[CVE-2026-46093][MODERATE REGULAR] mm/vmalloc: take vmap_purge_lock in shrinker

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

CVE: CVE-2026-46093
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: mm/vmalloc: take vmap_purge_lock in shrinker
Commit: 687ccdf582169cd680aeaf24cc953807c4cd4345
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=687ccdf582169cd680aeaf24cc953807c4cd4345
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46093
Analysis date: Wed, 27 May 2026 13:00:12 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline, manual review recommended
Manual review required: YES

Summary:
A race between vmalloc lazy purge and shrinker paths can run `decay_va_pool_node()` concurrently, potentially leaking vmap pool resources and causing local availability impact under memory pressure.

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

The original Linux kernel CVE announcement for CVE-2026-46093 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46093

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-46093	MODERATE	CHECK	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-362;CWE-667;*CWE-772;*CWE-401;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A race in the vmalloc vmap pool shrinker can occur because decay_va_pool_node can run concurrently from the lazy purge path and the shrinker path without the same purge serialization. This can leave vmap pool state inconsistent and may leak virtual address pool resources under memory pressure. For the CVSS the PR:L is used because a local process may indirectly trigger memory pressure and shrinker activity, but reliable triggering depends on workload and timing. The issue is not network reachable. Impact is mainly local availability through resource leak or vmalloc pressure. No UAF, double free, arbitrary write, or privilege escalation primitive is shown by this patch.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline, manual review recommended (with actual score 3)  SKIP CVE-2026-46093  SKIP The Fixes patch not applied yet, so unlikely that actual: 7679ba6b36dbb300b757b672d6a32a606499e14b YES  NO NO unknown 	MAYBE	SIMPLEFIX RACE LEAK LINUS MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Borderline, manual review recommended**::

## 2. Signal breakdown

* Local trigger through memory pressure: +1
  A local process can indirectly increase vmalloc pressure and trigger shrinker activity, but it does not directly control the vulnerable function call.

* Availability impact plausible: +1
  The commit explicitly mentions races and possible leaks in vmap pool handling, which can affect vmalloc resource availability under pressure.

* Broad core MM subsystem: +1 paranoid only
  `vmalloc` and shrinkers are core memory-management paths, so resource-management bugs here deserve some extra review even without memory corruption.

* Hard or timing-dependent race: -1
  The issue requires concurrent execution of `decay_va_pool_node()` from lazy purge and shrinker paths.

* No memory corruption primitive: +0
  The patch does not show UAF, double free, OOB write, arbitrary write, page-cache corruption, or privilege escalation.

* No remote reachability: +0
  This is local memory-management behavior, not a network-triggerable path.

## 3. Reachability analysis

The realistic trigger is local workload-induced memory pressure that causes vmalloc shrinker activity while lazy vmap purge is also active. A normal local user may contribute to memory pressure, but reliable exploitation depends on timing, allocation patterns, and kernel memory state. Containers do not materially improve reachability except where they can generate enough memory pressure against the host. The path is generally present in kernels with the vmap pool shrinker, but the bug is not directly exposed as a simple syscall primitive.

## 4. Severity interpretation

This behaves like an ordinary-to-borderline Moderate resource leak race in core MM. The realistic impact is availability degradation through leaked or inconsistent vmap pool resources. The patch does not support memory corruption, information disclosure, arbitrary write, or privilege escalation. Manual review is reasonable because it is a race in core memory management, but it should not be escalated to Important without additional evidence.

## 5. One-sentence report phrase

A race between vmalloc lazy purge and shrinker paths can run `decay_va_pool_node()` concurrently, potentially leaking vmap pool resources and causing local availability impact under memory pressure.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED.

The issue is timing-dependent and appears limited to resource leakage, but it affects core MM resource management and should be reviewed before auto-closing.

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

Patch: mm/vmalloc: take vmap_purge_lock in shrinker
Commit: 687ccdf582169cd680aeaf24cc953807c4cd4345
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=687ccdf582169cd680aeaf24cc953807c4cd4345

Commit description:

decay_va_pool_node() can be invoked concurrently from two paths:
__purge_vmap_area_lazy() when pools are being purged, and the shrinker via
vmap_node_shrink_scan().

However, decay_va_pool_node() is not safe to run concurrently, and the
shrinker path currently lacks serialization, leading to races and possible
leaks.

Protect decay_va_pool_node() by taking vmap_purge_lock in the shrinker
path to ensure serialization with purge users.

Link: https://lore.kernel.org/20260413192646.14683-1-urezki@gmail.com
Fixes: 7679ba6 ("mm: vmalloc: add a shrinker to drain vmap pools")
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Baoquan He <baoquan.he@linux.dev>
Cc: chenyichong <chenyichong@uniontech.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/vmalloc.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=687ccdf582169cd680aeaf24cc953807c4cd4345

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

The original Linux kernel CVE announcement for CVE-2026-46093 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46093

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: 2
  Paranoid ActionableScore: 3

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).