Fix memory leak when edge case is hit when registering xpath callback

This can happen if you have a valid callable name with a NUL byte in it,
on a non-interned string entry. This can be done by abusing anonymous
classes.

Closes phpGH-20452.

Author: ndossche

NEWS

@@ -11,6 +11,10 @@ PHP                                                                        NEWS
   . Fix crashes when trying to instantiate uninstantiable classes via date
     static constructors. (ndossche)
 
+- DOM:
+  . Fix memory leak when edge case is hit when registering xpath callback.
+    (ndossche)
+
 - Opcache:
   . Fixed bug GH-20329 (opcache.file_cache broken with full interned string
     buffer). (Arnaud)

ext/dom/tests/DOMXPath_callables_errors.phpt

@@ -57,6 +57,19 @@ try {
     echo $e->getMessage(), "\n";
 }
 
+$x = new class {
+    public static function dump() {}
+};
+
+$classes = get_declared_classes();
+
+try {
+    $str = str_repeat($classes[count($classes) - 1] . '::dump', random_int(1, 1));
+    $xpath->registerPhpFunctions([$str]);
+} catch (Throwable $e) {
+    echo $e->getMessage(), "\n";
+}
+
 ?>
 --EXPECT--
 DOMXPath::registerPhpFunctions(): Argument #1 ($restrict) must be a callable, function "nonexistent" not found or invalid function name
@@ -67,3 +80,4 @@ DOMXPath::registerPhpFunctions(): Argument #1 ($restrict) must be an array with
 DOMXPath::registerPhpFunctions(): Argument #1 ($restrict) must be an array containing valid callback names
 DOMXPath::registerPhpFunctions(): Argument #1 ($restrict) must be an array containing valid callback names
 DOMXPath::registerPhpFunctions(): Argument #1 ($restrict) must be a valid callback name
+DOMXPath::registerPhpFunctions(): Argument #1 ($restrict) must be an array containing valid callback names

ext/dom/xpath_callbacks.c

@@ -206,14 +206,16 @@ static zend_result php_dom_xpath_callback_ns_update_method_handler(
 			ZVAL_PTR(&registered_value, fcc);
 
 			if (!key) {
-				zend_string *str = zval_try_get_string(entry);
+				zend_string *tmp_str;
+				zend_string *str = zval_try_get_tmp_string(entry, &tmp_str);
 				if (str && php_dom_xpath_is_callback_name_valid_and_throw(str, name_validation, true)) {
 					zend_hash_update(&ns->functions, str, &registered_value);
 					if (register_func) {
 						register_func(ctxt, namespace, str);
 					}
-					zend_string_release_ex(str, false);
+					zend_tmp_string_release(tmp_str);
 				} else {
+					zend_tmp_string_release(tmp_str);
 					zend_fcc_dtor(fcc);
 					efree(fcc);
 					return FAILURE;