netdev - Re: [PATCH bpf-next] net: veth: account total xdp_frame len running ndo_xdp

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Date:   Mon, 7 Feb 2022 18:39:54 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     bpf <bpf@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Toshiaki Makita <toshiaki.makita1@...il.com>
Subject: Re: [PATCH bpf-next] net: veth: account total xdp_frame len running ndo_xdp_xmit

On Tue, Feb 1, 2022 at 2:46 AM Lorenzo Bianconi <lorenzo@...nel.org> wrote:
>
> Introduce xdp_get_frame_len utility routine to get the xdp_frame full
> length and account total frame size running XDP_REDIRECT of a
> non-linear xdp frame into a veth device.
>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> ---
>  drivers/net/veth.c |  4 ++--
>  include/net/xdp.h  | 14 ++++++++++++++
>  2 files changed, 16 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
> index 354a963075c5..22ecaf8b8f98 100644
> --- a/drivers/net/veth.c
> +++ b/drivers/net/veth.c
> @@ -493,7 +493,7 @@ static int veth_xdp_xmit(struct net_device *dev, int n,
>                 struct xdp_frame *frame = frames[i];
>                 void *ptr = veth_xdp_to_ptr(frame);
>
> -               if (unlikely(frame->len > max_len ||
> +               if (unlikely(xdp_get_frame_len(frame) > max_len ||
>                              __ptr_ring_produce(&rq->xdp_ring, ptr)))
>                         break;

Looks correct, but could you explain what happens without this fix?

Any other drivers might have the same issue?