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/at91_can.c b/drivers/net/can/at91_can.c
index cbe3fce53e3b..d0ec17878ffc 100644
--- a/drivers/net/can/at91_can.c
+++ b/drivers/net/can/at91_can.c
@@ -474,7 +474,7 @@ static void at91_read_mb(struct net_device *dev, unsigned int mb,
         reg_msr = at91_read(priv, AT91_MSR(mb));
         if (reg_msr & AT91_MSR_MRTR)
                 cf->can_id |= CAN_RTR_FLAG;
-        cf->can_dlc = min_t(__u8, (reg_msr >> 16) & 0xf, 8);
+        cf->can_dlc = get_can_dlc((reg_msr >> 16) & 0xf);
 
         *(u32 *)(cf->data + 0) = at91_read(priv, AT91_MDL(mb));
         *(u32 *)(cf->data + 4) = at91_read(priv, AT91_MDH(mb));