CVE-2025-40316: drm/mediatek: Fix device use-after-free on unbind

CVE-2025-40316: drm/mediatek: Fix device use-after-free on unbind

[Greg Kroah-Hartman]

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

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

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

drm/mediatek: Fix device use-after-free on unbind

A recent change fixed device reference leaks when looking up drm
platform device driver data during bind() but failed to remove a partial
fix which had been added by commit 80805b62ea5b ("drm/mediatek: Fix
kobject put for component sub-drivers").

This results in a reference imbalance on component bind() failures and
on unbind() which could lead to a user-after-free.

Make sure to only drop the references after retrieving the driver data
by effectively reverting the previous partial fix.

Note that holding a reference to a device does not prevent its driver
data from going away so there is no point in keeping the reference.

The Linux kernel CVE team has assigned CVE-2025-40316 to this issue.


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

	Issue introduced in 6.6.105 with commit 7d98166183d627c0b9daca7672b2191fae0f8a03 and fixed in 6.6.117 with commit a5a896f8315de358a2932e2c23c42d550256046a
	Issue introduced in 6.12.45 with commit 31ce7c089b50c3d3056c37e0e25e7535e4428ae1 and fixed in 6.12.58 with commit 0142fe895986addf35885b43440718e567121155
	Issue introduced in 6.17 with commit 1f403699c40f0806a707a9a6eed3b8904224021a and fixed in 6.17.8 with commit 8ba827e09eb586e952d10e39406fa02d10bb591e
	Issue introduced in 6.17 with commit 1f403699c40f0806a707a9a6eed3b8904224021a and fixed in 6.18 with commit 926d002e6d7e2f1fd5c1b53cf6208153ee7d380d
	Issue introduced in 6.16.5 with commit fae58d0155a979a8c414bbc12db09dd4b2f910d0

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-2025-40316
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/mediatek/mtk_drm_drv.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/a5a896f8315de358a2932e2c23c42d550256046a
	https://git.kernel.org/stable/c/0142fe895986addf35885b43440718e567121155
	https://git.kernel.org/stable/c/8ba827e09eb586e952d10e39406fa02d10bb591e
	https://git.kernel.org/stable/c/926d002e6d7e2f1fd5c1b53cf6208153ee7d380d