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From:   Christian Ehrig <cehrig@cloudflare.com>
To:     bpf@vger.kernel.org
Cc:     cehrig@cloudflare.com, kernel-team@cloudflare.com,
        Alexei Starovoitov <ast@kernel.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
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        Kaixi Fan <fankaixi.li@bytedance.com>,
        KP Singh <kpsingh@kernel.org>, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Mykola Lysenko <mykolal@fb.com>, netdev@vger.kernel.org,
        Paul Chaignon <paul@isovalent.com>,
        Shmulik Ladkani <shmulik@metanetworks.com>,
        Song Liu <song@kernel.org>,
        Stanislav Fomichev <sdf@google.com>, Yonghong Song <yhs@fb.com>
Subject: [PATCH bpf-next v2 0/3] Add FOU support for externally controlled ipip devices
Date:   Mon,  3 Apr 2023 14:12:06 +0200
Message-Id: <cover.1680520500.git.cehrig@cloudflare.com>
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Precedence: bulk

This patch set adds support for using FOU or GUE encapsulation with
an ipip device operating in collect-metadata mode and a set of kfuncs
for controlling encap parameters exposed to a BPF tc-hook.

BPF tc-hooks allow us to read tunnel metadata (like remote IP addresses)
in the ingress path of an externally controlled tunnel interface via
the bpf_skb_get_tunnel_{key,opt} bpf-helpers. Packets can then be
redirected to the same or a different externally controlled tunnel
interface by overwriting metadata via the bpf_skb_set_tunnel_{key,opt}
helpers and a call to bpf_redirect. This enables us to redirect packets
between tunnel interfaces - and potentially change the encapsulation
type - using only a single BPF program.

Today this approach works fine for a couple of tunnel combinations.
For example: redirecting packets between Geneve and GRE interfaces or
GRE and plain ipip interfaces. However, redirecting using FOU or GUE is
not supported today. The ip_tunnel module does not allow us to egress
packets using additional UDP encapsulation from an ipip device in
collect-metadata mode.

Patch 1 lifts this restriction by adding a struct ip_tunnel_encap to
the tunnel metadata. It can be filled by a new BPF kfunc introduced
in Patch 2 and evaluated by the ip_tunnel egress path. This will allow
us to use FOU and GUE encap with externally controlled ipip devices.

Patch 2 introduces two new BPF kfuncs: bpf_skb_{set,get}_fou_encap.
These helpers can be used to set and get UDP encap parameters from the
BPF tc-hook doing the packet redirect.

Patch 3 adds BPF tunnel selftests using the two kfuncs.

---
v2:
 - Fixes for checkpatch.pl
 - Fixes for kernel test robot

Christian Ehrig (3):
  ipip,ip_tunnel,sit: Add FOU support for externally controlled ipip
    devices
  bpf,fou: Add bpf_skb_{set,get}_fou_encap kfuncs
  selftests/bpf: Test FOU kfuncs for externally controlled ipip devices

 include/net/fou.h                             |   2 +
 include/net/ip_tunnels.h                      |  28 +++--
 net/ipv4/Makefile                             |   2 +-
 net/ipv4/fou_bpf.c                            | 119 ++++++++++++++++++
 net/ipv4/fou_core.c                           |   5 +
 net/ipv4/ip_tunnel.c                          |  22 +++-
 net/ipv4/ipip.c                               |   1 +
 net/ipv6/sit.c                                |   2 +-
 .../selftests/bpf/progs/test_tunnel_kern.c    | 117 +++++++++++++++++
 tools/testing/selftests/bpf/test_tunnel.sh    |  81 ++++++++++++
 10 files changed, 362 insertions(+), 17 deletions(-)
 create mode 100644 net/ipv4/fou_bpf.c

-- 
2.39.2