[PATCH 4.19 05/23] Bluetooth: Fix l2cap_disconnect_req deadlock

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

From: Ying Hsu <yinghsu@chromium.org>

[ Upstream commit 02c5ea5246a44d6ffde0fddebfc1d56188052976 ]

L2CAP assumes that the locks conn->chan_lock and chan->lock are
acquired in the order conn->chan_lock, chan->lock to avoid
potential deadlock.
For example, l2sock_shutdown acquires these locks in the order:
  mutex_lock(&conn->chan_lock)
  l2cap_chan_lock(chan)

However, l2cap_disconnect_req acquires chan->lock in
l2cap_get_chan_by_scid first and then acquires conn->chan_lock
before calling l2cap_chan_del. This means that these locks are
acquired in unexpected order, which leads to potential deadlock:
  l2cap_chan_lock(c)
  mutex_lock(&conn->chan_lock)

This patch releases chan->lock before acquiring the conn_chan_lock
to avoid the potential deadlock.

Fixes: a2a9339e1c9d ("Bluetooth: L2CAP: Fix use-after-free in l2cap_disconnect_{req,rsp}")
Signed-off-by: Ying Hsu <yinghsu@chromium.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/bluetooth/l2cap_core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 94d40a20ab958..d91ddcd54e278 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -4362,7 +4362,9 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn,
 
 	chan->ops->set_shutdown(chan);
 
+	l2cap_chan_unlock(chan);
 	mutex_lock(&conn->chan_lock);
+	l2cap_chan_lock(chan);
 	l2cap_chan_del(chan, ECONNRESET);
 	mutex_unlock(&conn->chan_lock);
 
@@ -4401,7 +4403,9 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn,
 		return 0;
 	}
 
+	l2cap_chan_unlock(chan);
 	mutex_lock(&conn->chan_lock);
+	l2cap_chan_lock(chan);
 	l2cap_chan_del(chan, 0);
 	mutex_unlock(&conn->chan_lock);
 
-- 
2.39.2