- dtucker@cvs.openbsd.org 2010/01/11 01:39:46

[openssh-git.git] / ssh.c

/* $OpenBSD: ssh.c,v 1.331 2010/01/11 01:39:46 dtucker 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 SMARTCARD
#include "scard.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 identity_file] [-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 (strcmp(optarg, "check") == 0)
                                muxclient_command = SSHMUX_COMMAND_ALIVE_CHECK;
                        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 SMARTCARD
                        options.smartcard_device = xstrdup(optarg);
#else
                        fprintf(stderr, "no support for smartcards.\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 (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)
                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) {
                logit("Allocated port %u for remote forward to %s:%d",
                        packet_get_int(),
                        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;

        debug3("client_setup_stdio_fwd %s:%d", host_to_connect,
            port_to_connect);
        if ((c = channel_connect_stdio_fwd(host_to_connect, port_to_connect))
            == 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, void *arg)
{
        extern char **environ;
        const char *display;
        int interactive = tty_flag;

        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;
#ifdef SMARTCARD
        Key **keys;

        if (options.smartcard_device != NULL &&
            options.num_identity_files < SSH_MAX_IDENTITY_FILES &&
            (keys = sc_get_keys(options.smartcard_device, NULL)) != NULL) {
                int count = 0;
                for (i = 0; keys[i] != NULL; i++) {
                        count++;
                        memmove(&options.identity_files[1],
                            &options.identity_files[0],
                            sizeof(char *) * (SSH_MAX_IDENTITY_FILES - 1));
                        memmove(&options.identity_keys[1],
                            &options.identity_keys[0],
                            sizeof(Key *) * (SSH_MAX_IDENTITY_FILES - 1));
                        options.num_identity_files++;
                        options.identity_keys[0] = keys[i];
                        options.identity_files[0] = sc_get_key_label(keys[i]);
                }
                if (options.num_identity_files > SSH_MAX_IDENTITY_FILES)
                        options.num_identity_files = SSH_MAX_IDENTITY_FILES;
                i = count;
                xfree(keys);
        }
#endif /* SMARTCARD */
        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 < options.num_identity_files; i++) {
                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]);
                options.identity_files[i] = filename;
                options.identity_keys[i] = public;
        }
        bzero(pwname, strlen(pwname));
        xfree(pwname);
        bzero(pwdir, strlen(pwdir));
        xfree(pwdir);
}