HCTF 2018 Warmup (API functions)

0x01 Title Description

Look at the hint

look urlhave filea feel of what's possible to use pseudo-protocol, try the next, not a thing
to sweep through the catalog, find ./source.phpthe source file
source code is as follows

<?php
    class emmm
    {
        public static function checkFile(&$page)
        {
            $whitelist = ["source"=>"source.php","hint"=>"hint.php"];
            if (! isset($page) || !is_string($page)) {
                echo "you can't see it";
                return false;
            }

            if (in_array($page, $whitelist)) {
                return true;
            }

            $_page = mb_substr(
                $page,
                0,
                mb_strpos($page . '?', '?')
            );
            if (in_array($_page, $whitelist)) {
                return true;
            }

            $_page = urldecode($page);
            $_page = mb_substr(
                $_page,
                0,
                mb_strpos($_page . '?', '?')
            );
            if (in_array($_page, $whitelist)) {
                return true;
            }
            echo "you can't see it";
            return false;
        }
    }

    if (! empty($_REQUEST['file'])
        && is_string($_REQUEST['file'])
        && emmm::checkFile($_REQUEST['file'])
    ) {
        include $_REQUEST['file'];
        exit;
    } else {
        echo "<br><img src=\"https://i.loli.net/2018/11/01/5bdb0d93dc794.jpg\" />";
    }  
?>

0x02 solution to a problem

Read the file contains, whether before checkFile $ _page function takes a file argument first question mark field and check the file name as the file parameter so configured whitelisthint.php?/../../../../../ffffllllaaaagggg

The principle is hint.php?/treated as a directory, the directory after the jump like (this only applies to linux)
and the includefunction is not the same mkdirfunction, if there is no table of contents will error