From f9fcde32abe1c3bca7d3ab036f34862c92b606c3 Mon Sep 17 00:00:00 2001
From: catch <catch@35733.no-reply.drupal.org>
Date: Fri, 18 Dec 2020 09:45:37 +0000
Subject: [PATCH] Issue #3036494 by Berdir, alexpott, rgpublic, cilefen,
 kerasai, regilero: Race condition in ImageStyle::createDerivative()

---
 core/lib/Drupal/Core/File/FileSystem.php | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/core/lib/Drupal/Core/File/FileSystem.php b/core/lib/Drupal/Core/File/FileSystem.php
index e7e4c7a1947..8547f6e98fd 100644
--- a/core/lib/Drupal/Core/File/FileSystem.php
+++ b/core/lib/Drupal/Core/File/FileSystem.php
@@ -520,12 +520,22 @@ class FileSystem implements FileSystemInterface {
     }
 
     if (!is_dir($directory)) {
+      if (!($options & static::CREATE_DIRECTORY)) {
+        return FALSE;
+      }
+
       // Let mkdir() recursively create directories and use the default
       // directory permissions.
-      if ($options & static::CREATE_DIRECTORY) {
-        return @$this->mkdir($directory, NULL, TRUE);
+      $success = @$this->mkdir($directory, NULL, TRUE);
+      if ($success) {
+        return TRUE;
+      }
+      // If the operation failed, check again if the directory was created
+      // by another process/server, only report a failure if not. In this case
+      // we still need to ensure the directory is writable.
+      if (!is_dir($directory)) {
+        return FALSE;
       }
-      return FALSE;
     }
 
     $writable = is_writable($directory);