8000 [3.11] gh-97514: Don't use Linux abstract sockets for multiprocessing (GH-98501) by miss-islington · Pull Request #98502 · python/cpython · GitHub
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[3.11] gh-97514: Don't use Linux abstract sockets for multiprocessing (GH-98501) #98502

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Merged
merged 1 commit into from
Oct 20, 2022
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[3.11] gh-97514: Don't use Linux abstract sockets for multiprocessing (GH-98501) #98502

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gh-97514: Don't use Linux abstract sockets for multiprocessing (GH-98501 
)

Linux abstract sockets are insecure as they lack any form of filesystem
permissions so their use allows anyone on the system to inject code into
the process.

This removes the default preference for abstract sockets in
multiprocessing introduced in Python 3.9+ via
#18866 while fixing
#84031.

Explicit use of an abstract socket by a user now generates a
RuntimeWarning.  If we choose to keep this warning, it should be
backported to the 3.7 and 3.8 branches.
(cherry picked from commit 49f6106)

Co-authored-by: Gregory P. Smith <greg@krypto.org>
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@gpshead @miss-islington
gpshead authored and miss-islington committed Oct 20, 2022
commit bf6166555bc371002306c5ba9b894e49c4afd488
5 changes: 0 additions & 5 deletions Lib/multiprocessing/connection.py
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Expand Up @@ -73,11 +73,6 @@ def arbitrary_address(family):
if family == 'AF_INET':
return ('localhost', 0)
elif family == 'AF_UNIX':
# Prefer abstract sockets if possible to avoid problems with the address
# size. When coding portable applications, some implementations have
# sun_path as short as 92 bytes in the sockaddr_un struct.
if util.abstract_sockets_supported:
return f"\0listener-{os.getpid()}-{next(_mmap_counter)}"
return tempfile.mktemp(prefix='listener-', dir=util.get_temp_dir())
elif family == 'AF_PIPE':
return tempfile.mktemp(prefix=r'\\.\pipe\pyc-%d-%d-' %
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15 changes: 15 additions & 0 deletions Misc/NEWS.d/next/Security/2022-09-07-10-42-00.gh-issue-97514.Yggdsl.rst
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@@ -0,0 +1,15 @@
On Linux the :mod:`multiprocessing` module returns to using filesystem backed
unix domain sockets for communication with the *forkserver* process instead of
the Linux abstract socket namespace. Only code that chooses to use the
:ref:`"forkserver" start method <multiprocessing-start-methods>` is affected.

Abstract sockets have no permissions and could allow any user on the system in
the same `network namespace
<https://man7.org/linux/man-pages/man7/network_namespaces.7.html>`_ (often the
whole system) to inject code into the multiprocessing *forkserver* process.
This was a potential privilege escalation. Filesystem based socket permissions
restrict this to the *forkserver* process user as was the default in Python 3.8
and earlier.

This prevents Linux `CVE-2022-42919
<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-42919>`_.
0