CVE-2026-74520: iommu/iommufd: Fix IOPF group ownership UAF

In the Linux kernel, the following vulnerability has been resolved:

iommu/iommufd: Fix IOPF group ownership UAF

iopfgroupalloc() links each last-page IOPF group into the generic IOPF pending list before invoking the domain fault handler. iommufdfaultiopfhandler() also queued an accepted group in the IOMMUFD deliver list without removing it from the generic pending list.

When detach or HWPT replacement drops the device's IOPF reference count to zero, an IOMMU driver may call iopfqueueremovedevice(). That function responds to and frees groups through the generic pending list without removing the same groups from IOMMUFD's deliver list or response xarray. A later read, response, or cleanup can then access the freed group and cause a UAF.

Fix this by dequeuing an accepted group from the generic pending list before IOMMUFD queues it for userspace response. Make iopfgroupresponse() send a response regardless of pending-list membership, so the dequeued group can still be completed by IOMMUFD.