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Diffstat (limited to '')
| -rw-r--r-- | src/tls/tls_client.c | 1230 |
1 files changed, 1230 insertions, 0 deletions
diff --git a/src/tls/tls_client.c b/src/tls/tls_client.c new file mode 100644 index 0000000..f3263b6 --- /dev/null +++ b/src/tls/tls_client.c @@ -0,0 +1,1230 @@ +/*++ +/* NAME +/* tls_client +/* SUMMARY +/* client-side TLS engine +/* SYNOPSIS +/* #include <tls.h> +/* +/* TLS_APPL_STATE *tls_client_init(init_props) +/* const TLS_CLIENT_INIT_PROPS *init_props; +/* +/* TLS_SESS_STATE *tls_client_start(start_props) +/* const TLS_CLIENT_START_PROPS *start_props; +/* +/* TLS_SESS_STATE *tls_client_post_connect(TLScontext, start_props) +/* TLS_SESS_STATE *TLScontext; +/* const TLS_CLIENT_START_PROPS *start_props; +/* +/* void tls_client_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 clients, +/* the OpenSSL library and the TLS entropy and cache manager. +/* +/* The SMTP client will attempt to verify the server hostname +/* against the names listed in the server certificate. When +/* a hostname match is required, the verification fails +/* on certificate verification or hostname mis-match errors. +/* When no hostname match is required, hostname verification +/* failures are logged but they do not affect the TLS handshake +/* or the SMTP session. +/* +/* The rules for peer name wild-card matching differ between +/* RFC 2818 (HTTP over TLS) and RFC 2830 (LDAP over TLS), while +/* RFC RFC3207 (SMTP over TLS) does not specify a rule at all. +/* Postfix uses a restrictive match algorithm. One asterisk +/* ('*') is allowed as the left-most component of a wild-card +/* certificate name; it matches the left-most component of +/* the peer hostname. +/* +/* Another area where RFCs aren't always explicit is the +/* handling of dNSNames in peer certificates. RFC 3207 (SMTP +/* over TLS) does not mention dNSNames. Postfix follows the +/* strict rules in RFC 2818 (HTTP over TLS), section 3.1: The +/* Subject Alternative Name/dNSName has precedence over +/* CommonName. If at least one dNSName is provided, Postfix +/* verifies those against the peer hostname and ignores the +/* CommonName, otherwise Postfix verifies the CommonName +/* against the peer hostname. +/* +/* tls_client_init() is called once when the SMTP client +/* initializes. +/* Certificate details are also decided during this phase, +/* so peer-specific certificate selection is not possible. +/* +/* tls_client_start() activates the TLS session over an established +/* stream. We expect that network buffers are flushed and +/* the TLS handshake can begin immediately. +/* +/* tls_client_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. This consists of one or more of +/* TLS_CERT_FLAG_PRESENT, TLS_CERT_FLAG_ALTNAME, TLS_CERT_FLAG_TRUSTED, +/* TLS_CERT_FLAG_MATCHED and TLS_CERT_FLAG_SECURED. +/* .IP TLScontext->peer_CN +/* Extracted CommonName of the peer, or zero-length string if the +/* information could not be extracted. +/* .IP TLScontext->issuer_CN +/* Extracted CommonName of the issuer, or zero-length string if the +/* information could not be extracted. +/* .IP TLScontext->peer_cert_fprint +/* At the fingerprint security level, if the peer presented a certificate +/* the fingerprint of the certificate. +/* .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 TLS library historically provides, +/* including tls_client_stop() and the underlying tls_stream(3) +/* and tls_bio_ops(3) routines. +/* +/* With the current TLS library implementation, this means +/* that an event-driven application is responsible for calling +/* and retrying SSL_connect(), SSL_read(), SSL_write() and +/* SSL_shutdown(). +/* +/* To maintain control over TLS I/O, an event-driven client +/* invokes tls_client_start() with a null VSTREAM argument and +/* with an fd argument that specifies the I/O file descriptor. +/* Then, tls_client_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_connect(), and if successful, +/* for invoking tls_client_post_connect() to finish the work +/* that was started by tls_client_start(). In case of unrecoverable +/* failure, tls_client_post_connect() 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 +/* +/* Wietse Venema +/* Google, Inc. +/* 111 8th Avenue +/* New York, NY 10011, USA +/* +/* Victor Duchovni +/* Morgan Stanley +/*--*/ + +/* System library. */ + +#include <sys_defs.h> + +#ifdef USE_TLS +#include <string.h> + +#ifdef STRCASECMP_IN_STRINGS_H +#include <strings.h> +#endif + +/* Utility library. */ + +#include <argv.h> +#include <mymalloc.h> +#include <vstring.h> +#include <vstream.h> +#include <stringops.h> +#include <msg.h> +#include <iostuff.h> /* non-blocking */ +#include <midna_domain.h> + +/* Global library. */ + +#include <mail_params.h> + +/* TLS library. */ + +#include <tls_mgr.h> +#define TLS_INTERNAL +#include <tls.h> + +/* Application-specific. */ + +#define STR vstring_str +#define LEN VSTRING_LEN + +/* load_clnt_session - load session from client cache (non-callback) */ + +static SSL_SESSION *load_clnt_session(TLS_SESS_STATE *TLScontext) +{ + const char *myname = "load_clnt_session"; + SSL_SESSION *session = 0; + VSTRING *session_data = vstring_alloc(2048); + + /* + * Prepare the query. + */ + if (TLScontext->log_mask & TLS_LOG_CACHE) + /* serverid contains transport:addr:port information */ + msg_info("looking for session %s in %s cache", + TLScontext->serverid, TLScontext->cache_type); + + /* + * We only get here if the cache_type is not empty. This code is not + * called unless caching is enabled and the cache_type is stored in the + * server SSL context. + */ + if (TLScontext->cache_type == 0) + msg_panic("%s: null client session cache type in session lookup", + myname); + + /* + * Look up and activate the SSL_SESSION object. Errors are non-fatal, + * since caching is only an optimization. + */ + if (tls_mgr_lookup(TLScontext->cache_type, TLScontext->serverid, + session_data) == TLS_MGR_STAT_OK) { + session = tls_session_activate(STR(session_data), LEN(session_data)); + if (session) { + if (TLScontext->log_mask & TLS_LOG_CACHE) + /* serverid contains transport:addr:port information */ + msg_info("reloaded session %s from %s cache", + TLScontext->serverid, TLScontext->cache_type); + } + } + + /* + * Clean up. + */ + vstring_free(session_data); + + return (session); +} + +/* new_client_session_cb - name new session and save it to client cache */ + +static int new_client_session_cb(SSL *ssl, SSL_SESSION *session) +{ + const char *myname = "new_client_session_cb"; + TLS_SESS_STATE *TLScontext; + VSTRING *session_data; + + /* + * The cache name (if caching is enabled in tlsmgr(8)) and the cache ID + * string for this session are stored in the TLScontext. It cannot be + * null at this point. + */ + if ((TLScontext = SSL_get_ex_data(ssl, TLScontext_index)) == 0) + msg_panic("%s: null TLScontext in new session callback", myname); + + /* + * We only get here if the cache_type is not empty. This callback is not + * set unless caching is enabled and the cache_type is stored in the + * server SSL context. + */ + if (TLScontext->cache_type == 0) + msg_panic("%s: null session cache type in new session callback", + myname); + + if (TLScontext->log_mask & TLS_LOG_CACHE) + /* serverid contains transport:addr:port information */ + msg_info("save session %s to %s cache", + TLScontext->serverid, TLScontext->cache_type); + + /* + * Passivate and save the session object. Errors are non-fatal, since + * caching is only an optimization. + */ + if ((session_data = tls_session_passivate(session)) != 0) { + tls_mgr_update(TLScontext->cache_type, TLScontext->serverid, + STR(session_data), LEN(session_data)); + vstring_free(session_data); + } + + /* + * Clean up. + */ + SSL_SESSION_free(session); /* 200502 */ + + return (1); +} + +/* uncache_session - remove session from the external cache */ + +static void uncache_session(SSL_CTX *ctx, TLS_SESS_STATE *TLScontext) +{ + SSL_SESSION *session = SSL_get_session(TLScontext->con); + + SSL_CTX_remove_session(ctx, session); + if (TLScontext->cache_type == 0 || TLScontext->serverid == 0) + return; + + if (TLScontext->log_mask & TLS_LOG_CACHE) + /* serverid contains transport:addr:port information */ + msg_info("remove session %s from client cache", TLScontext->serverid); + + tls_mgr_delete(TLScontext->cache_type, TLScontext->serverid); +} + +/* tls_client_init - initialize client-side TLS engine */ + +TLS_APPL_STATE *tls_client_init(const TLS_CLIENT_INIT_PROPS *props) +{ + long off = 0; + int cachable; + int scache_timeout; + SSL_CTX *client_ctx; + 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 client-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 + + /* + * 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. RFC2487 is only specified for TLSv1, but + * we want to be as compatible as possible, so we will start off with a + * SSLv2 greeting allowing the best we can offer: TLSv1. We can restrict + * this with the options setting later, anyhow. + */ + ERR_clear_error(); + client_ctx = SSL_CTX_new(TLS_client_method()); + if (client_ctx == 0) { + msg_warn("cannot allocate client 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(client_ctx, 0); +#endif + + /* + * See the verify callback in tls_verify.c + */ + SSL_CTX_set_verify_depth(client_ctx, props->verifydepth + 1); + + /* + * Protocol selection is destination dependent, so we delay the protocol + * selection options to the per-session SSL object. + */ + off |= tls_bug_bits(); + SSL_CTX_set_options(client_ctx, off); + + /* Enable all supported protocols */ +#if OPENSSL_VERSION_NUMBER >= 0x1010000fUL + SSL_CTX_set_min_proto_version(client_ctx, 0); +#endif + + /* + * Set the call-back routine for verbose logging. + */ + if (log_mask & TLS_LOG_DEBUG) + SSL_CTX_set_info_callback(client_ctx, tls_info_callback); + + /* + * Load the CA public key certificates for both the client cert and for + * the verification of server 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(client_ctx, + props->CAfile, props->CApath) < 0) { + /* tls_set_ca_certificate_info() already logs a warning. */ + SSL_CTX_free(client_ctx); /* 200411 */ + return (0); + } + + /* + * We do not need a client certificate, so the certificates are only + * loaded (and checked) if supplied. A clever client would handle + * multiple client certificates and decide based on the list of + * acceptable CAs, sent by the server, which certificate to submit. + * OpenSSL does however not do this and also has no call-back hooks to + * easily implement it. + * + * Load the client 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). The client + * certificate is presented after the server chooses the session cipher, + * so we will just present the right cert for the chosen cipher (if it + * uses certificates). + */ + if (tls_set_my_certificate_key_info(client_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(client_ctx); /* 200411 */ + return (0); + } + + /* + * 2015-12-05: Ephemeral RSA removed from OpenSSL 1.1.0-dev + */ +#if OPENSSL_VERSION_NUMBER < 0x10100000L + + /* + * 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(client_ctx, tls_tmp_rsa_cb); +#endif + + /* + * With OpenSSL 1.0.2 and later the client EECDH curve list becomes + * configurable with the preferred curve negotiated via the supported + * curves extension. + */ + tls_auto_eecdh_curves(client_ctx, var_tls_eecdh_auto); + + /* + * Finally, the setup for the server certificate checking, done "by the + * book". + */ + SSL_CTX_set_verify(client_ctx, SSL_VERIFY_NONE, + tls_verify_certificate_callback); + + /* + * Initialize the session cache. + * + * Since the client does not search an internal cache, we simply disable it. + * It is only useful for expiring old sessions, but we do that in the + * tlsmgr(8). + * + * 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). + */ + if (tls_mgr_policy(props->cache_type, &cachable, + &scache_timeout) != TLS_MGR_STAT_OK) + scache_timeout = 0; + if (scache_timeout <= 0) + cachable = 0; + + /* + * Allocate an application context, and populate with mandatory protocol + * and cipher data. + */ + app_ctx = tls_alloc_app_context(client_ctx, 0, log_mask); + + /* + * The external session cache is implemented by the tlsmgr(8) process. + */ + if (cachable) { + + app_ctx->cache_type = mystrdup(props->cache_type); + + /* + * OpenSSL does not use callbacks to load sessions from a client + * cache, so we must invoke that function directly. Apparently, + * OpenSSL does not provide a way to pass session names from here to + * call-back routines that do session lookup. + * + * OpenSSL can, however, automatically save newly created sessions for + * us by callback (we create the session name in the call-back + * function). + * + * XXX gcc 2.95 can't compile #ifdef .. #endif in the expansion of + * SSL_SESS_CACHE_CLIENT | SSL_SESS_CACHE_NO_INTERNAL_STORE | + * SSL_SESS_CACHE_NO_AUTO_CLEAR. + */ +#ifndef SSL_SESS_CACHE_NO_INTERNAL_STORE +#define SSL_SESS_CACHE_NO_INTERNAL_STORE 0 +#endif + + SSL_CTX_set_session_cache_mode(client_ctx, + SSL_SESS_CACHE_CLIENT | + SSL_SESS_CACHE_NO_INTERNAL_STORE | + SSL_SESS_CACHE_NO_AUTO_CLEAR); + SSL_CTX_sess_set_new_cb(client_ctx, new_client_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 to + * twice the cache lifetime. This way a session always lasts longer + * than its lifetime in the cache. + */ + SSL_CTX_set_timeout(client_ctx, 2 * scache_timeout); + } + return (app_ctx); +} + +/* match_servername - match servername against pattern */ + +static int match_servername(const char *certid, + const TLS_CLIENT_START_PROPS *props) +{ + const ARGV *cmatch_argv; + const char *nexthop = props->nexthop; + const char *hname = props->host; + const char *domain; + const char *parent; + const char *aname; + int match_subdomain; + int i; + int idlen; + int domlen; + + if ((cmatch_argv = props->matchargv) == 0) + return 0; + +#ifndef NO_EAI + + /* + * DNS subjectAltNames are required to be ASCII. + * + * Per RFC 6125 Section 6.4.4 Matching the CN-ID, follows the same rules + * (6.4.1, 6.4.2 and 6.4.3) that apply to subjectAltNames. In + * particular, 6.4.2 says that the reference identifier is coerced to + * ASCII, but no conversion is stated or implied for the CN-ID, so it + * seems it only matches if it is all ASCII. Otherwise, it is some other + * sort of name. + */ + if (!allascii(certid)) + return (0); + if (!allascii(nexthop) && (aname = midna_domain_to_ascii(nexthop)) != 0) { + if (msg_verbose) + msg_info("%s asciified to %s", nexthop, aname); + nexthop = aname; + } +#endif + + /* + * Match the certid against each pattern until we find a match. + */ + for (i = 0; i < cmatch_argv->argc; ++i) { + match_subdomain = 0; + if (!strcasecmp(cmatch_argv->argv[i], "nexthop")) + domain = nexthop; + else if (!strcasecmp(cmatch_argv->argv[i], "hostname")) + domain = hname; + else if (!strcasecmp(cmatch_argv->argv[i], "dot-nexthop")) { + domain = nexthop; + match_subdomain = 1; + } else { + domain = cmatch_argv->argv[i]; + if (*domain == '.') { + if (domain[1]) { + ++domain; + match_subdomain = 1; + } + } +#ifndef NO_EAI + + /* + * Besides U+002E (full stop) IDNA2003 allows labels to be + * separated by any of the Unicode variants U+3002 (ideographic + * full stop), U+FF0E (fullwidth full stop), and U+FF61 + * (halfwidth ideographic full stop). Their respective UTF-8 + * encodings are: E38082, EFBC8E and EFBDA1. + * + * IDNA2008 does not permit (upper) case and other variant + * differences in U-labels. The midna_domain_to_ascii() function, + * based on UTS46, normalizes such differences away. + * + * The IDNA to_ASCII conversion does not allow empty leading labels, + * so we handle these explicitly here. + */ + else { + unsigned char *cp = (unsigned char *) domain; + + if ((cp[0] == 0xe3 && cp[1] == 0x80 && cp[2] == 0x82) + || (cp[0] == 0xef && cp[1] == 0xbc && cp[2] == 0x8e) + || (cp[0] == 0xef && cp[1] == 0xbd && cp[2] == 0xa1)) { + if (domain[3]) { + domain = domain + 3; + match_subdomain = 1; + } + } + } + if (!allascii(domain) + && (aname = midna_domain_to_ascii(domain)) != 0) { + if (msg_verbose) + msg_info("%s asciified to %s", domain, aname); + domain = aname; + } +#endif + } + + /* + * Sub-domain match: certid is any sub-domain of hostname. + */ + if (match_subdomain) { + if ((idlen = strlen(certid)) > (domlen = strlen(domain)) + 1 + && certid[idlen - domlen - 1] == '.' + && !strcasecmp(certid + (idlen - domlen), domain)) + return (1); + else + continue; + } + + /* + * Exact match and initial "*" match. The initial "*" in a certid + * matches one (if var_tls_multi_label is false) or more hostname + * components under the condition that the certid contains multiple + * hostname components. + */ + if (!strcasecmp(certid, domain) + || (certid[0] == '*' && certid[1] == '.' && certid[2] != 0 + && (parent = strchr(domain, '.')) != 0 + && (idlen = strlen(certid + 1)) <= (domlen = strlen(parent)) + && strcasecmp(var_tls_multi_wildcard == 0 ? parent : + parent + domlen - idlen, + certid + 1) == 0)) + return (1); + } + return (0); +} + +/* verify_extract_name - verify peer name and extract peer information */ + +static void verify_extract_name(TLS_SESS_STATE *TLScontext, X509 *peercert, + const TLS_CLIENT_START_PROPS *props) +{ + int i; + int r; + int matched = 0; + int dnsname_match; + int verify_peername = 0; + int log_certmatch; + int verbose; + const char *dnsname; + const GENERAL_NAME *gn; + general_name_stack_t *gens; + + /* + * On exit both peer_CN and issuer_CN should be set. + */ + TLScontext->issuer_CN = tls_issuer_CN(peercert, TLScontext); + + /* + * Is the certificate trust chain valid and trusted? + */ + if (SSL_get_verify_result(TLScontext->con) == X509_V_OK) + TLScontext->peer_status |= TLS_CERT_FLAG_TRUSTED; + + /* + * With fingerprint or dane we may already be done. Otherwise, verify the + * peername if using traditional PKI or DANE with trust-anchors. + */ + if (!TLS_CERT_IS_MATCHED(TLScontext) + && TLS_CERT_IS_TRUSTED(TLScontext) + && TLS_MUST_TRUST(props->tls_level)) + verify_peername = 1; + + /* Force cert processing so we can log the data? */ + log_certmatch = TLScontext->log_mask & TLS_LOG_CERTMATCH; + + /* Log cert details when processing? */ + verbose = log_certmatch || (TLScontext->log_mask & TLS_LOG_VERBOSE); + + if (verify_peername || log_certmatch) { + + /* + * Verify the dNSName(s) in the peer certificate against the nexthop + * and hostname. + * + * If DNS names are present, we use the first matching (or else simply + * the first) DNS name as the subject CN. The CommonName in the + * issuer DN is obsolete when SubjectAltName is available. This + * yields much less surprising logs, because we log the name we + * verified or a name we checked and failed to match. + * + * XXX: The nexthop and host name may both be the same network address + * rather than a DNS name. In this case we really should be looking + * for GEN_IPADD entries, not GEN_DNS entries. + * + * XXX: In ideal world the caller who used the address to build the + * connection would tell us that the nexthop is the connection + * address, but if that is not practical, we can parse the nexthop + * again here. + */ + gens = X509_get_ext_d2i(peercert, NID_subject_alt_name, 0, 0); + if (gens) { + r = sk_GENERAL_NAME_num(gens); + for (i = 0; i < r; ++i) { + gn = sk_GENERAL_NAME_value(gens, i); + if (gn->type != GEN_DNS) + continue; + + /* + * Even if we have an invalid DNS name, we still ultimately + * ignore the CommonName, because subjectAltName:DNS is + * present (though malformed). Replace any previous peer_CN + * if empty or we get a match. + * + * We always set at least an empty peer_CN if the ALTNAME cert + * flag is set. If not, we set peer_CN from the cert + * CommonName below, so peer_CN is always non-null on return. + */ + TLScontext->peer_status |= TLS_CERT_FLAG_ALTNAME; + dnsname = tls_dns_name(gn, TLScontext); + if (dnsname && *dnsname) { + if ((dnsname_match = match_servername(dnsname, props)) != 0) + matched++; + /* Keep the first matched name. */ + if (TLScontext->peer_CN + && ((dnsname_match && matched == 1) + || *TLScontext->peer_CN == 0)) { + myfree(TLScontext->peer_CN); + TLScontext->peer_CN = 0; + } + if (verbose) + msg_info("%s: %ssubjectAltName: %s", props->namaddr, + dnsname_match ? "Matched " : "", dnsname); + } + if (TLScontext->peer_CN == 0) + TLScontext->peer_CN = mystrdup(dnsname ? dnsname : ""); + if (matched && !log_certmatch) + break; + } + if (verify_peername && matched) + TLScontext->peer_status |= TLS_CERT_FLAG_MATCHED; + + /* + * (Sam Rushing, Ironport) Free stack *and* member GENERAL_NAME + * objects + */ + sk_GENERAL_NAME_pop_free(gens, GENERAL_NAME_free); + } + + /* + * No subjectAltNames, peer_CN is taken from CommonName. + */ + if (TLScontext->peer_CN == 0) { + TLScontext->peer_CN = tls_peer_CN(peercert, TLScontext); + if (*TLScontext->peer_CN) + matched = match_servername(TLScontext->peer_CN, props); + if (verify_peername && matched) + TLScontext->peer_status |= TLS_CERT_FLAG_MATCHED; + if (verbose) + msg_info("%s %sCommonName %s", props->namaddr, + matched ? "Matched " : "", TLScontext->peer_CN); + } else if (verbose) { + char *tmpcn = tls_peer_CN(peercert, TLScontext); + + /* + * Though the CommonName was superceded by a subjectAltName, log + * it when certificate match debugging was requested. + */ + msg_info("%s CommonName %s", TLScontext->namaddr, tmpcn); + myfree(tmpcn); + } + } else + TLScontext->peer_CN = tls_peer_CN(peercert, TLScontext); + + /* + * 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", props->namaddr); + } +} + +/* verify_extract_print - extract and verify peer fingerprint */ + +static void verify_extract_print(TLS_SESS_STATE *TLScontext, X509 *peercert, + const TLS_CLIENT_START_PROPS *props) +{ + TLScontext->peer_cert_fprint = tls_cert_fprint(peercert, props->mdalg); + TLScontext->peer_pkey_fprint = tls_pkey_fprint(peercert, props->mdalg); + + /* + * Whether the level is "dane" or "fingerprint" when the peer certificate + * is matched without resorting to a separate CA, we set both the trusted + * and matched bits. This simplifies logic in smtp_proto.c where "dane" + * must be trusted and matched, since some "dane" TLSA RRsets do use CAs. + * + * This also suppresses spurious logging of the peer certificate as + * untrusted in verify_extract_name(). + */ + if (TLS_DANE_HASEE(props->dane) + && tls_dane_match(TLScontext, TLS_DANE_EE, peercert, 0)) + TLScontext->peer_status |= + TLS_CERT_FLAG_TRUSTED | TLS_CERT_FLAG_MATCHED; +} + + /* + * This is the actual startup routine for the connection. We expect that the + * buffers are flushed and the "220 Ready to start TLS" was received by us, + * so that we can immediately start the TLS handshake process. + */ +TLS_SESS_STATE *tls_client_start(const TLS_CLIENT_START_PROPS *props) +{ + int sts; + int protomask; + const char *cipher_list; + SSL_SESSION *session = 0; + TLS_SESS_STATE *TLScontext; + TLS_APPL_STATE *app_ctx = props->ctx; + const char *sni = 0; + char *myserverid; + int log_mask = app_ctx->log_mask; + + /* + * When certificate verification is required, log trust chain validation + * errors even when disabled by default for opportunistic sessions. For + * DANE this only applies when using trust-anchor associations. + */ + if (TLS_MUST_TRUST(props->tls_level) + && (!TLS_DANE_BASED(props->tls_level) || TLS_DANE_HASTA(props->dane))) + log_mask |= TLS_LOG_UNTRUSTED; + + if (log_mask & TLS_LOG_VERBOSE) + msg_info("setting up TLS connection to %s", props->namaddr); + + /* + * First make sure we have valid protocol and cipher parameters + * + * Per-session protocol restrictions must be applied to the SSL connection, + * as restrictions in the global context cannot be cleared. + */ + protomask = tls_protocol_mask(props->protocols); + if (protomask == TLS_PROTOCOL_INVALID) { + /* tls_protocol_mask() logs no warning. */ + msg_warn("%s: Invalid TLS protocol list \"%s\": aborting TLS session", + props->namaddr, props->protocols); + return (0); + } + /* DANE requires SSLv3 or later, not SSLv2. */ + if (TLS_DANE_BASED(props->tls_level)) + protomask |= TLS_PROTOCOL_SSLv2; + + /* + * 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(). + * + * If session caching was enabled when TLS was initialized, the cache type + * is stored in the client SSL context. + */ + TLScontext = tls_alloc_sess_context(log_mask, props->namaddr); + TLScontext->cache_type = app_ctx->cache_type; + + if ((TLScontext->con = SSL_new(app_ctx->ssl_ctx)) == NULL) { + msg_warn("Could not allocate 'TLScontext->con' with SSL_new()"); + tls_print_errors(); + tls_free_context(TLScontext); + return (0); + } + + /* + * Per session cipher selection for sessions with mandatory encryption + * + * The cipherlist is applied to the global SSL context, since it is likely + * to stay the same between connections, so we make use of a 1-element + * cache to return the same result for identical inputs. + */ + 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); + + /* + * OpenSSL will ignore cached sessions that use the wrong protocol. So we + * do not need to filter out cached sessions with the "wrong" protocol, + * rather OpenSSL will simply negotiate a new session. + * + * We salt the session lookup key with the protocol list, so that sessions + * found in the cache are plausibly acceptable. + * + * By the time a TLS client is negotiating ciphers it has already offered to + * re-use a session, it is too late to renege on the offer. So we must + * not attempt to re-use sessions whose ciphers are too weak. We salt the + * session lookup key with the cipher list, so that sessions found in the + * cache are always acceptable. + * + * With DANE, (more generally any TLScontext where we specified explicit + * trust-anchor or end-entity certificates) the verification status of + * the SSL session depends on the specified list. Since we verify the + * certificate only during the initial handshake, we must segregate + * sessions with different TA lists. Note, that TA re-verification is + * not possible with cached sessions, since these don't hold the complete + * peer trust chain. Therefore, we compute a digest of the sorted TA + * parameters and append it to the serverid. + */ + myserverid = tls_serverid_digest(props, protomask, cipher_list); + + TLScontext->serverid = myserverid; + TLScontext->stream = props->stream; + TLScontext->mdalg = props->mdalg; + + /* Alias DANE digest info from props */ + TLScontext->dane = props->dane; + + 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); + } + + /* + * Apply session protocol restrictions. + */ + if (protomask != 0) + SSL_set_options(TLScontext->con, TLS_SSL_OP_PROTOMASK(protomask)); + +#ifdef SSL_SECOP_PEER + /* When authenticating the peer, use 80-bit plus OpenSSL security level */ + if (TLS_MUST_MATCH(props->tls_level)) + SSL_set_security_level(TLScontext->con, 1); +#endif + + /* + * XXX To avoid memory leaks we must always call SSL_SESSION_free() after + * calling SSL_set_session(), regardless of whether or not the session + * will be reused. + */ + if (TLScontext->cache_type) { + session = load_clnt_session(TLScontext); + if (session) { + SSL_set_session(TLScontext->con, session); + SSL_SESSION_free(session); /* 200411 */ + } + } +#ifdef TLSEXT_MAXLEN_host_name + if (TLS_DANE_BASED(props->tls_level)) { + + /* + * With DANE sessions, send an SNI hint. We don't care whether the + * server reports finding a matching certificate or not, so no + * callback is required to process the server response. Our use of + * SNI is limited to giving servers that are (mis)configured to use + * SNI the best opportunity to find the certificate they promised via + * the associated TLSA RRs. (Generally, server administrators should + * avoid SNI, and there are no plans to support SNI in the Postfix + * SMTP server). + * + * Per RFC7672, the required SNI name is the TLSA "base domain" (the one + * used to construct the "_25._tcp.<fqdn>" TLSA record DNS query). + * + * Since the hostname is DNSSEC-validated, it must be a DNS FQDN and + * thererefore valid for use with SNI. + */ + sni = props->dane->base_domain; + } else if (props->sni && *props->sni) { + if (strcmp(props->sni, "hostname") == 0) + sni = props->host; + else if (strcmp(props->sni, "nexthop") == 0) + sni = props->nexthop; + else + sni = props->sni; + } + if (sni && strlen(sni) <= TLSEXT_MAXLEN_host_name) { + + /* + * Failure to set a valid SNI hostname is a memory allocation error, + * and thus transient. Since we must not cache the session if we + * failed to send the SNI name, we have little choice but to abort. + */ + if (!SSL_set_tlsext_host_name(TLScontext->con, sni)) { + msg_warn("%s: error setting SNI hostname to: %s", props->namaddr, + sni); + tls_free_context(TLScontext); + return (0); + } + /* + * The saved value is not presently used client-side, but could later + * be logged if acked by the server (requires new client-side callback + * to detect the ack). For now this just maintains symmetry with the + * server code, where do record the received SNI for logging. + */ + TLScontext->peer_sni = mystrdup(sni); + if (log_mask & TLS_LOG_DEBUG) + msg_info("%s: SNI hostname: %s", props->namaddr, sni); + } +#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); + + tls_dane_set_callback(app_ctx->ssl_ctx, TLScontext); + + /* + * If we don't trigger the handshake in the library, leave control over + * SSL_connect/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 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_connect(vstream_fileno(props->stream), props->timeout, + TLScontext); + if (sts <= 0) { + if (ERR_peek_error() != 0) { + msg_info("SSL_connect error to %s: %d", props->namaddr, sts); + tls_print_errors(); + } else if (errno != 0) { + msg_info("SSL_connect error to %s: %m", props->namaddr); + } else { + msg_info("SSL_connect error to %s: lost connection", + props->namaddr); + } + uncache_session(app_ctx->ssl_ctx, TLScontext); + tls_free_context(TLScontext); + return (0); + } + return (tls_client_post_connect(TLScontext, props)); +} + +/* tls_client_post_connect - post-handshake processing */ + +TLS_SESS_STATE *tls_client_post_connect(TLS_SESS_STATE *TLScontext, + const TLS_CLIENT_START_PROPS *props) +{ + const SSL_CIPHER *cipher; + X509 *peercert; + + /* 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", TLScontext->namaddr); + + /* + * Do peername verification if requested and extract useful information + * from the certificate for later use. + */ + if ((peercert = SSL_get_peer_certificate(TLScontext->con)) != 0) { + TLScontext->peer_status |= TLS_CERT_FLAG_PRESENT; + + /* + * Peer name or fingerprint verification as requested. + * Unconditionally set peer_CN, issuer_CN and peer_cert_fprint. Check + * fingerprint first, and avoid logging verified as untrusted in the + * call to verify_extract_name(). + */ + verify_extract_print(TLScontext, peercert, props); + verify_extract_name(TLScontext, peercert, props); + + if (TLScontext->log_mask & + (TLS_LOG_CERTMATCH | TLS_LOG_VERBOSE | TLS_LOG_PEERCERT)) + msg_info("%s: subject_CN=%s, issuer_CN=%s, " + "fingerprint=%s, pkey_fingerprint=%s", props->namaddr, + TLScontext->peer_CN, TLScontext->issuer_CN, + TLScontext->peer_cert_fprint, + TLScontext->peer_pkey_fprint); + X509_free(peercert); + } else { + TLScontext->issuer_CN = mystrdup(""); + TLScontext->peer_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)); + + /* + * The TLS engine is active. Switch to the tls_timed_read/write() + * functions and make the TLScontext available to those functions. + */ + if (TLScontext->stream != 0) + tls_stream_start(props->stream, TLScontext); + + /* + * Fully secured only if trusted, matched and not insecure like halfdane. + * Should perhaps also exclude "verify" (as opposed to "secure") here, + * because that can be subject to insecure MX indirection, but that's + * rather incompatible. Users have been warned. + */ + if (TLS_CERT_IS_PRESENT(TLScontext) + && TLS_CERT_IS_TRUSTED(TLScontext) + && TLS_CERT_IS_MATCHED(TLScontext) + && !TLS_NEVER_SECURED(props->tls_level)) + TLScontext->peer_status |= TLS_CERT_FLAG_SECURED; + + /* + * With the handshake done, extract TLS 1.3 signature metadata. + */ + tls_get_signature_params(TLScontext); + + if (TLScontext->log_mask & TLS_LOG_SUMMARY) + tls_log_summary(TLS_ROLE_CLIENT, TLS_USAGE_NEW, TLScontext); + + tls_int_seed(); + + return (TLScontext); +} + +#endif /* USE_TLS */ |