---
id: CVE-2026-89956
title: >-
  In the Linux kernel, the following vulnerability has been resolved:


  s390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev
  objects


  In order to traverse or add/remove ap_matrix_mdev objects in the

  matrix_dev->mdev_list…
summary: >-
  In the Linux kernel, the following vulnerability has been resolved:


  s390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev
  objects


  In order to traverse or add/remove ap_matrix_mdev objects in the

  matrix_dev->mdev_list…
severity: none
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= 2c1ee8983aa377fef4f725162f4f3aa5f9575d4a <
    647916988272fe5ecb4bb30cd02b51af9960618a
  - >-
    Linux >= 2c1ee8983aa377fef4f725162f4f3aa5f9575d4a <
    0fd74477d05743d4cd9b25a3b667daa278d53b93
  - >-
    Linux >= 2c1ee8983aa377fef4f725162f4f3aa5f9575d4a <
    7fa61c29850d05e40ca9ed41bfdf57673023f581
  - Linux 6.0
published: '2026-09-16'
updated: '2026-09-16'
sourceUpdated: '2026-09-16T11:17:05.920'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89956'
references:
  - url: 'https://git.kernel.org/stable/c/0fd74477d05743d4cd9b25a3b667daa278d53b93'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/647916988272fe5ecb4bb30cd02b51af9960618a'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/7fa61c29850d05e40ca9ed41bfdf57673023f581'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
tags:
  - nvd
  - cve.org
ingestedAt: '2026-09-16T10:53:53.961Z'
epss: 0.00198
epssPercentile: 0.09833
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

s390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects

In order to traverse or add/remove ap_matrix_mdev objects in the
matrix_dev->mdev_list, the matrix_dev->guests_lock mutex must be held.
There are two functions that access the list without holding the mutex:

vfio_ap_mdev_probe function
~~~~~~~~~~~~~~~~~~~~~~~~~~~
The vfio_ap_mdev_probe function uses the matrix_dev->mdevs_lock
mutex to guard the add of a newly created ap_matrix_mdev object to the
matrix_dev->mdev_list. This mutex does not protect list access; its purpose
is to guard against concurrent access to fields contained in an
ap_matrix_mdev object. This could lead to kernel memory corruption or
use-after-free if another mdev is created or removed concurrently.

The adding of an ap_matrix_mdev object to matrix_dev->mdev_list
is now guarded by the matrix_dev->guests_lock which is the correct
way to protect against concurrent mdev_list access.

Also removed the following two lines of code because the matrix_mdev is
allocated via vfio_alloc_device macro which uses kzalloc, so req_trigger
and cfg_chg_trigger are already zero-initialised when the struct is
allocated before the call to vfio_register_emulated_iommu_dev. This
prevents a window whereby these triggers are set to NULL after
the device is exposed to userspace.

matrix_mdev->req_trigger = NULL;
matrix_mdev->cfg_chg_trigger = NULL;

vfio_ap_mdev_for_queue function
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The status_show function that supports display of the status attribute of
the devices in /sys/bus/ap/devices calls the vfio_ap_mdev_for_queue
function which iterates the matrix_dev->mdev_list to find the object
representing the queue device whose status is to be displayed. In order to
traverse this list, the matrix_dev->guests_lock mutex must be held.

To fix this, the guests_lock mutex is taken prior to taking the
matrix_dev->mdevs_lock mutex in the status_show function. It is taken
there rather than the vfio_ap_mdev_for_queue function - where it is
needed - because it must be taken prior to the mdevs_lock mutex in order to
adhere to the proper locking order and prevent a lockdep splat; also
because the mdevs_lock is needed there to access fields within
the matrix_mdev object in that function.

See the vfio-ap-locking.rst in the linux kernel tree.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.