view cli-authpasswd.c @ 1715:3974f087d9c0

Disallow leading lines before the ident for server (#102) Per RFC4253 4.2 clients must be able to process other lines of data before the version string, server behavior is not defined neither with MUST/SHOULD nor with MAY. If server process up to 50 lines too - it may cause too long hanging session with invalid/evil client that consume host resources and potentially may lead to DDoS on poor embedded boxes. Let's require first line from client to be version string and fail early if it's not - matches both RFC and real OpenSSH behavior.
author Vladislav Grishenko <themiron@users.noreply.github.com>
date Mon, 15 Jun 2020 18:22:18 +0500
parents 750ec4ec4cbe
children df8d8ec1801c
line wrap: on
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/*
 * Dropbear SSH
 * 
 * Copyright (c) 2002,2003 Matt Johnston
 * 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 "buffer.h"
#include "dbutil.h"
#include "session.h"
#include "ssh.h"
#include "runopts.h"

#if DROPBEAR_CLI_PASSWORD_AUTH

#if DROPBEAR_CLI_ASKPASS_HELPER
/* Returns 1 if we want to use the askpass program, 0 otherwise */
static int want_askpass()
{
	char* askpass_prog = NULL;

	askpass_prog = getenv("SSH_ASKPASS");
	return askpass_prog && 
		((!isatty(STDIN_FILENO) && getenv("DISPLAY") )
		 	|| getenv("SSH_ASKPASS_ALWAYS"));
}

/* returns a statically allocated password from a helper app, or NULL
 * on failure */
static char *gui_getpass(const char *prompt) {

	pid_t pid;
	int p[2], maxlen, len, status;
	static char buf[DROPBEAR_MAX_CLI_PASS + 1];
	char* helper = NULL;

	TRACE(("enter gui_getpass"))

	helper = getenv("SSH_ASKPASS");
	if (!helper)
	{
		TRACE(("leave gui_getpass: no askpass program"))
		return NULL;
	}

	if (pipe(p) < 0) {
		TRACE(("error creating child pipe"))
		return NULL;
	}

	pid = fork();

	if (pid < 0) {
		TRACE(("fork error"))
		return NULL;
	}

	if (!pid) {
		/* child */
		close(p[0]);
		if (dup2(p[1], STDOUT_FILENO) < 0) {
			TRACE(("error redirecting stdout"))
			exit(1);
		}
		close(p[1]);
		execlp(helper, helper, prompt, (char *)0);
		TRACE(("execlp error"))
		exit(1);
	}

	close(p[1]);
	maxlen = sizeof(buf);
	while (maxlen > 0) {
		len = read(p[0], buf + sizeof(buf) - maxlen, maxlen);
		if (len > 0) {
			maxlen -= len;
		} else {
			if (errno != EINTR)
				break;
		}
	}

	close(p[0]);

	while (waitpid(pid, &status, 0) < 0 && errno == EINTR)
		;
	if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
		return(NULL);

	len = sizeof(buf) - maxlen;
	buf[len] = '\0';
	if (len > 0 && buf[len - 1] == '\n')
		buf[len - 1] = '\0';

	TRACE(("leave gui_getpass"))
	return(buf);
}
#endif /* DROPBEAR_CLI_ASKPASS_HELPER */

void cli_auth_password() {

	char* password = NULL;
	char prompt[80];

	TRACE(("enter cli_auth_password"))
	CHECKCLEARTOWRITE();

	snprintf(prompt, sizeof(prompt), "%s@%s's password: ", 
				cli_opts.username, cli_opts.remotehost);
#if DROPBEAR_CLI_ASKPASS_HELPER
	if (want_askpass())
	{
		password = gui_getpass(prompt);
		if (!password) {
			dropbear_exit("No password");
		}
	} else
#endif
	{
		password = getpass_or_cancel(prompt);
	}

	buf_putbyte(ses.writepayload, SSH_MSG_USERAUTH_REQUEST);

	buf_putstring(ses.writepayload, cli_opts.username,
			strlen(cli_opts.username));

	buf_putstring(ses.writepayload, SSH_SERVICE_CONNECTION,
			SSH_SERVICE_CONNECTION_LEN);

	buf_putstring(ses.writepayload, AUTH_METHOD_PASSWORD,
			AUTH_METHOD_PASSWORD_LEN);

	buf_putbyte(ses.writepayload, 0); /* FALSE - so says the spec */

	buf_putstring(ses.writepayload, password, strlen(password));

	encrypt_packet();
	m_burn(password, strlen(password));

	TRACE(("leave cli_auth_password"))
}
#endif	/* DROPBEAR_CLI_PASSWORD_AUTH */