gh-104265 Disallow instantiation of `_csv.Reader` and `_csv.Writer` (#104266)

Lib/test/test_csv.py

@@ -10,7 +10,7 @@ import csv
 import gc
 import pickle
 from test import support
-from test.support import warnings_helper
+from test.support import warnings_helper, import_helper, check_disallow_instantiation
 from itertools import permutations
 from textwrap import dedent
 from collections import OrderedDict
@@ -1430,5 +1430,12 @@ class MiscTestCase(unittest.TestCase):
         # issue 44089
         class Foo(csv.Error): ...
 
+    @support.cpython_only
+    def test_disallow_instantiation(self):
+        _csv = import_helper.import_module("_csv")
+        for tp in _csv.Reader, _csv.Writer:
+            with self.subTest(tp=tp):
+                check_disallow_instantiation(self, tp)
+
 if __name__ == '__main__':
     unittest.main()

Misc/NEWS.d/next/Library/2023-05-07-19-56-45.gh-issue-104265.fVblry.rst

@@ -0,0 +1,4 @@
+Prevent possible crash by disallowing instantiation of the
+:class:`!_csv.Reader` and :class:`!_csv.Writer` types.
+The regression was introduced in 3.10.0a4 with PR 23224 (:issue:`14935`).
+Patch by Radislav Chugunov.

Modules/_csv.c

@@ -1000,7 +1000,7 @@ PyType_Spec Reader_Type_spec = {
     .name = "_csv.reader",
     .basicsize = sizeof(ReaderObj),
     .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC |
-              Py_TPFLAGS_IMMUTABLETYPE),
+              Py_TPFLAGS_IMMUTABLETYPE | Py_TPFLAGS_DISALLOW_INSTANTIATION),
     .slots = Reader_Type_slots
 };
 
@@ -1431,7 +1431,7 @@ PyType_Spec Writer_Type_spec = {
     .name = "_csv.writer",
     .basicsize = sizeof(WriterObj),
     .flags = (Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE | Py_TPFLAGS_HAVE_GC |
-              Py_TPFLAGS_IMMUTABLETYPE),
+              Py_TPFLAGS_IMMUTABLETYPE | Py_TPFLAGS_DISALLOW_INSTANTIATION),
     .slots = Writer_Type_slots,
 };