[CVE-2026-74427][MODERATE 7.0] afs: Fix netns teardown to cancel the preallocation charger

[CVE-2026-74427][MODERATE 7.0] afs: Fix netns teardown to cancel the preallocation charger

[AL-KERNEL]

CVE: CVE-2026-74427
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: afs: Fix netns teardown to cancel the preallocation charger
Commit: 63ccaf1bdf8be2330f47f9b5b233dd3fd04acbd9
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=63ccaf1bdf8be2330f47f9b5b233dd3fd04acbd9
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74427
Analysis date: Sun, 16 Aug 2026 03:49:15 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
AFS net namespace teardown can race with the rxrpc preallocation charger work item, allowing the worker to run or be requeued after teardown starts and creating a plausible lifetime UAF leading at least to local kernel DoS.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-74427 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74427

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: 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-2026-74427	MODERATE	CHECK WITH IMPACT FROM ORIG NN NONE	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-362;*CWE-416;*CWE-664;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'AFS network namespace teardown can race with the rxrpc preallocation charger work item. The work item may continue running or be requeued while the namespace is being deleted, and it operates on AFS per net state whose lifetime is ending. This creates a plausible workqueue lifetime use-after-free candidate and can at least crash the kernel or hang teardown. For the CVSS the PR:L is used in the paranoid score because reliable triggering may be possible for a local user or container context that can create and tear down network namespaces or otherwise control AFS namespace lifetime. The issue is not directly network reachable by packets alone, but incoming rxrpc or AFS callback traffic can help hit the race during teardown. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to memory corruption, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4)	YES	DISK SIMPLEFIX SKIP LINUS  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Paranoid score signals:

* Local unprivileged trigger: +1. In permissive user namespace or container setups, a local user may be able to create and tear down network namespaces or otherwise influence namespace lifetime.
* Network-assisted external influence: +1. Incoming rxrpc or AFS callback traffic can help requeue the charger during teardown, but this is not a pure remote trigger.
* Memory corruption, weak or indirect corruption candidate: +1. The patch prevents a work item from running or being requeued after the AFS net namespace is being deleted, which is a plausible stale lifetime or UAF candidate.
* Real lifetime corruption: +1. The affected object is tied to per-net AFS state and an async workqueue item, so the bug is in object lifetime ordering.
* Reliable kernel crash or strong DoS: +1. A stale work item operating on teardown state can plausibly crash the kernel or hang namespace teardown.
* Availability impact realistic: +1. The impact is host-wide kernel availability, not only failure of one userspace operation.
* Hard or unreliable race: -1. Triggering depends on a teardown window and concurrent charger or incoming-call activity.

Conservative score interpretation:

* Typical triggering requires privileged namespace or AFS setup control, so privilege constraints lower the practical score.
* No attacker-controlled reclaim, overwrite, type confusion, or demonstrated LPE primitive is shown.
* Conservative result remains manual-review relevant because this is an async workqueue lifetime bug.

## 3. Reachability analysis

The bug is primarily locally reachable through AFS network namespace teardown while the rxrpc preallocation charger can still run or be requeued. Incoming rxrpc or AFS callback traffic may assist the race, but packets alone do not normally initiate namespace teardown, so this should not be scored as fully remote reachable. In typical deployments, creating or tearing down the relevant namespace and AFS state may require administrative capabilities. In containerized or user namespace enabled environments, the practical privilege requirement may be lower than full host root.

Call-site confidence: medium-high. The patch shows the relevant teardown path, charger worker, and incoming-call requeue site, but not the final free path for the full per-net AFS object lifetime.

## 4. Severity interpretation

This behaves like an actionable Moderate issue rather than an ordinary low-risk cleanup. The realistic impact is local DoS through a race in async workqueue teardown. The theoretical concern is a workqueue lifetime UAF, but the patch does not show controlled reuse, write-after-free, type confusion, refcount takeover, or a practical privilege escalation primitive. Therefore it should not be promoted to a strong Important candidate solely on the patch, but it should not be auto-closed.

## 5. One-sentence report phrase

AFS net namespace teardown can race with the rxrpc preallocation charger work item, allowing the worker to run or be requeued after teardown starts and creating a plausible lifetime UAF leading at least to local kernel DoS.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: async workqueue lifetime bugs during namespace teardown are historically prone to underestimated UAF impact, and this patch directly adds `cancel_work_sync()` plus `net->live` guards to prevent stale worker execution or requeueing.

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

Patch: afs: Fix netns teardown to cancel the preallocation charger
Commit: 63ccaf1bdf8be2330f47f9b5b233dd3fd04acbd9
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=63ccaf1bdf8be2330f47f9b5b233dd3fd04acbd9

Commit description:

Fix the teardown of an afs network namespace to make sure it cancels the
work item that keeps the preallocated rxrpc call/conn/peer queue charged
before incoming calls are disabled (i.e. listen 0).

Also, if net->live is false because the afs netns is being deleted, make
afs_charge_preallocation() skip charging and make afs_rx_new_call() avoid
requeuing the charger.

(This was found by AI review).

Fixes: 00e9071 ("rxrpc: Preallocate peers, conns and calls for incoming service requests")
Reported-by: Simon Horman <horms@kernel.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Li Daming <d4n.for.sec@gmail.com>
cc: Ren Wei <n05ec@lzu.edu.cn>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeffrey Altman <jaltman@auristor.com>
cc: linux-afs@lists.infradead.org
cc: stable@kernel.org
Link: https://patch.msgid.link/20260609140911.838677-5-dhowells@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/afs/rxrpc.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=63ccaf1bdf8be2330f47f9b5b233dd3fd04acbd9

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

The original Linux kernel CVE announcement for CVE-2026-74427 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74427

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: 3
  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: MODERATE
KPANIC detected for this report: NO
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).