bpo-46785: Fix race condition between os.stat() and unlink on Windows (GH-31858)

This commit is contained in:
Itai Steinherz 2022-05-03 02:19:13 +03:00 committed by GitHub
parent ebb8b512e9
commit 39e6b8ae6a
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4 changed files with 57 additions and 1 deletions

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@ -24,6 +24,7 @@ import subprocess
import sys
import sysconfig
import tempfile
import textwrap
import time
import types
import unittest
@ -2883,6 +2884,49 @@ class Win32NtTests(unittest.TestCase):
self.assertEqual(0, handle_delta)
@support.requires_subprocess()
def test_stat_unlink_race(self):
# bpo-46785: the implementation of os.stat() falls back to reading
# the parent directory if CreateFileW() fails with a permission
# error. If reading the parent directory fails because the file or
# directory are subsequently unlinked, or because the volume or
# share are no longer available, then the original permission error
# should not be restored.
filename = os_helper.TESTFN
self.addCleanup(os_helper.unlink, filename)
deadline = time.time() + 5
command = textwrap.dedent("""\
import os
import sys
import time
filename = sys.argv[1]
deadline = float(sys.argv[2])
while time.time() < deadline:
try:
with open(filename, "w") as f:
pass
except OSError:
pass
try:
os.remove(filename)
except OSError:
pass
""")
with subprocess.Popen([sys.executable, '-c', command, filename, str(deadline)]) as proc:
while time.time() < deadline:
try:
os.stat(filename)
except FileNotFoundError as e:
assert e.winerror == 2 # ERROR_FILE_NOT_FOUND
try:
proc.wait(1)
except subprocess.TimeoutExpired:
proc.terminate()
@os_helper.skip_unless_symlink
class NonLocalSymlinkTests(unittest.TestCase):

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@ -1705,6 +1705,7 @@ Anthony Starks
David Steele
Oliver Steele
Greg Stein
Itai Steinherz
Marek Stepniowski
Baruch Sterin
Chris Stern

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@ -0,0 +1 @@
Fix race condition between :func:`os.stat` and unlinking a file on Windows, by using errors codes returned by ``FindFirstFileW()`` when appropriate in ``win32_xstat_impl``.

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@ -1890,7 +1890,17 @@ win32_xstat_impl(const wchar_t *path, struct _Py_stat_struct *result,
/* Try reading the parent directory. */
if (!attributes_from_dir(path, &fileInfo, &tagInfo.ReparseTag)) {
/* Cannot read the parent directory. */
SetLastError(error);
switch (GetLastError()) {
case ERROR_FILE_NOT_FOUND: /* File cannot be found */
case ERROR_PATH_NOT_FOUND: /* File parent directory cannot be found */
case ERROR_NOT_READY: /* Drive exists but unavailable */
case ERROR_BAD_NET_NAME: /* Remote drive unavailable */
break;
/* Restore the error from CreateFileW(). */
default:
SetLastError(error);
}
return -1;
}
if (fileInfo.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) {