Add MOSQ_OPT_SSL_CTX and MOSQ_OPT_SSL_CTX_WITH_DEFAULTS options.

Closes #567 and #715.

ChangeLog.txt

@@ -97,6 +97,12 @@ Client library features:
 - Add mosquitto_connect_with_flags_callback_set(), which allows a second
   connect callback to be used which also exposes the connect flags parameter.
   Closes #738 and #128.
+- Add MOSQ_OPT_SSL_CTX option to allow a user specified SSL_CTX to be used
+  instead of the one generated by libmosquitto. This allows greater control
+  over what options can be set. Closes #715.
+- Add MOSQ_OPT_SSL_CTX_WITH_DEFAULTS to work with MOSQ_OPT_SSL_CTX and have
+  the default libmosquitto SSL_CTX configuration applied to the user provided
+  SSL_CTX. Closes #567.
 
 Client library fixes:
 - Fix incorrect PSK key being used if it had leading zeroes.

lib/mosquitto.c

@@ -172,6 +172,7 @@ int mosquitto_reinitialise(struct mosquitto *mosq, const char *id, bool clean_se
 	mosq->threaded = mosq_ts_none;
 #ifdef WITH_TLS
 	mosq->ssl = NULL;
+	mosq->ssl_ctx = NULL;
 	mosq->tls_cert_reqs = SSL_VERIFY_PEER;
 	mosq->tls_insecure = false;
 	mosq->want_write = false;

lib/mosquitto.h

@@ -90,6 +90,8 @@ enum mosq_err_t {
 /* Error values */
 enum mosq_opt_t {
 	MOSQ_OPT_PROTOCOL_VERSION = 1,
+	MOSQ_OPT_SSL_CTX = 2,
+	MOSQ_OPT_SSL_CTX_WITH_DEFAULTS = 3,
 };
 
 /* MQTT specification restricts client ids to a maximum of 23 characters */
@@ -960,10 +962,27 @@ libmosq_EXPORT int mosquitto_threaded_set(struct mosquitto *mosq, bool threaded)
  *	value -  the option specific value.
  *
  * Options:
- *	MOSQ_OPT_PROTOCOL_VERSION - value must be an int, set to either
- *	                            MQTT_PROTOCOL_V31 or MQTT_PROTOCOL_V311. Must
- *	                            be set before the client connects. Defaults to
- *	                            MQTT_PROTOCOL_V31.
+ *	MOSQ_OPT_PROTOCOL_VERSION
+ *	          Value must be an int, set to either MQTT_PROTOCOL_V31 or
+ *	          MQTT_PROTOCOL_V311. Must be set before the client connects.
+ *	          Defaults to MQTT_PROTOCOL_V31.
+ *
+ *	MOSQ_OPT_SSL_CTX
+ *	          Pass an openssl SSL_CTX to be used when creating TLS connections
+ *	          rather than libmosquitto creating its own.  This must be called
+ *	          before connecting to have any effect. If you use this option, the
+ *	          onus is on you to ensure that you are using secure settings.
+ *	          Setting to NULL means that libmosquitto will use its own SSL_CTX
+ *	          if TLS is to be used.
+ *
+ *	MOSQ_OPT_SSL_CTX_WITH_DEFAULTS
+ *	          Value must be an int set to 1 or 0. If set to 1, then the user
+ *	          specified SSL_CTX passed in using MOSQ_OPT_SSL_CTX will have the
+ *	          default options applied to it. This means that you only need to
+ *	          change the values that are relevant to you. If you use this
+ *	          option then you must configure the TLS options as normal, i.e.
+ *	          you should use <mosquitto_tls_set> to configure the cafile/capath
+ *	          as a minimum.
  */
 libmosq_EXPORT int mosquitto_opts_set(struct mosquitto *mosq, enum mosq_opt_t option, void *value);
 

lib/mosquitto_internal.h

@@ -188,6 +188,7 @@ struct mosquitto {
 	char *tls_psk_identity;
 	int tls_cert_reqs;
 	bool tls_insecure;
+	bool ssl_ctx_defaults;
 #endif
 	bool want_write;
 	bool want_connect;

lib/net_mosq.c

@@ -442,14 +442,21 @@ int net__socket_connect_tls(struct mosquitto *mosq)
 }
 #endif
 
-int net__socket_connect_step3(struct mosquitto *mosq, const char *host, uint16_t port, const char *bind_address, bool blocking)
+
+static int net__init_ssl_ctx(struct mosquitto *mosq)
 {
 #ifdef WITH_TLS
 	int ret;
-	BIO *bio;
-#endif
 
-#ifdef WITH_TLS
+	if(mosq->ssl_ctx){
+		if(!mosq->ssl_ctx_defaults){
+			return MOSQ_ERR_SUCCESS;
+		}else if(!mosq->tls_cafile && !mosq->tls_capath && !mosq->tls_psk){
+			log__printf(mosq, MOSQ_LOG_ERR, "Error: MOSQ_OPT_SSL_CTX_WITH_DEFAULTS used without specifying cafile, capath or psk.");
+			return MOSQ_ERR_INVAL;
+		}
+	}
+
 	if(mosq->tls_cafile || mosq->tls_capath || mosq->tls_psk){
 #if OPENSSL_VERSION_NUMBER >= 0x10001000L
 		if(!mosq->tls_version){
@@ -572,7 +579,22 @@ int net__socket_connect_step3(struct mosquitto *mosq, const char *host, uint16_t
 			SSL_CTX_set_psk_client_callback(mosq->ssl_ctx, psk_client_callback);
 #endif
 		}
+	}
+
+#endif
+	return MOSQ_ERR_SUCCESS;
+}
+
+
+int net__socket_connect_step3(struct mosquitto *mosq, const char *host, uint16_t port, const char *bind_address, bool blocking)
+{
+#ifdef WITH_TLS
+	BIO *bio;
+
+	int rc = net__init_ssl_ctx(mosq);
+	if(rc) return rc;
 
+	if(mosq->ssl_ctx){
 		mosq->ssl = SSL_new(mosq->ssl_ctx);
 		if(!mosq->ssl){
 			COMPAT_CLOSE(mosq->sock);

lib/options.c

@@ -277,6 +277,20 @@ int mosquitto_opts_set(struct mosquitto *mosq, enum mosq_opt_t option, void *val
 				return MOSQ_ERR_INVAL;
 			}
 			break;
+		case MOSQ_OPT_SSL_CTX:
+#ifdef WITH_TLS
+			mosq->ssl_ctx = (SSL_CTX *)value;
+			break;
+#else
+			return MOSQ_ERR_UNSUPPORTED;
+#endif
+		case MOSQ_OPT_SSL_CTX_WITH_DEFAULTS:
+#ifdef WITH_TLS
+			mosq->ssl_ctx_defaults = true;
+			break;
+#else
+			return MOSQ_ERR_UNSUPPORTED;
+#endif
 		default:
 			return MOSQ_ERR_INVAL;
 	}