[CVE-2026-53135][LOW] drm/amd/display: Fix NULL deref and buffer over-read in SDP debugfs

[CVE-2026-53135][LOW] drm/amd/display: Fix NULL deref and buffer over-read in SDP debugfs

[AL-KERNEL]

CVE: CVE-2026-53135
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/amd/display: Fix NULL deref and buffer over-read in SDP debugfs
Commit: ee9cfcf77a8e8af637396dc00966df5f701e661c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee9cfcf77a8e8af637396dc00966df5f701e661c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53135
Analysis date: Fri, 31 Jul 2026 16:53:13 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: YES

Summary:
A local write to the amdgpu SDP debugfs node can trigger a NULL pointer dereference when the connector has no bound CRTC, and the same path can over-read the caller supplied user buffer, but typical impact is privileged local DoS rather than information disclosure or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-53135 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53135

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: 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-2026-53135	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	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:N/A:H';**CWE-476;CWE-126;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'A NULL pointer dereference in dp_sdp_message_debugfs_write() can occur when connector base state or state crtc is NULL while a local process writes to the amdgpu SDP debugfs node. The same path can also read beyond the user supplied buffer because the old code did not clamp the copy length to the write size. This is a local debugfs control path and is not network reachable. For the CVSS the PR:L is used in the paranoid score only for non default deployments where a less privileged local user can write to the affected debugfs node. In typical deployments PR:H is more realistic because debugfs access is restricted to administrators. Impact is mainly denial of service via kernel crash. The user buffer over read may cause limited confidentiality concern only for data reachable from the calling user address space, not a direct kernel memory disclosure or privilege escalation primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-53135  SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	WRITE OOB DANGER SIMPLEFIX KERNEL_PANIC_PLUS_UAF HARDWARE DEBUGFS  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 NULL dereference can crash the kernel when writing to the affected debugfs node while the connector has no bound CRTC.
* Requires admin/root/CAP in typical deployments: -2. debugfs access is normally administrator-only or restricted to highly privileged local users.
* Hard or state-dependent trigger: -1. The NULL dereference depends on a connector state window such as hot-plug before the next atomic commit.
* Rare/non-default exposure path: -1. The vulnerable interface is an AMD display debugfs node, not a default unprivileged syscall or network path.
* Floor applied at 0.

Paranoid signals:

* Local unprivileged trigger: +1. Counted only for non-default deployments where the affected debugfs node is writable by a less privileged local user.
* Reliable kernel crash / strong DoS: +1. A successful trigger can cause a kernel crash.
* No memory-corruption bonus. The NULL dereference is an invalid pointer dereference, and the copy_from_user issue is a user-buffer over-read, not kernel memory disclosure or a write primitive.
* No LPE bonus. The patch does not show UAF, OOB write, object reuse, callback control, refcount abuse, or attacker-controlled overwrite.
* No confidentiality bonus in the main score. The over-read reads beyond the caller supplied user buffer, not from kernel memory or another security domain.

## 3. Reachability analysis

The bug is local-only and requires writing to the amdgpu SDP debugfs node. In typical deployments this requires administrator-level access because debugfs is restricted or not mounted for unprivileged users. Namespaces normally do not make this broadly reachable unless a container or sandbox is explicitly given access to the host debugfs tree or the specific device debugfs node. There is no network trigger. Realistic exploitation is mainly a local privileged or misconfigured-debugfs kernel crash scenario.

Call-site confidence: medium. The vulnerable function and direct dereference/copy path are shown, but broader file permissions and exact debugfs mode are not included in the patch input.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like kernel issue rather than an Important-class vulnerability. The realistic impact is DoS through a NULL pointer dereference. The buffer over-read is not a kernel information leak because copy_from_user reads from the calling process address space. Theoretical escalation is not supported by the patch context, because there is no concrete memory corruption primitive beyond crash-oriented invalid dereference and no attacker-controlled kernel overwrite.

## 5. One-sentence report phrase

A local write to the amdgpu SDP debugfs node can trigger a NULL pointer dereference when the connector has no bound CRTC, and the same path can over-read the caller supplied user buffer, but typical impact is privileged local DoS rather than information disclosure or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED.
NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.

Reason: no remote reachability, no strong memory corruption primitive, no plausible LPE path, and typical access requires privileged debugfs write permissions.

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

Patch: drm/amd/display: Fix NULL deref and buffer over-read in SDP debugfs
Commit: ee9cfcf77a8e8af637396dc00966df5f701e661c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ee9cfcf77a8e8af637396dc00966df5f701e661c

Commit description:

[Why & How]
dp_sdp_message_debugfs_write() dereferences connector->base.state->crtc
without checking for NULL. A connector can be connected but not bound to
any CRTC (e.g. after hot-plug before the next atomic commit), causing a
kernel crash when writing to the sdp_message debugfs node.

The function also ignores the user-provided size argument and always
passes 36 bytes to copy_from_user(), reading past the user buffer when
size < 36.

Fix both issues by:
- Returning -ENODEV when connector->base.state or state->crtc is NULL
- Clamping write_size to min(size, sizeof(data))

Fixes: c7ba365 ("drm/amd/display: Generic SDP message access in amdgpu")
Assisted-by: Copilot:claude-opus-4.6
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Ray Wu <ray.wu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 6ab4c36 )
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_debugfs.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=ee9cfcf77a8e8af637396dc00966df5f701e661c

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

The original Linux kernel CVE announcement for CVE-2026-53135 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53135

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:H/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:N/A:H
  The Best / paranoid CVSS score: 5.3

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).