[CVE-2026-68281][LOW] drm/imagination: Count paired job fence as dependency in prepare_job()

[CVE-2026-68281][LOW] drm/imagination: Count paired job fence as dependency in prepare_job()

[AL-KERNEL]

CVE: CVE-2026-68281
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/imagination: Count paired job fence as dependency in prepare_job()
Commit: 02b0da249c8f78d2bbf9f498bbd371c66142b0af
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=02b0da249c8f78d2bbf9f498bbd371c66142b0af
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68281
Analysis date: Mon, 10 Aug 2026 16:32:21 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A logic error in the Imagination PowerVR DRM scheduler can undercount a paired job fence dependency, allowing a local user with DRM render access to trigger WARNs and possible GPU job timeouts, but no memory corruption or privilege escalation primitive is evident.

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

The original Linux kernel CVE announcement for CVE-2026-68281 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68281

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-2026-68281	LOW	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-682;**CWE-400;CWE-754;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A logic error in the Imagination PowerVR DRM scheduler path can make prepare_job undercount a paired job fence dependency for fragment jobs. When the fragment CCCB is almost full, this can wrongly unblock run_job even though the full command sequence cannot fit in the queue. The result can be a WARN in pvr_cccb_write_command_with_header and possible GPU job timeouts if later waiters depend on commands that were not written. For the CVSS the PR:L is used because a local user or process with access to the DRM render device may be able to submit jobs, while no administrative privileges are necessarily required in typical desktop or embedded deployments. The issue is not network reachable and does not provide a clear memory corruption primitive. Impact is denial of service affecting GPU job execution and possibly display or compute availability, not confirmed privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)  SKIP CVE-2026-68281 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	LOCK HARDWARE LINUS MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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

ActionableScore=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local user with access to the DRM render device may be able to submit PowerVR jobs. This does not require full administrative privileges in typical render-node deployments.

* Availability impact realistic: +1
  The commit describes WARNs and potential GPU job timeouts when the CCCB space is underestimated and the full command sequence is not written.

Not triggered:

* Remote reachable: +0
  This is not network reachable.

* Generic memory corruption: +0
  The patch fixes dependency accounting and scheduling admission. It does not show UAF, double free, OOB write, arbitrary write, refcount abuse, or type confusion.

* Privilege escalation plausible: +0
  No supported LPE primitive is visible. The issue is a logic/accounting bug leading to WARN and possible GPU job timeout.

* Reliable kernel crash / strong DoS: +0
  The evidence is WARN and potential job timeout, not a reliable host-wide kernel crash.

* High-control device API bonus: +0
  DRM job submission is a rich device API, but the patch does not show attacker control over kernel memory layout, object lifetime, refcounts, DMA ownership, or callback targets.

## 3. Reachability analysis

The likely trigger is local job submission through the Imagination PowerVR DRM driver. If the affected render node is exposed to untrusted local users, PR:L is the practical assumption. Containers or sandboxes may matter only if the DRM device is passed through or otherwise exposed. The path is not network reachable and depends on affected PowerVR hardware and this driver being present. Realistic exploitation requires creating paired geometry and fragment jobs while the fragment CCCB is close to full.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local GPU denial-of-service issue. The theoretical impact is degraded GPU scheduling, WARNs, and possible job timeouts. The patch does not support memory corruption, confidentiality impact, integrity impact, or privilege escalation. The issue should not be treated as Important based on the supplied evidence.

## 5. One-sentence report phrase

A logic error in the Imagination PowerVR DRM scheduler can undercount a paired job fence dependency, allowing a local user with DRM render access to trigger WARNs and possible GPU job timeouts, but no memory corruption or privilege escalation primitive is evident.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the issue is local, hardware and driver specific, DoS-only based on the patch, and lacks a concrete memory corruption or security-boundary bypass primitive.

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

Patch: drm/imagination: Count paired job fence as dependency in prepare_job()
Commit: 02b0da249c8f78d2bbf9f498bbd371c66142b0af
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=02b0da249c8f78d2bbf9f498bbd371c66142b0af

Commit description:

The DRM scheduler's prepare_job() callback counts the remaining
non-signaled native dependencies for a job, preventing job submission
until those (plus job data and fence update) can fit in the job queue's
CCCB.

This means checking which dependencies can be waited upon in the
firmware, i.e. whether they are backed by a UFO object, i.e. whether
their drm_sched_fence::parent has been assigned to a
pvr_queue_fence::base fence. That happens when the job owning the fence
is submitted to the firmware.

Paired geometry and fragment jobs are submitted at the same time, which
means the dependency between them can't be checked this way before
submission.

Update job_count_remaining_native_deps() to take into account the
dependency between paired jobs.

This fixes cases where prepare_job() underestimated the space left in
an almost full fragment CCCB, wrongly unblocking run_job(), which then
returned early without writing the full sequence of commands to the
CCCB.

The above lead to kernel warnings such as the following and potentially
job timeouts (depending on waiters on the missing commands):

  [  375.702979] WARNING: drivers/gpu/drm/imagination/pvr_cccb.c:178 at pvr_cccb_write_command_with_header+0x2c4/0x330 [powervr], CPU#1: kworker/u16:3/47
  [  375.703160] Modules linked in:
  [  375.703571] CPU: 1 UID: 0 PID: 47 Comm: kworker/u16:3 Tainted: G        W           7.0.0-rc2-g817eb6b11ad5 #40 PREEMPT
  [  375.703613] Tainted: [W]=WARN
  [  375.703627] Hardware name: Texas Instruments AM625 SK (DT)
  [  375.703645] Workqueue: powervr-sched drm_sched_run_job_work [gpu_sched]
  [  375.703741] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
  [  375.703764] pc : pvr_cccb_write_command_with_header+0x2c4/0x330 [powervr]
  [  375.703847] lr : pvr_queue_submit_job_to_cccb+0x578/0xa70 [powervr]
  [  375.703921] sp : ffff800084a97650
  [  375.703934] x29: ffff800084a97740 x28: 0000000000000958 x27: ffff80008565d000
  [  375.703979] x26: 0000000000000030 x25: ffff800084a97680 x24: 0000000000001000
  [  375.704017] x23: ffff800084a97820 x22: 1ffff00010952ecc x21: 0000000000000008
  [  375.704056] x20: 00000000000006a8 x19: ffff00002ff7da88 x18: 0000000000000000
  [  375.704093] x17: 0000000020020000 x16: 0000000000020000 x15: 0000000000000000
  [  375.704132] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
  [  375.704168] x11: 000000000000f2f2 x10: 00000000f3000000 x9 : 00000000f3f3f3f3
  [  375.704206] x8 : 00000000f2f2f200 x7 : ffff700010952ecc x6 : 0000000000000008
  [  375.704243] x5 : 0000000000000000 x4 : 1ffff00010acba00 x3 : 0000000000000000
  [  375.704279] x2 : 0000000000000007 x1 : 0000000000000fff x0 : 000000000000002f
  [  375.704317] Call trace:
  [  375.704331]  pvr_cccb_write_command_with_header+0x2c4/0x330 [powervr] (P)
  [  375.704411]  pvr_queue_submit_job_to_cccb+0x578/0xa70 [powervr]
  [  375.704487]  pvr_queue_run_job+0x3a4/0x990 [powervr]
  [  375.704562]  drm_sched_run_job_work+0x580/0xd48 [gpu_sched]
  [  375.704623]  process_one_work+0x520/0x1288
  [  375.704658]  worker_thread+0x3f0/0xb3c
  [  375.704680]  kthread+0x334/0x3d8
  [  375.704706]  ret_from_fork+0x10/0x20
  [  375.704736] ---[ end trace 0000000000000000 ]---

Fixes: eaf01ee ("drm/imagination: Implement job submission and scheduling")
Cc: stable@vger.kernel.org
Signed-off-by: Alessio Belle <alessio.belle@imgtec.com>
Reviewed-by: Brajesh Gupta <brajesh.gupta@imgtec.com>
Link: https://patch.msgid.link/20260330-job-submission-fixes-cleanup-v1-1-7de8c09cef8c@imgtec.com
Signed-off-by: Matt Coster <matt.coster@imgtec.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/imagination/pvr_cccb.c
  drivers/gpu/drm/imagination/pvr_queue.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=02b0da249c8f78d2bbf9f498bbd371c66142b0af

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

The original Linux kernel CVE announcement for CVE-2026-68281 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68281

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:L
  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).