[CVE-2026-68437][MODERATE REGULAR] drm/imagination: Fit paired fragment job in the correct CCCB

[CVE-2026-68437][MODERATE REGULAR] drm/imagination: Fit paired fragment job in the correct CCCB

[AL-KERNEL]

CVE: CVE-2026-68437
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/imagination: Fit paired fragment job in the correct CCCB
Commit: 15a9863929206911a08b6f62de9c5da6931dbc9e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=15a9863929206911a08b6f62de9c5da6931dbc9e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68437
Analysis date: Tue, 11 Aug 2026 21:06:08 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A local user with access to the affected PowerVR DRM device may trigger incorrect CCCB space accounting for paired fragment jobs, causing incomplete command submission, kernel warnings, and GPU job timeouts without evidence of memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-68437 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68437

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: YES

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
======================================================================

CVE-2026-68437	MODERATE	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-754;CWE-670;**CWE-400;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 PowerVR drm/imagination scheduler path can check CCCB space for a paired fragment job against the wrong queue. A local user able to submit GPU jobs through the DRM interface may cause prepare_job to believe that enough CCCB space is available, while run_job later cannot write the full command sequence. This can trigger kernel warnings and GPU job timeouts, resulting in denial of service for the affected GPU workload or graphics stack. For the CVSS the PR:L is used for the paranoid score because reliable triggering requires local code execution with access to the DRM device or render node, but does not necessarily require full administrative privileges. The issue is not network reachable. No confidentiality or integrity impact is assigned because the patch context indicates an incorrect queue and resource accounting problem rather than a proven UAF, OOB write, or arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)  SKIP CVE-2026-68437 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	LOCK INIT HARDWARE LINUS MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user with access to the DRM render node may be able to submit paired geometry and fragment jobs.
* Availability impact realistic: +1. The described failure can cause kernel warnings and GPU job timeouts, affecting the graphics or GPU workload.

Paranoid additional signal:

* Reliable strong DoS concern: +1. If the timeout path repeatedly wedges the GPU scheduler or affects graphics recovery, this can be treated as a stronger local DoS.

Signals not applied:

* No generic memory corruption. The patch shows wrong CCCB queue selection and incorrect resource accounting, not UAF, OOB write, double free, type confusion, or arbitrary write.
* No privilege escalation plausible signal. There is no demonstrated reclaim, object replacement, callback control, refcount abuse, or write primitive.
* No confidentiality or integrity impact. The bug affects scheduling and command submission completeness, not data disclosure or unauthorized modification.
* No remote reachability. The path is local DRM job submission, not network-facing.
* No high-control API bonus. GPU ioctls alone are not enough under the provided rule without evidence of exploitation-relevant memory layout, lifetime, callback, refcount, DMA mapping, or page ownership control.

## 3. Reachability analysis

The likely trigger is a local process that can submit jobs to the affected PowerVR DRM driver, commonly through a render node if exposed by system policy. Root is not inherently required, so PR:L is the practical paranoid interpretation.

Namespaces and containers may matter if the DRM device node is passed through to a container. Without device access, the bug is not reachable from an ordinary confined container.

The affected path is hardware and driver specific. It requires an Imagination PowerVR DRM environment and paired geometry and fragment job submission. It is not a broad default kernel path and is not remotely reachable.

Call-site confidence: high. The patch includes the relevant prepare_job path and the paired fragment dependency handling.

## 4. Severity interpretation

This behaves like an ordinary Moderate or borderline local DoS, not an Important-class kernel vulnerability. The realistic impact is GPU job timeout or graphics stack disruption. The theoretical concern is limited because the patch does not show memory corruption, stale lifetime use, attacker-controlled overwrite, or cross-object corruption.

The paranoid score reaches 3 only because local unprivileged DRM access plus potentially repeatable GPU timeout may justify manual review. It does not reach Actionable Moderate or Important under the given formula.

## 5. One-sentence report phrase

A local user with access to the affected PowerVR DRM device may trigger incorrect CCCB space accounting for paired fragment jobs, causing incomplete command submission, kernel warnings, and GPU job timeouts without evidence of memory corruption or privilege escalation.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

This is not a strong security candidate, but the GPU scheduler timeout behavior and local render node reachability justify a lightweight manual check before auto-closing.

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

Patch: drm/imagination: Fit paired fragment job in the correct CCCB
Commit: 15a9863929206911a08b6f62de9c5da6931dbc9e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=15a9863929206911a08b6f62de9c5da6931dbc9e

Commit description:

For geometry jobs with a paired fragment job, at the moment, the
DRM scheduler's prepare_job() callback:

- checks for internal (driver) dependencies for the geometry job;
- calls into pvr_queue_get_paired_frag_job_dep() to check for external
  dependencies for the fragment job (the two jobs are submitted together
  but the common scheduler code doesn't know about it, so this needs to
  be done at this point in time);
- calls into the prepare_job() callback again, but for the fragment job,
  to check its internal dependencies as well, passing the fragment job's
  drm_sched_job and the geometry job's drm_sched_entity / pvr_queue.

The problem with the last step is that pvr_queue_prepare_job() doesn't
always take the mismatched fragment job and geometry queue into account,
in particular when checking whether there is space for the fragment
command to be submitted, so the code ends up checking for space in the
geometry (i.e. wrong) CCCB.
The rest of the nested prepare_job() callback happens to work fine at
the moment as the other internal dependencies are not relevant for a
paired fragment job.

Move the initialisation of a paired fragment job's done fence and CCCB
fence to pvr_queue_get_paired_frag_job_dep(), inferring the correct
queue from the fragment job itself.

This fixes cases where prepare_job() wrongly assumed that there was
enough space for a paired fragment job in its own CCCB, 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):

  [  552.421075] WARNING: drivers/gpu/drm/imagination/pvr_cccb.c:178 at pvr_cccb_write_command_with_header+0x2c4/0x330 [powervr], CPU#2: kworker/u16:5/63
  [  552.421230] Modules linked in:
  [  552.421592] CPU: 2 UID: 0 PID: 63 Comm: kworker/u16:5 Tainted: G        W           7.0.0-rc2-gc5d053e4dccb #39 PREEMPT
  [  552.421625] Tainted: [W]=WARN
  [  552.421637] Hardware name: Texas Instruments AM625 SK (DT)
  [  552.421655] Workqueue: powervr-sched drm_sched_run_job_work [gpu_sched]
  [  552.421744] pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
  [  552.421766] pc : pvr_cccb_write_command_with_header+0x2c4/0x330 [powervr]
  [  552.421850] lr : pvr_queue_submit_job_to_cccb+0x57c/0xa74 [powervr]
  [  552.421923] sp : ffff800084c47650
  [  552.421936] x29: ffff800084c47740 x28: 0000000000000df8 x27: ffff800088a77000
  [  552.421979] x26: 0000000000000030 x25: ffff800084c47680 x24: 0000000000001000
  [  552.422017] x23: ffff800084c47820 x22: 1ffff00010988ecc x21: 0000000000000008
  [  552.422055] x20: 0000000000000208 x19: ffff000006ad5a88 x18: 0000000000000000
  [  552.422093] x17: 0000000020020000 x16: 0000000000020000 x15: 0000000000000000
  [  552.422130] x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
  [  552.422167] x11: 000000000000f2f2 x10: 00000000f3000000 x9 : 00000000f3f3f3f3
  [  552.422204] x8 : 00000000f2f2f200 x7 : ffff700010988ecc x6 : 0000000000000008
  [  552.422241] x5 : 0000000000000000 x4 : 1ffff0001114ee00 x3 : 0000000000000000
  [  552.422278] x2 : 0000000000000007 x1 : 0000000000000fff x0 : 000000000000002f
  [  552.422316] Call trace:
  [  552.422330]  pvr_cccb_write_command_with_header+0x2c4/0x330 [powervr] (P)
  [  552.422411]  pvr_queue_submit_job_to_cccb+0x57c/0xa74 [powervr]
  [  552.422486]  pvr_queue_run_job+0x3a4/0x990 [powervr]
  [  552.422562]  drm_sched_run_job_work+0x580/0xd48 [gpu_sched]
  [  552.422623]  process_one_work+0x520/0x1288
  [  552.422657]  worker_thread+0x3f0/0xb3c
  [  552.422679]  kthread+0x334/0x3d8
  [  552.422706]  ret_from_fork+0x10/0x20

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-v1-2-7de8c09cef8c@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=15a9863929206911a08b6f62de9c5da6931dbc9e

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

The original Linux kernel CVE announcement for CVE-2026-68437 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68437

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: 2
  Paranoid ActionableScore: 3

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).