An issue was discovered in drivers/xen/balloon.c in the Linux kernel before
5.2.3, as used in Xen through 4.12.x, allowing guest OS users to cause a
denial of service because of unrestricted resource consumption during the
mapping of guest memory, aka CID-6ef36ab967c7.

Julien Grall discovered that the Xen balloon memory driver in the Linux
kernel did not properly restrict the amount of memory set aside for page
mappings in some situations. An attacker could use this to cause a denial
of service (kernel memory exhaustion).