/*
* 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;
SSL_CIPHER_const SSL_CIPHER *cipher;
X509 *peercert;
TLS_SESS_STATE *TLScontext;
TLS_APPL_STATE *app_ctx = props->ctx;
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;
/*
* 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(app_ctx, "TLS", props->cipher_grade,
props->cipher_exclusions);
if (cipher_list == 0) {
msg_warn("%s: %s: aborting TLS session",
props->namaddr, vstring_str(app_ctx->why));
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);
/*
* 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;
TLScontext->serverid = myserverid;
TLScontext->stream = props->stream;
TLScontext->mdalg = props->mdalg;
/* Alias DANE digest info from props */
TLScontext->dane = props->dane;
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);
}
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));
/*
* 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)
&& strlen(props->host) <= TLSEXT_MAXLEN_host_name) {
/*
* 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).
*
* Since the hostname is DNSSEC-validated, it must be a DNS FQDN and
* thererefore valid for use with SNI. 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, props->host)) {
msg_warn("%s: error setting SNI hostname to: %s", props->namaddr,
props->host);
tls_free_context(TLScontext);
return (0);
}
if (log_mask & TLS_LOG_DEBUG)
msg_info("%s: SNI hostname: %s", props->namaddr, props->host);
}
#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);
/*
* Initialize the SSL connection to connect 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_connect_state(TLScontext->con);
/*
* Connect the SSL connection with the network socket.
*/
if (SSL_set_fd(TLScontext->con, 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);
}
/*
* Turn on non-blocking I/O so that we can enforce timeouts on network
* I/O.
*/
non_blocking(vstream_fileno(props->stream), NON_BLOCKING);
/*
* 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);
/*
* 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);
}
/* Turn off packet dump if only dumping the handshake */
if ((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 ((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.
*/
tls_stream_start(props->stream, TLScontext);
/*
* All the key facts in a single log entry.
*/
if (log_mask & TLS_LOG_SUMMARY)
msg_info("%s TLS connection established to %s: %s with cipher %s "
"(%d/%d bits)",
!TLS_CERT_IS_PRESENT(TLScontext) ? "Anonymous" :
TLS_CERT_IS_MATCHED(TLScontext) ? "Verified" :
TLS_CERT_IS_TRUSTED(TLScontext) ? "Trusted" : "Untrusted",
props->namaddr, TLScontext->protocol, TLScontext->cipher_name,
TLScontext->cipher_usebits, TLScontext->cipher_algbits);
tls_int_seed();
return (TLScontext);
}
char *tls_serverid_digest(const TLS_CLIENT_START_PROPS *props, long protomask,
const char *ciphers)
{
EVP_MD_CTX *mdctx;
const EVP_MD *md;
const char *mdalg;
unsigned char md_buf[EVP_MAX_MD_SIZE];
unsigned int md_len;
int ok = 1;
int i;
long sslversion;
VSTRING *result;
/*
* Try to use sha256: our serverid choice should be strong enough to
* resist 2nd-preimage attacks with a difficulty comparable to that of
* DANE TLSA digests. Failing that, we compute serverid digests with the
* default digest, but DANE requires sha256 and sha512, so if we must
* fall back to our default digest, DANE support won't be available. We
* panic if the fallback algorithm is not available, as it was verified
* available in tls_client_init() and must not simply vanish.
*/
if ((md = EVP_get_digestbyname(mdalg = "sha256")) == 0
&& (md = EVP_get_digestbyname(mdalg = props->mdalg)) == 0)
msg_panic("digest algorithm \"%s\" not found", mdalg);
/* Salt the session lookup key with the OpenSSL runtime version. */
sslversion = OpenSSL_version_num();
mdctx = EVP_MD_CTX_create();
checkok(EVP_DigestInit_ex(mdctx, md, NULL));
digest_string(props->helo ? props->helo : "");
digest_object(&sslversion);
digest_object(&protomask);
digest_string(ciphers);
/*
* All we get from the session cache is a single bit telling us whether
* the certificate is trusted or not, but we need to know whether the
* trust is CA-based (in that case we must do name checks) or whether it
* is a direct end-point match. We mustn't confuse the two, so it is
* best to process only TA trust in the verify callback and check the EE
* trust after. This works since re-used sessions always have access to
* the leaf certificate, while only the original session has the leaf and
* the full trust chain.
*
* Only the trust anchor matchlist is hashed into the session key. The end
* entity certs are not used to determine whether a certificate is
* trusted or not, rather these are rechecked against the leaf cert
* outside the verification callback, each time a session is created or
* reused.
*
* Therefore, the security context of the session does not depend on the EE
* matching data, which is checked separately each time. So we exclude
* the EE part of the DANE structure from the serverid digest.
*
* If the security level is "dane", we send SNI information to the peer.
* This may cause it to respond with a non-default certificate. Since
* certificates for sessions with no or different SNI data may not match,
* we must include the SNI name in the session id.
*/
if (props->dane) {
digest_dane(props->dane, ta);
#if 0
digest_dane(props->dane, ee); /* See above */
#endif
digest_string(TLS_DANE_BASED(props->tls_level) ? props->host : "");
}
checkok(EVP_DigestFinal_ex(mdctx, md_buf, &md_len));
EVP_MD_CTX_destroy(mdctx);
if (!ok)
msg_fatal("error computing %s message digest", mdalg);
/* Check for OpenSSL contract violation */
if (md_len > EVP_MAX_MD_SIZE)
msg_panic("unexpectedly large %s digest size: %u", mdalg, md_len);
/*
* Append the digest to the serverid. We don't compare this digest to
* any user-specified fingerprints. Therefore, we don't need to use a
* colon-separated format, which saves space in the TLS session cache and
* makes logging of session cache lookup keys more readable.
*
* This does however duplicate a few lines of code from the digest encoder
* for colon-separated cert and pkey fingerprints. If that is a
* compelling reason to consolidate, we could use that and append the
* result.
*/
result = vstring_alloc(strlen(props->serverid) + 1 + 2 * md_len);
vstring_strcpy(result, props->serverid);
VSTRING_ADDCH(result, '&');
for (i = 0; i < md_len; i++) {
VSTRING_ADDCH(result, hexcodes[(md_buf[i] & 0xf0) >> 4U]);
VSTRING_ADDCH(result, hexcodes[(md_buf[i] & 0x0f)]);
}
VSTRING_TERMINATE(result);
return (vstring_export(result));
}
