netdev - Re: [PATCH] virtio-net: make copy len check in xdp_linearize

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Message-ID: <CACGkMEtLso8QjvmjTQ=S_bbGxu11O_scRa8GT7z6MXfJbfzfRg@mail.gmail.com>
Date:   Mon, 13 Dec 2021 15:48:53 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     mengensun8801@...il.com
Cc:     davem <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>, bpf@...r.kernel.org,
        mengensun <mengensun@...cent.com>,
        MengLong Dong <imagedong@...cent.com>,
        ZhengXiong Jiang <mungerjiang@...cent.com>
Subject: Re: [PATCH] virtio-net: make copy len check in xdp_linearize_page

On Mon, Dec 13, 2021 at 12:50 PM <mengensun8801@...il.com> wrote:
>
> From: mengensun <mengensun@...cent.com>
>
> xdp_linearize_page asume ring elem size is smaller then page size
> when copy the first ring elem, but, there may be a elem size bigger
> then page size.
>
> add_recvbuf_mergeable may add a hole to ring elem, the hole size is
> not sure, according EWMA.

The logic is to try to avoid dropping packets in this case, so I
wonder if it's better to "fix" the add_recvbuf_mergeable().

Or another idea is to switch to use XDP generic here where we can use
skb_linearize() which should be more robust and we can drop the
xdp_linearize_page() logic completely.

Thanks

>
> so, fix it by check copy len,if checked failed, just dropped the
> whole frame, not make the memory dirty after the page.
>
> Signed-off-by: mengensun <mengensun@...cent.com>
> Reviewed-by: MengLong Dong <imagedong@...cent.com>
> Reviewed-by: ZhengXiong Jiang <mungerjiang@...cent.com>
> ---
>  drivers/net/virtio_net.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 36a4b7c195d5..844bdbd67ff7 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -662,8 +662,12 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
>                                        int page_off,
>                                        unsigned int *len)
>  {
> -       struct page *page = alloc_page(GFP_ATOMIC);
> +       struct page *page;
>
> +       if (*len > PAGE_SIZE - page_off)
> +               return NULL;
> +
> +       page = alloc_page(GFP_ATOMIC);
>         if (!page)
>                 return NULL;
>
> --
> 2.27.0
>