[CVE-2026-97586][MODERATE REGULAR] afs: Fix missing kunmap in afs_dir_search_bucket()

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

CVE: CVE-2026-97586
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: afs: Fix missing kunmap in afs_dir_search_bucket()
Commit: c5fa4eb9c4b2c744ba88fb4ff2d729a158e66832
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c5fa4eb9c4b2c744ba88fb4ff2d729a158e66832
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97586
Analysis date: Sat, 26 Sep 2026 06:49:23 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-97586 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97586

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-2026-97586	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-97586 CHECK WITH IMPACT FROM ORIG NN NONE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H';*CWE-772;CWE-404;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '6.5';DESCR 'afs_dir_search_bucket can return through its bad path without calling kunmap_local for iter block, leaving a temporary local page mapping active. Repeated processing of malformed or stale AFS directory blocks may unbalance the local mapping stack, exhaust mapping slots, or trigger a kernel warning or crash. The realistic impact is denial of service, with no concrete UAF, out of bounds access, information disclosure, or write primitive visible in the changed code. For the CVSS the PR:N value in the paranoid score represents a malicious or compromised AFS server that can supply malformed directory data without holding privileges on the client. The paranoid vector uses AV:A because exploitation depends on access through a configured AFS storage environment rather than arbitrary public network traffic. A local user performing directory operations on an affected AFS mount provides the more conservative base scenario with PR:L and AC:H.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)  SKIP CVE-2026-97586 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: a5b5beebcf96 YES  NO NO unknown 	MAYBE	DISK SIMPLEFIX SKIP LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap was applied.
* Final recommended bucket: **Borderline / manual review recommended**::

2. Signal breakdown

Conservative signals:

* +1 Concrete persistent kernel resource/reference leak. The `bad` path bypasses `kunmap_local()`, leaving a temporary mapping and its per-task mapping-stack state unreleased.
* +1 Local unprivileged trigger. Once an AFS filesystem is mounted and accessible, an ordinary user can perform repeated pathname lookups that reach directory-bucket searching. This does not imply that the local user controls the malformed directory data.
* Total: 2.

Additional paranoid signal:

* +1 Reliable kernel crash / strong DoS. Repeated bad-path exits can unbalance the local mapping stack and may eventually exhaust kmap slots or trigger a kernel BUG, warning, or fatal fault.
* Total: 3.

Not awarded:

* Remote reachability +2 was not awarded because the vulnerable path requires an already configured AFS mount and the supplied evidence does not prove that an arbitrary remote peer can directly reach it.
* No UAF signal. The mapped page is not shown to be freed and subsequently accessed through a stale reference.
* No repeated release/refcount signal. There is one missing `kunmap_local()`, not two lifetime-ending operations on the same reference.
* No structured stale-object leverage, controlled reclaim, arbitrary write, information disclosure, integrity impact, or privilege escalation is demonstrated.
* No extra Availability point was awarded because possible slot exhaustion and kernel failure describe the same DoS consequence.
* No negative privilege penalty was applied because host-admin privilege is not required for directory lookups after the mount has been provisioned.
* No niche-subsystem penalty was applied merely because AFS is less commonly deployed.

3. Reachability analysis

An ordinary local user with search access to an existing AFS mount can invoke pathname lookup and reach `afs_dir_search_bucket()`. Repeated triggering additionally requires a directory block that causes the `bad` path, such as malformed, inconsistent, or stale directory data.

A malicious or compromised AFS server may plausibly influence this data, but the supplied patch does not show the complete network receive and validation chain. An AFS mount or automount configuration is a prior administrative prerequisite, although the triggering lookup itself is below host-admin privilege. Therefore `HostAdminRequired=NO`, while direct remote-trigger scoring is withheld.

No namespace-specific capability is visible. The complete trigger does not depend on special hardware or a timing race.

4. Primitive and severity interpretation

The exact primitive is a missing release of a temporary local page mapping. It creates an unbalanced kmap-local state and a concrete resource-management defect, not a post-lifetime object access.

This is neither an active structured-object UAF nor fixed stale storage. There is no first operation that frees an object, no surviving dangling reference, and no second lifetime/refcount mutation. The appropriate classification is `CLASS_C` because the supported security consequence is invalid mapping state and potential crash or resource exhaustion.

The demonstrated defect supports denial of service after repeated triggering. Stronger confidentiality, integrity, or privilege-escalation consequences remain unsupported. `ImportantCandidate=NO` because there is no independently useful corruption or boundary-bypass primitive. `AutoDowngradeAllowed=YES` because the issue remains a constrained resource-cleanup defect without unresolved Class A or Class B leverage.

Operational severity is ordinary Moderate to borderline Moderate, with manual confirmation useful for the architecture-specific kmap failure mode and server-controlled reachability.

5. One-sentence report phrase

A missing kunmap_local call on the AFS directory search error path can leave temporary mappings active and repeated malformed directory lookups may exhaust local mapping slots or crash the kernel.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Confirm whether attacker-controlled AFS server data reliably reaches the `bad` path and whether affected architectures convert repeated missing unmaps into a host-wide fatal failure.

7. Call-site confidence

Call-site confidence: medium

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

Patch: afs: Fix missing kunmap in afs_dir_search_bucket()
Commit: c5fa4eb9c4b2c744ba88fb4ff2d729a158e66832
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c5fa4eb9c4b2c744ba88fb4ff2d729a158e66832

Commit description:

Fix afs_dir_search_bucket() to kunmap the block it's using in the "bad:"
path.

Fixes: a5b5bee ("afs: Use the contained hashtable to search a directory")
Closes: https://sashiko.dev/#/patchset/20260716103030.3065561-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260902121024.3328255-2-dhowells@redhat.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-fsdevel@vger.kernel.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:
  fs/afs/dir_search.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=c5fa4eb9c4b2c744ba88fb4ff2d729a158e66832

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

The original Linux kernel CVE announcement for CVE-2026-97586 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97586

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:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 6.5

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: 2
  Paranoid ActionableScore: 3

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).