Commit fcf04b14 authored by Gang Yan's avatar Gang Yan Committed by Paolo Abeni
Browse files

mptcp: sync the msk->sndbuf at accept() time 

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: 8005184f ("mptcp: refactor sndbuf auto-tuning")
Cc: stable@vger.kernel.org
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/602


Signed-off-by: default avatarGang Yan <yangang@kylinos.cn>
Acked-by: default avatarPaolo Abeni <pabeni@redhat.com>
Reviewed-by: default avatarMatthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: default avatarMatthieu Baerts (NGI0) <matttbe@kernel.org>
Link: https://patch.msgid.link/20260420-net-mptcp-sync-sndbuf-accept-v1-1-e3523e3aeb44@kernel.org


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent 1cb36e25

net/mptcp/protocol.c

+1 −1
Original line number Diff line number Diff line
@@ -3594,7 +3594,6 @@ struct sock *mptcp_sk_clone_init(const struct sock *sk, 
	 * uses the correct data

	 */

	mptcp_copy_inaddrs(nsk, ssk);

	__mptcp_propagate_sndbuf(nsk, ssk);



	mptcp_rcv_space_init(msk, ssk);

	msk->rcvq_space.time = mptcp_stamp();
@@ -4252,6 +4251,7 @@ static int mptcp_stream_accept(struct socket *sock, struct socket *newsock, 


		mptcp_graft_subflows(newsk);

		mptcp_rps_record_subflows(msk);

		__mptcp_propagate_sndbuf(newsk, mptcp_subflow_tcp_sock(subflow));



		/* Do late cleanup for the first subflow as necessary. Also

		 * deal with bad peers not doing a complete shutdown.