[CVE-2026-72176][MODERATE REGULAR] mm/damon/sysfs-schemes: put stats for scheme_add_dirs() internal error

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

CVE: CVE-2026-72176
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mm/damon/sysfs-schemes: put stats for scheme_add_dirs() internal error
Commit: 50a753171d255895e5dd41566986b48dcec06f31
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=50a753171d255895e5dd41566986b48dcec06f31
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72176
Analysis date: Sun, 16 Aug 2026 00:47:58 -0400
ActionableScore: 3
ActionableScore lower bound: 1
Actionable bucket: Borderline manual review recommended / not auto close until kobject lifetime is checked
Manual review required: YES

Summary:
A DAMON sysfs scheme setup error path can put the wrong kobject after `tried_regions` setup failure, leaking the `stats` object and potentially dereferencing an uninitialized `tried_regions` pointer, causing a local kernel crash under uncommon failure conditions.

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

The original Linux kernel CVE announcement for CVE-2026-72176 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72176

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
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CVE-2026-72176	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-476;*CWE-457;*CWE-401;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.8';DESCR 'DAMON sysfs scheme setup has a faulty error path after stats setup succeeds and tried_regions setup fails. The old path puts scheme tried_regions instead of scheme stats, which leaks the stats kobject and can dereference scheme tried_regions when it is NULL, uninitialized, or already released by the failing setup helper. This can crash the kernel and may also indicate unsafe kobject lifetime handling in a rare allocation or setup failure path. For the CVSS the PR:L is used for the paranoid score because delegated DAMON sysfs control or service contexts may allow a non full administrator process to reach the configuration path. The issue is not network reachable and requires local control plane interaction with DAMON sysfs plus an uncommon setup failure condition. Impact is at least local denial of service via kernel crash and in worst case may allow limited confidentiality or integrity impact due to invalid kobject lifetime handling and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / not auto close until kobject lifetime is checked (with actual score 2)	YES	INIT LEAK ERRORPATH LINUS MEMORY  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 3
* Final recommended bucket: **Borderline manual review recommended / not auto close until kobject lifetime is checked**::

## 2. Signal breakdown

Conservative signals:

* Weak/indirect corruption candidate: +1. The error path can dereference `scheme->tried_regions` when it is NULL or uninitialized.
* Real lifetime corruption: +1. The wrong kobject is put on the failure path, causing a leaked `stats` kobject and potentially invalid kobject lifetime handling.
* Reliable kernel crash / strong DoS if reached: +1. The bad path can lead to invalid pointer dereference in kernel context.
* Hard or unreliable condition: -1. Triggering requires an uncommon internal setup failure, likely allocation failure or partial sysfs object creation failure.
* Requires admin/root/CAP-like access in typical deployments: -2. DAMON sysfs configuration is normally administrator controlled.

Paranoid additions/adjustments:

* Weak LPE concern: +1. Invalid kobject lifetime handling deserves manual review, although no attacker-controlled reclaim, write primitive, or callback control is shown.
* Privilege penalty softened in paranoid interpretation: +1. Some deployments may delegate DAMON control to a monitoring service or reduced-privilege management context rather than full host-root equivalence.

## 3. Reachability analysis

The bug is local and not network reachable. A practical trigger requires access to DAMON sysfs scheme configuration plus an internal setup failure while creating the `tried_regions` directory after `stats` was already created. In typical systems this path is privileged and not reachable by an ordinary unprivileged user. Namespace or container impact is limited unless DAMON sysfs control is explicitly delegated into the container or exposed to a service account. The subsystem is not a common default attack surface, and the failure condition is uncommon, so realistic exploitation is mostly a crash or cleanup-path robustness issue.

## 4. Severity interpretation

This behaves more like a borderline Moderate issue than an Important-class vulnerability. The patch shows a real error-path lifetime bug and invalid pointer dereference risk, but it does not show attacker-controlled reuse, arbitrary write, type confusion, callback control, or a practical privilege-escalation primitive. Theoretical memory-safety concern exists because kobject lifetime is involved, but realistic evidence points mainly to local DoS under rare failure conditions.

## 5. One-sentence report phrase

A DAMON sysfs scheme setup error path can put the wrong kobject after `tried_regions` setup failure, leaking the `stats` object and potentially dereferencing an uninitialized `tried_regions` pointer, causing a local kernel crash under uncommon failure conditions.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: the issue is likely not urgent Important-class due to privileged local reachability and rare trigger conditions, but invalid kobject lifetime handling and possible uninitialized pointer dereference should not be auto-closed without review.

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

Patch: mm/damon/sysfs-schemes: put stats for scheme_add_dirs() internal error
Commit: 50a753171d255895e5dd41566986b48dcec06f31
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=50a753171d255895e5dd41566986b48dcec06f31

Commit description:

damon_sysfs_scheme_add_dirs() setup the tried_regions directory after the
stats directory setup is completed.  When the tried_regions directory
setup is failed, the setup function ensures the reference for the tried
regions directory is released.  Hence the error path should put references
on setup succeeded directory objects, starting from the stats directory.
However, the error path is putting the tried_regions directory instead of
the stats directory.

As a direct result, the stats directory object is leaked.  Worse yet, if
the tried_regions directory setup failed from the initial allocation, the
scheme->tried_regions field remains uninitialized.  The following
kobject_put(&scheme->tried_regions->kobj) call in the error path will
dereference the uninitialized memory.  The setup failures should not be
common.  But once it happens, the consequence is quite bad.

Fix this issue by correctly putting the stats directory instead of the
tried_regions directory.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/20260618005650.83868-3-sj@kernel.org
Link: https://lore.kernel.org/20260617005223.96813-1-sj@kernel.org [1]
Fixes: 5181b75 ("mm/damon/sysfs-schemes: implement schemes/tried_regions directory")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.2.x
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  mm/damon/sysfs-schemes.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=50a753171d255895e5dd41566986b48dcec06f31

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

The original Linux kernel CVE announcement for CVE-2026-72176 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72176

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:H/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: 1
  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).