CVE-2025-71296: drm/tests: shmem: Hold reservation lock around purge

CVE-2025-71296: drm/tests: shmem: Hold reservation lock around purge

[Greg Kroah-Hartman]

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

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

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

drm/tests: shmem: Hold reservation lock around purge

Acquire and release the GEM object's reservation lock around calls
to the object's purge operation. The tests use
drm_gem_shmem_purge_locked(), which led to errors such as show below.

[   58.709128] WARNING: CPU: 1 PID: 1354 at drivers/gpu/drm/drm_gem_shmem_helper.c:515 drm_gem_shmem_purge_locked+0x51c/0x740

Only export the new helper drm_gem_shmem_purge() for Kunit tests.
This is not an interface for regular drivers.

The Linux kernel CVE team has assigned CVE-2025-71296 to this issue.


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

	Issue introduced in 6.16 with commit 954907f7147dc43e0d1cd4d430c21d143d5fdf55 and fixed in 6.18.16 with commit cdf8bbbd9017adcfb91ad9a902198d4b507719a9
	Issue introduced in 6.16 with commit 954907f7147dc43e0d1cd4d430c21d143d5fdf55 and fixed in 6.19.6 with commit 8baeee2c1c0cdb3a8eac3b8f38156cce6ee1a69f
	Issue introduced in 6.16 with commit 954907f7147dc43e0d1cd4d430c21d143d5fdf55 and fixed in 7.0 with commit 3f41307d589c2f25d556d47b165df808124cd0c4

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-2025-71296
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/drm_gem_shmem_helper.c
	drivers/gpu/drm/tests/drm_gem_shmem_test.c
	include/drm/drm_gem_shmem_helper.h


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/cdf8bbbd9017adcfb91ad9a902198d4b507719a9
	https://git.kernel.org/stable/c/8baeee2c1c0cdb3a8eac3b8f38156cce6ee1a69f
	https://git.kernel.org/stable/c/3f41307d589c2f25d556d47b165df808124cd0c4