[CVE-2026-99147][MODERATE REGULAR] drm/exec: don't immediately add prelocked obj to array of locked objs

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-99147
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/exec: don't immediately add prelocked obj to array of locked objs
Commit: 96d9996e5dbcfabed052c0d9377a382c95fed607
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=96d9996e5dbcfabed052c0d9377a382c95fed607
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99147
Analysis date: Wed, 28 Oct 2026 22:55:39 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A local DRM workload can race contention recovery with GEM-object teardown, exposing an unreserved prelocked object to fence iteration and triggering a defensive BUG rather than a demonstrated memory overwrite.

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

The original Linux kernel CVE announcement for CVE-2026-99147 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99147

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: MODERATE REGULAR
Manual review required: NO

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

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-99147	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99147 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (final Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC)	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;*CWE-664;CWE-667;BEST CVSS score: '4.7';DESCR 'A drm_exec contention recovery path could place an implicitly prelocked GEM object in the locked object array before the driver explicitly encountered it again. If drm_exec held the final reference to an object being destroyed, the driver might never reserve a dma_fence slot for that object but could still visit it through drm_exec_for_each_locked_object and attempt to add a fence. The demonstrated outcomes are a warning or BUG_ON intended to stop unreserved fence insertion before random memory corruption, so the supported impact is local denial of service rather than a proven UAF or OOB write. For the CVSS the PR:L value reflects that an attacker normally needs local access to a DRM render device and control of a GPU workload. AC:H reflects the required contention and object lifetime timing window. The issue is not directly network reachable. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to MODERATE because the CVSS score, vector or bug class threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 2.6 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	LOCK LEAK DMAorINTERRUPT HARDWARE MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 2: active-state inconsistency +1, local below-host-admin trigger +1, plausible BUG/host crash +1, hard contention/lifetime timing -1.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 2; no additional proof-supported primitive exists.
* Paranoid score: 2.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 weak/indirect active-state corruption: contention recovery prematurely records an implicitly prelocked GEM object as explicitly locked despite no reserved fence slot.
* +1 local unprivileged trigger: supplied evidence grounds local DRM render-device access and attacker-controlled GPU workload below host-administrator privilege.
* +1 reliable kernel crash/DoS: later fence insertion can reach WARN or BUG_ON; only the fatal outcome is counted.
* -1 hard timing: triggering requires contention coinciding with the object-destruction/final-reference window.
* No extra availability point: it would duplicate the same BUG/crash.
* No UAF: `drm_exec` retains a reference, so the object remains alive.
* No confirmed OOB write, arbitrary write, or consumed corrupted memory: the stated WARN/BUG_ON prevents the feared random corruption.
* NEW52/B5-R does not apply: neither a confirmed retry-accumulated heap OOB write nor post-OOB structured-state consumption is shown.
* No authorization decision exists; B4-PENDING is inapplicable.

3. Reachability analysis

A local actor with DRM render-node access and control of a GPU workload can plausibly induce contention without host UID 0 or host-administrator powers. The exact device permissions and driver call sites are not supplied, but the supplied triage evidence supports PR:L rather than host administration. No namespace-scoped capability chain, prior privileged setup, special hardware rarity, or remote path is established. The required destruction/contention coincidence supports the timing penalty.

4. Primitive and severity reading

The primitive is an active DRM execution-container bookkeeping inconsistency: an implicit prelock is exposed to locked-object iteration before explicit driver locking and fence-slot reservation. Its demonstrated consumer attempts fence insertion and encounters a defensive warning or BUG_ON. This is CLASS_C crash/invalid-state behavior, not a real UAF or proven memory overwrite. Random memory corruption is explicitly the condition the guard prevents, not a demonstrated effect. Therefore ImportantCandidate is NO and automatic Moderate downgrade remains permissible.

5. One-sentence report phrase

A local DRM workload can race contention recovery with GEM-object teardown, exposing an unreserved prelocked object to fence iteration and triggering a defensive BUG rather than a demonstrated memory overwrite.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm affected driver call sites, render-node permissions, and whether any consumer can bypass the documented fence-reservation guard.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drm/exec: don't immediately add prelocked obj to array of locked objs
Commit: 96d9996e5dbcfabed052c0d9377a382c95fed607
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=96d9996e5dbcfabed052c0d9377a382c95fed607

Commit description:

When a contention is detected the drm_exec object grabs a reference to
the contended object, unlocks all other objects and pre-locks the
contended one before anything else.

The problem is that it is possible that this pre-locked object was about
to be destroyed and drm_exec is now holding the last reference to it.

So we never actually see this pre-locked object again to be explicitly
locked and so also never reserve a slot for a dma_fence object on it.

Should the driver now use drm_exec_for_each_locked_object() to add a new
fence to all locked objects we eventually see a warning or even a
BUG_ON() to prevent random memory corruption.

Fix this by keeping the prelocked object out of the array of locked objs
until it was explicitly mentioned by the driver again.

If the prelocked object is never mentioned again by the driver
just unlock and drop the reference at the end of the locking loop.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reported-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Reviewed-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Tested-by: Vitaly Prosyak <vitaly.prosyak@amd.com>
Fixes: 0959321 ("drm: execution context for GEM buffers v7")
CC: stable@vger.kernel.org # v6.6+
Link: https://lore.kernel.org/r/20261007124657.9664-1-christian.koenig@amd.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/drm_exec.c
  include/drm/drm_exec.h

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=96d9996e5dbcfabed052c0d9377a382c95fed607

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

The original Linux kernel CVE announcement for CVE-2026-99147 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99147

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: MODERATE
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).