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bpo-33929: multiprocessing: fix handle leak on race condition (GH-7921)

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Fix a race condition in Popen of
multiprocessing.popen_spawn_win32. The child process now duplicates
the read end of pipe instead of "stealing" it.

Previously, the read end of pipe was "stolen" by the child process,
but it leaked a handle if the child process had been terminated
before it could steal the handle from the parent process.
This commit is contained in:
Victor Stinner 2018-06-27 11:40:24 +02:00 • committed by GitHub
parent f15f66d275
commit 2cc9d21fff
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4 changed files with 34 additions and 6 deletions
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15
Lib/multiprocessing/popen_spawn_win32.py
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@ -18,6 +18,12 @@
WINEXE = (sys.platform == 'win32' and getattr(sys, 'frozen', False))
WINSERVICE = sys.executable.lower().endswith("pythonservice.exe")
def _close_handles(*handles):
for handle in handles:
_winapi.CloseHandle(handle)
#
# We define a Popen class similar to the one from subprocess, but
# whose constructor takes a process object as its argument.
@ -32,8 +38,12 @@ class Popen(object):
def __init__(self, process_obj):
prep_data = spawn.get_preparation_data(process_obj._name)
# read end of pipe will be "stolen" by the child process
# read end of pipe will be duplicated by the child process
# -- see spawn_main() in spawn.py.
#
# bpo-33929: Previously, the read end of pipe was "stolen" by the child
# process, but it leaked a handle if the child process had been
# terminated before it could steal the handle from the parent process.
rhandle, whandle = _winapi.CreatePipe(None, 0)
wfd = msvcrt.open_osfhandle(whandle, 0)
cmd = spawn.get_command_line(parent_pid=os.getpid(),
@ -56,7 +66,8 @@ def __init__(self, process_obj):
self.returncode = None
self._handle = hp
self.sentinel = int(hp)
self.finalizer = util.Finalize(self, _winapi.CloseHandle, (self.sentinel,))
self.finalizer = util.Finalize(self, _close_handles,
(self.sentinel, int(rhandle)))
# send information to child
set_spawning_popen(self)