Re: [PATCH net] tun: correct header offsets in napi frags mode

[David Miller]

From: Willem de Bruijn <willemdebruijn.ker...@gmail.com>
Date: Thu, 28 May 2020 13:05:32 -0400

> Temporarily pull ETH_HLEN to make control flow the same for frags and
> not frags. Then push the header just before calling napi_gro_frags.
 ...
>       case IFF_TAP:
> -             if (!frags)
> -                     skb->protocol = eth_type_trans(skb, tun->dev);
> +             if (frags && !pskb_may_pull(skb, ETH_HLEN)) {
> +                     err = -ENOMEM;
> +                     goto drop;
> +             }
> +             skb->protocol = eth_type_trans(skb, tun->dev);
 ...
>               /* Exercise flow dissector code path. */
> -             u32 headlen = eth_get_headlen(tun->dev, skb->data,
> -                                           skb_headlen(skb));
> +             skb_push(skb, ETH_HLEN);
> +             headlen = eth_get_headlen(tun->dev, skb->data,
> +                                       skb_headlen(skb));

I hate to be a stickler on wording in the commit message, but the
change is not really "pulling" the ethernet header from the SKB.

Instead it is invoking pskb_may_pull() which just makes sure the
header is there in the linear SKB data area.

Can you please refine this description and resubmit?

Thank you.