| 1 | /* $Cambridge: exim/src/src/tls-openssl.c,v 1.11 2007/03/13 09:50:22 ph10 Exp $ */ |
| 2 | |
| 3 | /************************************************* |
| 4 | * Exim - an Internet mail transport agent * |
| 5 | *************************************************/ |
| 6 | |
| 7 | /* Copyright (c) University of Cambridge 1995 - 2007 */ |
| 8 | /* See the file NOTICE for conditions of use and distribution. */ |
| 9 | |
| 10 | /* This module provides the TLS (aka SSL) support for Exim using the OpenSSL |
| 11 | library. It is #included into the tls.c file when that library is used. The |
| 12 | code herein is based on a patch that was originally contributed by Steve |
| 13 | Haslam. It was adapted from stunnel, a GPL program by Michal Trojnara. |
| 14 | |
| 15 | No cryptographic code is included in Exim. All this module does is to call |
| 16 | functions from the OpenSSL library. */ |
| 17 | |
| 18 | |
| 19 | /* Heading stuff */ |
| 20 | |
| 21 | #include <openssl/lhash.h> |
| 22 | #include <openssl/ssl.h> |
| 23 | #include <openssl/err.h> |
| 24 | #include <openssl/rand.h> |
| 25 | |
| 26 | /* Structure for collecting random data for seeding. */ |
| 27 | |
| 28 | typedef struct randstuff { |
| 29 | time_t t; |
| 30 | pid_t p; |
| 31 | } randstuff; |
| 32 | |
| 33 | /* Local static variables */ |
| 34 | |
| 35 | static BOOL verify_callback_called = FALSE; |
| 36 | static const uschar *sid_ctx = US"exim"; |
| 37 | |
| 38 | static SSL_CTX *ctx = NULL; |
| 39 | static SSL *ssl = NULL; |
| 40 | |
| 41 | static char ssl_errstring[256]; |
| 42 | |
| 43 | static int ssl_session_timeout = 200; |
| 44 | static BOOL verify_optional = FALSE; |
| 45 | |
| 46 | |
| 47 | |
| 48 | |
| 49 | |
| 50 | /************************************************* |
| 51 | * Handle TLS error * |
| 52 | *************************************************/ |
| 53 | |
| 54 | /* Called from lots of places when errors occur before actually starting to do |
| 55 | the TLS handshake, that is, while the session is still in clear. Always returns |
| 56 | DEFER for a server and FAIL for a client so that most calls can use "return |
| 57 | tls_error(...)" to do this processing and then give an appropriate return. A |
| 58 | single function is used for both server and client, because it is called from |
| 59 | some shared functions. |
| 60 | |
| 61 | Argument: |
| 62 | prefix text to include in the logged error |
| 63 | host NULL if setting up a server; |
| 64 | the connected host if setting up a client |
| 65 | |
| 66 | Returns: OK/DEFER/FAIL |
| 67 | */ |
| 68 | |
| 69 | static int |
| 70 | tls_error(uschar *prefix, host_item *host) |
| 71 | { |
| 72 | ERR_error_string(ERR_get_error(), ssl_errstring); |
| 73 | if (host == NULL) |
| 74 | { |
| 75 | log_write(0, LOG_MAIN, "TLS error on connection from %s (%s): %s", |
| 76 | (sender_fullhost != NULL)? sender_fullhost : US"local process", |
| 77 | prefix, ssl_errstring); |
| 78 | return DEFER; |
| 79 | } |
| 80 | else |
| 81 | { |
| 82 | log_write(0, LOG_MAIN, "TLS error on connection to %s [%s] (%s): %s", |
| 83 | host->name, host->address, prefix, ssl_errstring); |
| 84 | return FAIL; |
| 85 | } |
| 86 | } |
| 87 | |
| 88 | |
| 89 | |
| 90 | /************************************************* |
| 91 | * Callback to generate RSA key * |
| 92 | *************************************************/ |
| 93 | |
| 94 | /* |
| 95 | Arguments: |
| 96 | s SSL connection |
| 97 | export not used |
| 98 | keylength keylength |
| 99 | |
| 100 | Returns: pointer to generated key |
| 101 | */ |
| 102 | |
| 103 | static RSA * |
| 104 | rsa_callback(SSL *s, int export, int keylength) |
| 105 | { |
| 106 | RSA *rsa_key; |
| 107 | export = export; /* Shut picky compilers up */ |
| 108 | DEBUG(D_tls) debug_printf("Generating %d bit RSA key...\n", keylength); |
| 109 | rsa_key = RSA_generate_key(keylength, RSA_F4, NULL, NULL); |
| 110 | if (rsa_key == NULL) |
| 111 | { |
| 112 | ERR_error_string(ERR_get_error(), ssl_errstring); |
| 113 | log_write(0, LOG_MAIN|LOG_PANIC, "TLS error (RSA_generate_key): %s", |
| 114 | ssl_errstring); |
| 115 | return NULL; |
| 116 | } |
| 117 | return rsa_key; |
| 118 | } |
| 119 | |
| 120 | |
| 121 | |
| 122 | |
| 123 | /************************************************* |
| 124 | * Callback for verification * |
| 125 | *************************************************/ |
| 126 | |
| 127 | /* The SSL library does certificate verification if set up to do so. This |
| 128 | callback has the current yes/no state is in "state". If verification succeeded, |
| 129 | we set up the tls_peerdn string. If verification failed, what happens depends |
| 130 | on whether the client is required to present a verifiable certificate or not. |
| 131 | |
| 132 | If verification is optional, we change the state to yes, but still log the |
| 133 | verification error. For some reason (it really would help to have proper |
| 134 | documentation of OpenSSL), this callback function then gets called again, this |
| 135 | time with state = 1. In fact, that's useful, because we can set up the peerdn |
| 136 | value, but we must take care not to set the private verified flag on the second |
| 137 | time through. |
| 138 | |
| 139 | Note: this function is not called if the client fails to present a certificate |
| 140 | when asked. We get here only if a certificate has been received. Handling of |
| 141 | optional verification for this case is done when requesting SSL to verify, by |
| 142 | setting SSL_VERIFY_FAIL_IF_NO_PEER_CERT in the non-optional case. |
| 143 | |
| 144 | Arguments: |
| 145 | state current yes/no state as 1/0 |
| 146 | x509ctx certificate information. |
| 147 | |
| 148 | Returns: 1 if verified, 0 if not |
| 149 | */ |
| 150 | |
| 151 | static int |
| 152 | verify_callback(int state, X509_STORE_CTX *x509ctx) |
| 153 | { |
| 154 | static uschar txt[256]; |
| 155 | |
| 156 | X509_NAME_oneline(X509_get_subject_name(x509ctx->current_cert), |
| 157 | CS txt, sizeof(txt)); |
| 158 | |
| 159 | if (state == 0) |
| 160 | { |
| 161 | log_write(0, LOG_MAIN, "SSL verify error: depth=%d error=%s cert=%s", |
| 162 | x509ctx->error_depth, |
| 163 | X509_verify_cert_error_string(x509ctx->error), |
| 164 | txt); |
| 165 | tls_certificate_verified = FALSE; |
| 166 | verify_callback_called = TRUE; |
| 167 | if (!verify_optional) return 0; /* reject */ |
| 168 | DEBUG(D_tls) debug_printf("SSL verify failure overridden (host in " |
| 169 | "tls_try_verify_hosts)\n"); |
| 170 | return 1; /* accept */ |
| 171 | } |
| 172 | |
| 173 | if (x509ctx->error_depth != 0) |
| 174 | { |
| 175 | DEBUG(D_tls) debug_printf("SSL verify ok: depth=%d cert=%s\n", |
| 176 | x509ctx->error_depth, txt); |
| 177 | } |
| 178 | else |
| 179 | { |
| 180 | DEBUG(D_tls) debug_printf("SSL%s peer: %s\n", |
| 181 | verify_callback_called? "" : " authenticated", txt); |
| 182 | tls_peerdn = txt; |
| 183 | } |
| 184 | |
| 185 | if (!verify_callback_called) tls_certificate_verified = TRUE; |
| 186 | verify_callback_called = TRUE; |
| 187 | |
| 188 | return 1; /* accept */ |
| 189 | } |
| 190 | |
| 191 | |
| 192 | |
| 193 | /************************************************* |
| 194 | * Information callback * |
| 195 | *************************************************/ |
| 196 | |
| 197 | /* The SSL library functions call this from time to time to indicate what they |
| 198 | are doing. We copy the string to the debugging output when the level is high |
| 199 | enough. |
| 200 | |
| 201 | Arguments: |
| 202 | s the SSL connection |
| 203 | where |
| 204 | ret |
| 205 | |
| 206 | Returns: nothing |
| 207 | */ |
| 208 | |
| 209 | static void |
| 210 | info_callback(SSL *s, int where, int ret) |
| 211 | { |
| 212 | where = where; |
| 213 | ret = ret; |
| 214 | DEBUG(D_tls) debug_printf("SSL info: %s\n", SSL_state_string_long(s)); |
| 215 | } |
| 216 | |
| 217 | |
| 218 | |
| 219 | /************************************************* |
| 220 | * Initialize for DH * |
| 221 | *************************************************/ |
| 222 | |
| 223 | /* If dhparam is set, expand it, and load up the parameters for DH encryption. |
| 224 | |
| 225 | Arguments: |
| 226 | dhparam DH parameter file |
| 227 | |
| 228 | Returns: TRUE if OK (nothing to set up, or setup worked) |
| 229 | */ |
| 230 | |
| 231 | static BOOL |
| 232 | init_dh(uschar *dhparam) |
| 233 | { |
| 234 | BOOL yield = TRUE; |
| 235 | BIO *bio; |
| 236 | DH *dh; |
| 237 | uschar *dhexpanded; |
| 238 | |
| 239 | if (!expand_check(dhparam, US"tls_dhparam", &dhexpanded)) |
| 240 | return FALSE; |
| 241 | |
| 242 | if (dhexpanded == NULL) return TRUE; |
| 243 | |
| 244 | if ((bio = BIO_new_file(CS dhexpanded, "r")) == NULL) |
| 245 | { |
| 246 | log_write(0, LOG_MAIN, "DH: could not read %s: %s", dhexpanded, |
| 247 | strerror(errno)); |
| 248 | yield = FALSE; |
| 249 | } |
| 250 | else |
| 251 | { |
| 252 | if ((dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL)) == NULL) |
| 253 | { |
| 254 | log_write(0, LOG_MAIN, "DH: could not load params from %s", |
| 255 | dhexpanded); |
| 256 | yield = FALSE; |
| 257 | } |
| 258 | else |
| 259 | { |
| 260 | SSL_CTX_set_tmp_dh(ctx, dh); |
| 261 | DEBUG(D_tls) |
| 262 | debug_printf("Diffie-Hellman initialized from %s with %d-bit key\n", |
| 263 | dhexpanded, 8*DH_size(dh)); |
| 264 | DH_free(dh); |
| 265 | } |
| 266 | BIO_free(bio); |
| 267 | } |
| 268 | |
| 269 | return yield; |
| 270 | } |
| 271 | |
| 272 | |
| 273 | |
| 274 | |
| 275 | /************************************************* |
| 276 | * Initialize for TLS * |
| 277 | *************************************************/ |
| 278 | |
| 279 | /* Called from both server and client code, to do preliminary initialization of |
| 280 | the library. |
| 281 | |
| 282 | Arguments: |
| 283 | host connected host, if client; NULL if server |
| 284 | dhparam DH parameter file |
| 285 | certificate certificate file |
| 286 | privatekey private key |
| 287 | addr address if client; NULL if server (for some randomness) |
| 288 | |
| 289 | Returns: OK/DEFER/FAIL |
| 290 | */ |
| 291 | |
| 292 | static int |
| 293 | tls_init(host_item *host, uschar *dhparam, uschar *certificate, |
| 294 | uschar *privatekey, address_item *addr) |
| 295 | { |
| 296 | SSL_load_error_strings(); /* basic set up */ |
| 297 | OpenSSL_add_ssl_algorithms(); |
| 298 | |
| 299 | /* Create a context */ |
| 300 | |
| 301 | ctx = SSL_CTX_new((host == NULL)? |
| 302 | SSLv23_server_method() : SSLv23_client_method()); |
| 303 | |
| 304 | if (ctx == NULL) return tls_error(US"SSL_CTX_new", host); |
| 305 | |
| 306 | /* It turns out that we need to seed the random number generator this early in |
| 307 | order to get the full complement of ciphers to work. It took me roughly a day |
| 308 | of work to discover this by experiment. |
| 309 | |
| 310 | On systems that have /dev/urandom, SSL may automatically seed itself from |
| 311 | there. Otherwise, we have to make something up as best we can. Double check |
| 312 | afterwards. */ |
| 313 | |
| 314 | if (!RAND_status()) |
| 315 | { |
| 316 | randstuff r; |
| 317 | r.t = time(NULL); |
| 318 | r.p = getpid(); |
| 319 | |
| 320 | RAND_seed((uschar *)(&r), sizeof(r)); |
| 321 | RAND_seed((uschar *)big_buffer, big_buffer_size); |
| 322 | if (addr != NULL) RAND_seed((uschar *)addr, sizeof(addr)); |
| 323 | |
| 324 | if (!RAND_status()) |
| 325 | { |
| 326 | if (host == NULL) |
| 327 | { |
| 328 | log_write(0, LOG_MAIN, "TLS error on connection from %s: " |
| 329 | "unable to seed random number generator", |
| 330 | (sender_fullhost != NULL)? sender_fullhost : US"local process"); |
| 331 | return DEFER; |
| 332 | } |
| 333 | else |
| 334 | { |
| 335 | log_write(0, LOG_MAIN, "TLS error on connection to %s [%s]: " |
| 336 | "unable to seed random number generator", |
| 337 | host->name, host->address); |
| 338 | return FAIL; |
| 339 | } |
| 340 | } |
| 341 | } |
| 342 | |
| 343 | /* Set up the information callback, which outputs if debugging is at a suitable |
| 344 | level. */ |
| 345 | |
| 346 | SSL_CTX_set_info_callback(ctx, (void (*)())info_callback); |
| 347 | |
| 348 | /* The following patch was supplied by Robert Roselius */ |
| 349 | |
| 350 | #if OPENSSL_VERSION_NUMBER > 0x00906040L |
| 351 | /* Enable client-bug workaround. |
| 352 | Versions of OpenSSL as of 0.9.6d include a "CBC countermeasure" feature, |
| 353 | which causes problems with some clients (such as the Certicom SSL Plus |
| 354 | library used by Eudora). This option, SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS, |
| 355 | disables the coutermeasure allowing Eudora to connect. |
| 356 | Some poppers and MTAs use SSL_OP_ALL, which enables all such bug |
| 357 | workarounds. */ |
| 358 | /* XXX (Silently?) ignore failure here? XXX*/ |
| 359 | |
| 360 | if (!(SSL_CTX_set_options(ctx, SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS))) |
| 361 | return tls_error(US"SSL_CTX_set_option", host); |
| 362 | #endif |
| 363 | |
| 364 | /* Initialize with DH parameters if supplied */ |
| 365 | |
| 366 | if (!init_dh(dhparam)) return DEFER; |
| 367 | |
| 368 | /* Set up certificate and key */ |
| 369 | |
| 370 | if (certificate != NULL) |
| 371 | { |
| 372 | uschar *expanded; |
| 373 | if (!expand_check(certificate, US"tls_certificate", &expanded)) |
| 374 | return DEFER; |
| 375 | |
| 376 | if (expanded != NULL) |
| 377 | { |
| 378 | DEBUG(D_tls) debug_printf("tls_certificate file %s\n", expanded); |
| 379 | if (!SSL_CTX_use_certificate_chain_file(ctx, CS expanded)) |
| 380 | return tls_error(string_sprintf( |
| 381 | "SSL_CTX_use_certificate_chain_file file=%s", expanded), host); |
| 382 | } |
| 383 | |
| 384 | if (privatekey != NULL && |
| 385 | !expand_check(privatekey, US"tls_privatekey", &expanded)) |
| 386 | return DEFER; |
| 387 | |
| 388 | /* If expansion was forced to fail, key_expanded will be NULL. If the result |
| 389 | of the expansion is an empty string, ignore it also, and assume the private |
| 390 | key is in the same file as the certificate. */ |
| 391 | |
| 392 | if (expanded != NULL && *expanded != 0) |
| 393 | { |
| 394 | DEBUG(D_tls) debug_printf("tls_privatekey file %s\n", expanded); |
| 395 | if (!SSL_CTX_use_PrivateKey_file(ctx, CS expanded, SSL_FILETYPE_PEM)) |
| 396 | return tls_error(string_sprintf( |
| 397 | "SSL_CTX_use_PrivateKey_file file=%s", expanded), host); |
| 398 | } |
| 399 | } |
| 400 | |
| 401 | /* Set up the RSA callback */ |
| 402 | |
| 403 | SSL_CTX_set_tmp_rsa_callback(ctx, rsa_callback); |
| 404 | |
| 405 | /* Finally, set the timeout, and we are done */ |
| 406 | |
| 407 | SSL_CTX_set_timeout(ctx, ssl_session_timeout); |
| 408 | DEBUG(D_tls) debug_printf("Initialized TLS\n"); |
| 409 | return OK; |
| 410 | } |
| 411 | |
| 412 | |
| 413 | |
| 414 | |
| 415 | /************************************************* |
| 416 | * Get name of cipher in use * |
| 417 | *************************************************/ |
| 418 | |
| 419 | /* The answer is left in a static buffer, and tls_cipher is set to point |
| 420 | to it. |
| 421 | |
| 422 | Argument: pointer to an SSL structure for the connection |
| 423 | Returns: nothing |
| 424 | */ |
| 425 | |
| 426 | static void |
| 427 | construct_cipher_name(SSL *ssl) |
| 428 | { |
| 429 | static uschar cipherbuf[256]; |
| 430 | SSL_CIPHER *c; |
| 431 | uschar *ver; |
| 432 | int bits; |
| 433 | |
| 434 | switch (ssl->session->ssl_version) |
| 435 | { |
| 436 | case SSL2_VERSION: |
| 437 | ver = US"SSLv2"; |
| 438 | break; |
| 439 | |
| 440 | case SSL3_VERSION: |
| 441 | ver = US"SSLv3"; |
| 442 | break; |
| 443 | |
| 444 | case TLS1_VERSION: |
| 445 | ver = US"TLSv1"; |
| 446 | break; |
| 447 | |
| 448 | default: |
| 449 | ver = US"UNKNOWN"; |
| 450 | } |
| 451 | |
| 452 | c = SSL_get_current_cipher(ssl); |
| 453 | SSL_CIPHER_get_bits(c, &bits); |
| 454 | |
| 455 | string_format(cipherbuf, sizeof(cipherbuf), "%s:%s:%u", ver, |
| 456 | SSL_CIPHER_get_name(c), bits); |
| 457 | tls_cipher = cipherbuf; |
| 458 | |
| 459 | DEBUG(D_tls) debug_printf("Cipher: %s\n", cipherbuf); |
| 460 | } |
| 461 | |
| 462 | |
| 463 | |
| 464 | |
| 465 | |
| 466 | /************************************************* |
| 467 | * Set up for verifying certificates * |
| 468 | *************************************************/ |
| 469 | |
| 470 | /* Called by both client and server startup |
| 471 | |
| 472 | Arguments: |
| 473 | certs certs file or NULL |
| 474 | crl CRL file or NULL |
| 475 | host NULL in a server; the remote host in a client |
| 476 | optional TRUE if called from a server for a host in tls_try_verify_hosts; |
| 477 | otherwise passed as FALSE |
| 478 | |
| 479 | Returns: OK/DEFER/FAIL |
| 480 | */ |
| 481 | |
| 482 | static int |
| 483 | setup_certs(uschar *certs, uschar *crl, host_item *host, BOOL optional) |
| 484 | { |
| 485 | uschar *expcerts, *expcrl; |
| 486 | |
| 487 | if (!expand_check(certs, US"tls_verify_certificates", &expcerts)) |
| 488 | return DEFER; |
| 489 | |
| 490 | if (expcerts != NULL) |
| 491 | { |
| 492 | struct stat statbuf; |
| 493 | if (!SSL_CTX_set_default_verify_paths(ctx)) |
| 494 | return tls_error(US"SSL_CTX_set_default_verify_paths", host); |
| 495 | |
| 496 | if (Ustat(expcerts, &statbuf) < 0) |
| 497 | { |
| 498 | log_write(0, LOG_MAIN|LOG_PANIC, |
| 499 | "failed to stat %s for certificates", expcerts); |
| 500 | return DEFER; |
| 501 | } |
| 502 | else |
| 503 | { |
| 504 | uschar *file, *dir; |
| 505 | if ((statbuf.st_mode & S_IFMT) == S_IFDIR) |
| 506 | { file = NULL; dir = expcerts; } |
| 507 | else |
| 508 | { file = expcerts; dir = NULL; } |
| 509 | |
| 510 | /* If a certificate file is empty, the next function fails with an |
| 511 | unhelpful error message. If we skip it, we get the correct behaviour (no |
| 512 | certificates are recognized, but the error message is still misleading (it |
| 513 | says no certificate was supplied.) But this is better. */ |
| 514 | |
| 515 | if ((file == NULL || statbuf.st_size > 0) && |
| 516 | !SSL_CTX_load_verify_locations(ctx, CS file, CS dir)) |
| 517 | return tls_error(US"SSL_CTX_load_verify_locations", host); |
| 518 | |
| 519 | if (file != NULL) |
| 520 | { |
| 521 | SSL_CTX_set_client_CA_list(ctx, SSL_load_client_CA_file(CS file)); |
| 522 | } |
| 523 | } |
| 524 | |
| 525 | /* Handle a certificate revocation list. */ |
| 526 | |
| 527 | #if OPENSSL_VERSION_NUMBER > 0x00907000L |
| 528 | |
| 529 | /* This bit of code is now the version supplied by Lars Mainka. (I have |
| 530 | * merely reformatted it into the Exim code style.) |
| 531 | |
| 532 | * "From here I changed the code to add support for multiple crl's |
| 533 | * in pem format in one file or to support hashed directory entries in |
| 534 | * pem format instead of a file. This method now uses the library function |
| 535 | * X509_STORE_load_locations to add the CRL location to the SSL context. |
| 536 | * OpenSSL will then handle the verify against CA certs and CRLs by |
| 537 | * itself in the verify callback." */ |
| 538 | |
| 539 | if (!expand_check(crl, US"tls_crl", &expcrl)) return DEFER; |
| 540 | if (expcrl != NULL && *expcrl != 0) |
| 541 | { |
| 542 | struct stat statbufcrl; |
| 543 | if (Ustat(expcrl, &statbufcrl) < 0) |
| 544 | { |
| 545 | log_write(0, LOG_MAIN|LOG_PANIC, |
| 546 | "failed to stat %s for certificates revocation lists", expcrl); |
| 547 | return DEFER; |
| 548 | } |
| 549 | else |
| 550 | { |
| 551 | /* is it a file or directory? */ |
| 552 | uschar *file, *dir; |
| 553 | X509_STORE *cvstore = SSL_CTX_get_cert_store(ctx); |
| 554 | if ((statbufcrl.st_mode & S_IFMT) == S_IFDIR) |
| 555 | { |
| 556 | file = NULL; |
| 557 | dir = expcrl; |
| 558 | DEBUG(D_tls) debug_printf("SSL CRL value is a directory %s\n", dir); |
| 559 | } |
| 560 | else |
| 561 | { |
| 562 | file = expcrl; |
| 563 | dir = NULL; |
| 564 | DEBUG(D_tls) debug_printf("SSL CRL value is a file %s\n", file); |
| 565 | } |
| 566 | if (X509_STORE_load_locations(cvstore, CS file, CS dir) == 0) |
| 567 | return tls_error(US"X509_STORE_load_locations", host); |
| 568 | |
| 569 | /* setting the flags to check against the complete crl chain */ |
| 570 | |
| 571 | X509_STORE_set_flags(cvstore, |
| 572 | X509_V_FLAG_CRL_CHECK|X509_V_FLAG_CRL_CHECK_ALL); |
| 573 | } |
| 574 | } |
| 575 | |
| 576 | #endif /* OPENSSL_VERSION_NUMBER > 0x00907000L */ |
| 577 | |
| 578 | /* If verification is optional, don't fail if no certificate */ |
| 579 | |
| 580 | SSL_CTX_set_verify(ctx, |
| 581 | SSL_VERIFY_PEER | (optional? 0 : SSL_VERIFY_FAIL_IF_NO_PEER_CERT), |
| 582 | verify_callback); |
| 583 | } |
| 584 | |
| 585 | return OK; |
| 586 | } |
| 587 | |
| 588 | |
| 589 | |
| 590 | /************************************************* |
| 591 | * Start a TLS session in a server * |
| 592 | *************************************************/ |
| 593 | |
| 594 | /* This is called when Exim is running as a server, after having received |
| 595 | the STARTTLS command. It must respond to that command, and then negotiate |
| 596 | a TLS session. |
| 597 | |
| 598 | Arguments: |
| 599 | require_ciphers allowed ciphers |
| 600 | ------------------------------------------------------ |
| 601 | require_mac list of allowed MACs ) Not used |
| 602 | require_kx list of allowed key_exchange methods ) for |
| 603 | require_proto list of allowed protocols ) OpenSSL |
| 604 | ------------------------------------------------------ |
| 605 | |
| 606 | Returns: OK on success |
| 607 | DEFER for errors before the start of the negotiation |
| 608 | FAIL for errors during the negotation; the server can't |
| 609 | continue running. |
| 610 | */ |
| 611 | |
| 612 | int |
| 613 | tls_server_start(uschar *require_ciphers, uschar *require_mac, |
| 614 | uschar *require_kx, uschar *require_proto) |
| 615 | { |
| 616 | int rc; |
| 617 | uschar *expciphers; |
| 618 | |
| 619 | /* Check for previous activation */ |
| 620 | |
| 621 | if (tls_active >= 0) |
| 622 | { |
| 623 | log_write(0, LOG_MAIN, "STARTTLS received in already encrypted " |
| 624 | "connection from %s", |
| 625 | (sender_fullhost != NULL)? sender_fullhost : US"local process"); |
| 626 | smtp_printf("554 Already in TLS\r\n"); |
| 627 | return FAIL; |
| 628 | } |
| 629 | |
| 630 | /* Initialize the SSL library. If it fails, it will already have logged |
| 631 | the error. */ |
| 632 | |
| 633 | rc = tls_init(NULL, tls_dhparam, tls_certificate, tls_privatekey, NULL); |
| 634 | if (rc != OK) return rc; |
| 635 | |
| 636 | if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers)) |
| 637 | return FAIL; |
| 638 | |
| 639 | /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they |
| 640 | are separated by underscores. So that I can use either form in my tests, and |
| 641 | also for general convenience, we turn underscores into hyphens here. */ |
| 642 | |
| 643 | if (expciphers != NULL) |
| 644 | { |
| 645 | uschar *s = expciphers; |
| 646 | while (*s != 0) { if (*s == '_') *s = '-'; s++; } |
| 647 | DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers); |
| 648 | if (!SSL_CTX_set_cipher_list(ctx, CS expciphers)) |
| 649 | return tls_error(US"SSL_CTX_set_cipher_list", NULL); |
| 650 | } |
| 651 | |
| 652 | /* If this is a host for which certificate verification is mandatory or |
| 653 | optional, set up appropriately. */ |
| 654 | |
| 655 | tls_certificate_verified = FALSE; |
| 656 | verify_callback_called = FALSE; |
| 657 | |
| 658 | if (verify_check_host(&tls_verify_hosts) == OK) |
| 659 | { |
| 660 | rc = setup_certs(tls_verify_certificates, tls_crl, NULL, FALSE); |
| 661 | if (rc != OK) return rc; |
| 662 | verify_optional = FALSE; |
| 663 | } |
| 664 | else if (verify_check_host(&tls_try_verify_hosts) == OK) |
| 665 | { |
| 666 | rc = setup_certs(tls_verify_certificates, tls_crl, NULL, TRUE); |
| 667 | if (rc != OK) return rc; |
| 668 | verify_optional = TRUE; |
| 669 | } |
| 670 | |
| 671 | /* Prepare for new connection */ |
| 672 | |
| 673 | if ((ssl = SSL_new(ctx)) == NULL) return tls_error(US"SSL_new", NULL); |
| 674 | SSL_clear(ssl); |
| 675 | |
| 676 | /* Set context and tell client to go ahead, except in the case of TLS startup |
| 677 | on connection, where outputting anything now upsets the clients and tends to |
| 678 | make them disconnect. We need to have an explicit fflush() here, to force out |
| 679 | the response. Other smtp_printf() calls do not need it, because in non-TLS |
| 680 | mode, the fflush() happens when smtp_getc() is called. */ |
| 681 | |
| 682 | SSL_set_session_id_context(ssl, sid_ctx, Ustrlen(sid_ctx)); |
| 683 | if (!tls_on_connect) |
| 684 | { |
| 685 | smtp_printf("220 TLS go ahead\r\n"); |
| 686 | fflush(smtp_out); |
| 687 | } |
| 688 | |
| 689 | /* Now negotiate the TLS session. We put our own timer on it, since it seems |
| 690 | that the OpenSSL library doesn't. */ |
| 691 | |
| 692 | SSL_set_wfd(ssl, fileno(smtp_out)); |
| 693 | SSL_set_rfd(ssl, fileno(smtp_in)); |
| 694 | SSL_set_accept_state(ssl); |
| 695 | |
| 696 | DEBUG(D_tls) debug_printf("Calling SSL_accept\n"); |
| 697 | |
| 698 | sigalrm_seen = FALSE; |
| 699 | if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout); |
| 700 | rc = SSL_accept(ssl); |
| 701 | alarm(0); |
| 702 | |
| 703 | if (rc <= 0) |
| 704 | { |
| 705 | if (sigalrm_seen) Ustrcpy(ssl_errstring, "timed out"); |
| 706 | else ERR_error_string(ERR_get_error(), ssl_errstring); |
| 707 | log_write(0, LOG_MAIN, "TLS error on connection from %s (SSL_accept): %s", |
| 708 | (sender_fullhost != NULL)? sender_fullhost : US"local process", |
| 709 | ssl_errstring); |
| 710 | return FAIL; |
| 711 | } |
| 712 | |
| 713 | DEBUG(D_tls) debug_printf("SSL_accept was successful\n"); |
| 714 | |
| 715 | /* TLS has been set up. Adjust the input functions to read via TLS, |
| 716 | and initialize things. */ |
| 717 | |
| 718 | construct_cipher_name(ssl); |
| 719 | |
| 720 | DEBUG(D_tls) |
| 721 | { |
| 722 | uschar buf[2048]; |
| 723 | if (SSL_get_shared_ciphers(ssl, CS buf, sizeof(buf)) != NULL) |
| 724 | debug_printf("Shared ciphers: %s\n", buf); |
| 725 | } |
| 726 | |
| 727 | |
| 728 | ssl_xfer_buffer = store_malloc(ssl_xfer_buffer_size); |
| 729 | ssl_xfer_buffer_lwm = ssl_xfer_buffer_hwm = 0; |
| 730 | ssl_xfer_eof = ssl_xfer_error = 0; |
| 731 | |
| 732 | receive_getc = tls_getc; |
| 733 | receive_ungetc = tls_ungetc; |
| 734 | receive_feof = tls_feof; |
| 735 | receive_ferror = tls_ferror; |
| 736 | |
| 737 | tls_active = fileno(smtp_out); |
| 738 | return OK; |
| 739 | } |
| 740 | |
| 741 | |
| 742 | |
| 743 | |
| 744 | |
| 745 | /************************************************* |
| 746 | * Start a TLS session in a client * |
| 747 | *************************************************/ |
| 748 | |
| 749 | /* Called from the smtp transport after STARTTLS has been accepted. |
| 750 | |
| 751 | Argument: |
| 752 | fd the fd of the connection |
| 753 | host connected host (for messages) |
| 754 | addr the first address |
| 755 | dhparam DH parameter file |
| 756 | certificate certificate file |
| 757 | privatekey private key file |
| 758 | verify_certs file for certificate verify |
| 759 | crl file containing CRL |
| 760 | require_ciphers list of allowed ciphers |
| 761 | ------------------------------------------------------ |
| 762 | require_mac list of allowed MACs ) Not used |
| 763 | require_kx list of allowed key_exchange methods ) for |
| 764 | require_proto list of allowed protocols ) OpenSSL |
| 765 | ------------------------------------------------------ |
| 766 | timeout startup timeout |
| 767 | |
| 768 | Returns: OK on success |
| 769 | FAIL otherwise - note that tls_error() will not give DEFER |
| 770 | because this is not a server |
| 771 | */ |
| 772 | |
| 773 | int |
| 774 | tls_client_start(int fd, host_item *host, address_item *addr, uschar *dhparam, |
| 775 | uschar *certificate, uschar *privatekey, uschar *verify_certs, uschar *crl, |
| 776 | uschar *require_ciphers, uschar *require_mac, uschar *require_kx, |
| 777 | uschar *require_proto, int timeout) |
| 778 | { |
| 779 | static uschar txt[256]; |
| 780 | uschar *expciphers; |
| 781 | X509* server_cert; |
| 782 | int rc; |
| 783 | |
| 784 | rc = tls_init(host, dhparam, certificate, privatekey, addr); |
| 785 | if (rc != OK) return rc; |
| 786 | |
| 787 | tls_certificate_verified = FALSE; |
| 788 | verify_callback_called = FALSE; |
| 789 | |
| 790 | if (!expand_check(require_ciphers, US"tls_require_ciphers", &expciphers)) |
| 791 | return FAIL; |
| 792 | |
| 793 | /* In OpenSSL, cipher components are separated by hyphens. In GnuTLS, they |
| 794 | are separated by underscores. So that I can use either form in my tests, and |
| 795 | also for general convenience, we turn underscores into hyphens here. */ |
| 796 | |
| 797 | if (expciphers != NULL) |
| 798 | { |
| 799 | uschar *s = expciphers; |
| 800 | while (*s != 0) { if (*s == '_') *s = '-'; s++; } |
| 801 | DEBUG(D_tls) debug_printf("required ciphers: %s\n", expciphers); |
| 802 | if (!SSL_CTX_set_cipher_list(ctx, CS expciphers)) |
| 803 | return tls_error(US"SSL_CTX_set_cipher_list", host); |
| 804 | } |
| 805 | |
| 806 | rc = setup_certs(verify_certs, crl, host, FALSE); |
| 807 | if (rc != OK) return rc; |
| 808 | |
| 809 | if ((ssl = SSL_new(ctx)) == NULL) return tls_error(US"SSL_new", host); |
| 810 | SSL_set_session_id_context(ssl, sid_ctx, Ustrlen(sid_ctx)); |
| 811 | SSL_set_fd(ssl, fd); |
| 812 | SSL_set_connect_state(ssl); |
| 813 | |
| 814 | /* There doesn't seem to be a built-in timeout on connection. */ |
| 815 | |
| 816 | DEBUG(D_tls) debug_printf("Calling SSL_connect\n"); |
| 817 | sigalrm_seen = FALSE; |
| 818 | alarm(timeout); |
| 819 | rc = SSL_connect(ssl); |
| 820 | alarm(0); |
| 821 | |
| 822 | if (rc <= 0) |
| 823 | { |
| 824 | if (sigalrm_seen) |
| 825 | { |
| 826 | log_write(0, LOG_MAIN, "TLS error on connection to %s [%s]: " |
| 827 | "SSL_connect timed out", host->name, host->address); |
| 828 | return FAIL; |
| 829 | } |
| 830 | else return tls_error(US"SSL_connect", host); |
| 831 | } |
| 832 | |
| 833 | DEBUG(D_tls) debug_printf("SSL_connect succeeded\n"); |
| 834 | |
| 835 | server_cert = SSL_get_peer_certificate (ssl); |
| 836 | tls_peerdn = US X509_NAME_oneline(X509_get_subject_name(server_cert), |
| 837 | CS txt, sizeof(txt)); |
| 838 | tls_peerdn = txt; |
| 839 | |
| 840 | construct_cipher_name(ssl); /* Sets tls_cipher */ |
| 841 | |
| 842 | tls_active = fd; |
| 843 | return OK; |
| 844 | } |
| 845 | |
| 846 | |
| 847 | |
| 848 | |
| 849 | |
| 850 | /************************************************* |
| 851 | * TLS version of getc * |
| 852 | *************************************************/ |
| 853 | |
| 854 | /* This gets the next byte from the TLS input buffer. If the buffer is empty, |
| 855 | it refills the buffer via the SSL reading function. |
| 856 | |
| 857 | Arguments: none |
| 858 | Returns: the next character or EOF |
| 859 | */ |
| 860 | |
| 861 | int |
| 862 | tls_getc(void) |
| 863 | { |
| 864 | if (ssl_xfer_buffer_lwm >= ssl_xfer_buffer_hwm) |
| 865 | { |
| 866 | int error; |
| 867 | int inbytes; |
| 868 | |
| 869 | DEBUG(D_tls) debug_printf("Calling SSL_read(%lx, %lx, %u)\n", (long)ssl, |
| 870 | (long)ssl_xfer_buffer, ssl_xfer_buffer_size); |
| 871 | |
| 872 | if (smtp_receive_timeout > 0) alarm(smtp_receive_timeout); |
| 873 | inbytes = SSL_read(ssl, CS ssl_xfer_buffer, ssl_xfer_buffer_size); |
| 874 | error = SSL_get_error(ssl, inbytes); |
| 875 | alarm(0); |
| 876 | |
| 877 | /* SSL_ERROR_ZERO_RETURN appears to mean that the SSL session has been |
| 878 | closed down, not that the socket itself has been closed down. Revert to |
| 879 | non-SSL handling. */ |
| 880 | |
| 881 | if (error == SSL_ERROR_ZERO_RETURN) |
| 882 | { |
| 883 | DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n"); |
| 884 | |
| 885 | receive_getc = smtp_getc; |
| 886 | receive_ungetc = smtp_ungetc; |
| 887 | receive_feof = smtp_feof; |
| 888 | receive_ferror = smtp_ferror; |
| 889 | |
| 890 | SSL_free(ssl); |
| 891 | ssl = NULL; |
| 892 | tls_active = -1; |
| 893 | tls_cipher = NULL; |
| 894 | tls_peerdn = NULL; |
| 895 | |
| 896 | return smtp_getc(); |
| 897 | } |
| 898 | |
| 899 | /* Handle genuine errors */ |
| 900 | |
| 901 | else if (error != SSL_ERROR_NONE) |
| 902 | { |
| 903 | DEBUG(D_tls) debug_printf("Got SSL error %d\n", error); |
| 904 | ssl_xfer_error = 1; |
| 905 | return EOF; |
| 906 | } |
| 907 | |
| 908 | ssl_xfer_buffer_hwm = inbytes; |
| 909 | ssl_xfer_buffer_lwm = 0; |
| 910 | } |
| 911 | |
| 912 | /* Something in the buffer; return next uschar */ |
| 913 | |
| 914 | return ssl_xfer_buffer[ssl_xfer_buffer_lwm++]; |
| 915 | } |
| 916 | |
| 917 | |
| 918 | |
| 919 | /************************************************* |
| 920 | * Read bytes from TLS channel * |
| 921 | *************************************************/ |
| 922 | |
| 923 | /* |
| 924 | Arguments: |
| 925 | buff buffer of data |
| 926 | len size of buffer |
| 927 | |
| 928 | Returns: the number of bytes read |
| 929 | -1 after a failed read |
| 930 | */ |
| 931 | |
| 932 | int |
| 933 | tls_read(uschar *buff, size_t len) |
| 934 | { |
| 935 | int inbytes; |
| 936 | int error; |
| 937 | |
| 938 | DEBUG(D_tls) debug_printf("Calling SSL_read(%lx, %lx, %u)\n", (long)ssl, |
| 939 | (long)buff, (unsigned int)len); |
| 940 | |
| 941 | inbytes = SSL_read(ssl, CS buff, len); |
| 942 | error = SSL_get_error(ssl, inbytes); |
| 943 | |
| 944 | if (error == SSL_ERROR_ZERO_RETURN) |
| 945 | { |
| 946 | DEBUG(D_tls) debug_printf("Got SSL_ERROR_ZERO_RETURN\n"); |
| 947 | return -1; |
| 948 | } |
| 949 | else if (error != SSL_ERROR_NONE) |
| 950 | { |
| 951 | return -1; |
| 952 | } |
| 953 | |
| 954 | return inbytes; |
| 955 | } |
| 956 | |
| 957 | |
| 958 | |
| 959 | |
| 960 | |
| 961 | /************************************************* |
| 962 | * Write bytes down TLS channel * |
| 963 | *************************************************/ |
| 964 | |
| 965 | /* |
| 966 | Arguments: |
| 967 | buff buffer of data |
| 968 | len number of bytes |
| 969 | |
| 970 | Returns: the number of bytes after a successful write, |
| 971 | -1 after a failed write |
| 972 | */ |
| 973 | |
| 974 | int |
| 975 | tls_write(const uschar *buff, size_t len) |
| 976 | { |
| 977 | int outbytes; |
| 978 | int error; |
| 979 | int left = len; |
| 980 | |
| 981 | DEBUG(D_tls) debug_printf("tls_do_write(%lx, %d)\n", (long)buff, left); |
| 982 | while (left > 0) |
| 983 | { |
| 984 | DEBUG(D_tls) debug_printf("SSL_write(SSL, %lx, %d)\n", (long)buff, left); |
| 985 | outbytes = SSL_write(ssl, CS buff, left); |
| 986 | error = SSL_get_error(ssl, outbytes); |
| 987 | DEBUG(D_tls) debug_printf("outbytes=%d error=%d\n", outbytes, error); |
| 988 | switch (error) |
| 989 | { |
| 990 | case SSL_ERROR_SSL: |
| 991 | ERR_error_string(ERR_get_error(), ssl_errstring); |
| 992 | log_write(0, LOG_MAIN, "TLS error (SSL_write): %s", ssl_errstring); |
| 993 | return -1; |
| 994 | |
| 995 | case SSL_ERROR_NONE: |
| 996 | left -= outbytes; |
| 997 | buff += outbytes; |
| 998 | break; |
| 999 | |
| 1000 | case SSL_ERROR_ZERO_RETURN: |
| 1001 | log_write(0, LOG_MAIN, "SSL channel closed on write"); |
| 1002 | return -1; |
| 1003 | |
| 1004 | default: |
| 1005 | log_write(0, LOG_MAIN, "SSL_write error %d", error); |
| 1006 | return -1; |
| 1007 | } |
| 1008 | } |
| 1009 | return len; |
| 1010 | } |
| 1011 | |
| 1012 | |
| 1013 | |
| 1014 | /************************************************* |
| 1015 | * Close down a TLS session * |
| 1016 | *************************************************/ |
| 1017 | |
| 1018 | /* This is also called from within a delivery subprocess forked from the |
| 1019 | daemon, to shut down the TLS library, without actually doing a shutdown (which |
| 1020 | would tamper with the SSL session in the parent process). |
| 1021 | |
| 1022 | Arguments: TRUE if SSL_shutdown is to be called |
| 1023 | Returns: nothing |
| 1024 | */ |
| 1025 | |
| 1026 | void |
| 1027 | tls_close(BOOL shutdown) |
| 1028 | { |
| 1029 | if (tls_active < 0) return; /* TLS was not active */ |
| 1030 | |
| 1031 | if (shutdown) |
| 1032 | { |
| 1033 | DEBUG(D_tls) debug_printf("tls_close(): shutting down SSL\n"); |
| 1034 | SSL_shutdown(ssl); |
| 1035 | } |
| 1036 | |
| 1037 | SSL_free(ssl); |
| 1038 | ssl = NULL; |
| 1039 | |
| 1040 | tls_active = -1; |
| 1041 | } |
| 1042 | |
| 1043 | /* End of tls-openssl.c */ |