[CVE-2026-99035][MODERATE 7.0] mmc: mtk-sd: Cancel request timeout work on remove

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

CVE: CVE-2026-99035
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: mmc: mtk-sd: Cancel request timeout work on remove
Commit: 9e799f25c420e759641eb25102967ea091fc758f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9e799f25c420e759641eb25102967ea091fc758f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99035
Analysis date: Mon, 26 Oct 2026 20:26:43 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
Platform-driver unbind can race an executing MMC timeout callback, causing post-removal accesses to freed host state and a credible kernel crash.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-99035 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99035

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: NO

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-2026-99035	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99035 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE_KPANIC RESULT=SAME V39_AEGIS_ONE_STEP_UP=MODERATE->MODERATE_KPANIC (final reconciliation agrees; DECISION: both MODERATE_KPANIC)	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-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A removal race in the mtk sd host driver allows an already running req_timeout callback to continue after the managed mmc_host storage and related resources can be freed. KASAN confirmed use after free accesses in msdc_request_done and msdc_recheck_sdio_irq during three unbind tests. A kernel crash is credible, and allocator reuse makes memory corruption or privilege escalation plausible for worst case review, although no controlled arbitrary write or information disclosure primitive is established. For the CVSS the PR:H base value reflects that driver unbind normally requires administrative device control. For the CVSS the PR:L paranoid value reflects deployments where device lifecycle operations are delegated to a less privileged service or container. Reliable triggering requires local access, an active request, driver removal, and winning the callback teardown race. The issue is not directly network reachable. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE to MODERATE_KPANIC because the CVSS score, vector or bug class threshold rule was applied. ActionableScore thresholds stage MODERATE_KPANIC to MODERATE because the ActionableScore threshold rule was applied. final reconciliation stage MODERATE to MODERATE_KPANIC because the cross model evidence reconciliation rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS and DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 1.9 and ActionableScore 1 with primitive class CLASS_B and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. Cross model aggregation changed the production result under an enabled evidence gated merge rule. The final reported impact is MODERATE_KPANIC.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)	MAYBE	UAF IMPROVEONLY LINUS TEST  INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=YES
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 1.
* Conservative score: 1; no floor or cap applies.
* Raw paranoid score: 2.
* Paranoid score: 2; reflects the supplied possibility of delegated device-lifecycle control.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +2 Real UAF: an already-running `req_timeout` callback continues accessing `host` after removal can free the managed `mmc_host`.
* +1 Reliable kernel crash/DoS: KASAN reproduced post-free accesses in both `msdc_request_done()` and `msdc_recheck_sdio_irq()`.
* Base −2 host-administrator-equivalent prerequisite: the evidenced trigger requires platform-driver unbind/removal of a host device.
* Paranoid −1 instead of −2: the supplied hints identify possible delegation to a less-privileged management service, but do not prove ordinary-user access.
* No race penalty: a race exists, but three unbind tests reproduced it; materially narrow or uncontrollable timing is not established.
* No controlled reclaim, attacker-shaped replacement, arbitrary write, callback control, disclosure, repeated refcount mutation, or separate C/I effect is shown.
* No extra availability point: it would duplicate the same crash.
* B5-R does not apply: no retry-accumulated heap OOB write exists.

3. Reachability analysis

The complete demonstrated sequence requires an active MMC request, a timeout callback already executing, and platform-driver removal. Normal driver unbind is host device-management authority, not a user/net namespace capability. Numeric UID 0 specifically is not established because capability-bearing management processes may perform removal. No remote path, ordinary local-user path, special namespace path, or prior delegated interface is proven. Hardware is required, but the evidence does not establish rare or physical-attacker-only hardware.

4. Primitive and severity reading

This is a real asynchronous teardown UAF involving fixed driver-owned host/context storage. The stale callback performs further structured accesses after removal, but no attacker-controlled replacement or useful post-reuse operation is demonstrated. The shown effect is KASAN-detected invalid access with credible kernel crash; allocator-reuse exploitation remains theoretical. It is constrained CLASS_B, not CLASS_A. ImportantCandidate is NO and auto-downgrade is allowed because the demonstrated full trigger is host-admin device removal and no material non-crash primitive remains unresolved.

5. One-sentence report phrase

Platform-driver unbind can race an executing MMC timeout callback, causing post-removal accesses to freed host state and a credible kernel crash.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm whether the affected product delegates MMC driver unbind or equivalent lifecycle control below host administrator authority.

7. Call-site confidence

Call-site confidence: high

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

Patch: mmc: mtk-sd: Cancel request timeout work on remove
Commit: 9e799f25c420e759641eb25102967ea091fc758f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9e799f25c420e759641eb25102967ea091fc758f

Commit description:

The driver queues req_timeout while a request is active.
msdc_request_done() uses cancel_delayed_work(), which does not wait for
a timeout callback that has already started.

The timeout callback calls mmc_request_done(), which wakes the request
waiter, and then continues to use host->dev_comp and check the SDIO IRQ.
During unbind, msdc_drv_remove() can return and the managed mmc_host can
be freed before the callback finishes.

KASAN reported use-after-free accesses in msdc_request_done() and
msdc_recheck_sdio_irq() in each of three unbind tests.  The same tests
completed without a kernel diagnostic after this change.

Call cancel_delayed_work_sync() after mmc_remove_host() has stopped new
requests and before the driver releases the host resources.

Fixes: 2084890 ("mmc: mediatek: Add Mediatek MMC driver")
Cc: stable@vger.kernel.org
Assisted-by: Codex:GPT-5
Signed-off-by: Yibo Tan <lhfff@tju.edu.cn>
Signed-off-by: Ulf Hansson <ulfh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/mmc/host/mtk-sd.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=9e799f25c420e759641eb25102967ea091fc758f

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

The original Linux kernel CVE announcement for CVE-2026-99035 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99035

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:L/I:L/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: 1
  Paranoid ActionableScore: 2

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).