path: root/ssh.c

/* $OpenBSD: ssh.c,v 1.338 2010/05/16 12:55:51 markus Exp $ */
/*
 * 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.
 * Copyright (c) 2000, 2001, 2002, 2003 Markus Friedl.  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"

#include <sys/types.h>
#ifdef HAVE_SYS_STAT_H
# include <sys/stat.h>
#endif
#include <sys/resource.h>
#include <sys/ioctl.h>
#include <sys/param.h>
#include <sys/socket.h>

#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#ifdef HAVE_PATHS_H
#include <paths.h>
#endif
#include <pwd.h>
#include <signal.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <netinet/in.h>
#include <arpa/inet.h>

#include <openssl/evp.h>
#include <openssl/err.h>
#include "openbsd-compat/openssl-compat.h"
#include "openbsd-compat/sys-queue.h"

#include "xmalloc.h"
#include "ssh.h"
#include "ssh1.h"
#include "ssh2.h"
#include "compat.h"
#include "cipher.h"
#include "packet.h"
#include "buffer.h"
#include "channels.h"
#include "key.h"
#include "authfd.h"
#include "authfile.h"
#include "pathnames.h"
#include "dispatch.h"
#include "clientloop.h"
#include "log.h"
#include "readconf.h"
#include "sshconnect.h"
#include "misc.h"
#include "kex.h"
#include "mac.h"
#include "sshpty.h"
#include "match.h"
#include "msg.h"
#include "uidswap.h"
#include "roaming.h"
#include "version.h"

#ifdef ENABLE_PKCS11
#include "ssh-pkcs11.h"
#endif

extern char *__progname;

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

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

/* don't exec a shell */
int no_shell_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 passphrase can be entered manually, and then ssh goes to the
 * background.
 */
int fork_after_authentication_flag = 0;

/* forward stdio to remote host and port */
char *stdio_forward_host = NULL;
int stdio_forward_port = 0;

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

/* optional user configfile */
char *config = NULL;

/*
 * 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;

/* Private host keys. */
Sensitive sensitive_data;

/* Original real UID. */
uid_t original_real_uid;
uid_t original_effective_uid;

/* command to be executed */
Buffer command;

/* Should we execute a command or invoke a subsystem? */
int subsystem_flag = 0;

/* # of replies received for global requests */
static int remote_forward_confirms_received = 0;

/* pid of proxycommand child process */
pid_t proxy_command_pid = 0;

/* mux.c */
extern int muxserver_sock;
extern u_int muxclient_command;

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

static void
usage(void)
{
	fprintf(stderr,
"usage: ssh [-1246AaCfgKkMNnqsTtVvXxYy] [-b bind_address] [-c cipher_spec]\n"
"           [-D [bind_address:]port] [-e escape_char] [-F configfile]\n"
"           [-I pkcs11] [-i identity_file]\n"
"           [-L [bind_address:]port:host:hostport]\n"
"           [-l login_name] [-m mac_spec] [-O ctl_cmd] [-o option] [-p port]\n"
"           [-R [bind_address:]port:host:hostport] [-S ctl_path]\n"
"           [-W host:port] [-w local_tun[:remote_tun]]\n"
"           [user@]hostname [command]\n"
	);
	exit(255);
}

static int ssh_session(void);
static int ssh_session2(void);
static void load_public_identity_files(void);

/* from muxclient.c */
void muxclient(const char *);
void muxserver_listen(void);

/*
 * Main program for the ssh client.
 */
int
main(int ac, char **av)
{
	int i, r, opt, exit_status, use_syslog;
	char *p, *cp, *line, *argv0, buf[MAXPATHLEN];
	struct stat st;
	struct passwd *pw;
	int dummy, timeout_ms;
	extern int optind, optreset;
	extern char *optarg;
	struct servent *sp;
	Forward fwd;

	/* Ensure that fds 0, 1 and 2 are open or directed to /dev/null */
	sanitise_stdfd();

	__progname = ssh_get_progname(av[0]);
	init_rng();

	/*
	 * 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();

	/*
	 * 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).
	 */
	PRIV_END;

#ifdef HAVE_SETRLIMIT
	/* 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));
	}
#endif
	/* Get user data. */
	pw = getpwuid(original_real_uid);
	if (!pw) {
		logit("You don't exist, go away!");
		exit(255);
	}
	/* Take a copy of the returned structure. */
	pw = pwcopy(pw);

	/*
	 * 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);

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

	/* Parse command-line arguments. */
	host = NULL;
	use_syslog = 0;
	argv0 = av[0];

 again:
	while ((opt = getopt(ac, av, "1246ab:c:e:fgi:kl:m:no:p:qstvx"
	    "ACD:F:I:KL:MNO:PR:S:TVw:W:XYy")) != -1) {
		switch (opt) {
		case '1':
			options.protocol = SSH_PROTO_1;
			break;
		case '2':
			options.protocol = SSH_PROTO_2;
			break;
		case '4':
			options.address_family = AF_INET;
			break;
		case '6':
			options.address_family = 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 'y':
			use_syslog = 1;
			break;
		case 'Y':
			options.forward_x11 = 1;
			options.forward_x11_trusted = 1;
			break;
		case 'g':
			options.gateway_ports = 1;
			break;
		case 'O':
			if (stdio_forward_host != NULL)
				fatal("Cannot specify multiplexing "
				    "command with -W");
			else if (muxclient_command != 0)
				fatal("Multiplexing command already specified");
			if (strcmp(optarg, "check") == 0)
				muxclient_command = SSHMUX_COMMAND_ALIVE_CHECK;
			else if (strcmp(optarg, "forward") == 0)
				muxclient_command = SSHMUX_COMMAND_FORWARD;
			else if (strcmp(optarg, "exit") == 0)
				muxclient_command = SSHMUX_COMMAND_TERMINATE;
			else
				fatal("Invalid multiplex command.");
			break;
		case 'P':	/* deprecated */
			options.use_privileged_port = 0;
			break;
		case 'a':
			options.forward_agent = 0;
			break;
		case 'A':
			options.forward_agent = 1;
			break;
		case 'k':
			options.gss_deleg_creds = 0;
			break;
		case 'K':
			options.gss_authentication = 1;
			options.gss_deleg_creds = 1;
			break;
		case 'i':
			if (stat(optarg, &st) < 0) {
				fprintf(stderr, "Warning: Identity file %s "
				    "not accessible: %s.\n", optarg,
				    strerror(errno));
				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 'I':
#ifdef ENABLE_PKCS11
			options.pkcs11_provider = xstrdup(optarg);
#else
			fprintf(stderr, "no support for PKCS#11.\n");
#endif
			break;
		case 't':
			if (tty_flag)
				force_tty_flag = 1;
			tty_flag = 1;
			break;
		case 'v':
			if (debug_flag == 0) {
				debug_flag = 1;
				options.log_level = SYSLOG_LEVEL_DEBUG1;
			} else {
				if (options.log_level < SYSLOG_LEVEL_DEBUG3)
					options.log_level++;
				break;
			}
			/* FALLTHROUGH */
		case 'V':
			fprintf(stderr, "%s, %s\n",
			    SSH_RELEASE, SSLeay_version(SSLEAY_VERSION));
			if (opt == 'V')
				exit(0);
			break;
		case 'w':
			if (options.tun_open == -1)
				options.tun_open = SSH_TUNMODE_DEFAULT;
			options.tun_local = a2tun(optarg, &options.tun_remote);
			if (options.tun_local == SSH_TUNID_ERR) {
				fprintf(stderr,
				    "Bad tun device '%s'\n", optarg);
				exit(255);
			}
			break;
		case 'W':
			if (stdio_forward_host != NULL)
				fatal("stdio forward already specified");
			if (muxclient_command != 0)
				fatal("Cannot specify stdio forward with -O");
			if (parse_forward(&fwd, optarg, 1, 0)) {
				stdio_forward_host = fwd.listen_host;
				stdio_forward_port = fwd.listen_port;
				xfree(fwd.connect_host);
			} else {
				fprintf(stderr,
				    "Bad stdio forwarding specification '%s'\n",
				    optarg);
				exit(255);
			}
			no_tty_flag = 1;
			no_shell_flag = 1;
			options.clear_forwardings = 1;
			options.exit_on_forward_failure = 1;
			break;
		case 'q':
			options.log_level = SYSLOG_LEVEL_QUIET;
			break;
		case 'e':
			if (optarg[0] == '^' && optarg[2] == 0 &&
			    (u_char) optarg[1] >= 64 &&
			    (u_char) optarg[1] < 128)
				options.escape_char = (u_char) optarg[1] & 31;
			else if (strlen(optarg) == 1)
				options.escape_char = (u_char) optarg[0];
			else if (strcmp(optarg, "none") == 0)
				options.escape_char = SSH_ESCAPECHAR_NONE;
			else {
				fprintf(stderr, "Bad escape character '%s'.\n",
				    optarg);
				exit(255);
			}
			break;
		case 'c':
			if (ciphers_valid(optarg)) {
				/* SSH2 only */
				options.ciphers = xstrdup(optarg);
				options.cipher = SSH_CIPHER_INVALID;
			} else {
				/* SSH1 only */
				options.cipher = cipher_number(optarg);
				if (options.cipher == -1) {
					fprintf(stderr,
					    "Unknown cipher type '%s'\n",
					    optarg);
					exit(255);
				}
				if (options.cipher == SSH_CIPHER_3DES)
					options.ciphers = "3des-cbc";
				else if (options.cipher == SSH_CIPHER_BLOWFISH)
					options.ciphers = "blowfish-cbc";
				else
					options.ciphers = (char *)-1;
			}
			break;
		case 'm':
			if (mac_valid(optarg))
				options.macs = xstrdup(optarg);
			else {
				fprintf(stderr, "Unknown mac type '%s'\n",
				    optarg);
				exit(255);
			}
			break;
		case 'M':
			if (options.control_master == SSHCTL_MASTER_YES)
				options.control_master = SSHCTL_MASTER_ASK;
			else
				options.control_master = SSHCTL_MASTER_YES;
			break;
		case 'p':
			options.port = a2port(optarg);
			if (options.port <= 0) {
				fprintf(stderr, "Bad port '%s'\n", optarg);
				exit(255);
			}
			break;
		case 'l':
			options.user = optarg;
			break;

		case 'L':
			if (parse_forward(&fwd, optarg, 0, 0))
				add_local_forward(&options, &fwd);
			else {
				fprintf(stderr,
				    "Bad local forwarding specification '%s'\n",
				    optarg);
				exit(255);
			}
			break;

		case 'R':
			if (parse_forward(&fwd, optarg, 0, 1)) {
				add_remote_forward(&options, &fwd);
			} else {
				fprintf(stderr,
				    "Bad remote forwarding specification "
				    "'%s'\n", optarg);
				exit(255);
			}
			break;

		case 'D':
			if (parse_forward(&fwd, optarg, 1, 0)) {
				add_local_forward(&options, &fwd);
			} else {
				fprintf(stderr,
				    "Bad dynamic forwarding specification "
				    "'%s'\n", optarg);
				exit(255);
			}
			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;
			line = xstrdup(optarg);
			if (process_config_line(&options, host ? host : "",
			    line, "command-line", 0, &dummy) != 0)
				exit(255);
			xfree(line);
			break;
		case 's':
			subsystem_flag = 1;
			break;
		case 'S':
			if (options.control_path != NULL)
				free(options.control_path);
			options.control_path = xstrdup(optarg);
			break;
		case 'b':
			options.bind_address = optarg;
			break;
		case 'F':
			config = optarg;
			break;
		default:
			usage();
		}
	}

	ac -= optind;
	av += optind;

	if (ac > 0 && !host) {
		if (strrchr(*av, '@')) {
			p = xstrdup(*av);
			cp = strrchr(p, '@');
			if (cp == NULL || cp == p)
				usage();
			options.user = p;
			*cp = '\0';
			host = ++cp;
		} else
			host = *av;
		if (ac > 1) {
			optind = optreset = 1;
			goto again;
		}
		ac--, av++;
	}

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

	SSLeay_add_all_algorithms();
	ERR_load_crypto_strings();

	/* 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 (!ac) {
		/* No command specified - execute shell on a tty. */
		tty_flag = 1;
		if (subsystem_flag) {
			fprintf(stderr,
			    "You must specify a subsystem to invoke.\n");
			usage();
		}
	} else {
		/* A command has been specified.  Store it into the buffer. */
		for (i = 0; i < ac; i++) {
			if (i)
				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;

	/* Force no tty */
	if (no_tty_flag || muxclient_command != 0)
		tty_flag = 0;
	/* Do not allocate a tty if stdin is not a tty. */
	if ((!isatty(fileno(stdin)) || stdin_null_flag) && !force_tty_flag) {
		if (tty_flag)
			logit("Pseudo-terminal will not be allocated because "
			    "stdin is not a terminal.");
		tty_flag = 0;
	}

	/*
	 * Initialize "log" output.  Since we are the client all output
	 * actually goes to stderr.
	 */
	log_init(argv0,
	    options.log_level == -1 ? SYSLOG_LEVEL_INFO : options.log_level,
	    SYSLOG_FACILITY_USER, !use_syslog);

	/*
	 * Read per-user configuration file.  Ignore the system wide config
	 * file if the user specifies a config file on the command line.
	 */
	if (config != NULL) {
		if (!read_config_file(config, host, &options, 0))
			fatal("Can't open user config file %.100s: "
			    "%.100s", config, strerror(errno));
	} else {
		r = snprintf(buf, sizeof buf, "%s/%s", pw->pw_dir,
		    _PATH_SSH_USER_CONFFILE);
		if (r > 0 && (size_t)r < sizeof(buf))
			(void)read_config_file(buf, host, &options, 1);

		/* Read systemwide configuration file after use config. */
		(void)read_config_file(_PATH_HOST_CONFIG_FILE, host,
		    &options, 0);
	}

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

	channel_set_af(options.address_family);

	/* reinit */
	log_init(argv0, options.log_level, SYSLOG_FACILITY_USER, !use_syslog);

	seed_rng();

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

	/* Get default port if port has not been set. */
	if (options.port == 0) {
		sp = getservbyname(SSH_SERVICE_NAME, "tcp");
		options.port = sp ? ntohs(sp->s_port) : SSH_DEFAULT_PORT;
	}

	if (options.local_command != NULL) {
		char thishost[NI_MAXHOST];

		if (gethostname(thishost, sizeof(thishost)) == -1)
			fatal("gethostname: %s", strerror(errno));
		snprintf(buf, sizeof(buf), "%d", options.port);
		debug3("expanding LocalCommand: %s", options.local_command);
		cp = options.local_command;
		options.local_command = percent_expand(cp, "d", pw->pw_dir,
		    "h", options.hostname? options.hostname : host,
                    "l", thishost, "n", host, "r", options.user, "p", buf,
                    "u", pw->pw_name, (char *)NULL);
		debug3("expanded LocalCommand: %s", options.local_command);
		xfree(cp);
	}

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

	/* force lowercase for hostkey matching */
	if (options.host_key_alias != NULL) {
		for (p = options.host_key_alias; *p; p++)
			if (isupper(*p))
				*p = (char)tolower(*p);
	}

	if (options.proxy_command != NULL &&
	    strcmp(options.proxy_command, "none") == 0) {
		xfree(options.proxy_command);
		options.proxy_command = NULL;
	}
	if (options.control_path != NULL &&
	    strcmp(options.control_path, "none") == 0) {
		xfree(options.control_path);
		options.control_path = NULL;
	}

	if (options.control_path != NULL) {
		char thishost[NI_MAXHOST];

		if (gethostname(thishost, sizeof(thishost)) == -1)
			fatal("gethostname: %s", strerror(errno));
		snprintf(buf, sizeof(buf), "%d", options.port);
		cp = tilde_expand_filename(options.control_path,
		    original_real_uid);
		xfree(options.control_path);
		options.control_path = percent_expand(cp, "p", buf, "h", host,
		    "r", options.user, "l", thishost, (char *)NULL);
		xfree(cp);
	}
	if (muxclient_command != 0 && options.control_path == NULL)
		fatal("No ControlPath specified for \"-O\" command");
	if (options.control_path != NULL)
		muxclient(options.control_path);

	timeout_ms = options.connection_timeout * 1000;

	/* Open a connection to the remote host. */
	if (ssh_connect(host, &hostaddr, options.port,
	    options.address_family, options.connection_attempts, &timeout_ms,
	    options.tcp_keep_alive, 
#ifdef HAVE_CYGWIN
	    options.use_privileged_port,
#else
	    original_effective_uid == 0 && options.use_privileged_port,
#endif
	    options.proxy_command) != 0)
		exit(255);

	if (timeout_ms > 0)
		debug3("timeout: %d ms remain after connect", timeout_ms);

	/*
	 * 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 we cannot access the private keys, load the public keys
	 * instead and try to execute the ssh-keysign helper instead.
	 */
	sensitive_data.nkeys = 0;
	sensitive_data.keys = NULL;
	sensitive_data.external_keysign = 0;
	if (options.rhosts_rsa_authentication ||
	    options.hostbased_authentication) {
		sensitive_data.nkeys = 3;
		sensitive_data.keys = xcalloc(sensitive_data.nkeys,
		    sizeof(Key));

		PRIV_START;
		sensitive_data.keys[0] = key_load_private_type(KEY_RSA1,
		    _PATH_HOST_KEY_FILE, "", NULL, NULL);
		sensitive_data.keys[1] = key_load_private_type(KEY_DSA,
		    _PATH_HOST_DSA_KEY_FILE, "", NULL, NULL);
		sensitive_data.keys[2] = key_load_private_type(KEY_RSA,
		    _PATH_HOST_RSA_KEY_FILE, "", NULL, NULL);
		PRIV_END;

		if (options.hostbased_authentication == 1 &&
		    sensitive_data.keys[0] == NULL &&
		    sensitive_data.keys[1] == NULL &&
		    sensitive_data.keys[2] == NULL) {
			sensitive_data.keys[1] = key_load_public(
			    _PATH_HOST_DSA_KEY_FILE, NULL);
			sensitive_data.keys[2] = key_load_public(
			    _PATH_HOST_RSA_KEY_FILE, NULL);
			sensitive_data.external_keysign = 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.
	 */
	if (original_effective_uid == 0) {
		PRIV_START;
		permanently_set_uid(pw);
	}

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

	/* load options.identity_files */
	load_public_identity_files();

	/* Expand ~ in known host file names. */
	/* XXX mem-leaks: */
	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);

	signal(SIGPIPE, SIG_IGN); /* ignore SIGPIPE early */

	/* Log into the remote system.  Never returns if the login fails. */
	ssh_login(&sensitive_data, host, (struct sockaddr *)&hostaddr,
	    pw, timeout_ms);

	/* We no longer need the private host keys.  Clear them now. */
	if (sensitive_data.nkeys != 0) {
		for (i = 0; i < sensitive_data.nkeys; i++) {
			if (sensitive_data.keys[i] != NULL) {
				/* Destroys contents safely */
				debug3("clear hostkey %d", i);
				key_free(sensitive_data.keys[i]);
				sensitive_data.keys[i] = NULL;
			}
		}
		xfree(sensitive_data.keys);
	}
	for (i = 0; i < options.num_identity_files; i++) {
		if (options.identity_files[i]) {
			xfree(options.identity_files[i]);
			options.identity_files[i] = NULL;
		}
		if (options.identity_keys[i]) {
			key_free(options.identity_keys[i]);
			options.identity_keys[i] = NULL;
		}
	}

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

	if (options.control_path != NULL && muxserver_sock != -1)
		unlink(options.control_path);

	/*
	 * Send SIGHUP to proxy command if used. We don't wait() in
	 * case it hangs and instead rely on init to reap the child
	 */
	if (proxy_command_pid > 1)
		kill(proxy_command_pid, SIGHUP);

	return exit_status;
}

/* Callback for remote forward global requests */
static void
ssh_confirm_remote_forward(int type, u_int32_t seq, void *ctxt)
{
	Forward *rfwd = (Forward *)ctxt;

	/* XXX verbose() on failure? */
	debug("remote forward %s for: listen %d, connect %s:%d",
	    type == SSH2_MSG_REQUEST_SUCCESS ? "success" : "failure",
	    rfwd->listen_port, rfwd->connect_host, rfwd->connect_port);
	if (type == SSH2_MSG_REQUEST_SUCCESS && rfwd->listen_port == 0) {
		rfwd->allocated_port = packet_get_int();
		logit("Allocated port %u for remote forward to %s:%d",
		    rfwd->allocated_port,
		    rfwd->connect_host, rfwd->connect_port);
	}
	
	if (type == SSH2_MSG_REQUEST_FAILURE) {
		if (options.exit_on_forward_failure)
			fatal("Error: remote port forwarding failed for "
			    "listen port %d", rfwd->listen_port);
		else
			logit("Warning: remote port forwarding failed for "
			    "listen port %d", rfwd->listen_port);
	}
	if (++remote_forward_confirms_received == options.num_remote_forwards) {
		debug("All remote forwarding requests processed");
		if (fork_after_authentication_flag) {
			fork_after_authentication_flag = 0;
			if (daemon(1, 1) < 0)
				fatal("daemon() failed: %.200s",
				    strerror(errno));
		}
	}
}

static void
client_cleanup_stdio_fwd(int id, void *arg)
{
	debug("stdio forwarding: done");
	cleanup_exit(0);
}

static int
client_setup_stdio_fwd(const char *host_to_connect, u_short port_to_connect)
{
	Channel *c;
	int in, out;

	debug3("client_setup_stdio_fwd %s:%d", host_to_connect,
	    port_to_connect);

	in = dup(STDIN_FILENO);
	out = dup(STDOUT_FILENO);
	if (in < 0 || out < 0)
		fatal("channel_connect_stdio_fwd: dup() in/out failed");

	if ((c = channel_connect_stdio_fwd(host_to_connect, port_to_connect,
	    in, out)) == NULL)
		return 0;
	channel_register_cleanup(c->self, client_cleanup_stdio_fwd, 0);
	return 1;
}

static void
ssh_init_forwarding(void)
{
	int success = 0;
	int i;

	if (stdio_forward_host != NULL) {
		if (!compat20) {
			fatal("stdio forwarding require Protocol 2");
		}
		if (!client_setup_stdio_fwd(stdio_forward_host,
		    stdio_forward_port))
			fatal("Failed to connect in stdio forward mode.");
	}

	/* Initiate local TCP/IP port forwardings. */
	for (i = 0; i < options.num_local_forwards; i++) {
		debug("Local connections to %.200s:%d forwarded to remote "
		    "address %.200s:%d",
		    (options.local_forwards[i].listen_host == NULL) ?
		    (options.gateway_ports ? "*" : "LOCALHOST") :
		    options.local_forwards[i].listen_host,
		    options.local_forwards[i].listen_port,
		    options.local_forwards[i].connect_host,
		    options.local_forwards[i].connect_port);
		success += channel_setup_local_fwd_listener(
		    options.local_forwards[i].listen_host,
		    options.local_forwards[i].listen_port,
		    options.local_forwards[i].connect_host,
		    options.local_forwards[i].connect_port,
		    options.gateway_ports);
	}
	if (i > 0 && success != i && options.exit_on_forward_failure)
		fatal("Could not request local forwarding.");
	if (i > 0 && success == 0)
		error("Could not request local forwarding.");

	/* Initiate remote TCP/IP port forwardings. */
	for (i = 0; i < options.num_remote_forwards; i++) {
		debug("Remote connections from %.200s:%d forwarded to "
		    "local address %.200s:%d",
		    (options.remote_forwards[i].listen_host == NULL) ?
		    "LOCALHOST" : options.remote_forwards[i].listen_host,
		    options.remote_forwards[i].listen_port,
		    options.remote_forwards[i].connect_host,
		    options.remote_forwards[i].connect_port);
		if (channel_request_remote_forwarding(
		    options.remote_forwards[i].listen_host,
		    options.remote_forwards[i].listen_port,
		    options.remote_forwards[i].connect_host,
		    options.remote_forwards[i].connect_port) < 0) {
			if (options.exit_on_forward_failure)
				fatal("Could not request remote forwarding.");
			else
				logit("Warning: Could not request remote "
				    "forwarding.");
		}
		client_register_global_confirm(ssh_confirm_remote_forward,
		    &options.remote_forwards[i]);
	}

	/* Initiate tunnel forwarding. */
	if (options.tun_open != SSH_TUNMODE_NO) {
		if (client_request_tun_fwd(options.tun_open,
		    options.tun_local, options.tun_remote) == -1) {
			if (options.exit_on_forward_failure)
				fatal("Could not request tunnel forwarding.");
			else
				error("Could not request tunnel forwarding.");
		}
	}			
}

static void
check_agent_present(void)
{
	if (options.forward_agent) {
		/* Clear agent forwarding if we don't have an agent. */
		if (!ssh_agent_present())
			options.forward_agent = 0;
	}
}

static int
ssh_session(void)
{
	int type;
	int interactive = 0;
	int have_tty = 0;
	struct winsize ws;
	char *cp;
	const char *display;

	/* 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();
		if (type == SSH_SMSG_SUCCESS)
			packet_start_compression(options.compression_level);
		else if (type == SSH_SMSG_FAILURE)
			logit("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_cstring(cp);

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

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

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

		/* Read response from the server. */
		type = packet_read();
		if (type == SSH_SMSG_SUCCESS) {
			interactive = 1;
			have_tty = 1;
		} else if (type == SSH_SMSG_FAILURE)
			logit("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. */
	display = getenv("DISPLAY");
	if (options.forward_x11 && display != NULL) {
		char *proto, *data;
		/* Get reasonable local authentication information. */
		client_x11_get_proto(display, options.xauth_location,
		    options.forward_x11_trusted, &proto, &data);
		/* Request forwarding with authentication spoofing. */
		debug("Requesting X11 forwarding with authentication "
		    "spoofing.");
		x11_request_forwarding_with_spoofing(0, display, proto, data);

		/* Read response from the server. */
		type = packet_read();
		if (type == SSH_SMSG_SUCCESS) {
			interactive = 1;
		} else if (type == SSH_SMSG_FAILURE) {
			logit("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);

	/* Request authentication agent forwarding if appropriate. */
	check_agent_present();

	if (options.forward_agent) {
		debug("Requesting authentication agent forwarding.");
		auth_request_forwarding();

		/* Read response from the server. */
		type = packet_read();
		packet_check_eom();
		if (type != SSH_SMSG_SUCCESS)
			logit("Warning: Remote host denied authentication agent forwarding.");
	}

	/* Initiate port forwardings. */
	ssh_init_forwarding();

	/* Execute a local command */
	if (options.local_command != NULL &&
	    options.permit_local_command)
		ssh_local_cmd(options.local_command);

	/*
	 * If requested and we are not interested in replies to remote
	 * forwarding requests, then let ssh continue in the background.
	 */
	if (fork_after_authentication_flag &&
	    (!options.exit_on_forward_failure ||
	    options.num_remote_forwards == 0)) {
		fork_after_authentication_flag = 0;
		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,
		    (u_char *)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 : SSH_ESCAPECHAR_NONE, 0);
}

/* request pty/x11/agent/tcpfwd/shell for channel */
static void
ssh_session2_setup(int id, int success, void *arg)
{
	extern char **environ;
	const char *display;
	int interactive = tty_flag;

	if (!success)
		return; /* No need for error message, channels code sens one */

	display = getenv("DISPLAY");
	if (options.forward_x11 && display != NULL) {
		char *proto, *data;
		/* Get reasonable local authentication information. */
		client_x11_get_proto(display, options.xauth_location,
		    options.forward_x11_trusted, &proto, &data);
		/* Request forwarding with authentication spoofing. */
		debug("Requesting X11 forwarding with authentication "
		    "spoofing.");
		x11_request_forwarding_with_spoofing(id, display, proto, data);
		interactive = 1;
		/* XXX wait for reply */
	}

	check_agent_present();
	if (options.forward_agent) {
		debug("Requesting authentication agent forwarding.");
		channel_request_start(id, "auth-agent-req@openssh.com", 0);
		packet_send();
	}

	client_session2_setup(id, tty_flag, subsystem_flag, getenv("TERM"),
	    NULL, fileno(stdin), &command, environ);

	packet_set_interactive(interactive);
}

/* open new channel for a session */
static int
ssh_session2_open(void)
{
	Channel *c;
	int window, packetmax, in, out, err;

	if (stdin_null_flag) {
		in = open(_PATH_DEVNULL, 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);

	window = CHAN_SES_WINDOW_DEFAULT;
	packetmax = CHAN_SES_PACKET_DEFAULT;
	if (tty_flag) {
		window >>= 1;
		packetmax >>= 1;
	}
	c = channel_new(
	    "session", SSH_CHANNEL_OPENING, in, out, err,
	    window, packetmax, CHAN_EXTENDED_WRITE,
	    "client-session", /*nonblock*/0);

	debug3("ssh_session2_open: channel_new: %d", c->self);

	channel_send_open(c->self);
	if (!no_shell_flag)
		channel_register_open_confirm(c->self,
		    ssh_session2_setup, NULL);

	return c->self;
}

static int
ssh_session2(void)
{
	int id = -1;

	/* XXX should be pre-session */
	ssh_init_forwarding();

	if (!no_shell_flag || (datafellows & SSH_BUG_DUMMYCHAN))
		id = ssh_session2_open();

	/* If we don't expect to open a new session, then disallow it */
	if (options.control_master == SSHCTL_MASTER_NO &&
	    (datafellows & SSH_NEW_OPENSSH)) {
		debug("Requesting no-more-sessions@openssh.com");
		packet_start(SSH2_MSG_GLOBAL_REQUEST);
		packet_put_cstring("no-more-sessions@openssh.com");
		packet_put_char(0);
		packet_send();
	}

	/* Execute a local command */
	if (options.local_command != NULL &&
	    options.permit_local_command)
		ssh_local_cmd(options.local_command);

	/* Start listening for multiplex clients */
	muxserver_listen();

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

	if (options.use_roaming)
		request_roaming();

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

static void
load_public_identity_files(void)
{
	char *filename, *cp, thishost[NI_MAXHOST];
	char *pwdir = NULL, *pwname = NULL;
	int i = 0;
	Key *public;
	struct passwd *pw;
	u_int n_ids;
	char *identity_files[SSH_MAX_IDENTITY_FILES];
	Key *identity_keys[SSH_MAX_IDENTITY_FILES];
#ifdef ENABLE_PKCS11
	Key **keys;
	int nkeys;
#endif /* PKCS11 */

	n_ids = 0;
	bzero(identity_files, sizeof(identity_files));
	bzero(identity_keys, sizeof(identity_keys));

#ifdef ENABLE_PKCS11
	if (options.pkcs11_provider != NULL &&
	    options.num_identity_files < SSH_MAX_IDENTITY_FILES &&
	    (pkcs11_init(!options.batch_mode) == 0) &&
	    (nkeys = pkcs11_add_provider(options.pkcs11_provider, NULL,
	    &keys)) > 0) {
		for (i = 0; i < nkeys; i++) {
			if (n_ids >= SSH_MAX_IDENTITY_FILES) {
				key_free(keys[i]);
				continue;
			}
			identity_keys[n_ids] = keys[i];
			identity_files[n_ids] =
			    xstrdup(options.pkcs11_provider); /* XXX */
			n_ids++;
		}
		xfree(keys);
	}
#endif /* ENABLE_PKCS11 */
	if ((pw = getpwuid(original_real_uid)) == NULL)
		fatal("load_public_identity_files: getpwuid failed");
	pwname = xstrdup(pw->pw_name);
	pwdir = xstrdup(pw->pw_dir);
	if (gethostname(thishost, sizeof(thishost)) == -1)
		fatal("load_public_identity_files: gethostname: %s",
		    strerror(errno));
	for (i = 0; i < options.num_identity_files; i++) {
		if (n_ids >= SSH_MAX_IDENTITY_FILES) {
			xfree(options.identity_files[i]);
			continue;
		}
		cp = tilde_expand_filename(options.identity_files[i],
		    original_real_uid);
		filename = percent_expand(cp, "d", pwdir,
		    "u", pwname, "l", thishost, "h", host,
		    "r", options.user, (char *)NULL);
		xfree(cp);
		public = key_load_public(filename, NULL);
		debug("identity file %s type %d", filename,
		    public ? public->type : -1);
		xfree(options.identity_files[i]);
		identity_files[n_ids] = filename;
		identity_keys[n_ids] = public;

		if (++n_ids >= SSH_MAX_IDENTITY_FILES)
			continue;

		/* Try to add the certificate variant too */
		xasprintf(&cp, "%s-cert", filename);
		public = key_load_public(cp, NULL);
		debug("identity file %s type %d", cp,
		    public ? public->type : -1);
		if (public == NULL) {
			xfree(cp);
			continue;
		}
		if (!key_is_cert(public)) {
			debug("%s: key %s type %s is not a certificate",
			    __func__, cp, key_type(public));
			key_free(public);
			xfree(cp);
			continue;
		}
		identity_keys[n_ids] = public;
		/* point to the original path, most likely the private key */
		identity_files[n_ids] = xstrdup(filename);
		n_ids++;
	}
	options.num_identity_files = n_ids;
	memcpy(options.identity_files, identity_files, sizeof(identity_files));
	memcpy(options.identity_keys, identity_keys, sizeof(identity_keys));

	bzero(pwname, strlen(pwname));
	xfree(pwname);
	bzero(pwdir, strlen(pwdir));
	xfree(pwdir);
}