Created attachment 13411 [details]
patch for master

Attached is a possible patch, under test.

Created attachment 13415 [details]
the problem stream (partial pcapng)

Created attachment 13416 [details]
subunit logs from the issue matching the capture

(In reply to Andrew Bartlett from comment #2)

Ok, I think we hit this in the server,
dcesrv_process_ncacn_packet:

      if (dce_conn->pending_call_list != NULL) {
             /*
              * concurrent requests are only allowed
              * if DCERPC_PFC_FLAG_CONC_MPX was negotiated.
              */
             if (!(dce_conn->state_flags & DCESRV_CALL_STATE_FLAG_MULTIPLEXED)) {
                     dcesrv_call_disconnect_after(call,
                                   "dcesrv_auth_request - "
                                   "existing pending call without CONN_MPX");
                     return dcesrv_fault(call,
                                         DCERPC_NCA_S_PROTO_ERROR);
             }
      }

So the fix is correct for now. We should really only do one outgoing operation
at a time.

(In reply to Stefan Metzmacher from comment #4)
That makes a lot of sense. 

Thanks!

Created attachment 13421 [details]
patch for 4.7 cherry-picked from master