From 5fae2fc7a13a155fec607dc0c985a73a82e26b97 Mon Sep 17 00:00:00 2001
From: Huong Nguyen <huongn@moodle.com>
Date: Mon, 5 Jul 2021 17:25:09 +0700
Subject: [PATCH] MDL-71922 file: Enhance endless recursion requests protection

---
 repository/url/lib.php | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/repository/url/lib.php b/repository/url/lib.php
index b3664a193b0..7b548e6be63 100644
--- a/repository/url/lib.php
+++ b/repository/url/lib.php
@@ -36,7 +36,11 @@ require_once(__DIR__.'/locallib.php');
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class repository_url extends repository {
+    /** @var int Maximum time of recursion. */
+    const MAX_RECURSION_TIME = 5;
     var $processedfiles = array();
+    /** @var int Recursion counter. */
+    var $recursioncounter = 0;
 
     /**
      * @param int $repositoryid
@@ -127,7 +131,16 @@ EOD;
             $url = htmlspecialchars_decode(url_to_absolute($baseurl, $relativeurl));
         }
         if (in_array($url, $this->processedfiles)) {
-            // avoid endless recursion
+            // Avoid endless recursion for the same URL with same parameters.
+            return;
+        }
+        // Remove the query string before check.
+        $recursioncheckurl = preg_replace('/\?.*/', '', $url);
+        if (in_array($recursioncheckurl, $this->processedfiles)) {
+            $this->recursioncounter++;
+        }
+        if ($this->recursioncounter >= self::MAX_RECURSION_TIME) {
+            // Avoid endless recursion for the same URL with different parameters.
             return;
         }
         $this->processedfiles[] = $url;