[PATCH bpf-next v2 0/3] Add FOU support for externally controlled ipip devices

Christian Ehrig
2023-04-03T11:13:14Z

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

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2.39.2