801
 802 /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they
 803 are separated by underscores. So that I can use either form in my tests, and
 804 also for general convenience, we turn underscores into hyphens here. */
 805
 806 if (expciphers != NULL)
 807   {
 808   uschar *s = expciphers;
 809   while (*s != 0) { if (*s == '_') *s = '-'; s++; }
 810   DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers);
 811   if (!SSL_CTX_set_cipher_list(ctx, CS expciphers))
 812     return tls_error(US"SSL_CTX_set_cipher_list", host, NULL);
 813   }
 814
 815 rc = setup_certs(verify_certs, crl, host, FALSE);
 816 if (rc != OK) return rc;
 817
 818 if ((ssl = SSL_new(ctx)) == NULL) return tls_error(US"SSL_new", host, NULL);
 819 SSL_set_session_id_context(ssl, sid_ctx, Ustrlen(sid_ctx));
 820 SSL_set_fd(ssl, fd);
 821 SSL_set_connect_state(ssl);
 822
 823 /* There doesn't seem to be a built-in timeout on connection. */
 824
 825 DEBUG(D_tls) debug_printf("Calling SSL_connect\n");
 826 sigalrm_seen = FALSE;
 827 alarm(timeout);
 828 rc = SSL_connect(ssl);
 829 alarm(0);
 830
 831 if (rc <= 0)
 832   return tls_error(US"SSL_connect", host, sigalrm_seen ? US"timed out" : NULL);
 833
 834 DEBUG(D_tls) debug_printf("SSL_connect succeeded\n");
 835
 836 server_cert = SSL_get_peer_certificate (ssl);
 837 tls_peerdn = US X509_NAME_oneline(X509_get_subject_name(server_cert),
 838   CS txt, sizeof(txt));
 839 tls_peerdn = txt;
 840
 841 construct_cipher_name(ssl);   /* Sets tls_cipher */
 842
 843 tls_active = fd;
 844 return OK;
 845 }
 846
 847
 848
 849
 850
 851 /*************************************************
 852 *            TLS version of getc                 *
 853 *************************************************/
 854
 855 /* This gets the next byte from the TLS input buffer. If the buffer is empty,
 856 it refills the buffer via the SSL reading function.
 857
 858 Arguments:  none
 859 Returns:    the next character or EOF
 860 */
 861
 862 int
 863 tls_getc(void)
 864 {
 865 if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm)
 866   {
 867   int error;
 868   int inbytes;
 869
 870   DEBUG(D_tls) debug_printf("Calling SSL_read(%lx, %lx, %u)\n", (long)ssl,
 871     (long)ssl_xfer_buffer, ssl_xfer_buffer_size);
 872
 873   if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
 874   inbytes = SSL_read(ssl, CS ssl_xfer_buffer, ssl_xfer_buffer_size);
 875   error = SSL_get_error(ssl, inbytes);
 876   alarm(0);
 877
 878   /* SSL_ERROR_ZERO_RETURN appears to mean that the SSL session has been
 879   closed down, not that the socket itself has been closed down. Revert to
 880   non-SSL handling. */
 881
 882   if (error == SSL_ERROR_ZERO_RETURN)
 883     {
 884     DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n");
 885
 886     receive_getc = smtp_getc;
 887     receive_ungetc = smtp_ungetc;
 888     receive_feof = smtp_feof;
 889     receive_ferror = smtp_ferror;
 890     receive_smtp_buffered = smtp_buffered;
 891
 892     SSL_free(ssl);
 893     ssl = NULL;
 894     tls_active = -1;
 895     tls_cipher = NULL;
 896     tls_peerdn = NULL;
 897
 898     return smtp_getc();
 899     }
 900
 901   /* Handle genuine errors */
 902
 903   else if (error == SSL_ERROR_SSL)
 904     {
 905     ERR_error_string(ERR_get_error(), ssl_errstring);
 906     log_write(0, LOG_MAIN, "TLS error (SSL_read): %s", ssl_errstring);
 907     ssl_xfer_error = 1;
 908     return EOF;
 909     }
 910
 911   else if (error != SSL_ERROR_NONE)
 912     {
 913     DEBUG(D_tls) debug_printf("Got SSL error %d\n", error);
 914     ssl_xfer_error = 1;
 915     return EOF;
 916     }
 917 #ifndef DISABLE_DKIM
 918   dkim_exim_verify_feed(ssl_xfer_buffer, inbytes);
 919 #endif
 920   ssl_xfer_buffer_hwm = inbytes;
 921   ssl_xfer_buffer_lwm = 0;
 922   }
 923
 924 /* Something in the buffer; return next uschar */
 925
 926 return ssl_xfer_buffer[ssl_xfer_buffer_lwm++];
 927 }
 928
 929
 930
 931 /*************************************************
 932 *          Read bytes from TLS channel           *
 933 *************************************************/
 934
 935 /*
 936 Arguments:
 937   buff      buffer of data
 938   len       size of buffer
 939
 940 Returns:    the number of bytes read
 941             -1 after a failed read
 942 */
 943
 944 int
 945 tls_read(uschar *buff, size_t len)
 946 {
 947 int inbytes;
 948 int error;
 949
 950 DEBUG(D_tls) debug_printf("Calling SSL_read(%lx, %lx, %u)\n", (long)ssl,
 951   (long)buff, (unsigned int)len);
 952
 953 inbytes = SSL_read(ssl, CS buff, len);
 954 error = SSL_get_error(ssl, inbytes);
 955
 956 if (error == SSL_ERROR_ZERO_RETURN)
 957   {
 958   DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n");
 959   return -1;
 960   }
 961 else if (error != SSL_ERROR_NONE)
 962   {
 963   return -1;
 964   }
 965
 966 return inbytes;
 967 }
 968
 969
 970
 971
 972
 973 /*************************************************
 974 *         Write bytes down TLS channel           *
 975 *************************************************/
 976
 977 /*
 978 Arguments:
 979   buff      buffer of data
 980   len       number of bytes
 981
 982 Returns:    the number of bytes after a successful write,
 983             -1 after a failed write
 984 */
 985
 986 int
 987 tls_write(const uschar *buff, size_t len)
 988 {
 989 int outbytes;
 990 int error;
 991 int left = len;
 992
 993 DEBUG(D_tls) debug_printf("tls_do_write(%lx, %d)\n", (long)buff, left);
 994 while (left > 0)
 995   {
 996   DEBUG(D_tls) debug_printf("SSL_write(SSL, %lx, %d)\n", (long)buff, left);
 997   outbytes = SSL_write(ssl, CS buff, left);
 998   error = SSL_get_error(ssl, outbytes);
 999   DEBUG(D_tls) debug_printf("outbytes=%d error=%d\n", outbytes, error);
1000   switch (error)
1001     {
1002     case SSL_ERROR_SSL:
1003     ERR_error_string(ERR_get_error(), ssl_errstring);
1004     log_write(0, LOG_MAIN, "TLS error (SSL_write): %s", ssl_errstring);
1005     return -1;
1006
1007     case SSL_ERROR_NONE:
1008     left -= outbytes;
1009     buff += outbytes;
1010     break;
1011
1012     case SSL_ERROR_ZERO_RETURN:
1013     log_write(0, LOG_MAIN, "SSL channel closed on write");
1014     return -1;
1015
1016     default:
1017     log_write(0, LOG_MAIN, "SSL_write error %d", error);
1018     return -1;
1019     }
1020   }
1021 return len;
1022 }
1023
1024
1025
1026 /*************************************************
1027 *         Close down a TLS session               *
1028 *************************************************/
1029
1030 /* This is also called from within a delivery subprocess forked from the
1031 daemon, to shut down the TLS library, without actually doing a shutdown (which
1032 would tamper with the SSL session in the parent process).
1033
1034 Arguments:   TRUE if SSL_shutdown is to be called
1035 Returns:     nothing
1036 */
1037
1038 void
1039 tls_close(BOOL shutdown)
1040 {
1041 if (tls_active < 0) return;  /* TLS was not active */
1042
1043 if (shutdown)
1044   {
1045   DEBUG(D_tls) debug_printf("tls_close(): shutting down SSL\n");
1046   SSL_shutdown(ssl);
1047   }
1048
1049 SSL_free(ssl);
1050 ssl = NULL;
1051
1052 tls_active = -1;
1053 }
1054
1055
1056
1057
1058 /*************************************************
1059 *         Report the library versions.           *
1060 *************************************************/
1061
1062 /* There have historically been some issues with binary compatibility in
1063 OpenSSL libraries; if Exim (like many other applications) is built against
1064 one version of OpenSSL but the run-time linker picks up another version,
1065 it can result in serious failures, including crashing with a SIGSEGV.  So
1066 report the version found by the compiler and the run-time version.
1067
1068 Arguments:   a FILE* to print the results to
1069 Returns:     nothing
1070 */
1071
1072 void
1073 tls_version_report(FILE *f)
1074 {
1075 fprintf(f, "OpenSSL compile-time version: %s\n", OPENSSL_VERSION_TEXT);
1076 fprintf(f, "OpenSSL runtime version: %s\n", SSLeay_version(SSLEAY_VERSION));
1077 }
1078
1079
1080
1081
1082 /*************************************************
1083 *        Pseudo-random number generation         *
1084 *************************************************/
1085
1086 /* Pseudo-random number generation.  The result is not expected to be
1087 cryptographically strong but not so weak that someone will shoot themselves
1088 in the foot using it as a nonce in input in some email header scheme or
1089 whatever weirdness they'll twist this into.  The result should handle fork()
1090 and avoid repeating sequences.  OpenSSL handles that for us.
1091
1092 Arguments:
1093   max       range maximum
1094 Returns     a random number in range [0, max-1]
1095 */
1096
1097 int
1098 pseudo_random_number(int max)
1099 {
1100 unsigned int r;
1101 int i, needed_len;
1102 uschar *p;
1103 uschar smallbuf[sizeof(r)];
1104
1105 if (max <= 1)
1106   return 0;
1107
1108 /* OpenSSL auto-seeds from /dev/random, etc, but this a double-check. */
1109 if (!RAND_status())
1110   {
1111   randstuff r;
1112   gettimeofday(&r.tv, NULL);
1113   r.p = getpid();
1114
1115   RAND_seed((uschar *)(&r), sizeof(r));
1116   }
1117 /* We're after pseudo-random, not random; if we still don't have enough data
1118 in the internal PRNG then our options are limited.  We could sleep and hope
1119 for entropy to come along (prayer technique) but if the system is so depleted
1120 in the first place then something is likely to just keep taking it.  Instead,
1121 we'll just take whatever little bit of pseudo-random we can still manage to
1122 get. */
1123
1124 needed_len = sizeof(r);
1125 /* Don't take 8 times more entropy than needed if int is 8 octets and we were
1126 asked for a number less than 10. */
1127 for (r = max, i = 0; r; ++i)
1128   r >>= 1;
1129 i = (i + 7) / 8;
1130 if (i < needed_len)
1131   needed_len = i;
1132
1133 /* We do not care if crypto-strong */
1134 (void) RAND_pseudo_bytes(smallbuf, needed_len);
1135 r = 0;
1136 for (p = smallbuf; needed_len; --needed_len, ++p)
1137   {
1138   r *= 256;
1139   r += *p;
1140   }
1141
1142 /* We don't particularly care about weighted results; if someone wants
1143 smooth distribution and cares enough then they should submit a patch then. */
1144 return r % max;
1145 }
1146
1147
1148
1149
1150 /*************************************************
1151 *        OpenSSL option parse                    *
1152 *************************************************/
1153
1154 /* Parse one option for tls_openssl_options_parse below
1155
1156 Arguments:
1157   name    one option name
1158   value   place to store a value for it
1159 Returns   success or failure in parsing
1160 */
1161
1162 struct exim_openssl_option {
1163   uschar *name;
1164   long    value;
1165 };
1166 /* We could use a macro to expand, but we need the ifdef and not all the
1167 options document which version they were introduced in.  Policylet: include
1168 all options unless explicitly for DTLS, let the administrator choose which
1169 to apply.
1170
1171 This list is current as of:
1172   ==>  0.9.8n  <==  */
1173 static struct exim_openssl_option exim_openssl_options[] = {
1174 /* KEEP SORTED ALPHABETICALLY! */
1175 #ifdef SSL_OP_ALL
1176   { "all", SSL_OP_ALL },
1177 #endif
1178 #ifdef SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
1179   { "allow_unsafe_legacy_renegotiation", SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION },
1180 #endif
1181 #ifdef SSL_OP_CIPHER_SERVER_PREFERENCE
1182   { "cipher_server_preference", SSL_OP_CIPHER_SERVER_PREFERENCE },
1183 #endif
1184 #ifdef SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
1185   { "dont_insert_empty_fragments", SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS },
1186 #endif
1187 #ifdef SSL_OP_EPHEMERAL_RSA
1188   { "ephemeral_rsa", SSL_OP_EPHEMERAL_RSA },
1189 #endif
1190 #ifdef SSL_OP_LEGACY_SERVER_CONNECT
1191   { "legacy_server_connect", SSL_OP_LEGACY_SERVER_CONNECT },
1192 #endif
1193 #ifdef SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
1194   { "microsoft_big_sslv3_buffer", SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER },
1195 #endif
1196 #ifdef SSL_OP_MICROSOFT_SESS_ID_BUG
1197   { "microsoft_sess_id_bug", SSL_OP_MICROSOFT_SESS_ID_BUG },
1198 #endif
1199 #ifdef SSL_OP_MSIE_SSLV2_RSA_PADDING
1200   { "msie_sslv2_rsa_padding", SSL_OP_MSIE_SSLV2_RSA_PADDING },
1201 #endif
1202 #ifdef SSL_OP_NETSCAPE_CHALLENGE_BUG
1203   { "netscape_challenge_bug", SSL_OP_NETSCAPE_CHALLENGE_BUG },
1204 #endif
1205 #ifdef SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
1206   { "netscape_reuse_cipher_change_bug", SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG },
1207 #endif
1208 #ifdef SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
1209   { "no_session_resumption_on_renegotiation", SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION },
1210 #endif
1211 #ifdef SSL_OP_SINGLE_DH_USE
1212   { "single_dh_use", SSL_OP_SINGLE_DH_USE },
1213 #endif
1214 #ifdef SSL_OP_SINGLE_ECDH_USE
1215   { "single_ecdh_use", SSL_OP_SINGLE_ECDH_USE },
1216 #endif
1217 #ifdef SSL_OP_SSLEAY_080_CLIENT_DH_BUG
1218   { "ssleay_080_client_dh_bug", SSL_OP_SSLEAY_080_CLIENT_DH_BUG },
1219 #endif
1220 #ifdef SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
1221   { "sslref2_reuse_cert_type_bug", SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG },
1222 #endif
1223 #ifdef SSL_OP_TLS_BLOCK_PADDING_BUG
1224   { "tls_block_padding_bug", SSL_OP_TLS_BLOCK_PADDING_BUG },
1225 #endif
1226 #ifdef SSL_OP_TLS_D5_BUG
1227   { "tls_d5_bug", SSL_OP_TLS_D5_BUG },
1228 #endif
1229 #ifdef SSL_OP_TLS_ROLLBACK_BUG
1230   { "tls_rollback_bug", SSL_OP_TLS_ROLLBACK_BUG },
1231 #endif
1232 };
1233 static int exim_openssl_options_size =
1234   sizeof(exim_openssl_options)/sizeof(struct exim_openssl_option);
1235
1236 static BOOL
1237 tls_openssl_one_option_parse(uschar *name, long *value)
1238 {
1239 int first = 0;
1240 int last = exim_openssl_options_size;
1241 while (last > first)
1242   {
1243   int middle = (first + last)/2;
1244   int c = Ustrcmp(name, exim_openssl_options[middle].name);
1245   if (c == 0)
1246     {
1247     *value = exim_openssl_options[middle].value;
1248     return TRUE;
1249     }
1250   else if (c > 0)
1251     first = middle + 1;
1252   else
1253     last = middle;
1254   }
1255 return FALSE;
1256 }
1257
1258
1259
1260
1261 /*************************************************
1262 *        OpenSSL option parsing logic            *
1263 *************************************************/
1264
1265 /* OpenSSL has a number of compatibility options which an administrator might
1266 reasonably wish to set.  Interpret a list similarly to decode_bits(), so that
1267 we look like log_selector.
1268
1269 Arguments:
1270   option_spec  the administrator-supplied string of options
1271   results      ptr to long storage for the options bitmap
1272 Returns        success or failure
1273 */
1274
1275 BOOL
1276 tls_openssl_options_parse(uschar *option_spec, long *results)
1277 {
1278 long result, item;
1279 uschar *s, *end;
1280 uschar keep_c;
1281 BOOL adding, item_parsed;
1282
1283 /* We grandfather in as default the one option which we used to set always. */
1284 #ifdef SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
1285 result = SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS;
1286 #else
1287 result = 0L;
1288 #endif
1289
1290 if (option_spec == NULL)
1291   {
1292   *results = result;
1293   return TRUE;
1294   }
1295
1296 for (s=option_spec; *s != '\0'; /**/)
1297   {
1298   while (isspace(*s)) ++s;
1299   if (*s == '\0')
1300     break;
1301   if (*s != '+' && *s != '-')
1302     {
1303     DEBUG(D_tls) debug_printf("malformed openssl option setting: "
1304         "+ or - expected but found \"%s\"", s);
1305     return FALSE;
1306     }
1307   adding = *s++ == '+';
1308   for (end = s; (*end != '\0') && !isspace(*end); ++end) /**/ ;
1309   keep_c = *end;
1310   *end = '\0';
1311   item_parsed = tls_openssl_one_option_parse(s, &item);
1312   if (!item_parsed)
1313     {
1314     DEBUG(D_tls) debug_printf("openssl option setting unrecognised: \"%s\"", s);
1315     return FALSE;
1316     }
1317   DEBUG(D_tls) debug_printf("openssl option, %s from %lx: %lx (%s)\n",
1318       adding ? "adding" : "removing", result, item, s);
1319   if (adding)
1320     result |= item;
1321   else
1322     result &= ~item;
1323   *end = keep_c;
1324   s = end;
1325   }
1326
1327 *results = result;
1328 return TRUE;
1329 }
1330
1331 /* End of tls-openssl.c */