CVE-2026-53193

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.