CVE-2026-68233: drm/vc4: Shut down BO cache timer before teardown

From: Greg Kroah-Hartman <[email protected]>

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

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

drm/vc4: Shut down BO cache timer before teardown

The BO cache timer callback schedules time_work, and time_work can rearm
the timer through vc4_bo_cache_free_old().

vc4_bo_cache_destroy() deletes the timer and then cancels the work, which
does not break that cycle: the work being cancelled can rearm the timer,
and the timer then queues work again after teardown.

Use timer_shutdown_sync() instead, so the timer cannot be rearmed and the
cycle ends with cancel_work_sync().

The Linux kernel CVE team has assigned CVE-2026-68233 to this issue.


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

	Issue introduced in 4.5 with commit c826a6e1064419f78855463cf29ce9e8b9d25bf4 and fixed in 6.18.42 with commit a38f2724eb93a78ba250b01e0caf3468df4d3956
	Issue introduced in 4.5 with commit c826a6e1064419f78855463cf29ce9e8b9d25bf4 and fixed in 7.1.6 with commit bac4c1a9af690b8635c6924872075c41d8763ed9
	Issue introduced in 4.5 with commit c826a6e1064419f78855463cf29ce9e8b9d25bf4 and fixed in 7.2-rc5 with commit 6273dd3ffb54ec581855b82ae77331b66028249c

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-2026-68233
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:
	drivers/gpu/drm/vc4/vc4_bo.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/a38f2724eb93a78ba250b01e0caf3468df4d3956
	https://git.kernel.org/stable/c/bac4c1a9af690b8635c6924872075c41d8763ed9
	https://git.kernel.org/stable/c/6273dd3ffb54ec581855b82ae77331b66028249c