linux-cve-announce - CVE-2023-53815: posix-timers: Prevent RT livelock in itimer

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Message-ID: <2025120945-CVE-2023-53815-5695@gregkh>
Date: Tue,  9 Dec 2025 09:02:36 +0900
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2023-53815: posix-timers: Prevent RT livelock in itimer_delete()

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

posix-timers: Prevent RT livelock in itimer_delete()

itimer_delete() has a retry loop when the timer is concurrently expired. On
non-RT kernels this just spin-waits until the timer callback has completed,
except for posix CPU timers which have HAVE_POSIX_CPU_TIMERS_TASK_WORK
enabled.

In that case and on RT kernels the existing task could live lock when
preempting the task which does the timer delivery.

Replace spin_unlock() with an invocation of timer_wait_running() to handle
it the same way as the other retry loops in the posix timer code.

The Linux kernel CVE team has assigned CVE-2023-53815 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 5.4 with commit ec8f954a40da8cd3d159713b608e901f0cd909a9 and fixed in 5.10.188 with commit f1be1ed32daa053484222f7f9beb2b16c624dffd
	Issue introduced in 5.4 with commit ec8f954a40da8cd3d159713b608e901f0cd909a9 and fixed in 5.15.121 with commit 0670c4c567b27bd8f999a943028f4fe60d1a1106
	Issue introduced in 5.4 with commit ec8f954a40da8cd3d159713b608e901f0cd909a9 and fixed in 6.1.39 with commit e7aff15ba29ba4b3052786b1636fa5c4aa39e179
	Issue introduced in 5.4 with commit ec8f954a40da8cd3d159713b608e901f0cd909a9 and fixed in 6.3.13 with commit f9bd298e3e4d3fd6e19f017789a42d0f332cd555
	Issue introduced in 5.4 with commit ec8f954a40da8cd3d159713b608e901f0cd909a9 and fixed in 6.4.4 with commit c1968bb8a28625cc95d2ad3ca872ab98c9c36d59
	Issue introduced in 5.4 with commit ec8f954a40da8cd3d159713b608e901f0cd909a9 and fixed in 6.5 with commit 9d9e522010eb5685d8b53e8a24320653d9d4cbbf

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2023-53815
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	kernel/time/posix-timers.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/f1be1ed32daa053484222f7f9beb2b16c624dffd
	https://git.kernel.org/stable/c/0670c4c567b27bd8f999a943028f4fe60d1a1106
	https://git.kernel.org/stable/c/e7aff15ba29ba4b3052786b1636fa5c4aa39e179
	https://git.kernel.org/stable/c/f9bd298e3e4d3fd6e19f017789a42d0f332cd555
	https://git.kernel.org/stable/c/c1968bb8a28625cc95d2ad3ca872ab98c9c36d59
	https://git.kernel.org/stable/c/9d9e522010eb5685d8b53e8a24320653d9d4cbbf