[PATCH v2 0/8] Allow checking SYN cookies from XDP and tc cls act

[Lorenz Bauer <lmb@cloudflare.com>]

This series adds the necessary helpers to determine wheter a given
(encapsulated) TCP packet belongs to a connection known to the network stack.

* bpf_skc_lookup_tcp gives access to request and timewait sockets
* bpf_tcp_check_syncookie identifies the final 3WHS ACK when syncookies
  are enabled

The goal is to be able to implement load-balancing approaches like
glb-director [1] or Beamer [2] in pure eBPF. Specifically, we'd like to replace
the functionality of the glb-redirect kernel module [3] by an XDP program or
tc classifier.

Thanks to Martin KaFai Lau for his review!

Changes in v2:
* Rename bpf_sk_check_syncookie to bpf_tcp_check_syncookie.
* Add bpf_skc_lookup_tcp. Without it bpf_tcp_check_syncookie doesn't make sense.
* Check tcp_synq_no_recent_overflow() in bpf_tcp_check_syncookie.
* Check th->syn in bpf_tcp_check_syncookie.
* Require CONFIG_IPV6 to be a built in.

1: https://github.com/github/glb-director
2: https://www.usenix.org/conference/nsdi18/presentation/olteanu
3: https://github.com/github/glb-director/tree/master/src/glb-redirect

Lorenz Bauer (8):
  bpf: track references based on is_acquire_func
  bpf: allow helpers to return PTR_TO_SOCK_COMMON
  bpf: add skc_lookup_tcp helper
  bpf: add helper to check for a valid SYN cookie
  tools: update include/uapi/linux/bpf.h
  selftests/bpf: allow specifying helper for BPF_SK_LOOKUP
  selftests/bpf: test references to sock_common
  selftests/bpf: add tests for bpf_tcp_check_syncookie and
    bpf_skc_lookup_tcp

 include/linux/bpf.h                           |   1 +
 include/uapi/linux/bpf.h                      |  36 ++-
 kernel/bpf/verifier.c                         |  33 +--
 net/core/filter.c                             | 185 ++++++++++++++-
 tools/include/uapi/linux/bpf.h                |  36 ++-
 tools/testing/selftests/bpf/.gitignore        |   1 +
 tools/testing/selftests/bpf/Makefile          |   5 +-
 tools/testing/selftests/bpf/bpf_helpers.h     |   8 +
 .../bpf/progs/test_tcp_check_syncookie_kern.c | 126 +++++++++++
 .../selftests/bpf/test_tcp_check_syncookie.sh |  81 +++++++
 .../bpf/test_tcp_check_syncookie_user.c       | 212 ++++++++++++++++++
 tools/testing/selftests/bpf/test_verifier.c   |   6 +-
 .../selftests/bpf/verifier/ref_tracking.c     | 126 +++++++----
 tools/testing/selftests/bpf/verifier/unpriv.c |   8 +-
 14 files changed, 789 insertions(+), 75 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/test_tcp_check_syncookie_kern.c
 create mode 100755 tools/testing/selftests/bpf/test_tcp_check_syncookie.sh
 create mode 100644 tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c

--
2.19.1