Fix GH-15833: Segmentation fault (access null pointer) in ext/spl/spl_array.c

We're accessing the object properties table directly in spl, but we're
not accounting for lazy objects. Upon accessing we should trigger the
initialization as spl is doing direct manipulations on the object
property table and expects a real object.

Closes GH-17235.

Author: nielsdos

NEWS

@@ -46,6 +46,10 @@ PHP                                                                        NEWS
   . Fixed bug GH-17330 (SNMP::setSecurity segfault on closed session).
     (David Carlier)
 
+- SPL:
+  . Fixed bug GH-15833 (Segmentation fault (access null pointer) in
+    ext/spl/spl_array.c). (nielsdos)
+
 02 Jan 2025, PHP 8.4.3
 
 - BcMath:

ext/spl/spl_array.c

@@ -40,6 +40,7 @@ PHPAPI zend_class_entry  *spl_ce_ArrayObject;
 
 typedef struct _spl_array_object {
 	zval              array;
+	HashTable         *sentinel_array;
 	uint32_t          ht_iter;
 	int               ar_flags;
 	unsigned char	  nApplyCount;
@@ -74,6 +75,19 @@ static inline HashTable **spl_array_get_hash_table_ptr(spl_array_object* intern)
 		return &Z_ARRVAL(intern->array);
 	} else {
 		zend_object *obj = Z_OBJ(intern->array);
+		/* Since we're directly playing with the properties table, we shall initialize the lazy object directly.
+		 * If we don't, it's possible to continue working with the wrong object in case we're using a proxy. */
+		if (UNEXPECTED(zend_lazy_object_must_init(obj))) {
+			obj = zend_lazy_object_init(obj);
+			if (UNEXPECTED(!obj)) {
+				if (!intern->sentinel_array) {
+					intern->sentinel_array = zend_new_array(0);
+				}
+				return &intern->sentinel_array;
+			}
+		}
+		/* should no longer be lazy */
+		ZEND_ASSERT(!zend_lazy_object_must_init(obj));
 		/* rebuild properties */
 		zend_std_get_properties_ex(obj);
 		if (GC_REFCOUNT(obj->properties) > 1) {
@@ -129,6 +143,10 @@ static void spl_array_object_free_storage(zend_object *object)
 		zend_hash_iterator_del(intern->ht_iter);
 	}
 
+	if (UNEXPECTED(intern->sentinel_array)) {
+		zend_array_release(intern->sentinel_array);
+	}
+
 	zend_object_std_dtor(&intern->std);
 
 	zval_ptr_dtor(&intern->array);
@@ -489,6 +507,9 @@ static void spl_array_write_dimension_ex(int check_inherited, zend_object *objec
 	uint32_t refcount = 0;
 	if (!offset || Z_TYPE_P(offset) == IS_NULL) {
 		ht = spl_array_get_hash_table(intern);
+		if (UNEXPECTED(ht == intern->sentinel_array)) {
+			return;
+		}
 		refcount = spl_array_set_refcount(intern->is_child, ht, 1);
 		zend_hash_next_index_insert(ht, value);
 
@@ -505,6 +526,10 @@ static void spl_array_write_dimension_ex(int check_inherited, zend_object *objec
 	}
 
 	ht = spl_array_get_hash_table(intern);
+	if (UNEXPECTED(ht == intern->sentinel_array)) {
+		spl_hash_key_release(&key);
+		return;
+	}
 	refcount = spl_array_set_refcount(intern->is_child, ht, 1);
 	if (key.key) {
 		zend_hash_update_ind(ht, key.key, value);

ext/spl/tests/gh15833_1.phpt

@@ -0,0 +1,22 @@
+--TEST--
+GH-15833 (Segmentation fault (access null pointer) in ext/spl/spl_array.c)
+--CREDITS--
+YuanchengJiang
+--FILE--
+<?php
+class C {
+    public int $a = 1;
+}
+$reflector = new ReflectionClass(C::class);
+$obj = $reflector->newLazyProxy(function ($obj) {
+    $obj = new C();
+    return $obj;
+});
+$recursiveArrayIterator = new RecursiveArrayIterator($obj);
+var_dump($recursiveArrayIterator->current());
+$recursiveArrayIterator->next();
+var_dump($recursiveArrayIterator->current());
+?>
+--EXPECT--
+int(1)
+NULL

ext/spl/tests/gh15833_2.phpt

@@ -0,0 +1,41 @@
+--TEST--
+GH-15833 (Segmentation fault (access null pointer) in ext/spl/spl_array.c)
+--CREDITS--
+YuanchengJiang
+--FILE--
+<?php
+class C {
+    public int $a = 1;
+}
+$reflector = new ReflectionClass(C::class);
+$obj = $reflector->newLazyProxy(function ($obj) {
+    static $counter = 0;
+    throw new Error('nope ' . ($counter++));
+});
+$recursiveArrayIterator = new RecursiveArrayIterator($obj);
+try {
+    var_dump($recursiveArrayIterator->current());
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+try {
+    var_dump($recursiveArrayIterator->current());
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+try {
+    $recursiveArrayIterator->next();
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+try {
+    var_dump($recursiveArrayIterator->current());
+} catch (Error $e) {
+    echo $e->getMessage(), "\n";
+}
+?>
+--EXPECT--
+nope 0
+nope 1
+nope 2
+nope 3