Fix GH-21687: array_walk creates references to readonly properties

By-ref callbacks throw the same "Cannot acquire reference to readonly
property" error foreach uses. By-val callbacks copy the value into a
temp so MAKE_REF does not corrupt the slot.

Closes GH-21687

Author: iliaal

Zend/tests/gh21687.phpt

@@ -0,0 +1,54 @@
+--TEST--
+GH-21687 (array_walk corrupts readonly and enum properties by wrapping them in IS_REFERENCE)
+--FILE--
+<?php
+enum Foo: int {
+    case Bar = 0;
+}
+
+$bar = Foo::Bar;
+array_walk($bar, function($v) {});
+var_dump($bar);
+
+try {
+    array_walk($bar, function(&$v) { $v = 1; });
+} catch (\Error $e) {
+    echo $e->getMessage() . "\n";
+}
+var_dump($bar);
+
+class MyObj {
+    public function __construct(public readonly string $name = "test") {}
+}
+
+$obj = new MyObj();
+array_walk($obj, function($v) {});
+echo $obj->name . "\n";
+
+try {
+    array_walk($obj, function(&$v) { $v = "modified"; });
+} catch (\Error $e) {
+    echo $e->getMessage() . "\n";
+}
+echo $obj->name . "\n";
+
+class Container {
+    public function __construct(public readonly array $items = ["a", "b"]) {}
+}
+$c = new Container();
+array_walk_recursive($c, function($v) {});
+var_dump($c->items);
+?>
+--EXPECT--
+enum(Foo::Bar)
+Cannot acquire reference to readonly property Foo::$name
+enum(Foo::Bar)
+test
+Cannot acquire reference to readonly property MyObj::$name
+test
+array(2) {
+  [0]=>
+  string(1) "a"
+  [1]=>
+  string(1) "b"
+}

ext/standard/array.c

@@ -1361,6 +1361,7 @@ static zend_result php_array_walk(
 {
 	zval args[3],		/* Arguments to userland function */
 		 retval,		/* Return value - unused */
+		 temp,
 		 *zv;
 	HashTable *target_hash = HASH_OF(array);
 	HashPosition pos;
@@ -1375,6 +1376,10 @@ static zend_result php_array_walk(
 		return result;
 	}
 
+	zend_function *callback = context->fci_cache.function_handler;
+	bool callback_by_ref = callback != NULL
+		&& ARG_SHOULD_BE_SENT_BY_REF(callback, 1);
+
 	/* Set up known arguments */
 	ZVAL_UNDEF(&args[1]);
 	if (userdata) {
@@ -1390,6 +1395,8 @@ static zend_result php_array_walk(
 
 	/* Iterate through hash */
 	do {
+		bool used_temp = false;
+
 		/* Retrieve value */
 		zv = zend_hash_get_current_data_ex(target_hash, &pos);
 		if (zv == NULL) {
@@ -1407,10 +1414,23 @@ static zend_result php_array_walk(
 			/* Add type source for property references. */
 			if (Z_TYPE_P(zv) != IS_REFERENCE && Z_TYPE_P(array) == IS_OBJECT) {
 				zend_property_info *prop_info =
-					zend_get_typed_property_info_for_slot(Z_OBJ_P(array), zv);
+					zend_get_property_info_for_slot(Z_OBJ_P(array), zv);
 				if (prop_info) {
-					ZVAL_NEW_REF(zv, zv);
-					ZEND_REF_ADD_TYPE_SOURCE(Z_REF_P(zv), prop_info);
+					if (UNEXPECTED(prop_info->flags & ZEND_ACC_READONLY)) {
+						if (callback_by_ref) {
+							zend_throw_error(NULL,
+								"Cannot acquire reference to readonly property %s::$%s",
+								ZSTR_VAL(prop_info->ce->name),
+								zend_get_unmangled_property_name(prop_info->name));
+							break;
+						}
+						ZVAL_COPY(&temp, zv);
+						zv = &temp;
+						used_temp = true;
+					} else if (ZEND_TYPE_IS_SET(prop_info->type)) {
+						ZVAL_NEW_REF(zv, zv);
+						ZEND_REF_ADD_TYPE_SOURCE(Z_REF_P(zv), prop_info);
+					}
 				}
 			}
 		}
@@ -1461,6 +1481,10 @@ static zend_result php_array_walk(
 
 		zval_ptr_dtor_str(&args[1]);
 
+		if (used_temp) {
+			zval_ptr_dtor(&temp);
+		}
+
 		if (result == FAILURE) {
 			break;
 		}