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, 3 insertions, 10 deletions

diff --git a/drivers/net/can/mcp251x.c b/drivers/net/can/mcp251x.c
index 78b1b69b2921..9c5a1537939c 100644
--- a/drivers/net/can/mcp251x.c
+++ b/drivers/net/can/mcp251x.c
@@ -403,9 +403,8 @@ static void mcp251x_hw_rx_frame(struct spi_device *spi, u8 *buf,
 
                 for (i = 1; i < RXBDAT_OFF; i++)
                         buf[i] = mcp251x_read_reg(spi, RXBCTRL(buf_idx) + i);
-                len = buf[RXBDLC_OFF] & RXBDLC_LEN_MASK;
-                if (len > 8)
-                        len = 8;
+
+                len = get_can_dlc(buf[RXBDLC_OFF] & RXBDLC_LEN_MASK);
                 for (; i < (RXBDAT_OFF + len); i++)
                         buf[i] = mcp251x_read_reg(spi, RXBCTRL(buf_idx) + i);
         } else {
@@ -455,13 +454,7 @@ static void mcp251x_hw_rx(struct spi_device *spi, int buf_idx)
                         (buf[RXBSIDL_OFF] >> RXBSIDL_SHIFT);
         }
         /* Data length */
-        frame->can_dlc = buf[RXBDLC_OFF] & RXBDLC_LEN_MASK;
-        if (frame->can_dlc > 8) {
-                dev_warn(&spi->dev, "invalid frame recevied\n");
-                priv->net->stats.rx_errors++;
-                dev_kfree_skb(skb);
-                return;
-        }
+        frame->can_dlc = get_can_dlc(buf[RXBDLC_OFF] & RXBDLC_LEN_MASK);
         memcpy(frame->data, buf + RXBDAT_OFF, frame->can_dlc);
 
         priv->net->stats.rx_packets++;