[Python-checkins] [3.12] gh-105436: The environment block should end with two null wchar_t values (GH-105495) (#105700)

[zooba]

https://github.com/python/cpython/commit/77bdeebdda3358186df6e6ba900c562ddaefaa5c
commit: 77bdeebdda3358186df6e6ba900c562ddaefaa5c
branch: 3.12
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: zooba <steve.dower at microsoft.com>
date: 2023-06-12T16:50:58Z
summary:

[3.12] gh-105436: The environment block should end with two null wchar_t values (GH-105495) (#105700)

gh-105436: The environment block should end with two null wchar_t values (GH-105495)
(cherry picked from commit 4f7d3b602d47d61137e82145f601dccfe6f6cd3c)

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

files:
A Misc/NEWS.d/next/Windows/2023-06-08-11-30-17.gh-issue-105436.1qlDxw.rst
M Lib/test/test_subprocess.py
M Modules/_winapi.c

diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 51ba423a0f1c9..3d4fffbb8e794 100644
--- a/Lib/test/test_subprocess.py
+++ b/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'); "
diff --git a/Misc/NEWS.d/next/Windows/2023-06-08-11-30-17.gh-issue-105436.1qlDxw.rst b/Misc/NEWS.d/next/Windows/2023-06-08-11-30-17.gh-issue-105436.1qlDxw.rst
new file mode 100644
index 0000000000000..1e3f298096cdd
--- /dev/null
+++ b/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.
diff --git a/Modules/_winapi.c b/Modules/_winapi.c
index bbc9facd227c9..d6d2f4a6a9b10 100644
--- a/Modules/_winapi.c
+++ b/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;