[Python-checkins] [3.9] gh-97514: Don't use Linux abstract sockets for multiprocessing (GH-98501) (#98504)

[ambv]

https://github.com/python/cpython/commit/b43496c01a554cf41ae654a0379efae18609ad39
commit: b43496c01a554cf41ae654a0379efae18609ad39
branch: 3.9
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: ambv <lukasz at langa.pl>
date: 2022-10-28T12:08:30+02:00
summary:

[3.9] gh-97514: Don't use Linux abstract sockets for multiprocessing (GH-98501) (#98504)

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
https://github.com/python/cpython/pull/18866 while fixing
https://github.com/python/cpython/issues/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 49f61068f49747164988ffc5a442d2a63874fc17)

Co-authored-by: Gregory P. Smith <greg at krypto.org>

files:
A Misc/NEWS.d/next/Security/2022-09-07-10-42-00.gh-issue-97514.Yggdsl.rst
M Lib/multiprocessing/connection.py

diff --git a/Lib/multiprocessing/connection.py b/Lib/multiprocessing/connection.py
index 510e4b5aba44..8e2facf92a94 100644
--- a/Lib/multiprocessing/connection.py
+++ b/Lib/multiprocessing/connection.py
@@ -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-' %
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
new file mode 100644
index 000000000000..02d95b570520
--- /dev/null
+++ b/Misc/NEWS.d/next/Security/2022-09-07-10-42-00.gh-issue-97514.Yggdsl.rst
@@ -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>`_.