[PATCH bpf-next v9 0/7] bpf: add BPF_LWT_ENCAP_IP option to bpf_lwt_push_encap

[Peter Oskolkov <posk@google.com>]

This patchset implements BPF_LWT_ENCAP_IP mode in bpf_lwt_push_encap
BPF helper. It enables BPF programs (specifically, BPF_PROG_TYPE_LWT_IN
and BPF_PROG_TYPE_LWT_XMIT prog types) to add IP encapsulation headers
to packets (e.g. IP/GRE, GUE, IPIP).

This is useful when thousands of different short-lived flows should be
encapped, each with different and dynamically determined destination.
Although lwtunnels can be used in some of these scenarios, the ability
to dynamically generate encap headers adds more flexibility, e.g.
when routing depends on the state of the host (reflected in global bpf
maps).

V2 changes: added flowi-based route lookup, IPv6 encapping, and
   encapping on ingress.

V3 changes: incorporated David Ahern's suggestions:
   - added l3mdev check/oif (patch 2)
   - sync bpf.h from include/uapi into tools/include/uapi
   - selftest tweaks

V4 changes: moved route lookup/dst change from bpf_push_ip_encap
   to when BPF_LWT_REROUTE is handled, as suggested by David Ahern.

V5 changes: added a check in lwt_xmit that skb->protocol stays the
   same if the skb is to be passed back to the stack (ret == BPF_OK).
   Again, suggested by David Ahern.

V6 changes: abandoned.

V7 changes: added handling of GSO packets (patch 3 in the patchset added),
   as suggested by BPF maintainers.

V8 changes:
   - fixed build errors when LWT or IPV6 are not enabled;
   - whitelisted TCP GSO instead of blacklisting SCTP and UDP GSO, as
     suggested by Willem de Bruijn;
   - added validation that pushed length cover needed headers when GRE/UDP
     encap is detected, as suggested by Willem de Bruijn;
   - a couple of minor/stylistic tweaks/fixed typos.

V9 changes:
   - fixed a kbuild test robot compiler warning;
   - added ipv6_route_input to ipv6_stub (patch 4 in the patchset
     added), and IPv6 routing functions are now invoked via ipv6_stub,
     as suggested by David Ahern.

Peter Oskolkov (7):
  bpf: add plumbing for BPF_LWT_ENCAP_IP in bpf_lwt_push_encap
  bpf: implement BPF_LWT_ENCAP_IP mode in bpf_lwt_push_encap
  bpf: handle GSO in bpf_lwt_push_encap
  ipv6_stub: add ipv6_route_input stub/proxy.
  bpf: add handling of BPF_LWT_REROUTE to lwt_bpf.c
  bpf: sync <kdir>/include/.../bpf.h with tools/include/.../bpf.h
  selftests: bpf: add test_lwt_ip_encap selftest

 include/net/addrconf.h                        |   1 +
 include/net/lwtunnel.h                        |   2 +
 include/uapi/linux/bpf.h                      |  26 +-
 net/core/filter.c                             |  49 ++-
 net/core/lwt_bpf.c                            | 261 +++++++++++++++
 net/ipv6/addrconf_core.c                      |   6 +
 net/ipv6/af_inet6.c                           |   7 +
 tools/include/uapi/linux/bpf.h                |  26 +-
 tools/testing/selftests/bpf/Makefile          |   5 +-
 .../testing/selftests/bpf/test_lwt_ip_encap.c |  85 +++++
 .../selftests/bpf/test_lwt_ip_encap.sh        | 311 ++++++++++++++++++
 11 files changed, 768 insertions(+), 11 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/test_lwt_ip_encap.c
 create mode 100755 tools/testing/selftests/bpf/test_lwt_ip_encap.sh

-- 
2.20.1.791.gb4d0f1c61a-goog