[PATCH 4.4 40/84] ALSA: seq: Cover unsubscribe_port() in list_mutex

From: Greg Kroah-Hartman
Date: Thu Jun 20 2019 - 14:01:26 EST

From: Takashi Iwai <tiwai@xxxxxxx>

commit 7c32ae35fbf9cffb7aa3736f44dec10c944ca18e upstream.

The call of unsubscribe_port() which manages the group count and
module refcount from delete_and_unsubscribe_port() looks racy; it's
not covered by the group list lock, and it's likely a cause of the
reported unbalance at port deletion. Let's move the call inside the
group list_mutex to plug the hole.

Reported-by: syzbot+e4c8abb920efa77bace9@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

sound/core/seq/seq_ports.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/sound/core/seq/seq_ports.c
+++ b/sound/core/seq/seq_ports.c
@@ -550,10 +550,10 @@ static void delete_and_unsubscribe_port(
grp->exclusive = 0;
- up_write(&grp->list_mutex);

if (!empty)
unsubscribe_port(client, port, grp, &subs->info, ack);
+ up_write(&grp->list_mutex);

/* connect two ports */