From 86da8debddf2149219cc1fbd9992121e6ff8d849 Mon Sep 17 00:00:00 2001 From: Steve Dower Date: Wed, 1 May 2024 20:57:29 +0100 Subject: [PATCH] gh-118486: Support mkdir(mode=0o700) on Windows --- Doc/library/os.rst | 7 + Doc/whatsnew/3.8.rst | 16 ++ Lib/test/test_os.py | 19 ++ Lib/test/test_tempfile.py | 28 +++ ...-05-01-20-57-09.gh-issue-118486.K44KJG.rst | 4 + Modules/posixmodule.c | 175 +++++++++++++++++- 6 files changed, 247 insertions(+), 2 deletions(-) create mode 100644 Misc/NEWS.d/next/Security/2024-05-01-20-57-09.gh-issue-118486.K44KJG.rst diff --git a/Doc/library/os.rst b/Doc/library/os.rst index d0a37a8bbdbf05..736a59a9216b6f 100644 --- a/Doc/library/os.rst +++ b/Doc/library/os.rst @@ -1909,6 +1909,10 @@ 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 `. @@ -1923,6 +1927,9 @@ features: .. versionchanged:: 3.6 Accepts a :term:`path-like object`. + .. versionchanged:: 3.8.20 + Windows now handles a *mode* of ``0o700``. + .. function:: makedirs(name, mode=0o777, exist_ok=False) diff --git a/Doc/whatsnew/3.8.rst b/Doc/whatsnew/3.8.rst index e5278da3f6a5be..e0eb5b4dc3f777 100644 --- a/Doc/whatsnew/3.8.rst +++ b/Doc/whatsnew/3.8.rst @@ -1046,6 +1046,13 @@ treat junctions as links. (Contributed by Steve Dower in :issue:`37834`.) +As of 3.8.20, :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 ------- @@ -1252,6 +1259,15 @@ in a standardized and extensible format, and offers several other benefits. (Contributed by C.A.M. Gerlach in :issue:`36268`.) +tempfile +-------- + +As of 3.8.20 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 --------- diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py index 5302b1ce575d4e..0274f791ba79bf 100644 --- a/Lib/test/test_os.py +++ b/Lib/test/test_os.py @@ -1380,6 +1380,25 @@ 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, "") + out2 = out2.replace(path2, "") + self.assertNotEqual(out1, out2) + def tearDown(self): path = os.path.join(support.TESTFN, 'dir1', 'dir2', 'dir3', 'dir4', 'dir5', 'dir6') diff --git a/Lib/test/test_tempfile.py b/Lib/test/test_tempfile.py index 8cb36f38a2a35c..9fe9d1d651433e 100644 --- a/Lib/test/test_tempfile.py +++ b/Lib/test/test_tempfile.py @@ -11,6 +11,7 @@ import contextlib import stat import weakref +import subprocess from unittest import mock import unittest @@ -760,6 +761,33 @@ 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 diff --git a/Misc/NEWS.d/next/Security/2024-05-01-20-57-09.gh-issue-118486.K44KJG.rst b/Misc/NEWS.d/next/Security/2024-05-01-20-57-09.gh-issue-118486.K44KJG.rst new file mode 100644 index 00000000000000..8ac48aac816a60 --- /dev/null +++ b/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. diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c index d7edabe5da08d1..4a08b3635dcc3f 100644 --- a/Modules/posixmodule.c +++ b/Modules/posixmodule.c @@ -40,6 +40,12 @@ #include "pycore_pystate.h" /* _PyRuntime */ #include "pythread.h" #include "structmember.h" + +#ifdef MS_WINDOWS +# include // SetEntriesInAcl +# include // SDDL_REVISION_1 +#endif + #ifndef MS_WINDOWS # include "posixmodule.h" #else @@ -4123,6 +4129,146 @@ os__path_splitroot_impl(PyObject *module, path_t *path) #endif /* MS_WINDOWS */ +#ifdef MS_WINDOWS + +/* We centralise SECURITY_ATTRIBUTE initialization based around +templates that will probably mostly match common POSIX mode settings. +The _Py_SECURITY_ATTRIBUTE_DATA structure contains temporary data, as +a constructed SECURITY_ATTRIBUTE structure typically refers to memory +that has to be alive while it's being used. + +Typical use will look like: + SECURITY_ATTRIBUTES *pSecAttr = NULL; + struct _Py_SECURITY_ATTRIBUTE_DATA secAttrData; + int error, error2; + + Py_BEGIN_ALLOW_THREADS + switch (mode) { + case 0x1C0: // 0o700 + error = initializeMkdir700SecurityAttributes(&pSecAttr, &secAttrData); + break; + ... + default: + error = initializeDefaultSecurityAttributes(&pSecAttr, &secAttrData); + break; + } + + if (!error) { + // do operation, passing pSecAttr + } + + // Unconditionally clear secAttrData. + error2 = clearSecurityAttributes(&pSecAttr, &secAttrData); + if (!error) { + error = error2; + } + Py_END_ALLOW_THREADS + + if (error) { + PyErr_SetFromWindowsErr(error); + return NULL; + } +*/ + +struct _Py_SECURITY_ATTRIBUTE_DATA { + SECURITY_ATTRIBUTES securityAttributes; + PACL acl; + SECURITY_DESCRIPTOR sd; + EXPLICIT_ACCESS_W ea[4]; + char sid[64]; +}; + +static int +initializeDefaultSecurityAttributes( + PSECURITY_ATTRIBUTES *securityAttributes, + struct _Py_SECURITY_ATTRIBUTE_DATA *data +) { + assert(securityAttributes); + assert(data); + *securityAttributes = NULL; + memset(data, 0, sizeof(*data)); + return 0; +} + +static int +initializeMkdir700SecurityAttributes( + PSECURITY_ATTRIBUTES *securityAttributes, + struct _Py_SECURITY_ATTRIBUTE_DATA *data +) { + assert(securityAttributes); + assert(data); + *securityAttributes = NULL; + memset(data, 0, sizeof(*data)); + + if (!InitializeSecurityDescriptor(&data->sd, SECURITY_DESCRIPTOR_REVISION) + || !SetSecurityDescriptorGroup(&data->sd, NULL, TRUE)) { + return GetLastError(); + } + + int use_alias = 0; + DWORD cbSid = sizeof(data->sid); + if (!CreateWellKnownSid(WinCreatorOwnerRightsSid, NULL, (PSID)data->sid, &cbSid)) { + use_alias = 1; + } + + data->securityAttributes.nLength = sizeof(SECURITY_ATTRIBUTES); + data->ea[0].grfAccessPermissions = GENERIC_ALL; + data->ea[0].grfAccessMode = SET_ACCESS; + data->ea[0].grfInheritance = SUB_CONTAINERS_AND_OBJECTS_INHERIT; + if (use_alias) { + data->ea[0].Trustee.TrusteeForm = TRUSTEE_IS_NAME; + data->ea[0].Trustee.TrusteeType = TRUSTEE_IS_ALIAS; + data->ea[0].Trustee.ptstrName = L"CURRENT_USER"; + } else { + data->ea[0].Trustee.TrusteeForm = TRUSTEE_IS_SID; + data->ea[0].Trustee.TrusteeType = TRUSTEE_IS_WELL_KNOWN_GROUP; + data->ea[0].Trustee.ptstrName = (LPWCH)(SID*)data->sid; + } + + data->ea[1].grfAccessPermissions = GENERIC_ALL; + data->ea[1].grfAccessMode = SET_ACCESS; + data->ea[1].grfInheritance = SUB_CONTAINERS_AND_OBJECTS_INHERIT; + data->ea[1].Trustee.TrusteeForm = TRUSTEE_IS_NAME; + data->ea[1].Trustee.TrusteeType = TRUSTEE_IS_ALIAS; + data->ea[1].Trustee.ptstrName = L"SYSTEM"; + + data->ea[2].grfAccessPermissions = GENERIC_ALL; + data->ea[2].grfAccessMode = SET_ACCESS; + data->ea[2].grfInheritance = SUB_CONTAINERS_AND_OBJECTS_INHERIT; + data->ea[2].Trustee.TrusteeForm = TRUSTEE_IS_NAME; + data->ea[2].Trustee.TrusteeType = TRUSTEE_IS_ALIAS; + data->ea[2].Trustee.ptstrName = L"ADMINISTRATORS"; + + int r = SetEntriesInAclW(3, data->ea, NULL, &data->acl); + if (r) { + return r; + } + if (!SetSecurityDescriptorDacl(&data->sd, TRUE, data->acl, FALSE)) { + return GetLastError(); + } + data->securityAttributes.lpSecurityDescriptor = &data->sd; + *securityAttributes = &data->securityAttributes; + return 0; +} + +static int +clearSecurityAttributes( + PSECURITY_ATTRIBUTES *securityAttributes, + struct _Py_SECURITY_ATTRIBUTE_DATA *data +) { + assert(securityAttributes); + assert(data); + *securityAttributes = NULL; + if (data->acl) { + if (LocalFree((void *)data->acl)) { + return GetLastError(); + } + } + return 0; +} + +#endif + /*[clinic input] os.mkdir @@ -4151,6 +4297,12 @@ os_mkdir_impl(PyObject *module, path_t *path, int mode, int dir_fd) /*[clinic end generated code: output=a70446903abe821f input=e965f68377e9b1ce]*/ { int result; +#ifdef MS_WINDOWS + int error = 0; + int pathError = 0; + SECURITY_ATTRIBUTES *pSecAttr = NULL; + struct _Py_SECURITY_ATTRIBUTE_DATA secAttrData; +#endif if (PySys_Audit("os.mkdir", "Oii", path->object, mode, dir_fd == DEFAULT_DIR_FD ? -1 : dir_fd) < 0) { @@ -4159,11 +4311,30 @@ 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); + switch (mode) { + case 0x1C0: // 0o700 + error = initializeMkdir700SecurityAttributes(&pSecAttr, &secAttrData); + break; + default: + error = initializeDefaultSecurityAttributes(&pSecAttr, &secAttrData); + break; + } + if (!error) { + result = CreateDirectoryW(path->wide, pSecAttr); + error = clearSecurityAttributes(&pSecAttr, &secAttrData); + } else { + // Ignore error from "clear" - we have a more interesting one already + clearSecurityAttributes(&pSecAttr, &secAttrData); + } Py_END_ALLOW_THREADS - if (!result) + if (error) { + PyErr_SetFromWindowsErr(error); + return NULL; + } + if (!result) { return path_error(path); + } #else Py_BEGIN_ALLOW_THREADS #if HAVE_MKDIRAT