[CVE-2026-98765][MODERATE REGULAR] USB: gadget: dummy-hcd: Fix wait for outstanding request completions

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

CVE: CVE-2026-98765
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: USB: gadget: dummy-hcd: Fix wait for outstanding request completions
Commit: 7ce4dca0d53b1c3cb2b7e7bb2e42bf5db860caf2
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7ce4dca0d53b1c3cb2b7e7bb2e42bf5db860caf2
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98765
Analysis date: Sat, 24 Oct 2026 10:12:50 -0400
ActionableScore: 4
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
dummy_hcd can report callback quiescence while a request completion is still executing, allowing teardown or module unload to race with active callback code and plausibly crash the kernel.

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

The original Linux kernel CVE announcement for CVE-2026-98765 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98765

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: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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

CVE-2026-98765	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-98765 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=1 LEGACY=MODERATE RESULT=DIFF (final 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:H/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-672;*CWE-416;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.4';DESCR 'A lifetime synchronization race in dummy_hcd omitted request completion callbacks from callback_usage. The synchronize_irq emulation could therefore return while usb_gadget_giveback_request was still executing, allowing gadget driver unbind and potentially module unload to overlap an active completion handler. The demonstrated impact is a kernel crash or other availability loss. Unloading module code or releasing driver state while the callback remains active also creates a plausible stale code or use after free condition, but no reliable arbitrary write or privilege escalation primitive is established. For the CVSS the PR:H value reflects that reliable triggering normally requires control over gadget driver teardown or module unloading. Exploitation also requires dummy_hcd to be enabled and a high complexity race window. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 6.4 and the production ActionableScore returned 4 with recommendation Borderline / manual review recommended. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage LOW to MODERATE_KPANIC because the ActionableScore threshold rule was applied. KP and FD specialist checks stage MODERATE_KPANIC to MODERATE because KP specialist did not establish a qualifying panic. The legacy KP specialist produced a review artifact and its decision was processed by the applicable KP rules. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 and DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 1.9 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was MODERATE_KPANIC. The models disagreed but the aggregation rules retained the production result. The final reported impact is MODERATE.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 4)	MAYBE	USB SIMPLEFIX HARDWARE LINUS  INCREASED_TO_MODERATE7_FROM_LOW_BASED_ON_GUESSCVSS_AND_ACTIONABLESCOREHIGHER4 DECREASED_TO_MODERATEREG_BASED_ON_FALSEPOSCHECKOFKP V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=4
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: 1 (+2 lifetime violation, +1 plausible kernel crash, -1 difficult teardown race, -1 unusual dummy_hcd setup).
* Conservative score: 4. Applied the real-UAF floor: 1 -> 4 because an active callback can outlive synchronization and teardown, while host-admin-only reachability is not positively established.
* Raw paranoid score: 1. No additional exploit primitive is technically established.
* Paranoid score: 4 after the same floor.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

* +2 Real lifetime violation: `callback_usage` omitted request-completion callbacks, allowing synchronization to return while `usb_gadget_giveback_request()` remains active and teardown may invalidate callback code or state.
* +1 Reliable crash/strong DoS plausible: unbind or module unload overlapping the callback can execute invalid code or access released driver state.
* -1 Hard race: exploitation requires completion callback execution to overlap teardown/unload.
* -1 Rare and difficult path: dummy_hcd is a specialized emulated UDC that must already be enabled and configured.
* No controlled reclaim, repeated refcount mutation, attacker-shaped replacement, arbitrary write, disclosure, or authorization bypass is shown.
* No separate availability point: it would duplicate the same crash.
* NEW52/B5-R does not apply: no retry-accumulated heap OOB write exists.

3. Reachability analysis

The patch establishes the synchronization defect but not a concrete userspace trigger or its permissions. Reliable triggering appears to require control over gadget teardown or module unloading, but the supplied evidence does not prove that every complete trigger requires host-admin-equivalent power. No namespace-scoped capability path is shown. The vulnerable configuration requires dummy_hcd and a bound gadget driver. The race window is timing-dependent and reportedly high complexity.

4. Primitive and severity reading

This is an active callback lifetime/synchronization violation, not fixed stale storage. The callback can continue after the emulated `synchronize_irq()` has declared callbacks quiescent, allowing unbind or module-code retirement to overlap active execution. That supports CLASS_B and RealUAF=YES, but the demonstrated consequence is crash/DoS. There is no specific post-free structured-field consumption, controlled reuse, second lifetime mutation, or useful corruption primitive. ImportantCandidate is therefore NO and constrained Moderate downgrade remains permissible.

5. One-sentence report phrase

dummy_hcd can report callback quiescence while a request completion is still executing, allowing teardown or module unload to race with active callback code and plausibly crash the kernel.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm the actual teardown interface, required privilege, and whether any gadget driver permits attacker-controlled state to survive into the overlapping completion callback.

7. Call-site confidence

Call-site confidence: medium

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

Patch: USB: gadget: dummy-hcd: Fix wait for outstanding request completions
Commit: 7ce4dca0d53b1c3cb2b7e7bb2e42bf5db860caf2
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7ce4dca0d53b1c3cb2b7e7bb2e42bf5db860caf2

Commit description:

The dummy-hcd driver emulates synchronize_irq() by waiting until its
private callback_usage counter drops to 0 (with the private lock not
held).  This counter is incremented whenever a gadget driver callback
occurs (which requires the private lock to be dropped), but not when a
request completion handler is called.

This is an oversight.  Request completion is triggered by timer
interrupts (emulating device IRQs in a real UDC), and the interrupt
handlers are supposed to have completed when the synchronize_irq()
emulation routine returns -- they aren't supposed to be in the middle
of a completion callback.  If this happens it can lead to a gadget
driver's unbind routine running before all outstanding request
completions have finished, maybe even allowing the gadget driver's
module to be unloaded while a completion handler is still running.

Fix the oversight by incrementing the callback_usage value across
request completion callbacks.

Link: https://lore.kernel.org/linux-usb/7a87e293-633c-4100-aa8d-91560ba5e5c5@rowland.harvard.edu/
Fixes: 7dbd8f4 ("USB: dummy-hcd: Fix erroneous synchronization change")
Tested-by: Minseo Kim <neck3922@gmail.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: stable <stable@kernel.org>
Link: https://patch.msgid.link/f23b9e1a-f110-441a-a1d8-95f442ec09d5@rowland.harvard.edu
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/gadget/udc/dummy_hcd.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=7ce4dca0d53b1c3cb2b7e7bb2e42bf5db860caf2

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

The original Linux kernel CVE announcement for CVE-2026-98765 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98765

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:H/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 6.4

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: 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).