[CVE-2026-89652][IMPORTANT] ceph: bound copied dentry name length in NFS export get_name

[CVE-2026-89652][IMPORTANT] ceph: bound copied dentry name length in NFS export get_name

[AL-KERNEL]

CVE: CVE-2026-89652
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: ceph: bound copied dentry name length in NFS export get_name
Commit: 61d9f27b191b838b96b697ce0bfaee39a138243a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=61d9f27b191b838b96b697ce0bfaee39a138243a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89652
Analysis date: Sat, 12 Sep 2026 02:21:17 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate
Manual review required: YES

Summary:
A malicious or compromised Ceph MDS can return an overlong name to a CephFS client re-exporting CephFS over NFS, causing an attacker-influenced slab out-of-bounds write in the kernel and at minimum a client crash with unresolved integrity impact.

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

The original Linux kernel CVE announcement for CVE-2026-89652 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89652

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: IMPORTANT
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-2026-89652	IMPORTANT	https://www.kernelcve.org/list/?q=CVE-2026-89652 CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-120;*CWE-20;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7.5';DESCR 'A slab out of bounds write in the CephFS NFS export get_name path can occur because ceph_get_name and __get_snap_name copied an MDS supplied name into a NAME_MAX sized buffer without validating the supplied length. A malicious or compromised Ceph MDS can return an overlong LOOKUPNAME or snap name and cause kernel memory corruption on a client that re exports CephFS over NFS. For the CVSS the PR:N because the attacker does not need a local account on the affected client when the malicious input is supplied by the remote MDS endpoint. The issue is network reachable only in the Ceph storage network or a trusted internal deployment where the client talks to the MDS. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to kernel memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate (with actual score 7)	YES	WRITE KASAN OOB DISK LINUS KPANIC 	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=6
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

## 1. ActionableScore

* Raw conservative score: 6
* Conservative score: 6
* Raw paranoid score: 7
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate**::

No floor or cap was applied. The paranoid score is emitted as the final ActionableScore because the patch establishes attacker-influenced kernel heap overwrite mechanics.

## 2. Signal breakdown

Positive signals:

* +2 Strong corruption primitive: MDS-supplied `dname_len` or snap `name_len` is used as the copy length into a `NAME_MAX`-sized caller buffer without bounds checking, producing a slab out-of-bounds write.
* +2 Network or adjacent-network reachable input source: the malformed name is supplied by a Ceph MDS over the CephFS client path. This is not public Internet exposure by default, but the attacker input crosses from a remote MDS endpoint into the client kernel.
* +1 Reliable kernel crash / strong DoS: KASAN reported slab out-of-bounds write, and kernel memory corruption can realistically crash the client.
* +1 Important filesystem/storage path: the bug is in CephFS NFS-export `get_name` handling, affecting filesystem export/name resolution semantics.
* Paranoid +1 Integrity plausible: the payload and length are MDS-influenced and the primitive is an out-of-bounds kernel write, so corruption of adjacent kernel state is plausible even though no exact target object is demonstrated.

Non-awarded or limited signals:

* RealUAF not awarded: this is an out-of-bounds write, not a lifetime bug.
* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Confidentiality impact not awarded: no read-back or disclosure path is established.
* Practical LPE chain not demonstrated.
* Extra availability point not awarded because the same crash/corruption consequence is already counted.
* No race or timing penalty: the issue is a deterministic missing length check, not a timing race.
* No host-admin penalty: attacker control is modeled as malicious or compromised MDS input, not victim host administration.

## 3. Reachability analysis

The direct malicious input source is a Ceph MDS response containing an overlong dentry or snap name. The affected client must have CephFS mounted and re-exported over NFS so that the NFS export `get_name` path reaches `ceph_get_name()` or `__get_snap_name()`.

The attacker does not need a local account on the affected client if they control, compromise, or can otherwise impersonate the relevant MDS endpoint. This is best treated as adjacent or internal storage-network reachability rather than broad Internet reachability. The issue is deployment-dependent because CephFS re-export over NFS is required, but that prerequisite does not make the primitive host-admin-only for the attacker.

Namespace-scoped privilege is not established. There is no evidence that user namespaces or network namespaces are material to the trigger. No special hardware dependency is present. No race repeatability issue is involved.

## 4. Primitive and severity interpretation

The exact primitive is an attacker-influenced slab out-of-bounds write in the kernel. The vulnerable code copies a remote MDS-provided name into a fixed `NAME_MAX` buffer and then writes a terminating NUL at the attacker-supplied length offset. This is an active kernel memory corruption primitive, not a pure validation warning and not a crash-only NULL dereference.

PrimitiveClass is CLASS_A because the patch directly establishes an attacker-influenced OOB write into kernel memory. The demonstrated consequence is kernel memory corruption and likely DoS. The speculative consequence is broader integrity impact or possible exploitation depending on adjacent object layout and allocator behavior, but no arbitrary write, controlled reclaim, or LPE chain is demonstrated.

ImportantCandidate is YES because this is a concrete remote/adjacent input driven kernel overwrite in a filesystem export path. AutoDowngradeAllowed is NO because automatically closing it as ordinary Moderate would discard a real kernel corruption primitive with unresolved exploitation leverage.

Likely operational severity is Important-class for affected deployments, especially where CephFS clients trust an MDS reachable over an internal storage network and re-export CephFS via NFS.

## 5. One-sentence report phrase

A malicious or compromised Ceph MDS can return an overlong name to a CephFS client re-exporting CephFS over NFS, causing an attacker-influenced slab out-of-bounds write in the kernel and at minimum a client crash with unresolved integrity impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: concrete attacker-influenced kernel OOB write is established, and the exact exploitability depends on buffer allocation context and adjacent kernel objects.

## 7. Call-site confidence

Call-site confidence: high

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

Patch: ceph: bound copied dentry name length in NFS export get_name
Commit: 61d9f27b191b838b96b697ce0bfaee39a138243a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=61d9f27b191b838b96b697ce0bfaee39a138243a

Commit description:

ceph_get_name() copies the MDS-supplied name into the caller's
NAME_MAX-sized buffer with memcpy(name, rinfo->dname, rinfo->dname_len)
and then writes name[rinfo->dname_len] = 0, without checking dname_len
against NAME_MAX. A malicious or buggy MDS that returns a LOOKUPNAME reply
with dname_len > NAME_MAX overflows the buffer. __get_snap_name() copies
rde->name / rde->name_len the same unchecked way.

Impact: a malicious or compromised Ceph MDS overflows the NAME_MAX name
buffer in a client's NFS-export get_name path, a slab out-of-bounds write
reported by KASAN. Reachable when a CephFS mount is re-exported over NFS.

Add ceph_export_copy_name(), which rejects lengths above NAME_MAX with
-ENAMETOOLONG before the copy, and use it in both ceph_get_name() and
__get_snap_name().

Cc: stable@vger.kernel.org
Fixes: 19913b4 ("ceph: add get_name() NFS export callback")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/ceph/export.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=61d9f27b191b838b96b697ce0bfaee39a138243a

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

The original Linux kernel CVE announcement for CVE-2026-89652 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89652

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:N/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).