Patch "ALSA: seq: Make ioctls race-free" has been added to the 4.9-stable tree

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

ALSA: seq: Make ioctls race-free

to the 4.9-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-make-ioctls-race-free.patch
and it can be found in the queue-4.9 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: Tue, 9 Jan 2018 23:11:03 +0100
Subject: ALSA: seq: Make ioctls race-free

From: Takashi Iwai <[email protected]>

commit b3defb791b26ea0683a93a4f49c77ec45ec96f10 upstream.

The ALSA sequencer ioctls have no protection against racy calls while the concurrent operations may lead to interfere with each other. As reported recently, for example, the concurrent calls of setting client pool with a combination of write calls may lead to either the unkillable dead-lock or UAF.

As a slightly big hammer solution, this patch introduces the mutex to make each ioctl exclusive. Although this may reduce performance via parallel ioctl calls, usually it's not demanded for sequencer usages, hence it should be negligible.

---
 sound/core/seq/seq_clientmgr.c |    3 +++
 sound/core/seq/seq_clientmgr.h |    1 +
 2 files changed, 4 insertions(+)

@@ -221,6 +221,7 @@ static struct snd_seq_client *seq_create
 	rwlock_init(&client->ports_lock);
 	mutex_init(&client->ports_mutex);
 	INIT_LIST_HEAD(&client->ports_list_head);
+	mutex_init(&client->ioctl_mutex);
 
 	/* find free slot in the client table */
 	spin_lock_irqsave(&clients_lock, flags);

@@ -2127,7 +2128,9 @@ static long snd_seq_ioctl(struct file *f
 			return -EFAULT;
 	}
 
+	mutex_lock(&client->ioctl_mutex);
 	err = handler->func(client, &buf);
+	mutex_unlock(&client->ioctl_mutex);
 	if (err >= 0) {
 		/* Some commands includes a bug in 'dir' field. */
 		if (handler->cmd == SNDRV_SEQ_IOCTL_SET_QUEUE_CLIENT ||

@@ -61,6 +61,7 @@ struct snd_seq_client {
 	struct list_head ports_list_head;
 	rwlock_t ports_lock;
 	struct mutex ports_mutex;
+	struct mutex ioctl_mutex;
 	int convert32;		/* convert 32->64bit */
 
 	/* output pool */

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

queue-4.9/alsa-pcm-remove-yet-superfluous-warn_on.patch queue-4.9/alsa-hda-apply-the-existing-quirk-to-imac-14-1.patch queue-4.9/alsa-hda-apply-headphone-noise-quirk-for-another-dell-xps-13-variant.patch queue-4.9/alsa-seq-make-ioctls-race-free.patch