[CVE-2026-90108][MODERATE REGULAR] net/smc: free stashed qentry before overwrite in REQ_ADD_LINK to ADD_LINK transition [ Upstream

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

CVE: CVE-2026-90108
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/smc: free stashed qentry before overwrite in REQ_ADD_LINK to ADD_LINK transition [ Upstream
Commit: 7dd55348c0d9399a9448847819e9f3904ae507ad
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7dd55348c0d9399a9448847819e9f3904ae507ad
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90108
Analysis date: Thu, 17 Sep 2026 14:40:51 -0400
ActionableScore: 4
ActionableScore lower bound: 3
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-2026-90108 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90108

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-2026-90108	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90108 CHECK WITH IMPACT FROM ORIG NN LOW	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:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'An SMC LLC flow can leak a queued LLC entry when a CONFIRM_LINK or ADD_LINK_CONT message is stashed during REQ_ADD_LINK state and a later ADD_LINK message overwrites flow qentry. The lost object has no consumer in this state, so the primitive is a memory leak rather than a demonstrated use after free or arbitrary write. For the CVSS the PR:N is used because a reachable SMC peer may trigger the protocol sequence without local privileges on the victim when SMC R is enabled. The issue is network adjacent rather than ordinary Internet reachable because SMC R and LLC processing are normally used in RDMA or data center environments. Impact is denial of service through resource exhaustion, with no concrete confidentiality or integrity primitive shown by the code path.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	LEAK IMPROVEONLY LINUS  INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3. No floor or cap applied.
* Raw paranoid score: 4
* Paranoid score: 4. No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Positive signals:

* +2 Remote or network-adjacent trigger. The vulnerable operation is reached by SMC LLC protocol messages from a peer, specifically CONFIRM_LINK or ADD_LINK_CONT followed by ADD_LINK in the relevant flow state.
* +1 Concrete persistent kernel resource/reference leak. The old stashed qentry allocation is overwritten and becomes unreachable without normal cleanup.
* Paranoid only +1 Sustained resource exhaustion concern. If a reachable SMC peer can repeat the protocol sequence, the leaked kmalloc objects may accumulate toward memory pressure or DoS.

Non-awarded signals:

* Real UAF not awarded. The old qentry is leaked, not freed and later used.
* Concrete repeated release/refcount not awarded. There is no first release that may end lifetime followed by a second lifetime mutation on the same dangling reference.
* Strong exploitation leverage not awarded. No controlled reclaim, arbitrary write, callback control, type confusion, or refcount takeover is established.
* Confidentiality and integrity not awarded. The primitive is a lost allocation without a disclosure or unauthorized modification path.
* Reliable kernel crash not awarded conservatively. The patch supports memory leak/resource exhaustion, not immediate panic.
* Race/timing penalty not applied. The issue is an ordered protocol/state transition, not an established hard race.
* Rare hardware penalty not applied. SMC-R/RDMA deployment limits exposure, but that alone is not enough for a concrete negative score.

3. Reachability analysis

The likely attacker is a reachable SMC peer that can influence LLC message ordering during SMC-Rv2 link handling. No local host-admin privilege is required on the victim once the SMC path is exposed and an SMC link group can be reached. The vector is better treated as network-adjacent rather than ordinary Internet-wide remote exposure, because SMC-R and LLC processing are normally used in RDMA or data-center environments.

Namespace-scoped privilege is not the relevant model here. The supplied evidence does not depend on a container or namespace capability path. Prior host setup is implicitly required in the operational sense that SMC-R must be enabled and usable, but that is deployment exposure rather than an attacker-held privilege. No special race repeatability penalty is supported because the bug follows from a valid sequence of protocol state transitions.

4. Primitive and severity interpretation

The exact primitive is a persistent kernel memory leak of a stashed `struct smc_llc_qentry`. It occurs when `flow->qentry` already contains a queued entry in `SMC_LLC_FLOW_REQ_ADD_LINK` state and the later ADD_LINK transition overwrites it via `smc_llc_flow_qentry_set()` without first deleting the old entry.

This is not an active structured UAF and not fixed stale storage. It is a lost ownership/reference cleanup bug. The demonstrated consequence is resource exhaustion DoS if the sequence can be repeated. The speculative consequence is host memory pressure, but no memory corruption or privilege escalation primitive is established.

PrimitiveClass is CLASS_C because the behavior is primarily DoS/resource leak without an independently useful corruption primitive. ImportantCandidate is NO because there is no UAF, no repeated lifetime mutation, no authorization bypass, and no concrete C/I impact. AutoDowngradeAllowed is YES because this is a constrained resource leak despite network-adjacent reachability.

5. One-sentence report phrase

An SMC LLC state transition can overwrite a stashed qentry without freeing it, allowing a reachable SMC peer to cause a repeatable kernel memory leak and potential denial of service in SMC-R deployments.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is in a network-adjacent protocol path and may be repeatable for resource exhaustion, but the established primitive is only a memory leak with no UAF, corruption, or privilege-escalation evidence.

7. Call-site confidence

Call-site confidence: high

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

Patch: net/smc: free stashed qentry before overwrite in REQ_ADD_LINK to ADD_LINK transition [ Upstream
Commit: 7dd55348c0d9399a9448847819e9f3904ae507ad
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7dd55348c0d9399a9448847819e9f3904ae507ad

Changed files:
  net/smc/smc_llc.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=7dd55348c0d9399a9448847819e9f3904ae507ad

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

The original Linux kernel CVE announcement for CVE-2026-90108 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90108

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:A/AC:H/PR:N/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:H
  The Best / paranoid CVSS score: 5.3

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: 3
  Paranoid ActionableScore: 4

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).