CVE-2026-98723: nvmet: copy the hostid into the ctrl before creating PR pc_refs

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

nvmet: copy the hostid into the ctrl before creating PR pcrefs

Commit 6202783184bf ("nvmet: Improve nvmetallocctrl() interface and implementation") added a second uuidcopy() of args->hostid near the end of nvmetallocctrl(), and commit 7b658153f1b8 ("nvmet: Remove duplicate uuidcopy") removed the original copy that sat before nvmetctrlinitpr() instead of the new one.

Since then nvmetctrlinitpr() snapshots ctrl->hostid into the per-controller per-namespace reservation refs while the uuidcopy() from the connect data runs later, after the controller is published. The ctrl is allocated with kzalloc(), so every pcref created on this path stores the nil UUID.

pcref->hostid has a single consumer: nvmetprsetctrltoabort() matches it against the preempted registrant's hostid to kill and drain the victim's in-flight I/O for Preempt and Abort. The match can never hit with the nil UUID, so whenever a namespace with reservations enabled exists before a host connects, which includes every reconnect, Preempt and Abort silently degrades into a plain Preempt: the preempting host sees success while the victim's in-flight I/O is still in the air.

Copy the hostid where the rest of the connect data is consumed, before the controller is published and before nvmetctrlinitpr() takes its snapshot.