allow only valid fd message lengths

Author: cymotive-eldad-sitbon

can/interfaces/socketcan/socketcan.py

@@ -238,7 +238,8 @@ def build_can_frame(msg: Message) -> bytes:
 
     data = bytes(msg.data).ljust(max_len, b"\x00")
 
-    return CAN_FRAME_HEADER_STRUCT.pack(can_id, len(msg.data), flags, msg.dlc) + data
+    data_len = min(i for i in can.util.CAN_FD_DLC if i >= len(msg.data))
+    return CAN_FRAME_HEADER_STRUCT.pack(can_id, data_len, flags, msg.dlc) + data
 
 
 def build_bcm_header(
@@ -321,6 +322,9 @@ def dissect_can_frame(frame: bytes) -> Tuple[int, int, int, bytes]:
         # Flags not valid in non-FD frames
         flags = 0
 
+    if data_len not in can.util.CAN_FD_DLC:
+        data_len = min(i for i in can.util.CAN_FD_DLC if i >= data_len)
+
     # Allow deprecated can frames with old struct
     if (
         data_len == constants.CAN_MAX_DLEN and