diff --git a/drivers/nfc/st21nfca/se.c b/drivers/nfc/st21nfca/se.c
index 8e1113ce139b..df8d27cf2956 100644
--- a/drivers/nfc/st21nfca/se.c
+++ b/drivers/nfc/st21nfca/se.c
@@ -300,6 +300,8 @@ int st21nfca_connectivity_event_received(struct nfc_hci_dev *hdev, u8 host,
 	int r = 0;
 	struct device *dev = &hdev->ndev->dev;
 	struct nfc_evt_transaction *transaction;
+	u32 aid_len;
+	u8 params_len;
 
 	pr_debug("connectivity gate event: %x\n", event);
 
@@ -308,50 +310,48 @@ int st21nfca_connectivity_event_received(struct nfc_hci_dev *hdev, u8 host,
 		r = nfc_se_connectivity(hdev->ndev, host);
 	break;
 	case ST21NFCA_EVT_TRANSACTION:
-		/*
-		 * According to specification etsi 102 622
+		/* According to specification etsi 102 622
 		 * 11.2.2.4 EVT_TRANSACTION Table 52
 		 * Description	Tag	Length
 		 * AID		81	5 to 16
 		 * PARAMETERS	82	0 to 255
+		 *
+		 * The key differences are aid storage length is variably sized
+		 * in the packet, but fixed in nfc_evt_transaction, and that the aid_len
+		 * is u8 in the packet, but u32 in the structure, and the tags in
+		 * the packet are not included in nfc_evt_transaction.
+		 *
+		 * size in bytes: 1          1       5-16 1             1           0-255
+		 * offset:        0          1       2    aid_len + 2   aid_len + 3 aid_len + 4
+		 * member name:   aid_tag(M) aid_len aid  params_tag(M) params_len  params
+		 * example:       0x81       5-16    X    0x82 0-255    X
 		 */
-		if (skb->len < NFC_MIN_AID_LENGTH + 2 ||
-		    skb->data[0] != NFC_EVT_TRANSACTION_AID_TAG)
+		if (skb->len < 2 || skb->data[0] != NFC_EVT_TRANSACTION_AID_TAG)
 			return -EPROTO;
 
-		transaction = devm_kzalloc(dev, skb->len - 2, GFP_KERNEL);
+		aid_len = skb->data[1];
+
+		if (skb->len < aid_len + 4 || aid_len > sizeof(transaction->aid))
+			return -EPROTO;
+
+		params_len = skb->data[aid_len + 3];
+
+		/* Verify PARAMETERS tag is (82), and final check that there is enough
+		 * space in the packet to read everything.
+		 */
+		if ((skb->data[aid_len + 2] != NFC_EVT_TRANSACTION_PARAMS_TAG) ||
+		    (skb->len < aid_len + 4 + params_len))
+			return -EPROTO;
+
+		transaction = devm_kzalloc(dev, sizeof(*transaction) + params_len, GFP_KERNEL);
 		if (!transaction)
 			return -ENOMEM;
 
-		transaction->aid_len = skb->data[1];
+		transaction->aid_len = aid_len;
+		transaction->params_len = params_len;
 
-		/* Checking if the length of the AID is valid */
-		if (transaction->aid_len > sizeof(transaction->aid)) {
-			devm_kfree(dev, transaction);
-			return -EINVAL;
-		}
-
-		memcpy(transaction->aid, &skb->data[2],
-		       transaction->aid_len);
-
-		/* Check next byte is PARAMETERS tag (82) */
-		if (skb->data[transaction->aid_len + 2] !=
-		    NFC_EVT_TRANSACTION_PARAMS_TAG) {
-			devm_kfree(dev, transaction);
-			return -EPROTO;
-		}
-
-		transaction->params_len = skb->data[transaction->aid_len + 3];
-
-		/* Total size is allocated (skb->len - 2) minus fixed array members */
-		if (transaction->params_len > ((skb->len - 2) -
-		    sizeof(struct nfc_evt_transaction))) {
-			devm_kfree(dev, transaction);
-			return -EINVAL;
-		}
-
-		memcpy(transaction->params, skb->data +
-		       transaction->aid_len + 4, transaction->params_len);
+		memcpy(transaction->aid, &skb->data[2], aid_len);
+		memcpy(transaction->params, &skb->data[aid_len + 4], params_len);
 
 		r = nfc_se_transaction(hdev->ndev, host, transaction);
 	break;