[CVE-2026-90201][MODERATE 7.0] net: page_pool: fix UAF in __page_pool_release_netmem_dma on xa_cmpxchg race [ Upstream

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

CVE: CVE-2026-90201
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: net: page_pool: fix UAF in __page_pool_release_netmem_dma on xa_cmpxchg race [ Upstream
Commit: bbfef303f980c1c078b8fa142e10a0e2fbcdd247
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bbfef303f980c1c078b8fa142e10a0e2fbcdd247
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90201
Analysis date: Thu, 17 Sep 2026 20:48:35 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review
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-2026-90201 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90201

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

CVE-2026-90201	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-90201 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-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A race in net page_pool DMA cleanup can cause a use-after-free when page_pool_destroy() runs page_pool_scrub() while another CPU returns a page through page_pool_put_netmem(). The scrub path iterates pool dma_mapped without holding a page reference, while the return path can drop the last page reference after losing xa_cmpxchg. This allows the scrub path to read or update netmem fields after the page has been freed. For the CVSS the PR:L is used in the paranoid score because reliable triggering may be possible for a local actor with delegated CAP_NET_ADMIN or similar control over NIC channel or ring reconfiguration. The issue is not directly network reachable by packets alone, but traffic such as iperf style load can help exercise the race while local reconfiguration is performed. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to UAF based memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6)	YES	REMOTE RACE UAF DMAorINTERRUPT HARDWARE TEST KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	YES	NO	checked

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

ActionableScore=6
ActionableScoreLower=5
PrimitiveClass=CLASS_B
RealUAF=YES
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=YES
ManualReview=REQUIRED
AutoDowngradeAllowed=NO

1. ActionableScore

* Raw conservative score: 5
* Conservative score: 5
* Raw paranoid score: 6
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**::

No floor or cap changed the score.

2. Signal breakdown

Conservative signals:

* +2 Real UAF / active lifetime violation. The commit directly states that page_pool_scrub() can touch a freed page because it iterates pool->dma_mapped without holding a page reference while another CPU returns and frees the page.
* +1 Reliable kernel crash / strong DoS. The demonstrated symptom is a WARN, but the established stale access to freed page/netmem storage in core networking DMA cleanup realistically supports kernel fault or crash.
* +1 Attacker-influenced repeatable lifetime manipulation. The reported trigger involves repeated NIC channel or ring reconfiguration with traffic, causing page_pool_destroy() and page return paths to race.
* +1 Privileged kernel/device-management memory corruption path. The stale path reads dma_addr and writes DMA index bits in pp_magic on freed netmem/page storage, affecting page/DMA ownership metadata rather than only diagnostic state.

Paranoid additional signal:

* +1 Weak LPE concern. The stale access includes a post-free write to netmem metadata and use of dma_addr for DMA unmap after the lifetime race, which is a meaningful unresolved corruption surface. This does not prove controlled reclaim or arbitrary write.

Non-awarded signals:

* Controlled reclaim not demonstrated.
* Arbitrary or directed kernel write not demonstrated.
* Direct remote reachability not established. Traffic helps exercise the race but packets alone are not shown to trigger the vulnerable lifetime transition.
* Concrete repeated release/refcount signal not awarded. The scrub path performs stale field access and DMA unmap, but the patch does not establish a second put/free/refcount mutation on the exact same dangling reference.
* Structured stale-object leverage not separately awarded beyond the weak paranoid concern because attacker-shaped replacement contents are not shown.
* Extra Availability not awarded because the same crash/DoS is already counted once.
* Confidentiality and integrity points are not awarded directly. The C/I concern is represented only as unresolved paranoid corruption leverage, not as proven disclosure or unauthorized modification.

Repeated-release/refcount checklist:

* First release can end lifetime: yes, the unref path can call put_page() and free the page.
* Exact same reference survives to a second lifetime mutation: not established.
* Second operation is a real lifetime/refcount mutation: no.
* Concrete repeated release/refcount +1 awarded: no.
* Paranoid repeated-refcount leverage +1 awarded: no.
* FLOOR 5 applied: no. Score already reaches 5 conservatively from independent signals.

3. Reachability analysis

The observed reproducer uses hns3 NIC channel or ring reconfiguration through ethtool -L or ethtool -G while traffic is running. That suggests a local control-plane trigger plus data-plane traffic. The local actor likely needs meaningful network device management rights, commonly CAP_NET_ADMIN over the affected physical NIC, but the supplied evidence does not fully resolve whether all reachable trigger paths require host-admin-equivalent privilege.

HostAdminRequired is therefore UNKNOWN rather than YES or NO. The complete namespace story is also unresolved. A namespaced CAP_NET_ADMIN model is not established merely by the networking subsystem, and the affected hns3 physical device path is not shown to be fully namespace-scoped.

Prior setup likely includes a page_pool-using NIC driver and DMA-mapped page pool operation. This is common in modern networking drivers, not rare hardware in the abstract, but the demonstrated report is tied to hns3 on arm64. The race is intermittent, but it is exercised under repeated reconfiguration and traffic, so no hard-race penalty is applied.

4. Primitive and severity interpretation

The exact primitive is a real use-after-free on netmem/page storage during page_pool DMA cleanup. The stale object is active kernel memory-management and DMA ownership state, not fixed passive storage. The stale scrub path can read dma_addr and clear DMA index bits after another CPU has dropped the last page reference.

This is CLASS_B because a concrete kernel lifetime/corruption primitive exists, but controlled reclaim, attacker-shaped replacement contents, arbitrary read/write, or demonstrated privilege escalation are not established. The demonstrated consequence is at least local DoS through WARN/fault/crash. The speculative consequence is stronger memory corruption impact if freed page storage is reused before stale metadata access completes.

ImportantCandidate is YES because this is not a simple crash-only NULL dereference. It is an active page_pool lifetime bug with post-free access to page/DMA metadata in a core networking memory path. AutoDowngradeAllowed is NO because automatic closure would lose an unresolved Class B UAF corruption primitive that needs manual Important-vs-Moderate review.

Likely operational severity is actionable Moderate at minimum, with Strong Important candidacy depending on whether manual analysis finds practical below-host-admin reachability, controlled reuse, or stronger corruption leverage.

5. One-sentence report phrase

A race in page_pool DMA cleanup can let page_pool_scrub() access and modify freed netmem/page metadata while another CPU returns the page, causing at least a kernel crash DoS and requiring manual review for unresolved UAF based corruption impact.

6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: concrete UAF with post-free access to page/DMA metadata is established, and exploitation leverage beyond crash is unresolved.

7. Call-site confidence

Call-site confidence: high

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

Patch: net: page_pool: fix UAF in __page_pool_release_netmem_dma on xa_cmpxchg race [ Upstream
Commit: bbfef303f980c1c078b8fa142e10a0e2fbcdd247
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bbfef303f980c1c078b8fa142e10a0e2fbcdd247

Changed files:
  net/core/page_pool.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=bbfef303f980c1c078b8fa142e10a0e2fbcdd247

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

The original Linux kernel CVE announcement for CVE-2026-90201 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90201

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:L/I:L/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: 5
  Paranoid ActionableScore: 6

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).