{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:12",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "In the Linux kernel, the following vulnerability has been resolved:  s390/vfio-ap: Fix dereference matrix_mdev-\u003ekvm 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-\u003ekvm-\u003elock mutex is taken without checking whether matrix_mdev-\u003ekvm is NULL or not. If matrix_mdev-\u003ekvm has never been set, trying to take the lock will trigger a NULL pointer dereference. This patch adds checks for matrix_mdev-\u003ekvm == NULL before taking the matrix_mdev-\u003ekvm-\u003elock mutex.  Note that the matrix_mdev-\u003ekvm-\u003elock mutex taken in the vfio_ap_mdev_hot_plug_config function is moved to the calling function along with the matrix_dev-\u003emdevs_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-\u003ekvm there before taking the kvm-\u003elock 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-\u003eguests_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-\u003emdevs_lock mutex must be taken in order to access    fields within the matrix_mdev structure  3. matrix_mdev-\u003ekvm-\u003elock mutex must be taken before the    matrix_dev-\u003emdevs_lock to prevent a lockdep splat.  4: The kvm-\u003elock 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-\u003ekvm to verify it    is not NULL before doing the hot plug of the guest's AP configuration.",
  "id": "DEBIAN-CVE-2026-89958",
  "modified": "2026-09-17T04:47:34.583123596Z",
  "published": "2026-09-16T11:17:06.177Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-89958"
    }
  ],
  "upstream": [
    "CVE-2026-89958"
  ]
}