Bluetooth: L2CAP: Fix use-after-free in l2cap_disconnect_{req,rsp}

Similar to commit d0be8347 ("Bluetooth: L2CAP: Fix use-after-free
caused by l2cap_chan_put"), just use l2cap_chan_hold_unless_zero to
prevent referencing a channel that is about to be destroyed.

Cc: stable@kernel.org
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Signed-off-by: Min Li <lm0963hack@gmail.com>

net/bluetooth/l2cap_core.c

@@ -4652,33 +4652,27 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn,
 
 	BT_DBG("scid 0x%4.4x dcid 0x%4.4x", scid, dcid);
 
-	mutex_lock(&conn->chan_lock);
-
-	chan = __l2cap_get_chan_by_scid(conn, dcid);
+	chan = l2cap_get_chan_by_scid(conn, dcid);
 	if (!chan) {
-		mutex_unlock(&conn->chan_lock);
 		cmd_reject_invalid_cid(conn, cmd->ident, dcid, scid);
 		return 0;
 	}
 
-	l2cap_chan_hold(chan);
-	l2cap_chan_lock(chan);
-
 	rsp.dcid = cpu_to_le16(chan->scid);
 	rsp.scid = cpu_to_le16(chan->dcid);
 	l2cap_send_cmd(conn, cmd->ident, L2CAP_DISCONN_RSP, sizeof(rsp), &rsp);
 
 	chan->ops->set_shutdown(chan);
 
+	mutex_lock(&conn->chan_lock);
 	l2cap_chan_del(chan, ECONNRESET);
+	mutex_unlock(&conn->chan_lock);
 
 	chan->ops->close(chan);
 
 	l2cap_chan_unlock(chan);
 	l2cap_chan_put(chan);
 
-	mutex_unlock(&conn->chan_lock);
-
 	return 0;
 }
 
@@ -4698,33 +4692,27 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn,
 
 	BT_DBG("dcid 0x%4.4x scid 0x%4.4x", dcid, scid);
 
-	mutex_lock(&conn->chan_lock);
-
-	chan = __l2cap_get_chan_by_scid(conn, scid);
+	chan = l2cap_get_chan_by_scid(conn, scid);
 	if (!chan) {
 		mutex_unlock(&conn->chan_lock);
 		return 0;
 	}
 
-	l2cap_chan_hold(chan);
-	l2cap_chan_lock(chan);
-
 	if (chan->state != BT_DISCONN) {
 		l2cap_chan_unlock(chan);
 		l2cap_chan_put(chan);
-		mutex_unlock(&conn->chan_lock);
 		return 0;
 	}
 
+	mutex_lock(&conn->chan_lock);
 	l2cap_chan_del(chan, 0);
+	mutex_unlock(&conn->chan_lock);
 
 	chan->ops->close(chan);
 
 	l2cap_chan_unlock(chan);
 	l2cap_chan_put(chan);
 
-	mutex_unlock(&conn->chan_lock);
-
 	return 0;
 }