static void dane_init(SMTP_TLS_POLICY *tls, SMTP_ITERATOR *iter)
{
TLS_DANE *dane;
if (!iter->port) {
msg_warn("%s: the \"dane\" security level is invalid for delivery via"
" unix-domain sockets", STR(iter->dest));
MARK_INVALID(tls->why, &tls->level);
return;
}
if (!tls_dane_avail()) {
dane_incompat(tls, iter, NONDANE_CONFIG,
"%s: %s configured, but no requisite library support",
STR(iter->dest), policy_name(tls->level));
return;
}
if (!(smtp_host_lookup_mask & SMTP_HOST_FLAG_DNS)
|| smtp_dns_support != SMTP_DNS_DNSSEC) {
dane_incompat(tls, iter, NONDANE_CONFIG,
"%s: %s configured with dnssec lookups disabled",
STR(iter->dest), policy_name(tls->level));
return;
}
/*
* If we ignore MX lookup errors, we also ignore DNSSEC security problems
* and thus avoid any reasonable expectation that we get the right DANE
* key material.
*/
if (smtp_mode && var_ign_mx_lookup_err) {
dane_incompat(tls, iter, NONDANE_CONFIG,
"%s: %s configured with MX lookup errors ignored",
STR(iter->dest), policy_name(tls->level));
return;
}
/*
* This is not optional, code in tls_dane.c assumes that the nexthop
* qname is already an fqdn. If we're using these flags to go from qname
* to rname, the assumption is invalid. Likewise we cannot add the qname
* to certificate name checks, ...
*/
if (smtp_dns_res_opt & (RES_DEFNAMES | RES_DNSRCH)) {
dane_incompat(tls, iter, NONDANE_CONFIG,
"%s: dns resolver options incompatible with %s TLS",
STR(iter->dest), policy_name(tls->level));
return;
}
/* When the MX name is present and insecure, DANE does not apply. */
if (iter->mx && !iter->mx->dnssec_valid) {
dane_incompat(tls, iter, NONDANE_DEST, "non DNSSEC destination");
return;
}
/* When TLSA lookups fail, we defer the message */
if ((dane = tls_dane_resolve(iter->port, "tcp", iter->rr,
var_smtp_tls_force_tlsa)) == 0) {
tls->level = TLS_LEV_INVALID;
dsb_simple(tls->why, "4.7.5", "TLSA lookup error for %s:%u",
STR(iter->host), ntohs(iter->port));
return;
}
if (tls_dane_notfound(dane)) {
dane_incompat(tls, iter, NONDANE_DEST, "no TLSA records found");
tls_dane_free(dane);
return;
}
/*
* Some TLSA records found, but none usable, per
*
* https://tools.ietf.org/html/draft-ietf-dane-srv-02#section-4
*
* we MUST use TLS, and SHALL use full PKIX certificate checks. The latter
* would be unwise for SMTP: no human present to "click ok" and risk of
* non-delivery in most cases exceeds risk of interception.
*
* We also have a form of Goedel's incompleteness theorem in play: any list
* of public root CA certs is either incomplete or inconsistent (for any
* given verifier some of the CAs are surely not trustworthy).
*/
if (tls_dane_unusable(dane)) {
dane_incompat(tls, iter, DANE_UNUSABLE, "TLSA records unusable");
tls_dane_free(dane);
return;
}
/*
* With DANE trust anchors, peername matching is not configurable.
*/
if (TLS_DANE_HASTA(dane)) {
tls->matchargv = argv_alloc(2);
argv_add(tls->matchargv, dane->base_domain, ARGV_END);
if (iter->mx) {
if (strcmp(iter->mx->qname, iter->mx->rname) == 0)
argv_add(tls->matchargv, iter->mx->qname, ARGV_END);
else
argv_add(tls->matchargv, iter->mx->rname,
iter->mx->qname, ARGV_END);
}
} else if (!TLS_DANE_HASEE(dane))
msg_panic("empty DANE match list");
tls->dane = dane;
tls->level = TLS_LEV_DANE;
return;
}
/*
* 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);
}
static void *policy_create(const char *unused_key, void *context)
{
SMTP_ITERATOR *iter = (SMTP_ITERATOR *) context;
int site_level;
const char *dest = STR(iter->dest);
const char *host = STR(iter->host);
/*
* Prepare a pristine policy object.
*/
SMTP_TLS_POLICY *tls = (SMTP_TLS_POLICY *) mymalloc(sizeof(*tls));
smtp_tls_policy_init(tls, dsb_create());
/*
* Compute the per-site TLS enforcement level. For compatibility with the
* original TLS patch, this algorithm is gives equal precedence to host
* and next-hop policies.
*/
tls->level = global_tls_level();
site_level = TLS_LEV_NOTFOUND;
if (tls_policy) {
tls_policy_lookup(tls, &site_level, dest, "next-hop destination");
} else if (tls_per_site) {
tls_site_lookup(tls, &site_level, dest, "next-hop destination");
if (site_level != TLS_LEV_INVALID
&& strcasecmp(dest, host) != 0)
tls_site_lookup(tls, &site_level, host, "server hostname");
/*
* Override a wild-card per-site policy with a more specific global
* policy.
*
* With the original TLS patch, 1) a per-site ENCRYPT could not override
* a global VERIFY, and 2) a combined per-site (NONE+MAY) policy
* produced inconsistent results: it changed a global VERIFY into
* NONE, while producing MAY with all weaker global policy settings.
*
* With the current implementation, a combined per-site (NONE+MAY)
* consistently overrides global policy with NONE, and global policy
* can override only a per-site MAY wildcard. That is, specific
* policies consistently override wildcard policies, and
* (non-wildcard) per-site policies consistently override global
* policies.
*/
if (site_level == TLS_LEV_MAY && tls->level > TLS_LEV_MAY)
site_level = tls->level;
}
switch (site_level) {
default:
tls->level = site_level;
case TLS_LEV_NOTFOUND:
break;
case TLS_LEV_INVALID:
return ((void *) tls);
}
/*
* DANE initialization may change the security level to something else,
* so do this early, so that we use the right level below. Note that
* "dane-only" changes to "dane" once we obtain the requisite TLSA
* records.
*/
if (tls->level == TLS_LEV_DANE || tls->level == TLS_LEV_DANE_ONLY)
dane_init(tls, iter);
if (tls->level == TLS_LEV_INVALID)
return ((void *) tls);
/*
* Use main.cf protocols setting if not set in per-destination table.
*/
if (tls->level > TLS_LEV_NONE && tls->protocols == 0)
tls->protocols =
mystrdup((tls->level == TLS_LEV_MAY) ?
var_smtp_tls_proto : var_smtp_tls_mand_proto);
/*
* Compute cipher grade (if set in per-destination table, else
* set_cipher() uses main.cf settings) and security level dependent
* cipher exclusion list.
*/
set_cipher_grade(tls);
/*
* Use main.cf cert_match setting if not set in per-destination table.
*/
switch (tls->level) {
case TLS_LEV_INVALID:
case TLS_LEV_NONE:
case TLS_LEV_MAY:
case TLS_LEV_ENCRYPT:
case TLS_LEV_DANE:
break;
case TLS_LEV_FPRINT:
if (tls->dane == 0)
tls->dane = tls_dane_alloc();
if (!TLS_DANE_HASEE(tls->dane)) {
tls_dane_add_ee_digests(tls->dane, var_smtp_tls_fpt_dgst,
var_smtp_tls_fpt_cmatch, "\t\n\r, ");
if (!TLS_DANE_HASEE(tls->dane)) {
msg_warn("nexthop domain %s: configured at fingerprint "
"security level, but with no fingerprints to match.",
dest);
MARK_INVALID(tls->why, &tls->level);
return ((void *) tls);
}
}
break;
case TLS_LEV_VERIFY:
case TLS_LEV_SECURE:
if (tls->matchargv == 0)
tls->matchargv =
argv_split(tls->level == TLS_LEV_VERIFY ?
var_smtp_tls_vfy_cmatch : var_smtp_tls_sec_cmatch,
"\t\n\r, :");
if (*var_smtp_tls_tafile) {
if (tls->dane == 0)
tls->dane = tls_dane_alloc();
if (!TLS_DANE_HASTA(tls->dane)
&& !load_tas(tls->dane, var_smtp_tls_tafile)) {
MARK_INVALID(tls->why, &tls->level);
return ((void *) tls);
}
}
break;
default:
msg_panic("unexpected TLS security level: %d", tls->level);
}
if (msg_verbose && tls->level != global_tls_level())
msg_info("%s TLS level: %s", "effective", policy_name(tls->level));
return ((void *) tls);
}
