gh-118486: Support mkdir(mode=0o700) on Windows (GH-118488)

Author: zooba

Doc/library/os.rst

@@ -2356,6 +2356,10 @@ features:
    platform-dependent.  On some platforms, they are ignored and you should call
    :func:`chmod` explicitly to set them.
 
+   On Windows, a *mode* of ``0o700`` is specifically handled to apply access
+   control to the new directory such that only the current user and
+   administrators have access. Other values of *mode* are ignored.
+
    This function can also support :ref:`paths relative to directory descriptors
    <dir_fd>`.
 
@@ -2370,6 +2374,9 @@ features:
    .. versionchanged:: 3.6
       Accepts a :term:`path-like object`.
 
+   .. versionchanged:: 3.12.4
+      Windows now handles a *mode* of ``0o700``.
+
 
 .. function:: makedirs(name, mode=0o777, exist_ok=False)
 

Doc/whatsnew/3.12.rst

@@ -778,6 +778,13 @@ os
   Both functions may be significantly faster on newer releases of
   Windows. (Contributed by Steve Dower in :gh:`99726`.)
 
+* As of 3.12.4, :func:`os.mkdir` and :func:`os.makedirs` on Windows
+  now support passing a *mode* value of ``0o700`` to apply access
+  control to the new directory. This implicitly affects
+  :func:`tempfile.mkdtemp` and is a mitigation for :cve:`2024-4030`.
+  Other values for *mode* continue to be ignored.
+  (Contributed by Steve Dower in :gh:`118486`.)
+
 os.path
 -------
 
@@ -925,6 +932,10 @@ tempfile
   *delete_on_close* (Contributed by Evgeny Zorin in :gh:`58451`.)
 * :func:`tempfile.mkdtemp` now always returns an absolute path, even if the
   argument provided to the *dir* parameter is a relative path.
+* As of 3.12.4 on Windows, the default mode ``0o700`` used by
+  :func:`tempfile.mkdtemp` now limits access to the new directory due to
+  changes to :func:`os.mkdir`. This is a mitigation for :cve:`2024-4030`.
+  (Contributed by Steve Dower in :gh:`118486`.)
 
 threading
 ---------

Lib/test/test_os.py

@@ -1797,6 +1797,25 @@ def test_exist_ok_existing_regular_file(self):
         self.assertRaises(OSError, os.makedirs, path, exist_ok=True)
         os.remove(path)
 
+    @unittest.skipUnless(os.name == 'nt', "requires Windows")
+    def test_win32_mkdir_700(self):
+        base = os_helper.TESTFN
+        path1 = os.path.join(os_helper.TESTFN, 'dir1')
+        path2 = os.path.join(os_helper.TESTFN, 'dir2')
+        # mode=0o700 is special-cased to override ACLs on Windows
+        # There's no way to know exactly how the ACLs will look, so we'll
+        # check that they are different from a regularly created directory.
+        os.mkdir(path1, mode=0o700)
+        os.mkdir(path2, mode=0o777)
+
+        out1 = subprocess.check_output(["icacls.exe", path1], encoding="oem")
+        out2 = subprocess.check_output(["icacls.exe", path2], encoding="oem")
+        os.rmdir(path1)
+        os.rmdir(path2)
+        out1 = out1.replace(path1, "<PATH>")
+        out2 = out2.replace(path2, "<PATH>")
+        self.assertNotEqual(out1, out2)
+
     def tearDown(self):
         path = os.path.join(os_helper.TESTFN, 'dir1', 'dir2', 'dir3',
                             'dir4', 'dir5', 'dir6')

Lib/test/test_tempfile.py

@@ -13,6 +13,7 @@
 import weakref
 import gc
 import shutil
+import subprocess
 from unittest import mock
 
 import unittest
@@ -803,6 +804,33 @@ def test_mode(self):
         finally:
             os.rmdir(dir)
 
+    @unittest.skipUnless(os.name == "nt", "Only on Windows.")
+    def test_mode_win32(self):
+        # Use icacls.exe to extract the users with some level of access
+        # Main thing we are testing is that the BUILTIN\Users group has
+        # no access. The exact ACL is going to vary based on which user
+        # is running the test.
+        dir = self.do_create()
+        try:
+            out = subprocess.check_output(["icacls.exe", dir], encoding="oem").casefold()
+        finally:
+            os.rmdir(dir)
+
+        dir = dir.casefold()
+        users = set()
+        found_user = False
+        for line in out.strip().splitlines():
+            acl = None
+            # First line of result includes our directory
+            if line.startswith(dir):
+                acl = line.removeprefix(dir).strip()
+            elif line and line[:1].isspace():
+                acl = line.strip()
+            if acl:
+                users.add(acl.partition(":")[0])
+
+        self.assertNotIn(r"BUILTIN\Users".casefold(), users)
+
     def test_collision_with_existing_file(self):
         # mkdtemp tries another name when a file with
         # the chosen name already exists

Misc/NEWS.d/next/Security/2024-05-01-20-57-09.gh-issue-118486.K44KJG.rst

@@ -0,0 +1,4 @@
+:func:`os.mkdir` on Windows now accepts *mode* of ``0o700`` to restrict
+the new directory to the current user. This fixes :cve:`2024-4030`
+affecting :func:`tempfile.mkdtemp` in scenarios where the base temporary
+directory is more permissive than the default.

Modules/posixmodule.c

@@ -32,6 +32,8 @@
 #  include <winioctl.h>
 #  include <lmcons.h>             // UNLEN
 #  include "osdefs.h"             // SEP
+#  include <aclapi.h>             // SetEntriesInAcl
+#  include <sddl.h>               // SDDL_REVISION_1
 #  if defined(MS_WINDOWS_DESKTOP) || defined(MS_WINDOWS_SYSTEM)
 #    define HAVE_SYMLINK
 #  endif /* MS_WINDOWS_DESKTOP | MS_WINDOWS_SYSTEM */
@@ -5342,6 +5344,12 @@ os_mkdir_impl(PyObject *module, path_t *path, int mode, int dir_fd)
 /*[clinic end generated code: output=a70446903abe821f input=a61722e1576fab03]*/
 {
     int result;
+#ifdef MS_WINDOWS
+    int error = 0;
+    int pathError = 0;
+    SECURITY_ATTRIBUTES secAttr = { sizeof(secAttr) };
+    SECURITY_ATTRIBUTES *pSecAttr = NULL;
+#endif
 #ifdef HAVE_MKDIRAT
     int mkdirat_unavailable = 0;
 #endif
@@ -5353,11 +5361,38 @@ os_mkdir_impl(PyObject *module, path_t *path, int mode, int dir_fd)
 
 #ifdef MS_WINDOWS
     Py_BEGIN_ALLOW_THREADS
-    result = CreateDirectoryW(path->wide, NULL);
+    if (mode == 0700 /* 0o700 */) {
+        ULONG sdSize;
+        pSecAttr = &secAttr;
+        // Set a discreationary ACL (D) that is protected (P) and includes
+        // inheritable (OICI) entries that allow (A) full control (FA) to
+        // SYSTEM (SY), Administrators (BA), and the owner (OW).
+        if (!ConvertStringSecurityDescriptorToSecurityDescriptorW(
+            L"D:P(A;OICI;FA;;;SY)(A;OICI;FA;;;BA)(A;OICI;FA;;;OW)",
+            SDDL_REVISION_1,
+            &secAttr.lpSecurityDescriptor,
+            &sdSize
+        )) {
+            error = GetLastError();
+        }
+    }
+    if (!error) {
+        result = CreateDirectoryW(path->wide, pSecAttr);
+        if (secAttr.lpSecurityDescriptor &&
+            // uncommonly, LocalFree returns non-zero on error, but still uses
+            // GetLastError() to see what the error code is
+            LocalFree(secAttr.lpSecurityDescriptor)) {
+            error = GetLastError();
+        }
+    }
     Py_END_ALLOW_THREADS
 
-    if (!result)
+    if (error) {
+        return PyErr_SetFromWindowsErr(error);
+    }
+    if (!result) {
         return path_error(path);
+    }
 #else
     Py_BEGIN_ALLOW_THREADS
 #if HAVE_MKDIRAT