[PATCH 0/1 2nd attempt] [SRU focal/linux-oem-5.6] CVE-2020-27675

[Tim Gardner]

[Impact]
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.

>From the Ubuntu security team:
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).

[Test Case]
No test case available

[Potential regression]
Clean back port from upstream commit.