[CVE-2026-89820][LOW] drm/amd/display: fix dc_lock leak on GPU reset error paths

[CVE-2026-89820][LOW] drm/amd/display: fix dc_lock leak on GPU reset error paths

[AL-KERNEL]

CVE: CVE-2026-89820
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/amd/display: fix dc_lock leak on GPU reset error paths
Commit: 295d2bf42061db490254e748f9344545bb7faf19
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=295d2bf42061db490254e748f9344545bb7faf19
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89820
Analysis date: Wed, 16 Sep 2026 12:34:02 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

======================================================================
ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-89820 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89820

The original announcement does not normally provide a security severity
estimate, CVSS assessment, or enough information to determine whether the
reported kernel bug represents a practically relevant security issue.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin. It combines
an autonomous classifier with LLM-assisted technical analysis and a
separate ActionableScore mechanism.

The purpose of this report is to prioritize Linux kernel CVEs before
manual review, identify cases that require prompt investigation, and
support automatic closure of issues that are unlikely to have meaningful
security impact.

Published priority for this report: LOW
Manual review required: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-89820	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89820 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-833;CWE-667;*CWE-772;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A GPU reset error path in the AMD display driver can return from dm_suspend or dm_resume while dc_lock remains held. This causes every later attempt to acquire the same mutex to block and can prevent GPU recovery, stall DRM operations, or leave the display subsystem unusable. For the CVSS the PR:L reflects that a local user with access to the DRM render interface may submit GPU workloads that contribute to a reset, although reliable triggering also depends on a failure in zero stream commit or DMUB initialization. The issue is not network reachable. Impact is denial of service through a persistent driver deadlock, with no supported UAF, OOB access, information disclosure, or privilege escalation primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)  SKIP CVE-2026-89820 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	LOCK SIMPLEFIX LEAK ERRORPATH HARDWARE  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Concrete persistent kernel resource/reference leak. The error paths retain `dc_lock` and fail to release `cached_dc_state`.
* +1 Strong device-subsystem DoS. Once the error return leaves `dc_lock` held, every later acquisition can block indefinitely, preventing GPU recovery and making the display subsystem unusable.
* No extra Availability point was awarded. The blocked recovery and unusable display are consequences of the same persistent mutex deadlock.
* No UAF, double release, stale reference use, OOB access, arbitrary write, controlled reclaim, or active-object corruption is established.
* No C/I, LPE, authorization-bypass, or security-boundary signal was awarded.
* No local-unprivileged bonus was awarded. A render-node user may contribute to a GPU reset, but the complete sequence also requires failure of zero-stream commit or DMUB initialization and is not established as user-controllable.
* No host-admin penalty was applied because host-admin-equivalent privilege is not positively established.
* No hardware rarity penalty was applied. AMD GPUs are hardware-specific but not inherently rare.

3. Reachability analysis

The vulnerable path occurs during AMD GPU reset and recovery. An ordinary process with DRM render-node access may submit workloads that contribute to a GPU hang or reset, but the supplied evidence does not establish that such a process can reliably cause the required `amdgpu_dm_commit_zero_streams()` or `dm_dmub_hw_init()` failure.

The complete trigger may instead depend on firmware, hardware, display-core state, or administrator-initiated recovery. Therefore, host-admin requirements remain unknown rather than being classified as either required or unnecessary.

A compositor, DRM master, display service, or administrator may have more influence over display state, but no complete below-host-admin trigger is shown. The operation concerns a host physical GPU and is not an attacker-created namespace-scoped capability path. There is no remote trigger, timing race, special boot mode, or independently demonstrated prior privileged setup.

4. Primitive and severity interpretation

The exact defect is an error-path mutex ownership and cleanup failure. `dm_suspend()` intentionally transfers ownership of `dc_lock` to the matching resume path, but selected failures return before that ownership is released. A similar early return exists after failed DMUB initialization in `dm_resume()`.

This is invalid lock state and persistent device-subsystem deadlock behavior, classified as CLASS_C. It is not a lifetime violation involving use after free. The added `dc_state_release()` performs missing state cleanup, but the supplied control flow does not show that the old state is dereferenced after release or released twice.

The demonstrated consequence is loss of GPU recovery and stalled DRM or display operations. A host-wide panic, memory corruption, confidentiality loss, integrity violation, or privilege escalation is not supported. The paranoid interpretation therefore does not receive additional points merely because a user might contribute to the initial reset.

ImportantCandidate is NO because no independently useful corruption or boundary-bypass primitive remains after excluding the deadlock. AutoDowngradeAllowed is YES because this is a constrained device recovery DoS with no unresolved exploitation leverage.

5. One-sentence report phrase

An AMD display GPU reset failure can return while `dc_lock` remains held, causing subsequent DRM operations to block indefinitely and leaving GPU recovery or the display subsystem unavailable.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch establishes a constrained mutex cleanup defect and device-level DoS without memory corruption, lifetime misuse, security-boundary bypass, or plausible privilege-escalation leverage.

7. Call-site confidence

Call-site confidence: medium

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: drm/amd/display: fix dc_lock leak on GPU reset error paths
Commit: 295d2bf42061db490254e748f9344545bb7faf19
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=295d2bf42061db490254e748f9344545bb7faf19

Commit description:

On GPU reset, dm_suspend() takes dc_lock and leaves it for dm_resume()
to drop. If amdgpu_dm_commit_zero_streams() or dm_dmub_hw_init() fails,
the function returns with the lock still held. The matching resume path
is then skipped, so every later dc_lock take hangs.

Release the cached DC state and unlock before returning the error.

Fixes: 3cf7a0b ("drm/amd/display: Catch failures for amdgpu_dm_commit_zero_streams()")
Fixes: 2b6943d ("drm/amd/display: Pass up errors for reset GPU that fails to init HW")
Cc: stable@vger.kernel.org
Signed-off-by: Linkai Gong <gonglinkai@kylinos.cn>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

Diff excerpt:

Not included in this email. See the upstream URL for the full patch.

Full patch:
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=295d2bf42061db490254e748f9344545bb7faf19

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-89820 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89820

The original CVE announcement normally does not include a security-level
estimate. In particular, it may not contain a CVSS assessment, an impact
level, or enough information to determine whether the reported bug is a
practically relevant security issue. One purpose of this parallel CVE list
is to provide that missing technical and prioritization information.

The original goal of the AL-KERNEL project was to prioritize Linux kernel
CVE analysis automatically before manual review. The system can also help
identify non-security issues that may be suitable for automatic closure.

This report was generated by AL-KERNEL, an AI-assisted Linux kernel
vulnerability analysis system developed by Alexander Larkin.

The first analysis stage combines an autonomous classifier with additional
LLM-based analysis. The autonomous classifier runs locally on a CPU and is
based on a backpropagation neural network. Together, these mechanisms
produce a technical vulnerability description, identify likely weakness
types, estimate CVSS severity, and provide input for ActionableScore.

Two CVSS estimates are retained because incomplete kernel vulnerability
information often permits more than one defensible interpretation:

  Conservative CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

The conservative vector represents a lower-impact interpretation.
The Best/paranoid vector intentionally represents a plausible upper-bound
interpretation and should not automatically be treated as demonstrated
real-world impact.

CVSS may also need to be adjusted for a particular Linux deployment,
because actual reachability, privileges, enabled kernel configuration,
hardware, namespaces, exposed device nodes, and other environmental
conditions can differ significantly between systems.

A separate ActionableScore mechanism evaluates practical remediation
urgency. Its analysis may include reachability, attack prerequisites,
subsystem exposure, memory-corruption characteristics, denial-of-service
reliability, and possible confidentiality, integrity, or
privilege-escalation impact.

  Conservative ActionableScore: unknown
  Paranoid ActionableScore: 2

The final base severity is taken directly from the second tab-separated
field of the AL-KERNEL classification result. ActionableScore does not
replace or independently override that final AL-KERNEL decision, and
if ActionableScore adjusted impact level of ALKERNEL, then you would see
self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7.

For an AL-KERNEL result of MODERATE, this report uses the following
additional presentation split:

  ActionableScore below 5   -> MODERATE REGULAR
  ActionableScore 5 or more -> MODERATE 7.0

The distinction between MODERATE REGULAR and MODERATE 7.0 makes it
possible to identify Moderate issues that should receive manual analysis
and fixes before lower-priority MODERATE REGULAR issues. In many cases,
MODERATE REGULAR fixes may wait for a later rebase or routine update.

There is one override in which MODERATE REGULAR becomes MODERATE 7.0
even when the ActionableScore is below 5. When the AL-KERNEL result
contains the KPANIC flag, a MODERATE result is always presented as
MODERATE 7.0. The KPANIC flag selected with few regexps without
usage of AI at all, so it helps to detect cases when Kernel Crash happens
and similar (to filter False-Negative results from the LLM usage).

KPANIC indicates that a reliable kernel crash, kernel panic, or similarly
serious kernel availability impact was identified by the classification
workflow.

AL-KERNEL base severity for this report: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

These results are intended to support engineering triage. They are
machine-generated estimates, and cases marked for manual review should
be validated by a human security engineer before final disposition.
For more info read docs linked from here: https://kernelcve.org/
(and you can submit you own patch there to generate such a report
for non-existant CVE-id yet).

Note that in many cases this AI tool selects higher severity, than
real is (means you can expect Importants instead of Moderate 7.0 or
Moderates 7.0 instead of regular Moderates). If you see such cases,
please use reply email interface to add additional manual analyses
info to this particular CVE.
And please, please, let me know when you see Lows instead of Importants
or Important instead of Low (because particular for such cases I
need to tune this AI tool to make it better for this one and next similar).
My contact email for such notifications is alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).