Use after free in Freebsd

Second, the audio buffer backing a mapping could be freed when the device was closed even though the mapping remained valid. The freed memory could then be reused elsewhere while still accessible through the stale mapping. The /dev/dsp device nodes are world-accessible by default. On a system with an audio device, either issue allows an unprivileged local user to read and write kernel memory, which can be used to escalate privileges, potentially gaining full control of the affected system. At a minimum, an attacker can crash the kernel, resulting in a Denial of Service (DoS).