In the Linux kernel, the following vulnerability has been resolved: ALSA: timer: Forcibly close timer instances at closing When snd_timer

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

ALSA: timer: Forcibly close timer instances at closing

When snd_timer object is freed via snd_timer_free() and still pending
snd_timer_instance objects are assigned to the timer object, it tries
to unlink all instances and just set NULL to each ti->timer, then
releases the resources immediately. The problem is, however, when
there are slave timer instances that are associated with a master
instance linked to this timer: namely, those slave instances still
point to the freed timer object although the master instance is
unlinked, which may lead to user-after-free. The bug can be easily
triggered particularly when a new userspace-driven timers
(CONFIG_SND_UTIMER) is involved, since it can create and delete the
timer object via a simple file open/close, while the other
applications may keep accessing to that timer.

This patch is an attempt to paper over the problem above: now instead
of just unlinking, call snd_timer_close_locked forcibly for each
pending timer instance, so that all assigned slave timer instances are
properly detached, too. Since snd_timer_close() might be called later
by the driver that created that instance, the check of
SNDRV_TIMER_IFLG_DEAD is added at the beginning, too.