ALSA: timer: Don't take register_mutex with copy_from/to_user()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: ALSA: timer: Don't take register_mutex with copy_from/to_user() The infamous mmap_lock taken in copy_from/to_user() can be often problematic when it's called inside another mutex, as they might lead to deadlocks. In the case of ALSA timer code, the bad pattern is with guard(mutex)(&register_mutex) that covers copy_from/to_user() -- which was mistakenly introduced at converting to guard(), and it had been carefully worked around in the past. This patch fixes those pieces simply by moving copy_from/to_user() out of the register mutex lock again.

References

• https://git.kernel.org/stable/c/15291b561d8cc835a2eea76b394070cf8e072771
• https://git.kernel.org/stable/c/296f7a9e15aab276db11206cbc1e2ae1215d7862
• https://git.kernel.org/stable/c/b074f47e55df93832bbbca1b524c501e6fea1c0d
• https://git.kernel.org/stable/c/3424c8f53bc63c87712a7fc22dc13d0cc85fb0d6