[CVE-2026-98749][MODERATE 7.0] tty: serial: max3100: shut down timer before freeing port

[CVE-2026-98749][MODERATE 7.0] tty: serial: max3100: shut down timer before freeing port

[AL-KERNEL]

CVE: CVE-2026-98749
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: tty: serial: max3100: shut down timer before freeing port
Commit: fb668620e3b163962dabe1a674725a07aa44ff4a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fb668620e3b163962dabe1a674725a07aa44ff4a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98749
Analysis date: Mon, 19 Oct 2026 04:39:06 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
A suspend and device-removal race in the MAX3100 serial driver can leave timer, IRQ, or workqueue activity operating on a freed port, causing a local kernel use-after-free and potential crash.

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

The original Linux kernel CVE announcement for CVE-2026-98749 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98749

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
======================================================================

CVE-2026-98749	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98749 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-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in the MAX3100 serial driver can leave the polling timer armed when the SPI device is removed during the suspend window. max3100_remove can then free the port while max3100_timeout still holds a reference to it, allowing the callback to access freed memory and rearm the timer. The IRQ and workqueue teardown order also permits a racing interrupt handler to interact with workqueue state during removal. For the CVSS the PR:L value in the paranoid score represents environments where device teardown is delegated to a reduced capability root, container manager, or service account. A standard system normally requires administrative privileges and is better represented by PR:H. The issue is local and is not network reachable. Impact is at least denial of service through a kernel crash. The use after free creates a plausible memory corruption path that may permit confidentiality, integrity, or privilege escalation impact in the worst case and requires manual review. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 3 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were 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 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 and V39_AEGIS_ONE_STEP_UP and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 4.1 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 Borderline / manual review recommended (with actual score 3)	MAYBE	INIT PRINTF-TTY UAF TIMER HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=3
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

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

2. Signal breakdown

* +2 Real UAF. `max3100_remove()` can free the port while `max3100_timeout()` retains access to it and can rearm its timer.
* +1 Realistic kernel crash or strong DoS. Timer, IRQ, or workqueue activity after teardown can dereference freed state or interact with a destroyed workqueue.
* No repeated-release point. The patch does not show two lifetime or refcount releases on the same dangling reference.
* No structured stale-object leverage point. The stale port is structured, but attacker-controlled reclaim, replacement contents, callback control, or useful field manipulation is not established.
* No active-state trust-boundary candidate. No guest, namespace, delegated interface, or privileged downstream consumer of attacker-corrupted structured state is established.
* No authorization signal. There is no DENY-to-ALLOW decision or omitted security check.
* No B5-R signal. There is no confirmed retry-accumulated heap OOB write.
* No B3-PENDING signal. There is no demonstrated write into shared or file-backed storage.
* No additional availability point. It would duplicate the same crash consequence.
* No C or I point. A useful disclosure, directed write, controlled reclaim, or protected-state modification is not demonstrated.
* No privilege penalty. SPI unbind commonly involves privileged device management, but the supplied evidence does not establish the complete attacker-facing trigger or prove that host-admin authority is always required.
* No race penalty. A suspend and removal window is required, but the evidence does not establish that it is narrow, one-shot, or materially uncontrollable.
* No rare-hardware penalty. MAX3100 hardware is required, but rarity and deployment difficulty are not sufficiently established merely from the driver identity.

3. Reachability analysis

The vulnerable sequence requires an initialized MAX3100 SPI serial device, system suspend, and device removal or driver unbind before normal resume cleanup. The supplied evidence does not identify whether an attacker uses privileged sysfs unbind, physical device removal, a device-management service, or another kernel-driven removal path. Therefore host-admin and UID 0 requirements remain unknown rather than assumed.

No namespace-scoped capability path is shown. No network trigger exists. The timer and IRQ races are technically concrete, but attacker control and repeatability of the complete suspend-unbind sequence are unresolved.

4. Primitive and severity interpretation

The exact primitive is asynchronous post-free access to a fixed driver context. `max3100_timeout()` may access the freed port and rearm its timer, while an interrupt handler can race with workqueue destruction. This is a real Class B lifetime violation.

The stale storage is closer to fixed teardown-related driver state than an attacker-shaped active replacement object. The patch does not establish controlled reclaim, arbitrary read or write, repeated refcount mutation, function-pointer control, or a security-boundary crossing. The demonstrated practical consequence is kernel crash or host DoS. Privilege escalation remains a generic UAF possibility rather than a patch-supported exploitation primitive.

ImportantCandidate is NO because meaningful leverage beyond the constrained teardown UAF is not established. AutoDowngradeAllowed is YES because the evidence supports a crash-oriented driver UAF without unresolved controlled corruption or authorization impact. Manual review remains recommended because an actual timer callback can execute after `kfree()`.

5. One-sentence report phrase

A suspend and device-removal race in the MAX3100 serial driver can leave timer, IRQ, or workqueue activity operating on a freed port, causing a local kernel use-after-free and potential crash.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

The UAF is concrete, but the complete attacker privilege boundary and any exploitation leverage beyond denial of service remain unresolved.

7. Call-site confidence

Call-site confidence: high

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

Patch: tty: serial: max3100: shut down timer before freeing port
Commit: fb668620e3b163962dabe1a674725a07aa44ff4a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=fb668620e3b163962dabe1a674725a07aa44ff4a

Commit description:

max3100_shutdown() stops the polling timer but returns early during
system suspend. If the SPI device is unbound before resume, the serial
core does not call max3100_shutdown() again, so max3100_remove() frees
the port while the timer remains armed. max3100_timeout() may then
access the freed port and re-arm the timer.

Add final timer teardown to max3100_remove() and use
timer_shutdown_sync() to prevent a racing callback from re-arming it.
Also free the IRQ and destroy the workqueue there before freeing the
port. Keep timer_delete_sync() in max3100_shutdown() so that a
subsequent open() can re-arm the timer.

The workqueue is created before request_irq() and destroyed on both
request_irq() failure and normal shutdown. Its presence at remove thus
identifies the IRQ left registered when suspend bypasses shutdown.

Free the IRQ before destroying the workqueue, in both
max3100_shutdown() and max3100_remove(), and cancel the pending work
in between. free_irq() waits for a running interrupt handler to
finish and no new handler can start afterwards, so a racing handler
cannot queue work on a workqueue that is being destroyed; the
force_end_work check in max3100_dowork() only narrows that window, as
a handler delayed between the check and queue_work() could still run
after the teardown has cleared the workqueue pointer. Cancelling the
work also keeps destroy_workqueue() from waiting on a queued work item
in case remove() ever runs while the freezable workqueue is still
frozen, e.g. device removal during the resume window, before
workqueues are thawed.

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

Fixes: 7831d56 ("tty: MAX3100")
Cc: stable@kernel.org # 6.2+
Assisted-by: Codex:gpt-5.6
Signed-off-by: Fan Wu <fanwu01@zju.edu.cn>
Link: https://patch.msgid.link/20260927055957.561030-1-fanwu01@zju.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/tty/serial/max3100.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=fb668620e3b163962dabe1a674725a07aa44ff4a

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

The original Linux kernel CVE announcement for CVE-2026-98749 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98749

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: unknown
  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: 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).