* [CVE-2026-99243][LOW] io-wq: order the exit bit against worker creation task work
@ 2026-11-04 3:07 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-11-04 3:07 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99243
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: io-wq: order the exit bit against worker creation task work
Commit: 67da3eec264aeb67835886720243ae2dc1463315
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=67da3eec264aeb67835886720243ae2dc1463315
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99243
Analysis date: Tue, 03 Nov 2026 23:07:13 -0400
ActionableScore: 1
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A weak-memory ordering race in io-wq can strand worker-creation task work and indefinitely block the triggering process during exit.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99243 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99243
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: LOW
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-2026-99243 LOW https://www.kernelcve.org/list/?q=CVE-2026-99243 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both LOW) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A memory ordering race between io_wq_exit_start and io_queue_worker_create can leave worker creation task work queued after workqueue exit has started. On weakly ordered architectures both sides may observe stale state, leaving worker_refs held and causing the exiting task to wait indefinitely for worker_done. For the CVSS the PR:L value is selected because a local user process must exercise io_uring and its io-wq worker lifecycle. AC:H reflects the required race window, weak memory ordering, and the condition where all rings have already been closed. The demonstrated primitive is a task exit hang and resource retention with no evidence of UAF, OOB access, information disclosure, arbitrary write, or privilege escalation. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 1 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. 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. The independent weaker Aegis shadow evaluated CVSS 3.1 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE LEAK HARDWARE DEBUGFS TEST IO_URING - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 1 (+1 local unprivileged trigger, +1 persistent reference/resource retention, -1 materially timing- and architecture-dependent race).
* Conservative score: 1; no floor or cap applies.
* Raw paranoid score: 1; no technically supported additional consequence.
* Paranoid score: 1.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Local unprivileged trigger: ordinary local processes can exercise io_uring and io-wq worker creation/exit without host-administrator privilege.
* +1 Concrete resource/reference retention: the missed cancellation leaves `worker_refs` held and the exiting task waiting indefinitely for `worker_done`.
* -1 Hard/special timing: both sides must observe stale state on a weakly ordered architecture, after all rings are closed so the alternate barrier is absent.
* No reliable kernel-crash point: the demonstrated result is a task-exit hang, not a panic or host-wide fatal fault.
* No extra availability point: broad exhaustion or persistent host-wide unavailability is not shown.
* No UAF, OOB write, stale-object consumption, authorization bypass, disclosure, or protected-state corruption is evidenced.
* NEW52/B5-R does not apply: there is no heap OOB write, retry-accumulated index, or later consumption of corrupted structured state.
* NEW53/B3-PENDING and NEW54/B4-PENDING do not apply.
3. Reachability analysis
A normal local user can invoke io_uring and exercise worker lifecycle operations. No UID 0, capability, namespace-scoped privilege, prior privileged setup, or special device is identified. Triggering nevertheless requires a weak-memory ordering window and the closed-all-rings exit state; repeatability and system-wide resource accumulation are not demonstrated.
4. Primitive and severity reading
The exact defect is missing memory ordering between setting `IO_WQ_BIT_EXIT`, adding worker-creation task work, and cancellation during exit. Both sides can miss each other, retaining `worker_refs` and deadlocking the initiating task’s exit. This is CLASS_C synchronization/availability behavior, not a lifetime-corruption primitive. Stronger effects such as kernel panic, memory corruption, cross-process impact, or privilege escalation are unsupported. ImportantCandidate is therefore NO, and ordinary downgrade is safe.
5. One-sentence report phrase
A weak-memory ordering race in io-wq can strand worker-creation task work and indefinitely block the triggering process during exit.
6. Manual review advice
NO MANUAL CHECK NEEDED
The patch supports only a constrained local task-exit hang and reference retention.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: io-wq: order the exit bit against worker creation task work
Commit: 67da3eec264aeb67835886720243ae2dc1463315
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=67da3eec264aeb67835886720243ae2dc1463315
Commit description:
io_wq_exit_workers() cancels task work for queued worker creation with
task_work_cancel_match(). That has a plain load of task->task_works.
io_queue_worker_create() adds the new entry and tests IO_WQ_BIT_EXIT to
cancel it if the workqueue is already on its way out.
That must be ordered. task_work_add() has a full barrier via cmpxchg().
But io_wq_exit_start() sets the bit with set_bit() which doesn't have
any memory ordering.
So afaict, on weakly ordered architectures the exiting task may load
task_works before the store of the bit is visible. The other side tests
the bit before the store is visible as well. So the entry remains queued
with worker_refs and the exiting task waits on worker_done indefinitely.
If the task still has rings then io_uring_del_tctx_node() provides the
barrier via test_and_set_bit() in io_wq_set_exit_on_idle(). When it
has closed all rings though that barrier is gone.
Add the barrier after the set_bit().
Fixes: 71a8538 ("io-wq: check for wq exit after adding new worker task_work")
Cc: [email protected]
Reviewed-by: Jens Axboe <[email protected]>
Acked-by: Oleg Nesterov <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Christian Brauner (Amutable) <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
io_uring/io-wq.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=67da3eec264aeb67835886720243ae2dc1463315
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99243 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99243
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:L/UI:N/S:U/C:N/I:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW
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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