Ensure we have a valid timezone identifier before trying to use it.

Validate the new timezone identifier during option update.
Fixes #17840.

git-svn-id: http://svn.automattic.com/wordpress/trunk@18323 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/options-general.php

@@ -182,7 +182,9 @@ if ( empty($tzstring) ) { // Create a UTC+- zone if no timezone string exists
 	?>
 	<br />
 	<?php
-	if ( function_exists('timezone_transitions_get') ) {
+	$allowed_zones = timezone_identifiers_list();
+	
+	if ( in_array( $tzstring, $allowed_zones) ) {
 		$found = false;
 		$date_time_zone_selected = new DateTimeZone($tzstring);
 		$tz_offset = timezone_offset_get($date_time_zone_selected, date_create());

wp-includes/formatting.php

@@ -2521,6 +2521,15 @@ function sanitize_option($option, $value) {
 			}
 			break;
 
+		case 'timezone_string':
+			$allowed_zones = timezone_identifiers_list();
+			if ( ! in_array( $value, $allowed_zones ) && ! empty( $value ) ) {
+				$value = get_option( $option ); // Resets option to stored value in the case of failed sanitization
+				if ( function_exists('add_settings_error') )
+					add_settings_error('timezone_string', 'invalid_timezone_string', __('The timezone you have entered is not valid. Please select a valid timezone.') );
+			}
+			break;
+
 		default :
 			$value = apply_filters("sanitize_option_{$option}", $value, $option);
 			break;