gh-111841: Fix os.putenv() and os.unsetenv() with embedded NUL on Windows (GH-111842)

Lib/test/test_os.py

@@ -1150,9 +1150,12 @@ def test_putenv_unsetenv(self):
     def test_putenv_unsetenv_error(self):
         # Empty variable name is invalid.
         # "=" and null character are not allowed in a variable name.
-        for name in ('', '=name', 'na=me', 'name=', 'name\0', 'na\0me'):
+        for name in ('', '=name', 'na=me', 'name='):
             self.assertRaises((OSError, ValueError), os.putenv, name, "value")
             self.assertRaises((OSError, ValueError), os.unsetenv, name)
+        for name in ('name\0', 'na\0me'):
+            self.assertRaises(ValueError, os.putenv, name, "value")
+            self.assertRaises(ValueError, os.unsetenv, name)
 
         if sys.platform == "win32":
             # On Windows, an environment variable string ("name=value" string)

Lib/test/test_posix.py

@@ -1011,20 +1011,20 @@ def test_environ(self):
             self.assertEqual(type(k), item_type)
             self.assertEqual(type(v), item_type)
 
-    @unittest.skipUnless(os.name == 'posix', "see bug gh-111841")
     def test_putenv(self):
         with self.assertRaises(ValueError):
             os.putenv('FRUIT\0VEGETABLE', 'cabbage')
-        with self.assertRaises(ValueError):
-            os.putenv(b'FRUIT\0VEGETABLE', b'cabbage')
         with self.assertRaises(ValueError):
             os.putenv('FRUIT', 'orange\0VEGETABLE=cabbage')
-        with self.assertRaises(ValueError):
-            os.putenv(b'FRUIT', b'orange\0VEGETABLE=cabbage')
         with self.assertRaises(ValueError):
             os.putenv('FRUIT=ORANGE', 'lemon')
-        with self.assertRaises(ValueError):
-            os.putenv(b'FRUIT=ORANGE', b'lemon')
+        if os.name == 'posix':
+            with self.assertRaises(ValueError):
+                os.putenv(b'FRUIT\0VEGETABLE', b'cabbage')
+            with self.assertRaises(ValueError):
+                os.putenv(b'FRUIT', b'orange\0VEGETABLE=cabbage')
+            with self.assertRaises(ValueError):
+                os.putenv(b'FRUIT=ORANGE', b'lemon')
 
     @unittest.skipUnless(hasattr(posix, 'getcwd'), 'test needs posix.getcwd()')
     def test_getcwd_long_pathnames(self):

Misc/NEWS.d/next/Library/2023-11-08-11-50-49.gh-issue-111841.iSqdQf.rst

@@ -0,0 +1,2 @@
+Fix truncating arguments on an embedded null character in :meth:`os.putenv`
+and :meth:`os.unsetenv` on Windows.

Modules/posixmodule.c

@@ -12280,7 +12280,6 @@ win32_putenv(PyObject *name, PyObject *value)
     }
 
     Py_ssize_t size;
-    /* PyUnicode_AsWideCharString() rejects embedded null characters */
     wchar_t *env = PyUnicode_AsWideCharString(unicode, &size);
     Py_DECREF(unicode);
 
@@ -12294,6 +12293,12 @@ win32_putenv(PyObject *name, PyObject *value)
         PyMem_Free(env);
         return NULL;
     }
+    if (wcslen(env) != (size_t)size) {
+        PyErr_SetString(PyExc_ValueError,
+                        "embedded null character");
+        PyMem_Free(env);
+        return NULL;
+    }
 
     /* _wputenv() and SetEnvironmentVariableW() update the environment in the
        Process Environment Block (PEB). _wputenv() also updates CRT 'environ'