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Keep the object alive across jsonSerialize() in json_encode() #22469

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Keep the object alive across jsonSerialize() in json_encode() #22469

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7 changes: 7 additions & 0 deletions ext/json/json_encoder.c
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Original file line number Diff line number Diff line change
Expand Up @@ -581,6 +581,11 @@ static zend_result php_json_encode_serializable_object(smart_str *buf, zend_obje

ZEND_GUARD_PROTECT_RECURSION(guard, JSON);

/* jsonSerialize() may run a user error handler that drops the last
* reference to the object; keep it alive so the recursion guard and the
* identity check below stay valid. */
GC_ADDREF(obj);

zend_function *json_serialize_method = zend_hash_str_find_ptr(&ce->function_table, ZEND_STRL("jsonserialize"));
ZEND_ASSERT(json_serialize_method != NULL && "This should be guaranteed prior to calling this function");
zend_call_known_function(json_serialize_method, obj, ce, &retval, 0, NULL, NULL);
Expand All @@ -590,6 +595,7 @@ static zend_result php_json_encode_serializable_object(smart_str *buf, zend_obje
smart_str_appendl(buf, "null", 4);
}
ZEND_GUARD_UNPROTECT_RECURSION(guard, JSON);
OBJ_RELEASE(obj);
return FAILURE;
}

Expand All @@ -604,6 +610,7 @@ static zend_result php_json_encode_serializable_object(smart_str *buf, zend_obje
}

zval_ptr_dtor(&retval);
OBJ_RELEASE(obj);

return return_code;
}
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21 changes: 21 additions & 0 deletions ext/json/tests/gh21024.phpt
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@@ -0,0 +1,21 @@
--TEST--
GH-21024 (UAF in json_encode() when jsonSerialize()'s error handler frees the object)
--EXTENSIONS--
json
--FILE--
<?php
class Bar implements JsonSerializable {
public function jsonSerialize(): mixed {
echo $undefined;
return ['k' => 1];
}
}
$arr = [new Bar];
$ref = &$arr[0];
set_error_handler(function () use (&$ref) { $ref = null; });
var_dump(json_encode($arr));
echo "survived\n";
?>
--EXPECT--
string(9) "[{"k":1}]"
survived
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