Bluetooth: hci_event: Fix not using key encryption size when its known

This fixes the regression introduced by 50c1241e6a8a ("Bluetooth: l2cap:
Check encryption key size on incoming connection") introduced a check for
l2cap_check_enc_key_size which checks for hcon->enc_key_size which may
not be initialized if HCI_OP_READ_ENC_KEY_SIZE is still pending.

If the key encryption size is known, due previously reading it using
HCI_OP_READ_ENC_KEY_SIZE, then store it as part of link_key/smp_ltk
structures so the next time the encryption is changed their values are
used as conn->enc_key_size thus avoiding the racing against
HCI_OP_READ_ENC_KEY_SIZE.

Now that the enc_size is stored as part of key the information the code
then attempts to check that there is no downgrade of security if
HCI_OP_READ_ENC_KEY_SIZE returns a value smaller than what has been
previously stored.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=220061
Link: https://bugzilla.kernel.org/show_bug.cgi?id=220063
Fixes: 522e9ed ("Bluetooth: l2cap: Check encryption key size on incoming connection")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

include/net/bluetooth/hci_core.h

@@ -1798,6 +1798,7 @@ struct hci_conn_params *hci_pend_le_action_lookup(struct list_head *list,
 void hci_uuids_clear(struct hci_dev *hdev);
 
 void hci_link_keys_clear(struct hci_dev *hdev);
+u8 *hci_conn_key_enc_size(struct hci_conn *conn);
 struct link_key *hci_find_link_key(struct hci_dev *hdev, bdaddr_t *bdaddr);
 struct link_key *hci_add_link_key(struct hci_dev *hdev, struct hci_conn *conn,
 				  bdaddr_t *bdaddr, u8 *val, u8 type,

net/bluetooth/hci_conn.c

@@ -3023,3 +3023,27 @@ void hci_conn_tx_dequeue(struct hci_conn *conn)
 
 	kfree_skb(skb);
 }
+
+u8 *hci_conn_key_enc_size(struct hci_conn *conn)
+{
+	if (conn->type == ACL_LINK) {
+		struct link_key *key;
+
+		key = hci_find_link_key(conn->hdev, &conn->dst);
+		if (!key)
+			return NULL;
+
+		return &key->pin_len;
+	} else if (conn->type == LE_LINK) {
+		struct smp_ltk *ltk;
+
+		ltk = hci_find_ltk(conn->hdev, &conn->dst, conn->dst_type,
+				   conn->role);
+		if (!ltk)
+			return NULL;
+
+		return &ltk->enc_size;
+	}
+
+	return NULL;
+}

net/bluetooth/hci_event.c

@@ -739,10 +739,17 @@ static u8 hci_cc_read_enc_key_size(struct hci_dev *hdev, void *data,
 			   handle);
 		conn->enc_key_size = 0;
 	} else {
+		u8 *key_enc_size = hci_conn_key_enc_size(conn);
+
 		conn->enc_key_size = rp->key_size;
 		status = 0;
 
-		if (conn->enc_key_size < hdev->min_enc_key_size) {
+		/* Attempt to check if the key size is too small or if it has
+		 * been downgraded from the last time it was stored as part of
+		 * the link_key.
+		 */
+		if (conn->enc_key_size < hdev->min_enc_key_size ||
+		    (key_enc_size && conn->enc_key_size < *key_enc_size)) {
 			/* As slave role, the conn->state has been set to
 			 * BT_CONNECTED and l2cap conn req might not be received
 			 * yet, at this moment the l2cap layer almost does
@@ -755,6 +762,10 @@ static u8 hci_cc_read_enc_key_size(struct hci_dev *hdev, void *data,
 			clear_bit(HCI_CONN_ENCRYPT, &conn->flags);
 			clear_bit(HCI_CONN_AES_CCM, &conn->flags);
 		}
+
+		/* Update the key encryption size with the connection one */
+		if (key_enc_size && *key_enc_size != conn->enc_key_size)
+			*key_enc_size = conn->enc_key_size;
 	}
 
 	hci_encrypt_cfm(conn, status);
@@ -3065,6 +3076,34 @@ static void hci_inquiry_result_evt(struct hci_dev *hdev, void *edata,
 	hci_dev_unlock(hdev);
 }
 
+static int hci_read_enc_key_size(struct hci_dev *hdev, struct hci_conn *conn)
+{
+	struct hci_cp_read_enc_key_size cp;
+	u8 *key_enc_size = hci_conn_key_enc_size(conn);
+
+	if (!read_key_size_capable(hdev)) {
+		conn->enc_key_size = HCI_LINK_KEY_SIZE;
+		return -EOPNOTSUPP;
+	}
+
+	bt_dev_dbg(hdev, "hcon %p", conn);
+
+	memset(&cp, 0, sizeof(cp));
+	cp.handle = cpu_to_le16(conn->handle);
+
+	/* If the key enc_size is already known, use it as conn->enc_key_size,
+	 * otherwise use hdev->min_enc_key_size so the likes of
+	 * l2cap_check_enc_key_size don't fail while waiting for
+	 * HCI_OP_READ_ENC_KEY_SIZE response.
+	 */
+	if (key_enc_size && *key_enc_size)
+		conn->enc_key_size = *key_enc_size;
+	else
+		conn->enc_key_size = hdev->min_enc_key_size;
+
+	return hci_send_cmd(hdev, HCI_OP_READ_ENC_KEY_SIZE, sizeof(cp), &cp);
+}
+
 static void hci_conn_complete_evt(struct hci_dev *hdev, void *data,
 				  struct sk_buff *skb)
 {
@@ -3157,23 +3196,11 @@ static void hci_conn_complete_evt(struct hci_dev *hdev, void *data,
 		if (ev->encr_mode == 1 && !test_bit(HCI_CONN_ENCRYPT, &conn->flags) &&
 		    ev->link_type == ACL_LINK) {
 			struct link_key *key;
-			struct hci_cp_read_enc_key_size cp;
 
 			key = hci_find_link_key(hdev, &ev->bdaddr);
 			if (key) {
 				set_bit(HCI_CONN_ENCRYPT, &conn->flags);
-
-				if (!read_key_size_capable(hdev)) {
-					conn->enc_key_size = HCI_LINK_KEY_SIZE;
-				} else {
-					cp.handle = cpu_to_le16(conn->handle);
-					if (hci_send_cmd(hdev, HCI_OP_READ_ENC_KEY_SIZE,
-							 sizeof(cp), &cp)) {
-						bt_dev_err(hdev, "sending read key size failed");
-						conn->enc_key_size = HCI_LINK_KEY_SIZE;
-					}
-				}
-
+				hci_read_enc_key_size(hdev, conn);
 				hci_encrypt_cfm(conn, ev->status);
 			}
 		}
@@ -3612,24 +3639,8 @@ static void hci_encrypt_change_evt(struct hci_dev *hdev, void *data,
 
 	/* Try reading the encryption key size for encrypted ACL links */
 	if (!ev->status && ev->encrypt && conn->type == ACL_LINK) {
-		struct hci_cp_read_enc_key_size cp;
-
-		/* Only send HCI_Read_Encryption_Key_Size if the
-		 * controller really supports it. If it doesn't, assume
-		 * the default size (16).
-		 */
-		if (!read_key_size_capable(hdev)) {
-			conn->enc_key_size = HCI_LINK_KEY_SIZE;
-			goto notify;
-		}
-
-		cp.handle = cpu_to_le16(conn->handle);
-		if (hci_send_cmd(hdev, HCI_OP_READ_ENC_KEY_SIZE,
-				 sizeof(cp), &cp)) {
-			bt_dev_err(hdev, "sending read key size failed");
-			conn->enc_key_size = HCI_LINK_KEY_SIZE;
+		if (hci_read_enc_key_size(hdev, conn))
 			goto notify;
-		}
 
 		goto unlock;
 	}