netdev - Re: [PATCH net v2] tun: correct header offsets in napi frags mode

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Date:   Mon, 01 Jun 2020 12:02:32 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     willemdebruijn.kernel@...il.com
Cc:     netdev@...r.kernel.org, willemb@...gle.com, ppenkov@...gle.com
Subject: Re: [PATCH net v2] tun: correct header offsets in napi frags mode

From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Date: Sat, 30 May 2020 15:41:31 -0400

> From: Willem de Bruijn <willemb@...gle.com>
> 
> Tun in IFF_NAPI_FRAGS mode calls napi_gro_frags. Unlike netif_rx and
> netif_gro_receive, this expects skb->data to point to the mac layer.
> 
> But skb_probe_transport_header, __skb_get_hash_symmetric, and
> xdp_do_generic in tun_get_user need skb->data to point to the network
> header. Flow dissection also needs skb->protocol set, so
> eth_type_trans has to be called.
> 
> Ensure the link layer header lies in linear as eth_type_trans pulls
> ETH_HLEN. Then take the same code paths for frags as for not frags.
> Push the link layer header back just before calling napi_gro_frags.
> 
> By pulling up to ETH_HLEN from frag0 into linear, this disables the
> frag0 optimization in the special case when IFF_NAPI_FRAGS is used
> with zero length iov[0] (and thus empty skb->linear).
> 
> Fixes: 90e33d459407 ("tun: enable napi_gro_frags() for TUN/TAP driver")
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>
> Acked-by: Petar Penkov <ppenkov@...gle.com>

Applied and queued up for -stable, thank you.