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From 85178d5849a4d9b5b46e7b91b1ebad7425139b44 Mon Sep 17 00:00:00 2001
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From: "Gregory P. Smith" <greg@krypto.org>
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Date: Thu, 20 Oct 2022 15:30:09 -0700
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Subject: [PATCH] gh-97514: Don't use Linux abstract sockets for
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multiprocessing (GH-98501)
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Linux abstract sockets are insecure as they lack any form of filesystem
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permissions so their use allows anyone on the system to inject code into
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the process.
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This removes the default preference for abstract sockets in
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multiprocessing introduced in Python 3.9+ via
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https://github.com/python/cpython/pull/18866 while fixing
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https://github.com/python/cpython/issues/84031.
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Explicit use of an abstract socket by a user now generates a
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RuntimeWarning. If we choose to keep this warning, it should be
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backported to the 3.7 and 3.8 branches.
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(cherry picked from commit 49f61068f49747164988ffc5a442d2a63874fc17)
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Co-authored-by: Gregory P. Smith <greg@krypto.org>
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---
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Lib/multiprocessing/connection.py | 5 -----
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.../2022-09-07-10-42-00.gh-issue-97514.Yggdsl.rst | 15 +++++++++++++++
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2 files changed, 15 insertions(+), 5 deletions(-)
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create mode 100644 Misc/NEWS.d/next/Security/2022-09-07-10-42-00.gh-issue-97514.Yggdsl.rst
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diff --git a/Lib/multiprocessing/connection.py b/Lib/multiprocessing/connection.py
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index 510e4b5aba44..8e2facf92a94 100644
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--- a/Lib/multiprocessing/connection.py
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+++ b/Lib/multiprocessing/connection.py
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@@ -73,11 +73,6 @@ def arbitrary_address(family):
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if family == 'AF_INET':
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return ('localhost', 0)
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elif family == 'AF_UNIX':
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- # Prefer abstract sockets if possible to avoid problems with the address
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- # size. When coding portable applications, some implementations have
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- # sun_path as short as 92 bytes in the sockaddr_un struct.
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- if util.abstract_sockets_supported:
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- return f"\0listener-{os.getpid()}-{next(_mmap_counter)}"
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return tempfile.mktemp(prefix='listener-', dir=util.get_temp_dir())
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elif family == 'AF_PIPE':
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return tempfile.mktemp(prefix=r'\\.\pipe\pyc-%d-%d-' %
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diff --git a/Misc/NEWS.d/next/Security/2022-09-07-10-42-00.gh-issue-97514.Yggdsl.rst b/Misc/NEWS.d/next/Security/2022-09-07-10-42-00.gh-issue-97514.Yggdsl.rst
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new file mode 100644
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index 000000000000..02d95b570520
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--- /dev/null
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+++ b/Misc/NEWS.d/next/Security/2022-09-07-10-42-00.gh-issue-97514.Yggdsl.rst
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@@ -0,0 +1,15 @@
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+On Linux the :mod:`multiprocessing` module returns to using filesystem backed
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+unix domain sockets for communication with the *forkserver* process instead of
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+the Linux abstract socket namespace. Only code that chooses to use the
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+:ref:`"forkserver" start method <multiprocessing-start-methods>` is affected.
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+
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+Abstract sockets have no permissions and could allow any user on the system in
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+the same `network namespace
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+<https://man7.org/linux/man-pages/man7/network_namespaces.7.html>`_ (often the
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+whole system) to inject code into the multiprocessing *forkserver* process.
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+This was a potential privilege escalation. Filesystem based socket permissions
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+restrict this to the *forkserver* process user as was the default in Python 3.8
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+and earlier.
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+
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+This prevents Linux `CVE-2022-42919
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+<https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-42919>`_.
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