Fix #77569: Write Acess Violation in DomImplementation

We must not assume that the zval IS_STRING.

Author: cmb69

NEWS

@@ -2,6 +2,9 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? 2020, PHP 7.2.28
 
+- DOM:
+  . Fixed bug #77569: (Write Acess Violation in DomImplementation). (Nikita,
+    cmb)
 
 23 Jan 2020, PHP 7.2.27
 

ext/dom/document.c

@@ -341,7 +341,7 @@ int dom_document_encoding_write(dom_object *obj, zval *newval)
 
 	str = zval_get_string(newval);
 
-	handler = xmlFindCharEncodingHandler(Z_STRVAL_P(newval));
+	handler = xmlFindCharEncodingHandler(ZSTR_VAL(str));
 
     if (handler != NULL) {
 		xmlCharEncCloseFunc(handler);

ext/dom/tests/bug77569.phpt

@@ -0,0 +1,14 @@
+--TEST--
+Bug #77569 (Write Acess Violation in DomImplementation)
+--SKIPIF--
+<?php
+if (!extension_loaded('dom')) die('skip dom extension not available');
+?>
+--FILE--
+<?php
+$imp = new DOMImplementation;
+$dom = $imp->createDocument("", "");
+$dom->encoding = null;
+?>
+--EXPECTF--
+Warning: main(): Invalid Document Encoding in %s on line %d