One of the pieces of feedback from recent review of BPF hooks for socket
lookup [0] was that new program types should use bpf_link-based attachment.

Unlike with cgroups-attached programs, there is no existing infrastructure
for using bpf_links with network namespaces. It is also not as simple as
updating a single bpf_prog pointer, like in case of direct program
attachment.

Due to that I've split out this work into its own series.

Series is organized as so:

Patches 1-4 prepare a space in struct net to keep state for attached BPF
programs, and massage the code in flow_dissector to make it attach type
agnostic to finally move under kernel/bpf/.

Patch 5, the most important one, introduces new bpf_link link type for
attaching to network namespace. As opposed to cgroups, we can't hold a
ref count on struct net from a bpf_link, so we get by with just RCU
protection.

I'd be grateful if someone more experienced using RCU could give this
patch a look. It is not exactly the textbook application of it.

Patches 6-8 make libbpf and bpftool aware of the new link type and add
tests to check that link create/update/query API works as intended.

Thanks to Lorenz and Marek for early feedback & reviews.

-jkbs

Cc: Lorenz Bauer <redacted>
Cc: Marek Majkowski <redacted>
Cc: Stanislav Fomichev <redacted>

[0] https://lore.kernel.org/bpf/20200511185218.1422406-1-jakub@cloudflare.com/ (local)

Jakub Sitnicki (8):
  flow_dissector: Don't grab update-side lock on prog detach from
    pre_exit
  flow_dissector: Pull locking up from prog attach callback
  net: Introduce netns_bpf for BPF programs attached to netns
  flow_dissector: Move out netns_bpf prog callbacks
  bpf: Add link-based BPF program attachment to network namespace
  libbpf: Add support for bpf_link-based netns attachment
  bpftool: Support link show for netns-attached links
  selftests/bpf: Add tests for attaching bpf_link to netns

 include/linux/bpf-netns.h                     |  64 +++
 include/linux/skbuff.h                        |  26 -
 include/net/flow_dissector.h                  |   6 +
 include/net/net_namespace.h                   |   4 +-
 include/net/netns/bpf.h                       |  18 +
 include/uapi/linux/bpf.h                      |   5 +
 kernel/bpf/Makefile                           |   1 +
 kernel/bpf/net_namespace.c                    | 387 ++++++++++++++
 kernel/bpf/syscall.c                          |  10 +-
 net/core/filter.c                             |   1 +
 net/core/flow_dissector.c                     | 124 +----
 tools/bpf/bpftool/link.c                      |  19 +
 tools/include/uapi/linux/bpf.h                |   5 +
 tools/lib/bpf/libbpf.c                        |  20 +-
 tools/lib/bpf/libbpf.h                        |   2 +
 tools/lib/bpf/libbpf.map                      |   1 +
 .../bpf/prog_tests/flow_dissector_reattach.c  | 500 +++++++++++++++++-
 17 files changed, 1026 insertions(+), 167 deletions(-)
 create mode 100644 include/linux/bpf-netns.h
 create mode 100644 include/net/netns/bpf.h
 create mode 100644 kernel/bpf/net_namespace.c

-- 
2.25.4