[CVE-2026-90390][LOW] md/bitmap: resume array on backlog_store() error path [ Upstream

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

CVE: CVE-2026-90390
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: md/bitmap: resume array on backlog_store() error path [ Upstream
Commit: 03aad318f0a1f039dddf98739e705fdca3bf0d86
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=03aad318f0a1f039dddf98739e705fdca3bf0d86
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90390
Analysis date: Fri, 18 Sep 2026 03:16:45 -0400
ActionableScore: 0
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-2026-90390 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90390

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-2026-90390	LOW	https://www.kernelcve.org/list/?q=CVE-2026-90390 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-703;CWE-755;CWE-667;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'md/bitmap backlog_store can leave an md array suspended on an error path when no write-mostly device exists. The function suspends the array before the validation check, but the failing path only unlocked mddev and did not resume the array, so later I/O to the affected md device can remain blocked. For the CVSS the PR:H value is used for the base score because writing this md control path normally requires storage administration privileges. For the paranoid score PR:L can be considered only where a less privileged service account or delegated storage management role can write md device attributes. The issue is not network reachable and the impact is denial of service for the affected storage array rather than memory corruption or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	LOCK DISK SIMPLEFIX ERRORPATH HARDWARE LINUS  INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

2. Signal breakdown

Positive signals:

* +1 Reliable local availability impact. backlog_store() can leave the md array suspended on the error path, and subsequent I/O to the affected array can remain blocked.
* +1 Important storage path. The affected object is an md array, so the operational impact may affect storage availability for that array.

Negative signals:

* -2 Host-admin-equivalent control is required. Writing the relevant md control attribute and changing md bitmap/backlog configuration is an administrative storage-management operation.

Non-awarded signals:

* Real UAF not awarded. No stale pointer, use-after-free, double free, refcount misuse, or post-lifetime object access is shown.
* Memory corruption not awarded. The patch fixes an error-path state cleanup bug, not an overwrite, OOB access, type confusion, or lifetime corruption primitive.
* Concrete repeated release/refcount not awarded. The changed call is unlock versus unlock_and_resume, not a second put/free/release on the same potentially dangling object.
* Remote reachability not awarded. The trigger is a local md control-plane write, not packet or network input.
* Local unprivileged trigger not awarded. The supplied evidence does not show that an ordinary user can write the md attribute.
* C/I impact not awarded. The demonstrated consequence is blocked I/O, not confidentiality loss or unauthorized modification.
* Extra Availability not awarded. The blocked I/O condition is already counted as the availability signal.

3. Reachability analysis

The vulnerable path is backlog_store() in drivers/md/md-bitmap.c, which is reached through md device configuration rather than ordinary file I/O or network traffic. The relevant operation changes md bitmap backlog behavior and is normally exposed through privileged md/sysfs control paths.

The complete trigger appears to require administrative control over the md device. No evidence shows that the operation is namespace-scoped or available to an attacker-created user namespace. There is no indication of a network path, special race window, or special hardware requirement beyond having an md array with no write-mostly device while attempting to set backlog.

HostAdminRequired is YES because the complete operation is an md storage administration action. NamespaceScopedPrivilege is NO because md array management is not shown to be delegated through attacker-controlled namespaces.

4. Primitive and severity interpretation

The exact primitive is an error-path state mismatch: the array is suspended before validation, and the failure path previously unlocked mddev without resuming the array. This leaves active md state in a suspended condition and can block later I/O.

This is not an active structured UAF, fixed stale storage UAF, RCU lifetime bug, repeated refcount mutation, or memory corruption issue. The demonstrated consequence is denial of service for the affected md array. The plausible worst case is operational storage unavailability until administrative recovery, not privilege escalation or kernel memory compromise.

PrimitiveClass is NONE because no meaningful corruption, ownership violation, authorization bypass, or lifetime primitive is established. ImportantCandidate is NO because the issue is a host-admin-triggered md control-plane DoS with no unresolved exploitation leverage beyond blocked I/O. AutoDowngradeAllowed is YES because automatic downgrade would not discard a concrete memory-corruption or security-boundary primitive.

5. One-sentence report phrase

md/bitmap backlog_store() could leave an md array suspended on an error path when no write-mostly device exists, causing subsequent I/O to the affected array to remain blocked until administrative recovery.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: this is a privileged local md control-plane error-path DoS with no UAF, no memory corruption, no authorization bypass, no network reachability, and no plausible privilege-escalation primitive in the supplied patch.

7. Call-site confidence

Call-site confidence: high

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

Patch: md/bitmap: resume array on backlog_store() error path [ Upstream
Commit: 03aad318f0a1f039dddf98739e705fdca3bf0d86
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=03aad318f0a1f039dddf98739e705fdca3bf0d86

Changed files:
  drivers/md/md-bitmap.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=03aad318f0a1f039dddf98739e705fdca3bf0d86

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

The original Linux kernel CVE announcement for CVE-2026-90390 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90390

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:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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).