[CVE-2026-80527][MODERATE REGULAR] ceph: fix hanging __ceph_get_caps() with stale mds_wanted [ Upstream

[CVE-2026-80527][MODERATE REGULAR] ceph: fix hanging __ceph_get_caps() with stale mds_wanted [ Upstream

[AL-KERNEL]

CVE: CVE-2026-80527
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ceph: fix hanging __ceph_get_caps() with stale mds_wanted [ Upstream
Commit: b5661524c5a45085a866864ca9b8ae2513dfd67a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b5661524c5a45085a866864ca9b8ae2513dfd67a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80527
Analysis date: Wed, 26 Aug 2026 12:55:34 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline Moderate / manual review recommended
Manual review required: YES

Summary:
A stale CephFS `mds_wanted` capability state can cause `__ceph_get_caps()` to wait indefinitely after MDS cap revocation, allowing a local CephFS user or storage-network participant to cause a denial of service through hung file operations.

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

The original Linux kernel CVE announcement for CVE-2026-80527 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80527

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-2026-80527	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;CWE-703;Other CVSS 'AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.8';DESCR 'A CephFS client can wait indefinitely in __ceph_get_caps() when local mds_wanted state says that FILE_RD is already wanted but the client no longer actually holds FILE_RD after MDS cap revocation. This can happen if the cap update that should request FILE_RD is lost or never effectively reaches the MDS after mds_wanted was raised, leaving the waiter blocked on i_cap_wq with no new request being sent. For the CVSS the PR:L is used because practical triggering requires a local CephFS user or another authenticated Ceph client able to create conflicting operations that cause cap revocation. The vector is treated as AV:A because CephFS is normally used on an internal storage or data center network rather than as a public Internet service. Impact is denial of service through a stuck read or cap acquisition path. No confidentiality or integrity impact is assigned because the patch indicates stale state and unbounded wait behavior, not UAF, OOB access, arbitrary write, or information disclosure.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline Moderate / manual review recommended (with actual score 3)	YES	DISK DMAorINTERRUPT IMPROVEONLY LINUS  INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline Moderate / manual review recommended**::

## 2. Signal breakdown

Conservative scoring:

* Local unprivileged trigger: +1. A local user or process using an already mounted CephFS can enter the affected read or cap acquisition path without needing kernel privileges.
* Availability impact realistic: +1. The bug can cause an indefinite wait in `__ceph_get_caps()`, hanging reads or related file operations.
* Important filesystem/storage path: +1. CephFS capability handling is a core distributed filesystem correctness and availability path.
* Hard or unreliable race / special state required: -1. Triggering depends on MDS cap revocation, stale `mds_wanted`, and a lost or ineffective cap update.

Conservative total: 2

Paranoid scoring:

* Remote reachable / network-triggerable: +2. In a CephFS deployment, another authenticated Ceph client or MDS-side interaction over the storage network can contribute to the cap revocation and stale state condition.
* Reliable strong DoS: +1. The waiter can sleep indefinitely until unrelated cap traffic wakes it or recovery happens.
* Important filesystem/storage path: +1. The bug affects CephFS cap acquisition and read availability.
* Availability impact realistic: +1. Persistent user-visible filesystem operation hangs are plausible.
* Hard or unreliable race / special state required: -1. The condition still requires a specific distributed state ordering and is not a simple packet-triggered crash.

Paranoid total: 4

No memory corruption, UAF, OOB access, arbitrary write, info leak, page-cache corruption, or privilege escalation primitive is supported by the patch.

## 3. Reachability analysis

The most realistic trigger is a user or service accessing CephFS while another client or MDS action causes cap revocation and the client keeps stale `mds_wanted` state. A local unprivileged user may trigger the read-side wait if CephFS is already mounted and accessible. Mounting or configuring CephFS itself is usually privileged, but use of an existing mount is not necessarily privileged.

Namespaces and containers matter if a CephFS mount is exposed inside a container. In that case, a containerized user may reach the affected path without host admin privileges, but the issue still depends on CephFS deployment and MDS/cap state behavior.

The path is not default-enabled on a generic Linux host. It requires CephFS usage. It is network-adjacent in storage-cluster deployments, not generally public Internet reachable.

## 4. Severity interpretation

This behaves like an ordinary to borderline Moderate availability issue, not an Important-class memory corruption vulnerability. The realistic impact is a stuck CephFS read or cap acquisition path. The paranoid score is higher because distributed CephFS state and storage-network interactions can make the hang operationally significant, but the patch does not show a corruption primitive or privilege escalation path.

## 5. One-sentence report phrase

A stale CephFS `mds_wanted` capability state can cause `__ceph_get_caps()` to wait indefinitely after MDS cap revocation, allowing a local CephFS user or storage-network participant to cause a denial of service through hung file operations.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the issue involves distributed CephFS client and MDS state interactions and may have meaningful operational availability impact in storage deployments, but it does not currently justify Important-class handling without additional evidence of memory corruption, privilege escalation, or broader filesystem integrity impact.

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

Patch: ceph: fix hanging __ceph_get_caps() with stale mds_wanted [ Upstream
Commit: b5661524c5a45085a866864ca9b8ae2513dfd67a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b5661524c5a45085a866864ca9b8ae2513dfd67a

Changed files:
  fs/ceph/caps.c
  fs/ceph/file.c
  fs/ceph/mds_client.h

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=b5661524c5a45085a866864ca9b8ae2513dfd67a

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

The original Linux kernel CVE announcement for CVE-2026-80527 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80527

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:A/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.8

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: 4

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).