Commit d8573936 authored by Takashi Iwai's avatar Takashi Iwai

ALSA: seq: Don't allow resizing pool in use

This is a fix for a (sort of) fallout in the recent commit
d15d662e ("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: d15d662e ("ALSA: seq: Fix racy pool initializations")
Reported-by: default avatar范龙飞 <long7573@126.com>
Reported-by: default avatarNicolai Stange <nstange@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent e312a869
......@@ -1838,6 +1838,9 @@ static int snd_seq_ioctl_set_client_pool(struct snd_seq_client *client,
(! 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);
......
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