diff options
Diffstat (limited to 'src/tls/tls_server.c')
| -rw-r--r-- | src/tls/tls_server.c | 1032 |
1 files changed, 1032 insertions, 0 deletions
diff --git a/src/tls/tls_server.c b/src/tls/tls_server.c new file mode 100644 index 0000000..8b94c3c --- /dev/null +++ b/src/tls/tls_server.c @@ -0,0 +1,1032 @@ +/*++ +/* NAME +/* tls_server 3 +/* SUMMARY +/* server-side TLS engine +/* SYNOPSIS +/* #include <tls.h> +/* +/* 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; +/* +/* TLS_SESS_STATE *tls_server_post_accept(TLScontext) +/* TLS_SESS_STATE *TLScontext; +/* +/* 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. +/* +/* See "EVENT_DRIVEN APPLICATIONS" below for using this code +/* in event-driven programs. +/* +/* 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_cert_fprint +/* 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. +/* EVENT_DRIVEN APPLICATIONS +/* .ad +/* .fi +/* Event-driven programs manage multiple I/O channels. Such +/* programs cannot use the synchronous VSTREAM-over-TLS +/* implementation that the current TLS library provides, +/* including tls_server_stop() and the underlying tls_stream(3) +/* and tls_bio_ops(3) routines. +/* +/* With the current TLS library implementation, this means +/* that the application is responsible for calling and retrying +/* SSL_accept(), SSL_read(), SSL_write() and SSL_shutdown(). +/* +/* To maintain control over TLS I/O, an event-driven server +/* invokes tls_server_start() with a null VSTREAM argument and +/* with an fd argument that specifies the I/O file descriptor. +/* Then, tls_server_start() performs all the necessary +/* preparations before the TLS handshake and returns a partially +/* populated TLS context. The event-driven application is then +/* responsible for invoking SSL_accept(), and if successful, +/* for invoking tls_server_post_accept() to finish the work +/* that was started by tls_server_start(). In case of unrecoverable +/* failure, tls_server_post_accept() destroys the TLS context +/* and returns a null pointer value. +/* 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 +/*--*/ + +/* 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> +#include <iostuff.h> /* non-blocking */ + +/* 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. */ + + /* + * 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"; + +#ifndef OPENSSL_NO_TLSEXT + /* + * We retain the cipher handle for lifetime of the process, it is not freed. + */ +static const EVP_CIPHER *tkt_cipher; +#endif + +#define GET_SID(s, v, lptr) ((v) = SSL_SESSION_get_id((s), (lptr))) + + /* OpenSSL 1.1.0 bitrot */ +#if OPENSSL_VERSION_NUMBER >= 0x10100000L +typedef const unsigned char *session_id_t; + +#else +typedef unsigned char *session_id_t; + +#endif + +/* get_server_session_cb - callback to retrieve session from server cache */ + +static SSL_SESSION *get_server_session_cb(SSL *ssl, session_id_t session_id, + int session_id_length, + int *unused_copy) +{ + const char *myname = "get_server_session_cb"; + TLS_SESS_STATE *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 + strlen(service))); \ + hex_encode(buf, (char *) (id), (len)); \ + vstring_sprintf_append(buf, "&s=%s", (service)); \ + vstring_sprintf_append(buf, "&l=%ld", (long) OpenSSL_version_num()); \ + } while (0) + + + GEN_CACHE_ID(cache_id, session_id, session_id_length, TLScontext->serverid); + + if (TLScontext->log_mask & TLS_LOG_CACHE) + 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), LEN(session_data)); + if (session && (TLScontext->log_mask & TLS_LOG_CACHE)) + msg_info("%s: reloaded session %s from %s cache", + TLScontext->namaddr, 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, TLS_SESS_STATE *TLScontext) +{ + VSTRING *cache_id; + SSL_SESSION *session = SSL_get_session(TLScontext->con); + const unsigned char *sid; + unsigned int sid_length; + + SSL_CTX_remove_session(ctx, session); + + if (TLScontext->cache_type == 0) + return; + + GET_SID(session, sid, &sid_length); + GEN_CACHE_ID(cache_id, sid, sid_length, TLScontext->serverid); + + if (TLScontext->log_mask & TLS_LOG_CACHE) + 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)); + 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; + TLS_SESS_STATE *TLScontext; + VSTRING *session_data; + const unsigned char *sid; + unsigned int sid_length; + + if ((TLScontext = SSL_get_ex_data(ssl, TLScontext_index)) == 0) + msg_panic("%s: null TLScontext in new session callback", myname); + + GET_SID(session, sid, &sid_length); + GEN_CACHE_ID(cache_id, sid, sid_length, TLScontext->serverid); + + if (TLScontext->log_mask & TLS_LOG_CACHE) + 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), LEN(session_data)); + + /* + * Clean up. + */ + if (session_data) + vstring_free(session_data); + vstring_free(cache_id); + SSL_SESSION_free(session); /* 200502 */ + + return (1); +} + +#define NOENGINE ((ENGINE *) 0) +#define TLS_TKT_NOKEYS -1 /* No keys for encryption */ +#define TLS_TKT_STALE 0 /* No matching keys for decryption */ +#define TLS_TKT_ACCEPT 1 /* Ticket decryptable and re-usable */ +#define TLS_TKT_REISSUE 2 /* Ticket decryptable, not re-usable */ + +/* ticket_cb - configure tls session ticket encrypt/decrypt context */ + +#if !defined(OPENSSL_NO_TLSEXT) + +static int ticket_cb(SSL *con, unsigned char name[], unsigned char iv[], + EVP_CIPHER_CTX * ctx, HMAC_CTX * hctx, int create) +{ + static const EVP_MD *sha256; + TLS_TICKET_KEY *key; + TLS_SESS_STATE *TLScontext = SSL_get_ex_data(con, TLScontext_index); + int timeout = ((int) SSL_CTX_get_timeout(SSL_get_SSL_CTX(con))) / 2; + + if ((!sha256 && (sha256 = EVP_sha256()) == 0) + || (key = tls_mgr_key(create ? 0 : name, timeout)) == 0 + || (create && RAND_bytes(iv, TLS_TICKET_IVLEN) <= 0)) + return (create ? TLS_TKT_NOKEYS : TLS_TKT_STALE); + + HMAC_Init_ex(hctx, key->hmac, TLS_TICKET_MACLEN, sha256, NOENGINE); + + if (create) { + EVP_EncryptInit_ex(ctx, tkt_cipher, NOENGINE, key->bits, iv); + memcpy((void *) name, (void *) key->name, TLS_TICKET_NAMELEN); + if (TLScontext->log_mask & TLS_LOG_CACHE) + msg_info("%s: Issuing session ticket, key expiration: %ld", + TLScontext->namaddr, (long) key->tout); + } else { + EVP_DecryptInit_ex(ctx, tkt_cipher, NOENGINE, key->bits, iv); + if (TLScontext->log_mask & TLS_LOG_CACHE) + msg_info("%s: Decrypting session ticket, key expiration: %ld", + TLScontext->namaddr, (long) key->tout); + } + TLScontext->ticketed = 1; + return (TLS_TKT_ACCEPT); +} + +#endif + +/* tls_server_init - initialize the server-side TLS engine */ + +TLS_APPL_STATE *tls_server_init(const TLS_SERVER_INIT_PROPS *props) +{ + SSL_CTX *server_ctx; + SSL_CTX *sni_ctx; + X509_STORE *cert_store; + long off = 0; + int verify_flags = SSL_VERIFY_NONE; + int cachable; + int scache_timeout; + int ticketable = 0; + int protomask; + TLS_APPL_STATE *app_ctx; + int log_mask; + + /* + * Convert user loglevel to internal logmask. + */ + log_mask = tls_log_mask(props->log_param, props->log_level); + + if (log_mask & TLS_LOG_VERBOSE) + msg_info("initializing the server-side TLS engine"); + + /* + * Load (mostly cipher related) TLS-library internal main.cf parameters. + */ + tls_param_init(); + + /* + * Detect mismatch between compile-time headers and run-time library. + */ + tls_check_version(); + +#if OPENSSL_VERSION_NUMBER < 0x10100000L + + /* + * 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(); +#endif + + /* + * Initialize the OpenSSL library, possibly loading its configuration + * file. + */ + if (tls_library_init() == 0) + return (0); + + /* + * 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. */ + msg_warn("Invalid TLS protocol list \"%s\": disabling TLS support", + props->protocols); + return (0); + } + + /* + * 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) { + msg_warn("Cannot allocate SSL application data index: " + "disabling TLS support"); + return (0); + } + } + + /* + * If the administrator specifies an unsupported digest algorithm, fail + * now, rather than in the middle of a TLS handshake. + */ + if (!tls_validate_digest(props->mdalg)) { + msg_warn("disabling TLS support"); + return (0); + } + + /* + * 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. + */ + ERR_clear_error(); + server_ctx = SSL_CTX_new(TLS_server_method()); + if (server_ctx == 0) { + msg_warn("cannot allocate server SSL_CTX: disabling TLS support"); + tls_print_errors(); + return (0); + } + sni_ctx = SSL_CTX_new(TLS_server_method()); + if (sni_ctx == 0) { + SSL_CTX_free(server_ctx); + msg_warn("cannot allocate server SNI SSL_CTX: disabling TLS support"); + tls_print_errors(); + return (0); + } +#ifdef SSL_SECOP_PEER + /* Backwards compatible security as a base for opportunistic TLS. */ + SSL_CTX_set_security_level(server_ctx, 0); + SSL_CTX_set_security_level(sni_ctx, 0); +#endif + + /* + * See the verify callback in tls_verify.c + */ + SSL_CTX_set_verify_depth(server_ctx, props->verifydepth + 1); + SSL_CTX_set_verify_depth(sni_ctx, props->verifydepth + 1); + + /* + * 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 (tls_mgr_policy(props->cache_type, &cachable, + &scache_timeout) != TLS_MGR_STAT_OK) + scache_timeout = 0; + if (scache_timeout <= 0) + cachable = 0; + + /* + * Presently we use TLS only with SMTP where truncation attacks are not + * possible as a result of application framing. If we ever use TLS in + * some other application protocol where truncation could be relevant, + * we'd need to disable truncation detection conditionally, or explicitly + * clear the option in that code path. + */ + off |= SSL_OP_IGNORE_UNEXPECTED_EOF; + + /* + * Protocol work-arounds, OpenSSL version dependent. + */ + off |= tls_bug_bits(); + + /* + * Add SSL_OP_NO_TICKET when the timeout is zero or library support is + * incomplete. + */ +#ifndef OPENSSL_NO_TLSEXT + ticketable = (*var_tls_tkt_cipher && scache_timeout > 0 + && !(off & SSL_OP_NO_TICKET)); + if (ticketable) { +#if OPENSSL_VERSION_PREREQ(3,0) + tkt_cipher = EVP_CIPHER_fetch(NULL, var_tls_tkt_cipher, NULL); +#else + tkt_cipher = EVP_get_cipherbyname(var_tls_tkt_cipher); +#endif + if (tkt_cipher == 0 + || EVP_CIPHER_mode(tkt_cipher) != EVP_CIPH_CBC_MODE + || EVP_CIPHER_iv_length(tkt_cipher) != TLS_TICKET_IVLEN + || EVP_CIPHER_key_length(tkt_cipher) < TLS_TICKET_IVLEN + || EVP_CIPHER_key_length(tkt_cipher) > TLS_TICKET_KEYLEN) { + msg_warn("%s: invalid value: %s; session tickets disabled", + VAR_TLS_TKT_CIPHER, var_tls_tkt_cipher); + ticketable = 0; + } + } + if (ticketable) { + SSL_CTX_set_tlsext_ticket_key_cb(server_ctx, ticket_cb); + + /* + * OpenSSL 1.1.1 introduces support for TLS 1.3, which can issue more + * than one ticket per handshake. While this may be appropriate for + * communication between browsers and webservers, it is not terribly + * useful for MTAs, many of which other than Postfix don't do TLS + * session caching at all, and Postfix has no mechanism for storing + * multiple session tickets, if more than one sent, the second + * clobbers the first. OpenSSL 1.1.1 servers default to issuing two + * tickets for non-resumption handshakes, we reduce this to one. Our + * ticket decryption callback already (since 2.11) asks OpenSSL to + * avoid issuing new tickets when the presented ticket is re-usable. + */ + SSL_CTX_set_num_tickets(server_ctx, 1); + } +#endif + if (!ticketable) + off |= SSL_OP_NO_TICKET; + + SSL_CTX_set_options(server_ctx, off); + + /* Enable all supported protocols */ +#if OPENSSL_VERSION_NUMBER >= 0x1010000fUL + SSL_CTX_set_min_proto_version(server_ctx, 0); + SSL_CTX_set_min_proto_version(sni_ctx, 0); +#endif + + /* + * Global protocol selection. + */ + if (protomask != 0) + SSL_CTX_set_options(server_ctx, TLS_SSL_OP_PROTOMASK(protomask)); + + /* + * Some sites may want to give the client less rope. On the other hand, + * this could trigger inter-operability issues, the client should not + * offer ciphers it implements poorly, but this hasn't stopped some + * vendors from getting it wrong. + */ + if (var_tls_preempt_clist) + SSL_CTX_set_options(server_ctx, SSL_OP_CIPHER_SERVER_PREFERENCE); + + /* Done with server_ctx options, clone to sni_ctx */ + SSL_CTX_clear_options(sni_ctx, ~0); + SSL_CTX_set_options(sni_ctx, SSL_CTX_get_options(server_ctx)); + + /* + * Set the call-back routine to debug handshake progress. + */ + if (log_mask & TLS_LOG_DEBUG) { + SSL_CTX_set_info_callback(server_ctx, tls_info_callback); + SSL_CTX_set_info_callback(sni_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 */ + SSL_CTX_free(sni_ctx); + return (0); + } + + /* + * Upref and share the cert store. Sadly we can't yet use + * SSL_CTX_set1_cert_store(3) which was added in OpenSSL 1.1.0. + */ + cert_store = SSL_CTX_get_cert_store(server_ctx); + X509_STORE_up_ref(cert_store); + SSL_CTX_set_cert_store(sni_ctx, cert_store); + + /* + * 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->chain_files, + 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 */ + SSL_CTX_free(sni_ctx); + return (0); + } + + /* + * 2015-12-05: Ephemeral RSA removed from OpenSSL 1.1.0-dev + */ +#if OPENSSL_VERSION_NUMBER < 0x10100000L + + /* + * According to OpenSSL documentation, a temporary RSA key is needed when + * export ciphers are in use, because the certified key cannot be + * directly used. + */ + SSL_CTX_set_tmp_rsa_callback(server_ctx, tls_tmp_rsa_cb); + SSL_CTX_set_tmp_rsa_callback(sni_ctx, tls_tmp_rsa_cb); +#endif + + /* + * 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); + SSL_CTX_set_tmp_dh_callback(sni_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. + */ + tls_set_eecdh_curve(server_ctx, props->eecdh_grade); + tls_set_eecdh_curve(sni_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); + SSL_CTX_set_verify(sni_ctx, verify_flags, + tls_verify_certificate_callback); + if (props->ask_ccert && *props->CAfile) { + STACK_OF(X509_NAME) *calist = SSL_load_client_CA_file(props->CAfile); + + if (calist == 0) { + /* Not generally critical */ + msg_warn("error loading client CA names from: %s", + props->CAfile); + tls_print_errors(); + } + SSL_CTX_set_client_CA_list(server_ctx, calist); + + if (calist != 0 && sk_X509_NAME_num(calist) > 0) { + calist = SSL_dup_CA_list(calist); + + if (calist == 0) { + msg_warn("error duplicating client CA names for SNI"); + tls_print_errors(); + } else { + SSL_CTX_set_client_CA_list(sni_ctx, calist); + } + } + } + + /* + * Initialize our own TLS server handle, before diving into the details + * of TLS session cache management. + */ + app_ctx = tls_alloc_app_context(server_ctx, sni_ctx, log_mask); + + if (cachable || ticketable || 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_INTERNAL | + SSL_SESS_CACHE_NO_AUTO_CLEAR); + if (cachable) { + app_ctx->cache_type = 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. We set the session + * lifetime to twice the cache lifetime, which is also the issuing + * and retired key validation lifetime of session tickets keys. This + * way a session always lasts longer than the server's ability to + * decrypt its session ticket. Otherwise, a bug in OpenSSL may fail + * to re-issue tickets when sessions decrypt, but are expired. + */ + SSL_CTX_set_timeout(server_ctx, 2 * 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) +{ + int sts; + TLS_SESS_STATE *TLScontext; + const char *cipher_list; + TLS_APPL_STATE *app_ctx = props->ctx; + int log_mask = app_ctx->log_mask; + + /* + * Implicitly enable logging of trust chain errors when verified certs + * are required. + */ + if (props->requirecert) + log_mask |= TLS_LOG_UNTRUSTED; + + if (log_mask & TLS_LOG_VERBOSE) + msg_info("setting up TLS connection from %s", props->namaddr); + + /* + * 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(log_mask, props->namaddr); + TLScontext->cache_type = app_ctx->cache_type; + + ERR_clear_error(); + if ((TLScontext->con = (SSL *) SSL_new(app_ctx->ssl_ctx)) == 0) { + msg_warn("Could not allocate 'TLScontext->con' with SSL_new()"); + tls_print_errors(); + tls_free_context(TLScontext); + return (0); + } + cipher_list = tls_set_ciphers(TLScontext, props->cipher_grade, + props->cipher_exclusions); + if (cipher_list == 0) { + /* already warned */ + tls_free_context(TLScontext); + return (0); + } + if (log_mask & TLS_LOG_VERBOSE) + msg_info("%s: TLS cipher list \"%s\"", props->namaddr, cipher_list); + + TLScontext->serverid = mystrdup(props->serverid); + TLScontext->am_server = 1; + TLScontext->stream = props->stream; + TLScontext->mdalg = props->mdalg; + + 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); + } +#ifdef SSL_SECOP_PEER + /* When authenticating the peer, use 80-bit plus OpenSSL security level */ + if (props->requirecert) + SSL_set_security_level(TLScontext->con, 1); +#endif + + /* + * 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); + + /* + * Connect the SSL connection with the network socket. + */ + if (SSL_set_fd(TLScontext->con, props->stream == 0 ? props->fd : + vstream_fileno(props->stream)) != 1) { + msg_info("SSL_set_fd error to %s", props->namaddr); + tls_print_errors(); + uncache_session(app_ctx->ssl_ctx, TLScontext); + tls_free_context(TLScontext); + return (0); + } + + /* + * If the debug level selected is high enough, all of the data is dumped: + * TLS_LOG_TLSPKTS will dump the SSL negotiation, TLS_LOG_ALLPKTS 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 (log_mask & TLS_LOG_TLSPKTS) + BIO_set_callback(SSL_get_rbio(TLScontext->con), tls_bio_dump_cb); + + /* + * If we don't trigger the handshake in the library, leave control over + * SSL_accept/read/write/etc with the application. + */ + if (props->stream == 0) + return (TLScontext); + + /* + * Turn on non-blocking I/O so that we can enforce timeouts on network + * I/O. + */ + non_blocking(vstream_fileno(props->stream), NON_BLOCKING); + + /* + * 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 handshake 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) { + if (ERR_peek_error() != 0) { + msg_info("SSL_accept error from %s: %d", props->namaddr, sts); + tls_print_errors(); + } else if (errno != 0) { + msg_info("SSL_accept error from %s: %m", props->namaddr); + } else { + msg_info("SSL_accept error from %s: lost connection", + props->namaddr); + } + tls_free_context(TLScontext); + return (0); + } + return (tls_server_post_accept(TLScontext)); +} + +/* tls_server_post_accept - post-handshake processing */ + +TLS_SESS_STATE *tls_server_post_accept(TLS_SESS_STATE *TLScontext) +{ + const SSL_CIPHER *cipher; + X509 *peer; + char buf[CCERT_BUFSIZ]; + + /* Turn off packet dump if only dumping the handshake */ + if ((TLScontext->log_mask & TLS_LOG_ALLPKTS) == 0) + 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_mask & TLS_LOG_CACHE) && TLScontext->session_reused) + msg_info("%s: Reusing old session%s", TLScontext->namaddr, + TLScontext->ticketed ? " (RFC 5077 session ticket)" : ""); + + /* + * 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 (TLScontext->log_mask & TLS_LOG_VERBOSE) { + X509_NAME_oneline(X509_get_subject_name(peer), + buf, sizeof(buf)); + msg_info("subject=%s", printable(buf, '?')); + X509_NAME_oneline(X509_get_issuer_name(peer), + buf, sizeof(buf)); + msg_info("issuer=%s", printable(buf, '?')); + } + TLScontext->peer_CN = tls_peer_CN(peer, TLScontext); + TLScontext->issuer_CN = tls_issuer_CN(peer, TLScontext); + TLScontext->peer_cert_fprint = tls_cert_fprint(peer, TLScontext->mdalg); + TLScontext->peer_pkey_fprint = tls_pkey_fprint(peer, TLScontext->mdalg); + + if (TLScontext->log_mask & (TLS_LOG_VERBOSE | TLS_LOG_PEERCERT)) { + msg_info("%s: subject_CN=%s, issuer=%s, fingerprint=%s" + ", pkey_fingerprint=%s", + TLScontext->namaddr, + TLScontext->peer_CN, TLScontext->issuer_CN, + TLScontext->peer_cert_fprint, + TLScontext->peer_pkey_fprint); + } + X509_free(peer); + + /* + * Give them a clue. Problems with trust chain verification are + * logged when the session is first negotiated, before the session is + * stored into the cache. We don't want mystery failures, so log the + * fact the real problem is to be found in the past. + */ + if (!TLS_CERT_IS_TRUSTED(TLScontext) + && (TLScontext->log_mask & TLS_LOG_UNTRUSTED)) { + if (TLScontext->session_reused == 0) + tls_log_verify_error(TLScontext); + else + msg_info("%s: re-using session with untrusted certificate, " + "look for details earlier in the log", + TLScontext->namaddr); + } + } else { + TLScontext->peer_CN = mystrdup(""); + TLScontext->issuer_CN = mystrdup(""); + TLScontext->peer_cert_fprint = mystrdup(""); + TLScontext->peer_pkey_fprint = 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)); + + /* + * If the library triggered the SSL handshake, switch to the + * tls_timed_read/write() functions and make the TLScontext available to + * those functions. Otherwise, leave control over SSL_read/write/etc. + * with the application. + */ + if (TLScontext->stream != 0) + tls_stream_start(TLScontext->stream, TLScontext); + + /* + * With the handshake done, extract TLS 1.3 signature metadata. + */ + tls_get_signature_params(TLScontext); + + /* + * All the key facts in a single log entry. + */ + if (TLScontext->log_mask & TLS_LOG_SUMMARY) + tls_log_summary(TLS_ROLE_SERVER, TLS_USAGE_NEW, TLScontext); + + tls_int_seed(); + + return (TLScontext); +} + +#endif /* USE_TLS */ |