src/src/tls-openssl.c

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