pythongh-103987: fix crash in mmap module

Lib/test/test_mmap.py

@@ -264,6 +264,23 @@ def test_bad_file_desc(self):
  # Try opening a bad file descriptor...
  self.assertRaises(OSError, mmap.mmap, -2, 4096)
 
+ def test_if_crash(self): # test for issue gh-103987
+ with open("TESTFN", "w+") as f:
+ f.write("foobar")
+ f.flush()
+
+ class X(object):
+ def __index__(self):
+ m.close()
+ return 1
+
+ m = mmap.mmap(f.fileno(), 6, access=mmap.ACCESS_READ)
+ self.assertEqual(m[1], 111)
+ with self.assertRaises(ValueError):
+ m[X()] # should not crash
+
+ m.close()
+
  def test_tougher_find(self):
  # Do a tougher .find() test. SF bug 515943 pointed out that, in 2.2,
  # searching for data with embedded \0 bytes didn't work.

Modules/mmapmodule.c

@@ -933,9 +933,9 @@ mmap_item(mmap_object *self, Py_ssize_t i)
 static PyObject *
 mmap_subscript(mmap_object *self, PyObject *item)
 {
- CHECK_VALID(NULL);
  if (PyIndex_Check(item)) {
  Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
+ CHECK_VALID(NULL);
  if (i == -1 && PyErr_Occurred())
  return NULL;
  if (i < 0)