view listener.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 ce3ce75a6e04
children
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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 "listener.h"
#include "session.h"
#include "dbutil.h"

void listeners_initialise() {

	/* just one slot to start with */
	ses.listeners = (struct Listener**)m_malloc(sizeof(struct Listener*));
	ses.listensize = 1;
	ses.listeners[0] = NULL;

}

void set_listener_fds(fd_set * readfds) {

	unsigned int i, j;
	struct Listener *listener;

	/* check each in turn */
	for (i = 0; i < ses.listensize; i++) {
		listener = ses.listeners[i];
		if (listener != NULL) {
			for (j = 0; j < listener->nsocks; j++) {
				FD_SET(listener->socks[j], readfds);
			}
		}
	}
}


void handle_listeners(const fd_set * readfds) {

	unsigned int i, j;
	struct Listener *listener;
	int sock;

	/* check each in turn */
	for (i = 0; i < ses.listensize; i++) {
		listener = ses.listeners[i];
		if (listener != NULL) {
			for (j = 0; j < listener->nsocks; j++) {
				sock = listener->socks[j];
				if (FD_ISSET(sock, readfds)) {
					listener->acceptor(listener, sock);
				}
			}
		}
	}
} /* Woo brace matching */


/* acceptor(int fd, void* typedata) is a function to accept connections, 
 * cleanup(void* typedata) happens when cleaning up */
struct Listener* new_listener(const int socks[], unsigned int nsocks,
		int type, void* typedata, 
		void (*acceptor)(const struct Listener* listener, int sock),
		void (*cleanup)(const struct Listener*)) {

	unsigned int i, j;
	struct Listener *newlisten = NULL;
	/* try get a new structure to hold it */
	for (i = 0; i < ses.listensize; i++) {
		if (ses.listeners[i] == NULL) {
			break;
		}
	}

	/* or create a new one */
	if (i == ses.listensize) {
		if (ses.listensize > MAX_LISTENERS) {
			TRACE(("leave newlistener: too many already"))
			for (j = 0; j < nsocks; j++) {
				close(socks[i]);
			}
			return NULL;
		}
		
		ses.listeners = (struct Listener**)m_realloc(ses.listeners,
				(ses.listensize+LISTENER_EXTEND_SIZE)
				*sizeof(struct Listener*));

		ses.listensize += LISTENER_EXTEND_SIZE;

		for (j = i; j < ses.listensize; j++) {
			ses.listeners[j] = NULL;
		}
	}

	for (j = 0; j < nsocks; j++) {
		ses.maxfd = MAX(ses.maxfd, socks[j]);
	}

	TRACE(("new listener num %d ", i))

	newlisten = (struct Listener*)m_malloc(sizeof(struct Listener));
	newlisten->index = i;
	newlisten->type = type;
	newlisten->typedata = typedata;
	newlisten->nsocks = nsocks;
	memcpy(newlisten->socks, socks, nsocks * sizeof(int));
	newlisten->acceptor = acceptor;
	newlisten->cleanup = cleanup;

	ses.listeners[i] = newlisten;
	return newlisten;
}

/* Return the first listener which matches the type-specific comparison
 * function. Particularly needed for global requests, like tcp */
struct Listener * get_listener(int type, const void* typedata,
		int (*match)(const void*, const void*)) {

	unsigned int i;
	struct Listener* listener;

	for (i = 0, listener = ses.listeners[i]; i < ses.listensize; i++) {
		if (listener && listener->type == type
				&& match(typedata, listener->typedata)) {
			return listener;
		}
	}

	return NULL;
}

void remove_listener(struct Listener* listener) {

	unsigned int j;

	if (listener->cleanup) {
		listener->cleanup(listener);
	}

	for (j = 0; j < listener->nsocks; j++) {
		close(listener->socks[j]);
	}
	ses.listeners[listener->index] = NULL;
	m_free(listener);
}

void remove_all_listeners(void) {
	unsigned int i;
	for (i = 0; i < ses.listensize; i++) {
		if (ses.listeners[i]) {
			remove_listener(ses.listeners[i]);
		}
	}
	m_free(ses.listeners);
}