[CVE-2026-89986][LOW] mm/mempolicy: fix sleeping allocation in alloc_pages_bulk_weighted_interleave()

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

CVE: CVE-2026-89986
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm/mempolicy: fix sleeping allocation in alloc_pages_bulk_weighted_interleave()
Commit: bcb3d0c867ee40dc48e9c085bf328fbc679b6656
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bcb3d0c867ee40dc48e9c085bf328fbc679b6656
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89986
Analysis date: Wed, 16 Sep 2026 14:51:42 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-89986 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89986

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.

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

CVE-2026-89986	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89986 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:N/I:N/A:H';CWE-703;CWE-667;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'alloc_pages_bulk_weighted_interleave used a hardcoded GFP_KERNEL allocation for a temporary weights array even when the caller passed GFP_ATOMIC from an atomic or RCU context. A local task with MPOL_WEIGHTED_INTERLEAVE can reach this path when another kernel allocation path such as rhashtable rehash falls back to vmalloc and then calls bulk allocation through mempolicy handling. This can trigger a sleeping allocation warning or invalid context splat and may cause a local denial of service on systems that panic on warnings or treat such splats as fatal. For the CVSS the PR:L value is used because a local user context is needed to set or use the relevant memory policy and to drive the allocation path. The issue is not network reachable by itself. Impact is mainly availability loss, with no concrete evidence of information disclosure, integrity impact, UAF, OOB access, or arbitrary write.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2)  SKIP CVE-2026-89986 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DANGER SYZBOT 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
======================================================================

ActionableScore=2
ActionableScoreLower=1
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

2. Signal breakdown

Conservative positive signals:

* +1 Local unprivileged trigger. A local task can use MPOL_WEIGHTED_INTERLEAVE and can plausibly drive allocation paths that reach mempolicy bulk allocation.

Paranoid positive signals:

* +1 Local unprivileged trigger. Same as conservative.
* +1 Availability concern. The invalid sleeping allocation context can become a practical local DoS on systems configured to panic on warnings or where such splats are treated as fatal.

Negative or non-awarded signals:

* +0 Real UAF not awarded. The patch does not establish stale post-lifetime object use.
* +0 Memory corruption not awarded. The bug is an allocation-context mismatch, not OOB, UAF, double free, type confusion, or arbitrary write.
* +0 Reliable kernel crash not awarded conservatively. The supplied evidence establishes a might_alloc or sleeping function splat, not a guaranteed host-wide crash.
* +0 Confidentiality and integrity not awarded. No disclosure path, unauthorized write, or security boundary bypass is shown.
* +0 Remote reachability not awarded. The issue is reached through local task memory policy and kernel allocation paths, not network input directly.
* +0 Concrete resource leak not awarded. The temporary weights allocation is not described as persistently leaked.
* +0 Race penalty not applied. RCU or atomic context is part of the invalid-context condition, but no hard attacker timing race is required.
* +0 Host-admin penalty not applied. Host-admin-equivalent privilege is not positively established.
* +0 Rare subsystem penalty not applied. MPOL_WEIGHTED_INTERLEAVE is a feature-specific condition, but rarity alone is not enough for a negative point.

3. Reachability analysis

The evaluated attacker is a local user or local process. The relevant condition is that the current task has MPOL_WEIGHTED_INTERLEAVE mempolicy and reaches an allocation path where GFP_ATOMIC is passed through vmalloc and bulk allocation handling. The supplied call path is rhashtable_insert_slow under rcu_read_lock, then bucket_table_alloc, then vmalloc, then vm_area_alloc_pages, then alloc_pages_bulk_mempolicy_noprof, then alloc_pages_bulk_weighted_interleave.

Host administrator privilege is not positively established for the complete trigger. Namespace-scoped privilege is not the relevant model here. No direct network trigger is established. No special hardware is required. No hard race is established. The issue depends on a specific mempolicy mode and an allocation path that reaches vmalloc under atomic or RCU context.

4. Primitive and severity interpretation

The exact primitive is an invalid sleepable allocation request in atomic or RCU context caused by hardcoded GFP_KERNEL inside alloc_pages_bulk_weighted_interleave. This is not an active structured UAF and not fixed stale storage. There is no cleanup double release, no second refcount mutation, and no post-free object use.

PrimitiveClass is NONE because the evidence establishes a context-safety bug and warning or splat behavior, not a meaningful corruption, lifetime, ownership, authorization, or semantic reinterpretation primitive. The demonstrated consequence is a kernel warning or invalid-context splat. The paranoid consequence is local DoS only on systems where warnings become fatal or where repeated triggering materially disrupts service.

ImportantCandidate is NO because there is no established memory corruption, UAF, authorization bypass, shared-page ownership violation, or strong exploitation primitive. AutoDowngradeAllowed is YES because automatic downgrade would not discard an unresolved concrete kernel-corruption primitive.

Likely operational severity is ordinary Low to Moderate. It is mainly a correctness and availability issue, not an Important-class kernel security candidate.

5. One-sentence report phrase

alloc_pages_bulk_weighted_interleave used GFP_KERNEL for a temporary weights allocation even when called with GFP_ATOMIC from atomic or RCU context, allowing a local task using MPOL_WEIGHTED_INTERLEAVE to trigger an invalid sleeping allocation splat and possible local DoS on panic_on_warn systems.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The patch shows no UAF, OOB access, arbitrary write, information disclosure, authorization bypass, or concrete privilege escalation primitive. The issue can be handled as an ordinary low-actionability availability bug.

7. Call-site confidence

Call-site confidence: high

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

Patch: mm/mempolicy: fix sleeping allocation in alloc_pages_bulk_weighted_interleave()
Commit: bcb3d0c867ee40dc48e9c085bf328fbc679b6656
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=bcb3d0c867ee40dc48e9c085bf328fbc679b6656

Commit description:

syzbot reported a sleeping function called from invalid context splat in
bucket_table_alloc().

When rhashtable_insert_slow() rehashes the table under rcu_read_lock(), it
calls bucket_table_alloc(..., GFP_ATOMIC | __GFP_NOWARN).  If the bucket
table allocation uses vmalloc, __vmalloc_node_range_noprof() invokes
vm_area_alloc_pages() -> alloc_pages_bulk_mempolicy_noprof() with the
passed GFP_ATOMIC flags.

If the current task has an MPOL_WEIGHTED_INTERLEAVE mempolicy,
alloc_pages_bulk_weighted_interleave() is called and currently hardcodes
GFP_KERNEL when allocating the temporary weights array, triggering a
might_alloc() splat in atomic/RCU contexts.

Pass the gfp flags (masked with GFP_RECLAIM_MASK to strip page-allocator
zone modifiers like __GFP_HIGHMEM) received by
alloc_pages_bulk_weighted_interleave() to kmalloc() instead of hardcoding
GFP_KERNEL.  Since the weights buffer is immediately initialized in full,
kmalloc() is sufficient.

Link: https://lore.kernel.org/20260821170407.3721004-1-edumazet@google.com
Fixes: fa3bea4 ("mm/mempolicy: introduce MPOL_WEIGHTED_INTERLEAVE for weighted interleaving")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot+0dbf6d295b3350944f0b@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/lkml/6a88837e.ae6ddae5.3da009.0040.GAE@google.com/T/#u
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Gregory Price (Meta) <gourry@gourry.net>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Byungchul Park <byungchul@sk.com>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Zi Yan <ziy@nvidia.com>
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/mempolicy.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=bcb3d0c867ee40dc48e9c085bf328fbc679b6656

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

The original Linux kernel CVE announcement for CVE-2026-89986 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89986

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:L/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.7

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: 1
  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).