CVE-2022-49291

In the Linux kernel, the following vulnerability has been resolved:

ALSA: pcm: Fix races among concurrent hwparams and hwfree calls

Currently we have neither proper check nor protection against the concurrent calls of PCM hwparams and hwfree ioctls, which may result in a UAF. Since the existing PCM stream lock can't be used for protecting the whole ioctl operations, we need a new mutex to protect those racy calls.

This patch introduced a new mutex, runtime->buffermutex, and applies it to both hwparams and hwfree ioctl code paths. Along with it, the both functions are slightly modified (the mmapcount check is moved into the state-check block) for code simplicity.