s390/vfio-ap: Fix dereference matrix_mdev->kvm without checking for NULL

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-89958
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-16 11:17:06 UTC
Updated2026-09-16 11:17:06 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: s390/vfio-ap: Fix dereference matrix_mdev->kvm without checking for NULL The ap_driver structure has two fields which are function pointers to callbacks: * .on_config_changed: called at the start of the AP bus scan function to notify the device driver that the host AP configuration has changed and the associated AP devices will be added or removed accordingly. This gives the implementor a chance to evaluate the configuration changes and respond to them before the associated devices are added or removed. * .on_scan_complete: Called at the end of the AP bus scan function to notify the device driver that the host AP configuration has changed and the AP devices have been added or removed accordingly. This gives the implementor the opportunity to respond to the changes after the associated devices are added or removed. These two callbacks are implemented in the vfio_ap device driver via the vfio_ap_on_cfg_changed and vfio_ap_on_scan_complete functions respectively. Within the call stack of these two callback functions the matrix_mdev->kvm->lock mutex is taken without checking whether matrix_mdev->kvm is NULL or not. If matrix_mdev->kvm has never been set, trying to take the lock will trigger a NULL pointer dereference. This patch adds checks for matrix_mdev->kvm == NULL before taking the matrix_mdev->kvm->lock mutex. Note that the matrix_mdev->kvm->lock mutex taken in the vfio_ap_mdev_hot_plug_config function is moved to the calling function along with the matrix_dev->mdevs_lock which is needed there to access the fields of the matrix_mdev. It makes little sense to make the change the check for matrix_mdev->kvm there before taking the kvm->lock mutex only to have to move it out via another patch, so it is done in this patch. It is important to make note of the following: 1. The matrix_dev->guests_lock is acquired at the start of both callback functions. This ensures that matrix_mdev will not be removed via the vfio_ap_mdev_remove function because it too takes matrix_dev_guests_lock before removing the object; so, matrix_mdev will be available for the duration of the callback functions. 2. The matrix_dev->mdevs_lock mutex must be taken in order to access fields within the matrix_mdev structure 3. matrix_mdev->kvm->lock mutex must be taken before the matrix_dev->mdevs_lock to prevent a lockdep splat. 4: The kvm->lock must be held while plugging the guest's AP configuration into its SIE state description via the vfio_ap_mdev_update_guest_apcb function. 5. The vfio_ap_mdev_update_guest_apcb checks matrix_mdev->kvm to verify it is not NULL before doing the hot plug of the guest's AP configuration.

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected eeb386aeb5b7c8d2dae6a3ba49255d8a97803182 5e932abfcce6189d067fffb0eb8214443bc04374 git Not specified
CNA Linux Linux affected eeb386aeb5b7c8d2dae6a3ba49255d8a97803182 334b435b951353f934d5110c4630e0cb58d2f9a7 git Not specified
CNA Linux Linux affected eeb386aeb5b7c8d2dae6a3ba49255d8a97803182 178ea7a1c2c3c0c01d14b8f60aa35f1e0cdc6b78 git Not specified
CNA Linux Linux affected eeb386aeb5b7c8d2dae6a3ba49255d8a97803182 4f7e869d0db24ae07b4c888fd3bc21554eef775d git Not specified
CNA Linux Linux affected eeb386aeb5b7c8d2dae6a3ba49255d8a97803182 d50346801b4f144e42b49cd4f1496010498ab114 git Not specified
CNA Linux Linux affected 6.0 Not specified
CNA Linux Linux unaffected 6.0 semver Not specified
CNA Linux Linux unaffected 6.6.157 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.110 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.51 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.5 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc1 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/5e932abfcce6189d067fffb0eb8214443bc04374 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/178ea7a1c2c3c0c01d14b8f60aa35f1e0cdc6b78 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/d50346801b4f144e42b49cd4f1496010498ab114 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/334b435b951353f934d5110c4630e0cb58d2f9a7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/4f7e869d0db24ae07b4c888fd3bc21554eef775d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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