MPTCP connection requests toward a listening socket created by the
in-kernel PM for a port based signal endpoint will never be accepted,
they need to be explicitly rejected.

- Patch 1: Explicitly reject such requests. A fix for >= v5.12.

- Patch 2: Cover this case in the MPTCP selftests to avoid regressions.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Changes in v2:
- This new version fixes the root cause for the issue Cong Wang sent a
  patch for a few weeks ago, see the v1, and the explanations below. The
  new version is very different from the v1, from a different author.
  Thanks to Cong Wang for the first analysis, and to Paolo for having
  spot the root cause, and sent a fix for it.
- Link to v1: https://lore.kernel.org/r/20240908180620.822579-1-xiyou.wangcong@gmail.com
- Link: https://lore.kernel.org/r/a5289a0d-2557-40b8-9575-6f1a0bbf06e4@redhat.com

---
Paolo Abeni (2):
      mptcp: prevent MPC handshake on port-based signal endpoints
      selftests: mptcp: join: test for prohibited MPC to port-based endp

 net/mptcp/mib.c                                 |   1 +
 net/mptcp/mib.h                                 |   1 +
 net/mptcp/pm_netlink.c                          |   1 +
 net/mptcp/protocol.h                            |   1 +
 net/mptcp/subflow.c                             |  11 +++
 tools/testing/selftests/net/mptcp/mptcp_join.sh | 117 +++++++++++++++++-------
 6 files changed, 101 insertions(+), 31 deletions(-)
---
base-commit: 174714f0e505070a16be6fbede30d32b81df789f
change-id: 20241014-net-mptcp-mpc-port-endp-4f88bd428ec7

Best regards,
-- 
Matthieu Baerts (NGI0) <matttbe@kernel.org>