[CVE-2026-52960][MODERATE REGULAR] ceph: put folios not suitable for writeback

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

CVE: CVE-2026-52960
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ceph: put folios not suitable for writeback
Commit: 86921e890fe1dea9791fb70bec552516fd47716a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=86921e890fe1dea9791fb70bec552516fd47716a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52960
Analysis date: Mon, 06 Jul 2026 19:27:13 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Ordinary Moderate / Low-like with limited Actionable Moderate concern
Manual review required: YES

Summary:
A CephFS writeback reference leak can occur when unsuitable folios are removed from a folio batch without folio_put, allowing repeated local writeback activity to cause memory pressure or resource exhaustion DoS.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-52960 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52960

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-52960	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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-772;*CWE-401;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'A reference leak in the CephFS writeback path can occur because ceph_process_folio_batch removes folios from the batch without dropping the reference held by filemap_get_folios. Repeated writeback activity that hits the ENODATA path or the folio_clear_dirty_for_io failure path can keep folios referenced longer than intended and may lead to memory pressure or resource exhaustion. For the CVSS the PR:L is used because a local user or process with write access to a mounted CephFS filesystem may be able to trigger writeback activity, while no administrative privileges are normally required for ordinary file writes. The issue is not directly network reachable from an attacker to the kernel client unless the attacker already has local filesystem access through the Ceph mount. Impact is denial of service only. There is no supported confidentiality or integrity impact because the primitive is a reference leak rather than UAF, OOB access, or arbitrary write.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like with limited Actionable Moderate concern (with actual score 4) 	YES	DISK SIMPLEFIX LINUS 	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Ordinary Moderate / Low-like with limited Actionable Moderate concern**::

## 2. Signal breakdown

* Local unprivileged trigger: +1. A local user or process with write access to a mounted CephFS filesystem may be able to create dirty folios and trigger writeback.
* Real lifetime or reference management bug: +1. The patch adds missing folio_put calls, so the bug is a folio reference leak.
* Availability impact realistic: +1. Repeated triggering can keep folios referenced and may cause memory pressure or resource exhaustion.
* Important filesystem or storage path: +1. The affected code is in the CephFS writeback path.
* Special condition or limited trigger path: -1 for conservative scoring. The leak requires CephFS writeback and the specific ENODATA or folio_clear_dirty_for_io failure paths.

No generic memory corruption, UAF, double free, OOB write, page-cache corruption, or privilege escalation primitive is supported by the patch.

## 3. Reachability analysis

The likely trigger is local filesystem activity on a mounted CephFS client. Ordinary file writes can be enough to enter writeback paths, but the leaking branches require specific folio suitability or dirty-state conditions. No direct network trigger from an unauthenticated remote attacker is shown. Namespaces do not materially change the analysis unless an untrusted container or tenant is given write access to the CephFS mount. The path is not default on all Linux systems because CephFS must be mounted and used.

Call-site confidence: high, because the changed function and the folio batch reference semantics are visible in the patch and commit message.

## 4. Severity interpretation

This behaves like a resource leak / availability issue, not an Important-class memory corruption vulnerability. The theoretical worst case is sustained memory pressure or system-wide DoS if the leak can be repeatedly triggered on an active CephFS client. Realistic exploitation evidence for privilege escalation, confidentiality impact, or integrity impact is not present. This should generally be treated as ordinary Moderate or Low-like operational risk, with higher priority only for environments where untrusted users can heavily write to CephFS mounts.

## 5. One-sentence report phrase

A CephFS writeback reference leak can occur when unsuitable folios are removed from a folio batch without folio_put, allowing repeated local writeback activity to cause memory pressure or resource exhaustion DoS.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a reference leak without evidence of UAF, OOB access, arbitrary write, page-cache corruption, or privilege escalation. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED for generic triage unless the affected deployment exposes CephFS write access to untrusted users at scale.

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UPSTREAM PATCH SUMMARY
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Patch: ceph: put folios not suitable for writeback
Commit: 86921e890fe1dea9791fb70bec552516fd47716a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=86921e890fe1dea9791fb70bec552516fd47716a

Commit description:

The batch holds references to the folios (see `filemap_get_folios`,
`folio_batch_release`), so we need to `folio_put` the folios we remove.

Tested on v6.18.

Cc: stable@vger.kernel.org
Link: https://tracker.ceph.com/issues/74156
Signed-off-by: Hristo Venev <hristo@venev.name>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/ceph/addr.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=86921e890fe1dea9791fb70bec552516fd47716a

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

The original Linux kernel CVE announcement for CVE-2026-52960 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52960

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: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: 3
  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).