* [CVE-2026-98656][IMPORTANT] iio: trigger: cancel reenable_work before freeing trigger
@ 2026-10-19 2:50 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-19 2:50 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98656
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: iio: trigger: cancel reenable_work before freeing trigger
Commit: cf513df1a2c75566cdc802d9da47f62e8d6cfd18
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cf513df1a2c75566cdc802d9da47f62e8d6cfd18
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98656
Analysis date: Sun, 18 Oct 2026 22:50:39 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES
Summary:
A queued IIO reenable worker can outlive and dereference its freed trigger owner, creating a race-based kernel use-after-free with directly plausible denial of service and unresolved callback-related exploitation potential.
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ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98656 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98656
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: IMPORTANT
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
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CVE-2026-98656 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-98656 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=4 LEGACY=IMPORTANT RESULT=DIFF INDEPENDENT_LEGACY=IMPORTANT INDEPENDENT_RESULT=DIFF TEMP_KPANIC_MERGE=IMPORTANT_WINS_DISAGREEMENT PRE_MERGE_LEGACY=IMPORTANT (final Legacy and Aegis differ; FINAL: IMPORTANT, 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 race in the IIO trigger lifetime allows reenable_work queued by iio_trigger_notify_done_atomic() to outlive the owning iio_trigger object. A final in flight IRQ can queue the worker while trigger release proceeds, after which the worker derives the freed trigger through container_of() and dereferences stale memory. The directly supported impact is a local kernel crash and denial of service. Because this is a concrete use-after-free involving an embedded work item and later access to reclaimed memory, reuse of the allocation may create a path to confidentiality impact, integrity impact, or privilege escalation in the worst case. For the CVSS the PR:L in the paranoid score reflects a local user who can exercise an accessible IIO data path while device removal, hot unplug, or another teardown event occurs concurrently. Reliable standalone triggering may still require administrative control over device teardown, which supports PR:H for the base score. AC:H applies because exploitation depends on winning the timing window between the final IRQ, queued work, and object release. The issue is not network reachable and is limited to systems with an affected IIO trigger and a reachable teardown path. Impact is at least a local denial of service via kernel crash and in the worst case may include confidentiality and integrity impact due to use-after-free behavior. YES REQUIRES MANUAL CHECK Automated impact decision path. The original SimpleNet classifier selected MODERATE_KPANIC. The primary LLM estimated paranoid CVSS 7 and the production ActionableScore returned 5 with recommendation Actionable Moderate / Strong Important candidate requiring manual review. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were CVSS and initial triage stage MODERATE_KPANIC to IMPORTANT because the CVSS score, vector or bug class threshold rule was applied. 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 produced a review artifact and its decision was processed by the applicable downgrade and preservation rules. Exact triggered rule markers were INCREASED_TO_HIGH_BASED_ON_GUESSCVSS and TEMP_KPANIC_MERGE_IMPORTANT_WINS. The independent weaker Aegis shadow evaluated CVSS 4.4 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 IMPORTANT.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 5) MAYBE UAF HARDWARE LINUS KPANIC KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS TEMP_KPANIC_MERGE_IMPORTANT_WINS - - checked
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ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=5
ActionableScoreLower=4
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 4
* Raw paranoid score: 2
* Paranoid score: 5
* Applied conservative floor: 2 -> 4 under the real UAF floor because deferred work concretely accesses its owner after lifetime termination and host-admin privilege is not established.
* Applied paranoid floor: 2 -> 5 because the stale active object is used to invoke its reenable operation, leaving callback-related post-reuse behavior unresolved even though controlled reclaim is not demonstrated.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::
2. Signal breakdown
Positive signals:
* +2 Real UAF. `iio_trig_release()` can free `struct iio_trigger` while its embedded `reenable_work` remains queued. The worker later reconstructs and dereferences the freed owner through `container_of()`.
* +1 Realistic kernel crash. Accessing the freed trigger and its reenable operation can cause an Oops or panic.
* No extra availability point was awarded because this would duplicate the same crash consequence.
Negative signals:
* -1 Narrow asynchronous teardown race. The vulnerable ordering requires an in-flight IRQ to queue work immediately around the final device release. The teardown transition is one-shot, and evidence that an attacker can repeatedly control both sides is absent.
Important non-awarded signals:
* Controlled reclaim or attacker-shaped replacement contents are not demonstrated.
* Arbitrary read, arbitrary write, disclosure, and privilege escalation are not demonstrated.
* Structured stale-object leverage was not awarded as a separate point because attacker influence over reclaimed contents is unresolved.
* Strong callback control was not awarded. The stale path reaches `reenable`, but control over the stale operations pointer is not established.
* No active lifetime manipulation point was awarded because one actor controlling both IRQ generation and trigger destruction is not established.
* No concrete repeated release or refcount mutation exists. The bug is asynchronous stale use, not a second `put`, `free`, or refcount decrement.
* FLOOR 5 was not applied for repeated release. It was applied only to the paranoid assessment because the stale active object participates in callback-related processing.
* NEW52 B5-R does not apply because there is no retry-accumulated heap OOB write.
* NEW53 B3-PENDING does not apply because there is no shared-backing write.
* V33 and V34 do not apply because there is no attacker-corrupted active networking metadata or downstream networking trust boundary.
* B4 authorization preservation does not apply because no DENY-to-ALLOW decision or omitted capability check exists.
3. Reachability analysis
The complete attacker model is unresolved. The work can be armed by an IRQ while an IIO trigger is active, but object destruction occurs through the device core final `put_device()` path. The supplied evidence does not establish whether an ordinary user can initiate the relevant trigger activity, force the final release, or coordinate both operations.
Administrative driver unbind or device removal may provide a teardown path, while physical hot unplug may create teardown without host-admin action. Neither path proves that an attacker below host administration controls the complete sequence. Therefore `HostAdminRequired=UNKNOWN` rather than YES or NO.
No user-namespace or delegated-capability path is shown. The presence of an IIO userspace interface alone does not prove that the complete trigger destruction sequence is namespace-scoped. No network reachability exists. A compatible IIO trigger device and an in-flight IRQ are prerequisites.
The race appears narrow because work must remain queued across final release. Its practical repeatability depends on the driver, interrupt source, device-removal mechanism, and whether userspace can keep the trigger active during teardown.
4. Primitive and severity interpretation
The exact primitive is an asynchronous use-after-free of an active structured `iio_trigger`. This is not fixed stale DMA storage. The worker derives the freed trigger from the embedded `work_struct` and proceeds toward the trigger reenable operation.
The release function is a destructor, but the stale use is not merely passive cleanup metadata access. It occurs in an independently scheduled worker and reaches active trigger behavior. This creates unresolved callback-related exploitation surface. However, no controlled slab reclaim, replacement object, attacker-controlled operations pointer, directed write, disclosure, or privilege escalation is established.
There is no concrete repeated release or refcount operation. `cancel_work_sync()` fixes outstanding asynchronous work rather than preventing a second lifetime mutation.
The issue is therefore CLASS_B rather than CLASS_A. Kernel crash and denial of service are directly plausible. Confidentiality, integrity impact, and local privilege escalation remain theoretical worst cases rather than patch-supported consequences.
`ImportantCandidate=YES` preserves review of the stale callback path. It does not claim proven Important severity. `AutoDowngradeAllowed=NO` is selected because automatically treating the issue as ordinary crash-only cleanup could discard unresolved active-object callback behavior.
5. One-sentence report phrase
A queued IIO reenable worker can outlive and dereference its freed trigger owner, creating a race-based kernel use-after-free with directly plausible denial of service and unresolved callback-related exploitation potential.
6. Manual review recommendation
MANUAL CHECK REQUIRED
Review the exact `reenable_work` callback, trigger allocator and slab reuse, affected drivers, userspace access to trigger activity, and whether a below-host-admin actor can coordinate IRQ generation with device teardown or hot unplug.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: iio: trigger: cancel reenable_work before freeing trigger
Commit: cf513df1a2c75566cdc802d9da47f62e8d6cfd18
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cf513df1a2c75566cdc802d9da47f62e8d6cfd18
Commit description:
iio_trigger_notify_done_atomic() defers ->reenable() into
trig->reenable_work on the system workqueue, and the worker dereferences
the owning trigger through container_of(). Nothing cancels this work
before iio_trig_release() frees the trigger, so a worker armed by the
last in-flight IRQ can outlive the free and touch freed memory.
Cancel it at the top of iio_trig_release(), which every free path
reaches through the device core's final put_device().
Found by an in-house static analysis tool.
Fixes: 9020ef6 ("iio: trigger: Fix a scheduling whilst atomic issue seen on tsc2046")
Cc: [email protected]
Assisted-by: Codex:gpt-5.6
Signed-off-by: Fan Wu <[email protected]>
Signed-off-by: Jonathan Cameron <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/iio/industrialio-trigger.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=cf513df1a2c75566cdc802d9da47f62e8d6cfd18
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98656 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98656
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: 4
Paranoid ActionableScore: 5
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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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