Fix UAF in tidy when tidySetErrorBuffer() fails

We should not free `intern` as its stored in the object store as well,
so the object store will already free it, leading to a UAF when the
object store tries to read the object's fields.

Closes phpGH-20276.

Author: ndossche

NEWS

@@ -74,10 +74,10 @@ PHP                                                                        NEWS
   . Fixed bug GH-19798: XP_SOCKET XP_SSL (Socket stream modules): Incorrect
     condition for Win32/Win64. (Jakub Zelenka)
 
-
 - Tidy:
   . Fixed GH-19021 (improved tidyOptGetCategory detection).
     (arjendekorte, David Carlier, Peter Kokot)
+  . Fix UAF in tidy when tidySetErrorBuffer() fails. (nielsdos)
 
 - XMLReader:
   . Fix arginfo/zpp violations when LIBXML_SCHEMAS_ENABLED is not available.

ext/tidy/tidy.c

@@ -434,7 +434,7 @@ static zend_object *tidy_object_new(zend_class_entry *class_type, zend_object_ha
 				efree(intern->ptdoc->errbuf);
 				tidyRelease(intern->ptdoc->doc);
 				efree(intern->ptdoc);
-				efree(intern);
+				/* TODO: convert to exception */
 				php_error_docref(NULL, E_ERROR, "Could not set Tidy error buffer");
 			}