[CVE-2026-68235][LOW] drm/amd/display: dce100: skip non-DP stream encoders for DP MST

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

CVE: CVE-2026-68235
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/amd/display: dce100: skip non-DP stream encoders for DP MST
Commit: bfe28ce019c2d667d98071262da33d8bba122919
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bfe28ce019c2d667d98071262da33d8bba122919
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68235
Analysis date: Mon, 10 Aug 2026 11:52:30 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A DP MST encoder selection bug in AMD DCE100 display code can select an analog encoder without DP callbacks, causing a NULL function pointer dereference and kernel crash on affected DCE8 hardware during display configuration.

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

The original Linux kernel CVE announcement for CVE-2026-68235 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68235

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.

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

CVE-2026-68235	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-476;CWE-703;CWE-754;Other CVSS 'AV:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A NULL pointer dereference in the AMD display DCE100 DP MST path can occur when the fallback stream encoder selection returns an analog encoder for a DisplayPort MST stream. The analog encoder does not provide DP callbacks such as dp_set_stream_attribute, so a later atomic commit can call a NULL function pointer in link_set_dpms_on and crash the kernel. For the CVSS the PR:L is used for the higher paranoid local scenario because an unprivileged local seat user or local process may be able to trigger display configuration changes, while the simplest observed trigger is physical DP MST hotplug or boot with a second MST monitor connected. The issue is not network reachable and is limited to affected AMD DCE8 class hardware such as Bonaire with DP MST. Impact is denial of service only via kernel oops, with no supported path to information disclosure or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-68235 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DANGER HARDWARE  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
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Reliable kernel crash / strong DoS: +1. The commit explicitly reports a kernel oops when DP MST fallback selects an analog encoder and later dereferences a missing DP callback.
* Physical-only or rare hardware-only condition: -2. The observed trigger requires affected AMD DCE8-class hardware, e.g. Bonaire, plus DP MST topology or hotplug behavior.
* No generic memory corruption: +0. This is a NULL function pointer dereference from wrong encoder selection, not UAF, OOB write, double free, refcount corruption, or attacker-controlled overwrite.
* No LPE signal: +0. The patch does not support privilege escalation, object replacement, callback control by attacker, arbitrary write, or information disclosure.

Paranoid signals:

* Local unprivileged trigger: +1. A local graphical seat user or local process may be able to trigger display reconfiguration or modeset paths on an affected system.
* Reliable kernel crash / strong DoS: +1. The failure mode is a direct kernel oops during atomic commit.
* Rare hardware and topology constraint: -1. Even under the local-trigger interpretation, the issue is limited to specific AMD display hardware and DP MST configurations.

Call-site confidence: high. The commit names the downstream crash path through link_set_dpms_on(), and the patch directly prevents returning a non-DP-capable stream encoder for a DP signal.

## 3. Reachability analysis

The simplest demonstrated trigger is physical or local display activity: DP MST daisy chain, hotplugging a second monitor, or booting with the second MST monitor connected. A local unprivileged desktop user may plausibly trigger display reconfiguration, so the paranoid interpretation treats this as local PR:L. It is not network reachable. Containers and namespaces do not materially improve reachability unless they also control the host display stack, which is not typical. The affected path is hardware-specific and requires older AMD DCE8-class display hardware with DP MST.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like kernel DoS, not an Important-class vulnerability. The theoretical issue is a NULL function pointer dereference, but the pointer value is not attacker-controlled and there is no supported memory corruption primitive beyond a crash. Realistic impact is availability loss on affected display setups. Confidentiality, integrity, and privilege escalation are not supported by the patch context.

## 5. One-sentence report phrase

A DP MST encoder selection bug in AMD DCE100 display code can select an analog encoder without DP callbacks, causing a NULL function pointer dereference and kernel crash on affected DCE8 hardware during display configuration.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

The issue is hardware-specific, not network reachable, and shows DoS-only behavior without UAF, OOB write, arbitrary write, info leak, or plausible LPE path.

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

Patch: drm/amd/display: dce100: skip non-DP stream encoders for DP MST
Commit: bfe28ce019c2d667d98071262da33d8bba122919
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bfe28ce019c2d667d98071262da33d8bba122919

Commit description:

On DCE8-class ASICs (e.g. Bonaire), the resource pool contains digital
DIG stream encoders plus one analog DAC encoder. When assigning a stream
encoder for a second DisplayPort MST stream, if the preferred digital
encoder is already acquired, dce100_find_first_free_match_stream_enc_for_link()
falls back to the first free pool entry. That entry may be the analog
encoder, whose funcs table lacks DP hooks such as dp_set_stream_attribute.
The subsequent atomic commit then dereferences NULL function pointers in
link_set_dpms_on() and crashes.

Skip encoders without dp_set_stream_attribute when the stream uses a DP
signal (including MST). Use dc_is_dp_signal(stream->signal) for the MST
fallback path instead of checking only the link connector signal.

Tested on:
- GPU: AMD Radeon R7 260X (Bonaire / DCE8)
- Board: Supermicro C9X299-PG300
- Setup: DP MST daisy chain, hotplug second monitor or have it connected on boot
- Kernel: 7.1.3 (issue observed since 6.19)
- Result: kernel oops without patch; dual monitors stable with patch

Signed-off-by: Andriy Korud <a.korud@gmail.com>
Closes: https://gitlab.freedesktop.org/drm/amd/-/work_items/5162
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 28ec649 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/display/dc/resource/dce100/dce100_resource.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=bfe28ce019c2d667d98071262da33d8bba122919

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

The original Linux kernel CVE announcement for CVE-2026-68235 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68235

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:P/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  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: 0
  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).