Data race in rebuild_settings()

[euantorano]

MyBB 1.8 has a race condition where if multiple admins update a setting, any setting, simultaneously then it could lead to settings.php getting corrupted. I spoke to Euan about it, and he suggested something like flock() or similar to solve the problem.

Here's the actual implementation of rebuild_settings():

function rebuild_settings()
{
    global $db, $mybb;
    if(!file_exists(MYBB_ROOT."inc/settings.php"))
    {
        $mode = "x";
    }
    else
    {
        $mode = "w";
    }
    $options = array(
        "order_by" => "title",
        "order_dir" => "ASC"
    );
    $query = $db->simple_select("settings", "value, name", "", $options);
    $settings = null;
    while($setting = $db->fetch_array($query))
    {
        $mybb->settings[$setting['name']] = $setting['value'];
        $setting['value'] = addcslashes($setting['value'], '\\"$');
        $settings .= "\$settings['{$setting['name']}'] = \"{$setting['value']}\";\n";
    }
    $settings = "<"."?php\n/*********************************\ \n  DO NOT EDIT THIS FILE, PLEASE USE\n  THE SETTINGS EDITOR\n\*********************************/\n\n$settings\n";
    $file = @fopen(MYBB_ROOT."inc/settings.php", $mode);
    @fwrite($file, $settings);
    @fclose($file);
    $GLOBALS['settings'] = &$mybb->settings;
} 

Original thread: Data race in rebuild_settings()