[CVE-2026-46150][IMPORTANT] fanotify: fix false positive on permission events

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

CVE: CVE-2026-46150
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: fanotify: fix false positive on permission events
Commit: 895ebbedf88318607c24acc0f591c74b165e1d0a
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=895ebbedf88318607c24acc0f591c74b165e1d0a
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46150
Analysis date: Thu, 28 May 2026 12:19:29 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A detached fsnotify mark from an unrelated group could cause fanotify permission-event preparation to fail incorrectly, allowing local access to bypass a userspace-enforced file permission policy.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-46150 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46150

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-46150	IMPORTANT	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:H/I:H/A:N';CWE-863;CWE-284;CWE-362;CWE-367;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:N';BEST CVSS score: '6.3';DESCR 'fsnotify permission event preparation could fail on a detached mark that belonged to an unrelated group, causing the current fanotify permission check to be bypassed instead of skipping that unrelated mark. A local user may benefit when accessing a file protected by a fanotify permission policy while another group mark is being removed, although reliable triggering depends on a race with mark detachment. For the CVSS the PR:L is used because the attacker needs local access to the protected object and the relevant filesystem event path, not full administrative privileges. The issue is not network reachable. Impact is a security policy bypass with possible confidentiality or integrity impact for files protected by fanotify based scanners or access-control daemons, with no supported kernel memory corruption or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7) 	MAYBE	DISK SIMPLEFIX LINUS  KPANIC INCREASED_TO_MODERATE7_FROM_MODERATE_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user can access a protected file and trigger the relevant filesystem event path.
* Security-boundary bypass with sensitive-object access: +2. The bug can bypass fanotify permission checks, which are commonly used by scanners, DLP agents, sandboxing, and access-control daemons.
* Confidentiality impact plausible: +1. Bypassing permission events may allow reads that the fanotify policy would have denied.
* Integrity impact plausible: +1. Bypassing permission events may allow writes or modifications that the policy would have denied.
* Hard/racy condition: -1. The bypass depends on a race with detached marks from another group.

Paranoid additional signals:

* Cross-boundary / policy bypass: +1. This can undermine a userspace-mediated security policy boundary.
* Practical sensitive-object access concern: +1. If fanotify protects sensitive paths, bypassing the permission event can expose files or operations that policy intended to block.

Not counted:

* No kernel memory corruption.
* No UAF, OOB write, arbitrary write, or information leak from kernel memory.
* No direct privilege escalation primitive.
* No network reachability.

## 3. Reachability analysis

The attacker is local and needs access to the filesystem object whose access is mediated by a fanotify permission group. The vulnerable condition occurs when an unrelated group has a detached mark that causes `fsnotify_get_mark_safe()` to fail, and the code treats that as a failure of the current permission group rather than skipping it.

Namespaces and containers matter because fanotify-based security policies may be used around container or sandbox file access. The attacker does not need to be root, but reliable exploitation depends on racing mark detachment and the protected access.

## 4. Severity interpretation

This is an actionable Moderate at minimum and a Strong Important candidate where fanotify is used as an access-control boundary. The key issue is not memory safety but a permission-check bypass.

The realistic impact depends heavily on deployment. If fanotify is only used for observation, severity is lower. If it enforces file access policy, confidentiality and integrity impact can be significant.

## 5. One-sentence report phrase

A detached fsnotify mark from an unrelated group could cause fanotify permission-event preparation to fail incorrectly, allowing local access to bypass a userspace-enforced file permission policy.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

This is a potential access-control bypass. Review is required to determine whether fanotify permission events are used for security enforcement in the affected environment.

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

Patch: fanotify: fix false positive on permission events
Commit: 895ebbedf88318607c24acc0f591c74b165e1d0a
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=895ebbedf88318607c24acc0f591c74b165e1d0a

Commit description:

fsnotify_get_mark_safe() may return false for a mark on an unrelated group,
which results in bypassing the permission check.

Fix by skipping over detached marks that are not in the current group.

CC: stable@vger.kernel.org
Fixes: abc7757 ("fsnotify: Provide framework for dropping SRCU lock in ->handle_event")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Link: https://patch.msgid.link/20260410144950.156160-1-mszeredi@redhat.com
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/notify/fsnotify.c
  fs/notify/mark.c
  include/linux/fsnotify_backend.h

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=895ebbedf88318607c24acc0f591c74b165e1d0a

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

The original Linux kernel CVE announcement for CVE-2026-46150 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46150

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:L/I:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
  The Best / paranoid CVSS score: 6.3

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: 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).