can: Fix data length code handling in rx path

A valid CAN dataframe can have a data length code (DLC) of 0 .. 8 data bytes.

When reading the CAN controllers register the 4-bit value may contain values
from 0 .. 15 which may exceed the reserved space in the socket buffer!

The ISO 11898-1 Chapter 8.4.2.3 (DLC field) says that register values > 8
should be reduced to 8 without any error reporting or frame drop.

This patch introduces a new helper macro to cast a given 4-bit data length
code (dlc) to __u8 and ensure the DLC value to be max. 8 bytes.

The different handlings in the rx path of the CAN netdevice drivers are fixed.

Signed-off-by: Oliver Hartkopp <oliver@hartkopp.net>
Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 1 insertions, 1 deletions

diff --git a/drivers/net/can/usb/ems_usb.c b/drivers/net/can/usb/ems_usb.c
index 591eb0eb1c2b..efbb05c71bf4 100644
--- a/drivers/net/can/usb/ems_usb.c
+++ b/drivers/net/can/usb/ems_usb.c
@@ -316,7 +316,7 @@ static void ems_usb_rx_can_msg(struct ems_usb *dev, struct ems_cpc_msg *msg)
                 return;
 
         cf->can_id = le32_to_cpu(msg->msg.can_msg.id);
-        cf->can_dlc = min_t(u8, msg->msg.can_msg.length, 8);
+        cf->can_dlc = get_can_dlc(msg->msg.can_msg.length & 0xF);
 
         if (msg->type == CPC_MSG_TYPE_EXT_CAN_FRAME ||
             msg->type == CPC_MSG_TYPE_EXT_RTR_FRAME)