/*++ * NAME * tls_server 3 * SUMMARY * server-side TLS engine * SYNOPSIS * #include * * TLS_APPL_STATE *tls_server_init(props) * const TLS_SERVER_INIT_PROPS *props; * * TLS_SESS_STATE *tls_server_start(props) * const TLS_SERVER_START_PROPS *props; * * void tls_server_stop(app_ctx, stream, failure, TLScontext) * TLS_APPL_STATE *app_ctx; * VSTREAM *stream; * int failure; * TLS_SESS_STATE *TLScontext; * DESCRIPTION * This module is the interface between Postfix TLS servers, * the OpenSSL library, and the TLS entropy and cache manager. * * tls_server_init() is called once when the SMTP server * initializes. * Certificate details are also decided during this phase, * so that peer-specific behavior is not possible. * * tls_server_start() activates the TLS feature for the VSTREAM * passed as argument. We assume that network buffers are flushed * and the TLS handshake can begin immediately. * * tls_server_stop() sends the "close notify" alert via * SSL_shutdown() to the peer and resets all connection specific * TLS data. As RFC2487 does not specify a separate shutdown, it * is assumed that the underlying TCP connection is shut down * immediately afterwards. Any further writes to the channel will * be discarded, and any further reads will report end-of-file. * If the failure flag is set, no SSL_shutdown() handshake is performed. * * Once the TLS connection is initiated, information about the TLS * state is available via the TLScontext structure: * .IP TLScontext->protocol * the protocol name (SSLv2, SSLv3, TLSv1), * .IP TLScontext->cipher_name * the cipher name (e.g. RC4/MD5), * .IP TLScontext->cipher_usebits * the number of bits actually used (e.g. 40), * .IP TLScontext->cipher_algbits * the number of bits the algorithm is based on (e.g. 128). * .PP * The last two values may differ from each other when export-strength * encryption is used. * * If the peer offered a certificate, part of the certificate data are * available as: * .IP TLScontext->peer_status * A bitmask field that records the status of the peer certificate * verification. One or more of TLS_CERT_FLAG_PRESENT and * TLS_CERT_FLAG_TRUSTED. * .IP TLScontext->peer_CN * Extracted CommonName of the peer, or zero-length string * when information could not be extracted. * .IP TLScontext->issuer_CN * Extracted CommonName of the issuer, or zero-length string * when information could not be extracted. * .IP TLScontext->peer_fingerprint * Fingerprint of the certificate, or zero-length string when no peer * certificate is available. * .PP * If no peer certificate is presented the peer_status is set to 0. * LICENSE * .ad * .fi * This software is free. You can do with it whatever you want. * The original author kindly requests that you acknowledge * the use of his software. * AUTHOR(S) * Originally written by: * Lutz Jaenicke * BTU Cottbus * Allgemeine Elektrotechnik * Universitaetsplatz 3-4 * D-03044 Cottbus, Germany * * Updated by: * Wietse Venema * IBM T.J. Watson Research * P.O. Box 704 * Yorktown Heights, NY 10598, USA * * Victor Duchovni * Morgan Stanley *--*/ #include "StdAfx.h" #ifdef USE_TLS #ifdef ACL_UNIX # include #endif #include #include "dict.h" /* Global library. */ #include "tls_params.h" /* TLS library. */ #include "tls.h" #include "tls_mgr.h" #include "tls_private.h" #define STR(x) acl_vstring_str(x) #define LEN(x) ACL_VSTRING_LEN(x) /* Application-specific. */ /* * The session_id_context indentifies the service that created a session. * This information is used to distinguish between multiple TLS-based * servers running on the same server. We use the name of the mail system. */ static const char server_session_id_context[] = "Postfix/TLS"; #define GEN_CACHE_ID(buf, id, len, service) \ do { \ buf = acl_vstring_alloc(2 * (len) + 1 + strlen(service) + 3); \ acl_hex_encode(buf, (char *) (id), (len)); \ acl_vstring_sprintf_append(buf, "&s=%s", (service)); \ } while (0) /* get_server_session_cb - callback to retrieve session from server cache */ static SSL_SESSION *get_server_session_cb(SSL *ssl, unsigned char *session_id, int session_id_length, int *unused_copy acl_unused) { const char *myname = "get_server_session_cb"; TLS_SESS_STATE *TLScontext; ACL_VSTRING *cache_id; ACL_VSTRING *session_data = acl_vstring_alloc(2048); SSL_SESSION *session = 0; if ((TLScontext = SSL_get_ex_data(ssl, TLScontext_index)) == 0) acl_msg_panic("%s: null TLScontext in session lookup callback", myname); GEN_CACHE_ID(cache_id, session_id, session_id_length, TLScontext->serverid); if (TLScontext->log_level >= 2) acl_msg_info("%s: looking up session %s in %s cache", TLScontext->namaddr, STR(cache_id), TLScontext->cache_type); /* * Load the session from cache and decode it. */ if (tls_mgr_lookup(TLScontext->cache_type, STR(cache_id), session_data) == TLS_MGR_STAT_OK) { session = tls_session_activate(STR(session_data), (int) LEN(session_data)); if (session && (TLScontext->log_level >= 2)) acl_msg_info("%s: reloaded session %s from %s cache", TLScontext->namaddr, STR(cache_id), TLScontext->cache_type); } /* * Clean up. */ acl_vstring_free(cache_id); acl_vstring_free(session_data); return (session); } #if 0 /* uncache_session - remove session from internal & external cache */ static void uncache_session(SSL_CTX *ctx, TLS_SESS_STATE *TLScontext) { ACL_VSTRING *cache_id; SSL_SESSION *session = SSL_get_session(TLScontext->con); SSL_CTX_remove_session(ctx, session); if (TLScontext->cache_type == 0) return; GEN_CACHE_ID(cache_id, session->session_id, session->session_id_length, TLScontext->serverid); if (TLScontext->log_level >= 2) acl_msg_info("%s: remove session %s from %s cache", TLScontext->namaddr, STR(cache_id), TLScontext->cache_type); tls_mgr_delete(TLScontext->cache_type, STR(cache_id)); acl_vstring_free(cache_id); } #endif /* new_server_session_cb - callback to save session to server cache */ static int new_server_session_cb(SSL *ssl, SSL_SESSION *session) { const char *myname = "new_server_session_cb"; ACL_VSTRING *cache_id; TLS_SESS_STATE *TLScontext; ACL_VSTRING *session_data; if ((TLScontext = SSL_get_ex_data(ssl, TLScontext_index)) == 0) acl_msg_panic("%s: null TLScontext in new session callback", myname); GEN_CACHE_ID(cache_id, session->session_id, session->session_id_length, TLScontext->serverid); if (TLScontext->log_level >= 2) acl_msg_info("%s: save session %s to %s cache", TLScontext->namaddr, STR(cache_id), TLScontext->cache_type); /* * Passivate and save the session state. */ session_data = tls_session_passivate(session); if (session_data) { tls_mgr_update(TLScontext->cache_type, STR(cache_id), STR(session_data), (int) LEN(session_data)); /* * Clean up. */ acl_vstring_free(session_data); } acl_vstring_free(cache_id); SSL_SESSION_free(session); /* 200502 */ return (1); } /* tls_server_int - initialize the server-side TLS engine */ void tls_server_init() { tls_params_init(); if (!var_tlsmgr_stand_alone) tlsmgr_local_start(NULL); tls_threads_init(); } /* tls_server_setup - setup the server-side TLS engine */ int tls_server_setup(const TLS_SERVER_INIT_PROPS *props) { const char *myname = "tls_server_setup"; const EVP_MD *md_alg; unsigned int md_len; if (props->log_level >= 2) acl_msg_info("initializing the server-side TLS engine"); /* * Detect mismatch between compile-time headers and run-time library. */ tls_check_version(); /* * Initialize the OpenSSL library by the book! To start with, we must * initialize the algorithms. We want cleartext error messages instead of * just error codes, so we load the error_strings. */ SSL_load_error_strings(); OpenSSL_add_ssl_algorithms(); /* * Create an application data index for SSL objects, so that we can * attach TLScontext information; this information is needed inside * tls_verify_certificate_callback(). */ if (TLScontext_index < 0) { if ((TLScontext_index = SSL_get_ex_new_index(0, 0, 0, 0, 0)) < 0) { acl_msg_warn("%s: Cannot allocate SSL application data index: " "disabling TLS support", myname); return (-1); } } /* * If the administrator specifies an unsupported digest algorithm, fail * now, rather than in the middle of a TLS handshake. */ if ((md_alg = EVP_get_digestbyname(props->fpt_dgst)) == 0) { acl_msg_warn("%s: Digest algorithm \"%s\" not found: disabling TLS support", myname, props->fpt_dgst); return (-1); } /* * Sanity check: Newer shared libraries may use larger digests. */ if ((md_len = EVP_MD_size(md_alg)) > EVP_MAX_MD_SIZE) { acl_msg_warn("%s: Digest algorithm \"%s\" output size %u too large:" " disabling TLS support", myname, props->fpt_dgst, md_len); return (-1); } /* * Initialize the PRNG (Pseudo Random Number Generator) with some seed * from external and internal sources. Don't enable TLS without some real * entropy. */ if (var_tls_daemon_rand_bytes > 0 && tls_ext_seed(var_tls_daemon_rand_bytes) < 0) { acl_msg_warn("%s: no entropy for TLS key generation: disabling TLS support", myname); return (-1); } tls_int_seed(); return (0); } TLS_APPL_STATE *tls_server_create(const TLS_SERVER_INIT_PROPS *props) { const char *myname = "tls_server_create"; SSL_CTX *server_ctx; long off = 0; int verify_flags = SSL_VERIFY_NONE; int cachable; int protomask; TLS_APPL_STATE *app_ctx; tls_mgr_open(NULL); /* * First validate the protocols. If these are invalid, we can't continue. */ protomask = tls_protocol_mask(props->protocols); if (protomask == TLS_PROTOCOL_INVALID) { /* tls_protocol_mask() logs no warning. */ acl_msg_warn("%s: Invalid TLS protocol list \"%s\": disabling TLS support", myname, props->protocols); return (0); } /* * The SSL/TLS specifications require the client to send a message in the * oldest specification it understands with the highest level it * understands in the message. Netscape communicator can still * communicate with SSLv2 servers, so it sends out a SSLv2 client hello. * To deal with it, our server must be SSLv2 aware (even if we don't like * SSLv2), so we need to have the SSLv23 server here. If we want to limit * the protocol level, we can add an option to not use SSLv2/v3/TLSv1 * later. */ ERR_clear_error(); if ((server_ctx = SSL_CTX_new(SSLv23_server_method())) == 0) { acl_msg_warn("%s: cannot allocate server SSL_CTX: disabling TLS support", myname); tls_print_errors(); return (0); } /* * See the verify callback in tls_verify.c */ SSL_CTX_set_verify_depth(server_ctx, props->verifydepth + 1); /* * Protocol work-arounds, OpenSSL version dependent. */ off |= tls_bug_bits(); SSL_CTX_set_options(server_ctx, off); /* * Global protocol selection. */ if (protomask != 0) SSL_CTX_set_options(server_ctx, ((protomask & TLS_PROTOCOL_TLSv1) ? SSL_OP_NO_TLSv1 : 0L) | ((protomask & TLS_PROTOCOL_SSLv3) ? SSL_OP_NO_SSLv3 : 0L) | ((protomask & TLS_PROTOCOL_SSLv2) ? SSL_OP_NO_SSLv2 : 0L)); /* * Set the call-back routine to debug handshake progress. */ if (props->log_level >= 2) SSL_CTX_set_info_callback(server_ctx, tls_info_callback); /* * Load the CA public key certificates for both the server cert and for * the verification of client certificates. As provided by OpenSSL we * support two types of CA certificate handling: One possibility is to * add all CA certificates to one large CAfile, the other possibility is * a directory pointed to by CApath, containing separate files for each * CA with softlinks named after the hash values of the certificate. The * first alternative has the advantage that the file is opened and read * at startup time, so that you don't have the hassle to maintain another * copy of the CApath directory for chroot-jail. */ if (tls_set_ca_certificate_info(server_ctx, props->CAfile, props->CApath) < 0) { /* tls_set_ca_certificate_info() already logs a warning. */ SSL_CTX_free(server_ctx); /* 200411 */ return (0); } /* * Load the server public key certificate and private key from file and * check whether the cert matches the key. We can use RSA certificates * ("cert") DSA certificates ("dcert") or ECDSA certificates ("eccert"). * All three can be made available at the same time. The CA certificates * for all three are handled in the same setup already finished. Which * one is used depends on the cipher negotiated (that is: the first * cipher listed by the client which does match the server). A client * with RSA only (e.g. Netscape) will use the RSA certificate only. A * client with openssl-library will use RSA first if not especially * changed in the cipher setup. */ if (tls_set_my_certificate_key_info(server_ctx, props->cert_file, props->key_file, props->dcert_file, props->dkey_file, props->eccert_file, props->eckey_file) < 0) { /* tls_set_my_certificate_key_info() already logs a warning. */ SSL_CTX_free(server_ctx); /* 200411 */ return (0); } /* * According to the OpenSSL documentation, temporary RSA key is needed * export ciphers are in use. We have to provide one, so well, we just do * it. */ SSL_CTX_set_tmp_rsa_callback(server_ctx, tls_tmp_rsa_cb); /* * Diffie-Hellman key generation parameters can either be loaded from * files (preferred) or taken from compiled in values. First, set the * callback that will select the values when requested, then load the * (possibly) available DH parameters from files. We are generous with * the error handling, since we do have default values compiled in, so we * will not abort but just log the error message. */ SSL_CTX_set_tmp_dh_callback(server_ctx, tls_tmp_dh_cb); if (*props->dh1024_param_file != 0) tls_set_dh_from_file(props->dh1024_param_file, 1024); if (*props->dh512_param_file != 0) tls_set_dh_from_file(props->dh512_param_file, 512); /* * Enable EECDH if available, errors are not fatal, we just keep going * with any remaining key-exchange algorithms. */ (void) tls_set_eecdh_curve(server_ctx, props->eecdh_grade); /* * If we want to check client certificates, we have to indicate it in * advance. By now we only allow to decide on a global basis. If we want * to allow certificate based relaying, we must ask the client to provide * one with SSL_VERIFY_PEER. The client now can decide, whether it * provides one or not. We can enforce a failure of the negotiation with * SSL_VERIFY_FAIL_IF_NO_PEER_CERT, if we do not allow a connection * without one. In the "server hello" following the initialization by the * "client hello" the server must provide a list of CAs it is willing to * accept. Some clever clients will then select one from the list of * available certificates matching these CAs. Netscape Communicator will * present the list of certificates for selecting the one to be sent, or * it will issue a warning, if there is no certificate matching the * available CAs. * * With regard to the purpose of the certificate for relaying, we might like * a later negotiation, maybe relaying would already be allowed for other * reasons, but this would involve severe changes in the internal postfix * logic, so we have to live with it the way it is. */ if (props->ask_ccert) verify_flags = SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE; SSL_CTX_set_verify(server_ctx, verify_flags, tls_verify_certificate_callback); if (*props->CAfile) SSL_CTX_set_client_CA_list(server_ctx, SSL_load_client_CA_file(props->CAfile)); /* * Initialize our own TLS server handle, before diving into the details * of TLS session cache management. */ app_ctx = tls_alloc_app_context(server_ctx); /* * The session cache is implemented by the tlsmgr(8) server. * * XXX 200502 Surprise: when OpenSSL purges an entry from the in-memory * cache, it also attempts to purge the entry from the on-disk cache. * This is undesirable, especially when we set the in-memory cache size * to 1. For this reason we don't allow OpenSSL to purge on-disk cache * entries, and leave it up to the tlsmgr process instead. Found by * Victor Duchovni. */ if (props->cache_type == 0 || tls_mgr_policy(props->cache_type, &cachable) != TLS_MGR_STAT_OK) cachable = 0; if (cachable || props->set_sessid) { /* * Initialize the session cache. * * With a large number of concurrent smtpd(8) processes, it is not a * good idea to cache multiple large session objects in each process. * We set the internal cache size to 1, and don't register a * "remove_cb" so as to avoid deleting good sessions from the * external cache prematurely (when the internal cache is full, * OpenSSL removes sessions from the external cache also)! * * This makes SSL_CTX_remove_session() not useful for flushing broken * sessions from the external cache, so we must delete them directly * (not via a callback). * * Set a session id context to identify to what type of server process * created a session. In our case, the context is simply the name of * the mail system: "Postfix/TLS". */ SSL_CTX_sess_set_cache_size(server_ctx, 1); SSL_CTX_set_session_id_context(server_ctx, (void *) &server_session_id_context, sizeof(server_session_id_context)); SSL_CTX_set_session_cache_mode(server_ctx, SSL_SESS_CACHE_SERVER | SSL_SESS_CACHE_NO_AUTO_CLEAR); if (cachable) { app_ctx->cache_type = acl_mystrdup(props->cache_type); SSL_CTX_sess_set_get_cb(server_ctx, get_server_session_cb); SSL_CTX_sess_set_new_cb(server_ctx, new_server_session_cb); } /* * OpenSSL ignores timed-out sessions. We need to set the internal * cache timeout at least as high as the external cache timeout. This * applies even if no internal cache is used. */ SSL_CTX_set_timeout(server_ctx, props->scache_timeout); } else { /* * If we have no external cache, disable all caching. No use wasting * server memory resources with sessions they are unlikely to be able * to reuse. */ SSL_CTX_set_session_cache_mode(server_ctx, SSL_SESS_CACHE_OFF); } return (app_ctx); } /* * This is the actual startup routine for a new connection. We expect that * the SMTP buffers are flushed and the "220 Ready to start TLS" was sent to * the client, so that we can immediately start the TLS handshake process. */ TLS_SESS_STATE *tls_server_start(const TLS_SERVER_START_PROPS *props) { const char *myname = "tls_server_start"; int sts; TLS_SESS_STATE *TLScontext; SSL_CIPHER *cipher; X509 *peer; char buf[CCERT_BUFSIZ]; const char *cipher_list; TLS_APPL_STATE *app_ctx = props->ctx; if (props->log_level >= 1) acl_msg_info("%s: setting up TLS connection from %s", myname, props->namaddr); cipher_list = tls_set_ciphers(app_ctx, "TLS", props->cipher_grade, props->cipher_exclusions); if (cipher_list == 0) { acl_msg_warn("%s: %s: %s: aborting TLS session", myname, props->namaddr, acl_vstring_str(app_ctx->why)); return (0); } if (props->log_level >= 2) acl_msg_info("%s: %s: TLS cipher list \"%s\"", myname, props->namaddr, cipher_list); /* * Allocate a new TLScontext for the new connection and get an SSL * structure. Add the location of TLScontext to the SSL to later retrieve * the information inside the tls_verify_certificate_callback(). */ TLScontext = tls_alloc_sess_context(props->log_level, props->namaddr); TLScontext->cache_type = app_ctx->cache_type; TLScontext->serverid = acl_mystrdup(props->serverid); TLScontext->am_server = 1; ERR_clear_error(); if ((TLScontext->con = (SSL *) SSL_new(app_ctx->ssl_ctx)) == 0) { acl_msg_warn("%s: Could not allocate 'TLScontext->con' with SSL_new()", myname); tls_print_errors(); tls_free_context(TLScontext); return (0); } if (!SSL_set_ex_data(TLScontext->con, TLScontext_index, TLScontext)) { acl_msg_warn("%s: Could not set application data for 'TLScontext->con'", myname); tls_print_errors(); tls_free_context(TLScontext); return (0); } /* * The TLS connection is realized by a BIO_pair, so obtain the pair. * * XXX There is no need to store the internal_bio handle in the TLScontext * structure. It will be attached to and destroyed with TLScontext->con. * The network_bio, however, needs to be freed explicitly, so we need to * store its handle in TLScontext. */ if (!BIO_new_bio_pair(&TLScontext->internal_bio, TLS_BIO_BUFSIZE, &TLScontext->network_bio, TLS_BIO_BUFSIZE)) { acl_msg_warn("%s: Could not obtain BIO_pair", myname); tls_print_errors(); tls_free_context(TLScontext); return (0); } /* * Before really starting anything, try to seed the PRNG a little bit * more. */ tls_int_seed(); if (var_tls_daemon_rand_bytes > 0) (void) tls_ext_seed(var_tls_daemon_rand_bytes); /* * Initialize the SSL connection to accept state. This should not be * necessary anymore since 0.9.3, but the call is still in the library * and maintaining compatibility never hurts. */ SSL_set_accept_state(TLScontext->con); /* * Connect the SSL connection with the Postfix side of the BIO-pair for * reading and writing. */ SSL_set_bio(TLScontext->con, TLScontext->internal_bio, TLScontext->internal_bio); /* * If the debug level selected is high enough, all of the data is dumped: * 3 will dump the SSL negotiation, 4 will dump everything. * * We do have an SSL_set_fd() and now suddenly a BIO_ routine is called? * Well there is a BIO below the SSL routines that is automatically * created for us, so we can use it for debugging purposes. */ if (props->log_level >= 3) BIO_set_callback(SSL_get_rbio(TLScontext->con), tls_bio_dump_cb); /* * Start TLS negotiations. This process is a black box that invokes our * call-backs for session caching and certificate verification. * * Error handling: If the SSL handhake fails, we print out an error message * and remove all TLS state concerning this session. */ sts = tls_bio_accept(ACL_VSTREAM_SOCK(props->stream), props->timeout, TLScontext); if (sts <= 0) { acl_msg_info("SSL_accept error from %s: %d", props->namaddr, sts); tls_print_errors(); tls_free_context(TLScontext); return (0); } /* Only loglevel==4 dumps everything */ if (props->log_level < 4) BIO_set_callback(SSL_get_rbio(TLScontext->con), 0); /* * The caller may want to know if this session was reused or if a new * session was negotiated. */ TLScontext->session_reused = SSL_session_reused(TLScontext->con); if (TLScontext->log_level >= 2 && TLScontext->session_reused) acl_msg_info("%s: Reusing old session", TLScontext->namaddr); /* * Let's see whether a peer certificate is available and what is the * actual information. We want to save it for later use. */ peer = SSL_get_peer_certificate(TLScontext->con); if (peer != NULL) { TLScontext->peer_status |= TLS_CERT_FLAG_PRESENT; if (SSL_get_verify_result(TLScontext->con) == X509_V_OK) TLScontext->peer_status |= TLS_CERT_FLAG_TRUSTED; if (props->log_level >= 2) { X509_NAME_oneline(X509_get_subject_name(peer), buf, sizeof(buf)); acl_msg_info("subject=%s", buf); X509_NAME_oneline(X509_get_issuer_name(peer), buf, sizeof(buf)); acl_msg_info("issuer=%s", buf); } TLScontext->peer_CN = tls_peer_CN(peer, TLScontext); TLScontext->issuer_CN = tls_issuer_CN(peer, TLScontext); TLScontext->peer_fingerprint = tls_fingerprint(peer, props->fpt_dgst); if (props->log_level >= 1) { acl_msg_info("%s: %s: subject_CN=%s, issuer=%s, fingerprint=%s", props->namaddr, TLS_CERT_IS_TRUSTED(TLScontext) ? "Trusted" : "Untrusted", TLScontext->peer_CN, TLScontext->issuer_CN, TLScontext->peer_fingerprint); } X509_free(peer); } else { TLScontext->peer_CN = acl_mystrdup(""); TLScontext->issuer_CN = acl_mystrdup(""); TLScontext->peer_fingerprint = acl_mystrdup(""); } /* * Finally, collect information about protocol and cipher for logging */ TLScontext->protocol = SSL_get_version(TLScontext->con); cipher = SSL_get_current_cipher(TLScontext->con); TLScontext->cipher_name = SSL_CIPHER_get_name(cipher); TLScontext->cipher_usebits = SSL_CIPHER_get_bits(cipher, &(TLScontext->cipher_algbits)); /* * The TLS engine is active. Switch to the tls_timed_read/write() * functions and make the TLScontext available to those functions. */ tls_stream_start(props->stream, TLScontext); /* * All the key facts in a single log entry. */ if (props->log_level >= 1) acl_msg_info("%s TLS connection established from %s: %s with cipher %s " "(%d/%d bits)", !TLS_CERT_IS_PRESENT(TLScontext) ? "Anonymous" : TLS_CERT_IS_TRUSTED(TLScontext) ? "Trusted" : "Untrusted", props->namaddr, TLScontext->protocol, TLScontext->cipher_name, TLScontext->cipher_usebits, TLScontext->cipher_algbits); tls_int_seed(); return (TLScontext); } #endif /* USE_TLS */