commit 4dff5c7b upstream.

snd_timer_user_read() has a potential race among parallel reads, as
qhead and qused are updated outside the critical section due to
copy_to_user() calls.  Move them into the critical section, and also
sanitize the relevant code a bit.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>