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

{
  "id": "69b92f90bf0d30c45a2a3efd4f4304944f3456f88b86966265a7a91aac381852",
  "url": "https://osv.dev/vulnerability/CVE-2026-89956",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "s390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects",
    "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 ~~~~~~~~~~",
    "evidence": "osv:CVE-2026-89956",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
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            "value": "6.1.191",
            "evidence": "/affected/1/ranges"
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            "evidence": "/affected/1/ranges"
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            "value": "6.18.51",
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          {
            "value": "7.2.5",
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    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-89956",
      "aliases": [
        "CVE-2026-89956"
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      "affected": [
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                  "fixed": "647916988272fe5ecb4bb30cd02b51af9960618a"
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      ],
      "modified": "2026-11-01T02:31:01.727148339Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/0fd74477d05743d4cd9b25a3b667daa278d53b93",
        "https://git.kernel.org/stable/c/22dc712c170efc1a549e3f872467c880be995ac7",
        "https://git.kernel.org/stable/c/3ea443510739468238324234eaab0d37922283f5",
        "https://git.kernel.org/stable/c/530ee1cc71562b6799b9ece187b6c1b757a2c6fa",
        "https://git.kernel.org/stable/c/647916988272fe5ecb4bb30cd02b51af9960618a",
        "https://git.kernel.org/stable/c/7fa61c29850d05e40ca9ed41bfdf57673023f581",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89956.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-89956",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
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    "related_cves": [
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        "value": "CVE-2026-89956",
        "evidence": "/id"
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    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 514344,
  "published_at": "2026-09-16T10:32:39.847+00:00"
}