Describe CVE-2021-47511.
What is CVE-2021-47511?
In the Linux kernel, the following vulnerability has been resolved:

ALSA: pcm: oss: Fix negative period/buffer sizes

The period size calculation in OSS layer may receive a negative value
as an error, but the code there assumes only the positive values and
handle them with size_t.  Due to that, a too big value may be passed
to the lower layers.

This patch changes the code to handle with ssize_t and adds the proper
error checks appropriately..