Fix GH-16589: UAF in SplDoublyLinked->serialize()

Closes GH-16611.

Author: nielsdos

NEWS

@@ -105,6 +105,7 @@ PHP                                                                        NEWS
   . Fixed bug GH-16588 (UAF in Observer->serialize). (nielsdos)
   . Fix GH-16477 (Segmentation fault when calling __debugInfo() after failed
     SplFileObject::__constructor). (Girgias)
+  . Fixed bug GH-16589 (UAF in SplDoublyLinked->serialize()). (nielsdos)
 
 - Standard:
   . Fixed bug GH-16293 (Failed assertion when throwing in assert() callback with

ext/spl/spl_dllist.c

@@ -44,10 +44,13 @@ PHPAPI zend_class_entry  *spl_ce_SplStack;
 	efree(elem); \
 }
 
-#define SPL_LLIST_CHECK_DELREF(elem) if ((elem) && !--SPL_LLIST_RC(elem)) { \
+#define SPL_LLIST_CHECK_DELREF_EX(elem, on_free) if ((elem) && !--SPL_LLIST_RC(elem)) { \
 	efree(elem); \
+	on_free \
 }
 
+#define SPL_LLIST_CHECK_DELREF(elem) SPL_LLIST_CHECK_DELREF_EX(elem, ;)
+
 #define SPL_LLIST_ADDREF(elem) SPL_LLIST_RC(elem)++
 #define SPL_LLIST_CHECK_ADDREF(elem) if (elem) SPL_LLIST_RC(elem)++
 
@@ -1024,8 +1027,12 @@ PHP_METHOD(SplDoublyLinkedList, serialize)
 		smart_str_appendc(&buf, ':');
 		next = current->next;
 
+		SPL_LLIST_CHECK_ADDREF(next);
+
 		php_var_serialize(&buf, &current->data, &var_hash);
 
+		SPL_LLIST_CHECK_DELREF_EX(next, break;);
+
 		current = next;
 	}
 

ext/spl/tests/gh16589.phpt

@@ -0,0 +1,23 @@
+--TEST--
+GH-16589 (UAF in SplDoublyLinked->serialize())
+--CREDITS--
+chibinz
+--FILE--
+<?php
+
+class C {
+    function __serialize(): array {
+        global $list;
+        $list->pop();
+        return [];
+    }
+}
+
+$list = new SplDoublyLinkedList;
+$list->add(0, new C);
+$list->add(1, 1);
+var_dump($list->serialize());
+
+?>
+--EXPECT--
+string(17) "i:0;:O:1:"C":0:{}"