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

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

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

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

pc_ref->hostid has a single consumer: nvmet_pr_set_ctrl_to_abort()
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 nvmet_ctrl_init_pr() takes its
snapshot.