NFC: digital: Implement NFC-DEP max payload lengths

The maximum payload for NFC-DEP exchanges (i.e., the
number of bytes between SoD and EoD) is negotiated
using the ATR_REQ, ATR_RES, and PSL_REQ commands.
The valid maximum lengths are 64, 128, 192, and 254
bytes.

Currently, NFC-DEP code assumes that both sides are
always using 254 byte maximums and ignores attempts
by the peer to change it.  Instead, implement the
negotiation code, enforce the local maximum when
receiving data from the peer, and don't send payloads
that exceed the remote's maximum.  The default local
maximum is 254 bytes.

Reviewed-by: Thierry Escande <thierry.escande@linux.intel.com>
Tested-by: Thierry Escande <thierry.escande@linux.intel.com>
Signed-off-by: Mark A. Greer <mgreer@animalcreek.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

include/net/nfc/digital.h

@@ -227,6 +227,9 @@ struct nfc_digital_dev {
 	u8 curr_nfc_dep_pni;
 	u8 did;
 
+	u8 local_payload_max;
+	u8 remote_payload_max;
+
 	u16 target_fsc;
 
 	int (*skb_check_crc)(struct sk_buff *skb);

net/nfc/digital_dep.c

@@ -34,9 +34,12 @@
 
 #define DIGITAL_DID_MAX	14
 
-#define DIGITAL_LR_BITS_PAYLOAD_SIZE_254B 0x30
-#define DIGITAL_FSL_BITS_PAYLOAD_SIZE_254B \
-				(DIGITAL_LR_BITS_PAYLOAD_SIZE_254B >> 4)
+#define DIGITAL_PAYLOAD_SIZE_MAX	254
+#define DIGITAL_PAYLOAD_BITS_TO_PP(s)	(((s) & 0x3) << 4)
+#define DIGITAL_PAYLOAD_PP_TO_BITS(s)	(((s) >> 4) & 0x3)
+#define DIGITAL_PAYLOAD_BITS_TO_FSL(s)	((s) & 0x3)
+#define DIGITAL_PAYLOAD_FSL_TO_BITS(s)	((s) & 0x3)
+
 #define DIGITAL_GB_BIT	0x02
 
 #define DIGITAL_NFC_DEP_PFB_TYPE(pfb) ((pfb) & 0xE0)
@@ -101,6 +104,32 @@ struct digital_dep_req_res {
 static void digital_in_recv_dep_res(struct nfc_digital_dev *ddev, void *arg,
 				    struct sk_buff *resp);
 
+static const u8 digital_payload_bits_map[4] = {
+	[0] = 64,
+	[1] = 128,
+	[2] = 192,
+	[3] = 254
+};
+
+static u8 digital_payload_bits_to_size(u8 payload_bits)
+{
+	if (payload_bits >= ARRAY_SIZE(digital_payload_bits_map))
+		return 0;
+
+	return digital_payload_bits_map[payload_bits];
+}
+
+static u8 digital_payload_size_to_bits(u8 payload_size)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(digital_payload_bits_map); i++)
+		if (digital_payload_bits_map[i] == payload_size)
+			return i;
+
+	return 0xff;
+}
+
 static void digital_skb_push_dep_sod(struct nfc_digital_dev *ddev,
 				     struct sk_buff *skb)
 {
@@ -202,6 +231,7 @@ static int digital_in_send_psl_req(struct nfc_digital_dev *ddev,
 	struct sk_buff *skb;
 	struct digital_psl_req *psl_req;
 	int rc;
+	u8 payload_size, payload_bits;
 
 	skb = digital_skb_alloc(ddev, sizeof(*psl_req));
 	if (!skb)
@@ -215,7 +245,13 @@ static int digital_in_send_psl_req(struct nfc_digital_dev *ddev,
 	psl_req->cmd = DIGITAL_CMD_PSL_REQ;
 	psl_req->did = 0;
 	psl_req->brs = (0x2 << 3) | 0x2; /* 424F both directions */
-	psl_req->fsl = DIGITAL_FSL_BITS_PAYLOAD_SIZE_254B;
+
+	payload_size = min(ddev->local_payload_max, ddev->remote_payload_max);
+	payload_bits = digital_payload_size_to_bits(payload_size);
+	psl_req->fsl = DIGITAL_PAYLOAD_BITS_TO_FSL(payload_bits);
+
+	ddev->local_payload_max = payload_size;
+	ddev->remote_payload_max = payload_size;
 
 	digital_skb_push_dep_sod(ddev, skb);
 
@@ -234,7 +270,7 @@ static void digital_in_recv_atr_res(struct nfc_digital_dev *ddev, void *arg,
 {
 	struct nfc_target *target = arg;
 	struct digital_atr_res *atr_res;
-	u8 gb_len;
+	u8 gb_len, payload_bits;
 	int rc;
 
 	if (IS_ERR(resp)) {
@@ -264,6 +300,14 @@ static void digital_in_recv_atr_res(struct nfc_digital_dev *ddev, void *arg,
 
 	atr_res = (struct digital_atr_res *)resp->data;
 
+	payload_bits = DIGITAL_PAYLOAD_PP_TO_BITS(atr_res->pp);
+	ddev->remote_payload_max = digital_payload_bits_to_size(payload_bits);
+
+	if (!ddev->remote_payload_max) {
+		rc = -EINVAL;
+		goto exit;
+	}
+
 	rc = nfc_set_remote_general_bytes(ddev->nfc_dev, atr_res->gb, gb_len);
 	if (rc)
 		goto exit;
@@ -295,6 +339,7 @@ int digital_in_send_atr_req(struct nfc_digital_dev *ddev,
 	struct digital_atr_req *atr_req;
 	uint size;
 	int rc;
+	u8 payload_bits;
 
 	size = DIGITAL_ATR_REQ_MIN_SIZE + gb_len;
 
@@ -323,7 +368,9 @@ int digital_in_send_atr_req(struct nfc_digital_dev *ddev,
 	atr_req->bs = 0;
 	atr_req->br = 0;
 
-	atr_req->pp = DIGITAL_LR_BITS_PAYLOAD_SIZE_254B;
+	ddev->local_payload_max = DIGITAL_PAYLOAD_SIZE_MAX;
+	payload_bits = digital_payload_size_to_bits(ddev->local_payload_max);
+	atr_req->pp = DIGITAL_PAYLOAD_BITS_TO_PP(payload_bits);
 
 	if (gb_len) {
 		atr_req->pp |= DIGITAL_GB_BIT;
@@ -403,6 +450,11 @@ static void digital_in_recv_dep_res(struct nfc_digital_dev *ddev, void *arg,
 		goto exit;
 	}
 
+	if (resp->len > ddev->local_payload_max) {
+		rc = -EMSGSIZE;
+		goto exit;
+	}
+
 	size = sizeof(struct digital_dep_req_res);
 	dep_res = (struct digital_dep_req_res *)resp->data;
 
@@ -498,6 +550,9 @@ int digital_in_send_dep_req(struct nfc_digital_dev *ddev,
 
 	skb_push(skb, sizeof(struct digital_dep_req_res));
 
+	if (skb->len > ddev->remote_payload_max)
+		return -EMSGSIZE;
+
 	dep_req = (struct digital_dep_req_res *)skb->data;
 	dep_req->dir = DIGITAL_NFC_DEP_FRAME_DIR_OUT;
 	dep_req->cmd = DIGITAL_CMD_DEP_REQ;
@@ -564,6 +619,11 @@ static void digital_tg_recv_dep_req(struct nfc_digital_dev *ddev, void *arg,
 		goto exit;
 	}
 
+	if (resp->len > ddev->local_payload_max) {
+		rc = -EMSGSIZE;
+		goto exit;
+	}
+
 	size = sizeof(struct digital_dep_req_res);
 	dep_req = (struct digital_dep_req_res *)resp->data;
 
@@ -639,6 +699,10 @@ int digital_tg_send_dep_res(struct nfc_digital_dev *ddev, struct sk_buff *skb)
 	struct digital_dep_req_res *dep_res;
 
 	skb_push(skb, sizeof(struct digital_dep_req_res));
+
+	if (skb->len > ddev->remote_payload_max)
+		return -EMSGSIZE;
+
 	dep_res = (struct digital_dep_req_res *)skb->data;
 
 	dep_res->dir = DIGITAL_NFC_DEP_FRAME_DIR_IN;
@@ -719,7 +783,7 @@ static void digital_tg_recv_psl_req(struct nfc_digital_dev *ddev, void *arg,
 	int rc;
 	struct digital_psl_req *psl_req;
 	u8 rf_tech;
-	u8 dsi;
+	u8 dsi, payload_size, payload_bits;
 
 	if (IS_ERR(resp)) {
 		rc = PTR_ERR(resp);
@@ -764,6 +828,18 @@ static void digital_tg_recv_psl_req(struct nfc_digital_dev *ddev, void *arg,
 		goto exit;
 	}
 
+	payload_bits = DIGITAL_PAYLOAD_FSL_TO_BITS(psl_req->fsl);
+	payload_size = digital_payload_bits_to_size(payload_bits);
+
+	if (!payload_size || (payload_size > min(ddev->local_payload_max,
+						 ddev->remote_payload_max))) {
+		rc = -EINVAL;
+		goto exit;
+	}
+
+	ddev->local_payload_max = payload_size;
+	ddev->remote_payload_max = payload_size;
+
 	rc = digital_tg_send_psl_res(ddev, psl_req->did, rf_tech);
 
 exit:
@@ -795,7 +871,7 @@ static int digital_tg_send_atr_res(struct nfc_digital_dev *ddev,
 {
 	struct digital_atr_res *atr_res;
 	struct sk_buff *skb;
-	u8 *gb;
+	u8 *gb, payload_bits;
 	size_t gb_len;
 	int rc;
 
@@ -816,7 +892,11 @@ static int digital_tg_send_atr_res(struct nfc_digital_dev *ddev,
 	atr_res->cmd = DIGITAL_CMD_ATR_RES;
 	memcpy(atr_res->nfcid3, atr_req->nfcid3, sizeof(atr_req->nfcid3));
 	atr_res->to = 8;
-	atr_res->pp = DIGITAL_LR_BITS_PAYLOAD_SIZE_254B;
+
+	ddev->local_payload_max = DIGITAL_PAYLOAD_SIZE_MAX;
+	payload_bits = digital_payload_size_to_bits(ddev->local_payload_max);
+	atr_res->pp = DIGITAL_PAYLOAD_BITS_TO_PP(payload_bits);
+
 	if (gb_len) {
 		skb_put(skb, gb_len);
 
@@ -844,7 +924,7 @@ void digital_tg_recv_atr_req(struct nfc_digital_dev *ddev, void *arg,
 	int rc;
 	struct digital_atr_req *atr_req;
 	size_t gb_len, min_size;
-	u8 poll_tech_count;
+	u8 poll_tech_count, payload_bits;
 
 	if (IS_ERR(resp)) {
 		rc = PTR_ERR(resp);
@@ -893,6 +973,14 @@ void digital_tg_recv_atr_req(struct nfc_digital_dev *ddev, void *arg,
 		goto exit;
 	}
 
+	payload_bits = DIGITAL_PAYLOAD_PP_TO_BITS(atr_req->pp);
+	ddev->remote_payload_max = digital_payload_bits_to_size(payload_bits);
+
+	if (!ddev->remote_payload_max) {
+		rc = -EINVAL;
+		goto exit;
+	}
+
 	ddev->did = atr_req->did;
 
 	rc = digital_tg_configure_hw(ddev, NFC_DIGITAL_CONFIG_FRAMING,