[CVE-2026-98024][MODERATE REGULAR] s390/ism: folio_put() after error [ Upstream

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

CVE: CVE-2026-98024
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: s390/ism: folio_put() after error [ Upstream
Commit: 890e2ef726904d1d8328e4b9f5090eeb8761b9d1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=890e2ef726904d1d8328e4b9f5090eeb8761b9d1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98024
Analysis date: Fri, 25 Sep 2026 11:42:00 -0400
ActionableScore: 1
ActionableScore lower bound: 0
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-2026-98024 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98024

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: NO

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-98024	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98024 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:H/I:H/A:H';CWE-590;CWE-763;*CWE-787;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'An incorrect free in the s390 ISM DMB allocation error path occurs because memory allocated with folio_alloc is released with kfree. If the error path is reached after DMB allocation, the invalid free can corrupt slab allocator state and cause a kernel crash. For the CVSS the PR:L is used because an attacker needs local access to exercise an ISM related workload or networking path. The issue is not shown to be directly network reachable by the patch. The normal impact is local denial of service. The invalid free is also a concrete memory corruption condition, so the paranoid score uses C:H I:H A:H and requires manual validation of reachability and exploitability on affected s390 ISM systems.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	DANGER UAF NETWORK LINUS MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	YES	NO	checked

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

ActionableScore=1
ActionableScoreLower=0
PrimitiveClass=CLASS_B
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::

The conservative score identifies a concrete invalid-free corruption condition but does not count a demonstrated attacker trigger or demonstrated crash. The paranoid score adds one point for a realistic kernel-failure consequence because passing folio-backed memory to kfree can corrupt or invalidly manipulate slab allocator state.

2. Signal breakdown

* +1 Concrete invalid-free kernel-corruption primitive in paranoid analysis. `folio_alloc()` returns folio-backed page memory, while the error path calls `kfree(dmb->cpu_addr)`. The commit explicitly states that this can cause slab allocator corruption.
* No separate strong corruption or Class A score. The patch does not establish attacker control of the address passed to kfree, allocator placement, freed-page contents, a target object, or a subsequent controlled allocation.
* No local-unprivileged-trigger point. The supplied diff does not establish that an ordinary local user can drive the complete ISM DMB allocation failure path.
* No remote-reachability point. The affected operation is an internal s390 ISM driver allocation error path. No direct network packet path is shown.
* No UAF base signal. The `dmb->cpu_addr = NULL` additions prevent a possible future accidental stale-pointer use, but the supplied context does not show an existing later dereference or stale use after the erroneous free.
* No concrete repeated release or refcount signal. The patch contains one erroneous release operation on the error path. It does not establish a first lifetime-ending release followed by a second release of the same surviving reference.
* No confidentiality or integrity impact points. Slab corruption is concrete, but the patch does not establish a disclosure path, controlled write, protected-object modification, controlled reclaim, or privilege escalation.
* No strong DoS point in the conservative score. The commit identifies allocator corruption but supplies no crash trace or demonstrated reliable host panic.
* The s390 ISM path is specialized and requires an affected IBM Z ISM-capable environment. This limits practical exposure, but no separate numeric hardware penalty was applied because the supplied material does not establish that an attacker needs physical access or that the error path is otherwise impossible to reach remotely or locally.

3. Reachability analysis

The vulnerable path is reached only after `ism_alloc_dmb()` successfully allocates a folio-backed DMB buffer and subsequently enters its `out_free` error path. The supplied patch does not show the caller, the exact failing operation, or which actor can induce that failure.

ISM is an IBM s390 networking and shared-memory subsystem associated with specialized platform hardware. Affected deployment requires ISM-capable s390 hardware and an enabled driver path. This is not sufficient to conclude that host-admin privilege is required, because the complete trigger chain is not visible. It is also insufficient to conclude that an ordinary local user can trigger the failure.

No namespace-scoped capability path is shown. No evidence establishes that user namespaces, network namespaces, delegated capabilities, or container-root privileges can create the required ISM device state or induce the relevant allocation error. Therefore, `HostAdminRequired=UNKNOWN` and `NamespaceScopedPrivilege=UNKNOWN` are appropriate.

No direct remote trigger is established. Although ISM is networking-related, the defect is in a device/DMA buffer allocation error cleanup path, and the supplied evidence does not show that untrusted network traffic can cause the required error after allocation.

4. Primitive and severity interpretation

The exact primitive is an invalid deallocation: folio-backed memory returned by `folio_alloc()` is passed to `kfree()` on an allocation-error unwind path. This is a concrete kernel memory-management error because `kfree()` expects a compatible slab/kmalloc allocation and may corrupt or incorrectly process slab allocator state.

This is not a demonstrated real UAF. The patch clears `dmb->cpu_addr` after `folio_put()` to prevent future accidental use of the released address, but no visible caller or later operation proves that a stale pointer is actually dereferenced in the vulnerable version.

The affected storage is fixed driver/DMA-related buffer storage, not an established attacker-reclaimed active structured object. No controlled replacement, post-free field consumption, callback dispatch, arbitrary write, refcount takeover, or security-boundary bypass is established. The demonstrated consequence is allocator-state corruption and a plausible kernel crash or DoS. Privilege escalation remains speculative and is not scored.

This is therefore `CLASS_B`, because a real potentially exploitable kernel-corruption primitive exists, but the patch does not demonstrate useful attacker control beyond the invalid free. `ImportantCandidate=NO` because the available evidence supports neither controlled corruption nor meaningful unresolved post-lifetime leverage. `AutoDowngradeAllowed=YES` because this is not a demonstrated UAF, repeated release, authorization bypass, controlled corruption, or attacker-reachable security-boundary primitive.

Likely operational severity is low on most systems because the code is limited to affected s390 ISM deployments and requires an error path after DMB allocation. Manual inspection remains appropriate for deployments that actively use ISM and can identify whether unprivileged or network-facing workloads can induce this path.

5. One-sentence report phrase

An invalid free in the s390 ISM DMB allocation error path releases folio-backed memory with kfree, which can corrupt slab allocator state and potentially cause a kernel crash, but attacker reachability and exploit control are not established.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Verify the `ism_alloc_dmb()` callers and error conditions to determine whether an unprivileged local workload, a peer-driven ISM or SMC-D connection, or device/firmware behavior can reliably reach `out_free` after `folio_alloc()` succeeds.

7. Call-site confidence

Call-site confidence: low

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

Patch: s390/ism: folio_put() after error [ Upstream
Commit: 890e2ef726904d1d8328e4b9f5090eeb8761b9d1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=890e2ef726904d1d8328e4b9f5090eeb8761b9d1

Changed files:
  drivers/s390/net/ism_drv.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=890e2ef726904d1d8328e4b9f5090eeb8761b9d1

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

The original Linux kernel CVE announcement for CVE-2026-98024 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98024

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:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 0
  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: 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).