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Make protocol 2 MaxAuthTries behaviour a little more sensible:

Check whether client has exceeded MaxAuthTries before running
an authentication method and skip it if they have, previously it
would always allow one try (for "none" auth).

Preincrement failure count before post-auth test - previously this
checked and postincremented, also to allow one "none" try.

Together, these two changes always count the "none" auth method
which could be skipped by a malicious client (e.g. an SSH worm)
to get an extra attempt at a real auth method. They also make
MaxAuthTries=0 a useful way to block users entirely (esp. in a
sshd_config Match block).

Also, move sending of any preauth banner from "none" auth method
to the first call to input_userauth_request(), so worms that skip
the "none" method get to see it too.

/* $OpenBSD: auth2-none.c,v 1.15 2008/07/02 12:36:39 djm Exp $ */
/*
 * Copyright (c) 2000 Markus Friedl.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <sys/types.h>

#include "xmalloc.h"
#include "key.h"
#include "hostfile.h"
#include "auth.h"
#include "packet.h"
#include "log.h"
#include "buffer.h"
#include "servconf.h"
#include "compat.h"
#include "ssh2.h"
#ifdef GSSAPI
#include "ssh-gss.h"
#endif
#include "monitor_wrap.h"

/* import */
extern ServerOptions options;

/* "none" is allowed only one time */
static int none_enabled = 1;

static int
userauth_none(Authctxt *authctxt)
{
	none_enabled = 0;
	packet_check_eom();
	if (options.password_authentication)
		return (PRIVSEP(auth_password(authctxt, "")));
	return (0);
}

Authmethod method_none = {
	"none",
	userauth_none,
	&none_enabled
};