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/*++
/* NAME
/* smtp_tls_policy 3
/* SUMMARY
/* SMTP_TLS_POLICY structure management
/* SYNOPSIS
/* #include "smtp.h"
/*
/* void smtp_tls_list_init()
/*
/* int smtp_tls_policy_cache_query(why, tls, iter)
/* DSN_BUF *why;
/* SMTP_TLS_POLICY *tls;
/* SMTP_ITERATOR *iter;
/*
/* void smtp_tls_policy_dummy(tls)
/* SMTP_TLS_POLICY *tls;
/*
/* void smtp_tls_policy_cache_flush()
/* DESCRIPTION
/* smtp_tls_list_init() initializes lookup tables used by the TLS
/* policy engine.
/*
/* smtp_tls_policy_cache_query() returns a shallow copy of the
/* cached SMTP_TLS_POLICY structure for the iterator's
/* destination, host, port and DNSSEC validation status.
/* This copy is guaranteed to be valid until the next
/* smtp_tls_policy_cache_query() or smtp_tls_policy_cache_flush()
/* call. The caller can override the TLS security level without
/* corrupting the policy cache.
/* When any required table or DNS lookups fail, the TLS level
/* is set to TLS_LEV_INVALID, the "why" argument is updated
/* with the error reason and the result value is zero (false).
/*
/* smtp_tls_policy_dummy() initializes a trivial, non-cached,
/* policy with TLS disabled.
/*
/* smtp_tls_policy_cache_flush() destroys the TLS policy cache
/* and contents.
/*
/* Arguments:
/* .IP why
/* A pointer to a DSN_BUF which holds error status information when
/* the TLS policy lookup fails.
/* .IP tls
/* Pointer to TLS policy storage.
/* .IP iter
/* The literal next-hop or fall-back destination including
/* the optional [] and including the :port or :service;
/* the name of the remote host after MX and CNAME expansions
/* (see smtp_cname_overrides_servername for the handling
/* of hostnames that resolve to a CNAME record);
/* the printable address of the remote host;
/* the remote port in network byte order;
/* the DNSSEC validation status of the host name lookup after
/* MX and CNAME expansions.
/* 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)
/* TLS support originally 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
/*
/* Viktor Dukhovni
/*--*/
/* System library. */
#include <sys_defs.h>
#ifdef USE_TLS
#include <netinet/in.h> /* ntohs() for Solaris or BSD */
#include <arpa/inet.h> /* ntohs() for Linux or BSD */
#include <stdlib.h>
#include <string.h>
#ifdef STRCASECMP_IN_STRINGS_H
#include <strings.h>
#endif
/* Utility library. */
#include <msg.h>
#include <mymalloc.h>
#include <vstring.h>
#include <stringops.h>
#include <valid_utf8_hostname.h>
#include <ctable.h>
/* Global library. */
#include <mail_params.h>
#include <maps.h>
#include <dsn_buf.h>
/* DNS library. */
#include <dns.h>
/* Application-specific. */
#include "smtp.h"
/* XXX Cache size should scale with [sl]mtp_mx_address_limit. */
#define CACHE_SIZE 20
static CTABLE *policy_cache;
static int global_tls_level(void);
static void dane_init(SMTP_TLS_POLICY *, SMTP_ITERATOR *);
static MAPS *tls_policy; /* lookup table(s) */
static MAPS *tls_per_site; /* lookup table(s) */
/* smtp_tls_list_init - initialize per-site policy lists */
void smtp_tls_list_init(void)
{
if (*var_smtp_tls_policy) {
tls_policy = maps_create(VAR_LMTP_SMTP(TLS_POLICY),
var_smtp_tls_policy,
DICT_FLAG_LOCK | DICT_FLAG_FOLD_FIX
| DICT_FLAG_UTF8_REQUEST);
if (*var_smtp_tls_per_site)
msg_warn("%s ignored when %s is not empty.",
VAR_LMTP_SMTP(TLS_PER_SITE), VAR_LMTP_SMTP(TLS_POLICY));
return;
}
if (*var_smtp_tls_per_site) {
tls_per_site = maps_create(VAR_LMTP_SMTP(TLS_PER_SITE),
var_smtp_tls_per_site,
DICT_FLAG_LOCK | DICT_FLAG_FOLD_FIX
| DICT_FLAG_UTF8_REQUEST);
}
}
/* policy_name - printable tls policy level */
static const char *policy_name(int tls_level)
{
const char *name = str_tls_level(tls_level);
if (name == 0)
name = "unknown";
return name;
}
#define MARK_INVALID(why, levelp) do { \
dsb_simple((why), "4.7.5", "client TLS configuration problem"); \
*(levelp) = TLS_LEV_INVALID; } while (0)
/* tls_site_lookup - look up per-site TLS security level */
static void tls_site_lookup(SMTP_TLS_POLICY *tls, int *site_level,
const char *site_name, const char *site_class)
{
const char *lookup;
/*
* Look up a non-default policy. In case of multiple lookup results, the
* precedence order is a permutation of the TLS enforcement level order:
* VERIFY, ENCRYPT, NONE, MAY, NOTFOUND. I.e. we override MAY with a more
* specific policy including NONE, otherwise we choose the stronger
* enforcement level.
*/
if ((lookup = maps_find(tls_per_site, site_name, 0)) != 0) {
if (!strcasecmp(lookup, "NONE")) {
/* NONE overrides MAY or NOTFOUND. */
if (*site_level <= TLS_LEV_MAY)
*site_level = TLS_LEV_NONE;
} else if (!strcasecmp(lookup, "MAY")) {
/* MAY overrides NOTFOUND but not NONE. */
if (*site_level < TLS_LEV_NONE)
*site_level = TLS_LEV_MAY;
} else if (!strcasecmp(lookup, "MUST_NOPEERMATCH")) {
if (*site_level < TLS_LEV_ENCRYPT)
*site_level = TLS_LEV_ENCRYPT;
} else if (!strcasecmp(lookup, "MUST")) {
if (*site_level < TLS_LEV_VERIFY)
*site_level = TLS_LEV_VERIFY;
} else {
msg_warn("%s: unknown TLS policy '%s' for %s %s",
tls_per_site->title, lookup, site_class, site_name);
MARK_INVALID(tls->why, site_level);
return;
}
} else if (tls_per_site->error) {
msg_warn("%s: %s \"%s\": per-site table lookup error",
tls_per_site->title, site_class, site_name);
dsb_simple(tls->why, "4.3.0", "Temporary lookup error");
*site_level = TLS_LEV_INVALID;
return;
}
return;
}
/* tls_policy_lookup_one - look up destination TLS policy */
static void tls_policy_lookup_one(SMTP_TLS_POLICY *tls, int *site_level,
const char *site_name,
const char *site_class)
{
const char *lookup;
char *policy;
char *saved_policy;
char *tok;
const char *err;
char *name;
char *val;
static VSTRING *cbuf;
#undef FREE_RETURN
#define FREE_RETURN do { myfree(saved_policy); return; } while (0)
#define INVALID_RETURN(why, levelp) do { \
MARK_INVALID((why), (levelp)); FREE_RETURN; } while (0)
#define WHERE \
STR(vstring_sprintf(cbuf, "%s, %s \"%s\"", \
tls_policy->title, site_class, site_name))
if (cbuf == 0)
cbuf = vstring_alloc(10);
if ((lookup = maps_find(tls_policy, site_name, 0)) == 0) {
if (tls_policy->error) {
msg_warn("%s: policy table lookup error", WHERE);
MARK_INVALID(tls->why, site_level);
}
return;
}
saved_policy = policy = mystrdup(lookup);
if ((tok = mystrtok(&policy, CHARS_COMMA_SP)) == 0) {
msg_warn("%s: invalid empty policy", WHERE);
INVALID_RETURN(tls->why, site_level);
}
*site_level = tls_level_lookup(tok);
if (*site_level == TLS_LEV_INVALID) {
/* tls_level_lookup() logs no warning. */
msg_warn("%s: invalid security level \"%s\"", WHERE, tok);
INVALID_RETURN(tls->why, site_level);
}
/*
* Warn about ignored attributes when TLS is disabled.
*/
if (*site_level < TLS_LEV_MAY) {
while ((tok = mystrtok(&policy, CHARS_COMMA_SP)) != 0)
msg_warn("%s: ignoring attribute \"%s\" with TLS disabled",
WHERE, tok);
FREE_RETURN;
}
/*
* Errors in attributes may have security consequences, don't ignore
* errors that can degrade security.
*/
while ((tok = mystrtok(&policy, CHARS_COMMA_SP)) != 0) {
if ((err = split_nameval(tok, &name, &val)) != 0) {
msg_warn("%s: malformed attribute/value pair \"%s\": %s",
WHERE, tok, err);
INVALID_RETURN(tls->why, site_level);
}
/* Only one instance per policy. */
if (!strcasecmp(name, "ciphers")) {
if (*val == 0) {
msg_warn("%s: attribute \"%s\" has empty value", WHERE, name);
INVALID_RETURN(tls->why, site_level);
}
if (tls->grade) {
msg_warn("%s: attribute \"%s\" is specified multiple times",
WHERE, name);
INVALID_RETURN(tls->why, site_level);
}
tls->grade = mystrdup(val);
continue;
}
/* Only one instance per policy. */
if (!strcasecmp(name, "protocols")) {
if (tls->protocols) {
msg_warn("%s: attribute \"%s\" is specified multiple times",
WHERE, name);
INVALID_RETURN(tls->why, site_level);
}
tls->protocols = mystrdup(val);
continue;
}
/* Multiple instances per policy. */
if (!strcasecmp(name, "match")) {
if (*val == 0) {
msg_warn("%s: attribute \"%s\" has empty value", WHERE, name);
INVALID_RETURN(tls->why, site_level);
}
switch (*site_level) {
default:
msg_warn("%s: attribute \"%s\" invalid at security level "
"\"%s\"", WHERE, name, policy_name(*site_level));
INVALID_RETURN(tls->why, site_level);
break;
case TLS_LEV_FPRINT:
if (!tls->dane)
tls->dane = tls_dane_alloc();
tls_dane_add_ee_digests(tls->dane,
var_smtp_tls_fpt_dgst, val, "|");
break;
case TLS_LEV_VERIFY:
case TLS_LEV_SECURE:
if (tls->matchargv == 0)
tls->matchargv = argv_split(val, ":");
else
argv_split_append(tls->matchargv, val, ":");
break;
}
continue;
}
/* Only one instance per policy. */
if (!strcasecmp(name, "exclude")) {
if (tls->exclusions) {
msg_warn("%s: attribute \"%s\" is specified multiple times",
WHERE, name);
INVALID_RETURN(tls->why, site_level);
}
tls->exclusions = vstring_strcpy(vstring_alloc(10), val);
continue;
}
/* Multiple instances per policy. */
if (!strcasecmp(name, "tafile")) {
/* Only makes sense if we're using CA-based trust */
if (!TLS_MUST_PKIX(*site_level)) {
msg_warn("%s: attribute \"%s\" invalid at security level"
" \"%s\"", WHERE, name, policy_name(*site_level));
INVALID_RETURN(tls->why, site_level);
}
if (*val == 0) {
msg_warn("%s: attribute \"%s\" has empty value", WHERE, name);
INVALID_RETURN(tls->why, site_level);
}
if (!tls->dane)
tls->dane = tls_dane_alloc();
if (!tls_dane_load_trustfile(tls->dane, val)) {
INVALID_RETURN(tls->why, site_level);
}
continue;
}
msg_warn("%s: invalid attribute name: \"%s\"", WHERE, name);
INVALID_RETURN(tls->why, site_level);
}
FREE_RETURN;
}
/* tls_policy_lookup - look up destination TLS policy */
static void tls_policy_lookup(SMTP_TLS_POLICY *tls, int *site_level,
const char *site_name,
const char *site_class)
{
/*
* Only one lookup with [nexthop]:port, [nexthop] or nexthop:port These
* are never the domain part of localpart@domain, rather they are
* explicit nexthops from transport:nexthop, and match only the
* corresponding policy. Parent domain matching (below) applies only to
* sub-domains of the recipient domain.
*
* XXX UNIX-domain connections query with the pathname as destination.
*/
if (!valid_utf8_hostname(var_smtputf8_enable, site_name, DONT_GRIPE)) {
tls_policy_lookup_one(tls, site_level, site_name, site_class);
return;
}
do {
tls_policy_lookup_one(tls, site_level, site_name, site_class);
} while (*site_level == TLS_LEV_NOTFOUND
&& (site_name = strchr(site_name + 1, '.')) != 0);
}
/* load_tas - load one or more ta files */
static int load_tas(TLS_DANE *dane, const char *files)
{
int ret = 0;
char *save = mystrdup(files);
char *buf = save;
char *file;
do {
if ((file = mystrtok(&buf, CHARS_COMMA_SP)) != 0)
ret = tls_dane_load_trustfile(dane, file);
} while (file && ret);
myfree(save);
return (ret);
}
/* set_cipher_grade - Set cipher grade and exclusions */
static void set_cipher_grade(SMTP_TLS_POLICY *tls)
{
const char *mand_exclude = "";
const char *also_exclude = "";
/*
* Use main.cf cipher level if no per-destination value specified. With
* mandatory encryption at least encrypt, and with mandatory verification
* at least authenticate!
*/
switch (tls->level) {
case TLS_LEV_INVALID:
case TLS_LEV_NONE:
return;
case TLS_LEV_MAY:
if (tls->grade == 0)
tls->grade = mystrdup(var_smtp_tls_ciph);
break;
case TLS_LEV_ENCRYPT:
if (tls->grade == 0)
tls->grade = mystrdup(var_smtp_tls_mand_ciph);
mand_exclude = var_smtp_tls_mand_excl;
also_exclude = "eNULL";
break;
case TLS_LEV_HALF_DANE:
case TLS_LEV_DANE:
case TLS_LEV_DANE_ONLY:
case TLS_LEV_FPRINT:
case TLS_LEV_VERIFY:
case TLS_LEV_SECURE:
if (tls->grade == 0)
tls->grade = mystrdup(var_smtp_tls_mand_ciph);
mand_exclude = var_smtp_tls_mand_excl;
also_exclude = "aNULL";
break;
}
#define ADD_EXCLUDE(vstr, str) \
do { \
if (*(str)) \
vstring_sprintf_append((vstr), "%s%s", \
VSTRING_LEN(vstr) ? " " : "", (str)); \
} while (0)
/*
* The "exclude" policy table attribute overrides main.cf exclusion
* lists.
*/
if (tls->exclusions == 0) {
tls->exclusions = vstring_alloc(10);
ADD_EXCLUDE(tls->exclusions, var_smtp_tls_excl_ciph);
ADD_EXCLUDE(tls->exclusions, mand_exclude);
}
ADD_EXCLUDE(tls->exclusions, also_exclude);
}
/* policy_create - create SMTP TLS policy cache object (ctable call-back) */
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_utf8(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;
/* FALLTHROUGH */
case TLS_LEV_NOTFOUND:
break;
case TLS_LEV_INVALID:
tls->level = site_level;
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_DANE_BASED(tls->level))
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_HALF_DANE:
case TLS_LEV_DANE:
case TLS_LEV_DANE_ONLY:
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, CHARS_COMMA_SP);
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,
CHARS_COMMA_SP ":");
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);
}
/* policy_delete - free no longer cached policy (ctable call-back) */
static void policy_delete(void *item, void *unused_context)
{
SMTP_TLS_POLICY *tls = (SMTP_TLS_POLICY *) item;
if (tls->protocols)
myfree(tls->protocols);
if (tls->grade)
myfree(tls->grade);
if (tls->exclusions)
vstring_free(tls->exclusions);
if (tls->matchargv)
argv_free(tls->matchargv);
if (tls->dane)
tls_dane_free(tls->dane);
dsb_free(tls->why);
myfree((void *) tls);
}
/* smtp_tls_policy_cache_query - cached lookup of TLS policy */
int smtp_tls_policy_cache_query(DSN_BUF *why, SMTP_TLS_POLICY *tls,
SMTP_ITERATOR *iter)
{
VSTRING *key;
/*
* Create an empty TLS Policy cache on the fly.
*/
if (policy_cache == 0)
policy_cache =
ctable_create(CACHE_SIZE, policy_create, policy_delete, (void *) 0);
/*
* Query the TLS Policy cache, with a search key that reflects our shared
* values that also appear in other cache and table search keys.
*/
key = vstring_alloc(100);
smtp_key_prefix(key, ":", iter, SMTP_KEY_FLAG_NEXTHOP
| SMTP_KEY_FLAG_HOSTNAME
| SMTP_KEY_FLAG_PORT);
ctable_newcontext(policy_cache, (void *) iter);
*tls = *(SMTP_TLS_POLICY *) ctable_locate(policy_cache, STR(key));
vstring_free(key);
/*
* Report errors. Both error and non-error results are cached. We must
* therefore copy the cached DSN buffer content to the caller's buffer.
*/
if (tls->level == TLS_LEV_INVALID) {
/* XXX Simplify this by implementing a "copy" primitive. */
dsb_update(why,
STR(tls->why->status), STR(tls->why->action),
STR(tls->why->mtype), STR(tls->why->mname),
STR(tls->why->dtype), STR(tls->why->dtext),
"%s", STR(tls->why->reason));
return (0);
} else {
return (1);
}
}
/* smtp_tls_policy_cache_flush - flush TLS policy cache */
void smtp_tls_policy_cache_flush(void)
{
if (policy_cache != 0) {
ctable_free(policy_cache);
policy_cache = 0;
}
}
/* global_tls_level - parse and cache var_smtp_tls_level */
static int global_tls_level(void)
{
static int l = TLS_LEV_NOTFOUND;
if (l != TLS_LEV_NOTFOUND)
return l;
/*
* Compute the global TLS policy. This is the default policy level when
* no per-site policy exists. It also is used to override a wild-card
* per-site policy.
*
* We require that the global level is valid on startup.
*/
if (*var_smtp_tls_level) {
if ((l = tls_level_lookup(var_smtp_tls_level)) == TLS_LEV_INVALID)
msg_fatal("invalid tls security level: \"%s\"", var_smtp_tls_level);
} else if (var_smtp_enforce_tls)
l = var_smtp_tls_enforce_peername ? TLS_LEV_VERIFY : TLS_LEV_ENCRYPT;
else
l = var_smtp_use_tls ? TLS_LEV_MAY : TLS_LEV_NONE;
if (msg_verbose)
msg_info("%s TLS level: %s", "global", policy_name(l));
return l;
}
#define NONDANE_CONFIG 0 /* Administrator's fault */
#define NONDANE_DEST 1 /* Remote server's fault */
#define DANE_CANTAUTH 2 /* Remote server's fault */
static void PRINTFLIKE(4, 5) dane_incompat(SMTP_TLS_POLICY *tls,
SMTP_ITERATOR *iter,
int errtype,
const char *fmt,...)
{
va_list ap;
va_start(ap, fmt);
if (tls->level == TLS_LEV_DANE) {
tls->level = (errtype == DANE_CANTAUTH) ? TLS_LEV_ENCRYPT : TLS_LEV_MAY;
if (errtype == NONDANE_CONFIG)
vmsg_warn(fmt, ap);
else if (msg_verbose)
vmsg_info(fmt, ap);
} else { /* dane-only */
if (errtype == NONDANE_CONFIG) {
vmsg_warn(fmt, ap);
MARK_INVALID(tls->why, &tls->level);
} else {
tls->level = TLS_LEV_INVALID;
vdsb_simple(tls->why, "4.7.5", fmt, ap);
}
}
va_end(ap);
}
/* dane_init - special initialization for "dane" security level */
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 may not apply, we then
* either fail if DANE is mandatory or use regular opportunistic TLS if
* the insecure MX level is "may".
*/
if (iter->mx && !iter->mx->dnssec_valid
&& (tls->level == TLS_LEV_DANE_ONLY ||
smtp_tls_insecure_mx_policy <= TLS_LEV_MAY)) {
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_CANTAUTH, "TLSA records unusable");
tls_dane_free(dane);
return;
}
/*
* Perhaps downgrade to "encrypt" if MX is insecure.
*/
if (iter->mx && !iter->mx->dnssec_valid) {
if (smtp_tls_insecure_mx_policy == TLS_LEV_ENCRYPT) {
dane_incompat(tls, iter, DANE_CANTAUTH,
"Verification not possible, MX RRset is insecure");
tls_dane_free(dane);
return;
}
if (tls->level != TLS_LEV_DANE
|| smtp_tls_insecure_mx_policy != TLS_LEV_DANE)
msg_panic("wrong state for insecure MX host DANE policy");
/* For correct logging in tls_client_start() */
tls->level = TLS_LEV_HALF_DANE;
}
/*
* 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;
return;
}
#endif