[CVE-2026-68082][MODERATE 7.0] libceph: fix two unsafe bare decodes in decode_lockers()

[CVE-2026-68082][MODERATE 7.0] libceph: fix two unsafe bare decodes in decode_lockers()

[AL-KERNEL]

CVE: CVE-2026-68082
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: libceph: fix two unsafe bare decodes in decode_lockers()
Commit: a54be593d0b749161b08a1e56189b2cb9114267a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a54be593d0b749161b08a1e56189b2cb9114267a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68082
Analysis date: Sat, 08 Aug 2026 05:54:37 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious or compromised Ceph OSD can send malformed lock.get_info data that triggers slab out-of-bounds reads in libceph decode_lockers, potentially causing kernel crash behavior and limited lock-type semantic influence in affected Ceph kernel clients.

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

The original Linux kernel CVE announcement for CVE-2026-68082 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68082

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-2026-68082	MODERATE	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';CWE-125;*CWE-20;CWE-754;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '7';DESCR 'An out-of-bounds read in libceph decode_lockers can occur because ceph_decode_32 and ceph_decode_8 were used without bounds checks after a decoded structure boundary. A malicious or compromised Ceph OSD can return malformed lock.get_info data with struct_len 0 or with the cursor advanced exactly to the end of the buffer, causing slab OOB reads in the kernel client. For the CVSS the PR:N because the attacker does not need privileges on the client host, but must be able to act as a malicious or compromised Ceph OSD or tamper with OSD traffic. The issue is network reachable in Ceph deployments where the client accepts replies from such an OSD, but it is normally limited to internal storage networks rather than the public Internet. Impact is at least denial of service through a kernel crash or bad allocation behavior. The paranoid impact uses C:L/I:L/A:H because the bug is a real OOB read and one decoded byte can influence the lock type discriminator, but there is no strong evidence of an arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 6)	YES	REMOTE READ OOB INIT ERRORPATH NETWORK LINUS KPANIC  KPANIC DECREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCORELOWERTHAN7	NO	NO	checked

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

ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative score signals:

* Remote reachable / network-triggerable: +2
  A malicious or compromised Ceph OSD can trigger the bug against a kernel Ceph client by returning malformed `lock.get_info` data.

* Memory corruption, weak/indirect corruption candidate: +1
  The primitive is a slab out-of-bounds read, not an OOB write or UAF. The decoded values are then used as `num_lockers` and `type`, so this is more than a harmless parser bug.

* Reliable kernel crash / strong DoS: +1
  The OOB read can lead to KASAN reports, invalid allocation behavior, or kernel crash conditions.

* Integrity impact plausible: +1
  The one-byte OOB read feeds `*type`, which is used as a lock type discriminator by callers. This gives limited but plausible semantic influence.

* Important filesystem/storage path: +1
  This affects libceph client handling for Ceph/RBD locking paths, including RBD exclusive lock related flows.

* Corruption primitive highly constrained: -1
  There is no demonstrated attacker-controlled overwrite, UAF reclaim, arbitrary write, or direct disclosure primitive.

Paranoid additional signal:

* Confidentiality impact plausible: +1
  The bug is a real kernel OOB read. Although no direct user-visible disclosure path is shown, limited confidentiality concern is defensible for manual triage.

## 3. Reachability analysis

The likely attacker is a malicious or compromised Ceph OSD, or an actor able to tamper with OSD traffic. The victim does not need local code execution on the client host, so this is not a local-user-only issue. It is network reachable within Ceph deployments, but normally through internal storage networks rather than the public Internet.

Namespaces and containers do not materially reduce the client-side kernel impact if the host kernel Ceph client processes the malicious OSD response. The affected path is only relevant on systems using the kernel Ceph client and lock information paths such as RBD exclusive locking, so it is not a default exposure for generic Linux hosts.

## 4. Severity interpretation

This is stronger than an ordinary Moderate parser issue because it is network-triggerable inside the Ceph trust boundary and involves kernel slab OOB reads. It does not look like a clear Important-class LPE because the patch shows read-only OOB access, not UAF, OOB write, controlled object replacement, or arbitrary write.

The realistic impact is DoS plus limited semantic integrity concern. The paranoid interpretation supports Actionable Moderate handling due to the network-reachable kernel memory-safety primitive.

## 5. One-sentence report phrase

A malicious or compromised Ceph OSD can send malformed lock.get_info data that triggers slab out-of-bounds reads in libceph decode_lockers, potentially causing kernel crash behavior and limited lock-type semantic influence in affected Ceph kernel clients.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

Reason: this is a network-reachable kernel OOB read in a storage client trust boundary, with decoded OOB data influencing allocation count and lock type behavior.

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

Patch: libceph: fix two unsafe bare decodes in decode_lockers()
Commit: a54be593d0b749161b08a1e56189b2cb9114267a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a54be593d0b749161b08a1e56189b2cb9114267a

Commit description:

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

1. ceph_decode_32(p) at the num_lockers field has no preceding bounds
   check. ceph_start_decoding() accepts struct_len=0 as valid -- the
   internal ceph_decode_need(p, end, 0, bad) always passes -- so when an
   OSD sends struct_len=0, ceph_start_decoding() returns success with
   p == end. The immediately following bare ceph_decode_32(p) then reads
   4 bytes past the validated buffer boundary. The garbage value is
   passed directly to kzalloc_objs() as the locker count.

   The sibling function decode_watchers() in osd_client.c already uses
   ceph_decode_32_safe() after its own ceph_start_decoding() call.
   decode_lockers() was the only site using the bare variant.

2. ceph_decode_8(p) after the decode_locker() loop has no preceding
   bounds check. If an OSD crafts num_lockers such that the loop
   advances p exactly to end, the subsequent bare ceph_decode_8(p) reads
   one byte past the validated buffer boundary. The result is passed
   directly into *type, which is used as a lock type discriminator by
   callers, giving an OSD-controlled one-byte OOB read with direct
   influence over the lock type field.

Fix both by replacing bare operations with their safe variants:
  ceph_decode_32(p) -> ceph_decode_32_safe(p, end, *num_lockers,
                                           err_inval)
  ceph_decode_8(p)  -> ceph_decode_8_safe(p, end, *type,
                                          err_free_lockers)

The goto targets differ intentionally:
  err_inval: is a new label returning -EINVAL directly. It is used for
  the pre-allocation failure path where *lockers is not yet allocated
  and must not be passed to ceph_free_lockers().

  err_free_lockers: is the existing label. It is used for the
  post-allocation failure path where *lockers is allocated and must
  be freed.

ret is set to -EINVAL before ceph_decode_8_safe() so that
err_free_lockers returns the correct error code on bounds violation.
Without this, err_free_lockers would return a stale ret value (0 from
the successful decode_locker() loop), silently swallowing the error.

-EINVAL is correct for both failure paths. The data received from the
OSD is structurally malformed. -ENOMEM would misrepresent the failure
class to callers and to stable@ backporters triaging error paths.

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).

[ idryomov: trim changelog, formatting ]

Cc: stable@vger.kernel.org
Fixes: d4ed4a5 ("libceph: support for lock.lock_info")
Signed-off-by: Pavitra Jha <jhapavitra98@gmail.com>
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:
  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=a54be593d0b749161b08a1e56189b2cb9114267a

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

The original Linux kernel CVE announcement for CVE-2026-68082 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68082

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:H/PR:N/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/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: 5
  Paranoid ActionableScore: 6

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).

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