From: Norbert Szetei Date: Sun, 26 Jul 2026 08:01:45 +0000 (+0200) Subject: ALSA: timer: Clear SNDRV_TIMER_IFLG_DEAD once the close completes X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=c2744d5f3aea474513fd2298daecb94a952ce441;p=thirdparty%2Flinux.git 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. Fixes: da3039e91d1f ("ALSA: timer: Forcibly close timer instances at closing") Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-5 Signed-off-by: Norbert Szetei Link: https://patch.msgid.link/CA41AA48-75BF-45E9-A36D-3A5D2F124F60@doyensec.com Signed-off-by: Takashi Iwai --- diff --git a/sound/core/timer.c b/sound/core/timer.c index 07ef127b29e1..9407954034cf 100644 --- a/sound/core/timer.c +++ b/sound/core/timer.c @@ -458,6 +458,8 @@ static void remove_slave_links(struct snd_timer_instance *timeri, list_del_init(&slave->ack_list); list_del_init(&slave->active_list); } + /* the close is done; a reopen must not see the mark */ + timeri->flags &= ~SNDRV_TIMER_IFLG_DEAD; } /*