Fix #1346: [FR] Please allow back TLS 1.2. (#1349)

* 'tls-use-system-policy-versions' is introduced to allow Unbound to use
  any system available TLS version when serving TLS.

* Apply suggestions from code review

---------

Co-authored-by: Wouter Wijngaards <wcawijngaards@users.noreply.github.com>

daemon/remote.c

@@ -153,7 +153,7 @@ remote_setup_ctx(struct daemon_remote* rc, struct config_file* cfg)
 		log_crypto_err("could not SSL_CTX_new");
 		return 0;
 	}
-	if(!listen_sslctx_setup(rc->ctx)) {
+	if(!listen_sslctx_setup(rc->ctx, cfg->tls_use_system_policy_versions)) {
 		return 0;
 	}
 

daemon/unbound.c

@@ -473,7 +473,7 @@ setup_listen_sslctx(void** ctx, int is_dot, int is_doh, struct config_file* cfg)
 		cfg->tls_ciphers, cfg->tls_ciphersuites,
 		(cfg->tls_session_ticket_keys.first &&
 		cfg->tls_session_ticket_keys.first->str[0] != 0),
-		is_dot, is_doh))) {
+		is_dot, is_doh, cfg->tls_use_system_policy_versions))) {
 		fatal_exit("could not set up listen SSL_CTX");
 	}
 }

dnstap/unbound-dnstap-socket.c

@@ -347,7 +347,7 @@ static struct tap_socket* tap_socket_new_tlsaccept(char* ip,
 	s->ev_cb = ev_cb;
 	s->data = data;
 	s->sslctx = listen_sslctx_create(server_key, server_cert, verifypem,
-		NULL, NULL, 0, 0, 0);
+		NULL, NULL, 0, 0, 0, 0);
 	if(!s->sslctx) {
 		log_err("could not create ssl context");
 		free(s->ip);

doc/example.conf.in

@@ -932,21 +932,26 @@ server:
 	# https-port: 443
 	# quic-port: 853
 
+	# Also serve tls on these port numbers (eg. 443, ...), by listing
+	# tls-additional-port: portno for each of the port numbers.
+
 	# cipher setting for TLSv1.2
 	# tls-ciphers: "DHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-SHA256:DHE-RSA-AES128-SHA256:ECDHE-RSA-AES256-SHA384:ECDHE-RSA-AES128-SHA256"
 	# cipher setting for TLSv1.3
 	# tls-ciphersuites: "TLS_AES_128_GCM_SHA256:TLS_AES_128_CCM_8_SHA256:TLS_AES_128_CCM_SHA256:TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256"
 
-	# Pad responses to padded queries received over TLS
-	# pad-responses: yes
-
-	# Padded responses will be padded to the closest multiple of this size.
-	# pad-responses-block-size: 468
-
 	# Use the SNI extension for TLS connections.  Default is yes.
 	# Changing the value requires a reload.
 	# tls-use-sni: yes
 
+	# Allow general-purpose version-flexible TLS server configuration that
+	# may be further restricted by the system's policy.
+	# Use only if you want to support legacy TLS client connections.
+	# Default is no and Unbound will only use the latest available TLS
+	# version.
+	# Changing the value requires a reload.
+	# tls-use-system-policy-versions: no
+
 	# Add the secret file for TLS Session Ticket.
 	# Secret file must be 80 bytes of random data.
 	# First key use to encrypt and decrypt TLS session tickets.
@@ -967,15 +972,18 @@ server:
 	# and on other systems, the default openssl certificates
 	# tls-system-cert: no
 
+	# Pad responses to padded queries received over TLS
+	# pad-responses: yes
+
+	# Padded responses will be padded to the closest multiple of this size.
+	# pad-responses-block-size: 468
+
 	# Pad queries over TLS upstreams
 	# pad-queries: yes
 
 	# Padded queries will be padded to the closest multiple of this size.
 	# pad-queries-block-size: 128
 
-	# Also serve tls on these port numbers (eg. 443, ...), by listing
-	# tls-additional-port: portno for each of the port numbers.
-
 	# HTTP endpoint to provide DNS-over-HTTPS service on.
 	# http-endpoint: "/dns-query"
 

doc/unbound.conf.5.in

@@ -1218,6 +1218,47 @@ Default: \(dq\(dq
 .UNINDENT
 .INDENT 0.0
 .TP
+.B tls\-use\-sni: \fI<yes or no>\fP 
+Enable or disable sending the SNI extension on TLS connections.
+.sp
+\fBNOTE:\fP
+.INDENT 7.0
+.INDENT 3.5
+Changing the value requires a reload.
+.UNINDENT
+.UNINDENT
+.sp
+Default: yes
+.UNINDENT
+.INDENT 0.0
+.TP
+.B tls\-use\-system\-policy\-versions: \fI<yes or no>\fP 
+Enable or disable general\-puspose version\-flexible TLS server configuration
+when serving TLS.
+This will allow the whole list of available TLS versions provided by the
+crypto library, which may have been further restricted by the system\(aqs
+crypto policy.
+.sp
+By default Unbound only uses the latest available TLS version.
+.sp
+\fBCAUTION:\fP
+.INDENT 7.0
+.INDENT 3.5
+Use only if you want to support legacy TLS client connections.
+.UNINDENT
+.UNINDENT
+.sp
+\fBNOTE:\fP
+.INDENT 7.0
+.INDENT 3.5
+Changing the value requires a reload.
+.UNINDENT
+.UNINDENT
+.sp
+Default: no
+.UNINDENT
+.INDENT 0.0
+.TP
 .B pad\-responses: \fI<yes or no>\fP 
 If enabled, TLS serviced queries that contained an EDNS Padding option will
 cause responses padded to the closest multiple of the size specified in
@@ -1251,20 +1292,6 @@ Default: 128
 .UNINDENT
 .INDENT 0.0
 .TP
-.B tls\-use\-sni: \fI<yes or no>\fP 
-Enable or disable sending the SNI extension on TLS connections.
-.sp
-\fBNOTE:\fP
-.INDENT 7.0
-.INDENT 3.5
-Changing the value requires a reload.
-.UNINDENT
-.UNINDENT
-.sp
-Default: yes
-.UNINDENT
-.INDENT 0.0
-.TP
 .B https\-port: \fI<number>\fP 
 The port number on which to provide DNS\-over\-HTTPS service.
 Only interfaces configured with that port number as @number get the HTTPS

doc/unbound.conf.rst

@@ -1103,6 +1103,30 @@ These options are part of the **server:** clause.
     Default: ""
 
 
+@@UAHL@unbound.conf@tls-use-sni@@: *<yes or no>*
+    Enable or disable sending the SNI extension on TLS connections.
+
+    .. note:: Changing the value requires a reload.
+
+    Default: yes
+
+
+@@UAHL@unbound.conf@tls-use-system-policy-versions@@: *<yes or no>*
+    Enable or disable general-puspose version-flexible TLS server configuration
+    when serving TLS.
+    This will allow the whole list of available TLS versions provided by the
+    crypto library, which may have been further restricted by the system's
+    crypto policy.
+
+    By default Unbound only uses the latest available TLS version.
+
+    .. caution:: Use only if you want to support legacy TLS client connections.
+
+    .. note:: Changing the value requires a reload.
+
+    Default: no
+
+
 @@UAHL@unbound.conf@pad-responses@@: *<yes or no>*
     If enabled, TLS serviced queries that contained an EDNS Padding option will
     cause responses padded to the closest multiple of the size specified in
@@ -1132,14 +1156,6 @@ These options are part of the **server:** clause.
     Default: 128
 
 
-@@UAHL@unbound.conf@tls-use-sni@@: *<yes or no>*
-    Enable or disable sending the SNI extension on TLS connections.
-
-    .. note:: Changing the value requires a reload.
-
-    Default: yes
-
-
 @@UAHL@unbound.conf@https-port@@: *<number>*
     The port number on which to provide DNS-over-HTTPS service.
     Only interfaces configured with that port number as @number get the HTTPS

util/config_file.c

@@ -129,6 +129,7 @@ config_create(void)
 	cfg->tls_cert_bundle = NULL;
 	cfg->tls_win_cert = 0;
 	cfg->tls_use_sni = 1;
+	cfg->tls_use_system_policy_versions = 0;
 	cfg->https_port = UNBOUND_DNS_OVER_HTTPS_PORT;
 	if(!(cfg->http_endpoint = strdup("/dns-query"))) goto error_exit;
 	cfg->http_max_streams = 100;
@@ -628,6 +629,7 @@ int config_set_option(struct config_file* cfg, const char* opt,
 	else S_STR("tls-ciphers:", tls_ciphers)
 	else S_STR("tls-ciphersuites:", tls_ciphersuites)
 	else S_YNO("tls-use-sni:", tls_use_sni)
+	else S_YNO("tls-use-system-policy-versions:", tls_use_system_policy_versions)
 	else S_NUMBER_NONZERO("https-port:", https_port)
 	else S_STR("http-endpoint:", http_endpoint)
 	else S_NUMBER_NONZERO("http-max-streams:", http_max_streams)
@@ -1179,6 +1181,7 @@ config_get_option(struct config_file* cfg, const char* opt,
 	else O_STR(opt, "tls-ciphers", tls_ciphers)
 	else O_STR(opt, "tls-ciphersuites", tls_ciphersuites)
 	else O_YNO(opt, "tls-use-sni", tls_use_sni)
+	else O_YNO(opt, "tls-use-system-policy-versions", tls_use_system_policy_versions)
 	else O_DEC(opt, "https-port", https_port)
 	else O_STR(opt, "http-endpoint", http_endpoint)
 	else O_UNS(opt, "http-max-streams", http_max_streams)

util/config_file.h

@@ -148,6 +148,8 @@ struct config_file {
 	char* tls_ciphersuites;
 	/** if SNI is to be used */
 	int tls_use_sni;
+	/** if all TLS versions can be used; based on system policy (if any) */
+	int tls_use_system_policy_versions;
 
 	/** port on which to provide DNS over HTTPS service */
 	int https_port;

util/configlexer.lex

@@ -262,6 +262,7 @@ tls-session-ticket-keys{COLON}	{ YDVAR(1, VAR_TLS_SESSION_TICKET_KEYS) }
 tls-ciphers{COLON}		{ YDVAR(1, VAR_TLS_CIPHERS) }
 tls-ciphersuites{COLON}		{ YDVAR(1, VAR_TLS_CIPHERSUITES) }
 tls-use-sni{COLON}		{ YDVAR(1, VAR_TLS_USE_SNI) }
+tls-use-system-policy-versions{COLON}		{ YDVAR(1, VAR_TLS_USE_SYSTEM_POLICY_VERSIONS) }
 https-port{COLON}		{ YDVAR(1, VAR_HTTPS_PORT) }
 http-endpoint{COLON}		{ YDVAR(1, VAR_HTTP_ENDPOINT) }
 http-max-streams{COLON}		{ YDVAR(1, VAR_HTTP_MAX_STREAMS) }

util/configparser.y

@@ -199,6 +199,7 @@ extern struct config_parser_state* cfg_parser;
 %token VAR_DISCARD_TIMEOUT VAR_WAIT_LIMIT VAR_WAIT_LIMIT_COOKIE
 %token VAR_WAIT_LIMIT_NETBLOCK VAR_WAIT_LIMIT_COOKIE_NETBLOCK
 %token VAR_STREAM_WAIT_SIZE VAR_TLS_CIPHERS VAR_TLS_CIPHERSUITES VAR_TLS_USE_SNI
+%token VAR_TLS_USE_SYSTEM_POLICY_VERSIONS
 %token VAR_IPSET VAR_IPSET_NAME_V4 VAR_IPSET_NAME_V6
 %token VAR_TLS_SESSION_TICKET_KEYS VAR_RPZ VAR_TAGS VAR_RPZ_ACTION_OVERRIDE
 %token VAR_RPZ_CNAME_OVERRIDE VAR_RPZ_LOG VAR_RPZ_LOG_NAME
@@ -346,6 +347,7 @@ content_server: server_num_threads | server_verbosity | server_port |
 	server_tls_ciphersuites | server_tls_session_ticket_keys |
 	server_answer_cookie | server_cookie_secret | server_ip_ratelimit_cookie |
 	server_tls_use_sni | server_edns_client_string |
+	server_tls_use_system_policy_versions |
 	server_edns_client_string_opcode | server_nsid |
 	server_zonemd_permissive_mode | server_max_reuse_tcp_queries |
 	server_tcp_reuse_timeout | server_tcp_auth_query_timeout |
@@ -1154,6 +1156,15 @@ server_tls_use_sni: VAR_TLS_USE_SNI STRING_ARG
 		free($2);
 	}
 	;
+server_tls_use_system_policy_versions: VAR_TLS_USE_SYSTEM_POLICY_VERSIONS STRING_ARG
+	{
+		OUTYY(("P(server_tls_use_system_policy_versions:%s)\n", $2));
+		if(strcmp($2, "yes") != 0 && strcmp($2, "no") != 0)
+			yyerror("expected yes or no.");
+		else cfg_parser->cfg->tls_use_system_policy_versions = (strcmp($2, "yes")==0);
+		free($2);
+	}
+	;
 server_https_port: VAR_HTTPS_PORT STRING_ARG
 	{
 		OUTYY(("P(server_https_port:%s)\n", $2));

util/net_help.c

@@ -1226,7 +1226,7 @@ setup_ticket_keys_cb(void* sslctx)
 #endif /* HAVE_SSL */
 
 int
-listen_sslctx_setup(void* ctxt)
+listen_sslctx_setup(void* ctxt, int use_system_versions)
 {
 #ifdef HAVE_SSL
 	SSL_CTX* ctx = (SSL_CTX*)ctxt;
@@ -1238,35 +1238,37 @@ listen_sslctx_setup(void* ctxt)
 		return 0;
 	}
 #endif
-	if((SSL_CTX_set_options(ctx, SSL_OP_NO_SSLv3) & SSL_OP_NO_SSLv3)
-		!= SSL_OP_NO_SSLv3){
-		log_crypto_err("could not set SSL_OP_NO_SSLv3");
-		return 0;
-	}
+	if(!use_system_versions) {
+		if((SSL_CTX_set_options(ctx, SSL_OP_NO_SSLv3) & SSL_OP_NO_SSLv3)
+			!= SSL_OP_NO_SSLv3){
+			log_crypto_err("could not set SSL_OP_NO_SSLv3");
+			return 0;
+		}
 #if defined(SSL_OP_NO_TLSv1) && defined(SSL_OP_NO_TLSv1_1)
-	/* if we have tls 1.1 disable 1.0 */
-	if((SSL_CTX_set_options(ctx, SSL_OP_NO_TLSv1) & SSL_OP_NO_TLSv1)
-		!= SSL_OP_NO_TLSv1){
-		log_crypto_err("could not set SSL_OP_NO_TLSv1");
-		return 0;
-	}
+		/* if we have tls 1.1 disable 1.0 */
+		if((SSL_CTX_set_options(ctx, SSL_OP_NO_TLSv1) & SSL_OP_NO_TLSv1)
+			!= SSL_OP_NO_TLSv1){
+			log_crypto_err("could not set SSL_OP_NO_TLSv1");
+			return 0;
+		}
 #endif
 #if defined(SSL_OP_NO_TLSv1_1) && defined(SSL_OP_NO_TLSv1_2)
-	/* if we have tls 1.2 disable 1.1 */
-	if((SSL_CTX_set_options(ctx, SSL_OP_NO_TLSv1_1) & SSL_OP_NO_TLSv1_1)
-		!= SSL_OP_NO_TLSv1_1){
-		log_crypto_err("could not set SSL_OP_NO_TLSv1_1");
-		return 0;
-	}
+		/* if we have tls 1.2 disable 1.1 */
+		if((SSL_CTX_set_options(ctx, SSL_OP_NO_TLSv1_1) & SSL_OP_NO_TLSv1_1)
+			!= SSL_OP_NO_TLSv1_1){
+			log_crypto_err("could not set SSL_OP_NO_TLSv1_1");
+			return 0;
+		}
 #endif
 #if defined(SSL_OP_NO_TLSv1_2) && defined(SSL_OP_NO_TLSv1_3)
-	/* if we have tls 1.3 disable 1.2 */
-	if((SSL_CTX_set_options(ctx, SSL_OP_NO_TLSv1_2) & SSL_OP_NO_TLSv1_2)
-		!= SSL_OP_NO_TLSv1_2){
-		log_crypto_err("could not set SSL_OP_NO_TLSv1_2");
-		return 0;
-	}
+		/* if we have tls 1.3 disable 1.2 */
+		if((SSL_CTX_set_options(ctx, SSL_OP_NO_TLSv1_2) & SSL_OP_NO_TLSv1_2)
+			!= SSL_OP_NO_TLSv1_2){
+			log_crypto_err("could not set SSL_OP_NO_TLSv1_2");
+			return 0;
+		}
 #endif
+	}
 #if defined(SSL_OP_NO_RENEGOTIATION)
 	/* disable client renegotiation */
 	if((SSL_CTX_set_options(ctx, SSL_OP_NO_RENEGOTIATION) &
@@ -1341,7 +1343,7 @@ listen_sslctx_setup_2(void* ctxt)
 void* listen_sslctx_create(const char* key, const char* pem,
 	const char* verifypem, const char* tls_ciphers,
 	const char* tls_ciphersuites, int set_ticket_keys_cb,
-	int is_dot, int is_doh)
+	int is_dot, int is_doh, int use_system_versions)
 {
 #ifdef HAVE_SSL
 	SSL_CTX* ctx = SSL_CTX_new(SSLv23_server_method());
@@ -1359,7 +1361,7 @@ void* listen_sslctx_create(const char* key, const char* pem,
 		SSL_CTX_free(ctx);
 		return NULL;
 	}
-	if(!listen_sslctx_setup(ctx)) {
+	if(!listen_sslctx_setup(ctx, use_system_versions)) {
 		SSL_CTX_free(ctx);
 		return NULL;
 	}

util/net_help.h

@@ -478,9 +478,11 @@ void log_cert(unsigned level, const char* str, void* cert);
 /**
  * Set SSL_OP_NOxxx options on SSL context to disable bad crypto
  * @param ctxt: SSL_CTX*
+ * @param use_system_versions: rely on the system policy (if any) for allowed
+ *	TLS versions
  * @return false on failure.
  */
-int listen_sslctx_setup(void* ctxt);
+int listen_sslctx_setup(void* ctxt, int use_system_versions);
 
 /**
  * Further setup of listening SSL context, after keys loaded.
@@ -499,12 +501,14 @@ void listen_sslctx_setup_2(void* ctxt);
  *	to be set.
  * @param is_dot: if the TLS connection is for DoT to set the appropriate ALPN.
  * @param is_doh: if the TLS connection is for DoH to set the appropriate ALPN.
+ * @param use_system_versions: rely on the system policy (if any) for allowed
+ *	TLS versions
  * return SSL_CTX* or NULL on failure (logged).
  */
 void* listen_sslctx_create(const char* key, const char* pem,
 	const char* verifypem, const char* tls_ciphers,
 	const char* tls_ciphersuites, int set_ticket_keys_cb,
-	int is_dot, int is_doh);
+	int is_dot, int is_doh, int use_system_versions);
 
 /**
  * create SSL connect context

winrc/win_svc.c

@@ -369,7 +369,7 @@ service_init(int r, struct daemon** d, struct config_file** c)
 			cfg->tls_ciphers, cfg->tls_ciphersuites,
 			(cfg->tls_session_ticket_keys.first &&
 			cfg->tls_session_ticket_keys.first->str[0] != 0),
-			1, 0))) {
+			1, 0, cfg->tls_use_system_policy_versions))) {
 			fatal_exit("could not set up listen SSL_CTX");
 		}
 #ifdef HAVE_NGHTTP2_NGHTTP2_H
@@ -379,7 +379,7 @@ service_init(int r, struct daemon** d, struct config_file** c)
 				cfg->tls_ciphers, cfg->tls_ciphersuites,
 				(cfg->tls_session_ticket_keys.first &&
 				cfg->tls_session_ticket_keys.first->str[0] != 0),
-				0, 1))) {
+				0, 1, cfg->tls_use_system_policy_versions))) {
 				fatal_exit("could not set up listen doh SSL_CTX");
 			}
 		}