Re: [PATCH net-next 15/18] can: kvaser_usb: Update stats and state even if alloc_can_err_skb() fails

[Simon Horman <horms@kernel.org>]

On Fri, Jan 10, 2025 at 12:04:23PM +0100, Marc Kleine-Budde wrote:
> From: Jimmy Assarsson <extja@kvaser.com>
> 
> Ensure statistics, error counters, and CAN state are updated consistently,
> even when alloc_can_err_skb() fails during state changes or error message
> frame reception.
> 
> Signed-off-by: Jimmy Assarsson <extja@kvaser.com>
> Link: https://patch.msgid.link/20241230142645.128244-1-extja@kvaser.com
> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

...

> diff --git a/drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c b/drivers/net/can/usb/kvaser_usb/kvaser_usb_leaf.c

...

> @@ -1187,11 +1169,18 @@ static void kvaser_usb_leaf_rx_error(const struct kvaser_usb *dev,
>  		if (priv->can.restart_ms &&
>  		    old_state == CAN_STATE_BUS_OFF &&
>  		    new_state < CAN_STATE_BUS_OFF) {
> -			cf->can_id |= CAN_ERR_RESTARTED;
> +			if (cf)
> +				cf->can_id |= CAN_ERR_RESTARTED;
>  			netif_carrier_on(priv->netdev);
>  		}
>  	}
>  
> +	if (!skb) {
> +		stats->rx_dropped++;
> +		netdev_warn(priv->netdev, "No memory left for err_skb\n");
> +		return;
> +	}
> +
>  	switch (dev->driver_info->family) {
>  	case KVASER_LEAF:
>  		if (es->leaf.error_factor) {

Hi Jimmy and Marc,

The next line of this function is:

			cf->can_id |= CAN_ERR_BUSERROR | CAN_ERR_PROT;

Which dereferences cf. However, the check added at the top of
this hunk assumes that cf may be NULL. This doesn't seem consistent.

Flagged by Smatch.

> -- 
> 2.45.2
> 
> 
>