CVE-2026-74503

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

ALSA: timer: Clear SNDRV_TIMER_IFLG_DEAD once the close completes

snd_timer_close_locked() marks an instance with SNDRV_TIMER_IFLG_DEAD

and returns early when the flag is already set, but the flag is never

cleared again. A completed close ends in remove_slave_links(), which

leaves timeri->timer NULL, so a second close is already harmless through

the timer == NULL path; the early return can only be reached by an

instance that was opened again in between. For such an instance the

close unlinks nothing, so snd_timer_instance_free() frees an object that

is still on timer->open_list_head, still on snd_timer_master_list if it

was opened with a slave key, still owns any adopted slaves, and still

holds its timer and module references.

snd_seq_timer_open() reopens an instance exactly like that: it retries

its fallback open on the same object after a failure that has already

run snd_timer_close_locked() internally. An unprivileged user with

access to /dev/snd/timer and /dev/snd/seq can force that failure, since

snd_timer_check_master() returns -EBUSY when a pending slave matches the

new master's (slave_class, slave_id) key and the target timer has

reached max_instances, and SNDRV_TIMER_IOCTL_SELECT with dev_class =

SNDRV_TIMER_CLASS_SLAVE keeps the caller-supplied dev_sclass, so a

sequencer queue's key can be forged. The freed instance is afterwards

dereferenced by any further snd_timer_open() on that timer, by

snd_timer_check_slave(), and by /proc/asound/timers, which faults on the

stale ti->owner pointer.

The flag only has to be visible while the close is in progress, which is

all its other users need. Clear it in remove_slave_links(), under the

same timer->lock that sets it, once the instance is off every list.