Patch "ALSA: seq: Clear client entry before deleting else at closing" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

ALSA: seq: Clear client entry before deleting else at closing

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
alsa-seq-clear-client-entry-before-deleting-else-at-closing.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Takashi Iwai <[email protected]>
Date: Fri, 9 Mar 2018 22:23:31 +0100
Subject: ALSA: seq: Clear client entry before deleting else at closing

From: Takashi Iwai <[email protected]>

commit a2ff19f7b70118ced291a28d5313469914de451b upstream.

When releasing a client, we need to clear the clienttab[] entry at first, then call snd_seq_queue_client_leave(). Otherwise, the in-flight cell in the queue might be picked up by the timer interrupt via snd_seq_check_queue() before calling snd_seq_queue_client_leave(), and it's delivered to another queue while the client is clearing queues. This may eventually result in an uncleared cell remaining in a queue, and the later snd_seq_pool_delete() may need to wait for a long time until the event gets really processed.

By moving the clienttab[] clearance at the beginning of release, any event delivery of a cell belonging to this client will fail at a later point, since snd_seq_client_ptr() returns NULL. Thus the cell that was picked up by the timer interrupt will be returned immediately without further delivery, and the long stall of snd_seq_delete_pool() can be avoided, too.

---
 sound/core/seq/seq_clientmgr.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -255,12 +255,12 @@ static int seq_free_client1(struct snd_s
 
 	if (!client)
 		return 0;
-	snd_seq_delete_all_ports(client);
-	snd_seq_queue_client_leave(client->number);
 	spin_lock_irqsave(&clients_lock, flags);
 	clienttablock[client->number] = 1;
 	clienttab[client->number] = NULL;
 	spin_unlock_irqrestore(&clients_lock, flags);
+	snd_seq_delete_all_ports(client);
+	snd_seq_queue_client_leave(client->number);
 	snd_use_lock_sync(&client->use_lock);
 	snd_seq_queue_client_termination(client->number);
 	if (client->pool)

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/alsa-pcm-fix-uaf-in-snd_pcm_oss_get_formats.patch queue-4.15/alsa-seq-fix-possible-uaf-in-snd_seq_check_queue.patch queue-4.15/alsa-hda-revert-power_save-option-default-value.patch queue-4.15/alsa-seq-clear-client-entry-before-deleting-else-at-closing.patch