net: nfc: Propagate ISO14443 type A target ATS to userspace via netlink

Add a 20-byte field ats to struct nfc_target and expose it as
NFC_ATTR_TARGET_ATS via the netlink interface. The payload contains
'historical bytes' that help to distinguish cards from one another.
The information is commonly used to assemble an emulated ATR similar
to that reported by smart cards with contacts.

Add a 20-byte field target_ats to struct nci_dev to hold the payload
obtained in nci_rf_intf_activated_ntf_packet() and copy it to over to
nfc_target.ats in nci_activate_target(). The approach is similar
to the handling of 'general bytes' within ATR_RES.

Replace the hard-coded size of rats_res within struct
activation_params_nfca_poll_iso_dep by the equal constant NFC_ATS_MAXSIZE
now defined in nfc.h

Within NCI, the information corresponds to the 'RATS Response' activation
parameter that omits the initial length byte TL. This loses no
information and is consistent with our handling of SENSB_RES that
also drops the first (constant) byte.

Tested with nxp_nci_i2c on a few type A targets including an
ICAO 9303 compliant passport.

I refrain from the corresponding change to digital_in_recv_ats()
to have the few drivers based on digital.h fill nfc_target.ats,
as I have no way to test it. That class of drivers appear not to set
NFC_ATTR_TARGET_SENSB_RES either. Consider a separate patch to propagate
(all) the parameters.

Signed-off-by: Juraj Šarinay <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Paolo Abeni <[e-mail]>

include/net/nfc/nci.h

···
 #define NCI_OP_RF_INTF_ACTIVATED_NTF	nci_opcode_pack(NCI_GID_RF_MGMT, 0x05)
 struct activation_params_nfca_poll_iso_dep {
 	__u8	rats_res_len;
-	__u8	rats_res[20];
+	__u8	rats_res[NFC_ATS_MAXSIZE];
 };
 
 struct activation_params_nfcb_poll_iso_dep {

include/net/nfc/nci_core.h

···
 	/* stored during intf_activated_ntf */
 	__u8 remote_gb[NFC_MAX_GT_LEN];
 	__u8 remote_gb_len;
+
+	/* stored during intf_activated_ntf */
+	__u8 target_ats[NFC_ATS_MAXSIZE];
+	__u8 target_ats_len;
 };
 
 /* ----- NCI Devices ----- */

include/net/nfc/nfc.h

···
  *	is a type A one. The %sens_res most significant byte must be byte 2
  *	as described by the NFC Forum digital specification (i.e. the platform
  *	configuration one) while %sens_res least significant byte is byte 1.
+ * @ats_len: length of Answer To Select in bytes
+ * @ats: Answer To Select returned by an ISO 14443 Type A target upon activation
  */
 struct nfc_target {
 	u32 idx;
···
 	u8 is_iso15693;
 	u8 iso15693_dsfid;
 	u8 iso15693_uid[NFC_ISO15693_UID_MAXSIZE];
+	u8 ats_len;
+	u8 ats[NFC_ATS_MAXSIZE];
 };
 
 /**

include/uapi/linux/nfc.h

···
  * @NFC_ATTR_VENDOR_SUBCMD: Vendor specific sub command
  * @NFC_ATTR_VENDOR_DATA: Vendor specific data, to be optionally passed
  *	to a vendor specific command implementation
+ * @NFC_ATTR_TARGET_ATS: ISO 14443 type A target Answer To Select
  */
 enum nfc_attrs {
 	NFC_ATTR_UNSPEC,
···
 	NFC_ATTR_VENDOR_ID,
 	NFC_ATTR_VENDOR_SUBCMD,
 	NFC_ATTR_VENDOR_DATA,
+	NFC_ATTR_TARGET_ATS,
 /* private: internal use only */
 	__NFC_ATTR_AFTER_LAST
 };
···
 #define NFC_GB_MAXSIZE			48
 #define NFC_FIRMWARE_NAME_MAXSIZE	32
 #define NFC_ISO15693_UID_MAXSIZE	8
+#define NFC_ATS_MAXSIZE			20
 
 /* NFC protocols */
 #define NFC_PROTO_JEWEL		1

net/nfc/nci/core.c

···
 }
 EXPORT_SYMBOL(nci_core_conn_close);
 
+static void nci_set_target_ats(struct nfc_target *target, struct nci_dev *ndev)
+{
+	if (ndev->target_ats_len > 0) {
+		target->ats_len = ndev->target_ats_len;
+		memcpy(target->ats, ndev->target_ats, target->ats_len);
+	}
+}
+
 static int nci_set_local_general_bytes(struct nfc_dev *nfc_dev)
 {
 	struct nci_dev *ndev = nfc_get_drvdata(nfc_dev);
···
 				 msecs_to_jiffies(NCI_RF_DISC_SELECT_TIMEOUT));
 	}
 
-	if (!rc)
+	if (!rc) {
 		ndev->target_active_prot = protocol;
+		if (protocol == NFC_PROTO_ISO14443)
+			nci_set_target_ats(target, ndev);
+	}
 
 	return rc;
 }

net/nfc/nci/ntf.c

···
 	switch (ntf->activation_rf_tech_and_mode) {
 	case NCI_NFC_A_PASSIVE_POLL_MODE:
 		nfca_poll = &ntf->activation_params.nfca_poll_iso_dep;
-		nfca_poll->rats_res_len = min_t(__u8, *data++, 20);
+		nfca_poll->rats_res_len = min_t(__u8, *data++, NFC_ATS_MAXSIZE);
 		pr_debug("rats_res_len %d\n", nfca_poll->rats_res_len);
 		if (nfca_poll->rats_res_len > 0) {
 			memcpy(nfca_poll->rats_res,
···
 		pr_err("unsupported activation_rf_tech_and_mode 0x%x\n",
 		       ntf->activation_rf_tech_and_mode);
 		return NCI_STATUS_RF_PROTOCOL_ERROR;
+	}
+
+	return NCI_STATUS_OK;
+}
+
+static int nci_store_ats_nfc_iso_dep(struct nci_dev *ndev,
+				     const struct nci_rf_intf_activated_ntf *ntf)
+{
+	ndev->target_ats_len = 0;
+
+	if (ntf->activation_params_len <= 0)
+		return NCI_STATUS_OK;
+
+	if (ntf->activation_params.nfca_poll_iso_dep.rats_res_len > NFC_ATS_MAXSIZE) {
+		pr_debug("ATS too long\n");
+		return NCI_STATUS_RF_PROTOCOL_ERROR;
+	}
+
+	if (ntf->activation_params.nfca_poll_iso_dep.rats_res_len > 0) {
+		ndev->target_ats_len = ntf->activation_params.nfca_poll_iso_dep.rats_res_len;
+		memcpy(ndev->target_ats, ntf->activation_params.nfca_poll_iso_dep.rats_res,
+		       ndev->target_ats_len);
 	}
 
 	return NCI_STATUS_OK;
···
 			err = nci_store_general_bytes_nfc_dep(ndev, &ntf);
 			if (err != NCI_STATUS_OK)
 				pr_err("unable to store general bytes\n");
+		}
+
+		/* store ATS to be reported later in nci_activate_target */
+		if (ntf.rf_interface == NCI_RF_INTERFACE_ISO_DEP &&
+		    ntf.activation_rf_tech_and_mode == NCI_NFC_A_PASSIVE_POLL_MODE) {
+			err = nci_store_ats_nfc_iso_dep(ndev, &ntf);
+			if (err != NCI_STATUS_OK)
+				pr_err("unable to store ATS\n");
 		}
 	}
 

net/nfc/netlink.c

···
 			goto nla_put_failure;
 	}
 
+	if (target->ats_len > 0 &&
+	    nla_put(msg, NFC_ATTR_TARGET_ATS, target->ats_len,
+		    target->ats))
+		goto nla_put_failure;
+
 	genlmsg_end(msg, hdr);
 	return 0;