[CVE-2026-99050][MODERATE 7.0] gpio: mpsse: fix race when arming the IRQ poll worker

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

CVE: CVE-2026-99050
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: gpio: mpsse: fix race when arming the IRQ poll worker
Commit: 76390ac0bca7e5058b7482eb4d951c3bda5df812
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=76390ac0bca7e5058b7482eb4d951c3bda5df812
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99050
Analysis date: Tue, 27 Oct 2026 01:00:35 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
A narrow USB disconnect race can leave an orphaned GPIO polling worker accessing a freed MPSSE driver context, causing a constrained crash-capable UAF.

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

The original Linux kernel CVE announcement for CVE-2026-99050 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99050

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.

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

CVE-2026-99050	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99050 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 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:P/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in gpio_mpsse_irq_enable scheduled gpio_mpsse_poll before publishing the worker in priv workers. A concurrent USB disconnect could miss that worker, free mpsse_priv, and leave the queued or running worker accessing freed kernel memory. This is a concrete use-after-free with at least kernel crash impact and a plausible but unproven path to corruption of a reused object. For the CVSS the PR:N value applies to the physical vector because unplugging the device requires no logical account, while AV:P and AC:H represent physical access and the narrow race window. For the CVSS the paranoid PR:L value represents a local user or delegated service able to manipulate USB or GPIO device lifecycle operations repeatedly. The issue is not directly network reachable and requires an affected USB MPSSE GPIO device or an equivalent controllable device environment. Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. 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 2.0 and ActionableScore 4 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 0)	MAYBE	DANGER INIT RACE UAF HARDWARE LINUS  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 KPANIC V39_AEGIS_ONE_STEP_UP MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=0
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 base score: 0.
* Conservative score: 0; no floor applies because this is a specialized fixed driver-context teardown UAF.
* Raw paranoid score: 0.
* Paranoid score: 0; stronger reuse or attacker-controlled corruption is not established.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +2 — Real UAF: `schedule_work()` preceded list publication, allowing disconnect to miss the worker, free `mpsse_priv`, and leave `gpio_mpsse_poll()` accessing it.
* +1 — Plausible kernel crash from asynchronous access to freed driver state.
* -2 — An affected, relatively specialized USB MPSSE GPIO device and device-disconnect lifecycle are materially required.
* -1 — The trigger requires the narrow interval between work scheduling and list publication.
* No floor 4/5: the stale object is a fixed driver context reached during device teardown; no controlled replacement, post-free contents, repeated refcount mutation, or broader active-object processing is shown.
* No confidentiality, integrity, arbitrary-write, controlled-reclaim, authorization-bypass, or extra availability points are awarded.

3. Reachability analysis

The complete trigger is unresolved. Physical unplug can initiate disconnect without a logical account, but the evidence does not show that the same actor can cause or repeatedly coordinate concurrent `gpio_mpsse_irq_enable()`. The hinted local/delegated lifecycle model is plausible but unproven. No namespace capability, host UID requirement, prior delegation, or ordinary-user device interface is established. The race appears timing-sensitive and hardware-dependent.

4. Primitive and severity reading

This is a concrete asynchronous UAF of fixed USB-driver state: disconnect frees `mpsse_priv`, after which an orphaned poll worker accesses it. The shown effect is crash-capable stale access. It is CLASS_B rather than CLASS_A because controlled reclaim, attacker-shaped replacement data, directed writes, callbacks, and useful consumption of reused structured fields are not shown. There is no second release or refcount mutation. ImportantCandidate is NO and auto-downgrade is allowed because the demonstrated primitive remains a constrained teardown/device-context UAF rather than a material unknown cross-boundary corruption chain.

5. One-sentence report phrase

A narrow USB disconnect race can leave an orphaned GPIO polling worker accessing a freed MPSSE driver context, causing a constrained crash-capable UAF.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm actual lifecycle permissions and whether software-controlled disconnect/rebind can make the race repeatable below host administrator privilege.

7. Call-site confidence

Call-site confidence: high

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

Patch: gpio: mpsse: fix race when arming the IRQ poll worker
Commit: 76390ac0bca7e5058b7482eb4d951c3bda5df812
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=76390ac0bca7e5058b7482eb4d951c3bda5df812

Commit description:

gpio_mpsse_irq_enable() arms the poll worker before publishing it:
schedule_work() runs before the worker is added to priv->workers. If
gpio_mpsse_disconnect() walks the list in that window it misses the
worker, and once disconnect returns, the USB core frees mpsse_priv
while the orphaned gpio_mpsse_poll() work keeps accessing it, causing
a use-after-free.

Fix this by publishing and arming the worker in one irq_spin
critical section. Teardown walks the same list under irq_spin, so a
worker found on the list is guaranteed to be armed, and
cancel_work_sync() handles it whether it is queued or running.

A worker armed after the disconnect walk would still be missed, so
also set a new priv->dying flag under irq_spin before the teardown
walk, and check it in the same critical section, freeing it via
kfree_rcu() instead when the device is going away, since kfree()
would be called with the IRQ core's raw spinlock held and may sleep
on PREEMPT_RT. schedule_work() is safe to call with irq_spin held,
and the next probe gets a fresh mpsse_priv, so the flag never needs
to be cleared.

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

Fixes: 179ef11 ("gpio: mpsse: ensure worker is torn down")
Cc: stable@vger.kernel.org
Co-developed-by: Song Li <songl@zju.edu.cn>
Signed-off-by: Song Li <songl@zju.edu.cn>
Signed-off-by: Fan Wu <fanwu01@zju.edu.cn>
Link: https://patch.msgid.link/20260929093646.18419-1-fanwu01@zju.edu.cn
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/gpio/gpio-mpsse.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=76390ac0bca7e5058b7482eb4d951c3bda5df812

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

The original Linux kernel CVE announcement for CVE-2026-99050 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99050

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:P/AC:H/PR:N/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: 0

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).