view cli-main.c @ 1790:42745af83b7d

Introduce extra delay before closing unauthenticated sessions To make it harder for attackers, introduce a delay to keep an unauthenticated session open a bit longer, thus blocking a connection slot until after the delay. Without this, while there is a limit on the amount of attempts an attacker can make at the same time (MAX_UNAUTH_PER_IP), the time taken by dropbear to handle one attempt is still short and thus for each of the allowed parallel attempts many attempts can be chained one after the other. The attempt rate is then: "MAX_UNAUTH_PER_IP / <process time of one attempt>". With the delay, this rate becomes: "MAX_UNAUTH_PER_IP / UNAUTH_CLOSE_DELAY".
author Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
date Wed, 15 Feb 2017 13:53:04 +0100
parents d1b279aa5ed1
children f0a524208d97
line wrap: on
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/*
 * Dropbear - a SSH2 server
 * SSH client implementation
 * 
 * Copyright (c) 2002,2003 Matt Johnston
 * Copyright (c) 2004 by Mihnea Stoenescu
 * All rights reserved.
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE. */

#include "includes.h"
#include "dbutil.h"
#include "runopts.h"
#include "session.h"
#include "dbrandom.h"
#include "crypto_desc.h"
#include "netio.h"
#include "fuzz.h"

#if DROPBEAR_CLI_PROXYCMD
static void cli_proxy_cmd(int *sock_in, int *sock_out, pid_t *pid_out);
static void kill_proxy_sighandler(int signo);
#endif

#if defined(DBMULTI_dbclient) || !DROPBEAR_MULTI
#if defined(DBMULTI_dbclient) && DROPBEAR_MULTI
int cli_main(int argc, char ** argv) {
#else
int main(int argc, char ** argv) {
#endif

	int sock_in, sock_out;
	struct dropbear_progress_connection *progress = NULL;

	_dropbear_exit = cli_dropbear_exit;
	_dropbear_log = cli_dropbear_log;

	disallow_core();

	seedrandom();
	crypto_init();

	cli_getopts(argc, argv);

#ifndef DISABLE_SYSLOG
	if (opts.usingsyslog) {
		startsyslog("dbclient");
	}
#endif

	TRACE(("user='%s' host='%s' port='%s' bind_address='%s' bind_port='%s'", cli_opts.username,
				cli_opts.remotehost, cli_opts.remoteport, cli_opts.bind_address, cli_opts.bind_port))

	if (signal(SIGPIPE, SIG_IGN) == SIG_ERR) {
		dropbear_exit("signal() error");
	}

	pid_t proxy_cmd_pid = 0;
#if DROPBEAR_CLI_PROXYCMD
	if (cli_opts.proxycmd) {
		cli_proxy_cmd(&sock_in, &sock_out, &proxy_cmd_pid);
		m_free(cli_opts.proxycmd);
		if (signal(SIGINT, kill_proxy_sighandler) == SIG_ERR ||
			signal(SIGTERM, kill_proxy_sighandler) == SIG_ERR ||
			signal(SIGHUP, kill_proxy_sighandler) == SIG_ERR) {
			dropbear_exit("signal() error");
		}
	} else
#endif
	{
		progress = connect_remote(cli_opts.remotehost, cli_opts.remoteport, 
			cli_connected, &ses, cli_opts.bind_address, cli_opts.bind_port);
		sock_in = sock_out = -1;
	}

	cli_session(sock_in, sock_out, progress, proxy_cmd_pid);

	/* not reached */
	return -1;
}
#endif /* DBMULTI stuff */

static void exec_proxy_cmd(const void *user_data_cmd) {
	const char *cmd = user_data_cmd;
	char *usershell;

	usershell = m_strdup(get_user_shell());
	run_shell_command(cmd, ses.maxfd, usershell);
	dropbear_exit("Failed to run '%s'\n", cmd);
}

#if DROPBEAR_CLI_PROXYCMD
static void cli_proxy_cmd(int *sock_in, int *sock_out, pid_t *pid_out) {
	char * ex_cmd = NULL;
	size_t ex_cmdlen;
	int ret;

	/* File descriptor "-j &3" */
	if (*cli_opts.proxycmd == '&') {
		char *p = cli_opts.proxycmd + 1;
		int sock = strtoul(p, &p, 10);
		/* must be a single number, and not stdin/stdout/stderr */
		if (sock > 2 && sock < 1024 && *p == '\0') {
			*sock_in = sock;
			*sock_out = sock;
			return;
		}
	}

	/* Normal proxycommand */

	/* So that spawn_command knows which shell to run */
	fill_passwd(cli_opts.own_user);

	ex_cmdlen = strlen(cli_opts.proxycmd) + 6; /* "exec " + command + '\0' */
	ex_cmd = m_malloc(ex_cmdlen);
	snprintf(ex_cmd, ex_cmdlen, "exec %s", cli_opts.proxycmd);

	ret = spawn_command(exec_proxy_cmd, ex_cmd,
			sock_out, sock_in, NULL, pid_out);
	m_free(ex_cmd);
	if (ret == DROPBEAR_FAILURE) {
		dropbear_exit("Failed running proxy command");
		*sock_in = *sock_out = -1;
	}
}

static void kill_proxy_sighandler(int UNUSED(signo)) {
	kill_proxy_command();
	_exit(1);
}

#endif /* DROPBEAR_CLI_PROXYCMD */