From 7ee3aca00a0dffc9cb5906a24005a8c61d5bce14 Mon Sep 17 00:00:00 2001 From: Gareth Rees Date: Fri, 28 Oct 2022 19:17:04 +0100 Subject: [PATCH] gh-92452: Avoid race in initialization of sysconfig._CONFIG_VARS MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Co-authored-by: Filipe Laíns --- Lib/sysconfig.py | 140 ++++++++++-------- ...2-05-08-08-47-32.gh-issue-92452.3pNHe6.rst | 2 + 2 files changed, 82 insertions(+), 60 deletions(-) create mode 100644 Misc/NEWS.d/next/Library/2022-05-08-08-47-32.gh-issue-92452.3pNHe6.rst diff --git a/Lib/sysconfig.py b/Lib/sysconfig.py index ebe37118274222..73c25684db20c9 100644 --- a/Lib/sysconfig.py +++ b/Lib/sysconfig.py @@ -2,6 +2,7 @@ import os import sys +import threading from os.path import pardir, realpath __all__ = [ @@ -172,7 +173,11 @@ def joinuser(*args): _BASE_PREFIX = os.path.normpath(sys.base_prefix) _EXEC_PREFIX = os.path.normpath(sys.exec_prefix) _BASE_EXEC_PREFIX = os.path.normpath(sys.base_exec_prefix) +# Mutex guarding initialization of _CONFIG_VARS. +_CONFIG_VARS_LOCK = threading.RLock() _CONFIG_VARS = None +# True iff _CONFIG_VARS has been fully initialized. +_CONFIG_VARS_INITIALIZED = False _USER_BASE = None # Regexes needed for parsing Makefile (and similar syntaxes, @@ -626,6 +631,71 @@ def get_path(name, scheme=get_default_scheme(), vars=None, expand=True): return get_paths(scheme, vars, expand)[name] +def _init_config_vars(): + global _CONFIG_VARS + _CONFIG_VARS = {} + # Normalized versions of prefix and exec_prefix are handy to have; + # in fact, these are the standard versions used most places in the + # Distutils. + _CONFIG_VARS['prefix'] = _PREFIX + _CONFIG_VARS['exec_prefix'] = _EXEC_PREFIX + _CONFIG_VARS['py_version'] = _PY_VERSION + _CONFIG_VARS['py_version_short'] = _PY_VERSION_SHORT + _CONFIG_VARS['py_version_nodot'] = _PY_VERSION_SHORT_NO_DOT + _CONFIG_VARS['installed_base'] = _BASE_PREFIX + _CONFIG_VARS['base'] = _PREFIX + _CONFIG_VARS['installed_platbase'] = _BASE_EXEC_PREFIX + _CONFIG_VARS['platbase'] = _EXEC_PREFIX + _CONFIG_VARS['projectbase'] = _PROJECT_BASE + _CONFIG_VARS['platlibdir'] = sys.platlibdir + try: + _CONFIG_VARS['abiflags'] = sys.abiflags + except AttributeError: + # sys.abiflags may not be defined on all platforms. + _CONFIG_VARS['abiflags'] = '' + try: + _CONFIG_VARS['py_version_nodot_plat'] = sys.winver.replace('.', '') + except AttributeError: + _CONFIG_VARS['py_version_nodot_plat'] = '' + + if os.name == 'nt': + _init_non_posix(_CONFIG_VARS) + _CONFIG_VARS['VPATH'] = sys._vpath + if os.name == 'posix': + _init_posix(_CONFIG_VARS) + if _HAS_USER_BASE: + # Setting 'userbase' is done below the call to the + # init function to enable using 'get_config_var' in + # the init-function. + _CONFIG_VARS['userbase'] = _getuserbase() + + # Always convert srcdir to an absolute path + srcdir = _CONFIG_VARS.get('srcdir', _PROJECT_BASE) + if os.name == 'posix': + if _PYTHON_BUILD: + # If srcdir is a relative path (typically '.' or '..') + # then it should be interpreted relative to the directory + # containing Makefile. + base = os.path.dirname(get_makefile_filename()) + srcdir = os.path.join(base, srcdir) + else: + # srcdir is not meaningful since the installation is + # spread about the filesystem. We choose the + # directory containing the Makefile since we know it + # exists. + srcdir = os.path.dirname(get_makefile_filename()) + _CONFIG_VARS['srcdir'] = _safe_realpath(srcdir) + + # OS X platforms require special customization to handle + # multi-architecture, multi-os-version installers + if sys.platform == 'darwin': + import _osx_support + _osx_support.customize_config_vars(_CONFIG_VARS) + + global _CONFIG_VARS_INITIALIZED + _CONFIG_VARS_INITIALIZED = True + + def get_config_vars(*args): """With no arguments, return a dictionary of all configuration variables relevant for the current platform. @@ -636,66 +706,16 @@ def get_config_vars(*args): With arguments, return a list of values that result from looking up each argument in the configuration variable dictionary. """ - global _CONFIG_VARS - if _CONFIG_VARS is None: - _CONFIG_VARS = {} - # Normalized versions of prefix and exec_prefix are handy to have; - # in fact, these are the standard versions used most places in the - # Distutils. - _CONFIG_VARS['prefix'] = _PREFIX - _CONFIG_VARS['exec_prefix'] = _EXEC_PREFIX - _CONFIG_VARS['py_version'] = _PY_VERSION - _CONFIG_VARS['py_version_short'] = _PY_VERSION_SHORT - _CONFIG_VARS['py_version_nodot'] = _PY_VERSION_SHORT_NO_DOT - _CONFIG_VARS['installed_base'] = _BASE_PREFIX - _CONFIG_VARS['base'] = _PREFIX - _CONFIG_VARS['installed_platbase'] = _BASE_EXEC_PREFIX - _CONFIG_VARS['platbase'] = _EXEC_PREFIX - _CONFIG_VARS['projectbase'] = _PROJECT_BASE - _CONFIG_VARS['platlibdir'] = sys.platlibdir - try: - _CONFIG_VARS['abiflags'] = sys.abiflags - except AttributeError: - # sys.abiflags may not be defined on all platforms. - _CONFIG_VARS['abiflags'] = '' - try: - _CONFIG_VARS['py_version_nodot_plat'] = sys.winver.replace('.', '') - except AttributeError: - _CONFIG_VARS['py_version_nodot_plat'] = '' - - if os.name == 'nt': - _init_non_posix(_CONFIG_VARS) - _CONFIG_VARS['VPATH'] = sys._vpath - if os.name == 'posix': - _init_posix(_CONFIG_VARS) - if _HAS_USER_BASE: - # Setting 'userbase' is done below the call to the - # init function to enable using 'get_config_var' in - # the init-function. - _CONFIG_VARS['userbase'] = _getuserbase() - - # Always convert srcdir to an absolute path - srcdir = _CONFIG_VARS.get('srcdir', _PROJECT_BASE) - if os.name == 'posix': - if _PYTHON_BUILD: - # If srcdir is a relative path (typically '.' or '..') - # then it should be interpreted relative to the directory - # containing Makefile. - base = os.path.dirname(get_makefile_filename()) - srcdir = os.path.join(base, srcdir) - else: - # srcdir is not meaningful since the installation is - # spread about the filesystem. We choose the - # directory containing the Makefile since we know it - # exists. - srcdir = os.path.dirname(get_makefile_filename()) - _CONFIG_VARS['srcdir'] = _safe_realpath(srcdir) - - # OS X platforms require special customization to handle - # multi-architecture, multi-os-version installers - if sys.platform == 'darwin': - import _osx_support - _osx_support.customize_config_vars(_CONFIG_VARS) + + # Avoid claiming the lock once initialization is complete. + if not _CONFIG_VARS_INITIALIZED: + with _CONFIG_VARS_LOCK: + # Test again with the lock held to avoid races. Note that + # we test _CONFIG_VARS here, not _CONFIG_VARS_INITIALIZED, + # to ensure that recursive calls to get_config_vars() + # don't re-enter init_config_vars(). + if _CONFIG_VARS is None: + _init_config_vars() if args: vals = [] diff --git a/Misc/NEWS.d/next/Library/2022-05-08-08-47-32.gh-issue-92452.3pNHe6.rst b/Misc/NEWS.d/next/Library/2022-05-08-08-47-32.gh-issue-92452.3pNHe6.rst new file mode 100644 index 00000000000000..25d6477aa9138a --- /dev/null +++ b/Misc/NEWS.d/next/Library/2022-05-08-08-47-32.gh-issue-92452.3pNHe6.rst @@ -0,0 +1,2 @@ +Fixed a race condition that could cause :func:`sysconfig.get_config_var` to +incorrectly return :const:`None` in multi-threaded programs.