diff mbox series

ALSA: seq: Fix race of snd_seq_timer_open()

Message ID 20210610152059.24633-1-tiwai@suse.de (mailing list archive)
State New
Headers show
Series ALSA: seq: Fix race of snd_seq_timer_open() | expand

Commit Message

Takashi Iwai June 10, 2021, 3:20 p.m. UTC
The timer instance per queue is exclusive, and snd_seq_timer_open()
should have managed the concurrent accesses.  It looks as if it's
checking the already existing timer instance at the beginning, but
it's not right, because there is no protection, hence any later
concurrent call of snd_seq_timer_open() may override the timer
instance easily.  This may result in UAF, as the leftover timer
instance can keep running while the queue itself gets closed, as
spotted by syzkaller recently.

For avoiding the race, add a proper check at the assignment of
tmr->timeri again, and return -EBUSY if it's been already registered.

Reported-by: syzbot+ddc1260a83ed1cbf6fb5@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/000000000000dce34f05c42f110c@google.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/core/seq/seq_timer.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/sound/core/seq/seq_timer.c b/sound/core/seq/seq_timer.c
index 1645e4142e30..9863be6fd43e 100644
--- a/sound/core/seq/seq_timer.c
+++ b/sound/core/seq/seq_timer.c
@@ -297,8 +297,16 @@  int snd_seq_timer_open(struct snd_seq_queue *q)
 		return err;
 	}
 	spin_lock_irq(&tmr->lock);
-	tmr->timeri = t;
+	if (tmr->timeri)
+		err = -EBUSY;
+	else
+		tmr->timeri = t;
 	spin_unlock_irq(&tmr->lock);
+	if (err < 0) {
+		snd_timer_close(t);
+		snd_timer_instance_free(t);
+		return err;
+	}
 	return 0;
 }