configure: Fixed typo in configure.ac

Signed-off-by: Steve Dickson <steved@redhat.com>
rpc.mountd: set nonblocking mode if no libtirpc

If mountd is built without libtirpc and it is started using "-p XXX"
option, the tcp listeners and the sockets waiting for UDP messages
are not in non-blocking mode. Thus if running with multiple threads (-t XX),
all threads will wake up from select on a connection request or a UDP
message, but only one thread will succeed. All others will wait on
accept() or read() for the next event.

Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: Steve Dickson <steved@redhat.com>
rpc.mountd: set nonblocking mode with libtirpc

If mountd is built with libtirpc the tcp listeners and the sockets
waiting for UDP messages are not in non-blocking mode. Thus if running
with multiple threads (-t XX), all threads will wake up from select on
a connection request or a UDP message, but only one thread will succeed.
All others will wait on accept() or read() for the next event.

Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: Steve Dickson <steved@redhat.com>
rpc.mountd: set libtirpc nonblocking mode to avoid DOS

This patch is experimental. In works fine in that it removes the
vulnerability against a DOS attack. rpc.mountd can be blocked by
a bad client, that sends many RPC requests but never reads the
responses. This might happen intentionally or caused by a wrong
network config (MTU). The patch switches on the nonblocking
mode of libtirpc. In that mode writes can block for a max of 2 seconds.
Attackers are forced to send requests slower, as libtirpc will close
a connection if it finds two requests to read at the same time.

Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Bodo Stroesser <bstroesser@ts.fujitsu.com>
Signed-off-by: Steve Dickson <steved@redhat.com>