Re: [PATCH net,stable-4.0] cdc_ncm: Fix tx_bytes statistics

[Ben Hutchings <ben.hutchings@codethink.co.uk>]

On Fri, 2015-05-22 at 13:15 +0200, Bjørn Mork wrote:
> The tx_curr_frame_payload field is u32. When we try to calculate a
> small negative delta based on it, we end up with a positive integer
> close to 2^32 instead.  So the tx_bytes pointer increases by about
> 2^32 for every transmitted frame.
> 
> Fix by calculating the delta as a signed long.

Told you I hadn't tested it.

Ben.

> Cc: Ben Hutchings <ben.hutchings@codethink.co.uk>
> Reported-by: Florian Bruhin <me@the-compiler.org>
> Fixes: 7a1e890e2168 ("usbnet: Fix tx_bytes statistic running backward in cdc_ncm")
> Signed-off-by: Bjørn Mork <bjorn@mork.no>
> ---
>  drivers/net/usb/cdc_ncm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/usb/cdc_ncm.c b/drivers/net/usb/cdc_ncm.c
> index c3e4da9e79ca..8067b8fbb0ee 100644
> --- a/drivers/net/usb/cdc_ncm.c
> +++ b/drivers/net/usb/cdc_ncm.c
> @@ -1182,7 +1182,7 @@ cdc_ncm_fill_tx_frame(struct usbnet *dev, struct sk_buff *skb, __le32 sign)
>  	 * payload data instead.
>  	 */
>  	usbnet_set_skb_tx_stats(skb_out, n,
> -				ctx->tx_curr_frame_payload - skb_out->len);
> +				(long)ctx->tx_curr_frame_payload - skb_out->len);
>  
>  	return skb_out;
>