[CVE-2026-80561][MODERATE 7.0] libceph: fix multiple unsafe decodes in decode_locker()

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

CVE: CVE-2026-80561
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: libceph: fix multiple unsafe decodes in decode_locker()
Commit: 1ed45c8d96498725eb54f740172f9068d8673906
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1ed45c8d96498725eb54f740172f9068d8673906
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80561
Analysis date: Wed, 26 Aug 2026 13:53:55 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
Unsafe decode operations in libceph `decode_locker()` allow a malicious or compromised Ceph OSD to trigger kernel slab out-of-bounds reads in a client processing `lock.get_info`, causing at least DoS and possible limited kernel memory disclosure.

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

The original Linux kernel CVE announcement for CVE-2026-80561 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80561

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.

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

CVE-2026-80561	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H';CWE-125;CWE-126;*CWE-20;Other CVSS 'AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '8.1';DESCR 'Unsafe decode operations in libceph decode_locker() can let a malicious or compromised Ceph OSD make a kernel client read past the validated decode buffer while processing lock.get_info data. The bug class is slab out of bounds read, with possible kernel crash and possible limited exposure of adjacent kernel memory if copied data is later consumed or logged. For the CVSS the PR:L is used because reliable triggering typically requires control of an OSD endpoint or an authenticated Ceph storage peer rather than ordinary unauthenticated Internet access. The issue is network reachable inside the Ceph storage network and can affect clients that issue the lock.get_info class method, for example during RBD exclusive lock handling. Impact is at least denial of service via kernel crash. For the paranoid score, choose the highest still defensible interpretation supported by the bug class and patch context, with preference for manual review sensitivity over autoclosed false negatives.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE READ OOB NETWORK LINUS KPANIC  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: **6**
* Paranoid score: **7**
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* **Remote reachable / network-triggerable: +2**
  The malformed data is supplied by a Ceph OSD over the Ceph storage network to a kernel Ceph client.

* **Reliable kernel crash / strong DoS: +1**
  The patch and description explicitly mention slab out-of-bounds reads from unsafe decode operations. Such parser OOB reads in kernel context can plausibly crash the client kernel.

* **Confidentiality impact plausible: +1**
  This is an OOB read, not only a NULL dereference. Adjacent kernel/slab data may be copied into decoded structures or later consumed/logged, so limited disclosure is plausible.

* **Important filesystem/storage path: +1**
  libceph/RBD locking is part of a storage client path. Failure affects kernel clients using Ceph storage features such as RBD exclusive lock handling.

* **Practical exploit chain demonstrated or strongly implied: +1**
  The advisory gives concrete malformed decode states and an attacker model: malicious or compromised OSD triggering the issue during `lock.get_info`.

Paranoid-only additional signal:

* **Weak/indirect memory-safety candidate: +1**
  The unchecked pointer advancement can move the decode pointer outside the validated buffer and make later bounds checks operate on a bogus decode position. This remains read-oriented, not an arbitrary write, but deserves manual-review elevation.

No signals awarded:

* No **strong LPE plausibility**. No reclaim, overwrite, callback control, refcount takeover, or arbitrary write is shown.
* No **generic strong memory corruption +2**. The supported primitive is OOB read, not OOB write/UAF/double-free.
* No **local unprivileged trigger**. The attacker is modeled as a malicious or compromised OSD or authenticated storage peer, not a local user on the victim.

## 3. Reachability analysis

The bug can be triggered by a malicious or compromised Ceph OSD that returns malformed `lock.get_info` data to a Linux kernel Ceph client. It is network-reachable in the Ceph storage network, but not generally Internet-reachable unless Ceph OSD traffic is exposed, which is uncommon.

Privileges are best interpreted as storage-peer level access rather than unauthenticated remote access. This supports PR:L in CVSS-style reasoning, because reliable triggering requires control of or authenticated participation as an OSD endpoint.

The affected path is not default-enabled on all Linux systems. It matters for systems using Ceph/libceph/RBD features, especially multi-tenant or shared storage deployments where OSD trust boundaries are relevant.

Call-site confidence: **medium**. The patch body shows the unsafe decoder directly, and the commit text identifies `lock.get_info` and RBD exclusive lock handling, but full caller context is not included in the diff.

## 4. Severity interpretation

This behaves as **Actionable Moderate at minimum and a Strong Important candidate under paranoid triage**.

Realistic impact is kernel-client DoS and possible limited kernel memory disclosure through OOB reads. Theoretical LPE is not supported by the patch because there is no write primitive, UAF reclaim path, callback corruption, or controlled object replacement. However, the issue is still security-relevant because it is a network-fed kernel parser bug in a storage protocol and the malformed peer is explicitly part of the attacker model.

## 5. One-sentence report phrase

Unsafe decode operations in libceph `decode_locker()` allow a malicious or compromised Ceph OSD to trigger kernel slab out-of-bounds reads in a client processing `lock.get_info`, causing at least DoS and possible limited kernel memory disclosure.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: this is a network-reachable storage-peer-triggered kernel OOB read with plausible confidentiality and availability impact, and it affects a trusted storage client parser rather than a purely local validation path.

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

Patch: libceph: fix multiple unsafe decodes in decode_locker()
Commit: 1ed45c8d96498725eb54f740172f9068d8673906
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1ed45c8d96498725eb54f740172f9068d8673906

Commit description:

decode_locker() in cls_lock_client.c contains three unsafe decode
operations that allow a malicious or compromised OSD to trigger
slab-out-of-bounds reads:

1. ceph_decode_copy() at the locker_id_t name field has no preceding
   bounds check. With p == end after ceph_start_decoding() accepts
   struct_len=0, this reads sizeof(ceph_entity_name) = 9 bytes past
   the validated buffer boundary.

2. *p += sizeof(struct ceph_timespec) after the locker_info_t header
   is an unchecked pointer advance. A malicious OSD can position p
   past end, causing all subsequent _safe checks to pass against a
   bogus boundary.

3. len = ceph_decode_32(p) has no preceding bounds check, and the
   immediately following *p += len is uncapped. A malicious OSD can
   send len=0xffffffff, advancing p gigabytes past end and escaping
   the decode window entirely.

Fix all three by replacing bare operations with their safe variants:
  ceph_decode_copy   -> ceph_decode_copy_safe
  *p += sizeof(...)  -> ceph_decode_skip_n
  ceph_decode_32(p)  -> ceph_decode_32_safe
  *p += len          -> ceph_decode_skip_n

A new label is added to return -EINVAL on any bounds violation.
-EINVAL is appropriate here: the data received from the OSD
is structurally malformed, which is an invalid argument to the decode
contract regardless of whether the caller or the wire is at fault.

Attacker model: a malicious or compromised OSD in a multi-tenant Ceph
deployment can trigger this against any kernel client that issues the
lock.get_info class method (e.g. during RBD exclusive lock acquisition)
without any further privileges beyond OSD session establishment.

[ idryomov: use ceph_decode_skip_string() to skip description, trim
  changelog ]

Cc: stable@vger.kernel.org
Fixes: d4ed4a5 ("libceph: support for lock.lock_info")
Signed-off-by: Pavitra Jha <jhapavitra98@gmail.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  net/ceph/cls_lock_client.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=1ed45c8d96498725eb54f740172f9068d8673906

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

The original Linux kernel CVE announcement for CVE-2026-80561 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80561

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:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 8.1

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: 6
  Paranoid ActionableScore: 7

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: YES
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
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My contact email for such notifications is alexanjelausa@gmail.com (and both
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