[CVE-2026-72080][MODERATE 7.0] fs/resctrl: Fix use-after-free during unmount [ Upstream

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

CVE: CVE-2026-72080
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: fs/resctrl: Fix use-after-free during unmount [ Upstream
Commit: 7b7bb07efe41bb646a93c4624aa2bb35df190342
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7b7bb07efe41bb646a93c4624aa2bb35df190342
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72080
Analysis date: Sat, 15 Aug 2026 20:41:50 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A race in resctrl teardown can let a concurrent local reader of a default resource group monitoring file dereference freed `mon_data` private data, causing a kernel UAF crash and requiring manual review for possible higher impact.

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

The original Linux kernel CVE announcement for CVE-2026-72080 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72080

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 7.0
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-2026-72080	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	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:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in resctrl unmount or failure teardown can leave a concurrent reader of a default resource group monitoring file with a stale mon_data private pointer. The reader can drop kernfs active protection and block on rdtgroup_mutex while teardown frees the monitoring private data and destroys the kernfs node. When the reader resumes, RDT_DELETED was not set for the static default group, so the code can treat the group as live and dereference freed kernel memory. For the CVSS the PR:L is used in the paranoid score because a local process with access to resctrl monitoring files may participate in the race during teardown, although reliable full control of mount or unmount operations is commonly administrative. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to use-after-free and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 4)	YES	DISK RACE UAF HARDWARE  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: 3
* Paranoid score: 5
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Paranoid scoring:

* Local unprivileged trigger: +1. A local process that can read resctrl monitoring event files can participate in the vulnerable read path.
* Memory corruption, weak primitive: +1. The patch describes a real stale pointer dereference of freed `mon_data`, but does not show attacker-controlled reclaim, overwrite, callback control, or type confusion.
* Real lifetime corruption: +1. This is a concrete UAF lifetime bug involving kernfs private data freed during teardown.
* Reliable kernel crash / strong DoS: +1. Dereferencing freed kernel private data from a kernfs read path can realistically crash the kernel.
* Availability impact realistic: +1. The failure mode is a host-kernel UAF/Oops class issue, not only a warning.
* Hard or unreliable race / special timing required: -1. The reader must overlap with resctrl unmount or failure teardown while blocked on `rdtgroup_mutex`.
* Broadly deployed exposure: +1. resctrl is present in common x86 server kernels, although the filesystem must be mounted and usable.

Conservative scoring is lower because reliable triggering of teardown or unmount is typically administrative, and the patch does not demonstrate a reclaim primitive or practical LPE chain.

## 3. Reachability analysis

The vulnerable path is local only. It is not network reachable. A reader of a default resource group monitoring file can enter `rdtgroup_mondata_show()` while teardown frees the associated `mon_data`. In typical deployments, mounting or unmounting resctrl requires administrative privileges, and resctrl is not necessarily mounted by default. Namespaces generally do not make resctrl a broadly unprivileged interface because resctrl is a global resource-control filesystem rather than an ordinary per-container filesystem. The realistic trigger requires a concurrent local reader plus resctrl teardown or failure teardown.

Call-site confidence: high. The commit message includes the relevant read path, teardown path, lock ordering, freed object, and stale dereference.

## 4. Severity interpretation

This is more than an ordinary Moderate because the patch fixes a concrete race-dependent UAF on kernel private data. However, it is not a proven Important LPE by itself because there is no demonstrated attacker-controlled reclaim, write-after-free, object replacement, callback dispatch, refcount takeover, or arbitrary write. Realistic impact is local DoS. Paranoid handling should keep it in manual-review scope because UAFs in kernel filesystem/control paths can be underestimated during early triage.

## 5. One-sentence report phrase

A race in resctrl teardown can let a concurrent local reader of a default resource group monitoring file dereference freed `mon_data` private data, causing a kernel UAF crash and requiring manual review for possible higher impact.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: concrete UAF plus race plus kernel private-data lifetime bug. No remote vector and no proven LPE primitive, but this should not be auto-closed because the bug class and stale kernfs private pointer access justify manual triage.

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

Patch: fs/resctrl: Fix use-after-free during unmount [ Upstream
Commit: 7b7bb07efe41bb646a93c4624aa2bb35df190342
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=7b7bb07efe41bb646a93c4624aa2bb35df190342

Changed files:
  fs/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=7b7bb07efe41bb646a93c4624aa2bb35df190342

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

The original Linux kernel CVE announcement for CVE-2026-72080 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72080

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:H/I:H/A:H
  The Best / paranoid CVSS score: 7

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: 3
  Paranoid ActionableScore: 5

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 7.0

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).