FreeBSD: VID-5027b62e-f680-11e9-a87f-a4badb2f4699 (CVE-2019-5612): FreeBSD -- kernel memory disclosure from /dev/midistat

Problem Description: The kernel driver for /dev/midistat implements a handler for read(2). This handler is not thread-safe, and a multi-threaded program can exploit races in the handler to cause it to copy out kernel memory outside the boundaries of midistat's data buffer. Impact: The races allow a program to read kernel memory within a 4GB window centered at midistat's data buffer. The buffer is allocated each time the device is opened, so an attacker is not limited to a static 4GB region of memory. On 32-bit platforms, an attempt to trigger the race may cause a page fault in kernel mode, leading to a panic.