[CVE-2026-89442][MODERATE REGULAR] platform/x86: ISST: Validate socket ID in clos_assoc ioctl

[CVE-2026-89442][MODERATE REGULAR] platform/x86: ISST: Validate socket ID in clos_assoc ioctl

[AL-KERNEL]

CVE: CVE-2026-89442
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: platform/x86: ISST: Validate socket ID in clos_assoc ioctl
Commit: 0d90ab5f80e19cddfeb0c9fab47a1f34aa932075
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0d90ab5f80e19cddfeb0c9fab47a1f34aa932075
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89442
Analysis date: Fri, 11 Sep 2026 19:23:27 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
The ISST CLOS_ASSOC ioctl can accept an out of range socket_id or a package without a bound SST instance, leading to an out of bounds pointer dereference or NULL pointer dereference and a local kernel crash.

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

The original Linux kernel CVE announcement for CVE-2026-89442 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89442

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.

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

CVE-2026-89442	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89442 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-193;CWE-125;**CWE-476;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.6';DESCR 'The ISST CLOS_ASSOC ioctl can dereference an invalid SST instance pointer because socket_id equal to topology_max_packages was accepted even though the sst_inst array has only topology_max_packages entries. The same path can also dereference a NULL sst_inst when the selected package has no bound TPMI SST instance. A local caller with access to the ISST device interface can trigger an out-of-bounds pointer read followed by dereference or a NULL pointer dereference, causing a kernel crash. For the CVSS the PR:L is used in the paranoid score because some deployments may expose the device interface to a local service account, container root, or delegated management user rather than only to full host root. The issue is not network reachable and requires local ioctl access on affected Intel SST TPMI systems. Impact is at least denial of service. Worst case may include limited confidentiality or integrity impact because the bug crosses an array boundary and dereferences the resulting pointer, but there is no clear arbitrary write primitive in the patch context.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	WRITE OOB SIMPLEFIX LOG IMPROVEONLY  LOWERED_FROM_HIGH_BASED_ON_NULLPTR DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	YES	NO	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2. No floor or cap applied.
* Raw paranoid score: 3
* Paranoid score: 3. No floor or cap applied.
* Final recommended bucket: **Borderline / manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* +1 Weak / indirect corruption candidate. User supplied `socket_id` can select `isst_common.sst_inst[topology_max_packages()]`, one entry past the allocated array, or select an in range NULL `sst_inst`.
* +1 Reliable kernel crash / strong DoS. The invalid or NULL `sst_inst` is dereferenced through `map_partition_power_domain_id()` and later `power_domain_info` access.

Paranoid additional signal:

* +1 Weak LPE concern. This is not only a plain NULL dereference path. The out of bounds array entry is interpreted as a structured SST instance pointer and passed into further driver logic. This gives enough unresolved object-selection concern to avoid treating it as fully trivial, but not enough for Class A or Important.

Non-awarded signals:

* RealUAF not awarded. No use-after-free or lifetime-after-release path is established.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality not awarded. The OOB read is internal pointer selection and no disclosure path to userspace is shown.
* Integrity not awarded conservatively. No unauthorized write to protected state is shown.
* Remote reachability not established. This is a local ioctl path.
* Strong LPE leverage not awarded. The patch does not show controlled replacement, callback control, credential manipulation, or refcount takeover.
* Extra Availability not awarded. The same crash is already counted once.
* No host-admin penalty applied because host-admin-equivalent access to the ioctl is not positively established from the supplied evidence.
* No hardware rarity penalty applied because driver-specific Intel SST TPMI exposure is a deployment limitation, but the evidence does not prove rare physical-only access as a required attack condition.

## 3. Reachability analysis

The trigger is a local ioctl call into the Intel Speed Select TPMI interface, specifically `isst_if_clos_assoc()`, with attacker controlled `clos_assoc.socket_id`.

The supplied patch does not show the device node permissions or the exact capability check protecting this ioctl. Therefore host-admin-equivalent privilege is not positively established, but ordinary unprivileged reachability is also not positively established.

`HostAdminRequired=UNKNOWN` is used. `NamespaceScopedPrivilege=NO` is used because this is not a namespace-scoped networking or filesystem operation, and no namespace capability path is indicated.

The issue requires affected Intel SST TPMI support and the relevant platform driver/interface to be present. No network trigger is indicated. No race is involved. The bug is a deterministic validation error.

## 4. Primitive and severity interpretation

The exact primitive is an unchecked user-controlled index into `isst_common.sst_inst[]`, combined with a missing NULL check before dereferencing the selected pointer.

This is an invalid object pointer / NULL pointer dereference issue, not a UAF. It is best classified as `CLASS_C` because the demonstrated consequence is a kernel crash or oops and no independently useful corruption primitive is established.

The active object is a structured driver object, but there is no evidence of controlled reclaim, attacker-shaped replacement contents, callback invocation, arbitrary read/write, or security-boundary bypass.

Conservative impact is local DoS. Paranoid interpretation keeps a weak object-selection concern because the OOB entry is consumed as a structured pointer, but this remains below Important-grade without stronger evidence.

`ImportantCandidate=NO` because the patch supports crash and weak invalid pointer interpretation, but not a strong corruption, UAF, authorization bypass, or LPE primitive.

`AutoDowngradeAllowed=YES` because no meaningful unresolved Class A or strong Class B primitive remains. Manual review is still recommended due to the OOB pointer dereference in a kernel ioctl path.

## 5. One-sentence report phrase

The ISST CLOS_ASSOC ioctl can accept an out of range socket_id or a package without a bound SST instance, leading to an out of bounds pointer dereference or NULL pointer dereference and a local kernel crash.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is most likely local DoS, but the one-past-array pointer is consumed as a structured driver object, so a quick human check of ioctl permissions and surrounding field use is appropriate.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: platform/x86: ISST: Validate socket ID in clos_assoc ioctl
Commit: 0d90ab5f80e19cddfeb0c9fab47a1f34aa932075
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0d90ab5f80e19cddfeb0c9fab47a1f34aa932075

Commit description:

isst_if_clos_assoc() validates the user-supplied socket_id with
'socket_id > topology_max_packages()', but isst_common.sst_inst[] is
allocated with topology_max_packages() entries, so the valid index range
is [0, topology_max_packages()).  The '>' comparison lets
socket_id == topology_max_packages() pass and index one entry past the
array.

In addition, isst_common.sst_inst[socket_id] is NULL for an in-range
package that has no bound TPMI SST instance, and the pointer is used
without a NULL check.  Both the out-of-bounds entry and the NULL pointer
are then dereferenced by map_partition_power_domain_id() and the
following power_domain_info access.

Reject socket_id >= topology_max_packages() and a NULL sst_inst, matching
the checks already performed by get_instance().

Fixes: 12a7d2c ("platform/x86: ISST: Add SST-CP support via TPMI")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-5
Signed-off-by: HyeongJun An <sammiee5311@gmail.com>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Link: https://patch.msgid.link/20260807144003.3498972-2-sammiee5311@gmail.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/platform/x86/intel/speed_select_if/isst_tpmi_core.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=0d90ab5f80e19cddfeb0c9fab47a1f34aa932075

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

The original Linux kernel CVE announcement for CVE-2026-89442 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89442

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:L/I:L/A:H
  The Best / paranoid CVSS score: 6.6

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: 2
  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).