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, 2 insertions, 1 deletions

diff --git a/drivers/net/can/mscan/mscan.c b/drivers/net/can/mscan/mscan.c
index bb06dfb..07346f88 100644
--- a/drivers/net/can/mscan/mscan.c
+++ b/drivers/net/can/mscan/mscan.c
@@ -297,7 +297,8 @@ static void mscan_get_rx_frame(struct net_device *dev, struct can_frame *frame)
 	frame->can_id |= can_id >> 1;
 	if (can_id & 1)
 		frame->can_id |= CAN_RTR_FLAG;
-	frame->can_dlc = in_8(&regs->rx.dlr) & 0xf;
+
+	frame->can_dlc = get_can_dlc(in_8(&regs->rx.dlr) & 0xf);
 
 	if (!(frame->can_id & CAN_RTR_FLAG)) {
 		void __iomem *data = &regs->rx.dsr1_0;