An exchange with a NFC target must complete within NCI_DATA_TIMEOUT.
A delay of 700 ms is not sufficient for cryptographic operations on smart
cards. CardOS 6.0 may need up to 1.3 seconds to perform 256-bit ECDH
or 3072-bit RSA. To prevent brute-force attacks, passports and similar
documents introduce even longer delays into access control protocols
(BAC/PACE).

The timeout should be higher, but not too much. The expiration allows
us to detect that a NFC target has disappeared.

Expose data_timeout as a parameter of nci.ko. Keep the value in uint
nci_data_timeout, set the default to 3 seconds. Point NCI_DATA_TIMEOUT
to the new variable.

Signed-off-by: Juraj Šarinay <juraj@sarinay.com>
---
 include/net/nfc/nci_core.h | 4 +++-
 net/nfc/nci/core.c         | 4 ++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/net/nfc/nci_core.h b/include/net/nfc/nci_core.h
index e180bdf2f82b..da62f0da1fb2 100644
--- a/include/net/nfc/nci_core.h
+++ b/include/net/nfc/nci_core.h
@@ -52,7 +52,9 @@ enum nci_state {
 #define NCI_RF_DISC_SELECT_TIMEOUT		5000
 #define NCI_RF_DEACTIVATE_TIMEOUT		30000
 #define NCI_CMD_TIMEOUT				5000
-#define NCI_DATA_TIMEOUT			700
+
+extern unsigned int nci_data_timeout;
+#define NCI_DATA_TIMEOUT			nci_data_timeout
 
 struct nci_dev;
 
diff --git a/net/nfc/nci/core.c b/net/nfc/nci/core.c
index fc921cd2cdff..089a8757dbbb 100644
--- a/net/nfc/nci/core.c
+++ b/net/nfc/nci/core.c
@@ -31,6 +31,10 @@
 #include <net/nfc/nci_core.h>
 #include <linux/nfc.h>
 
+unsigned int nci_data_timeout = 3000;
+module_param_named(data_timeout, nci_data_timeout, uint, 0644);
+MODULE_PARM_DESC(data_timeout, "Round-trip communication timeout in milliseconds");
+
 struct core_conn_create_data {
 	int length;
 	struct nci_core_conn_create_cmd *cmd;
-- 
2.47.2