[CVE-2026-98970][LOW] drm/vc4: Free the BO cache size list on teardown [ Upstream

[CVE-2026-98970][LOW] drm/vc4: Free the BO cache size list on teardown [ Upstream

[AL-KERNEL]

CVE: CVE-2026-98970
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: drm/vc4: Free the BO cache size list on teardown [ Upstream
Commit: bf2848e50bd73782c2942ec023b5b60231f16e9b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bf2848e50bd73782c2942ec023b5b60231f16e9b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98970
Analysis date: Mon, 26 Oct 2026 15:26:05 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
VC4 driver teardown leaks the BO cache size list on each privileged unbind, without evidence of memory corruption or reliable host-wide exhaustion.

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

The original Linux kernel CVE announcement for CVE-2026-98970 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98970

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-2026-98970	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98970 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both 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:N/I:N/A:H';*CWE-401;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.1';DESCR 'The VC4 BO cache teardown purges cached buffer objects but does not release the dynamically allocated size_list, leaving a persistent kernel memory leak after each driver unbind. The demonstrated primitive is limited resource retention with no UAF, invalid access, information disclosure, or memory corruption. For the CVSS the PR:H value is used because reaching the teardown path through driver unbind normally requires administrative device management privileges. A meaningful host availability impact would require many repeated bind and unbind cycles, and reliable system wide memory exhaustion is not established. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.1 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 2.0 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	MAYBE	SIMPLEFIX LEAK HARDWARE LINUS 	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: -1.
* Conservative score: 0 after lower-bound clamping.
* Raw paranoid score: -1.
* Paranoid score: 0 after lower-bound clamping.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 — Concrete persistent kernel resource leak: `size_list` remains allocated after `vc4_bo_cache_destroy()`; the added `kfree()` confirms the missing release.
* -2 — Host-administrator-equivalent prerequisite: the evidenced repetition mechanism is VC4 driver/device unbind or teardown, a host device-management operation rather than a render-node operation.
* No UAF, OOB access, stale dereference, double release, memory overwrite, authorization bypass, or protected-resource modification is shown.
* No reliable host-wide exhaustion or crash is established, so no DoS point is awarded.
* B5-R and B3-PENDING do not apply: there is neither an OOB write nor a shared-backing write.
* No confidentiality or integrity impact is supported.

3. Reachability analysis

The leak occurs during VC4 BO-cache destruction. Repeated accumulation requires repeated device bind/unbind or equivalent teardown/reinitialization. The supplied evidence supports host-level device-management privilege, not ordinary render-node ioctl access or a namespace-scoped capability. Numeric host UID 0 is not strictly established because an appropriately capable administrative process could potentially perform the operation. No race, unusual hardware penalty, or separate prior setup penalty is scored.

4. Primitive and severity reading

The exact defect is a missing `kfree()` for a dynamically allocated cache size list. It retains kernel heap memory but does not leave an escaping stale pointer or corrupt active state. The patch shows only one allocation leak per teardown; practical system-wide exhaustion would require many privileged lifecycle cycles and is not demonstrated. PrimitiveClass is therefore NONE rather than a memory-corruption class. Important review preservation is unwarranted, and automatic downgrade is safe.

5. One-sentence report phrase

VC4 driver teardown leaks the BO cache size list on each privileged unbind, without evidence of memory corruption or reliable host-wide exhaustion.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch establishes only a small host-admin-triggered teardown leak with no unresolved corruption or security-boundary primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: drm/vc4: Free the BO cache size list on teardown [ Upstream
Commit: bf2848e50bd73782c2942ec023b5b60231f16e9b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bf2848e50bd73782c2942ec023b5b60231f16e9b

Changed files:
  drivers/gpu/drm/vc4/vc4_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=bf2848e50bd73782c2942ec023b5b60231f16e9b

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

The original Linux kernel CVE announcement for CVE-2026-98970 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98970

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:L/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:N/I:N/A:H
  The Best / paranoid CVSS score: 4.1

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: unknown
  Paranoid ActionableScore: 0

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).