CVE-2026-89955s390/vfio-ap: Fix NULL deref in status_show() during queue probe

Official description

In the Linux kernel, the following vulnerability has been resolved: s390/vfio-ap: Fix NULL deref in status_show() during queue probe When vfio_ap_mdev_probe_queue() creates the sysfs attribute group, the queue's driver data has not yet been set. A concurrent read of the 'status' attribute can therefore call dev_get_drvdata() and get NULL, which is then passed directly to vfio_ap_mdev_for_queue() where q->apqn is unconditionally dereferenced, causing a NULL pointer dereference. Fix this by acquiring the update locks before calling sysfs_create_group(). The status_show() function acquires guests_lock before reading the driver data, so any concurrent read will block until after dev_set_drvdata() has been called and the update locks are released. As a bonus, the APQN no longer needs to be read from the queue struct after allocation — it can be read directly from apdev before allocation and stored in a local variable, which is then assigned to q->apqn once the allocation succeeds.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/10606c9af18baed75cd180b96ee695441aa15134
• https://git.kernel.org/stable/c/31fa0a8a3c337ed2d200166d6926ab23c14f8b2e
• https://git.kernel.org/stable/c/e102ce0f4af99dff769a4b1b4daa4cc6bd5ad2d9
• https://git.kernel.org/stable/c/69632952aca04caa71e49953b6949fc04e788e67
• https://git.kernel.org/stable/c/7db2511fc601ca3a6e3fb1bdce02261c3c3167c3
• https://git.kernel.org/stable/c/dd6f4ef6f8a37412909ad787c837332fb070159c