Fix GH-14639: Member access within null pointer in ext/spl/spl_observer.c

`spl_object_storage_attach_handle` creates an entry already, but only
fills it in at the end with `spl_object_storage_create_element` which
allocates memory. In this case the allocation fails and we're left with
a NULL slot. Doing the allocation first isn't an option because we want
to check whether the slot is occupied before allocating memory.
The simplest solution is to set the entry to NULL and check for a NULL
pointer upon destruction.

Closes GH-14849.

Author: nielsdos

NEWS

@@ -40,6 +40,10 @@ PHP                                                                        NEWS
    . Fixed bug GH-14638 (null dereference after XML parsing failure).
      (David Carlier)
 
+- SPL:
+  . Fixed bug GH-14639 (Member access within null pointer in
+    ext/spl/spl_observer.c). (nielsdos)
+
 - Standard:
   . Fix 32-bit wordwrap test failures. (orlitzky)
   . Fixed bug GH-14774 (time_sleep_until overflow). (David Carlier)

ext/spl/spl_observer.c

@@ -118,9 +118,11 @@ static void spl_object_storage_free_hash(spl_SplObjectStorage *intern, zend_hash
 static void spl_object_storage_dtor(zval *element) /* {{{ */
 {
 	spl_SplObjectStorageElement *el = Z_PTR_P(element);
-	zend_object_release(el->obj);
-	zval_ptr_dtor(&el->inf);
-	efree(el);
+	if (el) {
+		zend_object_release(el->obj);
+		zval_ptr_dtor(&el->inf);
+		efree(el);
+	}
 } /* }}} */
 
 static spl_SplObjectStorageElement* spl_object_storage_get(spl_SplObjectStorage *intern, zend_hash_key *key) /* {{{ */
@@ -168,8 +170,10 @@ static spl_SplObjectStorageElement *spl_object_storage_attach_handle(spl_SplObje
 		return pelement;
 	}
 
+	/* NULL initialization necessary because `spl_object_storage_create_element` could bail out due to OOM. */
+	ZVAL_PTR(entry_zv, NULL);
 	pelement = spl_object_storage_create_element(obj, inf);
-	ZVAL_PTR(entry_zv, pelement);
+	Z_PTR_P(entry_zv) = pelement;
 	return pelement;
 } /* }}} */
 

ext/spl/tests/gh14639.phpt

@@ -0,0 +1,21 @@
+--TEST--
+GH-14639 (Member access within null pointer in ext/spl/spl_observer.c)
+--INI--
+memory_limit=2M
+--SKIPIF--
+<?php
+if (getenv("USE_ZEND_ALLOC") === "0") {
+    die("skip Zend MM disabled");
+}
+?>
+--FILE--
+<?php
+$b = new SplObjectStorage();
+for ($i = 10000; $i > 0; $i--) {
+    $object = new StdClass();
+    $object->a = str_repeat("a", 2);
+    $b->attach($object);
+}
+?>
+--EXPECTF--
+Fatal error: Allowed memory size of %d bytes exhausted%s(tried to allocate %d bytes) in %s on line %d