[CVE-2026-74644][LOW] mm/damon/ops-common: putback folios on invalid migrate nid

[CVE-2026-74644][LOW] mm/damon/ops-common: putback folios on invalid migrate nid

[AL-KERNEL]

CVE: CVE-2026-74644
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm/damon/ops-common: putback folios on invalid migrate nid
Commit: 460181e4bb47a57776c64f0832c2096de8878cb3
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=460181e4bb47a57776c64f0832c2096de8878cb3
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74644
Analysis date: Sat, 22 Aug 2026 14:37:20 -0400
ActionableScore: 2
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
DAMON migration can leave folios isolated from the LRU with extra references when an invalid target NUMA node is used, allowing a privileged or delegated local actor to cause memory pinning and possible denial of service.

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

The original Linux kernel CVE announcement for CVE-2026-74644 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74644

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
======================================================================

CVE-2026-74644	LOW	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'DAMON migration handling can leave folios isolated from the LRU when damon_migrate_pages is called with an invalid target NUMA node such as NUMA_NO_NODE. The affected folios keep the extra reference taken by folio_isolate_lru and the caller then loses the local list, so pages can remain off the LRU while the mapping exists and may stay pinned after the mapping is gone. This is a resource leak and memory pinning issue rather than a use after free, because the pages are retained instead of being freed too early. For the CVSS the PR:L is used for the paranoid case because delegated DAMON control or a service account with access to DAMON sysfs could trigger the issue without full host root, while typical deployments require administrator privileges. The issue is not network reachable and the expected impact is denial of service through memory pressure or reduced reclaim efficiency.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)  SKIP CVE-2026-74644 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DANGER SIMPLEFIX LINUS MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**

## 2. Signal breakdown

Conservative signals:

* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2
  DAMON/DAMOS configuration is normally controlled by privileged users through DAMON sysfs/debugfs or administrator managed tooling.
* Rare AND difficult-to-reach subsystem/configuration: -1
  DAMON migration schemes are not a default exposed data path for ordinary users.
* Availability impact realistic: +1
  Folios can remain off LRU and pinned, which can degrade reclaim and eventually contribute to memory pressure.

Conservative total is capped at 0 after negative signals.

Paranoid signals:

* Local delegated trigger concern: +1
  In environments where DAMON control is delegated to a service account or reduced privilege administrator, this may be reachable without full host-root control.
* Reliable resource exhaustion concern: +1
  Repeated invalid migration actions can accumulate off-LRU or pinned folios and create a practical DoS pressure pattern.
* Availability impact realistic: +1
  The bug affects memory reclaim behavior and can persist beyond the original mapping lifetime.
* Rare/difficult DAMON configuration: -1
  The affected path still depends on DAMON migration configuration and invalid target nid use.

Paranoid total: 2.

No memory corruption signal is awarded. This is a leak/pinning bug, not UAF, double-free, OOB write, arbitrary write, page-cache corruption, or object confusion.

## 3. Reachability analysis

The bug is local and configuration dependent. A typical attacker needs administrative control over DAMON/DAMOS migration policy, so ordinary unprivileged users usually cannot trigger it directly. Namespaces or containers do not normally expose DAMON control safely to untrusted users, but a delegated monitoring or tuning service account could reduce the practical privilege requirement in some deployments.

The path is not network reachable and not a common default kernel data path. Exploitation requires DAMON migration actions with an invalid target NUMA node such as NUMA_NO_NODE.

Call-site confidence: medium. The commit describes the relevant callers, damon_pa_migrate() and damos_va_migrate(), and the patch fixes the early return path in damon_migrate_pages().

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource management issue, not an Important-class vulnerability. The practical impact is memory pinning and reduced reclaim efficiency, potentially causing local DoS under sustained abuse. There is no supported privilege escalation primitive and no evidence of confidentiality or integrity impact.

Theoretical impact is limited to resource exhaustion. Realistic exploitation requires privileged or delegated DAMON control and specific migration configuration.

## 5. One-sentence report phrase

DAMON migration can leave folios isolated from the LRU with extra references when an invalid target NUMA node is used, allowing a privileged or delegated local actor to cause memory pinning and possible denial of service.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a local DAMON resource leak and memory pinning issue without evidence of memory corruption, security-boundary bypass, network reachability, or privilege escalation.

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

Patch: mm/damon/ops-common: putback folios on invalid migrate nid
Commit: 460181e4bb47a57776c64f0832c2096de8878cb3
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=460181e4bb47a57776c64f0832c2096de8878cb3

Commit description:

damon_pa_migrate() and damos_va_migrate() isolate folios into a local list
and then call damon_migrate_pages().  When target_nid is invalid
(including the scheme default NUMA_NO_NODE / -1), damon_migrate_pages()
returns early without putting the folios back to the LRU.

Callers then discard the list head while those folios remain isolated with
an extra reference taken by folio_isolate_lru().  The pages stay off the
LRU for as long as the mapping exists (anon active+inactive counts drop
while RSS does not), and the leftover references can pin the pages after
the mapping is gone.

Put the folios back on the invalid-nid path so ignored migration requests
still return them to the LRU.

Link: https://lore.kernel.org/20260726014815.1280757-1-dayou5941@163.com
Fixes: 7e6c313 ("mm/damon/ops-common: ignore migration request to invalid nodes")
Assisted-by: Cursor:grok-4.5
Reviewed-by: SJ Park <sj@kernel.org>
Signed-off-by: liyouhong <liyouhong@kylinos.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  mm/damon/ops-common.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=460181e4bb47a57776c64f0832c2096de8878cb3

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

The original Linux kernel CVE announcement for CVE-2026-74644 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74644

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:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.5

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: 2

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).