[CVE-2026-52990][MODERATE REGULAR] fsnotify: fix inode reference leak in fsnotify_recalc_mask() [ Upstream

[CVE-2026-52990][MODERATE REGULAR] fsnotify: fix inode reference leak in fsnotify_recalc_mask() [ Upstream

[AL-KERNEL]

CVE: CVE-2026-52990
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: fsnotify: fix inode reference leak in fsnotify_recalc_mask() [ Upstream
Commit: 8c8afa6444e6bdc145d2bf2f3aeeca6da3e36b42
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8c8afa6444e6bdc145d2bf2f3aeeca6da3e36b42
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52990
Analysis date: Fri, 26 Jun 2026 07:27:34 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Low-like, borderline manual review only if fsnotify abuse is considered relevant in the environment
Manual review required: NO

Summary:
A race in fsnotify inode reference accounting can leak an inode reference when HAS_IREF transitions from set to cleared, allowing a local user to cause a hung unmount or superblock shutdown path under timing-dependent conditions.

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

The original Linux kernel CVE announcement for CVE-2026-52990 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52990

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: NO

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-2026-52990	MODERATE	CHECK	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-362;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'fsnotify_recalc_mask() can race with mark removal and lose the required inode reference drop when the connector HAS_IREF state changes from set to cleared. This leaves a leaked inode reference and can make fsnotify_sb_delete block during unmount or superblock shutdown, resulting in a local denial of service. For the CVSS the PR:L is used because a local process must create or remove fsnotify marks to reach the race, while no network path is involved. AC:H is used because reliable triggering depends on a narrow timing window between adding an evictable mark and detaching another mark on the same connector. Impact is availability only in the base case, with no supported confidentiality or integrity primitive because the bug is a reference leak rather than memory corruption.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like, borderline manual review only if fsnotify abuse is considered relevant in the environment (with actual score 3) 	MAYBE	DISK INIT WARNONLY RACE LEAK LINUS  INCREASED_FROM_LOW_TO_MODERATE70_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN3 DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Low-like, borderline manual review only if fsnotify abuse is considered relevant in the environment**

## 2. Signal breakdown

* Local unprivileged trigger: +1
  fsnotify marks can commonly be created and removed by local users on objects they can access, so the race is reachable from local user context.

* Availability impact realistic: +1
  The leaked inode reference can block `fsnotify_sb_delete()` during unmount or superblock shutdown, producing a hung task and local DoS against unmount or cleanup paths.

* Broad/default/common subsystem: +1
  fsnotify/inotify/fanotify infrastructure is common and broadly enabled, although the exact race condition is narrow.

* Hard or unreliable race / special timing required: -1
  The described trigger requires a timing window between adding an evictable mark and detaching a non-evictable mark on the same connector.

* Paranoid additional strong DoS concern: +1
  In the paranoid interpretation, a persistent leaked inode reference can repeatedly block unmount or shutdown of affected filesystems, making the availability effect stronger than a transient warning.

No memory corruption signal is counted. The bug is an inode reference leak / lifetime accounting race, not a UAF, double free, OOB write, arbitrary write, or page-cache corruption primitive.

## 3. Reachability analysis

A local process that can create and remove fsnotify marks can potentially trigger the race. No network reachability is indicated. Namespaces or containers may make fsnotify usage available to reduced-privilege workloads, but the observed harmful effect is blocking unmount or superblock shutdown, which is usually noticed when a privileged cleanup path runs. The path is common in Linux systems, but reliable exploitation requires race timing and a suitable filesystem or mount lifecycle.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like local DoS issue, not an Important-class vulnerability. The realistic impact is a leaked inode reference causing a hung unmount path. There is no supported confidentiality or integrity impact and no practical privilege escalation primitive shown by the patch. The theoretical concern is limited to persistent availability impact from reference leakage, not memory corruption.

## 5. One-sentence report phrase

A race in fsnotify inode reference accounting can leak an inode reference when HAS_IREF transitions from set to cleared, allowing a local user to cause a hung unmount or superblock shutdown path under timing-dependent conditions.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be auto-closed or deferred in most triage flows because it is a local timing-dependent reference leak with DoS-only impact and no evidence of memory corruption, privilege escalation, information disclosure, or network reachability.

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

Patch: fsnotify: fix inode reference leak in fsnotify_recalc_mask() [ Upstream
Commit: 8c8afa6444e6bdc145d2bf2f3aeeca6da3e36b42
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8c8afa6444e6bdc145d2bf2f3aeeca6da3e36b42

Changed files:
  fs/notify/mark.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=8c8afa6444e6bdc145d2bf2f3aeeca6da3e36b42

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

The original Linux kernel CVE announcement for CVE-2026-52990 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-52990

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:L
  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: 2
  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).