ALSA: seq: Fix race at timer setup and close

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@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/core/seq/seq_queue.c b/sound/core/seq/seq_queue.c
index 7dfd0f429410df217291271003d11ab385fcfc54..0bec02e89d5118b3dffe1e22e88e423baa037491 100644 (file)
--- a/sound/core/seq/seq_queue.c
+++ b/sound/core/seq/seq_queue.c
@@ -142,8 +142,10 @@ 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... */