view compat.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 271c57aa3da5
children
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/*
 * Dropbear - a SSH2 server
 * 
 * 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.
 *
 * strlcat() is copyright as follows:
 * Copyright (c) 1998 Todd C. Miller <[email protected]>
 * 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.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED ``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.
 *
 * daemon() and getusershell() is copyright as follows:
 *
 * Copyright (c) 1990, 1993
 *      The Regents of the University of California.  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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 REGENTS OR CONTRIBUTORS 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.
*
* Modifications for Dropbear to getusershell() are by Paul Marinceu
*/

#include "includes.h"

#ifndef HAVE_GETUSERSHELL
static char **curshell, **shells, *strings;
static char **initshells();
#endif

#ifndef HAVE_STRLCPY
/* Implemented by matt as specified in freebsd 4.7 manpage.
 * We don't require great speed, is simply for use with sshpty code */
size_t strlcpy(char *dst, const char *src, size_t size) {

	size_t i;

	/* this is undefined, though size==0 -> return 0 */
	if (size < 1) {
		return 0;
	}

	for (i = 0; i < size-1; i++) {
		if (src[i] == '\0') {
			break;
		} else {
			dst[i] = src[i];
		}
	}

	dst[i] = '\0';
	return strlen(src);

}
#endif /* HAVE_STRLCPY */

#ifndef HAVE_STRLCAT
/* taken from openbsd-compat for OpenSSH 7.2p2 */
/* "$OpenBSD: strlcat.c,v 1.13 2005/08/08 08:05:37 espie Exp $"
 *
 * Appends src to string dst of size siz (unlike strncat, siz is the
 * full size of dst, not space left).  At most siz-1 characters
 * will be copied.  Always NUL terminates (unless siz <= strlen(dst)).
 * Returns strlen(src) + MIN(siz, strlen(initial dst)).
 * If retval >= siz, truncation occurred.
 */
size_t
strlcat(char *dst, const char *src, size_t siz)
{
	char *d = dst;
	const char *s = src;
	size_t n = siz;
	size_t dlen;

	/* Find the end of dst and adjust bytes left but don't go past end */
	while (n-- != 0 && *d != '\0')
		d++;
	dlen = d - dst;
	n = siz - dlen;

	if (n == 0)
		return(dlen + strlen(s));
	while (*s != '\0') {
		if (n != 1) {
			*d++ = *s;
			n--;
		}
		s++;
	}
	*d = '\0';

	return(dlen + (s - src));	/* count does not include NUL */
}
#endif /* HAVE_STRLCAT */

#ifndef HAVE_DAEMON
/* From NetBSD - daemonise a process */

int daemon(int nochdir, int noclose) {

	int fd;

	switch (fork()) {
		case -1:
			return (-1);
		case 0:
			break;
		default:
			_exit(0);
	}

	if (setsid() == -1)
		return -1;

	if (!nochdir)
		(void)chdir("/");

	if (!noclose && (fd = open(DROPBEAR_PATH_DEVNULL, O_RDWR, 0)) != -1) {
		(void)dup2(fd, STDIN_FILENO);
		(void)dup2(fd, STDOUT_FILENO);
		(void)dup2(fd, STDERR_FILENO);
		if (fd > STDERR_FILENO)
			(void)close(fd);
	}
	return 0;
}
#endif /* HAVE_DAEMON */

#ifndef HAVE_BASENAME

char *basename(const char *path) {

	char *foo = strrchr(path, '/');
	if (!foo)
	{
		return path;
	}
	return ++foo;
}

#endif /* HAVE_BASENAME */

#ifndef HAVE_GETUSERSHELL

/*
 * Get a list of shells from /etc/shells, if it exists.
 */
char * getusershell() {
	char *ret;

	if (curshell == NULL)
		curshell = initshells();
	ret = *curshell;
	if (ret != NULL)
		curshell++;
	return (ret);
}

void endusershell() {

	if (shells != NULL)
		free(shells);
	shells = NULL;
	if (strings != NULL)
		free(strings);
	strings = NULL;
	curshell = NULL;
}

void setusershell() {
	curshell = initshells();
}

static char **initshells() {
	/* don't touch this list. */
	static const char *okshells[] = { "/bin/sh", "/bin/csh", NULL };
	register char **sp, *cp;
	register FILE *fp;
	struct stat statb;
	int flen;

	if (shells != NULL)
		free(shells);
	shells = NULL;
	if (strings != NULL)
		free(strings);
	strings = NULL;
	if ((fp = fopen("/etc/shells", "rc")) == NULL)
		return (char **) okshells;
	if (fstat(fileno(fp), &statb) == -1) {
		(void)fclose(fp);
		return (char **) okshells;
	}
	if ((strings = malloc((u_int)statb.st_size + 1)) == NULL) {
		(void)fclose(fp);
		return (char **) okshells;
	}
	shells = calloc((unsigned)statb.st_size / 3, sizeof (char *));
	if (shells == NULL) {
		(void)fclose(fp);
		free(strings);
		strings = NULL;
		return (char **) okshells;
	}
	sp = shells;
	cp = strings;
	flen = statb.st_size;
	while (fgets(cp, flen - (cp - strings), fp) != NULL) {
		while (*cp != '#' && *cp != '/' && *cp != '\0')
			cp++;
		if (*cp == '#' || *cp == '\0')
			continue;
		*sp++ = cp;
		while (!isspace(*cp) && *cp != '#' && *cp != '\0')
			cp++;
		*cp++ = '\0';
	}
	*sp = NULL;
	(void)fclose(fp);
	return (shells);
}

#endif /* HAVE_GETUSERSHELL */