{"id":"CVE-2026-89956","title":"In the Linux kernel, the following vulnerability has been resolved:\n\ns390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects\n\nIn order to traverse or add/remove ap_matrix_mdev objects in the\nmatrix_dev->mdev_list…","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\ns390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects\n\nIn order to traverse or add/remove ap_matrix_mdev objects in the\nmatrix_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":0.09811,"slug":"CVE-2026-89956","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\ns390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects\n\nIn order to traverse or add/remove ap_matrix_mdev objects in the\nmatrix_dev->mdev_list, the matrix_dev->guests_lock mutex must be held.\nThere are two functions that access the list without holding the mutex:\n\nvfio_ap_mdev_probe function\n~~~~~~~~~~~~~~~~~~~~~~~~~~~\nThe vfio_ap_mdev_probe function uses the matrix_dev->mdevs_lock\nmutex to guard the add of a newly created ap_matrix_mdev object to the\nmatrix_dev->mdev_list. This mutex does not protect list access; its purpose\nis to guard against concurrent access to fields contained in an\nap_matrix_mdev object. This could lead to kernel memory corruption or\nuse-after-free if another mdev is created or removed concurrently.\n\nThe adding of an ap_matrix_mdev object to matrix_dev->mdev_list\nis now guarded by the matrix_dev->guests_lock which is the correct\nway to protect against concurrent mdev_list access.\n\nAlso removed the following two lines of code because the matrix_mdev is\nallocated via vfio_alloc_device macro which uses kzalloc, so req_trigger\nand cfg_chg_trigger are already zero-initialised when the struct is\nallocated before the call to vfio_register_emulated_iommu_dev. This\nprevents a window whereby these triggers are set to NULL after\nthe device is exposed to userspace.\n\nmatrix_mdev->req_trigger = NULL;\nmatrix_mdev->cfg_chg_trigger = NULL;\n\nvfio_ap_mdev_for_queue function\n~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\nThe status_show function that supports display of the status attribute of\nthe devices in /sys/bus/ap/devices calls the vfio_ap_mdev_for_queue\nfunction which iterates the matrix_dev->mdev_list to find the object\nrepresenting the queue device whose status is to be displayed. In order to\ntraverse this list, the matrix_dev->guests_lock mutex must be held.\n\nTo fix this, the guests_lock mutex is taken prior to taking the\nmatrix_dev->mdevs_lock mutex in the status_show function. It is taken\nthere rather than the vfio_ap_mdev_for_queue function - where it is\nneeded - because it must be taken prior to the mdevs_lock mutex in order to\nadhere to the proper locking order and prevent a lockdep splat; also\nbecause the mdevs_lock is needed there to access fields within\nthe matrix_mdev object in that function.\n\nSee the vfio-ap-locking.rst in the linux kernel tree.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}