[CVE-2026-89440][MODERATE 7.0] mmc: via-sdmmc: stop card-detect handling on probe failure

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

CVE: CVE-2026-89440
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: mmc: via-sdmmc: stop card-detect handling on probe failure
Commit: efe7f25dd27e35063477b4b0e7eed3675669fd99
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=efe7f25dd27e35063477b4b0e7eed3675669fd99
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89440
Analysis date: Sat, 12 Sep 2026 00:06:58 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
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
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The original Linux kernel CVE announcement for CVE-2026-89440 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89440

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 7.0
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
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CVE-2026-89440	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89440 CHECK WITH IMPACT FROM ORIG NN LOW	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-416;CWE-459;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'via-sdmmc can leave the SD card detect IRQ registered when mmc_add_host fails during probe. After the probe error path releases the host and unmaps MMIO, a later card detect interrupt or queued carddet_work can still dereference sdhost and its MMIO base, creating a use-after-free and stale MMIO access in kernel context. For the CVSS the PR:L is used for the paranoid score because a delegated device management context, reduced capability root, or service account with driver bind and device reset control may be enough in some deployments, although full administrative control is more typical. The issue is not network reachable and requires the affected VIA SD/MMC controller plus a probe failure window. Impact is at least local denial of service via kernel crash. In the paranoid view, the freed object is later used by an interrupt handler and workqueue, so confidentiality and integrity impact are kept high enough for manual review rather than treating it as a pure crash only.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	YES	ERRORPATH UAF DMAorINTERRUPT HARDWARE LINUS KPANIC 	YES	NO	checked

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

ActionableScore=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 4
* Raw paranoid score: 3
* Paranoid score: 4
* Applied floor/cap: Real UAF floor 4 applied because the IRQ/workqueue path can use `sdhost` after host teardown, and host-admin-equivalent triggering is not positively established. No floor 5 applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Positive signals:

* +2 Real UAF / active lifetime violation: `request_irq()` registers the card-detect interrupt, but on `mmc_add_host()` failure the old error path went directly to unmap/release without freeing the IRQ or cancelling `carddet_work`. The IRQ handler and work item can therefore run after the host object lifetime has ended.
* +1 Reliable kernel crash / strong DoS: `via_sdc_isr()` dereferences `sdhost` and MMIO state, and `via_sdc_card_detect()` reaches the freed object via `container_of()`. A kernel fault or crash is a realistic consequence.

Negative signals:

* No -2 host-admin penalty: host-admin-equivalent privilege is not positively established by the supplied input. Deliberate reproduction may require driver/device management, but the evidence does not fully resolve the complete trigger boundary.
* No -1 race penalty: this is primarily an ordered probe-failure cleanup bug plus later asynchronous IRQ/work execution, not a narrow attacker-controlled race.
* No hardware rarity penalty applied: the VIA SD/MMC controller is hardware-specific, but the input does not establish that the required hardware is rare enough or physical-only enough to justify a scoring reduction under the strict evidence rules.

Non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality and integrity impact not awarded. The stale use can crash, but no disclosure, controlled replacement, callback control, or useful write primitive is established.
* Structured stale-object leverage not awarded because the stale object is a fixed driver context and the demonstrated stale use is IRQ/workqueue dereference after failed probe cleanup.
* Weak LPE not awarded merely because the bug is a UAF.
* Concrete repeated release/refcount signal not awarded. The patch does not show a first lifetime release followed by a second `put`/`release`/refcount mutation on the exact same dangling reference.
* Extra Availability not awarded because the same crash/DoS is already counted once.
* Remote reachability not established.

Repeated release/refcount checklist:

* First release can end lifetime: not established as a repeated-release pattern.
* Exact same reference survives to a second lifetime mutation: not established.
* Second operation is a real lifetime/refcount mutation: no.
* +1 Concrete repeated release/refcount awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no.

3. Reachability analysis

The vulnerable path is reached when the VIA SD/MMC PCI driver probe registers and enables the SD card-detect interrupt, then `mmc_add_host()` fails. After that failure, a later card-detect interrupt or queued `carddet_work` can run against the torn-down host state.

Ordinary unprivileged local triggering is not established. A reliable deliberate trigger likely requires some combination of affected hardware, probe failure conditions, and possibly driver bind/unbind, reset, module, or fault-injection control. Those operations are often administrative, but the supplied evidence does not prove that host-admin-equivalent privilege is required in every complete trigger path. Therefore `HostAdminRequired=UNKNOWN`.

This is not network reachable. It is not namespace-scoped. No evidence shows that an attacker-created user or network namespace can instantiate the PCI device, drive the full probe failure, and trigger the IRQ/work path. Prior host setup is likely in practice because the affected hardware and driver must exist, but the scoring does not subtract for unsupported restrictive deployment assumptions.

Race repeatability is limited by the need for a probe failure and later asynchronous IRQ/work execution. However, the main bug is missing cleanup in a deterministic error path, not a narrow timing race.

4. Primitive and severity interpretation

The exact primitive is a post-lifetime use of the `sdhost` driver context by an interrupt handler and a workqueue item after probe failure cleanup failed to unregister/cancel them.

This is an active structured object in the sense that `sdhost` contains MMIO pointers and work state, but the stale storage is effectively a fixed driver context tied to device probe teardown. The demonstrated stale operations are dereference, MMIO-base use, and workqueue execution after teardown. The evidence supports a real Class B lifetime bug, but not a Class A strong corruption primitive.

This is closer to an asynchronous cleanup/probe-failure UAF than to a controlled reclaim or repeated refcount corruption case. No concrete second release/refcount mutation exists. The first lifetime operation and the second stale operation are not a repeated `put` or refcount mutation pair.

Demonstrated consequence: local kernel crash or host DoS.

Speculative consequence: stronger exploitation through heap reuse is theoretically possible for many UAFs, but the supplied patch does not establish attacker-controlled reclaim, replacement object shaping, callback use, arbitrary read/write, or privilege escalation.

`ImportantCandidate=NO` because the evidence shows a constrained driver lifetime UAF with crash-oriented behavior and no meaningful unresolved exploitation leverage beyond the ordinary UAF. `AutoDowngradeAllowed=YES` because this fits the constrained Class B cleanup/asynchronous stale-object category: real UAF, but no repeated lifetime mutation, no controlled reclaim, no boundary bypass, and no C/I primitive.

Likely operational severity: borderline Moderate, worth manual review because it is a real kernel UAF, but not a strong Important candidate from the supplied evidence alone.

5. One-sentence report phrase

A via-sdmmc probe failure can leave the card detect IRQ and carddet_work active after host teardown, allowing later post-lifetime sdhost dereferences and stale MMIO access that can crash the kernel.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the bug is a real UAF in an IRQ/workqueue lifetime path, but the demonstrated impact is crash/DoS and the patch does not establish controlled reclaim, repeated refcount mutation, authorization bypass, or privilege escalation.

7. Call-site confidence

Call-site confidence: high

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

Patch: mmc: via-sdmmc: stop card-detect handling on probe failure
Commit: efe7f25dd27e35063477b4b0e7eed3675669fd99
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=efe7f25dd27e35063477b4b0e7eed3675669fd99

Commit description:

request_irq() registers the SD card-detect interrupt and the probe enables
it before mmc_add_host() runs. If mmc_add_host() fails, the error path only
unmaps the registers and returns: the interrupt stays registered, so the
handler keeps running against the host once it is freed. via_sdc_isr()
dereferences sdhost and its MMIO base and schedules carddet_work, which
via_sdc_card_detect() also runs against freed memory through its
container_of() dereference.

Add a probe-error path that disables and frees the interrupt and cancels
carddet_work before unmapping. carddet_work can re-enable the device
interrupt via via_reset_pcictrl(), which restores PCIINTCTRL, so mask it
again after cancelling the work.

This issue was found by an in-house static analysis tool and confirmed by
manual code review.

Fixes: e4e46fb ("mmc: via-sdmmc: fix return value check of mmc_add_host()")
Cc: stable@vger.kernel.org
Assisted-by: Codex:gpt-5.6
Signed-off-by: Fan Wu <fanwu01@zju.edu.cn>
Signed-off-by: Ulf Hansson <ulfh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/mmc/host/via-sdmmc.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=efe7f25dd27e35063477b4b0e7eed3675669fd99

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

The original Linux kernel CVE announcement for CVE-2026-89440 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89440

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:H/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: unknown
  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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).