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

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

[gregkh]

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 <stable@vger.kernel.org> know about it.


>From b3defb791b26ea0683a93a4f49c77ec45ec96f10 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Tue, 9 Jan 2018 23:11:03 +0100
Subject: ALSA: seq: Make ioctls race-free

From: Takashi Iwai <tiwai@suse.de>

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.

Reported-by: Luo Quan <a4651386@163.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -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 ||
--- a/sound/core/seq/seq_clientmgr.h
+++ b/sound/core/seq/seq_clientmgr.h
@@ -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 tiwai@suse.de 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