[CVE-2026-68107][MODERATE REGULAR] drm/amdgpu/vcn4: avoid rereading IB param length

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

CVE: CVE-2026-68107
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/amdgpu/vcn4: avoid rereading IB param length
Commit: bbbe6a2a8d8dc87243438d3ffea2083b52d882d9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bbbe6a2a8d8dc87243438d3ffea2083b52d882d9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68107
Analysis date: Mon, 10 Aug 2026 13:59:08 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline manual review recommended / not auto-close
Manual review required: YES

Summary:
A local TOCTOU in the amdgpu VCN4 IB parser can cause inconsistent command traversal when the IB parameter length changes between reads, with likely impact limited to local DoS or validation bypass unless further memory corruption is demonstrated.

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

The original Linux kernel CVE announcement for CVE-2026-68107 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68107

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.

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

CVE-2026-68107	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-367;CWE-362;*CWE-20;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A TOCTOU issue in the amdgpu VCN4 command parser can occur because the IB parameter length is read once during vcn_v4_0_enc_find_ib_param and then read again later when advancing to the next parameter. If the IB contents can change between these reads, command parsing may become inconsistent and can potentially cause a hang, invalid traversal, or bypass of expected VCN scheduling validation. For the CVSS the PR:L is used because reliable triggering requires local code execution with access to the DRM render node or an equivalent GPU submission interface. The issue is not network reachable and is triggered through local GPU command submission rather than packet traffic. Impact is at least local denial of service. In the paranoid interpretation, limited confidentiality or integrity impact is kept because parser confusion in a kernel GPU driver may require manual review, but the patch does not show a strong memory corruption primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / not auto-close (with actual score 4)  SKIP CVE-2026-68107 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	INIT SIMPLEFIX HARDWARE  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / not auto-close**

## 2. Signal breakdown

* Local unprivileged trigger: +1. The affected path is GPU command submission through amdgpu, commonly reachable by local users with access to DRM render nodes.
* Memory corruption, weak/indirect corruption candidate: +1. The bug is a TOCTOU in IB command parsing where the length used for traversal may differ from the length previously validated. This supports parser confusion, but not a proven UAF, OOB write, arbitrary write, or controlled object replacement.
* Availability impact realistic: +1. Inconsistent IB traversal can plausibly cause a hang, invalid parsing path, or driver failure, but the patch does not show a demonstrated panic.
* Broad/default/common subsystem exposure: +1 in paranoid score. amdgpu render nodes are common on affected AMD systems, although VCN4 is hardware-specific.
* Hard or unreliable race / special timing required: -1. The issue depends on changing IB contents between two reads, so reliable triggering likely requires a timing window.

Not awarded:

* No strong memory corruption +2. The patch does not show UAF, double free, OOB write, heap overwrite, refcount takeover, or arbitrary write.
* No strong LPE plausibility +2. There is no demonstrated reclaim, callback control, type confusion, or write primitive.
* No remote/network trigger. This is local GPU command submission, not packet or network input.

## 3. Reachability analysis

A local user or process with access to the amdgpu DRM render node can potentially reach the affected VCN4 command parser through command submission. This is not remotely reachable over the network. Containers may matter if the GPU render node is passed through to a container, in which case a reduced-privilege container user could still reach the driver. The path is hardware-dependent and applies to affected AMD VCN4-capable systems, but render-node access is common on desktop and GPU-enabled compute deployments.

Call-site confidence: medium. The patch includes the relevant parser loop and use of the returned index and length, but not the full userspace submission and IB lifetime path.

## 4. Severity interpretation

This behaves more like a borderline actionable Moderate than an Important vulnerability. The theoretical concern is parser confusion caused by a TOCTOU on attacker-influenced IB contents. The realistic evidence supports local DoS or validation bypass concern, but not a concrete privilege escalation primitive. Manual review is still useful because GPU command parsers are complex kernel attack surfaces and the bug affects length-based traversal of untrusted command buffers.

## 5. One-sentence report phrase

A local TOCTOU in the amdgpu VCN4 IB parser can cause inconsistent command traversal when the IB parameter length changes between reads, with likely impact limited to local DoS or validation bypass unless further memory corruption is demonstrated.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is not a proven Important-class memory corruption bug, but it is a local TOCTOU in a GPU command parser reachable via render-node style interfaces, so it should not be auto-closed without checking whether IB mutation can lead to an OOB traversal, scheduler restriction bypass, or driver crash.

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

Patch: drm/amdgpu/vcn4: avoid rereading IB param length
Commit: bbbe6a2a8d8dc87243438d3ffea2083b52d882d9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bbbe6a2a8d8dc87243438d3ffea2083b52d882d9

Commit description:

Reuse the parameter length returned by
vcn_v4_0_enc_find_ib_param() instead of rereading it from
the IB.

This avoids a potential TOCTOU issue if the IB contents
change between reads.

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Reviewed-by: David Rosca <david.rosca@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit dbb02b4 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/amdgpu/vcn_v4_0.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=bbbe6a2a8d8dc87243438d3ffea2083b52d882d9

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

The original Linux kernel CVE announcement for CVE-2026-68107 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68107

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:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 3
  Paranoid ActionableScore: 4

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).