[PATCH 4.9 34/86] ALSA: seq: Dont allow resizing pool in use

Greg Kroah-Hartman
2018-03-16T15:22:57Z

From: Takashi Iwai <tiwai@suse.de>

commit d85739367c6d56e475c281945c68fdb05ca74b4c upstream.

This is a fix for a (sort of) fallout in the recent commit
d15d662e89fc ("ALSA: seq: Fix racy pool initializations") for
CVE-2018-1000004.
As the pool resize deletes the existing cells, it may lead to a race
when another thread is writing concurrently, eventually resulting a
UAF.

A simple workaround is not to allow the pool resizing when the pool is
in use. It's an invalid behavior in anyway.

Fixes: d15d662e89fc ("ALSA: seq: Fix racy pool initializations")
Reported-by: 范龙飞 <long7573@126.com>
Reported-by: Nicolai Stange <nstange@suse.de>
Cc: <stable@vger.kernel.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 +++
1 file changed, 3 insertions(+)

--- a/sound/core/seq/seq_clientmgr.c
+++ b/sound/core/seq/seq_clientmgr.c
@@ -1835,6 +1835,9 @@ static int snd_seq_ioctl_set_client_pool
(! snd_seq_write_pool_allocated(client) ||
info->output_pool != client->pool->size)) {
if (snd_seq_write_pool_allocated(client)) {
+ /* is the pool in use? */
+ if (atomic_read(&client->pool->counter))
+ return -EBUSY;
/* remove all existing cells */
snd_seq_pool_mark_closing(client->pool);
snd_seq_queue_client_leave_cells(client->number);