Bluetooth: Use the stored LTK for restabilishing security

Now that it's possible that the exchanged key is present in
the link key list, we may be able to estabilish security with
an already existing key, without need to perform any SMP
procedure.
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@openbossa.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

net/bluetooth/smp.c

@@ -480,6 +480,17 @@ int smp_conn_security(struct l2cap_conn *conn, __u8 sec_level)
 
 	if (hcon->link_mode & HCI_LM_MASTER) {
 		struct smp_cmd_pairing cp;
+		struct link_key *key;
+
+		key = hci_find_link_key_type(hcon->hdev, conn->dst,
+							HCI_LK_SMP_LTK);
+		if (key) {
+			struct key_master_id *master = (void *) key->data;
+
+			hci_le_start_enc(hcon, master->ediv, master->rand,
+								key->val);
+			goto done;
+		}
 
 		build_pairing_cmd(conn, &cp, NULL, authreq);
 		conn->preq[0] = SMP_CMD_PAIRING_REQ;
@@ -495,6 +506,7 @@ int smp_conn_security(struct l2cap_conn *conn, __u8 sec_level)
 		smp_send_cmd(conn, SMP_CMD_SECURITY_REQ, sizeof(cp), &cp);
 	}
 
+done:
 	hcon->pending_sec_level = sec_level;
 	set_bit(HCI_CONN_ENCRYPT_PEND, &hcon->pend);