[CVE-2026-72015][MODERATE REGULAR] fs/resctrl: Fix double-add of pseudo-locked region's RMID to free list [ Upstream

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

CVE: CVE-2026-72015
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: fs/resctrl: Fix double-add of pseudo-locked region's RMID to free list [ Upstream
Commit: 9168176894332312c12ef052e784735dbf4ffe3f
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9168176894332312c12ef052e784735dbf4ffe3f
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72015
Analysis date: Sun, 16 Aug 2026 01:22:44 -0400
ActionableScore: 4
ActionableScore lower bound: 2
Actionable bucket: Borderline manual review recommended / Ordinary Moderate but not clean auto-close
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-72015 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72015

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.

======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-72015	MODERATE	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:H/UI:N/S:U/C:N/I:L/A:H';CWE-675;*CWE-672;CWE-415;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:L';BEST CVSS score: '5.1';DESCR 'A logical double-free in resctrl can occur when a pseudo-locked group RMID is freed during setup and then freed again during rmdir_all_sub. The second free can add the same RMID entry to rmid_free_lru again, creating a resource free-list corruption condition rather than a normal heap double-free. For the CVSS the PR:H is used because reliable triggering normally requires administrator-level access to resctrl configuration, pseudo-locking setup, and filesystem unmount or group removal operations. The issue is local only and is not network reachable. Impact is mainly denial of service or integrity impact to resctrl RMID allocation and monitoring state, with possible kernel warning or crash during later list or RMID handling.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline manual review recommended / Ordinary Moderate but not clean auto-close (with actual score 3)	YES	DANGER DISK UAF HARDWARE  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	NO	NO	checked

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

ActionableScore=4
ActionableScoreLower=2

1. ActionableScore
* Conservative score: 2
* Paranoid score: 4
* Final recommended bucket: **Borderline manual review recommended / Ordinary Moderate but not clean auto-close**::

2. Signal breakdown
* Memory corruption, Weak/indirect corruption candidate: +1. This is not a normal heap double-free, but the same RMID entry can be added twice to rmid_free_lru, creating kernel resource free-list corruption.
* Real lifetime corruption: +1. The bug is explicitly a double-free style lifetime error for an RMID resource.
* Privileged kernel/resource-management state corruption: +1 in paranoid scoring. resctrl RMID allocation state is trusted kernel resource-management metadata.
* Integrity impact plausible: +1 in paranoid scoring. The corrupted RMID free list can affect RMID allocation and monitoring correctness.
* Availability impact plausible: +1 in paranoid scoring. Later list/RMID handling could plausibly lead to WARN/Oops or broken resctrl behavior.
* Requires admin/root/CAP_SYS_ADMIN in typical deployments: -2. Creating pseudo-locked resctrl regions and unmounting/removing resctrl groups normally requires administrative control.
* Rare/configuration-dependent subsystem: -1 conservative only. This requires resctrl with pseudo-locking support and specific setup.

3. Reachability analysis
The trigger is local and privileged in normal deployments. An attacker would need control over resctrl configuration, creation of a pseudo-locked region, and a later teardown path such as unmount or rmdir_all_sub. Containers or delegated environments could matter only if resctrl control is exposed to a reduced-privilege administrator, but that is not typical. The path is not network reachable and not default user-facing. Realistic exploitation looks more like privileged local DoS or resource-state corruption than direct LPE.

4. Severity interpretation
This behaves like ordinary Moderate with manual-review value, not an Important-class issue by default. The theoretical concern is kernel linked-list/resource free-list corruption caused by a double-add of the same RMID entry. The realistic evidence supports corrupted resctrl accounting/monitoring state and possible crash, but not attacker-controlled reclaim, arbitrary write, callback control, type confusion, or privilege escalation.

5. One-sentence report phrase
A pseudo-locked resctrl group can have its RMID freed during setup and then freed again during teardown, causing the same RMID entry to be added twice to rmid_free_lru and potentially corrupting resctrl resource-management state.

6. Manual review recommendation
MANUAL CHECK RECOMMENDED. The issue is privileged and configuration-dependent, but the double-free style linked-list corruption in kernel resource-management metadata is enough to avoid fully automatic closure.

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

Patch: fs/resctrl: Fix double-add of pseudo-locked region's RMID to free list [ Upstream
Commit: 9168176894332312c12ef052e784735dbf4ffe3f
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9168176894332312c12ef052e784735dbf4ffe3f

Changed files:
  arch/x86/kernel/cpu/resctrl/rdtgroup.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=9168176894332312c12ef052e784735dbf4ffe3f

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

The original Linux kernel CVE announcement for CVE-2026-72015 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72015

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:L/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:L/A:H
  The Best / paranoid CVSS score: 5.1

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: 4

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).