[dbus] Handle missing mode setting gracefully. Fixes MER#1576

If usb mode setting is not present in usb-moded.ini and override is not
specified in kernel command line, get_mode_setting() will return null.
The handler for "get_config" D-Bus method call does not check the return
value and using the null value triggers abort from sanity checks at
libdbus. Attempting to pass NULL as string via D-Bus causes abort.

Use MODE_UNDEFINED as fallback in case the setting value is not defined.

Also remove potential memory leaks in the code used for determining the
mode setting value and use correct function for releasing the resulting
dynamically allocated string.

Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>

src/usb_moded-config.c

@@ -310,21 +310,21 @@ static char * get_kcmdline_string(const char *entry)
       {
 	if(!strcmp(entry, NETWORK_IP_KEY))
 	{
-		ret = g_strdup(network_tokens[0]);
+		g_free(ret), ret = g_strdup(network_tokens[0]);
 		log_debug("Command line ip = %s\n", ret);
 	}
 	if(!strcmp(entry, NETWORK_GATEWAY_KEY))
 	{
 		/* gateway might be empty, so we do not want to return an empty string */
 		if(strlen(network_tokens[2]) > 2)
 		{
-		  ret = g_strdup(network_tokens[2]);
+		  g_free(ret), ret = g_strdup(network_tokens[2]);
 		  log_debug("Command line gateway = %s\n", ret);
 		}
 	}
 	if(!strcmp(entry, NETWORK_NETMASK_KEY))
 	{
-		ret = g_strdup(network_tokens[3]);
+		g_free(ret), ret = g_strdup(network_tokens[3]);
 		log_debug("Command line netmask = %s\n", ret);
 	}
       } 

src/usb_moded-dbus.c

@@ -304,9 +304,16 @@ static DBusHandlerResult msg_handler(DBusConnection *const connection, DBusMessa
 	{
 		char *config = get_mode_setting();
 
+		if(!config)
+		{
+			/* Config is corrupted or we do not have a mode
+			 * configured, fallback to undefined. */
+			config = g_strdup(MODE_UNDEFINED);
+		}
+
 		if((reply = dbus_message_new_method_return(msg)))
 			dbus_message_append_args (reply, DBUS_TYPE_STRING, &config, DBUS_TYPE_INVALID);
-		free(config);
+		g_free(config);
 	}
 	else if(!strcmp(member, USB_MODE_LIST))
 	{