[PATCH 3.10 16/53] ALSA: seq: Fix race at timer setup and close

From: Greg Kroah-Hartman
Date: Wed Jan 27 2016 - 15:07:46 EST

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


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: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

sound/core/seq/seq_queue.c | 2 ++
1 file changed, 2 insertions(+)

--- 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(i
static void queue_delete(struct snd_seq_queue *q)
/* stop and release the timer */
+ mutex_lock(&q->timer_mutex);
+ mutex_unlock(&q->timer_mutex);
/* wait until access free */
/* release resources... */