freebsd-nq/crypto/openssh/ssh.c

/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Ssh client program.  This program can be used to log into a remote machine.
 * The software supports strong authentication, encryption, and forwarding
 * of X11, TCP/IP, and authentication connections.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 *
 * Copyright (c) 1999 Niels Provos.  All rights reserved.
 *
 * Modified to work with SSL by Niels Provos <provos@citi.umich.edu>
 * in Canada (German citizen).
 *
 * 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.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``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.
 */

#include "includes.h"
RCSID("$OpenBSD: ssh.c,v 1.69 2000/10/27 07:32:19 markus Exp $");
RCSID("$FreeBSD$");

#include <openssl/evp.h>
#include <openssl/dsa.h>
#include <openssl/rsa.h>

#include "xmalloc.h"
#include "ssh.h"
#include "packet.h"
#include "buffer.h"
#include "readconf.h"
#include "uidswap.h"

#include "ssh2.h"
#include "compat.h"
#include "channels.h"
#include "key.h"
#include "authfd.h"
#include "authfile.h"

extern char *__progname;

/* Flag indicating whether IPv4 or IPv6.  This can be set on the command line.
   Default value is AF_UNSPEC means both IPv4 and IPv6. */
int IPv4or6 = AF_UNSPEC;

/* Flag indicating whether debug mode is on.  This can be set on the command line. */
int debug_flag = 0;

/* Flag indicating whether a tty should be allocated */
int tty_flag = 0;

/* don't exec a shell */
int no_shell_flag = 0;
int no_tty_flag = 0;

/*
 * Flag indicating that nothing should be read from stdin.  This can be set
 * on the command line.
 */
int stdin_null_flag = 0;

/*
 * Flag indicating that ssh should fork after authentication.  This is useful
 * so that the pasphrase can be entered manually, and then ssh goes to the
 * background.
 */
int fork_after_authentication_flag = 0;

/*
 * General data structure for command line options and options configurable
 * in configuration files.  See readconf.h.
 */
Options options;

/*
 * Name of the host we are connecting to.  This is the name given on the
 * command line, or the HostName specified for the user-supplied name in a
 * configuration file.
 */
char *host;

/* socket address the host resolves to */
struct sockaddr_storage hostaddr;

/*
 * Flag to indicate that we have received a window change signal which has
 * not yet been processed.  This will cause a message indicating the new
 * window size to be sent to the server a little later.  This is volatile
 * because this is updated in a signal handler.
 */
volatile int received_window_change_signal = 0;

/* Value of argv[0] (set in the main program). */
char *av0;

/* Flag indicating whether we have a valid host private key loaded. */
int host_private_key_loaded = 0;

/* Host private key. */
RSA *host_private_key = NULL;

/* Original real UID. */
uid_t original_real_uid;

/* command to be executed */
Buffer command;

/* Prints a help message to the user.  This function never returns. */

void
usage()
{
	fprintf(stderr, "Usage: %s [options] host [command]\n", av0);
	fprintf(stderr, "Options:\n");
	fprintf(stderr, "  -l user     Log in using this user name.\n");
	fprintf(stderr, "  -n          Redirect input from /dev/null.\n");
	fprintf(stderr, "  -A          Enable authentication agent forwarding.\n");
	fprintf(stderr, "  -a          Disable authentication agent forwarding.\n");
#ifdef AFS
	fprintf(stderr, "  -k          Disable Kerberos ticket and AFS token forwarding.\n");
#endif				/* AFS */
        fprintf(stderr, "  -X          Enable X11 connection forwarding.\n");
	fprintf(stderr, "  -x          Disable X11 connection forwarding.\n");
	fprintf(stderr, "  -i file     Identity for RSA authentication (default: ~/.ssh/identity).\n");
	fprintf(stderr, "  -t          Tty; allocate a tty even if command is given.\n");
	fprintf(stderr, "  -T          Do not allocate a tty.\n");
	fprintf(stderr, "  -v          Verbose; display verbose debugging messages.\n");
	fprintf(stderr, "              Multiple -v increases verbosity.\n");
	fprintf(stderr, "  -V          Display version number only.\n");
	fprintf(stderr, "  -P          Don't allocate a privileged port.\n");
	fprintf(stderr, "  -q          Quiet; don't display any warning messages.\n");
	fprintf(stderr, "  -f          Fork into background after authentication.\n");
	fprintf(stderr, "  -e char     Set escape character; ``none'' = disable (default: ~).\n");

	fprintf(stderr, "  -c cipher   Select encryption algorithm: "
			"``3des'', "
			"``blowfish''\n");
	fprintf(stderr, "  -p port     Connect to this port.  Server must be on the same port.\n");
	fprintf(stderr, "  -L listen-port:host:port   Forward local port to remote address\n");
	fprintf(stderr, "  -R listen-port:host:port   Forward remote port to local address\n");
	fprintf(stderr, "              These cause %s to listen for connections on a port, and\n", av0);
	fprintf(stderr, "              forward them to the other side by connecting to host:port.\n");
	fprintf(stderr, "  -C          Enable compression.\n");
	fprintf(stderr, "  -N          Do not execute a shell or command.\n");
	fprintf(stderr, "  -g          Allow remote hosts to connect to forwarded ports.\n");
	fprintf(stderr, "  -4          Use IPv4 only.\n");
	fprintf(stderr, "  -6          Use IPv6 only.\n");
	fprintf(stderr, "  -2          Force protocol version 2.\n");
	fprintf(stderr, "  -o 'option' Process the option as if it was read from a configuration file.\n");
	exit(1);
}

/*
 * Connects to the given host using rsh (or prints an error message and exits
 * if rsh is not available).  This function never returns.
 */
void
rsh_connect(char *host, char *user, Buffer * command)
{
	char *args[10];
	int i;

	log("Using rsh.  WARNING: Connection will not be encrypted.");
	/* Build argument list for rsh. */
	i = 0;
#ifndef	_PATH_RSH
#define	_PATH_RSH	"/usr/bin/rsh"
#endif
	args[i++] = _PATH_RSH;
	/* host may have to come after user on some systems */
	args[i++] = host;
	if (user) {
		args[i++] = "-l";
		args[i++] = user;
	}
	if (buffer_len(command) > 0) {
		buffer_append(command, "\0", 1);
		args[i++] = buffer_ptr(command);
	}
	args[i++] = NULL;
	if (debug_flag) {
		for (i = 0; args[i]; i++) {
			if (i != 0)
				fprintf(stderr, " ");
			fprintf(stderr, "%s", args[i]);
		}
		fprintf(stderr, "\n");
	}
	execv(_PATH_RSH, args);
	perror(_PATH_RSH);
	exit(1);
}

int ssh_session(void);
int ssh_session2(void);

/*
 * Main program for the ssh client.
 */
int
main(int ac, char **av)
{
	int i, opt, optind, exit_status, ok;
	u_short fwd_port, fwd_host_port;
	char *optarg, *cp, buf[256];
	struct stat st;
	struct passwd *pw, pwcopy;
	int dummy;
	uid_t original_effective_uid;

	/*
	 * Save the original real uid.  It will be needed later (uid-swapping
	 * may clobber the real uid).
	 */
	original_real_uid = getuid();
	original_effective_uid = geteuid();

	/* If we are installed setuid root be careful to not drop core. */
	if (original_real_uid != original_effective_uid) {
		struct rlimit rlim;
		rlim.rlim_cur = rlim.rlim_max = 0;
		if (setrlimit(RLIMIT_CORE, &rlim) < 0)
			fatal("setrlimit failed: %.100s", strerror(errno));
	}
	/*
	 * Use uid-swapping to give up root privileges for the duration of
	 * option processing.  We will re-instantiate the rights when we are
	 * ready to create the privileged port, and will permanently drop
	 * them when the port has been created (actually, when the connection
	 * has been made, as we may need to create the port several times).
	 */
	temporarily_use_uid(original_real_uid);

	/*
	 * Set our umask to something reasonable, as some files are created
	 * with the default umask.  This will make them world-readable but
	 * writable only by the owner, which is ok for all files for which we
	 * don't set the modes explicitly.
	 */
	umask(022);

	/* Save our own name. */
	av0 = av[0];

	/* Initialize option structure to indicate that no values have been set. */
	initialize_options(&options);

	/* Parse command-line arguments. */
	host = NULL;

	/* If program name is not one of the standard names, use it as host name. */
	if (strchr(av0, '/'))
		cp = strrchr(av0, '/') + 1;
	else
		cp = av0;
	if (strcmp(cp, "rsh") && strcmp(cp, "ssh") && strcmp(cp, "rlogin") &&
	    strcmp(cp, "slogin") && strcmp(cp, "remsh"))
		host = cp;

	for (optind = 1; optind < ac; optind++) {
		if (av[optind][0] != '-') {
			if (host)
				break;
			if ((cp = strchr(av[optind], '@'))) {
				if(cp == av[optind])
					usage();
				options.user = av[optind];
				*cp = '\0';
				host = ++cp;
			} else
				host = av[optind];
			continue;
		}
		opt = av[optind][1];
		if (!opt)
			usage();
		if (strchr("eilcpLRo", opt)) {	/* options with arguments */
			optarg = av[optind] + 2;
			if (strcmp(optarg, "") == 0) {
				if (optind >= ac - 1)
					usage();
				optarg = av[++optind];
			}
		} else {
			if (av[optind][2])
				usage();
			optarg = NULL;
		}
		switch (opt) {
		case '2':
			options.protocol = SSH_PROTO_2;
			break;
		case '4':
			IPv4or6 = AF_INET;
			break;
		case '6':
			IPv4or6 = AF_INET6;
			break;
		case 'n':
			stdin_null_flag = 1;
			break;
		case 'f':
			fork_after_authentication_flag = 1;
			stdin_null_flag = 1;
			break;
		case 'x':
			options.forward_x11 = 0;
			break;
		case 'X':
			options.forward_x11 = 1;
			break;
		case 'g':
			options.gateway_ports = 1;
			break;
		case 'P':
			options.use_privileged_port = 0;
			break;
		case 'a':
			options.forward_agent = 0;
			break;
		case 'A':
			options.forward_agent = 1;
			break;
#ifdef AFS
		case 'k':
			options.krb4_tgt_passing = 0;
			options.krb5_tgt_passing = 0;
			options.afs_token_passing = 0;
			break;
#endif
		case 'i':
			if (stat(optarg, &st) < 0) {
				fprintf(stderr, "Warning: Identity file %s does not exist.\n",
					optarg);
				break;
			}
			if (options.num_identity_files >= SSH_MAX_IDENTITY_FILES)
				fatal("Too many identity files specified (max %d)",
				      SSH_MAX_IDENTITY_FILES);
			options.identity_files[options.num_identity_files++] =
				xstrdup(optarg);
			break;
		case 't':
			tty_flag = 1;
			break;
		case 'v':
			if (0 == debug_flag) {
				debug_flag = 1;
				options.log_level = SYSLOG_LEVEL_DEBUG1;
			} else if (options.log_level < SYSLOG_LEVEL_DEBUG3) {
				options.log_level++;
				break;
			} else {
				fatal("Too high debugging level.\n");
			}
			/* fallthrough */
		case 'V':
			fprintf(stderr, "SSH Version %s, protocol versions %d.%d/%d.%d.\n",
			    SSH_VERSION,
			    PROTOCOL_MAJOR_1, PROTOCOL_MINOR_1,
			    PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2);
			fprintf(stderr, "Compiled with SSL (0x%8.8lx).\n", SSLeay());
			if (opt == 'V')
				exit(0);
			break;
		case 'q':
			options.log_level = SYSLOG_LEVEL_QUIET;
			break;
		case 'e':
			if (optarg[0] == '^' && optarg[2] == 0 &&
			    (unsigned char) optarg[1] >= 64 && (unsigned char) optarg[1] < 128)
				options.escape_char = (unsigned char) optarg[1] & 31;
			else if (strlen(optarg) == 1)
				options.escape_char = (unsigned char) optarg[0];
			else if (strcmp(optarg, "none") == 0)
				options.escape_char = -2;
			else {
				fprintf(stderr, "Bad escape character '%s'.\n", optarg);
				exit(1);
			}
			break;
		case 'c':
			if (ciphers_valid(optarg)) {
				/* SSH2 only */
				options.ciphers = xstrdup(optarg);
				options.cipher = SSH_CIPHER_ILLEGAL;
			} else {
				/* SSH1 only */
				Cipher *c = cipher_by_name(optarg);
				if (c == NULL || c->number < 0) {
					fprintf(stderr, "Unknown cipher type '%s'\n", optarg);
					exit(1);
				}
				options.cipher = c->number;
			}
			break;
		case 'p':
			options.port = atoi(optarg);
			break;
		case 'l':
			options.user = optarg;
			break;
		case 'R':
			if (sscanf(optarg, "%hu/%255[^/]/%hu", &fwd_port, buf,
			    &fwd_host_port) != 3 &&
			    sscanf(optarg, "%hu:%255[^:]:%hu", &fwd_port, buf,
			    &fwd_host_port) != 3) {
				fprintf(stderr, "Bad forwarding specification '%s'.\n", optarg);
				usage();
				/* NOTREACHED */
			}
			add_remote_forward(&options, fwd_port, buf, fwd_host_port);
			break;
		case 'L':
			if (sscanf(optarg, "%hu/%255[^/]/%hu", &fwd_port, buf,
			    &fwd_host_port) != 3 &&
			    sscanf(optarg, "%hu:%255[^:]:%hu", &fwd_port, buf,
			    &fwd_host_port) != 3) {
				fprintf(stderr, "Bad forwarding specification '%s'.\n", optarg);
				usage();
				/* NOTREACHED */
			}
			add_local_forward(&options, fwd_port, buf, fwd_host_port);
			break;
		case 'C':
			options.compression = 1;
			break;
		case 'N':
			no_shell_flag = 1;
			no_tty_flag = 1;
			break;
		case 'T':
			no_tty_flag = 1;
			break;
		case 'o':
			dummy = 1;
			if (process_config_line(&options, host ? host : "", optarg,
					 "command-line", 0, &dummy) != 0)
				exit(1);
			break;
		default:
			usage();
		}
	}

	/* Check that we got a host name. */
	if (!host)
		usage();

	SSLeay_add_all_algorithms();

	/* Initialize the command to execute on remote host. */
	buffer_init(&command);

	/*
	 * Save the command to execute on the remote host in a buffer. There
	 * is no limit on the length of the command, except by the maximum
	 * packet size.  Also sets the tty flag if there is no command.
	 */
	if (optind == ac) {
		/* No command specified - execute shell on a tty. */
		tty_flag = 1;
	} else {
		/* A command has been specified.  Store it into the
		   buffer. */
		for (i = optind; i < ac; i++) {
			if (i > optind)
				buffer_append(&command, " ", 1);
			buffer_append(&command, av[i], strlen(av[i]));
		}
	}

	/* Cannot fork to background if no command. */
	if (fork_after_authentication_flag && buffer_len(&command) == 0 && !no_shell_flag)
		fatal("Cannot fork into background without a command to execute.");

	/* Allocate a tty by default if no command specified. */
	if (buffer_len(&command) == 0)
		tty_flag = 1;

	/* Do not allocate a tty if stdin is not a tty. */
	if (!isatty(fileno(stdin))) {
		if (tty_flag)
			fprintf(stderr, "Pseudo-terminal will not be allocated because stdin is not a terminal.\n");
		tty_flag = 0;
	}
	/* force */
	if (no_tty_flag)
		tty_flag = 0;

	/* Get user data. */
	pw = getpwuid(original_real_uid);
	if (!pw) {
		fprintf(stderr, "You don't exist, go away!\n");
		exit(1);
	}
	/* Take a copy of the returned structure. */
	memset(&pwcopy, 0, sizeof(pwcopy));
	pwcopy.pw_name = xstrdup(pw->pw_name);
	pwcopy.pw_passwd = xstrdup(pw->pw_passwd);
	pwcopy.pw_uid = pw->pw_uid;
	pwcopy.pw_gid = pw->pw_gid;
	pwcopy.pw_dir = xstrdup(pw->pw_dir);
	pwcopy.pw_shell = xstrdup(pw->pw_shell);
	pwcopy.pw_class = xstrdup(pw->pw_class);
	pwcopy.pw_expire = pw->pw_expire;
	pwcopy.pw_change = pw->pw_change;
	pw = &pwcopy;

	/* Initialize "log" output.  Since we are the client all output
	   actually goes to the terminal. */
	log_init(av[0], options.log_level, SYSLOG_FACILITY_USER, 0);

	/* Read per-user configuration file. */
	snprintf(buf, sizeof buf, "%.100s/%.100s", pw->pw_dir, SSH_USER_CONFFILE);
	read_config_file(buf, host, &options);

	/* Read systemwide configuration file. */
	read_config_file(HOST_CONFIG_FILE, host, &options);

	/* Fill configuration defaults. */
	fill_default_options(&options);

	/* reinit */
	log_init(av[0], options.log_level, SYSLOG_FACILITY_USER, 0);

	/* check if RSA support exists */
	if ((options.protocol & SSH_PROTO_1) &&
	    rsa_alive() == 0) {
		log("%s: no RSA support in libssl and libcrypto.  See ssl(8).",
		    __progname);
		log("Disabling protocol version 1");
		options.protocol &= ~ (SSH_PROTO_1|SSH_PROTO_1_PREFERRED);
	}
	if (! options.protocol & (SSH_PROTO_1|SSH_PROTO_2)) {
		fprintf(stderr, "%s: No protocol version available.\n",
		    __progname);
 		exit(1);
	}

	if (options.user == NULL)
		options.user = xstrdup(pw->pw_name);

	if (options.hostname != NULL)
		host = options.hostname;

	/* Disable rhosts authentication if not running as root. */
	if (original_effective_uid != 0 || !options.use_privileged_port) {
		options.rhosts_authentication = 0;
		options.rhosts_rsa_authentication = 0;
	}
	/*
	 * If using rsh has been selected, exec it now (without trying
	 * anything else).  Note that we must release privileges first.
	 */
	if (options.use_rsh) {
		/*
		 * Restore our superuser privileges.  This must be done
		 * before permanently setting the uid.
		 */
		restore_uid();

		/* Switch to the original uid permanently. */
		permanently_set_uid(original_real_uid);

		/* Execute rsh. */
		rsh_connect(host, options.user, &command);
		fatal("rsh_connect returned");
	}
	/* Restore our superuser privileges. */
	restore_uid();

	/*
	 * Open a connection to the remote host.  This needs root privileges
	 * if rhosts_{rsa_}authentication is enabled.
	 */

	ok = ssh_connect(&host, &hostaddr, options.port,
			 options.connection_attempts,
			 !options.rhosts_authentication &&
			 !options.rhosts_rsa_authentication,
			 original_real_uid,
			 options.proxy_command);

	/*
	 * If we successfully made the connection, load the host private key
	 * in case we will need it later for combined rsa-rhosts
	 * authentication. This must be done before releasing extra
	 * privileges, because the file is only readable by root.
	 */
	if (ok && (options.protocol & SSH_PROTO_1)) {
		Key k;
		host_private_key = RSA_new();
		k.type = KEY_RSA;
		k.rsa = host_private_key;
		if (load_private_key(HOST_KEY_FILE, "", &k, NULL))
			host_private_key_loaded = 1;
	}
	/*
	 * Get rid of any extra privileges that we may have.  We will no
	 * longer need them.  Also, extra privileges could make it very hard
	 * to read identity files and other non-world-readable files from the
	 * user's home directory if it happens to be on a NFS volume where
	 * root is mapped to nobody.
	 */

	/*
	 * Note that some legacy systems need to postpone the following call
	 * to permanently_set_uid() until the private hostkey is destroyed
	 * with RSA_free().  Otherwise the calling user could ptrace() the
	 * process, read the private hostkey and impersonate the host.
	 * OpenBSD does not allow ptracing of setuid processes.
	 */
	permanently_set_uid(original_real_uid);

	/*
	 * Now that we are back to our own permissions, create ~/.ssh
	 * directory if it doesn\'t already exist.
	 */
	snprintf(buf, sizeof buf, "%.100s/%.100s", pw->pw_dir, SSH_USER_DIR);
	if (stat(buf, &st) < 0)
		if (mkdir(buf, 0700) < 0)
			error("Could not create directory '%.200s'.", buf);

	/* Check if the connection failed, and try "rsh" if appropriate. */
	if (!ok) {
		if (options.port != 0)
			log("Secure connection to %.100s on port %hu refused%.100s.",
			    host, options.port,
			    options.fallback_to_rsh ? "; reverting to insecure method" : "");
		else
			log("Secure connection to %.100s refused%.100s.", host,
			    options.fallback_to_rsh ? "; reverting to insecure method" : "");

		if (options.fallback_to_rsh) {
			rsh_connect(host, options.user, &command);
			fatal("rsh_connect returned");
		}
		exit(1);
	}
	/* Expand ~ in options.identity_files. */
	/* XXX mem-leaks */
	for (i = 0; i < options.num_identity_files; i++)
		options.identity_files[i] =
			tilde_expand_filename(options.identity_files[i], original_real_uid);
	for (i = 0; i < options.num_identity_files2; i++)
		options.identity_files2[i] =
			tilde_expand_filename(options.identity_files2[i], original_real_uid);
	/* Expand ~ in known host file names. */
	options.system_hostfile = tilde_expand_filename(options.system_hostfile,
	    original_real_uid);
	options.user_hostfile = tilde_expand_filename(options.user_hostfile,
	    original_real_uid);
	options.system_hostfile2 = tilde_expand_filename(options.system_hostfile2,
	    original_real_uid);
	options.user_hostfile2 = tilde_expand_filename(options.user_hostfile2,
	    original_real_uid);

	/* Log into the remote system.  This never returns if the login fails. */
	ssh_login(host_private_key_loaded, host_private_key,
		  host, (struct sockaddr *)&hostaddr, original_real_uid);

	/* We no longer need the host private key.  Clear it now. */
	if (host_private_key_loaded)
		RSA_free(host_private_key);	/* Destroys contents safely */

	exit_status = compat20 ? ssh_session2() : ssh_session();
	packet_close();
	return exit_status;
}

void
x11_get_proto(char *proto, int proto_len, char *data, int data_len)
{
	char line[512];
	FILE *f;
	int got_data = 0, i;

	if (options.xauth_location) {
		/* Try to get Xauthority information for the display. */
		snprintf(line, sizeof line, "%.100s list %.200s 2>/dev/null",
		    options.xauth_location, getenv("DISPLAY"));
		f = popen(line, "r");
		if (f && fgets(line, sizeof(line), f) &&
		    sscanf(line, "%*s %s %s", proto, data) == 2)
			got_data = 1;
		if (f)
			pclose(f);
	}
	/*
	 * If we didn't get authentication data, just make up some
	 * data.  The forwarding code will check the validity of the
	 * response anyway, and substitute this data.  The X11
	 * server, however, will ignore this fake data and use
	 * whatever authentication mechanisms it was using otherwise
	 * for the local connection.
	 */
	if (!got_data) {
		u_int32_t rand = 0;

		strlcpy(proto, "MIT-MAGIC-COOKIE-1", proto_len);
		for (i = 0; i < 16; i++) {
			if (i % 4 == 0)
				rand = arc4random();
			snprintf(data + 2 * i, data_len - 2 * i, "%02x", rand & 0xff);
			rand >>= 8;
		}
	}
}

int
ssh_session(void)
{
	int type;
	int i;
	int plen;
	int interactive = 0;
	int have_tty = 0;
	struct winsize ws;
	int authfd;
	char *cp;

	/* Enable compression if requested. */
	if (options.compression) {
		debug("Requesting compression at level %d.", options.compression_level);

		if (options.compression_level < 1 || options.compression_level > 9)
			fatal("Compression level must be from 1 (fast) to 9 (slow, best).");

		/* Send the request. */
		packet_start(SSH_CMSG_REQUEST_COMPRESSION);
		packet_put_int(options.compression_level);
		packet_send();
		packet_write_wait();
		type = packet_read(&plen);
		if (type == SSH_SMSG_SUCCESS)
			packet_start_compression(options.compression_level);
		else if (type == SSH_SMSG_FAILURE)
			log("Warning: Remote host refused compression.");
		else
			packet_disconnect("Protocol error waiting for compression response.");
	}
	/* Allocate a pseudo tty if appropriate. */
	if (tty_flag) {
		debug("Requesting pty.");

		/* Start the packet. */
		packet_start(SSH_CMSG_REQUEST_PTY);

		/* Store TERM in the packet.  There is no limit on the
		   length of the string. */
		cp = getenv("TERM");
		if (!cp)
			cp = "";
		packet_put_string(cp, strlen(cp));

		/* Store window size in the packet. */
		if (ioctl(fileno(stdin), TIOCGWINSZ, &ws) < 0)
			memset(&ws, 0, sizeof(ws));
		packet_put_int(ws.ws_row);
		packet_put_int(ws.ws_col);
		packet_put_int(ws.ws_xpixel);
		packet_put_int(ws.ws_ypixel);

		/* Store tty modes in the packet. */
		tty_make_modes(fileno(stdin));

		/* Send the packet, and wait for it to leave. */
		packet_send();
		packet_write_wait();

		/* Read response from the server. */
		type = packet_read(&plen);
		if (type == SSH_SMSG_SUCCESS) {
			interactive = 1;
			have_tty = 1;
		} else if (type == SSH_SMSG_FAILURE)
			log("Warning: Remote host failed or refused to allocate a pseudo tty.");
		else
			packet_disconnect("Protocol error waiting for pty request response.");
	}
	/* Request X11 forwarding if enabled and DISPLAY is set. */
	if (options.forward_x11 && getenv("DISPLAY") != NULL) {
		char proto[512], data[512];
		/* Get reasonable local authentication information. */
		x11_get_proto(proto, sizeof proto, data, sizeof data);
		/* Request forwarding with authentication spoofing. */
		debug("Requesting X11 forwarding with authentication spoofing.");
		x11_request_forwarding_with_spoofing(0, proto, data);

		/* Read response from the server. */
		type = packet_read(&plen);
		if (type == SSH_SMSG_SUCCESS) {
			interactive = 1;
		} else if (type == SSH_SMSG_FAILURE) {
			log("Warning: Remote host denied X11 forwarding.");
		} else {
			packet_disconnect("Protocol error waiting for X11 forwarding");
		}
	}
	/* Tell the packet module whether this is an interactive session. */
	packet_set_interactive(interactive, options.keepalives);

	/* Clear agent forwarding if we don\'t have an agent. */
	authfd = ssh_get_authentication_socket();
	if (authfd < 0)
		options.forward_agent = 0;
	else
		ssh_close_authentication_socket(authfd);

	/* Request authentication agent forwarding if appropriate. */
	if (options.forward_agent) {
		debug("Requesting authentication agent forwarding.");
		auth_request_forwarding();

		/* Read response from the server. */
		type = packet_read(&plen);
		packet_integrity_check(plen, 0, type);
		if (type != SSH_SMSG_SUCCESS)
			log("Warning: Remote host denied authentication agent forwarding.");
	}
	/* Initiate local TCP/IP port forwardings. */
	for (i = 0; i < options.num_local_forwards; i++) {
		debug("Connections to local port %d forwarded to remote address %.200s:%d",
		      options.local_forwards[i].port,
		      options.local_forwards[i].host,
		      options.local_forwards[i].host_port);
		channel_request_local_forwarding(options.local_forwards[i].port,
						 options.local_forwards[i].host,
						 options.local_forwards[i].host_port,
						 options.gateway_ports);
	}

	/* Initiate remote TCP/IP port forwardings. */
	for (i = 0; i < options.num_remote_forwards; i++) {
		debug("Connections to remote port %d forwarded to local address %.200s:%d",
		      options.remote_forwards[i].port,
		      options.remote_forwards[i].host,
		      options.remote_forwards[i].host_port);
		channel_request_remote_forwarding(options.remote_forwards[i].port,
						  options.remote_forwards[i].host,
						  options.remote_forwards[i].host_port);
	}

	/* If requested, let ssh continue in the background. */
	if (fork_after_authentication_flag)
		if (daemon(1, 1) < 0)
			fatal("daemon() failed: %.200s", strerror(errno));

	/*
	 * If a command was specified on the command line, execute the
	 * command now. Otherwise request the server to start a shell.
	 */
	if (buffer_len(&command) > 0) {
		int len = buffer_len(&command);
		if (len > 900)
			len = 900;
		debug("Sending command: %.*s", len, buffer_ptr(&command));
		packet_start(SSH_CMSG_EXEC_CMD);
		packet_put_string(buffer_ptr(&command), buffer_len(&command));
		packet_send();
		packet_write_wait();
	} else {
		debug("Requesting shell.");
		packet_start(SSH_CMSG_EXEC_SHELL);
		packet_send();
		packet_write_wait();
	}

	/* Enter the interactive session. */
	return client_loop(have_tty, tty_flag ? options.escape_char : -1, 0);
}

void
init_local_fwd(void)
{
	int i;
	/* Initiate local TCP/IP port forwardings. */
	for (i = 0; i < options.num_local_forwards; i++) {
		debug("Connections to local port %d forwarded to remote address %.200s:%d",
		      options.local_forwards[i].port,
		      options.local_forwards[i].host,
		      options.local_forwards[i].host_port);
		channel_request_local_forwarding(options.local_forwards[i].port,
						 options.local_forwards[i].host,
						 options.local_forwards[i].host_port,
						 options.gateway_ports);
	}
}

extern void client_set_session_ident(int id);

void
client_init(int id, void *arg)
{
	int len;
	debug("client_init id %d arg %d", id, (int)arg);

	if (no_shell_flag)
		goto done;

	if (tty_flag) {
		struct winsize ws;
		char *cp;
		cp = getenv("TERM");
		if (!cp)
			cp = "";
		/* Store window size in the packet. */
		if (ioctl(fileno(stdin), TIOCGWINSZ, &ws) < 0)
			memset(&ws, 0, sizeof(ws));

		channel_request_start(id, "pty-req", 0);
		packet_put_cstring(cp);
		packet_put_int(ws.ws_col);
		packet_put_int(ws.ws_row);
		packet_put_int(ws.ws_xpixel);
		packet_put_int(ws.ws_ypixel);
		packet_put_cstring("");		/* XXX: encode terminal modes */
		packet_send();
		/* XXX wait for reply */
	}
	if (options.forward_x11 &&
	    getenv("DISPLAY") != NULL) {
		char proto[512], data[512];
		/* Get reasonable local authentication information. */
		x11_get_proto(proto, sizeof proto, data, sizeof data);
		/* Request forwarding with authentication spoofing. */
		debug("Requesting X11 forwarding with authentication spoofing.");
		x11_request_forwarding_with_spoofing(id, proto, data);
		/* XXX wait for reply */
	}

	len = buffer_len(&command);
	if (len > 0) {
		if (len > 900)
			len = 900;
		debug("Sending command: %.*s", len, buffer_ptr(&command));
		channel_request_start(id, "exec", 0);
		packet_put_string(buffer_ptr(&command), len);
		packet_send();
	} else {
		channel_request(id, "shell", 0);
	}
	/* channel_callback(id, SSH2_MSG_OPEN_CONFIGMATION, client_init, 0); */
done:
	/* register different callback, etc. XXX */
	client_set_session_ident(id);
}

int
ssh_session2(void)
{
	int window, packetmax, id;
	int in, out, err;

	if (stdin_null_flag) {
		in = open("/dev/null", O_RDONLY);
	} else {
		in = dup(STDIN_FILENO);
	}
	out = dup(STDOUT_FILENO);
	err = dup(STDERR_FILENO);

	if (in < 0 || out < 0 || err < 0)
		fatal("dup() in/out/err failed");

	/* enable nonblocking unless tty */
	if (!isatty(in))
		set_nonblock(in);
	if (!isatty(out))
		set_nonblock(out);
	if (!isatty(err))
		set_nonblock(err);

	/* should be pre-session */
	init_local_fwd();
	
	/* If requested, let ssh continue in the background. */
	if (fork_after_authentication_flag)
		if (daemon(1, 1) < 0)
			fatal("daemon() failed: %.200s", strerror(errno));

	window = CHAN_SES_WINDOW_DEFAULT;
	packetmax = CHAN_SES_PACKET_DEFAULT;
	if (!tty_flag) {
		window *= 2;
		packetmax *=2;
	}
	id = channel_new(
	    "session", SSH_CHANNEL_OPENING, in, out, err,
	    window, packetmax, CHAN_EXTENDED_WRITE,
	    xstrdup("client-session"), /*nonblock*/0);

	channel_open(id);
	channel_register_callback(id, SSH2_MSG_CHANNEL_OPEN_CONFIRMATION, client_init, (void *)0);

	return client_loop(tty_flag, tty_flag ? options.escape_char : -1, id);
}