[v2,bpf-next,0/3] : Add socket destroy capability

Message

Aditi Ghag Feb. 23, 2023, 9:53 p.m. UTC

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 was presented at LPC 2022 -
https://lpc.events/event/16/contributions/1358/.
RFC discussion -
https://lore.kernel.org/netdev/CABG=zsBEh-P4NXk23eBJw7eajB5YJeRS7oPXnTAzs=[e-mail]/T/#u.
v1 patch series - 
https://lore.kernel.org/bpf/[e-mail]/

v2 highlights:
- Implemented batching support for UDP iterator.
- Converted bpf_sock_destroy helper to kfunc.
- Synchronous execution of destroy handlers to
  replace the previous workqueue implementation.
- Updated selftests to use the kfunc.

Notes to the reviewers (further details in commits description):

- 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`. Discussed it from the point of view of the verifier
with my colleague (Dylan Reimerink): the verifier has a `sock_common` BTF
ID for a subset of socket types. However, it may not always be safe to cast
from `sock_common *` to 'sock *', so I added a check for full sock
availability in the kfunc.

- The `vmlinux.h` import in the selftest prog unexpectedly led to libbpf
failing to load the program. As it turns out, the libbpf kfunc related
code doesn't seem to handle BTF `FWD` type for structs. I've attached debug
information about the issue in case the loader logic can accommodate such
gotchas. Although the error in this case was specific to the test imports.

- We previously discussed the possibility of using sockmap to store sockets
to be destroyed as an optimization, so that users may not need to iterate
over all the host-wide sockets. This approach needs more discussion on the
TCP side, as we may need to extend the logic that checks for certain TCP
states while inserting sockets in a sockmap. So I've skipped those self
test cases involving sockmap from the patch. (same as v1 patch)


Aditi Ghag (3):
  bpf: Implement batching in UDP iterator
  bpf: Add bpf_sock_destroy kfunc
  selftests/bpf: Add tests for bpf_sock_destroy

 net/core/filter.c                             |  55 +++++
 net/ipv4/tcp.c                                |  17 +-
 net/ipv4/udp.c                                | 231 +++++++++++++++++-
 .../selftests/bpf/prog_tests/sock_destroy.c   | 125 ++++++++++
 .../selftests/bpf/progs/sock_destroy_prog.c   | 110 +++++++++
 5 files changed, 522 insertions(+), 16 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