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CVE-2026-89956 json

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

published last mo. modified 12d ago also EUVD-2026-80556

cvss
—
not scored
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 13%
public exploits
0
none known

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, 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.

Patch / fix

  • Linux Linux 6.1.191, 6.6.160, 6.12.112, 6.18.51, 7.2.5, 7.3
  • linux Debian 13 6.12.113-1
  • linux Debian 14 7.2.6-1
  • linux-6.12 Debian 12 6.12.113-1~deb12u1

debian advisories DEBIAN-CVE-2026-89956

  • linux Ubuntu 26.04 LTS 7.0.0-42.42
  • linux-aws Ubuntu 26.04 LTS 7.0.0-1016.17
  • linux-gcp Ubuntu 26.04 LTS 7.0.0-1016.18
  • linux-ibm Ubuntu 26.04 LTS 7.0.0-1017.17
  • linux-riscv Ubuntu 26.04 LTS 7.0.0-42.42.1
  • linux-oracle Ubuntu 26.04 LTS 7.0.0-1015.16
  • linux-hwe-7.0 Ubuntu 24.04 LTS 7.0.0-42.42~24.04.1
  • linux-oem-7.0 Ubuntu 26.04 LTS 7.0.0-1017.17

ubuntu advisories UBUNTU-CVE-2026-89956

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel-source openSUSE Tumbleweed 7.2.7-1.1

opensuse advisories openSUSE-SU-2026:11880-1

  • kernel Azure Linux 3.0 6.6.161.1-1

azure linux advisories AZL-101556

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-89956 updated cvss 4.7

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

  • Red Hat Enterprise Linux 9 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +12 more Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    affected: workaround, no fix available
  • Red Hat Enterprise Linux AppStream (v. 9) rv 5.14.0-741.22.1.el9_9, perf 5.14.0-741.22.1.el9_9, rtla 5.14.0-741.22.1.el9_9, python3-perf 5.14.0-741.22.1.el9_9, kernel-devel-matched 5.14.0-741.22.1.el9_9, kernel-64k-devel-matched 5.14.0-741.22.1.el9_9, +7 more
    fixed: vendor fix RHSA-2026:99135
  • Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-264.16.1.el10_3, perf 6.12.0-264.16.1.el10_3, rtla 6.12.0-264.16.1.el10_3, python3-perf 6.12.0-264.16.1.el10_3, kernel-devel-matched 6.12.0-264.16.1.el10_3, kernel-64k-devel-matched 6.12.0-264.16.1.el10_3, +7 more
    fixed: vendor fix RHSA-2026:99133
  • Red Hat Enterprise Linux AppStream EUS (v.10.2) rv 6.12.0-211.75.1.el10_2, perf 6.12.0-211.75.1.el10_2, rtla 6.12.0-211.75.1.el10_2, python3-perf 6.12.0-211.75.1.el10_2, kernel-devel-matched 6.12.0-211.75.1.el10_2, kernel-64k-devel-matched 6.12.0-211.75.1.el10_2, +7 more
    fixed: vendor fix RHSA-2026:99139
  • Red Hat Enterprise Linux BaseOS (v. 9) kernel 5.14.0-741.22.1.el9_9, kernel-64k 5.14.0-741.22.1.el9_9, kernel-core 5.14.0-741.22.1.el9_9, kernel-tools 5.14.0-741.22.1.el9_9, kernel-modules 5.14.0-741.22.1.el9_9, kernel-64k-core 5.14.0-741.22.1.el9_9, +27 more
    fixed: vendor fix RHSA-2026:99135
  • Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-264.16.1.el10_3, kernel-64k 6.12.0-264.16.1.el10_3, kernel-core 6.12.0-264.16.1.el10_3, kernel-tools 6.12.0-264.16.1.el10_3, kernel-modules 6.12.0-264.16.1.el10_3, kernel-64k-core 6.12.0-264.16.1.el10_3, +28 more
    fixed: vendor fix RHSA-2026:99133
  • Red Hat Enterprise Linux BaseOS EUS (v.10.2) kernel 6.12.0-211.75.1.el10_2, kernel-64k 6.12.0-211.75.1.el10_2, kernel-core 6.12.0-211.75.1.el10_2, kernel-tools 6.12.0-211.75.1.el10_2, kernel-modules 6.12.0-211.75.1.el10_2, kernel-64k-core 6.12.0-211.75.1.el10_2, +28 more
    fixed: vendor fix RHSA-2026:99139
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) libperf 5.14.0-741.22.1.el9_9, kernel-debuginfo-common-s390x 5.14.0-741.22.1.el9_9, kernel-debuginfo-common-x86_64 5.14.0-741.22.1.el9_9, kernel-debuginfo-common-aarch64 5.14.0-741.22.1.el9_9, kernel-debuginfo-common-ppc64le 5.14.0-741.22.1.el9_9
    fixed: vendor fix RHSA-2026:99135
show 9 more
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-264.16.1.el10_3, kernel-debuginfo-common-s390x 6.12.0-264.16.1.el10_3, kernel-debuginfo-common-x86_64 6.12.0-264.16.1.el10_3, kernel-debuginfo-common-aarch64 6.12.0-264.16.1.el10_3, kernel-debuginfo-common-ppc64le 6.12.0-264.16.1.el10_3
    fixed: vendor fix RHSA-2026:99133
  • Red Hat Enterprise Linux CodeReady Linux Builder EUS (v.10.2) libperf 6.12.0-211.75.1.el10_2, kernel-debuginfo-common-s390x 6.12.0-211.75.1.el10_2, kernel-debuginfo-common-x86_64 6.12.0-211.75.1.el10_2, kernel-debuginfo-common-aarch64 6.12.0-211.75.1.el10_2, kernel-debuginfo-common-ppc64le 6.12.0-211.75.1.el10_2
    fixed: vendor fix RHSA-2026:99139
  • Red Hat Enterprise Linux Real Time (v. 9) kernel-rt 5.14.0-741.22.1.el9_9, kernel-rt-64k 5.14.0-741.22.1.el9_9, kernel-rt-core 5.14.0-741.22.1.el9_9, kernel-rt-modules 5.14.0-741.22.1.el9_9, kernel-rt-64k-core 5.14.0-741.22.1.el9_9, kernel-rt-debug-core 5.14.0-741.22.1.el9_9, +14 more
    fixed: vendor fix RHSA-2026:99135
  • Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-264.16.1.el10_3, kernel-rt-64k 6.12.0-264.16.1.el10_3, kernel-rt-core 6.12.0-264.16.1.el10_3, kernel-rt-modules 6.12.0-264.16.1.el10_3, kernel-rt-64k-core 6.12.0-264.16.1.el10_3, kernel-rt-debug-core 6.12.0-264.16.1.el10_3, +14 more
    fixed: vendor fix RHSA-2026:99133
  • Red Hat Enterprise Linux Real Time EUS (v.10.2) kernel-rt 6.12.0-211.75.1.el10_2, kernel-rt-64k 6.12.0-211.75.1.el10_2, kernel-rt-core 6.12.0-211.75.1.el10_2, kernel-rt-modules 6.12.0-211.75.1.el10_2, kernel-rt-64k-core 6.12.0-211.75.1.el10_2, kernel-rt-debug-core 6.12.0-211.75.1.el10_2, +14 more
    fixed: vendor fix RHSA-2026:99139
  • Red Hat Enterprise Linux Real Time for NFV (v. 9) kernel-rt 5.14.0-741.22.1.el9_9, kernel-rt-core 5.14.0-741.22.1.el9_9, kernel-rt-modules 5.14.0-741.22.1.el9_9, kernel-rt-debug-core 5.14.0-741.22.1.el9_9, kernel-rt-modules-core 5.14.0-741.22.1.el9_9, kernel-rt-debug-modules 5.14.0-741.22.1.el9_9, +5 more
    fixed: vendor fix RHSA-2026:99135
  • Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-264.16.1.el10_3, kernel-rt-core 6.12.0-264.16.1.el10_3, kernel-rt-modules 6.12.0-264.16.1.el10_3, kernel-rt-debug-core 6.12.0-264.16.1.el10_3, kernel-rt-modules-core 6.12.0-264.16.1.el10_3, kernel-rt-debug-modules 6.12.0-264.16.1.el10_3, +5 more
    fixed: vendor fix RHSA-2026:99133
  • Red Hat Enterprise Linux Real Time for NFV EUS (v.10.2) kernel-rt 6.12.0-211.75.1.el10_2, kernel-rt-core 6.12.0-211.75.1.el10_2, kernel-rt-modules 6.12.0-211.75.1.el10_2, kernel-rt-debug-core 6.12.0-211.75.1.el10_2, kernel-rt-modules-core 6.12.0-211.75.1.el10_2, kernel-rt-debug-modules 6.12.0-211.75.1.el10_2, +4 more
    fixed: vendor fix RHSA-2026:99139
  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-11).

Affected products

  • Linux Linux

Classification

Technology feeds

References

Sources

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