[CVE-2026-98211][MODERATE REGULAR] mmc: mmci: Fix use-after-free in busy-timeout work

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

CVE: CVE-2026-98211
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mmc: mmci: Fix use-after-free in busy-timeout work
Commit: af6fbf72e899932f330c4e5d0b84d985c922c633
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af6fbf72e899932f330c4e5d0b84d985c922c633
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98211
Analysis date: Fri, 09 Oct 2026 05:20:55 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
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-2026-98211 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98211

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-2026-98211	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98211 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: 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:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free can occur when ux500_busy_complete queues ux500_busy_timeout_work for an R1b command and mmci_remove releases the devm allocated mmci_host without first draining that work. The delayed callback may later dereference memory that has already been freed and possibly reused, resulting at least in a kernel crash or system denial of service. For the CVSS the PR:L in the paranoid score reflects a local user who can generate relevant MMC I/O while device removal is caused by a separate lifecycle or management event. Reliable direct removal normally requires administrative privileges, so the base score uses PR:H. AC:H applies because successful triggering depends on the timing between command completion, queued delayed work, controller removal, and object release. The issue is not network reachable and requires an affected MMCI controller with busy detection support. Because this is a concrete kernel use-after-free, reuse of the released allocation may theoretically permit confidentiality or integrity impact in addition to availability impact, although a practical privilege escalation primitive is not established.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	MAYBE	UAF  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

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

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +2 Real UAF. A queued `ux500_busy_timeout_work` can dereference its containing, devm-released `mmci_host` after `mmci_remove()` returns.
* +1 Reliable kernel crash or strong DoS. Executing delayed work through a freed driver context can realistically cause an Oops or panic.
* -2 Host-admin-equivalent trigger. The complete controllable sequence requires removing or unbinding the MMCI controller, which is a host device-management operation. Card removal alone does not remove the host controller.
* B5-R was not awarded. There is no retry-accumulated heap OOB write, accumulated index, or later consumption of an OOB-corrupted descriptor.
* No hard-race penalty was applied. Work must overlap teardown, but the evidence does not establish that the timing is exceptionally narrow or unreliable.
* No rare-hardware penalty was applied. An MMCI variant with busy detection is required, but the supplied evidence does not establish sufficiently rare or physical-only hardware.
* Controlled reclaim, attacker-shaped replacement contents, arbitrary read/write, callbacks through reclaimed data, disclosure, and privilege escalation are not demonstrated.
* Structured stale-object leverage was not awarded. This is a fixed asynchronous driver context used during teardown, with no evidence of useful post-reuse field consumption.
* No extra Availability point was awarded because it would duplicate the same possible kernel crash.
* No C/I or weak-LPE point was awarded merely because freed storage could theoretically be reused.
* There is no repeated release or refcount operation. The stale callback dereferences the object but does not perform a demonstrated second lifetime mutation.
* FLOOR 5 does not apply because this is a host-admin-gated, fixed asynchronous teardown UAF without repeated release or meaningful reuse leverage.

3. Reachability analysis

The vulnerable sequence requires an R1b command to queue the timeout work and subsequent removal of the MMCI host before that work is drained. Users with access to the MMC block device may influence I/O, but the supplied evidence does not show that they can invoke `mmci_remove()`.

Driver unbind, module removal, and equivalent AMBA device teardown are host device-management operations and are not user-namespace scoped. No network or remote trigger exists. No namespace capability provides the complete trigger.

An affected MMCI controller with `variant->busy_detect` and software busy-timeout support is required. The timing involves queued work or an in-progress IRQ overlapping controller removal, but a host administrator can deliberately create this state by issuing I/O and unbinding the driver.

4. Primitive and severity interpretation

The exact primitive is an asynchronous post-teardown use-after-free of the devm-allocated `mmci_host`. It is best treated as fixed stale driver storage rather than an attacker-replaceable active object.

This is CLASS_B because a genuine lifetime violation exists. The demonstrated consequence is a possible kernel crash. More serious memory corruption is theoretically possible if the allocation is reused, but the patch provides no controlled reclaim, attacker-controlled replacement, sensitive callback consumption, repeated refcount mutation, or directed corruption.

This is ordinary stale asynchronous cleanup use, not a second release or refcount mutation through a dangling reference. ImportantCandidate is therefore NO. AutoDowngradeAllowed is YES because meaningful exploitation leverage beyond crash is not established and the complete controllable trigger requires host administration.

Likely operational severity is Low to Moderate despite the genuine UAF.

5. One-sentence report phrase

A queued MMCI busy-timeout callback can dereference a devm-released host after privileged controller removal, creating a constrained teardown use-after-free whose demonstrated practical impact is kernel crash or denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether any affected platform can invoke the complete removal sequence below host-admin privilege or whether the delayed callback performs deeper stale structured access than is visible in the supplied patch.

7. Call-site confidence

Call-site confidence: medium

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

Patch: mmc: mmci: Fix use-after-free in busy-timeout work
Commit: af6fbf72e899932f330c4e5d0b84d985c922c633
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=af6fbf72e899932f330c4e5d0b84d985c922c633

Commit description:

ux500_busy_complete() can queue ux500_busy_timeout_work for an R1b
command, but mmci_remove() never cancels it. The work can subsequently
dereference the devm-allocated mmci_host after it has been released.

Mask the controller interrupts and disable the delayed work during
removal. This drains any queued instance and stops an IRQ handler that
is still in progress from queueing the work again once it has been
disabled.

This issue was found by an in-house static analysis tool.

Fixes: b1a6659 ("mmc: mmci: Add support for SW busy-end timeouts")
Cc: stable@vger.kernel.org # v6.10+
Assisted-by: Codex:gpt-5.6
Signed-off-by: Fan Wu <fanwu01@zju.edu.cn>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Ulf Hansson <ulfh@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/mmc/host/mmci.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=af6fbf72e899932f330c4e5d0b84d985c922c633

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

The original Linux kernel CVE announcement for CVE-2026-98211 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98211

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: 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).