[CVE-2026-80702][MODERATE 7.0] drm/vmwgfx: fix guest_memory_dirty bitfield clobbered as size

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

CVE: CVE-2026-80702
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: drm/vmwgfx: fix guest_memory_dirty bitfield clobbered as size
Commit: 21bbe38faee4a195d33a93e3908e307807f7745d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=21bbe38faee4a195d33a93e3908e307807f7745d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80702
Analysis date: Fri, 28 Aug 2026 06:23:54 -0400
ActionableScore: 8
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A wrong field assignment in vmwgfx can clobber guest_memory_size with boolean values, causing later revalidation code to compute invalid dirty ranges or buffer sizes and potentially read or write past the MOB bitmap, with PR:L in typical DRM-accessible guest deployments and impact ranging from local DoS to possible kernel memory corruption.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-80702 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80702

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 7.0
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-2026-80702	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:H/I:H/A:H';*CWE-787;CWE-125;CWE-682;CWE-704;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A wrong field assignment in vmwgfx can overwrite guest_memory_size with boolean values instead of updating guest_memory_dirty. Later revalidation paths may use the corrupted size while calculating dirty page ranges and buffer allocation sizes, which can cause zero length walks or wrap around ranges and lead to out-of-bounds read/write past the MOB bitmap. For the CVSS the PR:L is used because a local user in the guest may be able to reach vmwgfx through DRM device ioctls or render nodes depending on system policy. The issue is not directly network reachable. Impact is at least local denial of service via kernel crash and in the paranoid case may include confidentiality or integrity impact due to kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	SIMPLEFIX HARDWARE LINUS  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=8
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 8
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user in a VMware guest may be able to reach vmwgfx through DRM ioctls or render nodes depending on device permissions.
* Constrained kernel buffer overwrite: +1. The patch context describes read or write past the MOB bitmap, but the exact payload and target control are not demonstrated.
* Memory layout invariant restoration: +1. The bug corrupts an allocation-size field by writing boolean values into guest_memory_size instead of updating the dirty bitfield.
* Reliable kernel crash / strong DoS: +1. Wrong size values can produce zero-length walks or wrap-around ranges and lead to invalid memory access.
* Weak LPE concern: +1. Kernel OOB read/write in a GPU driver is a plausible escalation concern, but no reclaim, arbitrary write, or controlled overwrite primitive is shown.

Paranoid additional interpretation:

* Memory corruption, strong corruption primitive: +2 instead of constrained +1. The commit explicitly says subsequent paths may read or write past the MOB bitmap.
* Confidentiality impact plausible: +1. OOB read past a kernel bitmap may expose adjacent kernel data in some paths, though no disclosure path is proven.
* Integrity impact plausible: +1. OOB write past the bitmap may corrupt adjacent kernel memory or driver metadata.
* Broad/common virtualized exposure: +1. vmwgfx is a common VMware guest graphics driver and may be exposed to ordinary desktop or guest users through DRM permissions.

## 3. Reachability analysis

The likely trigger is local from inside the guest through vmwgfx resource lifecycle operations and revalidation paths. The bug is not directly network reachable. PR:L is the practical CVSS interpretation when local users can access the DRM node or render node. If the device node is restricted to root or a trusted graphics service, practical reachability is lower, but many graphical guest deployments expose DRM functionality to non-root users.

Namespaces and containers do not automatically make this reachable unless the vmwgfx DRM device is passed into the container. The affected path is configuration dependent on VMware graphics usage, but vmwgfx is a realistic and common virtualized graphics stack rather than an exotic debug-only subsystem.

Call-site confidence: medium. The patch text identifies the downstream users vmw_bo_dirty_transfer_to_res() and vmw_resource_buf_alloc(), but the full call paths and exact bitmap layout are not included in the provided diff.

## 4. Severity interpretation

This is not an ordinary cleanup or pure DoS-only bug. The field confusion changes an allocation-size value into 0 or 1 and later code uses that corrupted size for dirty range and buffer allocation calculations. That creates a plausible OOB read/write condition in kernel driver memory.

Conservatively, the issue is an Actionable Moderate because the primitive appears constrained and requires specific vmwgfx resource state transitions. Paranoid triage should treat it as a Strong Important candidate because kernel OOB write in a local GPU driver path can sometimes become privilege escalation even when the patch does not demonstrate a full exploit chain.

## 5. One-sentence report phrase

A wrong field assignment in vmwgfx can clobber guest_memory_size with boolean values, causing later revalidation code to compute invalid dirty ranges or buffer sizes and potentially read or write past the MOB bitmap, with PR:L in typical DRM-accessible guest deployments and impact ranging from local DoS to possible kernel memory corruption.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the patch context explicitly mentions read or write past the MOB bitmap, so this is a kernel memory corruption candidate rather than a simple warning or resource leak. The realistic exploitability is not proven, but the combination of local DRM reachability and OOB access is enough to require manual review.

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

Patch: drm/vmwgfx: fix guest_memory_dirty bitfield clobbered as size
Commit: 21bbe38faee4a195d33a93e3908e307807f7745d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=21bbe38faee4a195d33a93e3908e307807f7745d

Commit description:

Two sites in vmwgfx_resource.c assign boolean literals to
res->guest_memory_size, which is an unsigned long allocation-size
field; the intended target is the adjacent res->guest_memory_dirty
bitfield.  After the assignments the field holds 0 or 1 instead of
the resource's MOB allocation size:

  - vmw_resource_release()       writes 0 (false), and
  - vmw_resource_unbind_list()   writes 1 (true).

Subsequent revalidation paths read guest_memory_size when computing
the dirty page range (vmw_bo_dirty_transfer_to_res()) and the buffer
allocation size (vmw_resource_buf_alloc()), producing zero-length
walks or wrap-around ranges that read or write past the MOB bitmap.
The dirty-tracking intent of the original code (mark the resource as
dirtied since the last sync) is also lost, since guest_memory_dirty
is never updated.

Rename both assignments to guest_memory_dirty.

Fixes: 668b206 ("drm/vmwgfx: Stop using raw ttm_buffer_object's")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4.7
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Reviewed-by: Ian Forbes <ian.forbes@broadcom.com>
Link: https://patch.msgid.link/20260505222728.519626-2-zack.rusin@broadcom.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/vmwgfx/vmwgfx_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=21bbe38faee4a195d33a93e3908e307807f7745d

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

The original Linux kernel CVE announcement for CVE-2026-80702 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80702

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 5
  Paranoid ActionableScore: 8

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).