netdev - Re: [PATCH net-next v2] ip_tunnel: allow to inherit from VLAN encapsulated IP frames

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Date:   Wed, 6 Jul 2022 20:25:12 +0300
From:   Eyal Birger <eyal.birger@...il.com>
To:     Matthias May <matthias.may@...termo.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        yoshfuji@...ux-ipv6.org, dsahern@...nel.org, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2] ip_tunnel: allow to inherit from VLAN
 encapsulated IP frames

Hi,

On Wed, Jul 6, 2022 at 7:54 PM Matthias May <matthias.may@...termo.com> wrote:
>
> The current code allows to inherit the TOS, TTL, DF from the payload
> when skb->protocol is ETH_P_IP or ETH_P_IPV6.
> However when the payload is VLAN encapsulated (e.g because the tunnel
> is of type GRETAP), then this inheriting does not work, because the
> visible skb->protocol is of type ETH_P_8021Q.
>
> Add a check on ETH_P_8021Q and subsequently check the payload protocol.
>
> Signed-off-by: Matthias May <matthias.may@...termo.com>
> ---
> v1 -> v2:
>  - Add support for ETH_P_8021AD as suggested by Jakub Kicinski.
> ---
>  net/ipv4/ip_tunnel.c | 22 ++++++++++++++--------
>  1 file changed, 14 insertions(+), 8 deletions(-)
>
> diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
> index 94017a8c3994..bdcc0f1e83c8 100644
> --- a/net/ipv4/ip_tunnel.c
> +++ b/net/ipv4/ip_tunnel.c
> @@ -648,6 +648,13 @@ void ip_tunnel_xmit(struct sk_buff *skb, struct net_device *dev,
>         u8 tos, ttl;
>         __be32 dst;
>         __be16 df;
> +       __be16 *payload_protocol;
> +
> +       if (skb->protocol == htons(ETH_P_8021Q) ||
> +           skb->protocol == htons(ETH_P_8021AD))
> +               payload_protocol = (__be16 *)(skb->head + skb->network_header - 2);
> +       else
> +               payload_protocol = &skb->protocol;

Maybe it's better to use skb_protocol(skb, true) here instead of open
coding the vlan parsing?

Eyal