Adding upstream version 3.8.5.upstream/3.8.5

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 927 insertions, 0 deletions

diff --git a/src/smtp/smtp_tls_policy.c b/src/smtp/smtp_tls_policy.c
new file mode 100644
index 0000000..92a231d
--- /dev/null
+++ b/src/smtp/smtp_tls_policy.c
@@ -0,0 +1,927 @@
+/*++
+/* 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
+/*
+/*	Wietse Venema
+/*	Google, Inc.
+/*	111 8th Avenue
+/*	New York, NY 10011, 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_hostname.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;
+	}
+	/* Only one instance per policy. */
+	if (!strcasecmp(name, "servername")) {
+	    if (tls->sni) {
+		msg_warn("%s: attribute \"%s\" is specified multiple times",
+			 WHERE, name);
+		INVALID_RETURN(tls->why, site_level);
+	    }
+	    if (valid_hostname(val, DONT_GRIPE))
+		tls->sni = mystrdup(val);
+	    else {
+		msg_warn("%s: \"%s=%s\" specifies an invalid hostname",
+			 WHERE, name, val);
+		INVALID_RETURN(tls->why, site_level);
+	    }
+	    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_fpt_digests(tls->dane, val, "|", smtp_mode);
+		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;
+	}
+	/* Last one wins. */
+	if (!strcasecmp(name, "connection_reuse")) {
+	    if (strcasecmp(val, "yes") == 0) {
+		tls->conn_reuse = 1;
+	    } else if (strcasecmp(val, "no") == 0) {
+		tls->conn_reuse = 0;
+	    } else {
+		msg_warn("%s: attribute \"%s\" has bad value: \"%s\"",
+			 WHERE, name, 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());
+    tls->conn_reuse = var_smtp_tls_conn_reuse;
+
+    /*
+     * 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 and SNI settings 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);
+    if (tls->level > TLS_LEV_NONE && tls->sni == 0) {
+	if (!*var_smtp_tls_sni || valid_hostname(var_smtp_tls_sni, DONT_GRIPE))
+	    tls->sni = mystrdup(var_smtp_tls_sni);
+	else {
+	    msg_warn("\"%s = %s\" specifies an invalid hostname",
+		     VAR_LMTP_SMTP(TLS_SNI), var_smtp_tls_sni);
+	    MARK_INVALID(tls->why, &tls->level);
+	    return ((void *) tls);
+	}
+    }
+
+    /*
+     * 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->tlsa == 0) {
+	    tls_dane_add_fpt_digests(tls->dane, var_smtp_tls_fpt_cmatch,
+				     CHARS_COMMA_SP, smtp_mode);
+	    if (tls->dane->tlsa == 0) {
+		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->tlsa == 0
+		&& !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->sni)
+	myfree(tls->sni);
+    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_CUR_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 (dane->tlsa != 0) {
+	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
+	msg_panic("empty DANE match list");
+    tls->dane = dane;
+    return;
+}
+
+#endif