curl: Use after free in hyperfifo example

Summary: THIS ONLY IS AN ISSUE IN EXAMPLE CODE, NOT CURL ITSELF! In the hyperfifo example the event base is freed before the curlmulticleanup is called. This leads to a use after free in the addsocket callback, when libevent tries to lock a mutex in the base event during the curl shutdown. Link t...

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.

...