[CVE-2026-99179][MODERATE REGULAR] watch_queue: Fix note pool publication race in watch_queue_set_size()

[CVE-2026-99179][MODERATE REGULAR] watch_queue: Fix note pool publication race in watch_queue_set_size()

[AL-KERNEL]

CVE: CVE-2026-99179
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: watch_queue: Fix note pool publication race in watch_queue_set_size()
Commit: 811fb6d0b07605e8e8d93bde8748be4b3028809a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=811fb6d0b07605e8e8d93bde8748be4b3028809a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99179
Analysis date: Thu, 29 Oct 2026 00:38:57 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
An unprivileged local user can reliably race watch-queue initialization against key notification posting, causing a NULL pointer dereference and kernel panic without demonstrated memory corruption or privilege escalation.

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

The original Linux kernel CVE announcement for CVE-2026-99179 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99179

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: NO

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

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

CVE-2026-99179	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-99179 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=2 LEGACY=MODERATE RESULT=DIFF TEMP_DISTANCE_MERGE_SKIP=AEGIS_NO_POSITIVE_SEVERITY_EVIDENCE (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:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;**CWE-476;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A publication race in watch_queue_set_size can make a nonzero nr_notes visible before notes and notes_bitmap are safely visible to post_one_notification. An unprivileged local user can race IOC_WATCH_QUEUE_SET_SIZE on a notification pipe against KEYCTL_SETPERM on a watched key owned by that user, causing notes(0) to be dereferenced while notes is NULL and triggering a kernel panic. For the CVSS the PR:L value is selected because local execution in an unprivileged user context is required, although no administrative capability is needed. The confirmed primitive is a NULL pointer dereference with availability impact. There is no patch evidence of UAF, OOB access, arbitrary write, information disclosure, or privilege escalation. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were final reconciliation stage LOW to MODERATE 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 V30_AEGIS_DISTANCE_REVIEW_MODERATE and V41_INHERITED_KPANIC_PROMOTION_BLOCKED and MANUAL_REVIEW_REQUIRED. The independent weaker Aegis shadow evaluated CVSS 5.5 and ActionableScore 2 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 Ordinary Moderate (with actual score 2)	MAYBE	OOB NULLPTR RACE LEAK HARDWARE  V30_AEGIS_DISTANCE_REVIEW_MODERATE V41_INHERITED_KPANIC_PROMOTION_BLOCKED MANUAL_REVIEW_REQUIRED	-	-	checked

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

ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=NO
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO

1. ActionableScore

* Raw base score: 2.
* Conservative score: 2; no floor or cap applied.
* Raw paranoid score: 2.
* Paranoid score: 2; no technically supported stronger primitive.
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +1 Local unprivileged trigger: an unprivileged user can create the notification pipe, watch its own key, and race the size ioctl against `KEYCTL_SETPERM`.
* +1 Reliable kernel crash / strong DoS: the demonstrated publication race exposes `nr_notes > 0` while `notes` remains NULL, causing `notes[0]` dereference and kernel panic.
* +0 Invalid-pointer concern: this is a NULL dereference, not a separately useful corruption primitive.
* No race penalty: the report says the attacker triggers it reliably using two CPUs.
* No extra availability point: the panic is already counted.
* No UAF, heap OOB write, controlled reclaim, arbitrary write, disclosure, authorization bypass, or integrity effect is shown.
* NEW52/B5-R does not apply: there is no retry-accumulated heap OOB write or later consumption of corrupted structured state.
* NEW53/B3-PENDING does not apply: no shared-backing write occurs.
* NEW54/B4-PENDING does not apply: no mandatory authorization decision changes from DENY to ALLOW.

3. Reachability analysis

The complete trigger is positively shown for a normal local unprivileged user operating on its own key and notification pipe. No host UID 0, administrative capability, namespace-scoped capability, prior privileged setup, special hardware, or unusual boot configuration is identified. The race is repeatable rather than shown to require narrow or uncontrollable timing. Remote reachability is not supported.

4. Primitive and severity reading

The exact defect is an ordering failure during publication of an active note pool: the consumer can observe the nonzero bound before seeing the initialized page-array pointer. The resulting operation is a NULL array dereference with a demonstrated host panic. It is neither a UAF nor an OOB write, and no corrupted state survives for useful later consumption. Accordingly this is CLASS_C crash/DoS behavior, not an Important-preserving corruption primitive. Auto-downgrade remains allowed because no material non-crash exploit leverage or unresolved trust-boundary chain is shown.

5. One-sentence report phrase

An unprivileged local user can reliably race watch-queue initialization against key notification posting, causing a NULL pointer dereference and kernel panic without demonstrated memory corruption or privilege escalation.

6. Manual review advice

MANUAL CHECK RECOMMENDED

Confirm affected-kernel configuration and panic behavior, but the supplied evidence supports only local availability impact.

7. Call-site confidence

Call-site confidence: high

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

Patch: watch_queue: Fix note pool publication race in watch_queue_set_size()
Commit: 811fb6d0b07605e8e8d93bde8748be4b3028809a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=811fb6d0b07605e8e8d93bde8748be4b3028809a

Commit description:

There is a race between watch_queue_set_size() and post_one_notification().
watch_queue_set_size() publishes wqueue->notes, notes_bitmap, nr_pages and
nr_notes with plain stores, and post_one_notification() reads them with
plain loads under a different lock, so nothing orders the four stores
against the poster's loads: depending on the build, notes can be stored
last (gcc 14 on x86-64 does this).  Since keyctl_watch_key() lets a watch
attach to a queue before it is sized, post_one_notification() can already
be running on another CPU at that moment: it reads nr_notes > 0, passes
its bounds check, and then reads notes while it is still NULL,
dereferencing notes[0].

An unprivileged user triggers this reliably by watching one of its own
keys through a notification pipe and racing ioctl(IOC_WATCH_QUEUE_SET_SIZE)
on that pipe against keyctl(KEYCTL_SETPERM) on the key from another CPU,
triggering:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:post_one_notification.isra.0+0xa2/0x1e0
  Call Trace:
   __post_watch_notification+0x148/0x180
   keyctl_setperm_key+0x119/0x130
   do_syscall_64+0x108/0x4c0
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
  Kernel panic - not syncing: Fatal exception in interrupt

Fix this by publishing nr_notes last with smp_store_release(), and by
reading it once with smp_load_acquire() in post_one_notification() before
the bitmap and the page array are touched.  A poster that observes a
non-zero nr_notes then also observes the pool behind it; one that observes
zero drops the notification as before.

Fixes: c73be61 ("pipe: Add general notification queue support")
Reported-by: Dae R. Jeong <threeearcat@gmail.com>
Closes: https://lore.kernel.org/all/ZT-S8Q7tyutcvu_q@dragonet/
Reported-by: AutonomousCodeSecurity@microsoft.com
Suggested-by: Dae R. Jeong <threeearcat@gmail.com>
Signed-off-by: Cen Zhang (Microsoft) <cenzhang@linux.microsoft.com>
Link: https://patch.msgid.link/20261009224715.46121-1-cenzhang@linux.microsoft.com
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/watch_queue.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=811fb6d0b07605e8e8d93bde8748be4b3028809a

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

The original Linux kernel CVE announcement for CVE-2026-99179 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99179

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:H
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 2

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).