[PATCH v2] 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>
---

changes since v1:
- stop polling if device cannot be started (Thanks John)

 drivers/net/can/usb/gs_usb.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c
index 4328157bcbcf..6b7ced4bff3d 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);
@@ -985,16 +989,14 @@ static int gs_can_open(struct net_device *netdev)
 	if (rc < 0) {
 		netdev_err(netdev, "Couldn't start device (err=%d)\n", rc);
 		kfree(dm);
+		if (dev->feature & GS_CAN_FEATURE_HW_TIMESTAMP)
+			gs_usb_timestamp_stop(dev);
 		dev->can.state = CAN_STATE_STOPPED;
 		return rc;
 	}
 
 	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