[CVE-2026-98999][MODERATE 7.0] drm/xe: Fix stale pinned_link entry when fb-pin performs the final unpin

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

CVE: CVE-2026-98999
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: drm/xe: Fix stale pinned_link entry when fb-pin performs the final unpin
Commit: 3a11adcfd9a2de74d405bd3e8c4d7a1b328e4684
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3a11adcfd9a2de74d405bd3e8c4d7a1b328e4684
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98999
Analysis date: Tue, 27 Oct 2026 02:20:09 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
A mixed external/framebuffer pin lifecycle can leave a freed Xe BO linked in a live pinned-object list, causing later kernel list operations to consume and corrupt stale heap state.

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

The original Linux kernel CVE announcement for CVE-2026-98999 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98999

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-2026-98999	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98999 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE_KPANIC RESULT=SAME (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	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-416;*CWE-672;CWE-825;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A framebuffer final unpin can leave xe_bo pinned_link attached to a pinned object list when the same buffer was also externally pinned. After the buffer is freed, a later list walk or splice can access freed memory and corrupt list pointers, creating a concrete use after free candidate with possible kernel crash and potential local privilege escalation. For the CVSS the PR:L value reflects that local DRM access plus control of a framebuffer, DRM lease, display service, or equivalent graphics context is required. AC:H reflects the required mixed external and framebuffer pin lifecycle, final unpin ordering, object release, and later list processing. The issue is not directly network reachable. Base impact is CIA:LLH, while the paranoid CIA:HHH score covers the still defensible possibility that allocator reuse turns the stale list node into stronger kernel memory corruption. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. KP and FD specialist checks stage IMPORTANT to MODERATE_KPANIC because a specific evidence based protection or manual review veto was applied and FD false positive review allowed a downgrade. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and V33_ACTIVE_STATE_BOUNDARY_CANDIDATE and IMPORTANT_CANDIDATE_MANUAL_REVIEW and KP_ONLY_DOWNGRADE_VETO and DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH. The independent weaker Aegis shadow evaluated CVSS 3.7 and ActionableScore 2 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5)	MAYBE	LOCK DANGER INIT UAF HARDWARE KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS V33_ACTIVE_STATE_BOUNDARY_CANDIDATE IMPORTANT_CANDIDATE_MANUAL_REVIEW KP_ONLY_DOWNGRADE_VETO DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 3.
* Conservative score: 4. Real-UAF floor 4 applied: 3 -> 4.
* Raw paranoid score: 5.
* Paranoid score: 5; no floor or cap changed it.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

* +2 real UAF/lifetime breach: final framebuffer unpin can leave `pinned_link` attached after the BO is freed; a later list walk or splice consumes the stale node.
* +1 plausible kernel crash/strong DoS: traversal or mutation of an intrusive list through freed storage can fault or corrupt the list. No duplicate Availability point.
* Paranoid +1 attacker-influenced lifetime sequence: the supplied triage grounds a local graphics actor controlling the mixed external/framebuffer pin lifecycle and unpin ordering, although complete interface permissions remain unresolved.
* Paranoid +1 structured stale-object leverage: later list walking/splicing consumes and mutates linkage pointers embedded in freed storage, materially exceeding a shallow cleanup dereference.
* No race penalty: the defect follows an ordered pin/unpin/free/list-consumption sequence; narrow uncontrollable timing is not shown.
* No privilege penalty: host-admin-equivalent privilege is not positively established.
* Controlled reclaim, chosen adjacent object, arbitrary write, disclosure, LPE, and C/I impact are not shown.
* This is not B5-R: no retry-accumulated heap OOB write exists. It is also not B3-PENDING or B4-PENDING.

3. Reachability analysis

The required actor needs access to Intel Xe DRM objects and must combine external pinning, such as dma-buf export, with framebuffer scanout pinning, then cause the relevant final unpin, object release, and later pinned-list processing. The supplied summary identifies possible DRM lease, framebuffer, compositor, or display-service contexts, but the patch does not establish that a normal logged-in user or render-node-only client can complete every stage.

DRM master, compositor, delegated display service, and host administrator must therefore be distinguished; complete below-host-admin reachability is credible but unproven. No namespace-scoped capability chain or host UID 0 requirement is established. Intel Xe hardware is required, but no rare/physical-only penalty is justified. No separate privileged setup or hard race is proven.

4. Primitive and severity reading

This is an active structured-object UAF: a freed BO’s intrusive `pinned_link` remains in a live kernel list, and later privileged list operations read or modify stale linkage state. It is broader than an ordinary cleanup-only stale dereference, but there is no specific repeated put/refcount mutation and no controlled replacement, so it remains CLASS_B rather than CLASS_A.

Shown effects are stale-list consumption, list corruption, and plausible host crash. Stronger exploitation through allocator reuse is unresolved. The credible delegated graphics boundary plus attacker-influenced active-state corruption and a later privileged consumer make this an Important review candidate under the active-state/trust-boundary rule; the unresolved leverage must not be auto-downgraded.

5. One-sentence report phrase

A mixed external/framebuffer pin lifecycle can leave a freed Xe BO linked in a live pinned-object list, causing later kernel list operations to consume and corrupt stale heap state.

6. Manual review advice

MANUAL CHECK REQUIRED

Confirm the complete DRM permission model and whether an unprivileged, leased, or delegated graphics client can drive object freeing and subsequent list consumption, and assess reclaim control around the stale list node.

7. Call-site confidence

Call-site confidence: medium

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

Patch: drm/xe: Fix stale pinned_link entry when fb-pin performs the final unpin
Commit: 3a11adcfd9a2de74d405bd3e8c4d7a1b328e4684
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3a11adcfd9a2de74d405bd3e8c4d7a1b328e4684

Commit description:

xe_bo_pin_external() and xe_bo_unpin_external() maintain the bo's
pinned_link list membership in xe->pinned.late.external, based on
whether the current call is the outermost pin or the final unpin.
However, the same external bo's pin_count can also be raised and
lowered directly by __xe_pin_fb_vma()/__xe_unpin_fb_vma(), which pin
the bo as a display scanout buffer without going through
xe_bo_pin_external()/xe_bo_unpin_external() at all, and have no
notion of, or ownership over, pinned_link.

If a bo is pinned both externally (e.g. dma-buf export) and as an fb,
and the external unpin happens first, xe_bo_unpin_external() correctly
observes pin_count > 1 and leaves the bo on pinned_link. When the fb
unpin later performs the true last unpin (pin_count 1 -> 0), it never
touches pinned_link, leaving the bo linked on xe->pinned.late.external
indefinitely. Once the bo is subsequently freed, this stale list entry
points into freed memory, corrupting the list and risking a
use-after-free the next time the list is walked or spliced.

The backup object pin/unpin sites in xe_bo_notifier_prepare_pinned()/
xe_bo_notifier_unprepare_pinned() have the same bypass characteristic,
though they never add their bo to a pinned list, so are not affected
by this particular list-corruption issue.

Move the pinned_link removal into xe_bo_account_unpin(), which already
runs on every unpin path (kernel, external, framebuffer, backup
object) right before the true 1 -> 0 pin_count transition. Since
list_del_init() only operates on the node itself, this removal is
list-agnostic and safe to perform regardless of which list (external
or kernel_bo_present) the bo happens to be linked on, or which code
path is performing the final unpin. Drop the now-redundant explicit
list_del_init() calls in xe_bo_unpin_external() and xe_bo_unpin().

v2:
- New patch

v3:
- Rebased on changes to previous patch.

Fixes: 44e6949 ("drm/xe/display: Implement display support")
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: intel-xe@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v6.8+
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Assisted-by: LLM
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Link: https://patch.msgid.link/20261002100830.12297-3-thomas.hellstrom@linux.intel.com
(cherry picked from commit ca58d36 )
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpu/drm/xe/xe_bo.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=3a11adcfd9a2de74d405bd3e8c4d7a1b328e4684

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

The original Linux kernel CVE announcement for CVE-2026-98999 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98999

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: 4
  Paranoid ActionableScore: 5

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).