[CVE-2026-90081][MODERATE REGULAR] net/rds: use wq_has_sleeper() in rds_cong_map_updated() [ Upstream

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

CVE: CVE-2026-90081
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/rds: use wq_has_sleeper() in rds_cong_map_updated() [ Upstream
Commit: 2a809d7896dbf18e1ecfbdd930f71c9fc298b16d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2a809d7896dbf18e1ecfbdd930f71c9fc298b16d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90081
Analysis date: Fri, 18 Sep 2026 09:20:45 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-90081 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90081

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 REGULAR
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
======================================================================

CVE-2026-90081	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90081 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';CWE-362;CWE-667;*CWE-833;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '3.1';DESCR 'A memory ordering race in RDS congestion handling can cause the updater to observe an empty wait queue while a sender or poll waiter still observes the old congestion state. The resulting lost wakeup can leave rds_cong_wait blocked without a timeout until another congestion update or a signal arrives, while poll can miss the map update notification. For the CVSS the PR:N value is used for the paranoid network scenario because a peer able to send RDS congestion updates does not need a user account on the target, although access to the configured RDS cluster or storage fabric is required. AV:A and AC:H reflect the restricted peer network and the timing dependent race. Impact is limited to availability of affected RDS operations or applications, with no supported memory corruption, information disclosure, kernel privilege escalation, or system wide crash.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 2)  SKIP CVE-2026-90081 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DANGER IMPROVEONLY LINUS TEST  DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
ActionableScoreLower=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +1 Availability impact realistic. A lost wakeup can indefinitely block an RDS sender until another congestion update or signal arrives, and poll can miss the notification.

Paranoid additional signal:

* +2 Direct network influence. An RDS peer can supply the congestion-map update participating in the race. This is defensible for an attacker with access to the configured RDS fabric, but is deployment-dependent and therefore omitted from the conservative score.

Non-awarded signals:

* No UAF, stale post-lifetime object, OOB access, write primitive, or other kernel memory corruption is established.
* No reliable kernel crash or host-wide DoS is demonstrated.
* No confidentiality, integrity, authorization-bypass, or privilege-escalation signal is established.
* No extra availability point was awarded because only individual RDS operations or applications are shown to stall.
* No race penalty was applied. The ordering window exists, but the evidence does not establish that it is exceptionally narrow, one-shot, or difficult to repeat.
* No common-networking-path point was awarded because RDS congestion handling is not a general TCP/IP or common packet-processing path.
* No repeated release or refcount operation exists. The UAF floors and repeated-lifetime rules do not apply.

3. Reachability analysis

The local manifestation requires an RDS sender or poll waiter to register while a congestion-map update occurs. The update can arrive through `rds_tcp_cong_recv()` or `rds_ib_cong_recv()`, so a peer on an existing RDS fabric can influence the relevant updater path without host-administrator access on the victim.

The complete hostile-peer trigger remains deployment-dependent because the supplied evidence does not establish peer admission, authentication, or whether an arbitrary adjacent host can inject accepted RDS congestion updates. Existing RDS deployment and connectivity are prerequisites, but no special hardware is mandatory because the TCP path is affected as well as the InfiniBand path.

No namespace evidence establishes that the complete operation is available through attacker-created user or network namespaces. `NamespaceScopedPrivilege` is therefore UNKNOWN. The race is timing-dependent, but updates and waits can recur during ordinary RDS operation, so a hard-race deduction is not justified.

4. Primitive and severity interpretation

The exact primitive is a memory-ordering failure producing a lost wakeup. `atomic_inc()` and the plain `waitqueue_active()` load do not provide the full barrier needed to order congestion-state updates against waiter registration.

This is not a lifetime violation and does not involve stale storage. There is no cleanup-only UAF, repeated release, refcount mutation, controlled reclaim, or active structured-object corruption. The demonstrated consequence is an indefinitely blocked interruptible wait or a missed poll notification, recoverable through a later congestion update or signal.

The issue is CLASS_C because it produces constrained availability failure without an independently useful corruption primitive. Stronger consequences such as kernel compromise, information disclosure, privilege escalation, or system-wide failure are unsupported.

`ImportantCandidate=NO` because no Important-preserving primitive exists. `AutoDowngradeAllowed=YES` because the established impact is a constrained lost-wakeup DoS and no unresolved memory-corruption or security-boundary primitive would be discarded.

5. One-sentence report phrase

A memory-ordering race in RDS congestion handling can lose a wakeup and leave a sender or poll waiter blocked, with network influence possible from a peer on the configured RDS fabric but no demonstrated memory corruption or host-wide failure.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether untrusted peers can submit accepted congestion updates in the evaluated RDS deployment and whether application-level stalls can become broader service outages.

7. Call-site confidence

Call-site confidence: high

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

Patch: net/rds: use wq_has_sleeper() in rds_cong_map_updated() [ Upstream
Commit: 2a809d7896dbf18e1ecfbdd930f71c9fc298b16d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2a809d7896dbf18e1ecfbdd930f71c9fc298b16d

Changed files:
  include/linux/wait.h
  net/rds/cong.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=2a809d7896dbf18e1ecfbdd930f71c9fc298b16d

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

The original Linux kernel CVE announcement for CVE-2026-90081 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90081

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:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS score: 3.1

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: 1
  Paranoid ActionableScore: 3

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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR

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).