[CVE-2026-64184][LOW] mm/damon/sysfs-schemes: call missing mem_cgroup_iter_break()

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

CVE: CVE-2026-64184
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm/damon/sysfs-schemes: call missing mem_cgroup_iter_break()
Commit: 082351f9d40007414ad6af062b3a26fa02fd4b5f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=082351f9d40007414ad6af062b3a26fa02fd4b5f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64184
Analysis date: Sun, 19 Jul 2026 15:53:07 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A missing `mem_cgroup_iter_break()` in the DAMON sysfs memcg lookup path can leak cgroup references during privileged DAMON scheme configuration, potentially causing resource exhaustion after repeated operations but not memory corruption or privilege escalation.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-64184 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64184

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: LOW
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
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CVE-2026-64184	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';*CWE-772;CWE-404;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'damon_sysfs_memcg_path_to_id can leak a cgroup reference when it finds a matching memory cgroup and exits the mem_cgroup_iter loop without calling mem_cgroup_iter_break(). The bug is a resource reference leak rather than memory corruption. For the CVSS the PR:H is used because DAMON sysfs scheme configuration is normally restricted to root or CAP_SYS_ADMIN. The issue is not network reachable and requires local control of the DAMON sysfs configuration path. Impact is denial of service through possible resource exhaustion after repeated operations, with no supported confidentiality or integrity impact.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	SIMPLEFIX LEAK LINUS MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

* Availability impact realistic: +1 paranoid only. Repeated DAMON sysfs operations could theoretically accumulate leaked cgroup references and contribute to resource exhaustion.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. DAMON sysfs scheme configuration is normally an administrative interface.
* Rare or non-default subsystem exposure: -1. DAMON sysfs scheme filters are not a broadly exposed default attack surface.
* No memory corruption signal: +0. The patch fixes a missing `mem_cgroup_iter_break()` and describes a reference leak, not UAF, double free, OOB access, type confusion, or arbitrary write.
* No confidentiality or integrity signal: +0. There is no demonstrated readback, sensitive-object access, permission bypass, or writable corruption primitive.

## 3. Reachability analysis

The bug is reachable through local DAMON sysfs configuration paths, specifically when resolving a memcg path in `damon_sysfs_memcg_path_to_id()`. In typical deployments this requires root or CAP_SYS_ADMIN-like control over DAMON configuration. It is not network reachable. Containers or delegated environments could matter only if DAMON sysfs control is exposed to a reduced-privilege actor, which is uncommon and should be treated as environment-specific.

## 4. Severity interpretation

This behaves like a low-priority resource leak rather than an actionable memory corruption issue. The theoretical worst case is resource exhaustion after repeated privileged operations, but the patch does not support privilege escalation, sensitive data exposure, object reuse, UAF, or cross-boundary bypass. It should not be treated as Important-class.

## 5. One-sentence report phrase

A missing `mem_cgroup_iter_break()` in the DAMON sysfs memcg lookup path can leak cgroup references during privileged DAMON scheme configuration, potentially causing resource exhaustion after repeated operations but not memory corruption or privilege escalation.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a privileged local resource reference leak with no concrete memory corruption or security-boundary bypass primitive, so it can be handled as ordinary Low/Moderate maintenance unless the product exposes DAMON sysfs controls to untrusted users.

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

Patch: mm/damon/sysfs-schemes: call missing mem_cgroup_iter_break()
Commit: 082351f9d40007414ad6af062b3a26fa02fd4b5f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=082351f9d40007414ad6af062b3a26fa02fd4b5f

Commit description:

damon_sysfs_memcg_path_to_id() breaks mem_cgroup_iter() loop without
calling mem_cgroup_iter_break().  This leaks the cgroup reference.  Fix
the issue by calling mem_cgroup_iter_break() before the break.

The issue was discovered [1] by Sashiko.

Link: https://lore.kernel.org/20260426173625.86521-1-sj@kernel.org
Link: https://lore.kernel.org/20260423004148.74722-1-sj@kernel.org [1]
Fixes: 29cbb9a ("mm/damon/sysfs-schemes: implement scheme filters")
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: <stable@vger.kernel.org> # 6.3.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=082351f9d40007414ad6af062b3a26fa02fd4b5f

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

The original Linux kernel CVE announcement for CVE-2026-64184 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64184

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:L/PR:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.4

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: 0
  Paranoid ActionableScore: 1

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: LOW
KPANIC detected for this report: NO
Published priority for this report (same as in Subject): LOW

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).