[PATCH 3.16.y-ckt 092/180] ALSA: seq: Fix race at timer setup and close

From: Luis Henriques
Date: Wed Feb 03 2016 - 17:36:34 EST


3.16.7-ckt24 -stable review patch. If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Takashi Iwai <tiwai@xxxxxxx>

commit 3567eb6af614dac436c4b16a8d426f9faed639b3 upstream.

ALSA sequencer code has an open race between the timer setup ioctl and
the close of the client. This was triggered by syzkaller fuzzer, and
a use-after-free was caught there as a result.

This patch papers over it by adding a proper queue->timer_mutex lock
around the timer-related calls in the relevant code path.

Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
sound/core/seq/seq_queue.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/sound/core/seq/seq_queue.c b/sound/core/seq/seq_queue.c
index aad4878cee55..52defd86d8b4 100644
--- a/sound/core/seq/seq_queue.c
+++ b/sound/core/seq/seq_queue.c
@@ -144,8 +144,10 @@ static struct snd_seq_queue *queue_new(int owner, int locked)
static void queue_delete(struct snd_seq_queue *q)
{
/* stop and release the timer */
+ mutex_lock(&q->timer_mutex);
snd_seq_timer_stop(q->timer);
snd_seq_timer_close(q);
+ mutex_unlock(&q->timer_mutex);
/* wait until access free */
snd_use_lock_sync(&q->use_lock);
/* release resources... */