[CVE-2026-98832][LOW] blk-cgroup: save IRQ state in blkg_tryget_closest() [ Upstream

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

CVE: CVE-2026-98832
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: blk-cgroup: save IRQ state in blkg_tryget_closest() [ Upstream
Commit: 9fcf4317384ce6758c3127a6e8914c54cbb9c8cc
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9fcf4317384ce6758c3127a6e8914c54cbb9c8cc
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98832
Analysis date: Sat, 24 Oct 2026 03:59:39 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
Improper IRQ-state restoration during blkg creation can let dm-thin completion softirqs re-enter a held pool lock and deadlock the storage path.

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

The original Linux kernel CVE announcement for CVE-2026-98832 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98832

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-98832	LOW	https://www.kernelcve.org/list/?q=CVE-2026-98832 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:L/UI:N/S:U/C:N/I:N/A:H';CWE-667;*CWE-833;CWE-362;BEST CVSS score: '4.7';DESCR 'An IRQ state handling bug in blkg_tryget_closest can enable local interrupts while a caller still holds another spinlock with interrupts expected to remain disabled. In dm thin this allows an I/O completion softirq on the same CPU to re acquire pool lock through thin_endio or complete_mapping_preparation and deadlock the storage path. For the CVSS the PR:L value is used because an attacker normally needs local user or process access capable of generating I/O through an affected configured block device. AC:H reflects the required blk cgroup lookup miss, dm thin locking context, and completion timing. Availability impact can be high due to a stuck CPU or storage path. The code provides no UAF, OOB access, information leak, or write primitive to support confidentiality or integrity impact. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 1 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 2.5 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 1)	MAYBE	LOCK DEADLOCK HARDWARE 	-	-	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 1.
* Conservative score: 1; no floor or cap applied.
* Raw paranoid score: 1.
* Paranoid score: 1.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Local low-privilege trigger: the supplied call-path assessment supports a process generating I/O through an already configured affected dm-thin device.
* +1 Reliable strong DoS: incorrect IRQ restoration can permit a same-CPU completion softirq to re-acquire `pool->lock`, deadlocking the CPU or storage path.
* -1 Hard/special timing: exploitation requires a blkg lookup miss while inside the IRQ-disabled dm-thin path and suitably timed I/O completion.
* No extra availability point: storage unavailability is the consequence of the same deadlock.
* No memory-corruption, UAF, OOB-write, disclosure, integrity, authorization, or protected-resource primitive is shown.
* NEW52 B5-R does not apply: there is no retry-accumulated heap OOB write or later consumption of corrupted structured state.

3. Reachability analysis

A local process with access to an affected, preconfigured dm-thin block device can generate the relevant I/O; effective host-administrator power and UID 0 are not required for that data-path activity. Administrative setup of dm-thin and block cgroups is a deployment prerequisite, but not necessarily part of each trigger. No evidence establishes that the complete operation is namespace-scoped. The required miss and softirq interleaving make triggering timing-dependent.

4. Primitive and severity reading

The exact defect is unbalanced IRQ-state handling: `spin_unlock_irq()` enables interrupts despite the caller entering with interrupts disabled. The later completion softirq can recursively contend on the still-held dm-thin lock. This is a synchronization/deadlock primitive, classified CLASS_C. The shown impact is availability loss; corruption, privilege escalation, and authorization bypass are unsupported. Consequently, there is no Important-preserving primitive and automatic Moderate handling is acceptable.

5. One-sentence report phrase

Improper IRQ-state restoration during blkg creation can let dm-thin completion softirqs re-enter a held pool lock and deadlock the storage path.

6. Manual review advice

NO MANUAL CHECK NEEDED

The patch and supplied call path establish a timing-dependent availability defect without a material corruption or security-boundary primitive.

7. Call-site confidence

Call-site confidence: high

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

Patch: blk-cgroup: save IRQ state in blkg_tryget_closest() [ Upstream
Commit: 9fcf4317384ce6758c3127a6e8914c54cbb9c8cc
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9fcf4317384ce6758c3127a6e8914c54cbb9c8cc

Changed files:
  block/blk-cgroup.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=9fcf4317384ce6758c3127a6e8914c54cbb9c8cc

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

The original Linux kernel CVE announcement for CVE-2026-98832 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98832

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: unknown
  Paranoid ActionableScore: 1

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).