view svr-x11fwd.c @ 1659:d32bcb5c557d

Add Ed25519 support (#91) * Add support for Ed25519 as a public key type Ed25519 is a elliptic curve signature scheme that offers better security than ECDSA and DSA and good performance. It may be used for both user and host keys. OpenSSH key import and fuzzer are not supported yet. Initially inspired by Peter Szabo. * Add curve25519 and ed25519 fuzzers * Add import and export of Ed25519 keys
author Vladislav Grishenko <themiron@users.noreply.github.com>
date Wed, 11 Mar 2020 21:09:45 +0500
parents 79eef94ccea9
children a7cc3332d8ab
line wrap: on
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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. */

#include "includes.h"

#if DROPBEAR_X11FWD
#include "x11fwd.h"
#include "session.h"
#include "ssh.h"
#include "dbutil.h"
#include "chansession.h"
#include "channel.h"
#include "packet.h"
#include "buffer.h"
#include "auth.h"

#define X11BASEPORT 6000
#define X11BINDBASE 6010

static void x11accept(const struct Listener* listener, int sock);
static int bindport(int fd);
static int send_msg_channel_open_x11(int fd, const struct sockaddr_in* addr);

/* Check untrusted xauth strings for metacharacters */
/* Returns DROPBEAR_SUCCESS/DROPBEAR_FAILURE */
static int
xauth_valid_string(const char *s)
{
	size_t i;

	for (i = 0; s[i] != '\0'; i++) {
		if (!isalnum(s[i]) &&
		    s[i] != '.' && s[i] != ':' && s[i] != '/' &&
		    s[i] != '-' && s[i] != '_') {
			return DROPBEAR_FAILURE;
		}
	}
	return DROPBEAR_SUCCESS;
}


/* called as a request for a session channel, sets up listening X11 */
/* returns DROPBEAR_SUCCESS or DROPBEAR_FAILURE */
int x11req(struct ChanSess * chansess) {

	int fd = -1;

	if (!svr_pubkey_allows_x11fwd()) {
		return DROPBEAR_FAILURE;
	}

	/* we already have an x11 connection */
	if (chansess->x11listener != NULL) {
		return DROPBEAR_FAILURE;
	}

	chansess->x11singleconn = buf_getbool(ses.payload);
	chansess->x11authprot = buf_getstring(ses.payload, NULL);
	chansess->x11authcookie = buf_getstring(ses.payload, NULL);
	chansess->x11screennum = buf_getint(ses.payload);

	if (xauth_valid_string(chansess->x11authprot) == DROPBEAR_FAILURE ||
		xauth_valid_string(chansess->x11authcookie) == DROPBEAR_FAILURE) {
		dropbear_log(LOG_WARNING, "Bad xauth request");
		goto fail;
	}
	/* create listening socket */
	fd = socket(PF_INET, SOCK_STREAM, 0);
	if (fd < 0) {
		goto fail;
	}

	/* allocate port and bind */
	chansess->x11port = bindport(fd);
	if (chansess->x11port < 0) {
		goto fail;
	}

	/* listen */
	if (listen(fd, 20) < 0) {
		goto fail;
	}

	/* set non-blocking */
	setnonblocking(fd);

	/* listener code will handle the socket now.
	 * No cleanup handler needed, since listener_remove only happens
	 * from our cleanup anyway */
	chansess->x11listener = new_listener( &fd, 1, 0, chansess, x11accept, NULL);
	if (chansess->x11listener == NULL) {
		goto fail;
	}

	return DROPBEAR_SUCCESS;

fail:
	/* cleanup */
	m_free(chansess->x11authprot);
	m_free(chansess->x11authcookie);
	m_close(fd);

	return DROPBEAR_FAILURE;
}

/* accepts a new X11 socket */
/* returns DROPBEAR_FAILURE or DROPBEAR_SUCCESS */
static void x11accept(const struct Listener* listener, int sock) {

	int fd;
	struct sockaddr_in addr;
	socklen_t len;
	int ret;
	struct ChanSess * chansess = (struct ChanSess *)(listener->typedata);

	len = sizeof(addr);

	fd = accept(sock, (struct sockaddr*)&addr, &len);
	if (fd < 0) {
		return;
	}

	/* if single-connection we close it up */
	if (chansess->x11singleconn) {
		x11cleanup(chansess);
	}

	ret = send_msg_channel_open_x11(fd, &addr);
	if (ret == DROPBEAR_FAILURE) {
		close(fd);
	}
}

/* This is called after switching to the user, and sets up the xauth
 * and environment variables.  */
void x11setauth(const struct ChanSess *chansess) {

	char display[20]; /* space for "localhost:12345.123" */
	FILE * authprog = NULL;
	int val;

	if (chansess->x11listener == NULL) {
		return;
	}

	/* create the DISPLAY string */
	val = snprintf(display, sizeof(display), "localhost:%d.%u",
			chansess->x11port - X11BASEPORT, chansess->x11screennum);
	if (val < 0 || val >= (int)sizeof(display)) {
		/* string was truncated */
		return;
	}

	addnewvar("DISPLAY", display);

	/* create the xauth string */
	val = snprintf(display, sizeof(display), "unix:%d.%u",
			chansess->x11port - X11BASEPORT, chansess->x11screennum);
	if (val < 0 || val >= (int)sizeof(display)) {
		/* string was truncated */
		return;
	}

	/* code is strongly based on OpenSSH's */
	authprog = popen(XAUTH_COMMAND, "w");
	if (authprog) {
		fprintf(authprog, "add %s %s %s\n",
				display, chansess->x11authprot, chansess->x11authcookie);
		pclose(authprog);
	} else {
		fprintf(stderr, "Failed to run %s\n", XAUTH_COMMAND);
	}
}

void x11cleanup(struct ChanSess *chansess) {

	m_free(chansess->x11authprot);
	m_free(chansess->x11authcookie);

	TRACE(("chansess %p", (void*)chansess))
	if (chansess->x11listener != NULL) {
		remove_listener(chansess->x11listener);
		chansess->x11listener = NULL;
	}
}

static int x11_inithandler(struct Channel *channel) {
	channel->prio = DROPBEAR_CHANNEL_PRIO_INTERACTIVE;
	return 0;
}

static const struct ChanType chan_x11 = {
	0, /* sepfds */
	"x11",
	x11_inithandler, /* inithandler */
	NULL, /* checkclose */
	NULL, /* reqhandler */
	NULL, /* closehandler */
	NULL /* cleanup */
};


static int send_msg_channel_open_x11(int fd, const struct sockaddr_in* addr) {

	char* ipstring = NULL;

	if (send_msg_channel_open_init(fd, &chan_x11) == DROPBEAR_SUCCESS) {
		ipstring = inet_ntoa(addr->sin_addr);
		buf_putstring(ses.writepayload, ipstring, strlen(ipstring));
		buf_putint(ses.writepayload, addr->sin_port);

		encrypt_packet();
		return DROPBEAR_SUCCESS;
	} else {
		return DROPBEAR_FAILURE;
	}

}

/* returns the port bound to, or -1 on failure.
 * Will attempt to bind to a port X11BINDBASE (6010 usually) or upwards */
static int bindport(int fd) {

	struct sockaddr_in addr;
	uint16_t port;

	memset((void*)&addr, 0x0, sizeof(addr));
	addr.sin_family = AF_INET;
	addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);

	/* if we can't find one in 2000 ports free, something's wrong */
	for (port = X11BINDBASE; port < X11BINDBASE + 2000; port++) {
		addr.sin_port = htons(port);
		if (bind(fd, (struct sockaddr*)&addr, 
					sizeof(struct sockaddr_in)) == 0) {
			/* success */
			return port;
		}
		if (errno == EADDRINUSE) {
			/* try the next port */
			continue;
		}
		/* otherwise it was an error we don't know about */
		dropbear_log(LOG_DEBUG, "Failed to bind x11 socket");
		break;
	}
	return -1;
}
#endif /* DROPBEAR_X11FWD */