bpf: Add socket destroy capability

This patch adds the capability to destroy sockets in BPF. We plan to use
the capability in Cilium to force client sockets to reconnect when their
remote load-balancing backends are deleted. The other use case is
on-the-fly policy enforcement where existing socket connections prevented
by policies need to be terminated.

The use cases, and more details around
the selected approach were presented at LPC 2022 -
https://lpc.events/event/16/contributions/1358/.
RFC discussion -
https://lore.kernel.org/netdev/CABG=zsBEh-P4NXk23eBJw7eaj...
v6 patch series -
https://lore.kernel.org/bpf/20230418153148.2231644-1-adit...

v7 highlights:
Address review comments:
Martin:
- Refactored logic to get udp table to a separate commit.
- Addressed nits in the batching and test commits.
- Applied patch to filter and restrict the kfunc, and added a test.
Stan:
- Addressed nits in the network helper commit.
Paolo/Yonghong:
- Extended the first commit that revises locking in BPF TCP iterator
  with more details.
- Fixed comment formatting.

(Below notes are same as v6 patch series that are still relevant. Refer to
earlier patch series for other notes.)
- I hit a snag while writing the kfunc where verifier complained about the
  `sock_common` type passed from TCP iterator. With kfuncs, there don't
  seem to be any options available to pass BTF type hints to the verifier
  (equivalent of `ARG_PTR_TO_BTF_ID_SOCK_COMMON`, as was the case with the
  helper).  As a result, I changed the argument type of the sock_destory
  kfunc to `sock_common`.

Aditi Ghag (10):
  bpf: tcp: Avoid taking fast sock lock in iterator
  udp: seq_file: Helper function to match socket attributes
  bpf: udp: Encapsulate logic to get udp table
  udp: seq_file: Remove bpf_seq_afinfo from udp_iter_state
  bpf: udp: Implement batching for sockets iterator
  bpf: Add bpf_sock_destroy kfunc
  selftests/bpf: Add helper to get port using getsockname
  selftests/bpf: Test bpf_sock_destroy
  bpf: Add a kfunc filter function to 'struct btf_kfunc_id_set'
  selftests/bpf: Extend bpf_sock_destroy tests

 include/linux/btf.h                           |  18 +-
 include/net/udp.h                             |   1 -
 kernel/bpf/btf.c                              |  59 +++-
 kernel/bpf/verifier.c                         |   7 +-
 net/core/filter.c                             |  66 ++++
 net/ipv4/tcp.c                                |  10 +-
 net/ipv4/tcp_ipv4.c                           |   5 +-
 net/ipv4/udp.c                                | 287 +++++++++++++++---
 tools/testing/selftests/bpf/network_helpers.c |  23 ++
 tools/testing/selftests/bpf/network_helpers.h |   1 +
 .../selftests/bpf/prog_tests/sock_destroy.c   | 217 +++++++++++++
 .../selftests/bpf/progs/sock_destroy_prog.c   | 145 +++++++++
 .../bpf/progs/sock_destroy_prog_fail.c        |  22 ++
 13 files changed, 785 insertions(+), 76 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/sock_destroy.c
 create mode 100644 tools/testing/selftests/bpf/progs/sock_destroy_prog.c
 create mode 100644 tools/testing/selftests/bpf/progs/sock_destroy_prog_fail.c

-- 
2.34.1