Bluetooth: Add flag to track STK encryption

There are certain subtle differences in behavior when we're encrypted
with the STK, such as allowing re-encryption even though the security
level stays the same. Because of this, add a flag to track whether we're
encrypted with an STK or not.
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

include/net/bluetooth/hci_core.h

@@ -536,6 +536,7 @@ enum {
 	HCI_CONN_AUTH,
 	HCI_CONN_SECURE,
 	HCI_CONN_FIPS,
+	HCI_CONN_STK_ENCRYPT,
 };
 
 static inline bool hci_conn_ssp_enabled(struct hci_conn *conn)

net/bluetooth/hci_event.c

@@ -4365,8 +4365,11 @@ static void hci_le_ltk_request_evt(struct hci_dev *hdev, struct sk_buff *skb)
 	 * using a distributed LTK.
 	 */
 	if (ltk->type == SMP_STK) {
+		set_bit(HCI_CONN_STK_ENCRYPT, &conn->flags);
 		list_del(&ltk->list);
 		kfree(ltk);
+	} else {
+		clear_bit(HCI_CONN_STK_ENCRYPT, &conn->flags);
 	}
 
 	hci_dev_unlock(hdev);

net/bluetooth/smp.c

@@ -538,6 +538,7 @@ static u8 smp_random(struct smp_chan *smp)
 
 		hci_le_start_enc(hcon, ediv, rand, stk);
 		hcon->enc_key_size = smp->enc_key_size;
+		set_bit(HCI_CONN_STK_ENCRYPT, &hcon->flags);
 	} else {
 		u8 stk[16], auth;
 		__le64 rand = 0;
@@ -856,6 +857,9 @@ static bool smp_ltk_encrypt(struct l2cap_conn *conn, u8 sec_level)
 	hci_le_start_enc(hcon, key->ediv, key->rand, key->val);
 	hcon->enc_key_size = key->enc_size;
 
+	/* We never store STKs for master role, so clear this flag */
+	clear_bit(HCI_CONN_STK_ENCRYPT, &hcon->flags);
+
 	return true;
 }