/*++ /* NAME /* tls_server 3 /* SUMMARY /* server-side TLS engine /* SYNOPSIS /* #include <tls.h> /* /* SSL_CTX *tls_server_init(props) /* const tls_server_props *props; /* /* TLScontext_t *tls_server_start(props) /* const tls_server_start_props *props; /* /* void tls_server_stop(server_ctx, stream, failure, TLScontext) /* SSL_CTX *server_ctx; /* VSTREAM *stream; /* int failure; /* TLScontext_t *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, so we don't care about additional data /* coming through the channel. /* 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. /* /* The status of the peer certificate verification is available in /* TLScontext->peer_verified. It is set to 1 when the certificate could /* be verified. /* If the peer offered a certificate, part of the certificate data are /* available as: /* .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 null pointer when no /* certificate digest is available. /* .PP /* Otherwise these fields are set to null pointers. /* 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 /*--*/ /* System library. */ #include <sys_defs.h> #ifdef USE_TLS #include <unistd.h> #include <string.h> /* Utility library. */ #include <mymalloc.h> #include <vstring.h> #include <vstream.h> #include <dict.h> #include <stringops.h> #include <msg.h> #include <hex_code.h> /* Global library. */ #include <mail_params.h> /* TLS library. */ #include <tls_mgr.h> #define TLS_INTERNAL #include <tls.h> #define STR(x) vstring_str(x) #define LEN(x) VSTRING_LEN(x) /* Application-specific. */ /* We must keep some of the info available */ static const char hexcodes[] = "0123456789ABCDEF"; /* * 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 char server_session_id_context[] = "Postfix/TLS"; /* 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) { const char *myname = "get_server_session_cb"; TLScontext_t *TLScontext; VSTRING *cache_id; VSTRING *session_data = vstring_alloc(2048); SSL_SESSION *session = 0; if ((TLScontext = SSL_get_ex_data(ssl, TLScontext_index)) == 0) msg_panic("%s: null TLScontext in session lookup callback", myname); #define GEN_CACHE_ID(buf, id, len, service) \ do { \ buf = vstring_alloc(2 * (len) + 1 + strlen(service) + 3); \ hex_encode(buf, (char *) (id), (len)); \ vstring_sprintf_append(buf, "&s=%s", (service)); \ } while (0) GEN_CACHE_ID(cache_id, session_id, session_id_length, TLScontext->serverid); if (TLScontext->log_level >= 2) msg_info("looking up session %s in %s cache", 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), LEN(session_data)); if (session && (TLScontext->log_level >= 2)) msg_info("reloaded session %s from %s cache", STR(cache_id), TLScontext->cache_type); } /* * Clean up. */ vstring_free(cache_id); vstring_free(session_data); return (session); } /* uncache_session - remove session from internal & external cache */ static void uncache_session(SSL_CTX *ctx, TLScontext_t *TLScontext) { 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) msg_info("remove session %s from %s cache", STR(cache_id), TLScontext->cache_type); tls_mgr_delete(TLScontext->cache_type, STR(cache_id)); vstring_free(cache_id); } /* 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"; VSTRING *cache_id; TLScontext_t *TLScontext; VSTRING *session_data; if ((TLScontext = SSL_get_ex_data(ssl, TLScontext_index)) == 0) 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) msg_info("save session %s to %s cache", 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), LEN(session_data)); /* * Clean up. */ if (session_data) vstring_free(session_data); vstring_free(cache_id); SSL_SESSION_free(session); /* 200502 */ return (1); } /* tls_server_init - initialize the server-side TLS engine */ SSL_CTX *tls_server_init(const tls_server_props *props) { long off = 0; int verify_flags = SSL_VERIFY_NONE; SSL_CTX *server_ctx; int cachable; /* See skeleton at OpenSSL apps/s_server.c. */ if (props->log_level >= 2) 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(); /* * Initialize the PRNG (Pseudo Random Number Generator) with some seed * from external and internal sources. Don't enable TLS without some real * entropy. */ if (tls_ext_seed(var_tls_daemon_rand_bytes) < 0) { msg_warn("no entropy for TLS key generation: disabling TLS support"); return (0); } tls_int_seed(); /* * 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. */ server_ctx = SSL_CTX_new(SSLv23_server_method()); if (server_ctx == NULL) { tls_print_errors(); return (0); } /* * Protocol work-arounds, OpenSSL version dependent. */ off |= tls_bug_bits(); SSL_CTX_set_options(server_ctx, off); #define DISABLE_ALL (SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3 | SSL_OP_NO_TLSv1) /* * Global protocol selection. Not enabling any explicitly, enables all. */ if (props->protocols != 0 && props->protocols != TLS_ALL_PROTOCOLS) { long disable = DISABLE_ALL; if (props->protocols & TLS_PROTOCOL_TLSv1) disable &= ~SSL_OP_NO_TLSv1; if (props->protocols & TLS_PROTOCOL_SSLv3) disable &= ~SSL_OP_NO_SSLv3; if (props->protocols & TLS_PROTOCOL_SSLv2) disable &= ~SSL_OP_NO_SSLv2; SSL_CTX_set_options(server_ctx, disable); } /* * Set the call-back routine for verbose logging. */ if (props->log_level >= 2) SSL_CTX_set_info_callback(server_ctx, tls_info_callback); /* * Override the default cipher list with our own list. */ if (tls_set_cipher_list(server_ctx, props->cipherlist) == 0) { SSL_CTX_free(server_ctx); msg_warn("Invalid cipherlist \"%s\": disabling TLS support", props->cipherlist); return (0); /* Already logged */ } /* * 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) { 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 cannot run without (we do * not support ADH anonymous Diffie-Hellman ciphers as of now). We can * use RSA certificates ("cert") and DSA certificates ("dcert"), both can * be made available at the same time. The CA certificates for both 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) < 0) { 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_1024_from_file(props->dh1024_param_file); if (*props->dh512_param_file != 0) tls_set_dh_512_from_file(props->dh512_param_file); /* * 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)); /* * 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 (TLSscache_index < 0) TLSscache_index = SSL_CTX_get_ex_new_index(0, "TLScontext ex_data index", NULL, NULL, NULL); if (tls_mgr_policy(props->cache_type, &cachable) != TLS_MGR_STAT_OK) cachable = 0; if (cachable && !SSL_CTX_set_ex_data(server_ctx, TLSscache_index, (void *) props->cache_type)) { msg_warn("Session cache off: error saving cache type in SSL context."); tls_print_errors(); 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) { 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); } /* * Create a global index so that we can attach TLScontext information to * SSL objects; this information is needed inside * tls_verify_certificate_callback(). */ if (TLScontext_index < 0) TLScontext_index = SSL_get_ex_new_index(0, "TLScontext ex_data index", NULL, NULL, NULL); return (server_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. */ TLScontext_t *tls_server_start(const tls_server_start_props *props) { int sts; int j; int verify_flags; unsigned int n; TLScontext_t *TLScontext; SSL_CIPHER *cipher; X509 *peer; unsigned char md[EVP_MAX_MD_SIZE]; char buf[CCERT_BUFSIZ]; if (props->log_level >= 1) msg_info("setting up TLS connection from %s[%s]", props->peername, props->peeraddr); /* * 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_context(props->log_level, props->peername); TLScontext->cache_type = SSL_CTX_get_ex_data(props->ctx, TLSscache_index); TLScontext->serverid = mystrdup(props->serverid); if ((TLScontext->con = (SSL *) SSL_new(props->ctx)) == NULL) { msg_warn("Could not allocate 'TLScontext->con' with SSL_new()"); tls_print_errors(); tls_free_context(TLScontext); return (0); } if (!SSL_set_ex_data(TLScontext->con, TLScontext_index, TLScontext)) { msg_warn("Could not set application data for 'TLScontext->con'"); tls_print_errors(); tls_free_context(TLScontext); return (0); } /* * Set the verification parameters to be checked in * tls_verify_certificate_callback(). */ if (props->requirecert) { verify_flags = SSL_VERIFY_PEER | SSL_VERIFY_CLIENT_ONCE; verify_flags |= SSL_VERIFY_FAIL_IF_NO_PEER_CERT; TLScontext->enforce_verify_errors = 1; SSL_set_verify(TLScontext->con, verify_flags, tls_verify_certificate_callback); } else { TLScontext->enforce_verify_errors = 0; } TLScontext->enforce_CN = 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)) { msg_warn("Could not obtain BIO_pair"); 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(); (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(vstream_fileno(props->stream), props->timeout, TLScontext); if (sts <= 0) { msg_info("SSL_accept error from %s[%s]: %d", props->peername, props->peeraddr, 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 (props->log_level >= 2 && TLScontext->session_reused) msg_info("Reusing old session"); /* * 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) { if (SSL_get_verify_result(TLScontext->con) == X509_V_OK) TLScontext->peer_verified = 1; if (props->log_level >= 2) { X509_NAME_oneline(X509_get_subject_name(peer), buf, sizeof(buf)); msg_info("subject=%s", buf); X509_NAME_oneline(X509_get_issuer_name(peer), buf, sizeof(buf)); msg_info("issuer=%s", buf); } if (X509_digest(peer, EVP_md5(), md, &n) && n > 0) { TLScontext->peer_fingerprint = mymalloc(n * 3); for (j = 0; j < (int) n; j++) { TLScontext->peer_fingerprint[j * 3] = hexcodes[(md[j] & 0xf0) >> 4U]; TLScontext->peer_fingerprint[(j * 3) + 1] = hexcodes[(md[j] & 0x0f)]; if (j + 1 != (int) n) TLScontext->peer_fingerprint[(j * 3) + 2] = ':'; else TLScontext->peer_fingerprint[(j * 3) + 2] = '\0'; } if (props->log_level >= 1) msg_info("fingerprint=%s", TLScontext->peer_fingerprint); } if ((TLScontext->peer_CN = tls_peer_CN(peer)) == 0) TLScontext->peer_CN = mystrdup(""); if ((TLScontext->issuer_CN = tls_issuer_CN(peer)) == 0) TLScontext->issuer_CN = mystrdup(""); if (props->log_level >= 1) { if (TLScontext->peer_verified) msg_info("Verified: subject_CN=%s, issuer=%s", TLScontext->peer_CN, TLScontext->issuer_CN); else msg_info("Unverified: subject_CN=%s, issuer=%s", TLScontext->peer_CN, TLScontext->issuer_CN); } X509_free(peer); } /* * If this is a cached session, we have to check by hand if the cached * session peer was verified. */ if (props->requirecert) { if (!TLScontext->peer_verified || !TLScontext->peer_CN) { if (TLScontext->session_reused == 0) msg_panic("tls_server_start: peer was not verified"); msg_info("Re-used session without peer certificate removed"); uncache_session(props->ctx, TLScontext); tls_free_context(TLScontext); return (0); } } /* * 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); if (props->log_level >= 1) msg_info("TLS connection established from %s[%s]: %s with cipher %s (%d/%d bits)", props->peername, props->peeraddr, TLScontext->protocol, TLScontext->cipher_name, TLScontext->cipher_usebits, TLScontext->cipher_algbits); tls_int_seed(); return (TLScontext); } #endif /* USE_TLS */