netdev - Re: [PATCH] AF_PACKET doesnt strip VLAN information

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Date:   Mon, 30 Sep 2019 11:16:14 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Sriram Krishnan <srirakr2@...co.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        xe-linux-external@...co.com,
        "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] AF_PACKET doesnt strip VLAN information

On Mon, Sep 30, 2019 at 1:24 AM Sriram Krishnan <srirakr2@...co.com> wrote:
>
> When an application sends with AF_PACKET and places a vlan header on
> the raw packet; then the AF_PACKET needs to move the tag into the skb
> so that it gets processed normally through the rest of the transmit
> path.
>
> This is particularly a problem on Hyper-V where the host only allows
> vlan in the offload info.

This sounds like behavior that needs to be addressed in the driver, instead?

> Cc: xe-linux-external@...co.com
> ---
>  net/packet/af_packet.c | 26 ++++++++++++++++++++++++--
>  1 file changed, 24 insertions(+), 2 deletions(-)
>
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index e2742b0..cfe0904 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -1849,15 +1849,35 @@ static int packet_rcv_spkt(struct sk_buff *skb, struct net_device *dev,
>         return 0;
>  }
>
> -static void packet_parse_headers(struct sk_buff *skb, struct socket *sock)
> +static int packet_parse_headers(struct sk_buff *skb, struct socket *sock)
>  {
>         if ((!skb->protocol || skb->protocol == htons(ETH_P_ALL)) &&
>             sock->type == SOCK_RAW) {

If inside this branch, may miss packets with skb->protocol set to one
of the VLAN Ethertypes.

> +               __be16 ethertype;
> +
>                 skb_reset_mac_header(skb);
> +
> +               ethertype = eth_hdr(skb)->h_proto;
> +               /*
> +                * If Vlan tag is present in the packet
> +                *  move it to skb
> +               */
> +               if (eth_type_vlan(ethertype)) {
> +                       int err;
> +                       __be16 vlan_tci;
> +
> +                       err = __skb_vlan_pop(skb, &vlan_tci);
> +                       if (unlikely(err))
> +                               return err;
> +
> +                       __vlan_hwaccel_put_tag(skb, ethertype, vlan_tci);

What happens with multiple tags (QinQ)?

> +               }
> +
>                 skb->protocol = dev_parse_header_protocol(skb);
>         }
>
>         skb_probe_transport_header(skb);
> +       return 0;
>  }
>
>  /*
> @@ -1979,7 +1999,9 @@ static int packet_sendmsg_spkt(struct socket *sock, struct msghdr *msg,
>         if (unlikely(extra_len == 4))
>                 skb->no_fcs = 1;
>
> -       packet_parse_headers(skb, sock);
> +       err = packet_parse_headers(skb, sock);
> +       if (err)
> +               goto out_unlock;

This only tests the new return value in one of three callers of
packet_sendmsg_spkt.