FAILED: patch "[PATCH] ALSA: seq: close a re-opened queue timer in the destructor" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 2c4dc0ed50b05cd847a4b34b8cebf0775f19aeb9
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026072946-underdone-mule-5e1d@gregkh' --subject-prefix 'PATCH 5.10.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 2c4dc0ed50b05cd847a4b34b8cebf0775f19aeb9 Mon Sep 17 00:00:00 2001
From: Norbert Szetei <[email protected]>
Date: Tue, 14 Jul 2026 10:29:23 +0200
Subject: [PATCH] ALSA: seq: close a re-opened queue timer in the destructor

queue_delete() closes the queue timer, then frees it. snd_seq_timer_close() clears q->timer->timeri. snd_use_lock_sync() then drains borrowers, and snd_seq_timer_delete() frees q->timer.

A borrower can re-open the timer inside that window. A SET_QUEUE_CLIENT that took a queueptr() use_lock reference before the queue was unlinked runs snd_seq_timer_open() after the close. Open refuses re-open only while timeri is set, and the close just cleared it, so it re-opens timeri.

snd_seq_timer_delete() does not close that instance. Its snd_seq_timer_stop() is a no-op, because running was cleared first. So it frees q->timer with the instance still live. The queue is freed next.

The instance stays on the global timer with callback_data pointing at the freed queue. A non-owner START on the unlocked queue arms it. The next tick derefs the freed queue in snd_seq_timer_interrupt().

Reachable by an unprivileged user with access to /dev/snd/seq. No CAP and no queue ownership required.

Close any lingering instance in the destructor. There, ->timeri can no longer change: the queue is unlinked and all use_lock borrowers have drained, so no snd_seq_queue_use() can re-open it. Close it before clearing q->timer. snd_timer_close() waits for any in-flight snd_seq_timer_interrupt() to finish, and that callback still reads q->timer (via snd_seq_check_queue()), so q->timer must stay valid until it drains.

index 4cd7211ccf48..419288eec4bb 100644
@@ -61,12 +61,23 @@ struct snd_seq_timer *snd_seq_timer_new(void)
 void snd_seq_timer_delete(struct snd_seq_timer **tmr)
 {
 	struct snd_seq_timer *t = *tmr;
-	*tmr = NULL;
+	struct snd_timer_instance *ti;
 
 	if (t == NULL) {
 		pr_debug("ALSA: seq: snd_seq_timer_delete() called with NULL timer\n");
 		return;
 	}
+
+	scoped_guard(spinlock_irq, &t->lock) {
+		ti = t->timeri;
+		t->timeri = NULL;
+	}
+	if (ti) {
+		snd_timer_close(ti);
+		snd_timer_instance_free(ti);
+	}
+
+	*tmr = NULL;
 	t->running = 0;
 
 	/* reset time */

From: Norbert Szetei <[email protected]>

[ Upstream commit 2c4dc0ed50b05cd847a4b34b8cebf0775f19aeb9 ]

queue_delete() closes the queue timer, then frees it. snd_seq_timer_close() clears q->timer->timeri. snd_use_lock_sync() then drains borrowers, and snd_seq_timer_delete() frees q->timer.

A borrower can re-open the timer inside that window. A SET_QUEUE_CLIENT that took a queueptr() use_lock reference before the queue was unlinked runs snd_seq_timer_open() after the close. Open refuses re-open only while timeri is set, and the close just cleared it, so it re-opens timeri.

snd_seq_timer_delete() does not close that instance. Its snd_seq_timer_stop() is a no-op, because running was cleared first. So it frees q->timer with the instance still live. The queue is freed next.

The instance stays on the global timer with callback_data pointing at the freed queue. A non-owner START on the unlocked queue arms it. The next tick derefs the freed queue in snd_seq_timer_interrupt().

Reachable by an unprivileged user with access to /dev/snd/seq. No CAP and no queue ownership required.

Close any lingering instance in the destructor. There, ->timeri can no longer change: the queue is unlinked and all use_lock borrowers have drained, so no snd_seq_queue_use() can re-open it. Close it before clearing q->timer. snd_timer_close() waits for any in-flight snd_seq_timer_interrupt() to finish, and that callback still reads q->timer (via snd_seq_check_queue()), so q->timer must stay valid until it drains.

---
 sound/core/seq/seq_timer.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

index 9863be6fd43e1..50581120f2822 100644
@@ -58,12 +58,23 @@ struct snd_seq_timer *snd_seq_timer_new(void)
 void snd_seq_timer_delete(struct snd_seq_timer **tmr)
 {
 	struct snd_seq_timer *t = *tmr;
-	*tmr = NULL;
+	struct snd_timer_instance *ti;
 
 	if (t == NULL) {
 		pr_debug("ALSA: seq: snd_seq_timer_delete() called with NULL timer\n");
 		return;
 	}
+
+	spin_lock_irq(&t->lock);
+	ti = t->timeri;
+	t->timeri = NULL;
+	spin_unlock_irq(&t->lock);
+	if (ti) {
+		snd_timer_close(ti);
+		snd_timer_instance_free(ti);
+	}
+
+	*tmr = NULL;
 	t->running = 0;
 
 	/* reset time */

2.53.0