gh-111942: Fix crashes in TextIOWrapper.reconfigure() (GH-111976)

* Fix crash when encoding is not string or None.
* Fix crash when both line_buffering and write_through raise exception
  when converted ti int.
* Add a number of tests for constructor and reconfigure() method
  with invalid arguments.

Lib/test/test_io.py

@@ -77,6 +77,10 @@ def _default_chunk_size():
 )
 
 
+class BadIndex:
+    def __index__(self):
+        1/0
+
 class MockRawIOWithoutRead:
     """A RawIO implementation without read(), so as to exercise the default
     RawIO.read() which calls readinto()."""
@@ -2709,8 +2713,31 @@ def test_constructor(self):
         self.assertEqual(t.encoding, "utf-8")
         self.assertEqual(t.line_buffering, True)
         self.assertEqual("\xe9\n", t.readline())
-        self.assertRaises(TypeError, t.__init__, b, encoding="utf-8", newline=42)
-        self.assertRaises(ValueError, t.__init__, b, encoding="utf-8", newline='xyzzy')
+        invalid_type = TypeError if self.is_C else ValueError
+        with self.assertRaises(invalid_type):
+            t.__init__(b, encoding=42)
+        with self.assertRaises(UnicodeEncodeError):
+            t.__init__(b, encoding='\udcfe')
+        with self.assertRaises(ValueError):
+            t.__init__(b, encoding='utf-8\0')
+        with self.assertRaises(invalid_type):
+            t.__init__(b, encoding="utf-8", errors=42)
+        if support.Py_DEBUG or sys.flags.dev_mode or self.is_C:
+            with self.assertRaises(UnicodeEncodeError):
+                t.__init__(b, encoding="utf-8", errors='\udcfe')
+        if support.Py_DEBUG or sys.flags.dev_mode:
+            # TODO: If encoded to UTF-8, should also be checked for
+            # embedded null characters.
+            with self.assertRaises(ValueError):
+                t.__init__(b, encoding="utf-8", errors='replace\0')
+        with self.assertRaises(TypeError):
+            t.__init__(b, encoding="utf-8", newline=42)
+        with self.assertRaises(ValueError):
+            t.__init__(b, encoding="utf-8", newline='\udcfe')
+        with self.assertRaises(ValueError):
+            t.__init__(b, encoding="utf-8", newline='\n\0')
+        with self.assertRaises(ValueError):
+            t.__init__(b, encoding="utf-8", newline='xyzzy')
 
     def test_uninitialized(self):
         t = self.TextIOWrapper.__new__(self.TextIOWrapper)
@@ -3756,6 +3783,59 @@ def test_reconfigure_defaults(self):
 
         self.assertEqual(txt.detach().getvalue(), b'LF\nCRLF\r\n')
 
+    def test_reconfigure_errors(self):
+        txt = self.TextIOWrapper(self.BytesIO(), 'ascii', 'replace', '\r')
+        with self.assertRaises(TypeError):  # there was a crash
+            txt.reconfigure(encoding=42)
+        if self.is_C:
+            with self.assertRaises(UnicodeEncodeError):
+                txt.reconfigure(encoding='\udcfe')
+            with self.assertRaises(LookupError):
+                txt.reconfigure(encoding='locale\0')
+        # TODO: txt.reconfigure(encoding='utf-8\0')
+        # TODO: txt.reconfigure(encoding='nonexisting')
+        with self.assertRaises(TypeError):
+            txt.reconfigure(errors=42)
+        if self.is_C:
+            with self.assertRaises(UnicodeEncodeError):
+                txt.reconfigure(errors='\udcfe')
+        # TODO: txt.reconfigure(errors='ignore\0')
+        # TODO: txt.reconfigure(errors='nonexisting')
+        with self.assertRaises(TypeError):
+            txt.reconfigure(newline=42)
+        with self.assertRaises(ValueError):
+            txt.reconfigure(newline='\udcfe')
+        with self.assertRaises(ValueError):
+            txt.reconfigure(newline='xyz')
+        if not self.is_C:
+            # TODO: Should fail in C too.
+            with self.assertRaises(ValueError):
+                txt.reconfigure(newline='\n\0')
+        if self.is_C:
+            # TODO: Use __bool__(), not __index__().
+            with self.assertRaises(ZeroDivisionError):
+                txt.reconfigure(line_buffering=BadIndex())
+            with self.assertRaises(OverflowError):
+                txt.reconfigure(line_buffering=2**1000)
+            with self.assertRaises(ZeroDivisionError):
+                txt.reconfigure(write_through=BadIndex())
+            with self.assertRaises(OverflowError):
+                txt.reconfigure(write_through=2**1000)
+            with self.assertRaises(ZeroDivisionError):  # there was a crash
+                txt.reconfigure(line_buffering=BadIndex(),
+                                write_through=BadIndex())
+        self.assertEqual(txt.encoding, 'ascii')
+        self.assertEqual(txt.errors, 'replace')
+        self.assertIs(txt.line_buffering, False)
+        self.assertIs(txt.write_through, False)
+
+        txt.reconfigure(encoding='latin1', errors='ignore', newline='\r\n',
+                        line_buffering=True, write_through=True)
+        self.assertEqual(txt.encoding, 'latin1')
+        self.assertEqual(txt.errors, 'ignore')
+        self.assertIs(txt.line_buffering, True)
+        self.assertIs(txt.write_through, True)
+
     def test_reconfigure_newline(self):
         raw = self.BytesIO(b'CR\rEOF')
         txt = self.TextIOWrapper(raw, 'ascii', newline='\n')
@@ -4781,9 +4861,11 @@ def load_tests(loader, tests, pattern):
         if test.__name__.startswith("C"):
             for name, obj in c_io_ns.items():
                 setattr(test, name, obj)
+            test.is_C = True
         elif test.__name__.startswith("Py"):
             for name, obj in py_io_ns.items():
                 setattr(test, name, obj)
+            test.is_C = False
 
     suite = loader.suiteClass()
     for test in tests:

Misc/NEWS.d/next/Library/2023-11-10-22-08-28.gh-issue-111942.MDFm6v.rst

@@ -0,0 +1,2 @@
+Fix crashes in :meth:`io.TextIOWrapper.reconfigure` when pass invalid
+arguments, e.g. non-string encoding.

Modules/_io/textio.c

@@ -1284,30 +1284,40 @@ textiowrapper_change_encoding(textio *self, PyObject *encoding,
             errors = &_Py_ID(strict);
         }
     }
+    Py_INCREF(errors);
 
+    const char *c_encoding = PyUnicode_AsUTF8(encoding);
+    if (c_encoding == NULL) {
+        Py_DECREF(encoding);
+        Py_DECREF(errors);
+        return -1;
+    }
     const char *c_errors = PyUnicode_AsUTF8(errors);
     if (c_errors == NULL) {
         Py_DECREF(encoding);
+        Py_DECREF(errors);
         return -1;
     }
 
     // Create new encoder & decoder
     PyObject *codec_info = _PyCodec_LookupTextEncoding(
-        PyUnicode_AsUTF8(encoding), "codecs.open()");
+        c_encoding, "codecs.open()");
     if (codec_info == NULL) {
         Py_DECREF(encoding);
+        Py_DECREF(errors);
         return -1;
     }
     if (_textiowrapper_set_decoder(self, codec_info, c_errors) != 0 ||
             _textiowrapper_set_encoder(self, codec_info, c_errors) != 0) {
         Py_DECREF(codec_info);
         Py_DECREF(encoding);
+        Py_DECREF(errors);
         return -1;
     }
     Py_DECREF(codec_info);
 
     Py_SETREF(self->encoding, encoding);
-    Py_SETREF(self->errors, Py_NewRef(errors));
+    Py_SETREF(self->errors, errors);
 
     return _textiowrapper_fix_encoder_state(self);
 }
@@ -1338,6 +1348,26 @@ _io_TextIOWrapper_reconfigure_impl(textio *self, PyObject *encoding,
     int write_through;
     const char *newline = NULL;
 
+    if (encoding != Py_None && !PyUnicode_Check(encoding)) {
+        PyErr_Format(PyExc_TypeError,
+                "reconfigure() argument 'encoding' must be str or None, not %s",
+                Py_TYPE(encoding)->tp_name);
+        return NULL;
+    }
+    if (errors != Py_None && !PyUnicode_Check(errors)) {
+        PyErr_Format(PyExc_TypeError,
+                "reconfigure() argument 'errors' must be str or None, not %s",
+                Py_TYPE(errors)->tp_name);
+        return NULL;
+    }
+    if (newline_obj != NULL && newline_obj != Py_None &&
+        !PyUnicode_Check(newline_obj))
+    {
+        PyErr_Format(PyExc_TypeError,
+                "reconfigure() argument 'newline' must be str or None, not %s",
+                Py_TYPE(newline_obj)->tp_name);
+        return NULL;
+    }
     /* Check if something is in the read buffer */
     if (self->decoded_chars != NULL) {
         if (encoding != Py_None || errors != Py_None || newline_obj != NULL) {
@@ -1357,9 +1387,12 @@ _io_TextIOWrapper_reconfigure_impl(textio *self, PyObject *encoding,
 
     line_buffering = convert_optional_bool(line_buffering_obj,
                                            self->line_buffering);
+    if (line_buffering < 0) {
+        return NULL;
+    }
     write_through = convert_optional_bool(write_through_obj,
                                           self->write_through);
-    if (line_buffering < 0 || write_through < 0) {
+    if (write_through < 0) {
         return NULL;
     }