Media: Limit thumbnail file deletions to the same directory as the original file.

git-svn-id: https://develop.svn.wordpress.org/trunk@43392 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -5847,6 +5847,28 @@ function wp_delete_file( $file ) {
 	}
 }
 
+/**
+ * Deletes a file if its path is within the given directory.
+ *
+ * @since 4.9.7
+ *
+ * @param string $file      Absolute path to the file to delete.
+ * @param string $directory Absolute path to a directory.
+ * @return bool True on success, false on failure.
+ */
+function wp_delete_file_from_directory( $file, $directory ) {
+	$real_file = realpath( wp_normalize_path( $file ) );
+	$real_directory = realpath( wp_normalize_path( $directory ) );
+
+	if ( false === $real_file || false === $real_directory || strpos( wp_normalize_path( $real_file ), trailingslashit( wp_normalize_path( $real_directory ) ) ) !== 0 ) {
+		return false;
+	}
+
+	wp_delete_file( $file );
+
+	return true;
+}
+
 /**
  * Outputs a small JS snippet on preview tabs/windows to remove `window.name` on unload.
  *