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;
}
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;
}
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);
}
