netdev - Re: [PATCH net] ip6_tunnel: set inner ipproto before ip6_tnl

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Message-ID: <CA+FuTSe5szAPV0qDVU1Qa7e-XH6uO4eWELfzykOvpb0CJ0NbUA@mail.gmail.com>
Date:   Fri, 16 Oct 2020 13:55:43 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Alexander Ovechkin <ovov@...dex-team.ru>
Cc:     Network Development <netdev@...r.kernel.org>, vfedorenko@...ek.ru
Subject: Re: [PATCH net] ip6_tunnel: set inner ipproto before ip6_tnl_encap.

On Fri, Oct 16, 2020 at 7:14 AM Alexander Ovechkin <ovov@...dex-team.ru> wrote:
>
> ip6_tnl_encap assigns to proto transport protocol which
> encapsulates inner packet, but we must pass to set_inner_ipproto
> protocol of that inner packet.
>
> Calling set_inner_ipproto after ip6_tnl_encap might break gso.
> For example, in case of encapsulating ipv6 packet in fou6 packet, inner_ipproto
> would be set to IPPROTO_UDP instead of IPPROTO_IPV6. This would lead to
> incorrect calling sequence of gso functions:
> ipv6_gso_segment -> udp6_ufo_fragment -> skb_udp_tunnel_segment -> udp6_ufo_fragment
> instead of:
> ipv6_gso_segment -> udp6_ufo_fragment -> skb_udp_tunnel_segment -> ip6ip6_gso_segment
>
> Signed-off-by: Alexander Ovechkin <ovov@...dex-team.ru>

Commit 6c11fbf97e69 ("ip6_tunnel: add MPLS transmit support") moved
the call from ip6_tnl_encap's caller to inside ip6_tnl_encap.

It makes sense that that likely broke this behavior for UDP (L4) tunnels.

But it was moved on purpose to avoid setting the inner protocol to
IPPROTO_MPLS. That needs to use skb->inner_protocol to further
segment.

I suspect we need to set this before or after conditionally to avoid
breaking that use case.