[3.12] gh-105436: The environment block should end with two null wcha…

…r_t values (GH-105495) (#105700)

gh-105436: The environment block should end with two null wchar_t values (GH-105495)
(cherry picked from commit 4f7d3b6)

Co-authored-by: Dora203 <66343334+sku2000@users.noreply.github.com>

Lib/test/test_subprocess.py

@@ -1692,6 +1692,13 @@ def test_run_with_pathlike_path_and_arguments(self):
  res = subprocess.run(args)
  self.assertEqual(res.returncode, 57)
 
+ @unittest.skipUnless(mswindows, "Maybe test trigger a leak on Ubuntu")
+ def test_run_with_an_empty_env(self):
+ # gh-105436: fix subprocess.run(..., env={}) broken on Windows
+ args = [sys.executable, "-c", 'import sys; sys.exit(57)']
+ res = subprocess.run(args, env={})
+ self.assertEqual(res.returncode, 57)
+
  def test_capture_output(self):
  cp = self.run_python(("import sys;"
  "sys.stdout.write('BDFL'); "

Misc/NEWS.d/next/Windows/2023-06-08-11-30-17.gh-issue-105436.1qlDxw.rst

@@ -0,0 +1,2 @@
+Ensure that an empty environment block is terminated by two null characters,
+as is required by Windows.

Modules/_winapi.c

@@ -796,6 +796,17 @@ getenvironment(PyObject* environment)
  }
 
  envsize = PyList_GET_SIZE(keys);
+
+ if (envsize == 0) {
+ // A environment block must be terminated by two null characters --
+ // one for the last string and one for the block.
+ buffer = PyMem_Calloc(2, sizeof(wchar_t));
+ if (!buffer) {
+ PyErr_NoMemory();
+ }
+ goto cleanup;
+ }
+
  if (PyList_GET_SIZE(values) != envsize) {
  PyErr_SetString(PyExc_RuntimeError,
  "environment changed size during iteration");
@@ -869,7 +880,8 @@ getenvironment(PyObject* environment)
  *p++ = L'\0';
  assert(p == end);
 
- error:
+cleanup:
+error:
  Py_XDECREF(keys);
  Py_XDECREF(values);
  return buffer;