An issue was discovered in the Linux kernel through 5.9.1, as used with Xen
through 4.14.x. drivers/xen/events/events_base.c allows event-channel
removal during the event-handling loop (a race condition). This can cause a
use-after-free or NULL pointer dereference, as demonstrated by a dom0 crash
via events for an in-reconfiguration paravirtualized device, aka
CID-073d0552ead5.

Jinoh Kang discovered that the Xen event channel infrastructure in the
Linux kernel contained a race condition. An attacker in guest could
possibly use this to cause a denial of service (dom0 crash).