diff --git a/net/ethtool/cmis_fw_update.c b/net/ethtool/cmis_fw_update.c
index df5f344209c4..16190c97e1f7 100644
--- a/net/ethtool/cmis_fw_update.c
+++ b/net/ethtool/cmis_fw_update.c
@@ -44,6 +44,20 @@ enum cmis_cdb_fw_write_mechanism {
 	CMIS_CDB_FW_WRITE_MECHANISM_BOTH	= 0x11,
 };
 
+/* See section 9.7.2 "CMD 0101h: Start Firmware Download" in CMIS standard
+ * revision 5.2.
+ * struct cmis_cdb_start_fw_download_pl is a structured layout of the
+ * flat array, ethtool_cmis_cdb_request::payload.
+ */
+struct cmis_cdb_start_fw_download_pl {
+	__struct_group(cmis_cdb_start_fw_download_pl_h, head, /* no attrs */,
+			__be32	image_size;
+			__be32	resv1;
+	);
+	u8 vendor_data[ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH -
+		sizeof(struct cmis_cdb_start_fw_download_pl_h)];
+};
+
 static int
 cmis_fw_update_fw_mng_features_get(struct ethtool_cmis_cdb *cdb,
 				   struct net_device *dev,
@@ -86,6 +100,14 @@ cmis_fw_update_fw_mng_features_get(struct ethtool_cmis_cdb *cdb,
 	 */
 	cdb->read_write_len_ext = rpl->read_write_len_ext;
 	fw_mng->start_cmd_payload_size = rpl->start_cmd_payload_size;
+	if (fw_mng->start_cmd_payload_size >
+	    sizeof_field(struct cmis_cdb_start_fw_download_pl, vendor_data)) {
+		ethnl_module_fw_flash_ntf_err(dev, ntf_params,
+					      "Start cmd payload size exceeds max LPL payload",
+					      NULL);
+		return -EINVAL;
+	}
+
 	fw_mng->write_mechanism =
 		rpl->write_mechanism == CMIS_CDB_FW_WRITE_MECHANISM_LPL ?
 		CMIS_CDB_FW_WRITE_MECHANISM_LPL :
@@ -97,20 +119,6 @@ cmis_fw_update_fw_mng_features_get(struct ethtool_cmis_cdb *cdb,
 	return 0;
 }
 
-/* See section 9.7.2 "CMD 0101h: Start Firmware Download" in CMIS standard
- * revision 5.2.
- * struct cmis_cdb_start_fw_download_pl is a structured layout of the
- * flat array, ethtool_cmis_cdb_request::payload.
- */
-struct cmis_cdb_start_fw_download_pl {
-	__struct_group(cmis_cdb_start_fw_download_pl_h, head, /* no attrs */,
-			__be32	image_size;
-			__be32	resv1;
-	);
-	u8 vendor_data[ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH -
-		sizeof(struct cmis_cdb_start_fw_download_pl_h)];
-};
-
 static int
 cmis_fw_update_start_download(struct ethtool_cmis_cdb *cdb,
 			      struct ethtool_cmis_fw_update_params *fw_update,