Re: [PATCH mptcp-net] mptcp: use MPTCP_RST_EMPTCP for ACK HMAC validation failure

Matthieu Baerts
2026-04-28T11:16:04Z

Hi Shardul,

On 28/04/2026 01:49, Shardul Bankar wrote:
> When HMAC validation fails on a received ACK + MP_JOIN in
> subflow_syn_recv_sock(), the subflow is reset with reason
> MPTCP_RST_EPROHIBIT ("Administratively prohibited"). This is
> incorrect: HMAC validation failure is an MPTCP protocol-level
> error, not an administrative policy denial.
>
> The mirror site on the client, in subflow_finish_connect(), already
> uses MPTCP_RST_EMPTCP ("MPTCP-specific error") for the same kind of
> HMAC failure on the SYN/ACK + MP_JOIN. Use the same reason on the
> server side for symmetry and accuracy.

Now in our tree:

New patches for t/upstream-net and t/upstream:
- 1f2cd6a4c385: mptcp: use MPTCP_RST_EMPTCP for ACK HMAC validation failure
- Results: 718fa635acef..90cb02b20cf2 (export-net)
- Results: 8e163e999320..f68dc562c883 (export)

Tests are now in progress:

- export-net:
https://github.com/multipath-tcp/mptcp_net-next/commit/883745ff4a074154bb85f2be5a3aef39774f8e83/checks
- export:
https://github.com/multipath-tcp/mptcp_net-next/commit/6f26689671ac282704c85b27521e6b309771c544/checks

Cheers,
Matt
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