[PATCH 3/3] can: gs_usb: gs_can_open(): initialize time counter before starting device

[Marc Kleine-Budde <mkl@pengutronix.de>]

On busy networks the CAN controller might receive CAN frames directly
after starting it but before the timecounter is setup. This will lead
to NULL pointer deref while converting the converting the CAN frame's
timestamp with the timecounter.

Close the race window by setting up the timecounter before starting
the CAN controller.

Fixes: 45dfa45f52e6 ("can: gs_usb: add RX and TX hardware timestamp support")
Cc: John Whittington <git@jbrengineering.co.uk
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
---
 drivers/net/can/usb/gs_usb.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c
index fe4116bf925b..d3e229c62389 100644
--- a/drivers/net/can/usb/gs_usb.c
+++ b/drivers/net/can/usb/gs_usb.c
@@ -972,6 +972,10 @@ static int gs_can_open(struct net_device *netdev)
 	if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP)
 		flags |= GS_CAN_MODE_HW_TIMESTAMP;
 
+	/* start polling timestamp */
+	if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP)
+		gs_usb_timestamp_init(dev);
+
 	/* finally start device */
 	dev->can.state = CAN_STATE_ERROR_ACTIVE;
 	dm->mode = cpu_to_le32(GS_CAN_MODE_START);
@@ -991,10 +995,6 @@ static int gs_can_open(struct net_device *netdev)
 
 	kfree(dm);
 
-	/* start polling timestamp */
-	if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP)
-		gs_usb_timestamp_init(dev);
-
 	parent->active_channels++;
 	if (!(dev->can.ctrlmode & CAN_CTRLMODE_LISTENONLY))
 		netif_start_queue(netdev);
-- 
2.35.1