src/src/tls-openssl.c

   1 /*************************************************
   2 *     Exim - an Internet mail transport agent    *
   3 *************************************************/
   4
   5 /* Copyright (c) University of Cambridge 1995 - 2017 */
   6 /* See the file NOTICE for conditions of use and distribution. */
   7
   8 /* Portions Copyright (c) The OpenSSL Project 1999 */
   9
  10 /* This module provides the TLS (aka SSL) support for Exim using the OpenSSL
  11 library. It is #included into the tls.c file when that library is used. The
  12 code herein is based on a patch that was originally contributed by Steve
  13 Haslam. It was adapted from stunnel, a GPL program by Michal Trojnara.
  14
  15 No cryptographic code is included in Exim. All this module does is to call
  16 functions from the OpenSSL library. */
  17
  18
  19 /* Heading stuff */
  20
  21 #include <openssl/lhash.h>
  22 #include <openssl/ssl.h>
  23 #include <openssl/err.h>
  24 #include <openssl/rand.h>
  25 #ifndef OPENSSL_NO_ECDH
  26 # include <openssl/ec.h>
  27 #endif
  28 #ifndef DISABLE_OCSP
  29 # include <openssl/ocsp.h>
  30 #endif
  31 #ifdef EXPERIMENTAL_DANE
  32 # include <danessl.h>
  33 #endif
  34
  35
  36 #ifndef DISABLE_OCSP
  37 # define EXIM_OCSP_SKEW_SECONDS (300L)
  38 # define EXIM_OCSP_MAX_AGE (-1L)
  39 #endif
  40
  41 #if OPENSSL_VERSION_NUMBER >= 0x0090806fL && !defined(OPENSSL_NO_TLSEXT)
  42 # define EXIM_HAVE_OPENSSL_TLSEXT
  43 #endif
  44 #if OPENSSL_VERSION_NUMBER >= 0x00908000L
  45 # define EXIM_HAVE_RSA_GENKEY_EX
  46 #endif
  47 #if OPENSSL_VERSION_NUMBER >= 0x10100000L
  48 # define EXIM_HAVE_OCSP_RESP_COUNT
  49 #else
  50 # define EXIM_HAVE_EPHEM_RSA_KEX
  51 # define EXIM_HAVE_RAND_PSEUDO
  52 #endif
  53 #if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_SHA256)
  54 # define EXIM_HAVE_SHA256
  55 #endif
  56
  57 /*
  58  * X509_check_host provides sane certificate hostname checking, but was added
  59  * to OpenSSL late, after other projects forked off the code-base.  So in
  60  * addition to guarding against the base version number, beware that LibreSSL
  61  * does not (at this time) support this function.
  62  *
  63  * If LibreSSL gains a different API, perhaps via libtls, then we'll probably
  64  * opt to disentangle and ask a LibreSSL user to provide glue for a third
  65  * crypto provider for libtls instead of continuing to tie the OpenSSL glue
  66  * into even twistier knots.  If LibreSSL gains the same API, we can just
  67  * change this guard and punt the issue for a while longer.
  68  */
  69 #ifndef LIBRESSL_VERSION_NUMBER
  70 # if OPENSSL_VERSION_NUMBER >= 0x010100000L
  71 #  define EXIM_HAVE_OPENSSL_CHECKHOST
  72 # endif
  73 # if OPENSSL_VERSION_NUMBER >= 0x010000000L \
  74     && (OPENSSL_VERSION_NUMBER & 0x0000ff000L) >= 0x000002000L
  75 #  define EXIM_HAVE_OPENSSL_CHECKHOST
  76 # endif
  77 #endif
  78
  79 #if !defined(LIBRESSL_VERSION_NUMBER) \
  80     || LIBRESSL_VERSION_NUMBER >= 0x20010000L
  81 # if !defined(OPENSSL_NO_ECDH)
  82 #  if OPENSSL_VERSION_NUMBER >= 0x0090800fL
  83 #   define EXIM_HAVE_ECDH
  84 #  endif
  85 #  if OPENSSL_VERSION_NUMBER >= 0x10002000L
  86 #   define EXIM_HAVE_OPENSSL_EC_NIST2NID
  87 #  endif
  88 # endif
  89 #endif
  90
  91 #if !defined(EXIM_HAVE_OPENSSL_TLSEXT) && !defined(DISABLE_OCSP)
  92 # warning "OpenSSL library version too old; define DISABLE_OCSP in Makefile"
  93 # define DISABLE_OCSP
  94 #endif
  95
  96 /* Structure for collecting random data for seeding. */
  97
  98 typedef struct randstuff {
  99   struct timeval tv;
 100   pid_t          p;
 101 } randstuff;
 102
 103 /* Local static variables */
 104
 105 static BOOL client_verify_callback_called = FALSE;
 106 static BOOL server_verify_callback_called = FALSE;
 107 static const uschar *sid_ctx = US"exim";
 108
 109 /* We have three different contexts to care about.
 110
 111 Simple case: client, `client_ctx`
 112  As a client, we can be doing a callout or cut-through delivery while receiving
 113  a message.  So we have a client context, which should have options initialised
 114  from the SMTP Transport.
 115
 116 Server:
 117  There are two cases: with and without ServerNameIndication from the client.
 118  Given TLS SNI, we can be using different keys, certs and various other
 119  configuration settings, because they're re-expanded with $tls_sni set.  This
 120  allows vhosting with TLS.  This SNI is sent in the handshake.
 121  A client might not send SNI, so we need a fallback, and an initial setup too.
 122  So as a server, we start out using `server_ctx`.
 123  If SNI is sent by the client, then we as server, mid-negotiation, try to clone
 124  `server_sni` from `server_ctx` and then initialise settings by re-expanding
 125  configuration.
 126 */
 127
 128 static SSL_CTX *client_ctx = NULL;
 129 static SSL_CTX *server_ctx = NULL;
 130 static SSL     *client_ssl = NULL;
 131 static SSL     *server_ssl = NULL;
 132
 133 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
 134 static SSL_CTX *server_sni = NULL;
 135 #endif
 136
 137 static char ssl_errstring[256];
 138
 139 static int  ssl_session_timeout = 200;
 140 static BOOL client_verify_optional = FALSE;
 141 static BOOL server_verify_optional = FALSE;
 142
 143 static BOOL reexpand_tls_files_for_sni = FALSE;
 144
 145
 146 typedef struct tls_ext_ctx_cb {
 147   uschar *certificate;
 148   uschar *privatekey;
 149 #ifndef DISABLE_OCSP
 150   BOOL is_server;
 151   STACK_OF(X509) *verify_stack;         /* chain for verifying the proof */
 152   union {
 153     struct {
 154       uschar        *file;
 155       uschar        *file_expanded;
 156       OCSP_RESPONSE *response;
 157     } server;
 158     struct {
 159       X509_STORE    *verify_store;      /* non-null if status requested */
 160       BOOL          verify_required;
 161     } client;
 162   } u_ocsp;
 163 #endif
 164   uschar *dhparam;
 165   /* these are cached from first expand */
 166   uschar *server_cipher_list;
 167   /* only passed down to tls_error: */
 168   host_item *host;
 169   const uschar * verify_cert_hostnames;
 170 #ifndef DISABLE_EVENT
 171   uschar * event_action;
 172 #endif
 173 } tls_ext_ctx_cb;
 174
 175 /* should figure out a cleanup of API to handle state preserved per
 176 implementation, for various reasons, which can be void * in the APIs.
 177 For now, we hack around it. */
 178 tls_ext_ctx_cb *client_static_cbinfo = NULL;
 179 tls_ext_ctx_cb *server_static_cbinfo = NULL;
 180
 181 static int
 182 setup_certs(SSL_CTX *sctx, uschar *certs, uschar *crl, host_item *host, BOOL optional,
 183     int (*cert_vfy_cb)(int, X509_STORE_CTX *), uschar ** errstr );
 184
 185 /* Callbacks */
 186 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
 187 static int tls_servername_cb(SSL *s, int *ad ARG_UNUSED, void *arg);
 188 #endif
 189 #ifndef DISABLE_OCSP
 190 static int tls_server_stapling_cb(SSL *s, void *arg);
 191 #endif
 192
 193
 194 /*************************************************
 195 *               Handle TLS error                 *
 196 *************************************************/
 197
 198 /* Called from lots of places when errors occur before actually starting to do
 199 the TLS handshake, that is, while the session is still in clear. Always returns
 200 DEFER for a server and FAIL for a client so that most calls can use "return
 201 tls_error(...)" to do this processing and then give an appropriate return. A
 202 single function is used for both server and client, because it is called from
 203 some shared functions.
 204
 205 Argument:
 206   prefix    text to include in the logged error
 207   host      NULL if setting up a server;
 208             the connected host if setting up a client
 209   msg       error message or NULL if we should ask OpenSSL
 210   errstr    pointer to output error message
 211
 212 Returns:    OK/DEFER/FAIL
 213 */
 214
 215 static int
 216 tls_error(uschar * prefix, const host_item * host, uschar * msg, uschar ** errstr)
 217 {
 218 if (!msg)
 219   {
 220   ERR_error_string(ERR_get_error(), ssl_errstring);
 221   msg = US ssl_errstring;
 222   }
 223
 224 if (errstr) *errstr = string_sprintf("(%s): %s", prefix, msg);
 225 return host ? FAIL : DEFER;
 226 }
 227
 228
 229
 230 #ifdef EXIM_HAVE_EPHEM_RSA_KEX
 231 /*************************************************
 232 *        Callback to generate RSA key            *
 233 *************************************************/
 234
 235 /*
 236 Arguments:
 237   s          SSL connection
 238   export     not used
 239   keylength  keylength
 240
 241 Returns:     pointer to generated key
 242 */
 243
 244 static RSA *
 245 rsa_callback(SSL *s, int export, int keylength)
 246 {
 247 RSA *rsa_key;
 248 #ifdef EXIM_HAVE_RSA_GENKEY_EX
 249 BIGNUM *bn = BN_new();
 250 #endif
 251
 252 export = export;     /* Shut picky compilers up */
 253 DEBUG(D_tls) debug_printf("Generating %d bit RSA key...\n", keylength);
 254
 255 #ifdef EXIM_HAVE_RSA_GENKEY_EX
 256 if (  !BN_set_word(bn, (unsigned long)RSA_F4)
 257    || !(rsa_key = RSA_new())
 258    || !RSA_generate_key_ex(rsa_key, keylength, bn, NULL)
 259    )
 260 #else
 261 if (!(rsa_key = RSA_generate_key(keylength, RSA_F4, NULL, NULL)))
 262 #endif
 263
 264   {
 265   ERR_error_string(ERR_get_error(), ssl_errstring);
 266   log_write(0, LOG_MAIN|LOG_PANIC, "TLS error (RSA_generate_key): %s",
 267     ssl_errstring);
 268   return NULL;
 269   }
 270 return rsa_key;
 271 }
 272 #endif
 273
 274
 275
 276 /* Extreme debug
 277 #ifndef DISABLE_OCSP
 278 void
 279 x509_store_dump_cert_s_names(X509_STORE * store)
 280 {
 281 STACK_OF(X509_OBJECT) * roots= store->objs;
 282 int i;
 283 static uschar name[256];
 284
 285 for(i= 0; i<sk_X509_OBJECT_num(roots); i++)
 286   {
 287   X509_OBJECT * tmp_obj= sk_X509_OBJECT_value(roots, i);
 288   if(tmp_obj->type == X509_LU_X509)
 289     {
 290     X509 * current_cert= tmp_obj->data.x509;
 291     X509_NAME_oneline(X509_get_subject_name(current_cert), CS name, sizeof(name));
 292         name[sizeof(name)-1] = '\0';
 293     debug_printf(" %s\n", name);
 294     }
 295   }
 296 }
 297 #endif
 298 */
 299
 300
 301 #ifndef DISABLE_EVENT
 302 static int
 303 verify_event(tls_support * tlsp, X509 * cert, int depth, const uschar * dn,
 304   BOOL *calledp, const BOOL *optionalp, const uschar * what)
 305 {
 306 uschar * ev;
 307 uschar * yield;
 308 X509 * old_cert;
 309
 310 ev = tlsp == &tls_out ? client_static_cbinfo->event_action : event_action;
 311 if (ev)
 312   {
 313   DEBUG(D_tls) debug_printf("verify_event: %s %d\n", what, depth);
 314   old_cert = tlsp->peercert;
 315   tlsp->peercert = X509_dup(cert);
 316   /* NB we do not bother setting peerdn */
 317   if ((yield = event_raise(ev, US"tls:cert", string_sprintf("%d", depth))))
 318     {
 319     log_write(0, LOG_MAIN, "[%s] %s verify denied by event-action: "
 320                 "depth=%d cert=%s: %s",
 321               tlsp == &tls_out ? deliver_host_address : sender_host_address,
 322               what, depth, dn, yield);
 323     *calledp = TRUE;
 324     if (!*optionalp)
 325       {
 326       if (old_cert) tlsp->peercert = old_cert;  /* restore 1st failing cert */
 327       return 1;                     /* reject (leaving peercert set) */
 328       }
 329     DEBUG(D_tls) debug_printf("Event-action verify failure overridden "
 330       "(host in tls_try_verify_hosts)\n");
 331     }
 332   X509_free(tlsp->peercert);
 333   tlsp->peercert = old_cert;
 334   }
 335 return 0;
 336 }
 337 #endif
 338
 339 /*************************************************
 340 *        Callback for verification               *
 341 *************************************************/
 342
 343 /* The SSL library does certificate verification if set up to do so. This
 344 callback has the current yes/no state is in "state". If verification succeeded,
 345 we set the certificate-verified flag. If verification failed, what happens
 346 depends on whether the client is required to present a verifiable certificate
 347 or not.
 348
 349 If verification is optional, we change the state to yes, but still log the
 350 verification error. For some reason (it really would help to have proper
 351 documentation of OpenSSL), this callback function then gets called again, this
 352 time with state = 1.  We must take care not to set the private verified flag on
 353 the second time through.
 354
 355 Note: this function is not called if the client fails to present a certificate
 356 when asked. We get here only if a certificate has been received. Handling of
 357 optional verification for this case is done when requesting SSL to verify, by
 358 setting SSL_VERIFY_FAIL_IF_NO_PEER_CERT in the non-optional case.
 359
 360 May be called multiple times for different issues with a certificate, even
 361 for a given "depth" in the certificate chain.
 362
 363 Arguments:
 364   preverify_ok current yes/no state as 1/0
 365   x509ctx      certificate information.
 366   tlsp         per-direction (client vs. server) support data
 367   calledp      has-been-called flag
 368   optionalp    verification-is-optional flag
 369
 370 Returns:     0 if verification should fail, otherwise 1
 371 */
 372
 373 static int
 374 verify_callback(int preverify_ok, X509_STORE_CTX *x509ctx,
 375   tls_support *tlsp, BOOL *calledp, BOOL *optionalp)
 376 {
 377 X509 * cert = X509_STORE_CTX_get_current_cert(x509ctx);
 378 int depth = X509_STORE_CTX_get_error_depth(x509ctx);
 379 uschar dn[256];
 380
 381 X509_NAME_oneline(X509_get_subject_name(cert), CS dn, sizeof(dn));
 382 dn[sizeof(dn)-1] = '\0';
 383
 384 if (preverify_ok == 0)
 385   {
 386   log_write(0, LOG_MAIN, "[%s] SSL verify error: depth=%d error=%s cert=%s",
 387         tlsp == &tls_out ? deliver_host_address : sender_host_address,
 388     depth,
 389     X509_verify_cert_error_string(X509_STORE_CTX_get_error(x509ctx)),
 390     dn);
 391   *calledp = TRUE;
 392   if (!*optionalp)
 393     {
 394     if (!tlsp->peercert)
 395       tlsp->peercert = X509_dup(cert);  /* record failing cert */
 396     return 0;                           /* reject */
 397     }
 398   DEBUG(D_tls) debug_printf("SSL verify failure overridden (host in "
 399     "tls_try_verify_hosts)\n");
 400   }
 401
 402 else if (depth != 0)
 403   {
 404   DEBUG(D_tls) debug_printf("SSL verify ok: depth=%d SN=%s\n", depth, dn);
 405 #ifndef DISABLE_OCSP
 406   if (tlsp == &tls_out && client_static_cbinfo->u_ocsp.client.verify_store)
 407     {   /* client, wanting stapling  */
 408     /* Add the server cert's signing chain as the one
 409     for the verification of the OCSP stapled information. */
 410
 411     if (!X509_STORE_add_cert(client_static_cbinfo->u_ocsp.client.verify_store,
 412                              cert))
 413       ERR_clear_error();
 414     sk_X509_push(client_static_cbinfo->verify_stack, cert);
 415     }
 416 #endif
 417 #ifndef DISABLE_EVENT
 418     if (verify_event(tlsp, cert, depth, dn, calledp, optionalp, US"SSL"))
 419       return 0;                         /* reject, with peercert set */
 420 #endif
 421   }
 422 else
 423   {
 424   const uschar * verify_cert_hostnames;
 425
 426   if (  tlsp == &tls_out
 427      && ((verify_cert_hostnames = client_static_cbinfo->verify_cert_hostnames)))
 428         /* client, wanting hostname check */
 429     {
 430
 431 #ifdef EXIM_HAVE_OPENSSL_CHECKHOST
 432 # ifndef X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
 433 #  define X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS 0
 434 # endif
 435 # ifndef X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS
 436 #  define X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS 0
 437 # endif
 438     int sep = 0;
 439     const uschar * list = verify_cert_hostnames;
 440     uschar * name;
 441     int rc;
 442     while ((name = string_nextinlist(&list, &sep, NULL, 0)))
 443       if ((rc = X509_check_host(cert, CCS name, 0,
 444                   X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
 445                   | X509_CHECK_FLAG_SINGLE_LABEL_SUBDOMAINS,
 446                   NULL)))
 447         {
 448         if (rc < 0)
 449           {
 450           log_write(0, LOG_MAIN, "[%s] SSL verify error: internal error",
 451                 deliver_host_address);
 452           name = NULL;
 453           }
 454         break;
 455         }
 456     if (!name)
 457 #else
 458     if (!tls_is_name_for_cert(verify_cert_hostnames, cert))
 459 #endif
 460       {
 461       log_write(0, LOG_MAIN,
 462                 "[%s] SSL verify error: certificate name mismatch: "
 463                 "DN=\"%s\" H=\"%s\"",
 464                 deliver_host_address, dn, verify_cert_hostnames);
 465       *calledp = TRUE;
 466       if (!*optionalp)
 467         {
 468         if (!tlsp->peercert)
 469           tlsp->peercert = X509_dup(cert);      /* record failing cert */
 470         return 0;                               /* reject */
 471         }
 472       DEBUG(D_tls) debug_printf("SSL verify failure overridden (host in "
 473         "tls_try_verify_hosts)\n");
 474       }
 475     }
 476
 477 #ifndef DISABLE_EVENT
 478   if (verify_event(tlsp, cert, depth, dn, calledp, optionalp, US"SSL"))
 479     return 0;                           /* reject, with peercert set */
 480 #endif
 481
 482   DEBUG(D_tls) debug_printf("SSL%s verify ok: depth=0 SN=%s\n",
 483     *calledp ? "" : " authenticated", dn);
 484   if (!*calledp) tlsp->certificate_verified = TRUE;
 485   *calledp = TRUE;
 486   }
 487
 488 return 1;   /* accept, at least for this level */
 489 }
 490
 491 static int
 492 verify_callback_client(int preverify_ok, X509_STORE_CTX *x509ctx)
 493 {
 494 return verify_callback(preverify_ok, x509ctx, &tls_out,
 495   &client_verify_callback_called, &client_verify_optional);
 496 }
 497
 498 static int
 499 verify_callback_server(int preverify_ok, X509_STORE_CTX *x509ctx)
 500 {
 501 return verify_callback(preverify_ok, x509ctx, &tls_in,
 502   &server_verify_callback_called, &server_verify_optional);
 503 }
 504
 505
 506 #ifdef EXPERIMENTAL_DANE
 507
 508 /* This gets called *by* the dane library verify callback, which interposes
 509 itself.
 510 */
 511 static int
 512 verify_callback_client_dane(int preverify_ok, X509_STORE_CTX * x509ctx)
 513 {
 514 X509 * cert = X509_STORE_CTX_get_current_cert(x509ctx);
 515 uschar dn[256];
 516 int depth = X509_STORE_CTX_get_error_depth(x509ctx);
 517 #ifndef DISABLE_EVENT
 518 BOOL dummy_called, optional = FALSE;
 519 #endif
 520
 521 X509_NAME_oneline(X509_get_subject_name(cert), CS dn, sizeof(dn));
 522 dn[sizeof(dn)-1] = '\0';
 523
 524 DEBUG(D_tls) debug_printf("verify_callback_client_dane: %s depth %d %s\n",
 525   preverify_ok ? "ok":"BAD", depth, dn);
 526
 527 #ifndef DISABLE_EVENT
 528   if (verify_event(&tls_out, cert, depth, dn,
 529           &dummy_called, &optional, US"DANE"))
 530     return 0;                           /* reject, with peercert set */
 531 #endif
 532
 533 if (preverify_ok == 1)
 534   tls_out.dane_verified =
 535   tls_out.certificate_verified = TRUE;
 536 else
 537   {
 538   int err = X509_STORE_CTX_get_error(x509ctx);
 539   DEBUG(D_tls)
 540     debug_printf(" - err %d '%s'\n", err, X509_verify_cert_error_string(err));
 541   if (err == X509_V_ERR_APPLICATION_VERIFICATION)
 542     preverify_ok = 1;
 543   }
 544 return preverify_ok;
 545 }
 546
 547 #endif  /*EXPERIMENTAL_DANE*/
 548
 549
 550 /*************************************************
 551 *           Information callback                 *
 552 *************************************************/
 553
 554 /* The SSL library functions call this from time to time to indicate what they
 555 are doing. We copy the string to the debugging output when TLS debugging has
 556 been requested.
 557
 558 Arguments:
 559   s         the SSL connection
 560   where
 561   ret
 562
 563 Returns:    nothing
 564 */
 565
 566 static void
 567 info_callback(SSL *s, int where, int ret)
 568 {
 569 where = where;
 570 ret = ret;
 571 DEBUG(D_tls) debug_printf("SSL info: %s\n", SSL_state_string_long(s));
 572 }
 573
 574
 575
 576 /*************************************************
 577 *                Initialize for DH               *
 578 *************************************************/
 579
 580 /* If dhparam is set, expand it, and load up the parameters for DH encryption.
 581
 582 Arguments:
 583   sctx      The current SSL CTX (inbound or outbound)
 584   dhparam   DH parameter file or fixed parameter identity string
 585   host      connected host, if client; NULL if server
 586   errstr    error string pointer
 587
 588 Returns:    TRUE if OK (nothing to set up, or setup worked)
 589 */
 590
 591 static BOOL
 592 init_dh(SSL_CTX *sctx, uschar *dhparam, const host_item *host, uschar ** errstr)
 593 {
 594 BIO *bio;
 595 DH *dh;
 596 uschar *dhexpanded;
 597 const char *pem;
 598
 599 if (!expand_check(dhparam, US"tls_dhparam", &dhexpanded, errstr))
 600   return FALSE;
 601
 602 if (!dhexpanded || !*dhexpanded)
 603   bio = BIO_new_mem_buf(CS std_dh_prime_default(), -1);
 604 else if (dhexpanded[0] == '/')
 605   {
 606   if (!(bio = BIO_new_file(CS dhexpanded, "r")))
 607     {
 608     tls_error(string_sprintf("could not read dhparams file %s", dhexpanded),
 609           host, US strerror(errno), errstr);
 610     return FALSE;
 611     }
 612   }
 613 else
 614   {
 615   if (Ustrcmp(dhexpanded, "none") == 0)
 616     {
 617     DEBUG(D_tls) debug_printf("Requested no DH parameters.\n");
 618     return TRUE;
 619     }
 620
 621   if (!(pem = std_dh_prime_named(dhexpanded)))
 622     {
 623     tls_error(string_sprintf("Unknown standard DH prime \"%s\"", dhexpanded),
 624         host, US strerror(errno), errstr);
 625     return FALSE;
 626     }
 627   bio = BIO_new_mem_buf(CS pem, -1);
 628   }
 629
 630 if (!(dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL)))
 631   {
 632   BIO_free(bio);
 633   tls_error(string_sprintf("Could not read tls_dhparams \"%s\"", dhexpanded),
 634       host, NULL, errstr);
 635   return FALSE;
 636   }
 637
 638 /* Even if it is larger, we silently return success rather than cause things
 639  * to fail out, so that a too-large DH will not knock out all TLS; it's a
 640  * debatable choice. */
 641 if ((8*DH_size(dh)) > tls_dh_max_bits)
 642   {
 643   DEBUG(D_tls)
 644     debug_printf("dhparams file %d bits, is > tls_dh_max_bits limit of %d\n",
 645         8*DH_size(dh), tls_dh_max_bits);
 646   }
 647 else
 648   {
 649   SSL_CTX_set_tmp_dh(sctx, dh);
 650   DEBUG(D_tls)
 651     debug_printf("Diffie-Hellman initialized from %s with %d-bit prime\n",
 652       dhexpanded ? dhexpanded : US"default", 8*DH_size(dh));
 653   }
 654
 655 DH_free(dh);
 656 BIO_free(bio);
 657
 658 return TRUE;
 659 }
 660
 661
 662
 663
 664 /*************************************************
 665 *               Initialize for ECDH              *
 666 *************************************************/
 667
 668 /* Load parameters for ECDH encryption.
 669
 670 For now, we stick to NIST P-256 because: it's simple and easy to configure;
 671 it avoids any patent issues that might bite redistributors; despite events in
 672 the news and concerns over curve choices, we're not cryptographers, we're not
 673 pretending to be, and this is "good enough" to be better than no support,
 674 protecting against most adversaries.  Given another year or two, there might
 675 be sufficient clarity about a "right" way forward to let us make an informed
 676 decision, instead of a knee-jerk reaction.
 677
 678 Longer-term, we should look at supporting both various named curves and
 679 external files generated with "openssl ecparam", much as we do for init_dh().
 680 We should also support "none" as a value, to explicitly avoid initialisation.
 681
 682 Patches welcome.
 683
 684 Arguments:
 685   sctx      The current SSL CTX (inbound or outbound)
 686   host      connected host, if client; NULL if server
 687   errstr    error string pointer
 688
 689 Returns:    TRUE if OK (nothing to set up, or setup worked)
 690 */
 691
 692 static BOOL
 693 init_ecdh(SSL_CTX * sctx, host_item * host, uschar ** errstr)
 694 {
 695 #ifdef OPENSSL_NO_ECDH
 696 return TRUE;
 697 #else
 698
 699 EC_KEY * ecdh;
 700 uschar * exp_curve;
 701 int nid;
 702 BOOL rv;
 703
 704 if (host)       /* No ECDH setup for clients, only for servers */
 705   return TRUE;
 706
 707 # ifndef EXIM_HAVE_ECDH
 708 DEBUG(D_tls)
 709   debug_printf("No OpenSSL API to define ECDH parameters, skipping\n");
 710 return TRUE;
 711 # else
 712
 713 if (!expand_check(tls_eccurve, US"tls_eccurve", &exp_curve, errstr))
 714   return FALSE;
 715 if (!exp_curve || !*exp_curve)
 716   return TRUE;
 717
 718 /* "auto" needs to be handled carefully.
 719  * OpenSSL <  1.0.2: we do not select anything, but fallback to prime256v1
 720  * OpenSSL <  1.1.0: we have to call SSL_CTX_set_ecdh_auto
 721  *                   (openssl/ssl.h defines SSL_CTRL_SET_ECDH_AUTO)
 722  * OpenSSL >= 1.1.0: we do not set anything, the libray does autoselection
 723  *                   https://github.com/openssl/openssl/commit/fe6ef2472db933f01b59cad82aa925736935984b
 724  */
 725 if (Ustrcmp(exp_curve, "auto") == 0)
 726   {
 727 #if OPENSSL_VERSION_NUMBER < 0x10002000L
 728   DEBUG(D_tls) debug_printf(
 729     "ECDH OpenSSL < 1.0.2: temp key parameter settings: overriding \"auto\" with \"prime256v1\"\n");
 730   exp_curve = US"prime256v1";
 731 #else
 732 # if defined SSL_CTRL_SET_ECDH_AUTO
 733   DEBUG(D_tls) debug_printf(
 734     "ECDH OpenSSL 1.0.2+ temp key parameter settings: autoselection\n");
 735   SSL_CTX_set_ecdh_auto(sctx, 1);
 736   return TRUE;
 737 # else
 738   DEBUG(D_tls) debug_printf(
 739     "ECDH OpenSSL 1.1.0+ temp key parameter settings: default selection\n");
 740   return TRUE;
 741 # endif
 742 #endif
 743   }
 744
 745 DEBUG(D_tls) debug_printf("ECDH: curve '%s'\n", exp_curve);
 746 if (  (nid = OBJ_sn2nid       (CCS exp_curve)) == NID_undef
 747 #   ifdef EXIM_HAVE_OPENSSL_EC_NIST2NID
 748    && (nid = EC_curve_nist2nid(CCS exp_curve)) == NID_undef
 749 #   endif
 750    )
 751   {
 752   tls_error(string_sprintf("Unknown curve name tls_eccurve '%s'", exp_curve),
 753     host, NULL, errstr);
 754   return FALSE;
 755   }
 756
 757 if (!(ecdh = EC_KEY_new_by_curve_name(nid)))
 758   {
 759   tls_error(US"Unable to create ec curve", host, NULL, errstr);
 760   return FALSE;
 761   }
 762
 763 /* The "tmp" in the name here refers to setting a temporary key
 764 not to the stability of the interface. */
 765
 766 if ((rv = SSL_CTX_set_tmp_ecdh(sctx, ecdh) == 0))
 767   tls_error(string_sprintf("Error enabling '%s' curve", exp_curve), host, NULL, errstr);
 768 else
 769   DEBUG(D_tls) debug_printf("ECDH: enabled '%s' curve\n", exp_curve);
 770
 771 EC_KEY_free(ecdh);
 772 return !rv;
 773
 774 # endif /*EXIM_HAVE_ECDH*/
 775 #endif /*OPENSSL_NO_ECDH*/
 776 }
 777
 778
 779
 780
 781 #ifndef DISABLE_OCSP
 782 /*************************************************
 783 *       Load OCSP information into state         *
 784 *************************************************/
 785 /* Called to load the server OCSP response from the given file into memory, once
 786 caller has determined this is needed.  Checks validity.  Debugs a message
 787 if invalid.
 788
 789 ASSUMES: single response, for single cert.
 790
 791 Arguments:
 792   sctx            the SSL_CTX* to update
 793   cbinfo          various parts of session state
 794   expanded        the filename putatively holding an OCSP response
 795
 796 */
 797
 798 static void
 799 ocsp_load_response(SSL_CTX *sctx, tls_ext_ctx_cb *cbinfo, const uschar *expanded)
 800 {
 801 BIO * bio;
 802 OCSP_RESPONSE * resp;
 803 OCSP_BASICRESP * basic_response;
 804 OCSP_SINGLERESP * single_response;
 805 ASN1_GENERALIZEDTIME * rev, * thisupd, * nextupd;
 806 STACK_OF(X509) * sk;
 807 unsigned long verify_flags;
 808 int status, reason, i;
 809
 810 cbinfo->u_ocsp.server.file_expanded = string_copy(expanded);
 811 if (cbinfo->u_ocsp.server.response)
 812   {
 813   OCSP_RESPONSE_free(cbinfo->u_ocsp.server.response);
 814   cbinfo->u_ocsp.server.response = NULL;
 815   }
 816
 817 if (!(bio = BIO_new_file(CS cbinfo->u_ocsp.server.file_expanded, "rb")))
 818   {
 819   DEBUG(D_tls) debug_printf("Failed to open OCSP response file \"%s\"\n",
 820       cbinfo->u_ocsp.server.file_expanded);
 821   return;
 822   }
 823
 824 resp = d2i_OCSP_RESPONSE_bio(bio, NULL);
 825 BIO_free(bio);
 826 if (!resp)
 827   {
 828   DEBUG(D_tls) debug_printf("Error reading OCSP response.\n");
 829   return;
 830   }
 831
 832 if ((status = OCSP_response_status(resp)) != OCSP_RESPONSE_STATUS_SUCCESSFUL)
 833   {
 834   DEBUG(D_tls) debug_printf("OCSP response not valid: %s (%d)\n",
 835       OCSP_response_status_str(status), status);
 836   goto bad;
 837   }
 838
 839 if (!(basic_response = OCSP_response_get1_basic(resp)))
 840   {
 841   DEBUG(D_tls)
 842     debug_printf("OCSP response parse error: unable to extract basic response.\n");
 843   goto bad;
 844   }
 845
 846 sk = cbinfo->verify_stack;
 847 verify_flags = OCSP_NOVERIFY; /* check sigs, but not purpose */
 848
 849 /* May need to expose ability to adjust those flags?
 850 OCSP_NOSIGS OCSP_NOVERIFY OCSP_NOCHAIN OCSP_NOCHECKS OCSP_NOEXPLICIT
 851 OCSP_TRUSTOTHER OCSP_NOINTERN */
 852
 853 /* This does a full verify on the OCSP proof before we load it for serving
 854 up; possibly overkill - just date-checks might be nice enough.
 855
 856 OCSP_basic_verify takes a "store" arg, but does not
 857 use it for the chain verification, which is all we do
 858 when OCSP_NOVERIFY is set.  The content from the wire
 859 "basic_response" and a cert-stack "sk" are all that is used.
 860
 861 We have a stack, loaded in setup_certs() if tls_verify_certificates
 862 was a file (not a directory, or "system").  It is unfortunate we
 863 cannot used the connection context store, as that would neatly
 864 handle the "system" case too, but there seems to be no library
 865 function for getting a stack from a store.
 866 [ In OpenSSL 1.1 - ?  X509_STORE_CTX_get0_chain(ctx) ? ]
 867 We do not free the stack since it could be needed a second time for
 868 SNI handling.
 869
 870 Separately we might try to replace using OCSP_basic_verify() - which seems to not
 871 be a public interface into the OpenSSL library (there's no manual entry) -
 872 But what with?  We also use OCSP_basic_verify in the client stapling callback.
 873 And there we NEED it; we must verify that status... unless the
 874 library does it for us anyway?  */
 875
 876 if ((i = OCSP_basic_verify(basic_response, sk, NULL, verify_flags)) < 0)
 877   {
 878   DEBUG(D_tls)
 879     {
 880     ERR_error_string(ERR_get_error(), ssl_errstring);
 881     debug_printf("OCSP response verify failure: %s\n", US ssl_errstring);
 882     }
 883   goto bad;
 884   }
 885
 886 /* Here's the simplifying assumption: there's only one response, for the
 887 one certificate we use, and nothing for anything else in a chain.  If this
 888 proves false, we need to extract a cert id from our issued cert
 889 (tls_certificate) and use that for OCSP_resp_find_status() (which finds the
 890 right cert in the stack and then calls OCSP_single_get0_status()).
 891
 892 I'm hoping to avoid reworking a bunch more of how we handle state here. */
 893
 894 if (!(single_response = OCSP_resp_get0(basic_response, 0)))
 895   {
 896   DEBUG(D_tls)
 897     debug_printf("Unable to get first response from OCSP basic response.\n");
 898   goto bad;
 899   }
 900
 901 status = OCSP_single_get0_status(single_response, &reason, &rev, &thisupd, &nextupd);
 902 if (status != V_OCSP_CERTSTATUS_GOOD)
 903   {
 904   DEBUG(D_tls) debug_printf("OCSP response bad cert status: %s (%d) %s (%d)\n",
 905       OCSP_cert_status_str(status), status,
 906       OCSP_crl_reason_str(reason), reason);
 907   goto bad;
 908   }
 909
 910 if (!OCSP_check_validity(thisupd, nextupd, EXIM_OCSP_SKEW_SECONDS, EXIM_OCSP_MAX_AGE))
 911   {
 912   DEBUG(D_tls) debug_printf("OCSP status invalid times.\n");
 913   goto bad;
 914   }
 915
 916 supply_response:
 917   cbinfo->u_ocsp.server.response = resp;
 918 return;
 919
 920 bad:
 921   if (running_in_test_harness)
 922     {
 923     extern char ** environ;
 924     uschar ** p;
 925     if (environ) for (p = USS environ; *p != NULL; p++)
 926       if (Ustrncmp(*p, "EXIM_TESTHARNESS_DISABLE_OCSPVALIDITYCHECK", 42) == 0)
 927         {
 928         DEBUG(D_tls) debug_printf("Supplying known bad OCSP response\n");
 929         goto supply_response;
 930         }
 931     }
 932 return;
 933 }
 934 #endif  /*!DISABLE_OCSP*/
 935
 936
 937
 938
 939 /* Create and install a selfsigned certificate, for use in server mode */
 940
 941 static int
 942 tls_install_selfsign(SSL_CTX * sctx, uschar ** errstr)
 943 {
 944 X509 * x509 = NULL;
 945 EVP_PKEY * pkey;
 946 RSA * rsa;
 947 X509_NAME * name;
 948 uschar * where;
 949
 950 where = US"allocating pkey";
 951 if (!(pkey = EVP_PKEY_new()))
 952   goto err;
 953
 954 where = US"allocating cert";
 955 if (!(x509 = X509_new()))
 956   goto err;
 957
 958 where = US"generating pkey";
 959                 /* deprecated, use RSA_generate_key_ex() */
 960 if (!(rsa = RSA_generate_key(1024, RSA_F4, NULL, NULL)))
 961   goto err;
 962
 963 where = US"assigning pkey";
 964 if (!EVP_PKEY_assign_RSA(pkey, rsa))
 965   goto err;
 966
 967 X509_set_version(x509, 2);                              /* N+1 - version 3 */
 968 ASN1_INTEGER_set(X509_get_serialNumber(x509), 0);
 969 X509_gmtime_adj(X509_get_notBefore(x509), 0);
 970 X509_gmtime_adj(X509_get_notAfter(x509), (long)60 * 60);        /* 1 hour */
 971 X509_set_pubkey(x509, pkey);
 972
 973 name = X509_get_subject_name(x509);
 974 X509_NAME_add_entry_by_txt(name, "C",
 975                           MBSTRING_ASC, CUS "UK", -1, -1, 0);
 976 X509_NAME_add_entry_by_txt(name, "O",
 977                           MBSTRING_ASC, CUS "Exim Developers", -1, -1, 0);
 978 X509_NAME_add_entry_by_txt(name, "CN",
 979                           MBSTRING_ASC, CUS smtp_active_hostname, -1, -1, 0);
 980 X509_set_issuer_name(x509, name);
 981
 982 where = US"signing cert";
 983 if (!X509_sign(x509, pkey, EVP_md5()))
 984   goto err;
 985
 986 where = US"installing selfsign cert";
 987 if (!SSL_CTX_use_certificate(sctx, x509))
 988   goto err;
 989
 990 where = US"installing selfsign key";
 991 if (!SSL_CTX_use_PrivateKey(sctx, pkey))
 992   goto err;
 993
 994 return OK;
 995
 996 err:
 997   (void) tls_error(where, NULL, NULL, errstr);
 998   if (x509) X509_free(x509);
 999   if (pkey) EVP_PKEY_free(pkey);
1000   return DEFER;
1001 }
1002
1003
1004
1005
1006 /*************************************************
1007 *        Expand key and cert file specs          *
1008 *************************************************/
1009
1010 /* Called once during tls_init and possibly again during TLS setup, for a
1011 new context, if Server Name Indication was used and tls_sni was seen in
1012 the certificate string.
1013
1014 Arguments:
1015   sctx            the SSL_CTX* to update
1016   cbinfo          various parts of session state
1017   errstr          error string pointer
1018
1019 Returns:          OK/DEFER/FAIL
1020 */
1021
1022 static int
1023 tls_expand_session_files(SSL_CTX *sctx, tls_ext_ctx_cb *cbinfo,
1024   uschar ** errstr)
1025 {
1026 uschar *expanded;
1027
1028 if (!cbinfo->certificate)
1029   {
1030   if (cbinfo->host)                     /* client */
1031     return OK;
1032                                         /* server */
1033   if (tls_install_selfsign(sctx, errstr) != OK)
1034     return DEFER;
1035   }
1036 else
1037   {
1038   if (Ustrstr(cbinfo->certificate, US"tls_sni") ||
1039       Ustrstr(cbinfo->certificate, US"tls_in_sni") ||
1040       Ustrstr(cbinfo->certificate, US"tls_out_sni")
1041      )
1042     reexpand_tls_files_for_sni = TRUE;
1043
1044   if (!expand_check(cbinfo->certificate, US"tls_certificate", &expanded, errstr))
1045     return DEFER;
1046
1047   if (expanded != NULL)
1048     {
1049     DEBUG(D_tls) debug_printf("tls_certificate file %s\n", expanded);
1050     if (!SSL_CTX_use_certificate_chain_file(sctx, CS expanded))
1051       return tls_error(string_sprintf(
1052         "SSL_CTX_use_certificate_chain_file file=%s", expanded),
1053           cbinfo->host, NULL, errstr);
1054     }
1055
1056   if (cbinfo->privatekey != NULL &&
1057       !expand_check(cbinfo->privatekey, US"tls_privatekey", &expanded, errstr))
1058     return DEFER;
1059
1060   /* If expansion was forced to fail, key_expanded will be NULL. If the result
1061   of the expansion is an empty string, ignore it also, and assume the private
1062   key is in the same file as the certificate. */
1063
1064   if (expanded && *expanded)
1065     {
1066     DEBUG(D_tls) debug_printf("tls_privatekey file %s\n", expanded);
1067     if (!SSL_CTX_use_PrivateKey_file(sctx, CS expanded, SSL_FILETYPE_PEM))
1068       return tls_error(string_sprintf(
1069         "SSL_CTX_use_PrivateKey_file file=%s", expanded), cbinfo->host, NULL, errstr);
1070     }
1071   }
1072
1073 #ifndef DISABLE_OCSP
1074 if (cbinfo->is_server && cbinfo->u_ocsp.server.file)
1075   {
1076   if (!expand_check(cbinfo->u_ocsp.server.file, US"tls_ocsp_file", &expanded, errstr))
1077     return DEFER;
1078
1079   if (expanded && *expanded)
1080     {
1081     DEBUG(D_tls) debug_printf("tls_ocsp_file %s\n", expanded);
1082     if (  cbinfo->u_ocsp.server.file_expanded
1083        && (Ustrcmp(expanded, cbinfo->u_ocsp.server.file_expanded) == 0))
1084       {
1085       DEBUG(D_tls) debug_printf(" - value unchanged, using existing values\n");
1086       }
1087     else
1088       ocsp_load_response(sctx, cbinfo, expanded);
1089     }
1090   }
1091 #endif
1092
1093 return OK;
1094 }
1095
1096
1097
1098
1099 /*************************************************
1100 *            Callback to handle SNI              *
1101 *************************************************/
1102
1103 /* Called when acting as server during the TLS session setup if a Server Name
1104 Indication extension was sent by the client.
1105
1106 API documentation is OpenSSL s_server.c implementation.
1107
1108 Arguments:
1109   s               SSL* of the current session
1110   ad              unknown (part of OpenSSL API) (unused)
1111   arg             Callback of "our" registered data
1112
1113 Returns:          SSL_TLSEXT_ERR_{OK,ALERT_WARNING,ALERT_FATAL,NOACK}
1114 */
1115
1116 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
1117 static int
1118 tls_servername_cb(SSL *s, int *ad ARG_UNUSED, void *arg)
1119 {
1120 const char *servername = SSL_get_servername(s, TLSEXT_NAMETYPE_host_name);
1121 tls_ext_ctx_cb *cbinfo = (tls_ext_ctx_cb *) arg;
1122 int rc;
1123 int old_pool = store_pool;
1124 uschar * dummy_errstr;
1125
1126 if (!servername)
1127   return SSL_TLSEXT_ERR_OK;
1128
1129 DEBUG(D_tls) debug_printf("Received TLS SNI \"%s\"%s\n", servername,
1130     reexpand_tls_files_for_sni ? "" : " (unused for certificate selection)");
1131
1132 /* Make the extension value available for expansion */
1133 store_pool = POOL_PERM;
1134 tls_in.sni = string_copy(US servername);
1135 store_pool = old_pool;
1136
1137 if (!reexpand_tls_files_for_sni)
1138   return SSL_TLSEXT_ERR_OK;
1139
1140 /* Can't find an SSL_CTX_clone() or equivalent, so we do it manually;
1141 not confident that memcpy wouldn't break some internal reference counting.
1142 Especially since there's a references struct member, which would be off. */
1143
1144 if (!(server_sni = SSL_CTX_new(SSLv23_server_method())))
1145   {
1146   ERR_error_string(ERR_get_error(), ssl_errstring);
1147   DEBUG(D_tls) debug_printf("SSL_CTX_new() failed: %s\n", ssl_errstring);
1148   return SSL_TLSEXT_ERR_NOACK;
1149   }
1150
1151 /* Not sure how many of these are actually needed, since SSL object
1152 already exists.  Might even need this selfsame callback, for reneg? */
1153
1154 SSL_CTX_set_info_callback(server_sni, SSL_CTX_get_info_callback(server_ctx));
1155 SSL_CTX_set_mode(server_sni, SSL_CTX_get_mode(server_ctx));
1156 SSL_CTX_set_options(server_sni, SSL_CTX_get_options(server_ctx));
1157 SSL_CTX_set_timeout(server_sni, SSL_CTX_get_timeout(server_ctx));
1158 SSL_CTX_set_tlsext_servername_callback(server_sni, tls_servername_cb);
1159 SSL_CTX_set_tlsext_servername_arg(server_sni, cbinfo);
1160
1161 if (  !init_dh(server_sni, cbinfo->dhparam, NULL, &dummy_errstr)
1162    || !init_ecdh(server_sni, NULL, &dummy_errstr)
1163    )
1164   return SSL_TLSEXT_ERR_NOACK;
1165
1166 if (cbinfo->server_cipher_list)
1167   SSL_CTX_set_cipher_list(server_sni, CS cbinfo->server_cipher_list);
1168 #ifndef DISABLE_OCSP
1169 if (cbinfo->u_ocsp.server.file)
1170   {
1171   SSL_CTX_set_tlsext_status_cb(server_sni, tls_server_stapling_cb);
1172   SSL_CTX_set_tlsext_status_arg(server_sni, cbinfo);
1173   }
1174 #endif
1175
1176 if ((rc = setup_certs(server_sni, tls_verify_certificates, tls_crl, NULL, FALSE,
1177                       verify_callback_server, &dummy_errstr)) != OK)
1178   return SSL_TLSEXT_ERR_NOACK;
1179
1180 /* do this after setup_certs, because this can require the certs for verifying
1181 OCSP information. */
1182 if ((rc = tls_expand_session_files(server_sni, cbinfo, &dummy_errstr)) != OK)
1183   return SSL_TLSEXT_ERR_NOACK;
1184
1185 DEBUG(D_tls) debug_printf("Switching SSL context.\n");
1186 SSL_set_SSL_CTX(s, server_sni);
1187
1188 return SSL_TLSEXT_ERR_OK;
1189 }
1190 #endif /* EXIM_HAVE_OPENSSL_TLSEXT */
1191
1192
1193
1194
1195 #ifndef DISABLE_OCSP
1196
1197 /*************************************************
1198 *        Callback to handle OCSP Stapling        *
1199 *************************************************/
1200
1201 /* Called when acting as server during the TLS session setup if the client
1202 requests OCSP information with a Certificate Status Request.
1203
1204 Documentation via openssl s_server.c and the Apache patch from the OpenSSL
1205 project.
1206
1207 */
1208
1209 static int
1210 tls_server_stapling_cb(SSL *s, void *arg)
1211 {
1212 const tls_ext_ctx_cb *cbinfo = (tls_ext_ctx_cb *) arg;
1213 uschar *response_der;
1214 int response_der_len;
1215
1216 DEBUG(D_tls)
1217   debug_printf("Received TLS status request (OCSP stapling); %s response\n",
1218     cbinfo->u_ocsp.server.response ? "have" : "lack");
1219
1220 tls_in.ocsp = OCSP_NOT_RESP;
1221 if (!cbinfo->u_ocsp.server.response)
1222   return SSL_TLSEXT_ERR_NOACK;
1223
1224 response_der = NULL;
1225 response_der_len = i2d_OCSP_RESPONSE(cbinfo->u_ocsp.server.response,
1226                       &response_der);
1227 if (response_der_len <= 0)
1228   return SSL_TLSEXT_ERR_NOACK;
1229
1230 SSL_set_tlsext_status_ocsp_resp(server_ssl, response_der, response_der_len);
1231 tls_in.ocsp = OCSP_VFIED;
1232 return SSL_TLSEXT_ERR_OK;
1233 }
1234
1235
1236 static void
1237 time_print(BIO * bp, const char * str, ASN1_GENERALIZEDTIME * time)
1238 {
1239 BIO_printf(bp, "\t%s: ", str);
1240 ASN1_GENERALIZEDTIME_print(bp, time);
1241 BIO_puts(bp, "\n");
1242 }
1243
1244 static int
1245 tls_client_stapling_cb(SSL *s, void *arg)
1246 {
1247 tls_ext_ctx_cb * cbinfo = arg;
1248 const unsigned char * p;
1249 int len;
1250 OCSP_RESPONSE * rsp;
1251 OCSP_BASICRESP * bs;
1252 int i;
1253
1254 DEBUG(D_tls) debug_printf("Received TLS status response (OCSP stapling):");
1255 len = SSL_get_tlsext_status_ocsp_resp(s, &p);
1256 if(!p)
1257  {
1258   /* Expect this when we requested ocsp but got none */
1259   if (cbinfo->u_ocsp.client.verify_required && LOGGING(tls_cipher))
1260     log_write(0, LOG_MAIN, "Received TLS status callback, null content");
1261   else
1262     DEBUG(D_tls) debug_printf(" null\n");
1263   return cbinfo->u_ocsp.client.verify_required ? 0 : 1;
1264  }
1265
1266 if(!(rsp = d2i_OCSP_RESPONSE(NULL, &p, len)))
1267  {
1268   tls_out.ocsp = OCSP_FAILED;
1269   if (LOGGING(tls_cipher))
1270     log_write(0, LOG_MAIN, "Received TLS cert status response, parse error");
1271   else
1272     DEBUG(D_tls) debug_printf(" parse error\n");
1273   return 0;
1274  }
1275
1276 if(!(bs = OCSP_response_get1_basic(rsp)))
1277   {
1278   tls_out.ocsp = OCSP_FAILED;
1279   if (LOGGING(tls_cipher))
1280     log_write(0, LOG_MAIN, "Received TLS cert status response, error parsing response");
1281   else
1282     DEBUG(D_tls) debug_printf(" error parsing response\n");
1283   OCSP_RESPONSE_free(rsp);
1284   return 0;
1285   }
1286
1287 /* We'd check the nonce here if we'd put one in the request. */
1288 /* However that would defeat cacheability on the server so we don't. */
1289
1290 /* This section of code reworked from OpenSSL apps source;
1291    The OpenSSL Project retains copyright:
1292    Copyright (c) 1999 The OpenSSL Project.  All rights reserved.
1293 */
1294   {
1295     BIO * bp = NULL;
1296     int status, reason;
1297     ASN1_GENERALIZEDTIME *rev, *thisupd, *nextupd;
1298
1299     DEBUG(D_tls) bp = BIO_new_fp(stderr, BIO_NOCLOSE);
1300
1301     /*OCSP_RESPONSE_print(bp, rsp, 0);   extreme debug: stapling content */
1302
1303     /* Use the chain that verified the server cert to verify the stapled info */
1304     /* DEBUG(D_tls) x509_store_dump_cert_s_names(cbinfo->u_ocsp.client.verify_store); */
1305
1306     if ((i = OCSP_basic_verify(bs, cbinfo->verify_stack,
1307               cbinfo->u_ocsp.client.verify_store, 0)) <= 0)
1308       {
1309       tls_out.ocsp = OCSP_FAILED;
1310       if (LOGGING(tls_cipher))
1311         log_write(0, LOG_MAIN, "Received TLS cert status response, itself unverifiable");
1312       BIO_printf(bp, "OCSP response verify failure\n");
1313       ERR_print_errors(bp);
1314       goto failed;
1315       }
1316
1317     BIO_printf(bp, "OCSP response well-formed and signed OK\n");
1318
1319     /*XXX So we have a good stapled OCSP status.  How do we know
1320     it is for the cert of interest?  OpenSSL 1.1.0 has a routine
1321     OCSP_resp_find_status() which matches on a cert id, which presumably
1322     we should use. Making an id needs OCSP_cert_id_new(), which takes
1323     issuerName, issuerKey, serialNumber.  Are they all in the cert?
1324
1325     For now, carry on blindly accepting the resp. */
1326
1327       {
1328       OCSP_SINGLERESP * single;
1329
1330 #ifdef EXIM_HAVE_OCSP_RESP_COUNT
1331       if (OCSP_resp_count(bs) != 1)
1332 #else
1333       STACK_OF(OCSP_SINGLERESP) * sresp = bs->tbsResponseData->responses;
1334       if (sk_OCSP_SINGLERESP_num(sresp) != 1)
1335 #endif
1336         {
1337         tls_out.ocsp = OCSP_FAILED;
1338         log_write(0, LOG_MAIN, "OCSP stapling "
1339             "with multiple responses not handled");
1340         goto failed;
1341         }
1342       single = OCSP_resp_get0(bs, 0);
1343       status = OCSP_single_get0_status(single, &reason, &rev,
1344                   &thisupd, &nextupd);
1345       }
1346
1347     DEBUG(D_tls) time_print(bp, "This OCSP Update", thisupd);
1348     DEBUG(D_tls) if(nextupd) time_print(bp, "Next OCSP Update", nextupd);
1349     if (!OCSP_check_validity(thisupd, nextupd,
1350           EXIM_OCSP_SKEW_SECONDS, EXIM_OCSP_MAX_AGE))
1351       {
1352       tls_out.ocsp = OCSP_FAILED;
1353       DEBUG(D_tls) ERR_print_errors(bp);
1354       log_write(0, LOG_MAIN, "Server OSCP dates invalid");
1355       }
1356     else
1357       {
1358       DEBUG(D_tls) BIO_printf(bp, "Certificate status: %s\n",
1359                     OCSP_cert_status_str(status));
1360       switch(status)
1361         {
1362         case V_OCSP_CERTSTATUS_GOOD:
1363           tls_out.ocsp = OCSP_VFIED;
1364           i = 1;
1365           goto good;
1366         case V_OCSP_CERTSTATUS_REVOKED:
1367           tls_out.ocsp = OCSP_FAILED;
1368           log_write(0, LOG_MAIN, "Server certificate revoked%s%s",
1369               reason != -1 ? "; reason: " : "",
1370               reason != -1 ? OCSP_crl_reason_str(reason) : "");
1371           DEBUG(D_tls) time_print(bp, "Revocation Time", rev);
1372           break;
1373         default:
1374           tls_out.ocsp = OCSP_FAILED;
1375           log_write(0, LOG_MAIN,
1376               "Server certificate status unknown, in OCSP stapling");
1377           break;
1378         }
1379       }
1380   failed:
1381     i = cbinfo->u_ocsp.client.verify_required ? 0 : 1;
1382   good:
1383     BIO_free(bp);
1384   }
1385
1386 OCSP_RESPONSE_free(rsp);
1387 return i;
1388 }
1389 #endif  /*!DISABLE_OCSP*/
1390
1391
1392 /*************************************************
1393 *            Initialize for TLS                  *
1394 *************************************************/
1395
1396 /* Called from both server and client code, to do preliminary initialization
1397 of the library.  We allocate and return a context structure.
1398
1399 Arguments:
1400   ctxp            returned SSL context
1401   host            connected host, if client; NULL if server
1402   dhparam         DH parameter file
1403   certificate     certificate file
1404   privatekey      private key
1405   ocsp_file       file of stapling info (server); flag for require ocsp (client)
1406   addr            address if client; NULL if server (for some randomness)
1407   cbp             place to put allocated callback context
1408   errstr          error string pointer
1409
1410 Returns:          OK/DEFER/FAIL
1411 */
1412
1413 static int
1414 tls_init(SSL_CTX **ctxp, host_item *host, uschar *dhparam, uschar *certificate,
1415   uschar *privatekey,
1416 #ifndef DISABLE_OCSP
1417   uschar *ocsp_file,
1418 #endif
1419   address_item *addr, tls_ext_ctx_cb ** cbp, uschar ** errstr)
1420 {
1421 SSL_CTX * ctx;
1422 long init_options;
1423 int rc;
1424 tls_ext_ctx_cb * cbinfo;
1425
1426 cbinfo = store_malloc(sizeof(tls_ext_ctx_cb));
1427 cbinfo->certificate = certificate;
1428 cbinfo->privatekey = privatekey;
1429 #ifndef DISABLE_OCSP
1430 cbinfo->verify_stack = NULL;
1431 if ((cbinfo->is_server = host==NULL))
1432   {
1433   cbinfo->u_ocsp.server.file = ocsp_file;
1434   cbinfo->u_ocsp.server.file_expanded = NULL;
1435   cbinfo->u_ocsp.server.response = NULL;
1436   }
1437 else
1438   cbinfo->u_ocsp.client.verify_store = NULL;
1439 #endif
1440 cbinfo->dhparam = dhparam;
1441 cbinfo->server_cipher_list = NULL;
1442 cbinfo->host = host;
1443 #ifndef DISABLE_EVENT
1444 cbinfo->event_action = NULL;
1445 #endif
1446
1447 SSL_load_error_strings();          /* basic set up */
1448 OpenSSL_add_ssl_algorithms();
1449
1450 #ifdef EXIM_HAVE_SHA256
1451 /* SHA256 is becoming ever more popular. This makes sure it gets added to the
1452 list of available digests. */
1453 EVP_add_digest(EVP_sha256());
1454 #endif
1455
1456 /* Create a context.
1457 The OpenSSL docs in 1.0.1b have not been updated to clarify TLS variant
1458 negotiation in the different methods; as far as I can tell, the only
1459 *_{server,client}_method which allows negotiation is SSLv23, which exists even
1460 when OpenSSL is built without SSLv2 support.
1461 By disabling with openssl_options, we can let admins re-enable with the
1462 existing knob. */
1463
1464 if (!(ctx = SSL_CTX_new(host ? SSLv23_client_method() : SSLv23_server_method())))
1465   return tls_error(US"SSL_CTX_new", host, NULL, errstr);
1466
1467 /* It turns out that we need to seed the random number generator this early in
1468 order to get the full complement of ciphers to work. It took me roughly a day
1469 of work to discover this by experiment.
1470
1471 On systems that have /dev/urandom, SSL may automatically seed itself from
1472 there. Otherwise, we have to make something up as best we can. Double check
1473 afterwards. */
1474
1475 if (!RAND_status())
1476   {
1477   randstuff r;
1478   gettimeofday(&r.tv, NULL);
1479   r.p = getpid();
1480
1481   RAND_seed((uschar *)(&r), sizeof(r));
1482   RAND_seed((uschar *)big_buffer, big_buffer_size);
1483   if (addr != NULL) RAND_seed((uschar *)addr, sizeof(addr));
1484
1485   if (!RAND_status())
1486     return tls_error(US"RAND_status", host,
1487       US"unable to seed random number generator", errstr);
1488   }
1489
1490 /* Set up the information callback, which outputs if debugging is at a suitable
1491 level. */
1492
1493 DEBUG(D_tls) SSL_CTX_set_info_callback(ctx, (void (*)())info_callback);
1494
1495 /* Automatically re-try reads/writes after renegotiation. */
1496 (void) SSL_CTX_set_mode(ctx, SSL_MODE_AUTO_RETRY);
1497
1498 /* Apply administrator-supplied work-arounds.
1499 Historically we applied just one requested option,
1500 SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS, but when bug 994 requested a second, we
1501 moved to an administrator-controlled list of options to specify and
1502 grandfathered in the first one as the default value for "openssl_options".
1503
1504 No OpenSSL version number checks: the options we accept depend upon the
1505 availability of the option value macros from OpenSSL.  */
1506
1507 if (!tls_openssl_options_parse(openssl_options, &init_options))
1508   return tls_error(US"openssl_options parsing failed", host, NULL, errstr);
1509
1510 if (init_options)
1511   {
1512   DEBUG(D_tls) debug_printf("setting SSL CTX options: %#lx\n", init_options);
1513   if (!(SSL_CTX_set_options(ctx, init_options)))
1514     return tls_error(string_sprintf(
1515           "SSL_CTX_set_option(%#lx)", init_options), host, NULL, errstr);
1516   }
1517 else
1518   DEBUG(D_tls) debug_printf("no SSL CTX options to set\n");
1519
1520 /* Disable session cache unconditionally */
1521
1522 (void) SSL_CTX_set_session_cache_mode(ctx, SSL_SESS_CACHE_OFF);
1523
1524 /* Initialize with DH parameters if supplied */
1525 /* Initialize ECDH temp key parameter selection */
1526
1527 if (  !init_dh(ctx, dhparam, host, errstr)
1528    || !init_ecdh(ctx, host, errstr)
1529    )
1530   return DEFER;
1531
1532 /* Set up certificate and key (and perhaps OCSP info) */
1533
1534 if ((rc = tls_expand_session_files(ctx, cbinfo, errstr)) != OK)
1535   return rc;
1536
1537 /* If we need to handle SNI or OCSP, do so */
1538
1539 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
1540 # ifndef DISABLE_OCSP
1541   if (!(cbinfo->verify_stack = sk_X509_new_null()))
1542     {
1543     DEBUG(D_tls) debug_printf("failed to create stack for stapling verify\n");
1544     return FAIL;
1545     }
1546 # endif
1547
1548 if (host == NULL)               /* server */
1549   {
1550 # ifndef DISABLE_OCSP
1551   /* We check u_ocsp.server.file, not server.response, because we care about if
1552   the option exists, not what the current expansion might be, as SNI might
1553   change the certificate and OCSP file in use between now and the time the
1554   callback is invoked. */
1555   if (cbinfo->u_ocsp.server.file)
1556     {
1557     SSL_CTX_set_tlsext_status_cb(ctx, tls_server_stapling_cb);
1558     SSL_CTX_set_tlsext_status_arg(ctx, cbinfo);
1559     }
1560 # endif
1561   /* We always do this, so that $tls_sni is available even if not used in
1562   tls_certificate */
1563   SSL_CTX_set_tlsext_servername_callback(ctx, tls_servername_cb);
1564   SSL_CTX_set_tlsext_servername_arg(ctx, cbinfo);
1565   }
1566 # ifndef DISABLE_OCSP
1567 else                    /* client */
1568   if(ocsp_file)         /* wanting stapling */
1569     {
1570     if (!(cbinfo->u_ocsp.client.verify_store = X509_STORE_new()))
1571       {
1572       DEBUG(D_tls) debug_printf("failed to create store for stapling verify\n");
1573       return FAIL;
1574       }
1575     SSL_CTX_set_tlsext_status_cb(ctx, tls_client_stapling_cb);
1576     SSL_CTX_set_tlsext_status_arg(ctx, cbinfo);
1577     }
1578 # endif
1579 #endif
1580
1581 cbinfo->verify_cert_hostnames = NULL;
1582
1583 #ifdef EXIM_HAVE_EPHEM_RSA_KEX
1584 /* Set up the RSA callback */
1585 SSL_CTX_set_tmp_rsa_callback(ctx, rsa_callback);
1586 #endif
1587
1588 /* Finally, set the timeout, and we are done */
1589
1590 SSL_CTX_set_timeout(ctx, ssl_session_timeout);
1591 DEBUG(D_tls) debug_printf("Initialized TLS\n");
1592
1593 *cbp = cbinfo;
1594 *ctxp = ctx;
1595
1596 return OK;
1597 }
1598
1599
1600
1601
1602 /*************************************************
1603 *           Get name of cipher in use            *
1604 *************************************************/
1605
1606 /*
1607 Argument:   pointer to an SSL structure for the connection
1608             buffer to use for answer
1609             size of buffer
1610             pointer to number of bits for cipher
1611 Returns:    nothing
1612 */
1613
1614 static void
1615 construct_cipher_name(SSL *ssl, uschar *cipherbuf, int bsize, int *bits)
1616 {
1617 /* With OpenSSL 1.0.0a, this needs to be const but the documentation doesn't
1618 yet reflect that.  It should be a safe change anyway, even 0.9.8 versions have
1619 the accessor functions use const in the prototype. */
1620 const SSL_CIPHER *c;
1621 const uschar *ver;
1622
1623 ver = (const uschar *)SSL_get_version(ssl);
1624
1625 c = (const SSL_CIPHER *) SSL_get_current_cipher(ssl);
1626 SSL_CIPHER_get_bits(c, bits);
1627
1628 string_format(cipherbuf, bsize, "%s:%s:%u", ver,
1629   SSL_CIPHER_get_name(c), *bits);
1630
1631 DEBUG(D_tls) debug_printf("Cipher: %s\n", cipherbuf);
1632 }
1633
1634
1635 static void
1636 peer_cert(SSL * ssl, tls_support * tlsp, uschar * peerdn, unsigned bsize)
1637 {
1638 /*XXX we might consider a list-of-certs variable for the cert chain.
1639 SSL_get_peer_cert_chain(SSL*).  We'd need a new variable type and support
1640 in list-handling functions, also consider the difference between the entire
1641 chain and the elements sent by the peer. */
1642
1643 /* Will have already noted peercert on a verify fail; possibly not the leaf */
1644 if (!tlsp->peercert)
1645   tlsp->peercert = SSL_get_peer_certificate(ssl);
1646 /* Beware anonymous ciphers which lead to server_cert being NULL */
1647 if (tlsp->peercert)
1648   {
1649   X509_NAME_oneline(X509_get_subject_name(tlsp->peercert), CS peerdn, bsize);
1650   peerdn[bsize-1] = '\0';
1651   tlsp->peerdn = peerdn;                /*XXX a static buffer... */
1652   }
1653 else
1654   tlsp->peerdn = NULL;
1655 }
1656
1657
1658
1659
1660
1661 /*************************************************
1662 *        Set up for verifying certificates       *
1663 *************************************************/
1664
1665 /* Load certs from file, return TRUE on success */
1666
1667 static BOOL
1668 chain_from_pem_file(const uschar * file, STACK_OF(X509) * verify_stack)
1669 {
1670 BIO * bp;
1671 X509 * x;
1672
1673 if (!(bp = BIO_new_file(CS file, "r"))) return FALSE;
1674 while ((x = PEM_read_bio_X509(bp, NULL, 0, NULL)))
1675   sk_X509_push(verify_stack, x);
1676 BIO_free(bp);
1677 return TRUE;
1678 }
1679
1680
1681
1682 /* Called by both client and server startup
1683
1684 Arguments:
1685   sctx          SSL_CTX* to initialise
1686   certs         certs file or NULL
1687   crl           CRL file or NULL
1688   host          NULL in a server; the remote host in a client
1689   optional      TRUE if called from a server for a host in tls_try_verify_hosts;
1690                 otherwise passed as FALSE
1691   cert_vfy_cb   Callback function for certificate verification
1692   errstr        error string pointer
1693
1694 Returns:        OK/DEFER/FAIL
1695 */
1696
1697 static int
1698 setup_certs(SSL_CTX *sctx, uschar *certs, uschar *crl, host_item *host, BOOL optional,
1699     int (*cert_vfy_cb)(int, X509_STORE_CTX *), uschar ** errstr)
1700 {
1701 uschar *expcerts, *expcrl;
1702
1703 if (!expand_check(certs, US"tls_verify_certificates", &expcerts, errstr))
1704   return DEFER;
1705 DEBUG(D_tls) debug_printf("tls_verify_certificates: %s\n", expcerts);
1706
1707 if (expcerts && *expcerts)
1708   {
1709   /* Tell the library to use its compiled-in location for the system default
1710   CA bundle. Then add the ones specified in the config, if any. */
1711
1712   if (!SSL_CTX_set_default_verify_paths(sctx))
1713     return tls_error(US"SSL_CTX_set_default_verify_paths", host, NULL, errstr);
1714
1715   if (Ustrcmp(expcerts, "system") != 0)
1716     {
1717     struct stat statbuf;
1718
1719     if (Ustat(expcerts, &statbuf) < 0)
1720       {
1721       log_write(0, LOG_MAIN|LOG_PANIC,
1722         "failed to stat %s for certificates", expcerts);
1723       return DEFER;
1724       }
1725     else
1726       {
1727       uschar *file, *dir;
1728       if ((statbuf.st_mode & S_IFMT) == S_IFDIR)
1729         { file = NULL; dir = expcerts; }
1730       else
1731         {
1732         file = expcerts; dir = NULL;
1733 #ifndef DISABLE_OCSP
1734         /* In the server if we will be offering an OCSP proof, load chain from
1735         file for verifying the OCSP proof at load time. */
1736
1737         if (  !host
1738            && statbuf.st_size > 0
1739            && server_static_cbinfo->u_ocsp.server.file
1740            && !chain_from_pem_file(file, server_static_cbinfo->verify_stack)
1741            )
1742           {
1743           log_write(0, LOG_MAIN|LOG_PANIC,
1744             "failed to load cert hain from %s", file);
1745           return DEFER;
1746           }
1747 #endif
1748         }
1749
1750       /* If a certificate file is empty, the next function fails with an
1751       unhelpful error message. If we skip it, we get the correct behaviour (no
1752       certificates are recognized, but the error message is still misleading (it
1753       says no certificate was supplied).  But this is better. */
1754
1755       if (  (!file || statbuf.st_size > 0)
1756          && !SSL_CTX_load_verify_locations(sctx, CS file, CS dir))
1757         return tls_error(US"SSL_CTX_load_verify_locations", host, NULL, errstr);
1758
1759       /* Load the list of CAs for which we will accept certs, for sending
1760       to the client.  This is only for the one-file tls_verify_certificates
1761       variant.
1762       If a list isn't loaded into the server, but
1763       some verify locations are set, the server end appears to make
1764       a wildcard request for client certs.
1765       Meanwhile, the client library as default behaviour *ignores* the list
1766       we send over the wire - see man SSL_CTX_set_client_cert_cb.
1767       Because of this, and that the dir variant is likely only used for
1768       the public-CA bundle (not for a private CA), not worth fixing.
1769       */
1770       if (file)
1771         {
1772         STACK_OF(X509_NAME) * names = SSL_load_client_CA_file(CS file);
1773
1774         DEBUG(D_tls) debug_printf("Added %d certificate authorities.\n",
1775                                     sk_X509_NAME_num(names));
1776         SSL_CTX_set_client_CA_list(sctx, names);
1777         }
1778       }
1779     }
1780
1781   /* Handle a certificate revocation list. */
1782
1783 #if OPENSSL_VERSION_NUMBER > 0x00907000L
1784
1785   /* This bit of code is now the version supplied by Lars Mainka. (I have
1786   merely reformatted it into the Exim code style.)
1787
1788   "From here I changed the code to add support for multiple crl's
1789   in pem format in one file or to support hashed directory entries in
1790   pem format instead of a file. This method now uses the library function
1791   X509_STORE_load_locations to add the CRL location to the SSL context.
1792   OpenSSL will then handle the verify against CA certs and CRLs by
1793   itself in the verify callback." */
1794
1795   if (!expand_check(crl, US"tls_crl", &expcrl, errstr)) return DEFER;
1796   if (expcrl && *expcrl)
1797     {
1798     struct stat statbufcrl;
1799     if (Ustat(expcrl, &statbufcrl) < 0)
1800       {
1801       log_write(0, LOG_MAIN|LOG_PANIC,
1802         "failed to stat %s for certificates revocation lists", expcrl);
1803       return DEFER;
1804       }
1805     else
1806       {
1807       /* is it a file or directory? */
1808       uschar *file, *dir;
1809       X509_STORE *cvstore = SSL_CTX_get_cert_store(sctx);
1810       if ((statbufcrl.st_mode & S_IFMT) == S_IFDIR)
1811         {
1812         file = NULL;
1813         dir = expcrl;
1814         DEBUG(D_tls) debug_printf("SSL CRL value is a directory %s\n", dir);
1815         }
1816       else
1817         {
1818         file = expcrl;
1819         dir = NULL;
1820         DEBUG(D_tls) debug_printf("SSL CRL value is a file %s\n", file);
1821         }
1822       if (X509_STORE_load_locations(cvstore, CS file, CS dir) == 0)
1823         return tls_error(US"X509_STORE_load_locations", host, NULL, errstr);
1824
1825       /* setting the flags to check against the complete crl chain */
1826
1827       X509_STORE_set_flags(cvstore,
1828         X509_V_FLAG_CRL_CHECK|X509_V_FLAG_CRL_CHECK_ALL);
1829       }
1830     }
1831
1832 #endif  /* OPENSSL_VERSION_NUMBER > 0x00907000L */
1833
1834   /* If verification is optional, don't fail if no certificate */
1835
1836   SSL_CTX_set_verify(sctx,
1837     SSL_VERIFY_PEER | (optional? 0 : SSL_VERIFY_FAIL_IF_NO_PEER_CERT),
1838     cert_vfy_cb);
1839   }
1840
1841 return OK;
1842 }
1843
1844
1845
1846 /*************************************************
1847 *       Start a TLS session in a server          *
1848 *************************************************/
1849
1850 /* This is called when Exim is running as a server, after having received
1851 the STARTTLS command. It must respond to that command, and then negotiate
1852 a TLS session.
1853
1854 Arguments:
1855   require_ciphers   allowed ciphers
1856   errstr            pointer to error message
1857
1858 Returns:            OK on success
1859                     DEFER for errors before the start of the negotiation
1860                     FAIL for errors during the negotiation; the server can't
1861                       continue running.
1862 */
1863
1864 int
1865 tls_server_start(const uschar * require_ciphers, uschar ** errstr)
1866 {
1867 int rc;
1868 uschar * expciphers;
1869 tls_ext_ctx_cb * cbinfo;
1870 static uschar peerdn[256];
1871 static uschar cipherbuf[256];
1872
1873 /* Check for previous activation */
1874
1875 if (tls_in.active >= 0)
1876   {
1877   tls_error(US"STARTTLS received after TLS started", NULL, US"", errstr);
1878   smtp_printf("554 Already in TLS\r\n", FALSE);
1879   return FAIL;
1880   }
1881
1882 /* Initialize the SSL library. If it fails, it will already have logged
1883 the error. */
1884
1885 rc = tls_init(&server_ctx, NULL, tls_dhparam, tls_certificate, tls_privatekey,
1886 #ifndef DISABLE_OCSP
1887     tls_ocsp_file,
1888 #endif
1889     NULL, &server_static_cbinfo, errstr);
1890 if (rc != OK) return rc;
1891 cbinfo = server_static_cbinfo;
1892
1893 if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers, errstr))
1894   return FAIL;
1895
1896 /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they
1897 were historically separated by underscores. So that I can use either form in my
1898 tests, and also for general convenience, we turn underscores into hyphens here.
1899 */
1900
1901 if (expciphers)
1902   {
1903   uschar * s = expciphers;
1904   while (*s != 0) { if (*s == '_') *s = '-'; s++; }
1905   DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers);
1906   if (!SSL_CTX_set_cipher_list(server_ctx, CS expciphers))
1907     return tls_error(US"SSL_CTX_set_cipher_list", NULL, NULL, errstr);
1908   cbinfo->server_cipher_list = expciphers;
1909   }
1910
1911 /* If this is a host for which certificate verification is mandatory or
1912 optional, set up appropriately. */
1913
1914 tls_in.certificate_verified = FALSE;
1915 #ifdef EXPERIMENTAL_DANE
1916 tls_in.dane_verified = FALSE;
1917 #endif
1918 server_verify_callback_called = FALSE;
1919
1920 if (verify_check_host(&tls_verify_hosts) == OK)
1921   {
1922   rc = setup_certs(server_ctx, tls_verify_certificates, tls_crl, NULL,
1923                         FALSE, verify_callback_server, errstr);
1924   if (rc != OK) return rc;
1925   server_verify_optional = FALSE;
1926   }
1927 else if (verify_check_host(&tls_try_verify_hosts) == OK)
1928   {
1929   rc = setup_certs(server_ctx, tls_verify_certificates, tls_crl, NULL,
1930                         TRUE, verify_callback_server, errstr);
1931   if (rc != OK) return rc;
1932   server_verify_optional = TRUE;
1933   }
1934
1935 /* Prepare for new connection */
1936
1937 if (!(server_ssl = SSL_new(server_ctx)))
1938   return tls_error(US"SSL_new", NULL, NULL, errstr);
1939
1940 /* Warning: we used to SSL_clear(ssl) here, it was removed.
1941  *
1942  * With the SSL_clear(), we get strange interoperability bugs with
1943  * OpenSSL 1.0.1b and TLS1.1/1.2.  It looks as though this may be a bug in
1944  * OpenSSL itself, as a clear should not lead to inability to follow protocols.
1945  *
1946  * The SSL_clear() call is to let an existing SSL* be reused, typically after
1947  * session shutdown.  In this case, we have a brand new object and there's no
1948  * obvious reason to immediately clear it.  I'm guessing that this was
1949  * originally added because of incomplete initialisation which the clear fixed,
1950  * in some historic release.
1951  */
1952
1953 /* Set context and tell client to go ahead, except in the case of TLS startup
1954 on connection, where outputting anything now upsets the clients and tends to
1955 make them disconnect. We need to have an explicit fflush() here, to force out
1956 the response. Other smtp_printf() calls do not need it, because in non-TLS
1957 mode, the fflush() happens when smtp_getc() is called. */
1958
1959 SSL_set_session_id_context(server_ssl, sid_ctx, Ustrlen(sid_ctx));
1960 if (!tls_in.on_connect)
1961   {
1962   smtp_printf("220 TLS go ahead\r\n", FALSE);
1963   fflush(smtp_out);
1964   }
1965
1966 /* Now negotiate the TLS session. We put our own timer on it, since it seems
1967 that the OpenSSL library doesn't. */
1968
1969 SSL_set_wfd(server_ssl, fileno(smtp_out));
1970 SSL_set_rfd(server_ssl, fileno(smtp_in));
1971 SSL_set_accept_state(server_ssl);
1972
1973 DEBUG(D_tls) debug_printf("Calling SSL_accept\n");
1974
1975 sigalrm_seen = FALSE;
1976 if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
1977 rc = SSL_accept(server_ssl);
1978 alarm(0);
1979
1980 if (rc <= 0)
1981   {
1982   (void) tls_error(US"SSL_accept", NULL, sigalrm_seen ? US"timed out" : NULL, errstr);
1983   return FAIL;
1984   }
1985
1986 DEBUG(D_tls) debug_printf("SSL_accept was successful\n");
1987
1988 /* TLS has been set up. Adjust the input functions to read via TLS,
1989 and initialize things. */
1990
1991 peer_cert(server_ssl, &tls_in, peerdn, sizeof(peerdn));
1992
1993 construct_cipher_name(server_ssl, cipherbuf, sizeof(cipherbuf), &tls_in.bits);
1994 tls_in.cipher = cipherbuf;
1995
1996 DEBUG(D_tls)
1997   {
1998   uschar buf[2048];
1999   if (SSL_get_shared_ciphers(server_ssl, CS buf, sizeof(buf)) != NULL)
2000     debug_printf("Shared ciphers: %s\n", buf);
2001   }
2002
2003 /* Record the certificate we presented */
2004   {
2005   X509 * crt = SSL_get_certificate(server_ssl);
2006   tls_in.ourcert = crt ? X509_dup(crt) : NULL;
2007   }
2008
2009 /* Only used by the server-side tls (tls_in), including tls_getc.
2010    Client-side (tls_out) reads (seem to?) go via
2011    smtp_read_response()/ip_recv().
2012    Hence no need to duplicate for _in and _out.
2013  */
2014 ssl_xfer_buffer = store_malloc(ssl_xfer_buffer_size);
2015 ssl_xfer_buffer_lwm = ssl_xfer_buffer_hwm = 0;
2016 ssl_xfer_eof = ssl_xfer_error = 0;
2017
2018 receive_getc = tls_getc;
2019 receive_getbuf = tls_getbuf;
2020 receive_get_cache = tls_get_cache;
2021 receive_ungetc = tls_ungetc;
2022 receive_feof = tls_feof;
2023 receive_ferror = tls_ferror;
2024 receive_smtp_buffered = tls_smtp_buffered;
2025
2026 tls_in.active = fileno(smtp_out);
2027 return OK;
2028 }
2029
2030
2031
2032
2033 static int
2034 tls_client_basic_ctx_init(SSL_CTX * ctx,
2035     host_item * host, smtp_transport_options_block * ob, tls_ext_ctx_cb * cbinfo,
2036     uschar ** errstr)
2037 {
2038 int rc;
2039 /* stick to the old behaviour for compatibility if tls_verify_certificates is
2040    set but both tls_verify_hosts and tls_try_verify_hosts is not set. Check only
2041    the specified host patterns if one of them is defined */
2042
2043 if (  (  !ob->tls_verify_hosts
2044       && (!ob->tls_try_verify_hosts || !*ob->tls_try_verify_hosts)
2045       )
2046    || (verify_check_given_host(&ob->tls_verify_hosts, host) == OK)
2047    )
2048   client_verify_optional = FALSE;
2049 else if (verify_check_given_host(&ob->tls_try_verify_hosts, host) == OK)
2050   client_verify_optional = TRUE;
2051 else
2052   return OK;
2053
2054 if ((rc = setup_certs(ctx, ob->tls_verify_certificates,
2055       ob->tls_crl, host, client_verify_optional, verify_callback_client,
2056       errstr)) != OK)
2057   return rc;
2058
2059 if (verify_check_given_host(&ob->tls_verify_cert_hostnames, host) == OK)
2060   {
2061   cbinfo->verify_cert_hostnames =
2062 #ifdef SUPPORT_I18N
2063     string_domain_utf8_to_alabel(host->name, NULL);
2064 #else
2065     host->name;
2066 #endif
2067   DEBUG(D_tls) debug_printf("Cert hostname to check: \"%s\"\n",
2068                     cbinfo->verify_cert_hostnames);
2069   }
2070 return OK;
2071 }
2072
2073
2074 #ifdef EXPERIMENTAL_DANE
2075 static int
2076 dane_tlsa_load(SSL * ssl, host_item * host, dns_answer * dnsa, uschar ** errstr)
2077 {
2078 dns_record * rr;
2079 dns_scan dnss;
2080 const char * hostnames[2] = { CS host->name, NULL };
2081 int found = 0;
2082
2083 if (DANESSL_init(ssl, NULL, hostnames) != 1)
2084   return tls_error(US"hostnames load", host, NULL, errstr);
2085
2086 for (rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS);
2087      rr;
2088      rr = dns_next_rr(dnsa, &dnss, RESET_NEXT)
2089     ) if (rr->type == T_TLSA)
2090   {
2091   const uschar * p = rr->data;
2092   uint8_t usage, selector, mtype;
2093   const char * mdname;
2094
2095   usage = *p++;
2096
2097   /* Only DANE-TA(2) and DANE-EE(3) are supported */
2098   if (usage != 2 && usage != 3) continue;
2099
2100   selector = *p++;
2101   mtype = *p++;
2102
2103   switch (mtype)
2104     {
2105     default: continue;  /* Only match-types 0, 1, 2 are supported */
2106     case 0:  mdname = NULL; break;
2107     case 1:  mdname = "sha256"; break;
2108     case 2:  mdname = "sha512"; break;
2109     }
2110
2111   found++;
2112   switch (DANESSL_add_tlsa(ssl, usage, selector, mdname, p, rr->size - 3))
2113     {
2114     default:
2115       return tls_error(US"tlsa load", host, NULL, errstr);
2116     case 0:     /* action not taken */
2117     case 1:     break;
2118     }
2119
2120   tls_out.tlsa_usage |= 1<<usage;
2121   }
2122
2123 if (found)
2124   return OK;
2125
2126 log_write(0, LOG_MAIN, "DANE error: No usable TLSA records");
2127 return DEFER;
2128 }
2129 #endif  /*EXPERIMENTAL_DANE*/
2130
2131
2132
2133 /*************************************************
2134 *    Start a TLS session in a client             *
2135 *************************************************/
2136
2137 /* Called from the smtp transport after STARTTLS has been accepted.
2138
2139 Argument:
2140   fd               the fd of the connection
2141   host             connected host (for messages)
2142   addr             the first address
2143   tb               transport (always smtp)
2144   tlsa_dnsa        tlsa lookup, if DANE, else null
2145   errstr           error string pointer
2146
2147 Returns:           OK on success
2148                    FAIL otherwise - note that tls_error() will not give DEFER
2149                      because this is not a server
2150 */
2151
2152 int
2153 tls_client_start(int fd, host_item *host, address_item *addr,
2154   transport_instance * tb,
2155 #ifdef EXPERIMENTAL_DANE
2156   dns_answer * tlsa_dnsa,
2157 #endif
2158   uschar ** errstr)
2159 {
2160 smtp_transport_options_block * ob =
2161   (smtp_transport_options_block *)tb->options_block;
2162 static uschar peerdn[256];
2163 uschar * expciphers;
2164 int rc;
2165 static uschar cipherbuf[256];
2166
2167 #ifndef DISABLE_OCSP
2168 BOOL request_ocsp = FALSE;
2169 BOOL require_ocsp = FALSE;
2170 #endif
2171
2172 #ifdef EXPERIMENTAL_DANE
2173 tls_out.tlsa_usage = 0;
2174 #endif
2175
2176 #ifndef DISABLE_OCSP
2177   {
2178 # ifdef EXPERIMENTAL_DANE
2179   if (  tlsa_dnsa
2180      && ob->hosts_request_ocsp[0] == '*'
2181      && ob->hosts_request_ocsp[1] == '\0'
2182      )
2183     {
2184     /* Unchanged from default.  Use a safer one under DANE */
2185     request_ocsp = TRUE;
2186     ob->hosts_request_ocsp = US"${if or { {= {0}{$tls_out_tlsa_usage}} "
2187                                       "   {= {4}{$tls_out_tlsa_usage}} } "
2188                                  " {*}{}}";
2189     }
2190 # endif
2191
2192   if ((require_ocsp =
2193         verify_check_given_host(&ob->hosts_require_ocsp, host) == OK))
2194     request_ocsp = TRUE;
2195   else
2196 # ifdef EXPERIMENTAL_DANE
2197     if (!request_ocsp)
2198 # endif
2199       request_ocsp =
2200         verify_check_given_host(&ob->hosts_request_ocsp, host) == OK;
2201   }
2202 #endif
2203
2204 rc = tls_init(&client_ctx, host, NULL,
2205     ob->tls_certificate, ob->tls_privatekey,
2206 #ifndef DISABLE_OCSP
2207     (void *)(long)request_ocsp,
2208 #endif
2209     addr, &client_static_cbinfo, errstr);
2210 if (rc != OK) return rc;
2211
2212 tls_out.certificate_verified = FALSE;
2213 client_verify_callback_called = FALSE;
2214
2215 if (!expand_check(ob->tls_require_ciphers, US"tls_require_ciphers",
2216     &expciphers, errstr))
2217   return FAIL;
2218
2219 /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they
2220 are separated by underscores. So that I can use either form in my tests, and
2221 also for general convenience, we turn underscores into hyphens here. */
2222
2223 if (expciphers)
2224   {
2225   uschar *s = expciphers;
2226   while (*s) { if (*s == '_') *s = '-'; s++; }
2227   DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers);
2228   if (!SSL_CTX_set_cipher_list(client_ctx, CS expciphers))
2229     return tls_error(US"SSL_CTX_set_cipher_list", host, NULL, errstr);
2230   }
2231
2232 #ifdef EXPERIMENTAL_DANE
2233 if (tlsa_dnsa)
2234   {
2235   SSL_CTX_set_verify(client_ctx,
2236     SSL_VERIFY_PEER | SSL_VERIFY_FAIL_IF_NO_PEER_CERT,
2237     verify_callback_client_dane);
2238
2239   if (!DANESSL_library_init())
2240     return tls_error(US"library init", host, NULL, errstr);
2241   if (DANESSL_CTX_init(client_ctx) <= 0)
2242     return tls_error(US"context init", host, NULL, errstr);
2243   }
2244 else
2245
2246 #endif
2247
2248   if ((rc = tls_client_basic_ctx_init(client_ctx, host, ob,
2249       client_static_cbinfo, errstr)) != OK)
2250     return rc;
2251
2252 if ((client_ssl = SSL_new(client_ctx)) == NULL)
2253   return tls_error(US"SSL_new", host, NULL, errstr);
2254 SSL_set_session_id_context(client_ssl, sid_ctx, Ustrlen(sid_ctx));
2255 SSL_set_fd(client_ssl, fd);
2256 SSL_set_connect_state(client_ssl);
2257
2258 if (ob->tls_sni)
2259   {
2260   if (!expand_check(ob->tls_sni, US"tls_sni", &tls_out.sni, errstr))
2261     return FAIL;
2262   if (!tls_out.sni)
2263     {
2264     DEBUG(D_tls) debug_printf("Setting TLS SNI forced to fail, not sending\n");
2265     }
2266   else if (!Ustrlen(tls_out.sni))
2267     tls_out.sni = NULL;
2268   else
2269     {
2270 #ifdef EXIM_HAVE_OPENSSL_TLSEXT
2271     DEBUG(D_tls) debug_printf("Setting TLS SNI \"%s\"\n", tls_out.sni);
2272     SSL_set_tlsext_host_name(client_ssl, tls_out.sni);
2273 #else
2274     log_write(0, LOG_MAIN, "SNI unusable with this OpenSSL library version; ignoring \"%s\"\n",
2275           tls_out.sni);
2276 #endif
2277     }
2278   }
2279
2280 #ifdef EXPERIMENTAL_DANE
2281 if (tlsa_dnsa)
2282   if ((rc = dane_tlsa_load(client_ssl, host, tlsa_dnsa, errstr)) != OK)
2283     return rc;
2284 #endif
2285
2286 #ifndef DISABLE_OCSP
2287 /* Request certificate status at connection-time.  If the server
2288 does OCSP stapling we will get the callback (set in tls_init()) */
2289 # ifdef EXPERIMENTAL_DANE
2290 if (request_ocsp)
2291   {
2292   const uschar * s;
2293   if (  ((s = ob->hosts_require_ocsp) && Ustrstr(s, US"tls_out_tlsa_usage"))
2294      || ((s = ob->hosts_request_ocsp) && Ustrstr(s, US"tls_out_tlsa_usage"))
2295      )
2296     {   /* Re-eval now $tls_out_tlsa_usage is populated.  If
2297         this means we avoid the OCSP request, we wasted the setup
2298         cost in tls_init(). */
2299     require_ocsp = verify_check_given_host(&ob->hosts_require_ocsp, host) == OK;
2300     request_ocsp = require_ocsp
2301       || verify_check_given_host(&ob->hosts_request_ocsp, host) == OK;
2302     }
2303   }
2304 # endif
2305
2306 if (request_ocsp)
2307   {
2308   SSL_set_tlsext_status_type(client_ssl, TLSEXT_STATUSTYPE_ocsp);
2309   client_static_cbinfo->u_ocsp.client.verify_required = require_ocsp;
2310   tls_out.ocsp = OCSP_NOT_RESP;
2311   }
2312 #endif
2313
2314 #ifndef DISABLE_EVENT
2315 client_static_cbinfo->event_action = tb->event_action;
2316 #endif
2317
2318 /* There doesn't seem to be a built-in timeout on connection. */
2319
2320 DEBUG(D_tls) debug_printf("Calling SSL_connect\n");
2321 sigalrm_seen = FALSE;
2322 alarm(ob->command_timeout);
2323 rc = SSL_connect(client_ssl);
2324 alarm(0);
2325
2326 #ifdef EXPERIMENTAL_DANE
2327 if (tlsa_dnsa)
2328   DANESSL_cleanup(client_ssl);
2329 #endif
2330
2331 if (rc <= 0)
2332   return tls_error(US"SSL_connect", host, sigalrm_seen ? US"timed out" : NULL,
2333     errstr);
2334
2335 DEBUG(D_tls) debug_printf("SSL_connect succeeded\n");
2336
2337 peer_cert(client_ssl, &tls_out, peerdn, sizeof(peerdn));
2338
2339 construct_cipher_name(client_ssl, cipherbuf, sizeof(cipherbuf), &tls_out.bits);
2340 tls_out.cipher = cipherbuf;
2341
2342 /* Record the certificate we presented */
2343   {
2344   X509 * crt = SSL_get_certificate(client_ssl);
2345   tls_out.ourcert = crt ? X509_dup(crt) : NULL;
2346   }
2347
2348 tls_out.active = fd;
2349 return OK;
2350 }
2351
2352
2353
2354
2355
2356 static BOOL
2357 tls_refill(unsigned lim)
2358 {
2359 int error;
2360 int inbytes;
2361
2362 DEBUG(D_tls) debug_printf("Calling SSL_read(%p, %p, %u)\n", server_ssl,
2363   ssl_xfer_buffer, ssl_xfer_buffer_size);
2364
2365 if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout);
2366 inbytes = SSL_read(server_ssl, CS ssl_xfer_buffer,
2367                   MIN(ssl_xfer_buffer_size, lim));
2368 error = SSL_get_error(server_ssl, inbytes);
2369 alarm(0);
2370
2371 /* SSL_ERROR_ZERO_RETURN appears to mean that the SSL session has been
2372 closed down, not that the socket itself has been closed down. Revert to
2373 non-SSL handling. */
2374
2375 if (error == SSL_ERROR_ZERO_RETURN)
2376   {
2377   DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n");
2378
2379   receive_getc = smtp_getc;
2380   receive_getbuf = smtp_getbuf;
2381   receive_get_cache = smtp_get_cache;
2382   receive_ungetc = smtp_ungetc;
2383   receive_feof = smtp_feof;
2384   receive_ferror = smtp_ferror;
2385   receive_smtp_buffered = smtp_buffered;
2386
2387   SSL_free(server_ssl);
2388   server_ssl = NULL;
2389   tls_in.active = -1;
2390   tls_in.bits = 0;
2391   tls_in.cipher = NULL;
2392   tls_in.peerdn = NULL;
2393   tls_in.sni = NULL;
2394
2395   return FALSE;
2396   }
2397
2398 /* Handle genuine errors */
2399
2400 else if (error == SSL_ERROR_SSL)
2401   {
2402   ERR_error_string(ERR_get_error(), ssl_errstring);
2403   log_write(0, LOG_MAIN, "TLS error (SSL_read): %s", ssl_errstring);
2404   ssl_xfer_error = 1;
2405   return FALSE;
2406   }
2407
2408 else if (error != SSL_ERROR_NONE)
2409   {
2410   DEBUG(D_tls) debug_printf("Got SSL error %d\n", error);
2411   ssl_xfer_error = 1;
2412   return FALSE;
2413   }
2414
2415 #ifndef DISABLE_DKIM
2416 dkim_exim_verify_feed(ssl_xfer_buffer, inbytes);
2417 #endif
2418 ssl_xfer_buffer_hwm = inbytes;
2419 ssl_xfer_buffer_lwm = 0;
2420 return TRUE;
2421 }
2422
2423
2424 /*************************************************
2425 *            TLS version of getc                 *
2426 *************************************************/
2427
2428 /* This gets the next byte from the TLS input buffer. If the buffer is empty,
2429 it refills the buffer via the SSL reading function.
2430
2431 Arguments:  lim         Maximum amount to read/buffer
2432 Returns:    the next character or EOF
2433
2434 Only used by the server-side TLS.
2435 */
2436
2437 int
2438 tls_getc(unsigned lim)
2439 {
2440 if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm)
2441   if (!tls_refill(lim))
2442     return ssl_xfer_error ? EOF : smtp_getc(lim);
2443
2444 /* Something in the buffer; return next uschar */
2445
2446 return ssl_xfer_buffer[ssl_xfer_buffer_lwm++];
2447 }
2448
2449 uschar *
2450 tls_getbuf(unsigned * len)
2451 {
2452 unsigned size;
2453 uschar * buf;
2454
2455 if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm)
2456   if (!tls_refill(*len))
2457     {
2458     if (!ssl_xfer_error) return smtp_getbuf(len);
2459     *len = 0;
2460     return NULL;
2461     }
2462
2463 if ((size = ssl_xfer_buffer_hwm - ssl_xfer_buffer_lwm) > *len)
2464   size = *len;
2465 buf = &ssl_xfer_buffer[ssl_xfer_buffer_lwm];
2466 ssl_xfer_buffer_lwm += size;
2467 *len = size;
2468 return buf;
2469 }
2470
2471
2472 void
2473 tls_get_cache()
2474 {
2475 #ifndef DISABLE_DKIM
2476 int n = ssl_xfer_buffer_hwm - ssl_xfer_buffer_lwm;
2477 if (n > 0)
2478   dkim_exim_verify_feed(ssl_xfer_buffer+ssl_xfer_buffer_lwm, n);
2479 #endif
2480 }
2481
2482
2483 BOOL
2484 tls_could_read(void)
2485 {
2486 return ssl_xfer_buffer_lwm < ssl_xfer_buffer_hwm || SSL_pending(server_ssl) > 0;
2487 }
2488
2489
2490 /*************************************************
2491 *          Read bytes from TLS channel           *
2492 *************************************************/
2493
2494 /*
2495 Arguments:
2496   buff      buffer of data
2497   len       size of buffer
2498
2499 Returns:    the number of bytes read
2500             -1 after a failed read
2501
2502 Only used by the client-side TLS.
2503 */
2504
2505 int
2506 tls_read(BOOL is_server, uschar *buff, size_t len)
2507 {
2508 SSL *ssl = is_server ? server_ssl : client_ssl;
2509 int inbytes;
2510 int error;
2511
2512 DEBUG(D_tls) debug_printf("Calling SSL_read(%p, %p, %u)\n", ssl,
2513   buff, (unsigned int)len);
2514
2515 inbytes = SSL_read(ssl, CS buff, len);
2516 error = SSL_get_error(ssl, inbytes);
2517
2518 if (error == SSL_ERROR_ZERO_RETURN)
2519   {
2520   DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n");
2521   return -1;
2522   }
2523 else if (error != SSL_ERROR_NONE)
2524   return -1;
2525
2526 return inbytes;
2527 }
2528
2529
2530
2531
2532
2533 /*************************************************
2534 *         Write bytes down TLS channel           *
2535 *************************************************/
2536
2537 /*
2538 Arguments:
2539   is_server channel specifier
2540   buff      buffer of data
2541   len       number of bytes
2542   more      further data expected soon
2543
2544 Returns:    the number of bytes after a successful write,
2545             -1 after a failed write
2546
2547 Used by both server-side and client-side TLS.
2548 */
2549
2550 int
2551 tls_write(BOOL is_server, const uschar *buff, size_t len, BOOL more)
2552 {
2553 int outbytes, error, left;
2554 SSL *ssl = is_server ? server_ssl : client_ssl;
2555 static uschar * corked = NULL;
2556 static int c_size = 0, c_len = 0;
2557
2558 DEBUG(D_tls) debug_printf("%s(%p, %d%s)\n", __FUNCTION__,
2559   buff, left, more ? ", more" : "");
2560
2561 /* Lacking a CORK or MSG_MORE facility (such as GnuTLS has) we copy data when
2562 "more" is notified.  This hack is only ok if small amounts are involved AND only
2563 one stream does it, in one context (i.e. no store reset).  Currently it is used
2564 for the responses to the received SMTP MAIL , RCPT, DATA sequence, only. */
2565
2566 if (is_server && (more || corked))
2567   {
2568   corked = string_catn(corked, &c_size, &c_len, buff, len);
2569   if (more)
2570     return len;
2571   buff = CUS corked;
2572   len = c_len;
2573   corked = NULL; c_size = c_len = 0;
2574   }
2575
2576 for (left = len; left > 0;)
2577   {
2578   DEBUG(D_tls) debug_printf("SSL_write(SSL, %p, %d)\n", buff, left);
2579   outbytes = SSL_write(ssl, CS buff, left);
2580   error = SSL_get_error(ssl, outbytes);
2581   DEBUG(D_tls) debug_printf("outbytes=%d error=%d\n", outbytes, error);
2582   switch (error)
2583     {
2584     case SSL_ERROR_SSL:
2585       ERR_error_string(ERR_get_error(), ssl_errstring);
2586       log_write(0, LOG_MAIN, "TLS error (SSL_write): %s", ssl_errstring);
2587       return -1;
2588
2589     case SSL_ERROR_NONE:
2590       left -= outbytes;
2591       buff += outbytes;
2592       break;
2593
2594     case SSL_ERROR_ZERO_RETURN:
2595       log_write(0, LOG_MAIN, "SSL channel closed on write");
2596       return -1;
2597
2598     case SSL_ERROR_SYSCALL:
2599       log_write(0, LOG_MAIN, "SSL_write: (from %s) syscall: %s",
2600         sender_fullhost ? sender_fullhost : US"<unknown>",
2601         strerror(errno));
2602       return -1;
2603
2604     default:
2605       log_write(0, LOG_MAIN, "SSL_write error %d", error);
2606       return -1;
2607     }
2608   }
2609 return len;
2610 }
2611
2612
2613
2614 /*************************************************
2615 *         Close down a TLS session               *
2616 *************************************************/
2617
2618 /* This is also called from within a delivery subprocess forked from the
2619 daemon, to shut down the TLS library, without actually doing a shutdown (which
2620 would tamper with the SSL session in the parent process).
2621
2622 Arguments:   TRUE if SSL_shutdown is to be called
2623 Returns:     nothing
2624
2625 Used by both server-side and client-side TLS.
2626 */
2627
2628 void
2629 tls_close(BOOL is_server, BOOL shutdown)
2630 {
2631 SSL **sslp = is_server ? &server_ssl : &client_ssl;
2632 int *fdp = is_server ? &tls_in.active : &tls_out.active;
2633
2634 if (*fdp < 0) return;  /* TLS was not active */
2635
2636 if (shutdown)
2637   {
2638   DEBUG(D_tls) debug_printf("tls_close(): shutting down SSL\n");
2639   SSL_shutdown(*sslp);
2640   }
2641
2642 SSL_free(*sslp);
2643 *sslp = NULL;
2644
2645 *fdp = -1;
2646 }
2647
2648
2649
2650
2651 /*************************************************
2652 *  Let tls_require_ciphers be checked at startup *
2653 *************************************************/
2654
2655 /* The tls_require_ciphers option, if set, must be something which the
2656 library can parse.
2657
2658 Returns:     NULL on success, or error message
2659 */
2660
2661 uschar *
2662 tls_validate_require_cipher(void)
2663 {
2664 SSL_CTX *ctx;
2665 uschar *s, *expciphers, *err;
2666
2667 /* this duplicates from tls_init(), we need a better "init just global
2668 state, for no specific purpose" singleton function of our own */
2669
2670 SSL_load_error_strings();
2671 OpenSSL_add_ssl_algorithms();
2672 #if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_SHA256)
2673 /* SHA256 is becoming ever more popular. This makes sure it gets added to the
2674 list of available digests. */
2675 EVP_add_digest(EVP_sha256());
2676 #endif
2677
2678 if (!(tls_require_ciphers && *tls_require_ciphers))
2679   return NULL;
2680
2681 if (!expand_check(tls_require_ciphers, US"tls_require_ciphers", &expciphers,
2682                   &err))
2683   return US"failed to expand tls_require_ciphers";
2684
2685 if (!(expciphers && *expciphers))
2686   return NULL;
2687
2688 /* normalisation ripped from above */
2689 s = expciphers;
2690 while (*s != 0) { if (*s == '_') *s = '-'; s++; }
2691
2692 err = NULL;
2693
2694 ctx = SSL_CTX_new(SSLv23_server_method());
2695 if (!ctx)
2696   {
2697   ERR_error_string(ERR_get_error(), ssl_errstring);
2698   return string_sprintf("SSL_CTX_new() failed: %s", ssl_errstring);
2699   }
2700
2701 DEBUG(D_tls)
2702   debug_printf("tls_require_ciphers expands to \"%s\"\n", expciphers);
2703
2704 if (!SSL_CTX_set_cipher_list(ctx, CS expciphers))
2705   {
2706   ERR_error_string(ERR_get_error(), ssl_errstring);
2707   err = string_sprintf("SSL_CTX_set_cipher_list(%s) failed: %s",
2708                       expciphers, ssl_errstring);
2709   }
2710
2711 SSL_CTX_free(ctx);
2712
2713 return err;
2714 }
2715
2716
2717
2718
2719 /*************************************************
2720 *         Report the library versions.           *
2721 *************************************************/
2722
2723 /* There have historically been some issues with binary compatibility in
2724 OpenSSL libraries; if Exim (like many other applications) is built against
2725 one version of OpenSSL but the run-time linker picks up another version,
2726 it can result in serious failures, including crashing with a SIGSEGV.  So
2727 report the version found by the compiler and the run-time version.
2728
2729 Note: some OS vendors backport security fixes without changing the version
2730 number/string, and the version date remains unchanged.  The _build_ date
2731 will change, so we can more usefully assist with version diagnosis by also
2732 reporting the build date.
2733
2734 Arguments:   a FILE* to print the results to
2735 Returns:     nothing
2736 */
2737
2738 void
2739 tls_version_report(FILE *f)
2740 {
2741 fprintf(f, "Library version: OpenSSL: Compile: %s\n"
2742            "                          Runtime: %s\n"
2743            "                                 : %s\n",
2744            OPENSSL_VERSION_TEXT,
2745            SSLeay_version(SSLEAY_VERSION),
2746            SSLeay_version(SSLEAY_BUILT_ON));
2747 /* third line is 38 characters for the %s and the line is 73 chars long;
2748 the OpenSSL output includes a "built on: " prefix already. */
2749 }
2750
2751
2752
2753
2754 /*************************************************
2755 *            Random number generation            *
2756 *************************************************/
2757
2758 /* Pseudo-random number generation.  The result is not expected to be
2759 cryptographically strong but not so weak that someone will shoot themselves
2760 in the foot using it as a nonce in input in some email header scheme or
2761 whatever weirdness they'll twist this into.  The result should handle fork()
2762 and avoid repeating sequences.  OpenSSL handles that for us.
2763
2764 Arguments:
2765   max       range maximum
2766 Returns     a random number in range [0, max-1]
2767 */
2768
2769 int
2770 vaguely_random_number(int max)
2771 {
2772 unsigned int r;
2773 int i, needed_len;
2774 static pid_t pidlast = 0;
2775 pid_t pidnow;
2776 uschar *p;
2777 uschar smallbuf[sizeof(r)];
2778
2779 if (max <= 1)
2780   return 0;
2781
2782 pidnow = getpid();
2783 if (pidnow != pidlast)
2784   {
2785   /* Although OpenSSL documents that "OpenSSL makes sure that the PRNG state
2786   is unique for each thread", this doesn't apparently apply across processes,
2787   so our own warning from vaguely_random_number_fallback() applies here too.
2788   Fix per PostgreSQL. */
2789   if (pidlast != 0)
2790     RAND_cleanup();
2791   pidlast = pidnow;
2792   }
2793
2794 /* OpenSSL auto-seeds from /dev/random, etc, but this a double-check. */
2795 if (!RAND_status())
2796   {
2797   randstuff r;
2798   gettimeofday(&r.tv, NULL);
2799   r.p = getpid();
2800
2801   RAND_seed((uschar *)(&r), sizeof(r));
2802   }
2803 /* We're after pseudo-random, not random; if we still don't have enough data
2804 in the internal PRNG then our options are limited.  We could sleep and hope
2805 for entropy to come along (prayer technique) but if the system is so depleted
2806 in the first place then something is likely to just keep taking it.  Instead,
2807 we'll just take whatever little bit of pseudo-random we can still manage to
2808 get. */
2809
2810 needed_len = sizeof(r);
2811 /* Don't take 8 times more entropy than needed if int is 8 octets and we were
2812 asked for a number less than 10. */
2813 for (r = max, i = 0; r; ++i)
2814   r >>= 1;
2815 i = (i + 7) / 8;
2816 if (i < needed_len)
2817   needed_len = i;
2818
2819 #ifdef EXIM_HAVE_RAND_PSEUDO
2820 /* We do not care if crypto-strong */
2821 i = RAND_pseudo_bytes(smallbuf, needed_len);
2822 #else
2823 i = RAND_bytes(smallbuf, needed_len);
2824 #endif
2825
2826 if (i < 0)
2827   {
2828   DEBUG(D_all)
2829     debug_printf("OpenSSL RAND_pseudo_bytes() not supported by RAND method, using fallback.\n");
2830   return vaguely_random_number_fallback(max);
2831   }
2832
2833 r = 0;
2834 for (p = smallbuf; needed_len; --needed_len, ++p)
2835   {
2836   r *= 256;
2837   r += *p;
2838   }
2839
2840 /* We don't particularly care about weighted results; if someone wants
2841 smooth distribution and cares enough then they should submit a patch then. */
2842 return r % max;
2843 }
2844
2845
2846
2847
2848 /*************************************************
2849 *        OpenSSL option parse                    *
2850 *************************************************/
2851
2852 /* Parse one option for tls_openssl_options_parse below
2853
2854 Arguments:
2855   name    one option name
2856   value   place to store a value for it
2857 Returns   success or failure in parsing
2858 */
2859
2860 struct exim_openssl_option {
2861   uschar *name;
2862   long    value;
2863 };
2864 /* We could use a macro to expand, but we need the ifdef and not all the
2865 options document which version they were introduced in.  Policylet: include
2866 all options unless explicitly for DTLS, let the administrator choose which
2867 to apply.
2868
2869 This list is current as of:
2870   ==>  1.0.1b  <==
2871 Plus SSL_OP_SAFARI_ECDHE_ECDSA_BUG from 2013-June patch/discussion on openssl-dev
2872 */
2873 static struct exim_openssl_option exim_openssl_options[] = {
2874 /* KEEP SORTED ALPHABETICALLY! */
2875 #ifdef SSL_OP_ALL
2876   { US"all", SSL_OP_ALL },
2877 #endif
2878 #ifdef SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION
2879   { US"allow_unsafe_legacy_renegotiation", SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION },
2880 #endif
2881 #ifdef SSL_OP_CIPHER_SERVER_PREFERENCE
2882   { US"cipher_server_preference", SSL_OP_CIPHER_SERVER_PREFERENCE },
2883 #endif
2884 #ifdef SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS
2885   { US"dont_insert_empty_fragments", SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS },
2886 #endif
2887 #ifdef SSL_OP_EPHEMERAL_RSA
2888   { US"ephemeral_rsa", SSL_OP_EPHEMERAL_RSA },
2889 #endif
2890 #ifdef SSL_OP_LEGACY_SERVER_CONNECT
2891   { US"legacy_server_connect", SSL_OP_LEGACY_SERVER_CONNECT },
2892 #endif
2893 #ifdef SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER
2894   { US"microsoft_big_sslv3_buffer", SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER },
2895 #endif
2896 #ifdef SSL_OP_MICROSOFT_SESS_ID_BUG
2897   { US"microsoft_sess_id_bug", SSL_OP_MICROSOFT_SESS_ID_BUG },
2898 #endif
2899 #ifdef SSL_OP_MSIE_SSLV2_RSA_PADDING
2900   { US"msie_sslv2_rsa_padding", SSL_OP_MSIE_SSLV2_RSA_PADDING },
2901 #endif
2902 #ifdef SSL_OP_NETSCAPE_CHALLENGE_BUG
2903   { US"netscape_challenge_bug", SSL_OP_NETSCAPE_CHALLENGE_BUG },
2904 #endif
2905 #ifdef SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG
2906   { US"netscape_reuse_cipher_change_bug", SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG },
2907 #endif
2908 #ifdef SSL_OP_NO_COMPRESSION
2909   { US"no_compression", SSL_OP_NO_COMPRESSION },
2910 #endif
2911 #ifdef SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION
2912   { US"no_session_resumption_on_renegotiation", SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION },
2913 #endif
2914 #ifdef SSL_OP_NO_SSLv2
2915   { US"no_sslv2", SSL_OP_NO_SSLv2 },
2916 #endif
2917 #ifdef SSL_OP_NO_SSLv3
2918   { US"no_sslv3", SSL_OP_NO_SSLv3 },
2919 #endif
2920 #ifdef SSL_OP_NO_TICKET
2921   { US"no_ticket", SSL_OP_NO_TICKET },
2922 #endif
2923 #ifdef SSL_OP_NO_TLSv1
2924   { US"no_tlsv1", SSL_OP_NO_TLSv1 },
2925 #endif
2926 #ifdef SSL_OP_NO_TLSv1_1
2927 #if SSL_OP_NO_TLSv1_1 == 0x00000400L
2928   /* Error in chosen value in 1.0.1a; see first item in CHANGES for 1.0.1b */
2929 #warning OpenSSL 1.0.1a uses a bad value for SSL_OP_NO_TLSv1_1, ignoring
2930 #else
2931   { US"no_tlsv1_1", SSL_OP_NO_TLSv1_1 },
2932 #endif
2933 #endif
2934 #ifdef SSL_OP_NO_TLSv1_2
2935   { US"no_tlsv1_2", SSL_OP_NO_TLSv1_2 },
2936 #endif
2937 #ifdef SSL_OP_SAFARI_ECDHE_ECDSA_BUG
2938   { US"safari_ecdhe_ecdsa_bug", SSL_OP_SAFARI_ECDHE_ECDSA_BUG },
2939 #endif
2940 #ifdef SSL_OP_SINGLE_DH_USE
2941   { US"single_dh_use", SSL_OP_SINGLE_DH_USE },
2942 #endif
2943 #ifdef SSL_OP_SINGLE_ECDH_USE
2944   { US"single_ecdh_use", SSL_OP_SINGLE_ECDH_USE },
2945 #endif
2946 #ifdef SSL_OP_SSLEAY_080_CLIENT_DH_BUG
2947   { US"ssleay_080_client_dh_bug", SSL_OP_SSLEAY_080_CLIENT_DH_BUG },
2948 #endif
2949 #ifdef SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG
2950   { US"sslref2_reuse_cert_type_bug", SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG },
2951 #endif
2952 #ifdef SSL_OP_TLS_BLOCK_PADDING_BUG
2953   { US"tls_block_padding_bug", SSL_OP_TLS_BLOCK_PADDING_BUG },
2954 #endif
2955 #ifdef SSL_OP_TLS_D5_BUG
2956   { US"tls_d5_bug", SSL_OP_TLS_D5_BUG },
2957 #endif
2958 #ifdef SSL_OP_TLS_ROLLBACK_BUG
2959   { US"tls_rollback_bug", SSL_OP_TLS_ROLLBACK_BUG },
2960 #endif
2961 };
2962 static int exim_openssl_options_size =
2963   sizeof(exim_openssl_options)/sizeof(struct exim_openssl_option);
2964
2965
2966 static BOOL
2967 tls_openssl_one_option_parse(uschar *name, long *value)
2968 {
2969 int first = 0;
2970 int last = exim_openssl_options_size;
2971 while (last > first)
2972   {
2973   int middle = (first + last)/2;
2974   int c = Ustrcmp(name, exim_openssl_options[middle].name);
2975   if (c == 0)
2976     {
2977     *value = exim_openssl_options[middle].value;
2978     return TRUE;
2979     }
2980   else if (c > 0)
2981     first = middle + 1;
2982   else
2983     last = middle;
2984   }
2985 return FALSE;
2986 }
2987
2988
2989
2990
2991 /*************************************************
2992 *        OpenSSL option parsing logic            *
2993 *************************************************/
2994
2995 /* OpenSSL has a number of compatibility options which an administrator might
2996 reasonably wish to set.  Interpret a list similarly to decode_bits(), so that
2997 we look like log_selector.
2998
2999 Arguments:
3000   option_spec  the administrator-supplied string of options
3001   results      ptr to long storage for the options bitmap
3002 Returns        success or failure
3003 */
3004
3005 BOOL
3006 tls_openssl_options_parse(uschar *option_spec, long *results)
3007 {
3008 long result, item;
3009 uschar *s, *end;
3010 uschar keep_c;
3011 BOOL adding, item_parsed;
3012
3013 result = SSL_OP_NO_TICKET;
3014 /* Prior to 4.80 we or'd in SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS; removed
3015  * from default because it increases BEAST susceptibility. */
3016 #ifdef SSL_OP_NO_SSLv2
3017 result |= SSL_OP_NO_SSLv2;
3018 #endif
3019 #ifdef SSL_OP_SINGLE_DH_USE
3020 result |= SSL_OP_SINGLE_DH_USE;
3021 #endif
3022
3023 if (!option_spec)
3024   {
3025   *results = result;
3026   return TRUE;
3027   }
3028
3029 for (s=option_spec; *s != '\0'; /**/)
3030   {
3031   while (isspace(*s)) ++s;
3032   if (*s == '\0')
3033     break;
3034   if (*s != '+' && *s != '-')
3035     {
3036     DEBUG(D_tls) debug_printf("malformed openssl option setting: "
3037         "+ or - expected but found \"%s\"\n", s);
3038     return FALSE;
3039     }
3040   adding = *s++ == '+';
3041   for (end = s; (*end != '\0') && !isspace(*end); ++end) /**/ ;
3042   keep_c = *end;
3043   *end = '\0';
3044   item_parsed = tls_openssl_one_option_parse(s, &item);
3045   *end = keep_c;
3046   if (!item_parsed)
3047     {
3048     DEBUG(D_tls) debug_printf("openssl option setting unrecognised: \"%s\"\n", s);
3049     return FALSE;
3050     }
3051   DEBUG(D_tls) debug_printf("openssl option, %s from %lx: %lx (%s)\n",
3052       adding ? "adding" : "removing", result, item, s);
3053   if (adding)
3054     result |= item;
3055   else
3056     result &= ~item;
3057   s = end;
3058   }
3059
3060 *results = result;
3061 return TRUE;
3062 }
3063
3064 /* vi: aw ai sw=2
3065 */
3066 /* End of tls-openssl.c */