Potential bug using TCP for kinit to KDC communication

[Greg Hudson]

On 04/02/2012 11:30 AM, Oli Mlist wrote:
> - at the end of start_connection(), there is an ssflags local variable into
> which the SSF_READ flag is being set (among others), and this state is
> saved through cm_add_fd().
> - for TCP sockets, the service_tcp_fd() function is called, running a state
> machine.
> - inside service_tcp_fd(), for the CONNECTING  state, a check is made for
> the SSF_READ flag. If this flag is set, a comment tells the KDC is sending
> data to us, which is interpreted as an error, so the TCP socket is
> disconnected by the client. As seen above, this SSF_READ flag had been
> explicitly set at the end of start_connection().

The flags to service_tcp_fd() come from cm_get_ssflags(), which
processes the revents member of the pollfd, not the events member which
was set in cm_add_fd().  So, poll() is saying that a read on the TCP
socket wouldn't block, implying that there is either data to be read or
a socket error to be processed, neither of which happens during a
successful exchange.

> Thanks to let me know if this is indeed a but or whether I am missing
> something,

I put together a simple test case and was able to communicate with a KDC
over TCP.