[CVE-2026-90182][LOW] blk-iocost: clear delay state when freeing policy data [ Upstream

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

CVE: CVE-2026-90182
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: blk-iocost: clear delay state when freeing policy data [ Upstream
Commit: b9c16db833e3ff15d923282f94dddf0e10fab8c0
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b9c16db833e3ff15d923282f94dddf0e10fab8c0
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90182
Analysis date: Thu, 17 Sep 2026 17:04:56 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90182 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90182

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-2026-90182	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90182 CHECK WITH IMPACT FROM ORIG NN MODERATE	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-404;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'blk iocost can leave a block cgroup marked congested after policy data is freed because the explicit delay state is not cleared when the iocg is removed from active_iocgs and its timer is cancelled. Tasks in that cgroup and its descendants can then be treated as congested for the remaining lifetime of the blkcg, causing reduced readahead and possible throttling in swap related allocation paths. For the CVSS the PR:L is used for the paranoid view because a delegated cgroup manager or service account may be able to create and remove cgroups and generate IO debt, although normal system wide cgroup administration is usually privileged. The issue is not network reachable and is triggered through local cgroup and block IO control plane operations. Impact is denial of service through persistent performance degradation rather than kernel memory corruption or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	YES	INIT TIMER  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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

ActionableScore=2
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap was applied.

2. Signal breakdown

Positive signals:

* +1 Concrete persistent kernel resource or state leak: blkcg delay and congestion state can remain set after ioc_pd_free() removes the iocg from active_iocgs and cancels the waitq timer, leaving no normal path to clear the delay.
* +1 Availability impact realistic: affected tasks in the cgroup and descendants can suffer persistent performance degradation through reduced readahead and swap related throttling.

Negative signals:

* No host-admin penalty applied: host-admin-equivalent privilege is plausible for system-wide blkcg and blk-iocost administration, but the supplied evidence does not fully prove the complete privilege boundary.
* No race or timing penalty applied: this is a lifecycle state cleanup bug, not a narrow timing race.
* No rare subsystem penalty applied: blk-iocost is optional and configuration-dependent, but rarity alone is not established as a concrete reducing signal.

Non-awarded signals:

* RealUAF not awarded: no stale post-free object dereference or use-after-free is established.
* Concrete repeated release/refcount not awarded: the patch clears delay state and calls blkcg_clear_delay(), but it does not show a second put/release/free/refcount mutation through a dangling reference.
* Controlled reclaim, arbitrary write, OOB access, and memory corruption are not demonstrated.
* Confidentiality and integrity are not awarded because the effect is stale congestion accounting and throttling behavior, not data disclosure or unauthorized modification.
* Reliable kernel crash is not awarded because the described impact is performance degradation, not panic or fatal fault.
* Remote reachability is not established.
* Security-boundary bypass is not awarded because the issue does not defeat a cgroup isolation limit or authorization decision. It leaves a cgroup over-throttled rather than allowing escape or cross-cgroup resource theft.

3. Reachability analysis

The trigger requires blk-iocost policy data to be freed while the associated blkcg delay state remains active. Practically, this involves local cgroup and block I/O control-plane activity: generating sufficient I/O debt, entering explicit blkcg delay state, and later freeing the policy data or removing the relevant cgroup/policy state.

Ordinary unprivileged reachability is not established. System-wide cgroup and blk-iocost administration is commonly performed by privileged management code, but delegated cgroup management can exist in some deployments. The supplied patch does not prove that a normal unprivileged user can complete the full sequence, and it also does not prove that host-admin-equivalent privilege is always required. Therefore HostAdminRequired is UNKNOWN.

This is not a namespace-scoped capability issue based on the supplied evidence. NamespaceScopedPrivilege is NO. There is no network trigger. There is no special hardware prerequisite beyond use of blk-iocost and block cgroups. There is no hard race requirement.

4. Primitive and severity interpretation

The exact primitive is a stale persistent kernel accounting/state condition: blkcg delay state remains active after ioc_pd_free() removes the iocg from active processing paths and cancels its timer. This causes blk_cgroup_congested() to continue treating the cgroup and descendants as congested.

This is not active structured UAF, fixed stale storage UAF, double release, RCU lifetime corruption, arbitrary memory corruption, or authorization bypass. The demonstrated consequence is denial of service through persistent local performance degradation. The most plausible operational effect is reduced readahead and possible throttling in swap related anonymous folio allocation paths.

PrimitiveClass is NONE because no meaningful corruption, ownership violation, authorization bypass, UAF, or security-boundary primitive is established. ImportantCandidate is NO because the issue is performance DoS only and lacks memory corruption, privilege escalation, cross-boundary impact, or unresolved exploitation leverage. AutoDowngradeAllowed is YES because this can be handled as an ordinary Moderate or Low-like resource/state cleanup issue.

5. One-sentence report phrase

blk-iocost can leave a block cgroup permanently marked congested after policy data is freed, causing persistent local performance degradation for tasks in that cgroup and descendants without evidence of memory corruption, privilege escalation, or network reachability.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the patch supports a stale delay/congestion state cleanup bug with performance DoS impact only, and no UAF, repeated refcount mutation, authorization bypass, memory corruption, or network exposure is established.

7. Call-site confidence

Call-site confidence: high

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

Patch: blk-iocost: clear delay state when freeing policy data [ Upstream
Commit: b9c16db833e3ff15d923282f94dddf0e10fab8c0
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b9c16db833e3ff15d923282f94dddf0e10fab8c0

Changed files:
  block/blk-iocost.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=b9c16db833e3ff15d923282f94dddf0e10fab8c0

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

The original Linux kernel CVE announcement for CVE-2026-90182 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90182

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: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: 2

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).