[CVE-2026-72368][MODERATE REGULAR] cachefiles: Fix double unlock in nomem_d_alloc error path [ Upstream

[CVE-2026-72368][MODERATE REGULAR] cachefiles: Fix double unlock in nomem_d_alloc error path [ Upstream

[AL-KERNEL]

CVE: CVE-2026-72368
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: cachefiles: Fix double unlock in nomem_d_alloc error path [ Upstream
Commit: 26757dac15175f2a42e3537f1ba86e62456d48f1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=26757dac15175f2a42e3537f1ba86e62456d48f1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72368
Analysis date: Sat, 15 Aug 2026 20:56:11 -0400
ActionableScore: 4
ActionableScore lower bound: 3
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A double unlock in the cachefiles ENOMEM error path can corrupt the parent inode rwsem state after start_creating() has already released the lock, allowing a local workload on a cachefiles-enabled system to trigger a potential DoS through lock corruption.

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

The original Linux kernel CVE announcement for CVE-2026-72368 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72368

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.

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

CVE-2026-72368	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';CWE-667;CWE-362;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'A double unlock can occur in the cachefiles ENOMEM error path because start_creating already releases the parent inode lock when __start_dirop fails. The later nomem_d_alloc path calls inode_unlock again and can corrupt the rwsem state for the directory lock. This is primarily a local availability issue that may lead to warnings, deadlocks, a hung cache operation, or a kernel crash. For the CVSS the PR:L is used for the paranoid score because a local user or local process may trigger cache population on an already configured cachefiles setup, while reliable triggering also depends on reaching the ENOMEM path. The issue is not network reachable directly and requires local interaction with a system where cachefiles or FS-Cache is enabled. Impact is at least local denial of service. In the paranoid view, limited confidentiality or integrity impact is kept possible because corrupted locking state can weaken synchronization around kernel VFS objects, but the patch does not show a direct arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 4)  SKIP CVE-2026-72368 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 7ab96df840e60eb933abfe65fc5fe44e72f16dc0 YES  NO NO unknown 	MAYBE	LOCK DISK ERRORPATH LINUS  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=4
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 4
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

Triggered signals:

* Local unprivileged trigger: +1
  A local user or local process may indirectly trigger cachefiles directory creation or cache population if cachefiles or FS-Cache is already configured by the administrator.

* Memory corruption, weak or indirect corruption candidate: +1
  The bug is a double unlock of an inode rwsem. This corrupts synchronization state, but the patch does not show attacker-controlled overwrite, UAF reclaim, type confusion, arbitrary write, or callback control.

* Availability impact realistic: +1
  Corrupted rwsem state can plausibly lead to warnings, deadlock, hung cache operations, or kernel crash.

* Important filesystem/storage path: +1
  The affected code is in cachefiles namei handling and participates in filesystem cache directory creation, but there is no evidence of persistent filesystem metadata corruption.

Negative signals:

* Hard or unreliable trigger condition: -1
  The vulnerable path requires start_creating() to fail with -ENOMEM, which is a special error path and not a normal steady-state operation.

* Configuration-dependent subsystem: -1
  Practical exposure requires cachefiles or FS-Cache to be enabled and configured.

Paranoid-only interpretation:

* The paranoid score keeps the issue at 4 because rwsem corruption is more serious than a simple resource leak, but there is no concrete primitive for privilege escalation or arbitrary memory corruption.

## 3. Reachability analysis

The issue is local, not network reachable directly. It requires a system where cachefiles or FS-Cache is configured, and then a local workload must reach cachefiles_get_directory() while start_creating() fails with -ENOMEM. Namespace or container impact depends on whether an untrusted workload can cause cached filesystem activity on a host-configured cachefiles backend. Full cachefiles setup is administrative, but triggering cache population may be possible from less privileged local code after setup.

Call-site confidence: high. The patch and commit message include the relevant error path and the start_creating() behavior that already releases the parent inode lock.

## 4. Severity interpretation

This behaves more like a borderline Moderate issue than an Important-class vulnerability. The realistic impact is local DoS through corrupted lock state, deadlock, hung filesystem-cache operation, or crash. The theoretical concern is that corrupted synchronization around VFS objects could have secondary effects, but the patch does not support UAF reclaim, arbitrary write, object replacement, or a demonstrated LPE chain. Therefore it should not be auto-escalated to Important, but it is also not a trivial cleanup.

## 5. One-sentence report phrase

A double unlock in the cachefiles ENOMEM error path can corrupt the parent inode rwsem state after start_creating() has already released the lock, allowing a local workload on a cachefiles-enabled system to trigger a potential DoS through lock corruption.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the bug corrupts kernel lock state in a filesystem-cache path, which is more serious than a simple leak or warning, but the trigger depends on an ENOMEM error path and there is no demonstrated privilege-escalation primitive.

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

Patch: cachefiles: Fix double unlock in nomem_d_alloc error path [ Upstream
Commit: 26757dac15175f2a42e3537f1ba86e62456d48f1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=26757dac15175f2a42e3537f1ba86e62456d48f1

Changed files:
  fs/cachefiles/namei.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=26757dac15175f2a42e3537f1ba86e62456d48f1

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

The original Linux kernel CVE announcement for CVE-2026-72368 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72368

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:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H
  The Best / paranoid CVSS score: 5.8

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: 3
  Paranoid ActionableScore: 4

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).