Subject: CVE-2021-47534: drm/vc4: kms: Add missing drm_crtc_commit_put

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

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

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

drm/vc4: kms: Add missing drm_crtc_commit_put

Commit 9ec03d7f1ed3 ("drm/vc4: kms: Wait on previous FIFO users before a
commit") introduced a global state for the HVS, with each FIFO storing
the current CRTC commit so that we can properly synchronize commits.

However, the refcounting was off and we thus ended up leaking the
drm_crtc_commit structure every commit. Add a drm_crtc_commit_put to
prevent the leakage.

The Linux kernel CVE team has assigned CVE-2021-47534 to this issue.

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

	Issue introduced in 5.12 with commit 9ec03d7f1ed3 and fixed in 5.15.7 with commit 53f9601e908d
	Issue introduced in 5.12 with commit 9ec03d7f1ed3 and fixed in 5.16 with commit 049cfff8d53a

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-2021-47534
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_kms.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/53f9601e908d42481addd67cdb01a9288c611124
	https://git.kernel.org/stable/c/049cfff8d53a30cae3349ff71a4c01b7d9981bc2