Bluetooth: Fix deadlock and crash when SMP pairing times out

The l2cap_conn_del function tries to cancel_sync the security timer, but
when it's called from the timeout function itself a deadlock occurs.
Subsequently the "hcon->l2cap_data = NULL" that's supposed to protect
multiple calls to l2cap_conn_del never gets cleared and when the
connection finally drops we double free's etc which will crash the
kernel.

This patch fixes the issue by using the HCI_CONN_LE_SMP_PEND for
protecting against this. The same flag is also used for the same purpose
in other places in the SMP code.
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>

net/bluetooth/l2cap_core.c

@@ -1295,7 +1295,12 @@ static void security_timeout(struct work_struct *work)
 	struct l2cap_conn *conn = container_of(work, struct l2cap_conn,
 						security_timer.work);
 
+	BT_DBG("conn %p", conn);
+
+	if (test_and_clear_bit(HCI_CONN_LE_SMP_PEND, &conn->hcon->flags)) {
+		smp_chan_destroy(conn);
 		l2cap_conn_del(conn->hcon, ETIMEDOUT);
+	}
 }
 
 static struct l2cap_conn *l2cap_conn_add(struct hci_conn *hcon, u8 status)