[CVE-2026-89560][MODERATE 7.0] landlock: Require LANDLOCK_ACCESS_FS_MAKE_REG for whiteout creation

[CVE-2026-89560][MODERATE 7.0] landlock: Require LANDLOCK_ACCESS_FS_MAKE_REG for whiteout creation

[AL-KERNEL]

CVE: CVE-2026-89560
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: landlock: Require LANDLOCK_ACCESS_FS_MAKE_REG for whiteout creation
Commit: 627ce4902df1d737e99306daae5a87c68b876d16
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=627ce4902df1d737e99306daae5a87c68b876d16
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89560
Analysis date: Sat, 12 Sep 2026 02:40:01 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89560 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89560

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-2026-89560	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-89560 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:L/A:L';CWE-284;CWE-863;CWE-693;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N';BEST CVSS score: '4.4';DESCR 'Landlock did not consistently require the expected MAKE_REG permission when a sandboxed process created OverlayFS whiteout objects. In the renameat2 RENAME_WHITEOUT path, a directory entry could be created even when all LANDLOCK_ACCESS_FS_MAKE_* rights were denied, which makes this a local access control bypass rather than a memory corruption issue. For the CVSS the PR:L value is used because the attacker must already be able to run local code in a Landlock restricted process and reach the relevant filesystem operation. The issue is not network reachable. Impact is mainly low integrity impact through unauthorized whiteout creation and possible policy bypass. A low availability impact is defensible in the paranoid score because whiteouts can hide lower layer files in an OverlayFS view and may disrupt sandboxed workloads.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	DANGER HARDWARE LINUS  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN5 KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHERTHAN5 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_A
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5. No floor or cap applied.
* Raw paranoid score: 6
* Paranoid score: 6. No floor or cap applied.
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

2. Signal breakdown

Awarded conservative signals:

* +2 Concrete authorization decision bypass. Landlock could allow creation of a whiteout directory entry through renameat2(RENAME_WHITEOUT) even when all LANDLOCK_ACCESS_FS_MAKE_* rights were denied.
* +1 Local unprivileged trigger. Whiteout creation via renameat2 or mknod does not require host-admin-equivalent privilege when the process already has ordinary local execution and filesystem access in the relevant sandbox context.
* +1 Integrity plausible. The attacker can create an unauthorized filesystem object that affects OverlayFS name visibility semantics.
* +1 Practical exploit chain strongly implied. The commit explicitly identifies reachable syscall paths and states that renameat2(RENAME_WHITEOUT) could create a directory entry despite denied Landlock creation rights.

Additional paranoid signal:

* +1 Availability plausible. Whiteouts can hide lower-layer files in an OverlayFS view, so unauthorized whiteout creation can plausibly disrupt sandboxed workloads or application-visible filesystem state.

Non-awarded signals:

* RealUAF not awarded. No lifetime or stale-object primitive is established.
* Memory corruption not awarded. The patch changes access-control classification and permission checks, not memory safety.
* Confidentiality not awarded. No protected read or disclosure path is established.
* Strong LPE not awarded. No root escalation, credential modification, or privileged FD/resource theft is shown.
* Remote reachability not awarded. The trigger is local filesystem operation, not network input.
* Extra availability beyond the paranoid low-disruption interpretation not awarded. No kernel crash, filesystem shutdown, or host-wide DoS is shown.

3. Reachability analysis

The relevant attacker is a local process confined by a Landlock domain. The complete trigger is a local filesystem operation such as renameat2(RENAME_WHITEOUT) or mknod of a whiteout-like object, subject to ordinary filesystem reachability and Landlock policy. Host administrator privilege is not required for the vulnerable authorization decision itself.

This is not a namespace-capability issue. No CAP_NET_ADMIN, user namespace capability, or network namespace stage is needed for the assessed primitive. The issue depends on Landlock being used as a sandbox boundary and on a filesystem or userspace OverlayFS workflow where whiteouts are meaningful. That is a deployment prerequisite, but not a host-admin requirement for the sandboxed attacker once the Landlock policy and accessible paths exist.

No race, special hardware, boot option, or timing window is involved. The behavior is deterministic for the affected authorization path.

4. Primitive and severity interpretation

The exact primitive is an LSM authorization bypass for filesystem object creation. The vulnerable path misclassified or failed to check whiteout creation consistently, allowing an externally visible directory entry to be created when the intended Landlock MAKE permission should deny it.

This is Class A because the patch directly restores a missing mandatory access-control condition for a security boundary. It is not memory corruption and not a UAF. The demonstrated consequence is local Landlock policy bypass with low integrity impact. The paranoid consequence is limited availability disruption inside OverlayFS-style views due to unauthorized whiteout semantics.

ImportantCandidate=YES because Landlock is a security boundary and the bug is a concrete authorization decision bypass. AutoDowngradeAllowed=NO because automatically closing an LSM policy bypass would risk losing a meaningful security-boundary issue, even though the numeric score remains in the Actionable Moderate range rather than clear Important.

Likely operational severity is Actionable Moderate. It needs manual review for products relying on Landlock to confine untrusted workloads, especially with fuse-overlayfs or other userspace OverlayFS-style workflows.

5. One-sentence report phrase

Landlock incorrectly allowed OverlayFS whiteout creation through local filesystem operations even when the required MAKE permission was denied, enabling a sandboxed local process to bypass filesystem creation policy with low integrity and possible low availability impact.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is a concrete LSM authorization bypass affecting a sandbox security boundary, even though there is no memory corruption, no remote trigger, and no demonstrated privilege escalation.

7. Call-site confidence

Call-site confidence: high

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

Patch: landlock: Require LANDLOCK_ACCESS_FS_MAKE_REG for whiteout creation
Commit: 627ce4902df1d737e99306daae5a87c68b876d16
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=627ce4902df1d737e99306daae5a87c68b876d16

Commit description:

Whiteout objects are used in the upper layer of an OverlayFS to
indicate that the file with this name does not exist in the unified
view, even if it is present in one of the lower layer file systems.

For the userspace implementations of OverlayFS (fuse-overlayfs),
whiteout objects can be created from userspace as well:

* mknod(2) with S_IFCHR and makedev(0, 0)
* renameat2(2) with RENAME_WHITEOUT,
  creating the whiteout in the old place of the moved file.

This commit guards whiteout creation in both of these cases with
LANDLOCK_ACCESS_FS_MAKE_REG.  Whiteout objects are *not* considered
character devices and are not bound to a driver.

LANDLOCK_ACCESS_FS_MAKE_REG describes the same permission class as a
whiteout object: creating one is the only S_IFCHR creation that the VFS
exempts from CAP_MKNOD, so it is as unprivileged as creating a regular
file, while LANDLOCK_ACCESS_FS_MAKE_CHAR and
LANDLOCK_ACCESS_FS_MAKE_BLOCK keep meaning the creation of devices that
expose a kernel interface [1].

For the mknod(2) case, introduce a Landlock erratum.  The creation of
whiteout objects through mknod(2) was previously guarded using
LANDLOCK_ACCESS_FS_MAKE_CHAR, and it is now guarded using
LANDLOCK_ACCESS_FS_MAKE_REG.

For the renameat2(2) case, fix a bug: Before this commit, renameat2(2)
with RENAME_WHITEOUT would create a directory entry even when all
LANDLOCK_ACCESS_FS_MAKE_* rights were denied.

This does not affect normal renames within layered OverlayFS mounts:
When doing a regular rename() on a mounted fuse-overlayfs, it is the
fuse-overlayfs daemon that exercises renameat2() with RENAME_WHITEOUT,
and only the Landlock domain of that daemon is checked there.

Suggested-by: Christian Brauner <brauner@kernel.org>
Suggested-by: Mickaël Salaün <mic@digikod.net>
Cc: stable@vger.kernel.org
Fixes: cb2c7d1 ("landlock: Support filesystem access-control")
Depends-on: 49c9e09 ("landlock: Fix handling of disconnected directories")
Depends-on: fe72ce6 ("landlock: Add errata documentation section")
Signed-off-by: Günther Noack <gnoack@google.com>
Link: https://patch.msgid.link/20260720.chow9ohYie5b@digikod.net [1]
Link: https://patch.msgid.link/20260813093157.1436894-3-gnoack@google.com
[mic: Record why LANDLOCK_ACCESS_FS_MAKE_REG is the matching right, and
add link(2) to the user doc]
Signed-off-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  include/uapi/linux/landlock.h
  security/landlock/errata/abi-1.h
  security/landlock/fs.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=627ce4902df1d737e99306daae5a87c68b876d16

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

The original Linux kernel CVE announcement for CVE-2026-89560 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89560

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:L/PR:L/UI:N/S:U/C:N/I:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:L
  The Best / paranoid CVSS score: 4.4

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).

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).