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Commit1a07a01

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gh-132124: improve safety nets for creating AF_UNIX socket files (GH-134085)
* ensure that we can create AF_UNIX socket files* emit a warning if system-wide temporary directory is used
1 parente1f8914 commit1a07a01

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4 files changed

+87
-5
lines changed

4 files changed

+87
-5
lines changed

‎Lib/multiprocessing/connection.py‎

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -76,7 +76,7 @@ def arbitrary_address(family):
7676
iffamily=='AF_INET':
7777
return ('localhost',0)
7878
eliffamily=='AF_UNIX':
79-
returntempfile.mktemp(prefix='listener-',dir=util.get_temp_dir())
79+
returntempfile.mktemp(prefix='sock-',dir=util.get_temp_dir())
8080
eliffamily=='AF_PIPE':
8181
returntempfile.mktemp(prefix=r'\\.\pipe\pyc-%d-%d-'%
8282
(os.getpid(),next(_mmap_counter)),dir="")

‎Lib/multiprocessing/util.py‎

Lines changed: 77 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -19,7 +19,7 @@
1919
from .importprocess
2020

2121
__all__= [
22-
'sub_debug','debug','info','sub_warning','get_logger',
22+
'sub_debug','debug','info','sub_warning','warn','get_logger',
2323
'log_to_stderr','get_temp_dir','register_after_fork',
2424
'is_exiting','Finalize','ForkAwareThreadLock','ForkAwareLocal',
2525
'close_all_fds_except','SUBDEBUG','SUBWARNING',
@@ -34,6 +34,7 @@
3434
DEBUG=10
3535
INFO=20
3636
SUBWARNING=25
37+
WARNING=30
3738

3839
LOGGER_NAME='multiprocessing'
3940
DEFAULT_LOGGING_FORMAT='[%(levelname)s/%(processName)s] %(message)s'
@@ -53,6 +54,10 @@ def info(msg, *args):
5354
if_logger:
5455
_logger.log(INFO,msg,*args,stacklevel=2)
5556

57+
defwarn(msg,*args):
58+
if_logger:
59+
_logger.log(WARNING,msg,*args,stacklevel=2)
60+
5661
defsub_warning(msg,*args):
5762
if_logger:
5863
_logger.log(SUBWARNING,msg,*args,stacklevel=2)
@@ -121,6 +126,21 @@ def is_abstract_socket_namespace(address):
121126
# Function returning a temp directory which will be removed on exit
122127
#
123128

129+
# Maximum length of a socket file path is usually between 92 and 108 [1],
130+
# but Linux is known to use a size of 108 [2]. BSD-based systems usually
131+
# use a size of 104 or 108 and Windows does not create AF_UNIX sockets.
132+
#
133+
# [1]: https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/sys_un.h.html
134+
# [2]: https://man7.org/linux/man-pages/man7/unix.7.html.
135+
136+
ifsys.platform=='linux':
137+
_SUN_PATH_MAX=108
138+
elifsys.platform.startswith(('openbsd','freebsd')):
139+
_SUN_PATH_MAX=104
140+
else:
141+
# On Windows platforms, we do not create AF_UNIX sockets.
142+
_SUN_PATH_MAX=Noneifos.name=='nt'else92
143+
124144
def_remove_temp_dir(rmtree,tempdir):
125145
rmtree(tempdir)
126146

@@ -130,12 +150,67 @@ def _remove_temp_dir(rmtree, tempdir):
130150
ifcurrent_processisnotNone:
131151
current_process._config['tempdir']=None
132152

153+
def_get_base_temp_dir(tempfile):
154+
"""Get a temporary directory where socket files will be created.
155+
156+
To prevent additional imports, pass a pre-imported 'tempfile' module.
157+
"""
158+
ifos.name=='nt':
159+
returnNone
160+
# Most of the time, the default temporary directory is /tmp. Thus,
161+
# listener sockets files "$TMPDIR/pymp-XXXXXXXX/sock-XXXXXXXX" do
162+
# not have a path length exceeding SUN_PATH_MAX.
163+
#
164+
# If users specify their own temporary directory, we may be unable
165+
# to create those files. Therefore, we fall back to the system-wide
166+
# temporary directory /tmp, assumed to exist on POSIX systems.
167+
#
168+
# See https://github.com/python/cpython/issues/132124.
169+
base_tempdir=tempfile.gettempdir()
170+
# Files created in a temporary directory are suffixed by a string
171+
# generated by tempfile._RandomNameSequence, which, by design,
172+
# is 8 characters long.
173+
#
174+
# Thus, the length of socket filename will be:
175+
#
176+
# len(base_tempdir + '/pymp-XXXXXXXX' + '/sock-XXXXXXXX')
177+
sun_path_len=len(base_tempdir)+14+14
178+
ifsun_path_len<=_SUN_PATH_MAX:
179+
returnbase_tempdir
180+
# Fallback to the default system-wide temporary directory.
181+
# This ignores user-defined environment variables.
182+
#
183+
# On POSIX systems, /tmp MUST be writable by any application [1].
184+
# We however emit a warning if this is not the case to prevent
185+
# obscure errors later in the execution.
186+
#
187+
# On some legacy systems, /var/tmp and /usr/tmp can be present
188+
# and will be used instead.
189+
#
190+
# [1]: https://refspecs.linuxfoundation.org/FHS_3.0/fhs/ch03s18.html
191+
dirlist= ['/tmp','/var/tmp','/usr/tmp']
192+
try:
193+
base_system_tempdir=tempfile._get_default_tempdir(dirlist)
194+
exceptFileNotFoundError:
195+
warn("Process-wide temporary directory %s will not be usable for "
196+
"creating socket files and no usable system-wide temporary "
197+
"directory was found in %s",base_tempdir,dirlist)
198+
# At this point, the system-wide temporary directory is not usable
199+
# but we may assume that the user-defined one is, even if we will
200+
# not be able to write socket files out there.
201+
returnbase_tempdir
202+
warn("Ignoring user-defined temporary directory: %s",base_tempdir)
203+
# at most max(map(len, dirlist)) + 14 + 14 = 36 characters
204+
assertlen(base_system_tempdir)+14+14<=_SUN_PATH_MAX
205+
returnbase_system_tempdir
206+
133207
defget_temp_dir():
134208
# get name of a temp directory which will be automatically cleaned up
135209
tempdir=process.current_process()._config.get('tempdir')
136210
iftempdirisNone:
137211
importshutil,tempfile
138-
tempdir=tempfile.mkdtemp(prefix='pymp-')
212+
base_tempdir=_get_base_temp_dir(tempfile)
213+
tempdir=tempfile.mkdtemp(prefix='pymp-',dir=base_tempdir)
139214
info('created temp directory %s',tempdir)
140215
# keep a strong reference to shutil.rmtree(), since the finalizer
141216
# can be called late during Python shutdown

‎Lib/tempfile.py‎

Lines changed: 3 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -180,7 +180,7 @@ def _candidate_tempdir_list():
180180

181181
returndirlist
182182

183-
def_get_default_tempdir():
183+
def_get_default_tempdir(dirlist=None):
184184
"""Calculate the default directory to use for temporary files.
185185
This routine should be called exactly once.
186186
@@ -190,7 +190,8 @@ def _get_default_tempdir():
190190
service, the name of the test file must be randomized."""
191191

192192
namer=_RandomNameSequence()
193-
dirlist=_candidate_tempdir_list()
193+
ifdirlistisNone:
194+
dirlist=_candidate_tempdir_list()
194195

195196
fordirindirlist:
196197
ifdir!=_os.curdir:
Lines changed: 6 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,6 @@
1+
On POSIX-compliant systems,:func:`!multiprocessing.util.get_temp_dir` now
2+
ignores:envvar:`TMPDIR` (and similar environment variables) if the path
3+
length of ``AF_UNIX`` socket files exceeds the platform-specific maximum
4+
length when using the:ref:`forkserver
5+
<multiprocessing-start-method-forkserver>` start method. Patch by Bénédikt
6+
Tran.

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