Patch "ALSA: seq: Fix race during FIFO resize" has been added to the 4.4-stable tree

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

ALSA: seq: Fix race during FIFO resize

to the 4.4-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-fix-race-during-fifo-resize.patch
and it can be found in the queue-4.4 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, 24 Mar 2017 17:07:57 +0100
Subject: ALSA: seq: Fix race during FIFO resize

From: Takashi Iwai <[email protected]>

commit 2d7d54002e396c180db0c800c1046f0a3c471597 upstream.

When a new event is queued while processing to resize the FIFO in snd_seq_fifo_clear(), it may lead to a use-after-free, as the old pool that is being queued gets removed. For avoiding this race, we need to close the pool to be deleted and sync its usage before actually deleting it.

The issue was spotted by syzkaller.

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

@@ -265,6 +265,10 @@ int snd_seq_fifo_resize(struct snd_seq_f
 	/* NOTE: overflow flag is not cleared */
 	spin_unlock_irqrestore(&f->lock, flags);
 
+	/* close the old pool and wait until all users are gone */
+	snd_seq_pool_mark_closing(oldpool);
+	snd_use_lock_sync(&f->use_lock);
+
 	/* release cells in old pool */
 	for (cell = oldhead; cell; cell = next) {
 		next = cell->next;

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

queue-4.4/alsa-seq-fix-race-during-fifo-resize.patch queue-4.4/alsa-hda-fix-a-problem-for-lineout-on-a-dell-aio-machine.patch