On Mon, 2020-05-11 at 09:24 -0700, Christoph Paasch wrote:
> When the other MPTCP-peer uses 32-bit data-sequence numbers, we rely on
> map_seq to indicate how to expand to a 64-bit data-sequence number in
> expand_seq() when receiving data.
> 
> For new subflows, this field is not initialized, thus results in an
> "invalid" mapping being discarded.
> 
> Fix this by initializing map_seq upon subflow establishment time.
> 
> Fixes: f296234c98a8 ("mptcp: Add handling of incoming MP_JOIN requests")
> Signed-off-by: Christoph Paasch <cpaasch(a)apple.com>
> ---
>  net/mptcp/protocol.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> index e1f23016ed3f..32ea8d35489a 100644
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
> @@ -1629,6 +1629,8 @@ bool mptcp_finish_join(struct sock *sk)
>  
>  	ret = mptcp_pm_allow_new_subflow(msk);
>  	if (ret) {
> +		subflow->map_seq = msk->ack_seq;
> +
>  		/* active connections are already on conn_list */
>  		spin_lock_bh(&msk->join_list_lock);
>  		if (!WARN_ON_ONCE(!list_empty(&subflow->node)))

Reviewed-by: Paolo Abeni <pabeni(a)redhat.com>