[CVE-2026-64251][MODERATE 7.0] pwrseq: core: fix use-after-free in pwrseq_debugfs_seq_next()

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

CVE: CVE-2026-64251
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: pwrseq: core: fix use-after-free in pwrseq_debugfs_seq_next()
Commit: ba0b9f04c7a5f9887b8ce672eaf049502c0548ec
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ba0b9f04c7a5f9887b8ce672eaf049502c0548ec
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64251
Analysis date: Fri, 24 Jul 2026 12:38:57 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A local use-after-free in the pwrseq debugfs seq_file iterator can return a struct device pointer after its reference was dropped, allowing a reader of the affected debugfs file to trigger stale pointer access and likely kernel crash, with limited but nonzero escalation concern due to the real lifetime bug.

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

The original Linux kernel CVE announcement for CVE-2026-64251 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64251

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-2026-64251	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:H/I:H/A:H';*CWE-416;CWE-911;*CWE-664;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free can occur in the pwrseq debugfs seq_file iterator because pwrseq_debugfs_seq_next() returns a struct device pointer after its reference has already been dropped by automatic put_device cleanup. A local actor who can read the affected debugfs file can trigger seq_file iteration and may cause the kernel to access a stale device pointer. For the CVSS the PR:L is used for the paranoid score because a local user or service account with access to the debugfs interface can trigger the path, while many default systems restrict debugfs access to administrators. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to a real UAF primitive, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)  SKIP CVE-2026-64251 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 249ebf3f65f8530beb2cbfb91bff1d83ba88d23c YES  NO NO unknown 	MAYBE	INIT LEAK UAF HARDWARE DEBUGFS LINUS  KPANIC INCREASED_TO_MODERATE_FROM_LOW_BASED_ON_GUESSCVSS	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 5
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local trigger: +1
  Trigger is local through reading the affected pwrseq debugfs seq_file interface.

* Generic memory corruption: +2
  The commit explicitly describes a use-after-free where seq_file receives a struct device pointer after its reference was dropped.

* Real lifetime corruption: +1
  The bug is a device reference lifetime mismatch involving get_device(), put_device(), bus_find_next_device(), and seq_file start/next/stop ownership.

* Reliable kernel crash / strong DoS: +1
  A stale struct device pointer can be dereferenced by the seq_file iterator path, making kernel crash plausible.

* Rare or restricted exposure: -1
  The affected interface is debugfs and pwrseq-specific, not a broad default userspace API.

* Conservative privilege uncertainty: 0 to -1 considered, not fully applied
  Many systems restrict debugfs to root, but the vulnerable operation is file read once access exists. Reduced-privilege service accounts or nonstandard debugfs exposure can make this more relevant than full host-root-only.

* Weak LPE concern in paranoid score: +1
  This is a real UAF, but no attacker-controlled reclaim, type confusion, callback control, or write primitive is shown. This raises the paranoid score only modestly.

## 3. Reachability analysis

The bug can be triggered by a local actor able to read the affected pwrseq debugfs file. It is not network reachable. In typical production deployments, debugfs is often restricted to root or administrators, reducing practical exposure. However, debugfs permissions vary across systems and can be exposed to service accounts, diagnostics tooling, containers, or vendor debug environments. Namespaces do not inherently make this broadly unprivileged, but delegated or weakened debugfs access can lower the practical privilege requirement.

Call-site confidence: high, because the patch includes the affected seq_file callbacks and directly shows the reference ownership mismatch.

## 4. Severity interpretation

This behaves above an ordinary Moderate cleanup because the patch fixes an explicit UAF on struct device lifetime management. Realistic demonstrated impact is local DoS via stale pointer dereference. Theoretical privilege escalation is not strongly demonstrated because the patch does not show controlled reclaim, overwrite, callback dispatch, or object replacement. Therefore it is best treated as Actionable Moderate at minimum, with manual review recommended or required due to the real UAF primitive.

## 5. One-sentence report phrase

A local use-after-free in the pwrseq debugfs seq_file iterator can return a struct device pointer after its reference was dropped, allowing a reader of the affected debugfs file to trigger stale pointer access and likely kernel crash, with limited but nonzero escalation concern due to the real lifetime bug.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the issue is an explicit UAF in kernel object lifetime handling. Even though exposure is limited by debugfs access and no strong exploitation primitive is shown, UAF-class bugs should not be auto-closed without confirming permissions, object lifetime behavior, and whether stale struct device reuse is practically controllable.

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

Patch: pwrseq: core: fix use-after-free in pwrseq_debugfs_seq_next()
Commit: ba0b9f04c7a5f9887b8ce672eaf049502c0548ec
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ba0b9f04c7a5f9887b8ce672eaf049502c0548ec

Commit description:

pwrseq_debugfs_seq_next() declares 'next' with __free(put_device),
which causes put_device() to be called on the returned pointer when
the variable goes out of scope.  This results in a use-after-free
since the seq_file framework receives a pointer whose reference has
already been dropped.

Simply removing __free(put_device) would fix the UAF but would leak
the reference acquired by bus_find_next_device(), as stop() only
calls up_read(&pwrseq_sem) and never releases the device reference.

Fix this by making the reference counting consistent across all
seq_file callbacks, matching the standard pattern used by PCI and
SCSI:

- start(): use get_device() so it returns a referenced pointer.
- next(): explicitly put_device(curr) to release the previous
  device's reference (no NULL check needed - the seq_file framework
  only calls next() while the previous return was non-NULL).
- stop(): put_device(data) to release the last iterated device's
  reference, with a NULL guard since stop() may be called with NULL
  when start() returned NULL or next() reached end-of-sequence.

Cc: stable@vger.kernel.org
Fixes: 249ebf3 ("power: sequencing: implement the pwrseq core")
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Link: https://patch.msgid.link/20260616151049.1705503-1-vulab@iscas.ac.cn
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/power/sequencing/core.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=ba0b9f04c7a5f9887b8ce672eaf049502c0548ec

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

The original Linux kernel CVE announcement for CVE-2026-64251 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64251

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:L/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: 4
  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: YES
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).