nfc/nci: fix race with opening and closing

Previously we leverage NCI_UNREG and the lock inside nci_close_device to
prevent the race condition between opening a device and closing a
device. However, it still has problem because a failed opening command
will erase the NCI_UNREG flag and allow another opening command to
bypass the status checking.

This fix corrects that by making sure the NCI_UNREG is held.

Reported-by: [email protected]
Fixes: 48b71a9 ("NFC: add NCI_UNREG flag to eliminate the race")
Signed-off-by: Lin Ma <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: f0rm2l1n

net/nfc/nci/core.c

@@ -542,7 +542,7 @@ static int nci_open_device(struct nci_dev *ndev)
 		skb_queue_purge(&ndev->tx_q);
 
 		ndev->ops->close(ndev);
-		ndev->flags = 0;
+		ndev->flags &= BIT(NCI_UNREG);
 	}
 
 done: