Fix GH-16261: Reference invariant broken in mb_convert_variables()

The behaviour is weird in the sense that the reference must get
unwrapped. What ended up happening is that when destroying the old
reference the sources list was not cleaned properly. We add handling for
that. Normally we would use use ZEND_TRY_ASSIGN_STRINGL but that doesn't
work here as it would keep the reference and change values through
references (see bug #26639).

Closes GH-16272.

NEWS

@@ -56,6 +56,10 @@ PHP                                                                        NEWS
   . Fix GH-16136 (Memory leak in php_ldap_do_modify() when entry is not a
     proper dictionary). (Girgias)
 
+- MBString:
+  . Fixed bug GH-16261 (Reference invariant broken in mb_convert_variables()).
+    (nielsdos)
+
 - OpenSSL:
   . Fixed stub for openssl_csr_new. (Jakub Zelenka)
 

ext/mbstring/mbstring.c

@@ -3289,7 +3289,7 @@ static int mb_recursive_convert_variable(mbfl_buffer_converter *convd, zval *var
 		if (ret != NULL) {
 			zval_ptr_dtor(orig_var);
 			// TODO: avoid reallocation ???
-			ZVAL_STRINGL(orig_var, (char *)ret->val, ret->len);
+			ZVAL_STRINGL(orig_var, (const char *) ret->val, ret->len);
 			efree(ret->val);
 		}
 	} else if (Z_TYPE_P(var) == IS_ARRAY || Z_TYPE_P(var) == IS_OBJECT) {
@@ -3305,7 +3305,22 @@ static int mb_recursive_convert_variable(mbfl_buffer_converter *convd, zval *var
 
 		ht = HASH_OF(var);
 		if (ht != NULL) {
-			ZEND_HASH_FOREACH_VAL_IND(ht, entry) {
+			ZEND_HASH_FOREACH_VAL(ht, entry) {
+				/* Can be a typed property declaration, in which case we need to remove the reference from the source list.
+				 * Just using ZEND_TRY_ASSIGN_STRINGL is not sufficient because that would not unwrap the reference
+				 * and change values through references (see bug #26639). */
+				if (Z_TYPE_P(entry) == IS_INDIRECT) {
+					ZEND_ASSERT(Z_TYPE_P(var) == IS_OBJECT);
+
+					entry = Z_INDIRECT_P(entry);
+					if (Z_ISREF_P(entry) && Z_TYPE_P(Z_REFVAL_P(entry)) == IS_STRING) {
+						zend_property_info *info = zend_get_typed_property_info_for_slot(Z_OBJ_P(var), entry);
+						if (info) {
+							ZEND_REF_DEL_TYPE_SOURCE(Z_REF_P(entry), info);
+						}
+					}
+				}
+
 				if (mb_recursive_convert_variable(convd, entry)) {
 					if (Z_REFCOUNTED_P(var)) {
 						Z_UNPROTECT_RECURSION_P(var);

ext/mbstring/tests/gh16261.phpt

@@ -0,0 +1,44 @@
+--TEST--
+GH-16261 (Reference invariant broken in mb_convert_variables())
+--EXTENSIONS--
+mbstring
+--FILE--
+<?php
+class Test {
+    public string $x;
+    public string $y;
+    public array $z;
+}
+$test = new Test;
+$ref = "hello";
+$ref2 = "world";
+$ref3 = [&$ref2];
+$test->x =& $ref;
+$test->z =& $ref3;
+mb_convert_variables("EUC-JP", "Shift_JIS", $test);
+
+class Test2 {
+    public function __construct(public string $x) {}
+}
+$test2 = new Test2("foo");
+
+mb_convert_variables("EUC-JP", "Shift_JIS", $test->x);
+
+var_dump($test, $test2);
+?>
+--EXPECT--
+object(Test)#1 (2) {
+  ["x"]=>
+  string(5) "hello"
+  ["y"]=>
+  uninitialized(string)
+  ["z"]=>
+  &array(1) {
+    [0]=>
+    string(5) "world"
+  }
+}
+object(Test2)#2 (1) {
+  ["x"]=>
+  string(3) "foo"
+}