[CVE-2026-68270][MODERATE REGULAR] drm/sysfb: Avoid possible truncation with calculating visible size

[CVE-2026-68270][MODERATE REGULAR] drm/sysfb: Avoid possible truncation with calculating visible size

[AL-KERNEL]

CVE: CVE-2026-68270
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: drm/sysfb: Avoid possible truncation with calculating visible size
Commit: 154795885e8f0033c918c815aece543168bee670
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=154795885e8f0033c918c815aece543168bee670
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68270
Analysis date: Mon, 10 Aug 2026 19:55:48 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
An integer overflow in DRM sysfb visible framebuffer size calculation can truncate height by stride validation, potentially accepting incorrect framebuffer bounds when firmware or boot supplied values are unusually large.

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

The original Linux kernel CVE announcement for CVE-2026-68270 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68270

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
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CVE-2026-68270	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:H/UI:N/S:U/C:L/I:L/A:H';CWE-190;CWE-681;CWE-131;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.2';DESCR 'An integer overflow in drm_sysfb_get_visible_size_si() can truncate the visible framebuffer size because height and stride are multiplied with 32 bit arithmetic before the value is stored in u64. If very large screen_info values are supplied, the validated visible size can become smaller than the real height by stride requirement and the framebuffer range may be accepted with incorrect bounds. For the CVSS the PR:H is used because reliable triggering normally requires control over firmware supplied or boot supplied system framebuffer parameters, kexec, or another administrative path that can influence screen_info. The issue is not network reachable and is not triggered by normal packet or file input. Impact is primarily denial of service or display and framebuffer memory range misvalidation. In the paranoid interpretation, limited confidentiality or integrity impact is kept possible because this is a size calculation overflow in a kernel memory mapped framebuffer path, but the patch context does not support a higher privilege escalation claim.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 2)	YES	SIMPLEFIX HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Firmware-mediated external influence: +1. `screen_info`, height, and stride are normally firmware or boot supplied rather than ordinary user input.
* Availability impact realistic: +1. A truncated visible framebuffer size may cause incorrect validation and display or framebuffer mapping failures.
* Broad/default/common subsystem: +1. EFI/VESA system framebuffer support is common on many systems.
* Requires admin/root/boot/firmware control in typical deployments: -2. Reliable triggering normally requires control over firmware data, boot parameters, kexec, or equivalent privileged setup.

Conservative total: 1.

Paranoid additional signals:

* Weak/indirect corruption candidate: +1. The overflow affects a kernel size validation path and may cause an incorrect framebuffer range to be accepted.
* Privileged kernel/device-management memory corruption path: +1. The affected code is firmware-fed DRM/sysfb initialization logic operating in a trusted kernel display path.

Paranoid total: 3.

Not counted:

* No remote/network reachability.
* No local unprivileged trigger shown.
* No strong memory corruption primitive shown.
* No UAF, double-free, OOB write, arbitrary write, refcount abuse, callback control, or attacker-controlled reclaim shown.
* No Dirty-Pipe-like shared page or page-cache primitive.

## 3. Reachability analysis

The bug is triggered through unusually large framebuffer height and stride values reaching `drm_sysfb_get_visible_size_si()`. In normal deployments these values come from firmware, boot-time platform data, EFI/VESA framebuffer setup, or privileged boot/kexec paths.

A normal local unprivileged user cannot usually control these values. Containers and namespaces do not materially lower the privilege requirement because the affected state is established at host boot or early device initialization. The path is common on systems using EFI/VESA/sysfb display support, but realistic attacker influence is limited to firmware-mediated or administrator-controlled scenarios.

Call-site confidence: medium. The changed helper and validation purpose are visible, but broader caller behavior is not fully present in the provided patch.

## 4. Severity interpretation

This behaves more like a low-to-borderline Moderate issue than an Important-class vulnerability. The theoretical concern is that integer truncation may understate the visible framebuffer size and weaken bounds validation in a kernel-mapped framebuffer path. The realistic evidence supports misvalidation and possible DoS or display/framebuffer malfunction, not privilege escalation.

The paranoid score is raised to preserve manual-review sensitivity because this is an integer overflow in a kernel size validation path fed by trusted firmware or boot data. It is still capped well below Important because there is no demonstrated corruption primitive, no unprivileged runtime interface, and no network exposure.

## 5. One-sentence report phrase

An integer overflow in DRM sysfb visible framebuffer size calculation can truncate height by stride validation, potentially accepting incorrect framebuffer bounds when firmware or boot supplied values are unusually large.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.

Reason: this is not a clear auto-close because it affects a kernel framebuffer size validation path, but it also lacks evidence of a practical unprivileged trigger, network reachability, or strong memory corruption primitive.

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

Patch: drm/sysfb: Avoid possible truncation with calculating visible size
Commit: 154795885e8f0033c918c815aece543168bee670
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=154795885e8f0033c918c815aece543168bee670

Commit description:

Calculating the visible size of the system framebuffer can result in
truncation of the result. The calculation uses 32-bit arithmetics,
which can overflow if the values for height and stride are large. Fix
the issue by multiplying with mul_u32_u32().

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 32ae90c ("drm/sysfb: Add efidrm for EFI displays")
Fixes: a84eb6a ("drm/sysfb: Add vesadrm for VESA displays")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/dri-devel/20260617114027.1F2A71F000E9@smtp.kernel.org/
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v6.16+
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patch.msgid.link/20260618084327.46567-3-tzimmermann@suse.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/sysfb/drm_sysfb_screen_info.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=154795885e8f0033c918c815aece543168bee670

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

The original Linux kernel CVE announcement for CVE-2026-68270 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68270

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:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.2

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: 1
  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).