Leak in failed unserialize() with opcache

With opcache, zend_string_init_interned() will allocate non-interned strings at
runtime because shm is locked. Hence, we need to make sure to actually free this
string.

Fixes OSS-Fuzz #433303828
Closes GH-19211

NEWS

@@ -29,6 +29,10 @@ PHP                                                                        NEWS
 - Sockets:
   . Fix some potential crashes on incorrect argument value. (nielsdos)
 
+- Standard:
+  . Fixed OSS Fuzz #417078295 (Leak in failed unserialize() with opcache).
+    (ilutov)
+
 31 Jul 2025, PHP 8.3.24
 
 - Calendar:

ext/standard/tests/serialize/oss_fuzz_433303828.phpt

@@ -0,0 +1,13 @@
+--TEST--
+OSS-Fuzz #433303828
+--FILE--
+<?php
+
+unserialize('O:2:"yy": ');
+unserialize('O:2:"yy":: ');
+
+?>
+--EXPECTF--
+Warning: unserialize(): Error at offset 9 of 10 bytes in %s on line %d
+
+Warning: unserialize(): Error at offset 10 of 11 bytes in %s on line %d

ext/standard/var_unserializer.re

@@ -1310,10 +1310,12 @@ object ":" uiv ":" ["]	{
 	YYCURSOR = *p;
 
 	if (*(YYCURSOR) != ':') {
+		zend_string_release_ex(class_name, 0);
 		return 0;
 	}
 	if (*(YYCURSOR+1) != '{') {
 		*p = YYCURSOR+1;
+		zend_string_release_ex(class_name, 0);
 		return 0;
 	}