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

[Haiyang Zhang]

> -----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>;
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> Cc: linux-hyperv@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; bpf@xxxxxxxxxxxxxxx; Jiasheng Jiang
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> Subject: [PATCH] hv_netvsc: Fix potentionally overflow in
> netvsc_xdp_xmit()
> 
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> 
> 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