On passive MPTCP connections, the msk sndbuf is not updated correctly.
The root cause is an order issue in the accept path:
- tcp_check_req() -> subflow_syn_recv_sock() -> mptcp_sk_clone_init()
calls __mptcp_propagate_sndbuf() to copy the ssk sndbuf into msk
- Later, tcp_child_process() -> tcp_init_transfer() ->
tcp_sndbuf_expand() grows the ssk sndbuf.
So __mptcp_propagate_sndbuf() runs before the ssk sndbuf has been
expanded and the msk ends up with a much smaller sndbuf than the
subflow:
MPTCP: msk->sndbuf:20480, msk->first->sndbuf:2626560
Fix this by moving the __mptcp_propagate_sndbuf() call from
mptcp_sk_clone_init() -- the ssk sndbuf is not yet finalized there -- to
__mptcp_propagate_sndbuf() at accept() time, when the ssk sndbuf has
been fully expanded by tcp_sndbuf_expand().
Fixes: 8005184fd1 ("mptcp: refactor sndbuf auto-tuning")
Cc: stable@vger.kernel.org
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/602
Signed-off-by: Gang Yan <yangang@kylinos.cn>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260420-net-mptcp-sync-sndbuf-accept-v1-1-e3523e3aeb44@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
fcf04b1433