Created attachment 10967 [details]
patch to add support for multiplexed connections

Description:
============
Samba 4 was not handling multiplexed connections properly in dcerpc server. The implementation, committed in master in caaf89e899c2a3926fb9e54d1c86f1a9cd5d7618 is adding a flag similar to DCESRV_CALL_STATE_FLAG_ASYNC to dcesrv_call_state_flags to define whether a service supports this behavior or not.

Overview:
=========
Microsoft Exchange is implementing a DCERPC endpoint server
called async_emsmdb with a single asynchronous call named
EcDoAyncWaitEx. When Outlook sends a EcDoAsyncWaitEx request, the server
does not reply  unless there is either a notification for Outlook to
process or the timeout of 5 minutes is reached. Without this patch,
Microsoft Outlook clients block and do not move further with any of the
existing connections from DCERPC altered context unless the call to
EcDoAsyncWaitEx actually returns. With this patch, Outlook operates
properly and as expected.


Scope of the patch:
===================
I have identified that implementing this multiplexed connection behavior
was both required when:

    1. initializing a new connection, hence dcesrv_bind

    2. when altering an existing context, hence dcesrv_alter. However,
    in this specific case we don't have existing state_flags on the
    connection. It is therefore necessary to save  and retrieving the
    flags from the existing context to decide whether or not the
    DCERPC_PFC_FLAG_CONC_MPX should be applied to the state_flags of the
    current connection.