[CVE-2026-92503][MODERATE REGULAR] ext4: fix ABBA deadlock in ext4_xattr_inode_cache_find() [ Upstream

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

CVE: CVE-2026-92503
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: ext4: fix ABBA deadlock in ext4_xattr_inode_cache_find() [ Upstream
Commit: 7720fddd1fe344d14be258a2028f74ebf1569511
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7720fddd1fe344d14be258a2028f74ebf1569511
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92503
Analysis date: Thu, 17 Sep 2026 19:34:27 -0400
ActionableScore: 3
ActionableScore lower bound: unknown
Actionable bucket: Borderline / manual review recommended
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-2026-92503 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92503

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
======================================================================

CVE-2026-92503	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-92503 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-833;CWE-667;CWE-362;BEST CVSS score: '4.7';DESCR 'An ABBA deadlock in ext4 xattr handling can occur when ext4_xattr_inode_cache_find holds a reference to a shared mbcache entry and then calls ext4_iget for an EA inode that is being evicted. The caller can block waiting for inode eviction, while the eviction path can block waiting for the same mbcache entry reference to be released. This can leave ext4 operations stuck and can cause a local denial of service, especially when the affected filesystem is important for system operation. For the CVSS the PR:L is used because reliable triggering requires a local user or process able to run xattr workloads on an ext4 filesystem with ea_inode enabled, while the mount and filesystem feature setup is normally administrative. The issue is not network reachable by itself and does not show a concrete memory corruption, information disclosure, or privilege escalation primitive. Impact is denial of service via filesystem deadlock.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)	YES	LOCK DEADLOCK DANGER DISK INIT NOMEMCHK RACE IMPROVEONLY LINUS SYZBOT  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	YES	NO	checked

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

ActionableScore=3
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 3
* Conservative score: 3
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::

No floor or cap changed the score.

2. Signal breakdown

Positive signals:

* +1 Local below-host-admin trigger: a local user or process that can run xattr workloads on a writable ext4 filesystem with ea_inode enabled can plausibly reach the affected path.
* +1 Reliable DoS: the supplied report establishes an ABBA deadlock between ext4_xattr_inode_cache_find() and ext4_evict_ea_inode(), causing stuck filesystem operations.
* +1 Important filesystem path: ext4 xattr and EA inode handling are core filesystem paths, and a deadlock there can affect system availability when the filesystem is important.

Negative signals:

* No -1 hard race penalty: concurrency is required, but the issue was reported by syzbot/stress-ng and appears repeatable under load rather than a narrow one-shot timing window.
* No -1 rare subsystem penalty: ea_inode is a specific ext4 feature and limits exposure, but ext4 itself is common and the feature is not enough by itself to treat the bug as obscure.

Important non-awarded signals:

* No UAF or post-lifetime stale-object use is established.
* No concrete repeated release/refcount operation is established.
* No controlled reclaim, arbitrary write, OOB access, or type confusion is shown.
* No confidentiality or integrity impact is awarded.
* No privilege escalation signal is awarded.
* No network reachability is established.
* No authorization or security-boundary bypass is established.
* Extra availability is not double-counted beyond the same deadlock/DoS consequence.

Repeated-release/refcount check:

* First release can end lifetime: not applicable.
* Exact same reference survives: not established.
* Second lifetime/refcount mutation: not established.
* Concrete repeated release/refcount +1: not awarded.
* Paranoid repeated-refcount leverage +1: not awarded.
* FLOOR 5: not applied.

3. Reachability analysis

The evaluated attacker is a local user or local process with permission to create or modify extended attributes on an affected ext4 filesystem. The ea_inode filesystem feature or mount/format state is a prerequisite and is normally controlled by an administrator, but once such a filesystem is available the triggering xattr workload does not appear to require host-admin-equivalent privilege.

This is not namespace-scoped in the relevant sense. No network namespace, container capability, or delegated namespace capability is needed or shown. The issue is not directly network reachable.

There is prior privileged setup in the practical deployment sense because the filesystem must exist with ea_inode support enabled. That limits exposure, but it does not mean the runtime trigger itself requires host administrator privileges.

The deadlock requires concurrent xattr and eviction activity. The supplied report from syzbot/stress-ng supports practical repeatability under stress workloads, so this is treated as a concurrency-dependent local DoS rather than a speculative or extremely narrow race.

4. Primitive and severity interpretation

The exact primitive is an ABBA deadlock, not memory corruption. One path holds a shared mbcache_entry reference and then waits in ext4_iget() for an EA inode eviction to complete. The eviction path waits for that mbcache_entry reference to be released. The two waits can form a cycle and leave filesystem operations stuck.

This is not an active structured UAF and not fixed stale storage. It is a lock/lifetime-wait ordering problem involving mbcache entry references and inode eviction state. The demonstrated consequence is local denial of service through filesystem deadlock.

PrimitiveClass is CLASS_C because the established behavior is DoS/invalid wait-state behavior without an independently useful corruption primitive. ImportantCandidate is NO because there is no evidence of controlled memory corruption, authorization bypass, COW ownership violation, privileged resource theft, or LPE. AutoDowngradeAllowed is YES because the issue can be treated as an ordinary or borderline Moderate local DoS after manual confirmation of exposure.

Likely operational severity is Moderate-like. It should not be treated as Important solely from being in ext4, but it is worth manual review because it affects a core filesystem path and depends on a nontrivial concurrency/lifetime interaction.

5. One-sentence report phrase

An ext4 ea_inode xattr workload can deadlock ext4_iget() against EA inode eviction, allowing a local user with xattr access on an affected filesystem to cause a filesystem denial of service.

6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: this is a core filesystem deadlock with local DoS impact and deployment-dependent exposure through ea_inode, but the supplied evidence does not show memory corruption, privilege escalation, or a security-boundary bypass.

7. Call-site confidence

Call-site confidence: high

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

Patch: ext4: fix ABBA deadlock in ext4_xattr_inode_cache_find() [ Upstream
Commit: 7720fddd1fe344d14be258a2028f74ebf1569511
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7720fddd1fe344d14be258a2028f74ebf1569511

Changed files:
  fs/ext4/ext4.h
  fs/ext4/inode.c
  fs/ext4/xattr.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=7720fddd1fe344d14be258a2028f74ebf1569511

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

The original Linux kernel CVE announcement for CVE-2026-92503 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-92503

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: unknown
  Paranoid ActionableScore: 3

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).