Patch "ALSA: seq: Fix race during FIFO resize" has been added to the 4.9-stable tree

Patch "ALSA: seq: Fix race during FIFO resize" 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: Fix race during FIFO resize

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-fix-race-during-fifo-resize.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 2d7d54002e396c180db0c800c1046f0a3c471597 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Fri, 24 Mar 2017 17:07:57 +0100
Subject: ALSA: seq: Fix race during FIFO resize

From: Takashi Iwai <tiwai@suse.de>

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.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/sound/core/seq/seq_fifo.c
+++ b/sound/core/seq/seq_fifo.c
@@ -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 tiwai@suse.de are

queue-4.9/alsa-seq-fix-race-during-fifo-resize.patch
queue-4.9/alsa-hda-fix-a-problem-for-lineout-on-a-dell-aio-machine.patch