RE: [PATCH] hv_netvsc: Fix potentionally overflow in netvsc_xdp_xmit()

[Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>]

> -----Original Message-----
> From: Jiasheng Jiang <jiasheng@xxxxxxxxxxx>
> Sent: Tuesday, October 12, 2021 11:05 PM
> To: KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang Zhang
> <haiyangz@xxxxxxxxxxxxx>; Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>;
> wei.liu@xxxxxxxxxx; Dexuan Cui <decui@xxxxxxxxxxxxx>;
> davem@xxxxxxxxxxxxx; kuba@xxxxxxxxxx; ast@xxxxxxxxxx;
> daniel@xxxxxxxxxxxxx; hawk@xxxxxxxxxx; john.fastabend@xxxxxxxxx;
> andrii@xxxxxxxxxx; kafai@xxxxxx; songliubraving@xxxxxx; yhs@xxxxxx;
> kpsingh@xxxxxxxxxx
> Cc: linux-hyperv@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; bpf@xxxxxxxxxxxxxxx; Jiasheng Jiang
> <jiasheng@xxxxxxxxxxx>
> Subject: [PATCH] hv_netvsc: Fix potentionally overflow in
> netvsc_xdp_xmit()
> 
> [Some people who received this message don't often get email from
> jiasheng@xxxxxxxxxxx. Learn why this is important at
> http://aka.ms/LearnAboutSenderIdentification.]
> 
> Adding skb_rx_queue_recorded() to avoid the value of skb->queue_mapping
> to be 0. Otherwise the return value of skb_get_rx_queue() could be
> MAX_U16
> cause by overflow.
> 
> Fixes: 351e158 ("hv_netvsc: Add XDP support")
> Signed-off-by: Jiasheng Jiang <jiasheng@xxxxxxxxxxx>
> ---
>  drivers/net/hyperv/netvsc_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/hyperv/netvsc_drv.c
> b/drivers/net/hyperv/netvsc_drv.c
> index f682a55..e51201e 100644
> --- a/drivers/net/hyperv/netvsc_drv.c
> +++ b/drivers/net/hyperv/netvsc_drv.c
> @@ -807,7 +807,7 @@ static void netvsc_xdp_xmit(struct sk_buff *skb,
> struct net_device *ndev)
>  {
>         int rc;
> 
> -       skb->queue_mapping = skb_get_rx_queue(skb);
> +       skb->queue_mapping = skb_rx_queue_recorded(skb) ?
> skb_get_rx_queue(skb) : 0;
>         __skb_push(skb, ETH_HLEN);
> 

netvsc_xdp_xmit() is only called from netvsc_recv_callback() 
and after skb_record_rx_queue(skb, q_idx) is called:

        skb_record_rx_queue(skb, q_idx);

	  ......

        if (act == XDP_TX) {
                netvsc_xdp_xmit(skb, net);
                return NVSP_STAT_SUCCESS;
        }

So the existing code doesn't need this patch.

To avoid future misusing of netvsc_xdp_xmit() in other places, you
may just add a comment -- "This function should only be called 
after skb_record_rx_queue()".

Thanks,

- Haiyang