[CVE-2026-68272][MODERATE REGULAR] drm/amdgpu: validate CP_GFX_SHADOW chunk size in CS pass1

[CVE-2026-68272][MODERATE REGULAR] drm/amdgpu: validate CP_GFX_SHADOW chunk size in CS pass1

[AL-KERNEL]

CVE: CVE-2026-68272
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu: validate CP_GFX_SHADOW chunk size in CS pass1
Commit: 3f190956404da55560056ce20606010e18bc059c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3f190956404da55560056ce20606010e18bc059c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68272
Analysis date: Mon, 10 Aug 2026 15:34:55 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A local user with AMDGPU render-node access can submit an undersized CP_GFX_SHADOW CS chunk that reaches `amdgpu_cs_p2_shadow()` with `ZERO_SIZE_PTR` command data, causing a NULL-pointer style kernel fault and denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-68272 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68272

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-2026-68272	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-20;**CWE-476;CWE-754;BEST CVSS score: '5.5';DESCR 'An undersized AMDGPU_CHUNK_ID_CP_GFX_SHADOW chunk can reach amdgpu_cs_p2_shadow after vmemdup_array_user returns ZERO_SIZE_PTR for a zero length allocation. The pass2 code then treats chunk kdata as struct drm_amdgpu_cs_chunk_cp_gfx_shadow and reads the flags field, causing a kernel fault and local denial of service. For the CVSS the PR:L is used because a local process needs access to the amdgpu render node or the render group, but full administrative privileges are not required. The issue is not network reachable and is triggered through the local DRM CS ioctl path. Impact is kernel crash only. The patch context supports a NULL pointer style dereference rather than UAF, OOB write, or a controlled memory corruption primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)  SKIP CVE-2026-68272 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3

## 1. ActionableScore

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

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  The commit explicitly says the issue is reachable by an unprivileged process in the render group through the local AMDGPU CS ioctl path.

* Reliable kernel crash / strong DoS: +1
  A zero-length CP_GFX_SHADOW chunk can make `vmemdup_array_user()` return `ZERO_SIZE_PTR`, which is later dereferenced as `struct drm_amdgpu_cs_chunk_cp_gfx_shadow`, causing a kernel fault.

* Broad/default/common subsystem or broadly deployed exposure: +1
  AMDGPU render nodes are commonly exposed to local desktop or compute users on systems with AMD GPUs, although this is still hardware and device-access dependent.

Not triggered:

* Generic memory corruption: +0
  The demonstrated primitive is a NULL/ZERO_SIZE_PTR dereference, not UAF, double free, OOB write, type confusion, or controlled overwrite.

* Privilege escalation plausible: +0
  No reclaim, object replacement, callback control, write primitive, or type confusion is shown.

* Confidentiality impact plausible: +0
  No read-back or information disclosure path is indicated.

* Integrity impact plausible: +0
  No attacker-controlled write or policy bypass is indicated.

* Remote reachable: +0
  The affected path is a local DRM ioctl, not a network path.

## 3. Reachability analysis

A local process with access to the AMDGPU render node, typically through membership in the render group or equivalent device ACLs, can submit the malformed CS chunk. Full root privileges are not required, so this is not a PR:H style issue in practical triage terms.

Namespaces and containers may matter if the DRM render node is passed into a container. In that case, a containerized or reduced-privilege workload with GPU access could potentially trigger the same host kernel bug. The path is not network reachable and requires an AMDGPU device with the affected CS ioctl support exposed.

Call-site confidence: high. The commit describes the exact path from `amdgpu_cs_pass1()` to `amdgpu_cs_p2_shadow()` and identifies the dereference of `chunk->kdata`.

## 4. Severity interpretation

This behaves like an actionable local Moderate issue, not an Important-class vulnerability. The realistic impact is local denial of service through a kernel fault from a malformed GPU command submission.

The theoretical memory-corruption potential is low because the patch context supports a deterministic invalid pointer dereference of `ZERO_SIZE_PTR`. It does not show UAF, stale object reuse, writable corruption, object confusion, or a path toward privilege escalation.

## 5. One-sentence report phrase

A local user with AMDGPU render-node access can submit an undersized CP_GFX_SHADOW CS chunk that reaches `amdgpu_cs_p2_shadow()` with `ZERO_SIZE_PTR` command data, causing a NULL-pointer style kernel fault and denial of service.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

This should not be auto-closed purely as low-risk because it is a local unprivileged kernel crash through a commonly exposed GPU ioctl. However, no evidence supports memory corruption beyond invalid dereference or privilege escalation, so it does not look like a Strong Important candidate.

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

Patch: drm/amdgpu: validate CP_GFX_SHADOW chunk size in CS pass1
Commit: 3f190956404da55560056ce20606010e18bc059c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3f190956404da55560056ce20606010e18bc059c

Commit description:

Add a minimum-length check for the AMDGPU_CHUNK_ID_CP_GFX_SHADOW chunk in
amdgpu_cs_pass1(), matching the gate already present for the IB, FENCE and
BO_HANDLES chunk types.

The CP_GFX_SHADOW case previously shared a bare break with the dependency
and syncobj chunk types, which do not dereference a fixed-size struct. When
userspace submits this chunk with length_dw == 0, vmemdup_array_user() is
called with size 0 and returns ZERO_SIZE_PTR, which passes the IS_ERR()
check. amdgpu_cs_p2_shadow() then dereferences chunk->kdata as a struct
drm_amdgpu_cs_chunk_cp_gfx_shadow (reading shadow->flags), faulting on the
ZERO_SIZE_PTR and causing a NULL-pointer dereference.

This is reachable by an unprivileged process in the render group. Reject
undersized chunks with -EINVAL during pass1 so the bad submission is
rejected before pass2 ever dereferences the data.

Fixes: ac92870 ("drm/amdgpu: add gfx shadow CS IOCTL support")
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 7f61b2e )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdgpu/amdgpu_cs.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=3f190956404da55560056ce20606010e18bc059c

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

The original Linux kernel CVE announcement for CVE-2026-68272 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68272

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: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: 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).