Fix GH-14638: null dereference after XML parsing failure.

object document is null if the parsing had failed prior to cast to
string.

Author: devnexen

NEWS

@@ -31,6 +31,10 @@ PHP                                                                        NEWS
 - Shmop:
    . Fixed bug GH-14537 (shmop Windows 11 crashes the process). (nielsdos)
 
+- SimpleXML:
+   . Fixed bug GH-14638 (null dereference after XML parsing failure).
+     (David Carlier)
+
 04 Jul 2024, PHP 8.2.21
 
 - Core:

ext/simplexml/simplexml.c

@@ -1502,6 +1502,35 @@ static void sxe_add_namespaces(php_sxe_object *sxe, xmlNodePtr node, bool recurs
 	}
 } /* }}} */
 
+static inline void sxe_object_free_iterxpath(php_sxe_object *sxe)
+{
+	if (!Z_ISUNDEF(sxe->iter.data)) {
+		zval_ptr_dtor(&sxe->iter.data);
+		ZVAL_UNDEF(&sxe->iter.data);
+	}
+
+	if (sxe->iter.name) {
+		efree(sxe->iter.name);
+		sxe->iter.name = NULL;
+	}
+	if (sxe->iter.nsprefix) {
+		efree(sxe->iter.nsprefix);
+		sxe->iter.nsprefix = NULL;
+	}
+	if (!Z_ISUNDEF(sxe->tmp)) {
+		zval_ptr_dtor(&sxe->tmp);
+		ZVAL_UNDEF(&sxe->tmp);
+	}
+
+	php_libxml_node_decrement_resource((php_libxml_node_object *)sxe);
+
+	if (sxe->xpath) {
+		xmlXPathFreeContext(sxe->xpath);
+		sxe->xpath = NULL;
+	}
+}
+
+
 /* {{{ Return all namespaces in use */
 PHP_METHOD(SimpleXMLElement, getNamespaces)
 {
@@ -2156,29 +2185,7 @@ static void sxe_object_free_storage(zend_object *object)
 
 	zend_object_std_dtor(&sxe->zo);
 
-	if (!Z_ISUNDEF(sxe->iter.data)) {
-		zval_ptr_dtor(&sxe->iter.data);
-		ZVAL_UNDEF(&sxe->iter.data);
-	}
-
-	if (sxe->iter.name) {
-		efree(sxe->iter.name);
-		sxe->iter.name = NULL;
-	}
-	if (sxe->iter.nsprefix) {
-		efree(sxe->iter.nsprefix);
-		sxe->iter.nsprefix = NULL;
-	}
-	if (!Z_ISUNDEF(sxe->tmp)) {
-		zval_ptr_dtor(&sxe->tmp);
-		ZVAL_UNDEF(&sxe->tmp);
-	}
-
-	php_libxml_node_decrement_resource((php_libxml_node_object *)sxe);
-
-	if (sxe->xpath) {
-		xmlXPathFreeContext(sxe->xpath);
-	}
+	sxe_object_free_iterxpath(sxe);
 
 	if (sxe->properties) {
 		zend_hash_destroy(sxe->properties);
@@ -2378,11 +2385,12 @@ PHP_METHOD(SimpleXMLElement, __construct)
 	PHP_LIBXML_RESTORE_GLOBALS(read_file_or_memory);
 
 	if (!docp) {
-		((php_libxml_node_object *)sxe)->document = NULL;
 		zend_throw_exception(zend_ce_exception, "String could not be parsed as XML", 0);
 		RETURN_THROWS();
 	}
 
+	sxe_object_free_iterxpath(sxe);
+
 	sxe->iter.nsprefix = ns_len ? (xmlChar*)estrdup(ns) : NULL;
 	sxe->iter.isprefix = isprefix;
 	php_libxml_increment_doc_ref((php_libxml_node_object *)sxe, docp);

ext/simplexml/tests/gh14638.phpt

@@ -0,0 +1,25 @@
+--TEST--
+GH-14638: null pointer dereference on object cast __toString after failed XML parsing
+--EXTENSIONS--
+simplexml
+--CREDITS--
+YuanchengJiang
+--FILE--
+<?php
+$xml = '<?xml version="1.0" encoding="utf-8" ?>
+<test>
+</test>';
+$root = simplexml_load_string($xml);
+try {
+    $root->__construct("malformed");
+} catch (Exception $e) {
+    // Intentionally empty
+}
+echo $root;
+?>
+--EXPECTF--
+Warning: SimpleXMLElement::__construct(): Entity: line 1: parser error : Start tag expected, '<' not found in %s on line %d
+
+Warning: SimpleXMLElement::__construct(): malformed in %s on line %d
+
+Warning: SimpleXMLElement::__construct(): ^ in %s on line %d