linux-kernel - [PATCH AUTOSEL 4.14 05/24] ALSA: seq: Cover unsubscribe_port() in list

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Date:   Tue,  4 Jun 2019 19:23:56 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Takashi Iwai <tiwai@...e.de>,
        syzbot+e4c8abb920efa77bace9@...kaller.appspotmail.com,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH AUTOSEL 4.14 05/24] ALSA: seq: Cover unsubscribe_port() in list_mutex

From: Takashi Iwai <tiwai@...e.de>

[ Upstream commit 7c32ae35fbf9cffb7aa3736f44dec10c944ca18e ]

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@...kaller.appspotmail.com
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 sound/core/seq/seq_ports.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/core/seq/seq_ports.c b/sound/core/seq/seq_ports.c
index edcb7ab21bf5..c8fa4336bccd 100644
--- a/sound/core/seq/seq_ports.c
+++ b/sound/core/seq/seq_ports.c
@@ -550,10 +550,10 @@ static void delete_and_unsubscribe_port(struct snd_seq_client *client,
 		list_del_init(list);
 	grp->exclusive = 0;
 	write_unlock_irq(&grp->list_lock);
-	up_write(&grp->list_mutex);
 
 	if (!empty)
 		unsubscribe_port(client, port, grp, &subs->info, ack);
+	up_write(&grp->list_mutex);
 }
 
 /* connect two ports */
-- 
2.20.1