CVE-2026-74313: vduse: hold vduse_lock across IDR lookup in open path

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

vduse: hold vduselock across IDR lookup in open path

vdusedevopen() looks up struct vdusedev through the IDR and then acquires dev->lock only after vduselock has been dropped.

This leaves a window where a concurrent VDUSEDESTROYDEV can remove the same object from the IDR and free it before the open path locks the device, leading to a use-after-free.

Close this race by keeping vduselock held until dev->lock has been acquired in the open path, matching the lock ordering already used by the destroy path.