Re: [PATCH net] qmi_wwan: Clone the skb when in pass-through mode

["Bjørn Mork" <bjorn@mork.no>]

Kristian Evensen <kristian.evensen@gmail.com> writes:

> The skb that we pass to the rmnet driver is owned by usbnet and is freed
> soon after the rx_fixup() callback is called (in usbnet_bh()).  There is
> no guarantee that rmnet is done handling the skb before it is freed. We
> should clone the skb before we call netif_rx() to prevent use-after-free
> and misc. kernel oops.
>
> Fixes: 59e139cf0b32 ("net: qmi_wwan: Add pass through mode")
>
> Signed-off-by: Kristian Evensen <kristian.evensen@gmail.com>
> ---
>  drivers/net/usb/qmi_wwan.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/net/usb/qmi_wwan.c b/drivers/net/usb/qmi_wwan.c
> index db8d3a4f2678..5ac307eb0bfd 100644
> --- a/drivers/net/usb/qmi_wwan.c
> +++ b/drivers/net/usb/qmi_wwan.c
> @@ -620,6 +620,10 @@ static int qmi_wwan_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
>  		return qmimux_rx_fixup(dev, skb);
>  
>  	if (info->flags & QMI_WWAN_FLAG_PASS_THROUGH) {
> +		skb = skb_clone(skb, GFP_ATOMIC);
> +		if (!skb)
> +			return 0;
> +
>  		skb->protocol = htons(ETH_P_MAP);
>  		return (netif_rx(skb) == NET_RX_SUCCESS);
>  	}


Thanks for pointing this out.  But it still looks strange to me.  Why do
we call netif_rx(skb) here instead of just returning 1 and leave that
for usbnet_skb_return()?  With cloning we end up doing eth_type_trans()
on the duplicate - is that wise?


Bjørn