[PATCH ipsec-next,v4 0/3] xfrm: support collect metadata mode for xfrm interfaces

[Eyal Birger <eyal.birger@gmail.com>]

This series adds support for "collect_md" mode in XFRM interfaces.

This feature is useful for maintaining a large number of IPsec connections
with the benefits of using a network interface while reducing the overhead
of maintaining a large number of devices.

Currently this is possible by having multiple connections share a common
interface by sharing the if_id identifier and using some other criteria
to distinguish between them - such as different subnets or skb marks.
This becomes complex in multi-tenant environments where subnets collide
and the mark space is used for other purposes.

Since the xfrm interface uses the if_id as the differentiator when
looking for policies, setting the if_id in the dst_metadata framework
allows using a single interface for different connections while having
the ability to selectively steer traffic to each one. In addition the
xfrm interface "link" property can also be specified to affect underlying
routing in the context of VRFs.

The series is composed of the following steps:

- Introduce a new METADATA_XFRM metadata type to be used for this purpose.
  Reuse of the existing "METADATA_IP_TUNNEL" type was rejected in [0] as
  XFRM does not necessarily represent an IP tunnel.

- Add support for collect metadata mode in xfrm interfaces

- Allow setting the XFRM metadata from the LWT infrastructure

Future additions could allow setting/getting the XFRM metadata from eBPF
programs, TC, OVS, NF, etc.

[0] https://patchwork.kernel.org/project/netdevbpf/patch/20201121142823.3629805-1-eyal.birger@gmail.com/#23824575

Eyal Birger (3):
  net: allow storing xfrm interface metadata in metadata_dst
  xfrm: interface: support collect metadata mode
  xfrm: lwtunnel: add lwtunnel support for xfrm interfaces in collect_md
    mode

 include/net/dst_metadata.h    |  31 +++++
 include/net/xfrm.h            |  11 +-
 include/uapi/linux/if_link.h  |   1 +
 include/uapi/linux/lwtunnel.h |  10 ++
 net/core/lwtunnel.c           |   1 +
 net/xfrm/xfrm_input.c         |   7 +-
 net/xfrm/xfrm_interface.c     | 206 ++++++++++++++++++++++++++++++----
 net/xfrm/xfrm_policy.c        |  10 +-
 8 files changed, 248 insertions(+), 29 deletions(-)

----

v4: coding change as suggested by Nicolas Dichtel
v3: coding changes as suggested by Nikolay Aleksandrov and
    Nicolas Dichtel
v2: add "link" property as suggested by Nicolas Dichtel

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2.34.1