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gh-137335: Fix unlikely name conflicts for named pipes in multiprocessing and asyncio on Windows #137389

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Merged
serhiy-storchaka merged 9 commits into from
Feb 24, 2026
+57 −26
Merged

gh-137335: Fix unlikely name conflicts for named pipes in multiprocessing and asyncio on Windows #137389

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2a0a5e9
gh-137335: Fix unlikely nmae conflicts for named pipes in multiproces…
serhiy-storchaka Aug 4, 2025
5b91a56
Fix typo
serhiy-storchaka Aug 5, 2025
ed050a0
Do not use os.getpid() and tempfile._get_candidate_names().
serhiy-storchaka Aug 5, 2025
7363c99
Merge branch 'main' into temp-named-pipes
serhiy-storchaka Feb 5, 2026
5243b9e
Use os.urandom().
serhiy-storchaka Feb 5, 2026
81cb66e
Merge branch 'main' into temp-named-pipes
serhiy-storchaka Feb 10, 2026
5207bf6
Restore the PID and sequential number for debugging and reducing chan…
serhiy-storchaka Feb 10, 2026
cae80b9
Limit the number of attempts.
serhiy-storchaka Feb 10, 2026
de04089
Apply suggestion from @serhiy-storchaka
serhiy-storchaka Feb 10, 2026
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Do not use os.getpid() and tempfile._get_candidate_names().
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@serhiy-storchaka
serhiy-storchaka committed Aug 5, 2025
commit ed050a03a3870f7477fd5e3ff7eeba61a05b4d92
6 changes: 2 additions & 4 deletions Lib/asyncio/windows_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -8,8 +8,8 @@
import _winapi
import msvcrt
import os
import random
import subprocess
import tempfile
import warnings


Expand Down Expand Up @@ -48,12 +48,10 @@ def pipe(*, duplex=False, overlapped=(True, True), bufsize=BUFSIZE):
else:
flags_and_attribs = 0

prefix = fr'\\.\pipe\python-pipe-{os.getpid()}-'
names = tempfile._get_candidate_names()
h1 = h2 = None
try:
while True:
address = prefix + next(names)
address = r'\\.\pipe\python-pipe-' + random.randbytes(8).hex()
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@picnixz picnixz Aug 5, 2025 •
edited
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A comment:

we could use os.urandom(8).hex() but this would only reduce the number of loop iterations we would do until we find a suitable name. OTOH, this makes normal cases much slower (usually, we are not in the presence of an adversary that is trying to create pipes...), so we would be only doing the loop once.

Now, I'm actually worried that it if we're able to interact with the process that is creating the pipes, then we could actually recover enough samples from the underlying PRNG instance and get the original seed. But this is only if 1) there are no random calls in between and 2) we can get 624 consecutive 32-bit samples from the random source.

Condition 2) already holds because random.randbytes(8) is actually equivalent to two calls of random.randbytes(4) that are concatenated. Since reverting MT-19937 requires only consecutive 624 32-bit words, this is the same as doing 312 pipe creations where we don't have calls to random.* in between (and then inspect the named file). This could be possible in practice, especially if we're talking about the multiprocessing and the asyncio components which could have some interactivness (e.g., a server).

Therefore, I would still suggest using os.urandom(8).hex() even if it slows down the calls.

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@serhiy-storchaka serhiy-storchaka Feb 5, 2026

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Good catch, I did not thought about this.

Sorry for not answering immediately, I missed your comment.

try:
h1 = _winapi.CreateNamedPipe(
address, openmode, _winapi.PIPE_WAIT,
Expand Down
3 changes: 2 additions & 1 deletion Lib/multiprocessing/connection.py
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,7 @@
import errno
import io
import os
import random
import sys
import socket
import struct
Expand Down Expand Up @@ -75,7 +76,7 @@ def arbitrary_address(family):
elif family == 'AF_UNIX':
return tempfile.mktemp(prefix='sock-', dir=util.get_temp_dir())
elif family == 'AF_PIPE':
return fr'\\.\pipe\pyc-{os.getpid()}-{next(tempfile._get_candidate_names())}'
return r'\\.\pipe\pyc-' + random.randbytes(8).hex()
else:
raise ValueError('unrecognized family')

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