NFC: protect nci_data_exchange transactions

Protect 'cb' and 'cb_context' arguments in nci_data_exchange.
In fact, this implements a queue with max length of 1 data
exchange transactions in parallel.

Signed-off-by: Ilan Elias <[e-mail]>
Acked-by: Lauro Ramos Venancio <[e-mail]>
Signed-off-by: John W. Linville <[e-mail]>

include/net/nfc/nci_core.h

···
 	NCI_UP,
 	NCI_DISCOVERY,
 	NCI_POLL_ACTIVE,
+	NCI_DATA_EXCHANGE,
 };
 
 /* NCI timeouts */

net/nfc/nci/core.c

···
 						void *cb_context)
 {
 	struct nci_dev *ndev = nfc_get_drvdata(nfc_dev);
+	int rc;
 
 	nfc_dbg("entry, target_idx %d, len %d", target_idx, skb->len);
 
···
 		return -EINVAL;
 	}
 
+	if (test_and_set_bit(NCI_DATA_EXCHANGE, &ndev->flags))
+		return -EBUSY;
+
 	/* store cb and context to be used on receiving data */
 	ndev->data_exchange_cb = cb;
 	ndev->data_exchange_cb_context = cb_context;
 
-	return nci_send_data(ndev, ndev->conn_id, skb);
+	rc = nci_send_data(ndev, ndev->conn_id, skb);
+	if (rc)
+		clear_bit(NCI_DATA_EXCHANGE, &ndev->flags);
+
+	return rc;
 }
 
 static struct nfc_ops nci_nfc_ops = {

net/nfc/nci/data.c

···
 		/* no waiting callback, free skb */
 		kfree_skb(skb);
 	}
+
+	clear_bit(NCI_DATA_EXCHANGE, &ndev->flags);
 }
 
 /* ----------------- NCI TX Data ----------------- */

net/nfc/nci/ntf.c

···
 	}
 
 	/* complete the data exchange transaction, if exists */
-	if (ndev->data_exchange_cb)
+	if (test_bit(NCI_DATA_EXCHANGE, &ndev->flags))
 		nci_data_exchange_complete(ndev, NULL, -EIO);
 }