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[dragonfly.git] / crypto / openssh / ssh.c

/* $OpenBSD: ssh.c,v 1.445 2016/07/17 04:20:16 djm 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/socket.h>
#include <sys/wait.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 <limits.h>
#include <locale.h>

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

#ifdef WITH_OPENSSL
#include <openssl/evp.h>
#include <openssl/err.h>
#endif
#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 "canohost.h"
#include "compat.h"
#include "cipher.h"
#include "digest.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 "misc.h"
#include "readconf.h"
#include "sshconnect.h"
#include "kex.h"
#include "mac.h"
#include "sshpty.h"
#include "match.h"
#include "msg.h"
#include "uidswap.h"
#include "version.h"
#include "ssherr.h"
#include "myproposal.h"

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

extern char *__progname;

/* Saves a copy of argv for setproctitle emulation */
#ifndef HAVE_SETPROCTITLE
static char **saved_av;
#endif

/* 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 requested */
int 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 the current process should be backgrounded and
 * a new slave launched in the foreground for ControlPersist.
 */
int need_controlpersist_detach = 0;

/* Copies of flags for ControlPersist foreground slave */
int ostdin_null_flag, ono_shell_flag, otty_flag, orequest_tty;

/*
 * 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;

/*
 * 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;

/* 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 [-1246AaCfGgKkMNnqsTtVvXxYy] [-b bind_address] [-c cipher_spec]\n"
"           [-D [bind_address:]port] [-E log_file] [-e escape_char]\n"
"           [-F configfile] [-I pkcs11] [-i identity_file]\n"
"           [-J [user@]host[:port]] [-L address] [-l login_name] [-m mac_spec]\n"
"           [-O ctl_cmd] [-o option] [-p port] [-Q query_option] [-R address]\n"
"           [-S ctl_path] [-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);
static void main_sigchld_handler(int);

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

/* ~/ expand a list of paths. NB. assumes path[n] is heap-allocated. */
static void
tilde_expand_paths(char **paths, u_int num_paths)
{
        u_int i;
        char *cp;

        for (i = 0; i < num_paths; i++) {
                cp = tilde_expand_filename(paths[i], original_real_uid);
                free(paths[i]);
                paths[i] = cp;
        }
}

/*
 * Attempt to resolve a host name / port to a set of addresses and
 * optionally return any CNAMEs encountered along the way.
 * Returns NULL on failure.
 * NB. this function must operate with a options having undefined members.
 */
static struct addrinfo *
resolve_host(const char *name, int port, int logerr, char *cname, size_t clen)
{
        char strport[NI_MAXSERV];
        struct addrinfo hints, *res;
        int gaierr, loglevel = SYSLOG_LEVEL_DEBUG1;

        if (port <= 0)
                port = default_ssh_port();

        snprintf(strport, sizeof strport, "%d", port);
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = options.address_family == -1 ?
            AF_UNSPEC : options.address_family;
        hints.ai_socktype = SOCK_STREAM;
        if (cname != NULL)
                hints.ai_flags = AI_CANONNAME;
        if ((gaierr = getaddrinfo(name, strport, &hints, &res)) != 0) {
                if (logerr || (gaierr != EAI_NONAME && gaierr != EAI_NODATA))
                        loglevel = SYSLOG_LEVEL_ERROR;
                do_log2(loglevel, "%s: Could not resolve hostname %.100s: %s",
                    __progname, name, ssh_gai_strerror(gaierr));
                return NULL;
        }
        if (cname != NULL && res->ai_canonname != NULL) {
                if (strlcpy(cname, res->ai_canonname, clen) >= clen) {
                        error("%s: host \"%s\" cname \"%s\" too long (max %lu)",
                            __func__, name,  res->ai_canonname, (u_long)clen);
                        if (clen > 0)
                                *cname = '\0';
                }
        }
        return res;
}

/*
 * Attempt to resolve a numeric host address / port to a single address.
 * Returns a canonical address string.
 * Returns NULL on failure.
 * NB. this function must operate with a options having undefined members.
 */
static struct addrinfo *
resolve_addr(const char *name, int port, char *caddr, size_t clen)
{
        char addr[NI_MAXHOST], strport[NI_MAXSERV];
        struct addrinfo hints, *res;
        int gaierr;

        if (port <= 0)
                port = default_ssh_port();
        snprintf(strport, sizeof strport, "%u", port);
        memset(&hints, 0, sizeof(hints));
        hints.ai_family = options.address_family == -1 ?
            AF_UNSPEC : options.address_family;
        hints.ai_socktype = SOCK_STREAM;
        hints.ai_flags = AI_NUMERICHOST|AI_NUMERICSERV;
        if ((gaierr = getaddrinfo(name, strport, &hints, &res)) != 0) {
                debug2("%s: could not resolve name %.100s as address: %s",
                    __func__, name, ssh_gai_strerror(gaierr));
                return NULL;
        }
        if (res == NULL) {
                debug("%s: getaddrinfo %.100s returned no addresses",
                 __func__, name);
                return NULL;
        }
        if (res->ai_next != NULL) {
                debug("%s: getaddrinfo %.100s returned multiple addresses",
                    __func__, name);
                goto fail;
        }
        if ((gaierr = getnameinfo(res->ai_addr, res->ai_addrlen,
            addr, sizeof(addr), NULL, 0, NI_NUMERICHOST)) != 0) {
                debug("%s: Could not format address for name %.100s: %s",
                    __func__, name, ssh_gai_strerror(gaierr));
                goto fail;
        }
        if (strlcpy(caddr, addr, clen) >= clen) {
                error("%s: host \"%s\" addr \"%s\" too long (max %lu)",
                    __func__, name,  addr, (u_long)clen);
                if (clen > 0)
                        *caddr = '\0';
 fail:
                freeaddrinfo(res);
                return NULL;
        }
        return res;
}

/*
 * Check whether the cname is a permitted replacement for the hostname
 * and perform the replacement if it is.
 * NB. this function must operate with a options having undefined members.
 */
static int
check_follow_cname(int direct, char **namep, const char *cname)
{
        int i;
        struct allowed_cname *rule;

        if (*cname == '\0' || options.num_permitted_cnames == 0 ||
            strcmp(*namep, cname) == 0)
                return 0;
        if (options.canonicalize_hostname == SSH_CANONICALISE_NO)
                return 0;
        /*
         * Don't attempt to canonicalize names that will be interpreted by
         * a proxy or jump host unless the user specifically requests so.
         */
        if (!direct &&
            options.canonicalize_hostname != SSH_CANONICALISE_ALWAYS)
                return 0;
        debug3("%s: check \"%s\" CNAME \"%s\"", __func__, *namep, cname);
        for (i = 0; i < options.num_permitted_cnames; i++) {
                rule = options.permitted_cnames + i;
                if (match_pattern_list(*namep, rule->source_list, 1) != 1 ||
                    match_pattern_list(cname, rule->target_list, 1) != 1)
                        continue;
                verbose("Canonicalized DNS aliased hostname "
                    "\"%s\" => \"%s\"", *namep, cname);
                free(*namep);
                *namep = xstrdup(cname);
                return 1;
        }
        return 0;
}

/*
 * Attempt to resolve the supplied hostname after applying the user's
 * canonicalization rules. Returns the address list for the host or NULL
 * if no name was found after canonicalization.
 * NB. this function must operate with a options having undefined members.
 */
static struct addrinfo *
resolve_canonicalize(char **hostp, int port)
{
        int i, direct, ndots;
        char *cp, *fullhost, newname[NI_MAXHOST];
        struct addrinfo *addrs;

        if (options.canonicalize_hostname == SSH_CANONICALISE_NO)
                return NULL;

        /*
         * Don't attempt to canonicalize names that will be interpreted by
         * a proxy unless the user specifically requests so.
         */
        direct = option_clear_or_none(options.proxy_command) &&
            options.jump_host == NULL;
        if (!direct &&
            options.canonicalize_hostname != SSH_CANONICALISE_ALWAYS)
                return NULL;

        /* Try numeric hostnames first */
        if ((addrs = resolve_addr(*hostp, port,
            newname, sizeof(newname))) != NULL) {
                debug2("%s: hostname %.100s is address", __func__, *hostp);
                if (strcasecmp(*hostp, newname) != 0) {
                        debug2("%s: canonicalised address \"%s\" => \"%s\"",
                            __func__, *hostp, newname);
                        free(*hostp);
                        *hostp = xstrdup(newname);
                }
                return addrs;
        }

        /* If domain name is anchored, then resolve it now */
        if ((*hostp)[strlen(*hostp) - 1] == '.') {
                debug3("%s: name is fully qualified", __func__);
                fullhost = xstrdup(*hostp);
                if ((addrs = resolve_host(fullhost, port, 0,
                    newname, sizeof(newname))) != NULL)
                        goto found;
                free(fullhost);
                goto notfound;
        }

        /* Don't apply canonicalization to sufficiently-qualified hostnames */
        ndots = 0;
        for (cp = *hostp; *cp != '\0'; cp++) {
                if (*cp == '.')
                        ndots++;
        }
        if (ndots > options.canonicalize_max_dots) {
                debug3("%s: not canonicalizing hostname \"%s\" (max dots %d)",
                    __func__, *hostp, options.canonicalize_max_dots);
                return NULL;
        }
        /* Attempt each supplied suffix */
        for (i = 0; i < options.num_canonical_domains; i++) {
                *newname = '\0';
                xasprintf(&fullhost, "%s.%s.", *hostp,
                    options.canonical_domains[i]);
                debug3("%s: attempting \"%s\" => \"%s\"", __func__,
                    *hostp, fullhost);
                if ((addrs = resolve_host(fullhost, port, 0,
                    newname, sizeof(newname))) == NULL) {
                        free(fullhost);
                        continue;
                }
 found:
                /* Remove trailing '.' */
                fullhost[strlen(fullhost) - 1] = '\0';
                /* Follow CNAME if requested */
                if (!check_follow_cname(direct, &fullhost, newname)) {
                        debug("Canonicalized hostname \"%s\" => \"%s\"",
                            *hostp, fullhost);
                }
                free(*hostp);
                *hostp = fullhost;
                return addrs;
        }
 notfound:
        if (!options.canonicalize_fallback_local)
                fatal("%s: Could not resolve host \"%s\"", __progname, *hostp);
        debug2("%s: host %s not found in any suffix", __func__, *hostp);
        return NULL;
}

/*
 * Read per-user configuration file.  Ignore the system wide config
 * file if the user specifies a config file on the command line.
 */
static void
process_config_files(const char *host_arg, struct passwd *pw, int post_canon)
{
        char buf[PATH_MAX];
        int r;

        if (config != NULL) {
                if (strcasecmp(config, "none") != 0 &&
                    !read_config_file(config, pw, host, host_arg, &options,
                    SSHCONF_USERCONF | (post_canon ? SSHCONF_POSTCANON : 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, pw, host, host_arg,
                            &options, SSHCONF_CHECKPERM | SSHCONF_USERCONF |
                            (post_canon ? SSHCONF_POSTCANON : 0));

                /* Read systemwide configuration file after user config. */
                (void)read_config_file(_PATH_HOST_CONFIG_FILE, pw,
                    host, host_arg, &options,
                    post_canon ? SSHCONF_POSTCANON : 0);
        }
}

/* Rewrite the port number in an addrinfo list of addresses */
static void
set_addrinfo_port(struct addrinfo *addrs, int port)
{
        struct addrinfo *addr;

        for (addr = addrs; addr != NULL; addr = addr->ai_next) {
                switch (addr->ai_family) {
                case AF_INET:
                        ((struct sockaddr_in *)addr->ai_addr)->
                            sin_port = htons(port);
                        break;
                case AF_INET6:
                        ((struct sockaddr_in6 *)addr->ai_addr)->
                            sin6_port = htons(port);
                        break;
                }
        }
}

/*
 * Main program for the ssh client.
 */
int
main(int ac, char **av)
{
        struct ssh *ssh = NULL;
        int i, r, opt, exit_status, use_syslog, direct, config_test = 0;
        char *p, *cp, *line, *argv0, buf[PATH_MAX], *host_arg, *logfile;
        char thishost[NI_MAXHOST], shorthost[NI_MAXHOST], portstr[NI_MAXSERV];
        char cname[NI_MAXHOST], uidstr[32], *conn_hash_hex;
        struct stat st;
        struct passwd *pw;
        int timeout_ms;
        extern int optind, optreset;
        extern char *optarg;
        struct Forward fwd;
        struct addrinfo *addrs = NULL;
        struct ssh_digest_ctx *md;
        u_char conn_hash[SSH_DIGEST_MAX_LENGTH];

        ssh_malloc_init();      /* must be called before any mallocs */
        /* Ensure that fds 0, 1 and 2 are open or directed to /dev/null */
        sanitise_stdfd();

        __progname = ssh_get_progname(av[0]);

#ifndef HAVE_SETPROCTITLE
        /* Prepare for later setproctitle emulation */
        /* Save argv so it isn't clobbered by setproctitle() emulation */
        saved_av = xcalloc(ac + 1, sizeof(*saved_av));
        for (i = 0; i < ac; i++)
                saved_av[i] = xstrdup(av[i]);
        saved_av[i] = NULL;
        compat_init_setproctitle(ac, av);
        av = saved_av;
#endif

        /*
         * Discard other fds that are hanging around. These can cause problem
         * with backgrounded ssh processes started by ControlPersist.
         */
        closefrom(STDERR_FILENO + 1);

        /*
         * 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("No user exists for uid %lu", (u_long)original_real_uid);
                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);

        setlocale(LC_CTYPE, "");

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

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

 again:
        while ((opt = getopt(ac, av, "1246ab:c:e:fgi:kl:m:no:p:qstvx"
            "ACD:E:F:GI:J:KL:MNO:PQ:R: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 'E':
                        logfile = optarg;
                        break;
                case 'G':
                        config_test = 1;
                        break;
                case 'Y':
                        options.forward_x11 = 1;
                        options.forward_x11_trusted = 1;
                        break;
                case 'g':
                        options.fwd_opts.gateway_ports = 1;
                        break;
                case 'O':
                        if (options.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 if (strcmp(optarg, "stop") == 0)
                                muxclient_command = SSHMUX_COMMAND_STOP;
                        else if (strcmp(optarg, "cancel") == 0)
                                muxclient_command = SSHMUX_COMMAND_CANCEL_FWD;
                        else
                                fatal("Invalid multiplex command.");
                        break;
                case 'P':       /* deprecated */
                        options.use_privileged_port = 0;
                        break;
                case 'Q':
                        cp = NULL;
                        if (strcmp(optarg, "cipher") == 0)
                                cp = cipher_alg_list('\n', 0);
                        else if (strcmp(optarg, "cipher-auth") == 0)
                                cp = cipher_alg_list('\n', 1);
                        else if (strcmp(optarg, "mac") == 0)
                                cp = mac_alg_list('\n');
                        else if (strcmp(optarg, "kex") == 0)
                                cp = kex_alg_list('\n');
                        else if (strcmp(optarg, "key") == 0)
                                cp = key_alg_list(0, 0);
                        else if (strcmp(optarg, "key-cert") == 0)
                                cp = key_alg_list(1, 0);
                        else if (strcmp(optarg, "key-plain") == 0)
                                cp = key_alg_list(0, 1);
                        else if (strcmp(optarg, "protocol-version") == 0) {
#ifdef WITH_SSH1
                                cp = xstrdup("1\n2");
#else
                                cp = xstrdup("2");
#endif
                        }
                        if (cp == NULL)
                                fatal("Unsupported query \"%s\"", optarg);
                        printf("%s\n", cp);
                        free(cp);
                        exit(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':
                        p = tilde_expand_filename(optarg, original_real_uid);
                        if (stat(p, &st) < 0)
                                fprintf(stderr, "Warning: Identity file %s "
                                    "not accessible: %s.\n", p,
                                    strerror(errno));
                        else
                                add_identity_file(&options, NULL, p, 1);
                        free(p);
                        break;
                case 'I':
#ifdef ENABLE_PKCS11
                        free(options.pkcs11_provider);
                        options.pkcs11_provider = xstrdup(optarg);
#else
                        fprintf(stderr, "no support for PKCS#11.\n");
#endif
                        break;
                case 'J':
                        if (options.jump_host != NULL)
                                fatal("Only a single -J option permitted");
                        if (options.proxy_command != NULL)
                                fatal("Cannot specify -J with ProxyCommand");
                        if (parse_jump(optarg, &options, 1) == -1)
                                fatal("Invalid -J argument");
                        options.proxy_command = xstrdup("none");
                        break;
                case 't':
                        if (options.request_tty == REQUEST_TTY_YES)
                                options.request_tty = REQUEST_TTY_FORCE;
                        else
                                options.request_tty = REQUEST_TTY_YES;
                        break;
                case 'v':
                        if (debug_flag == 0) {
                                debug_flag = 1;
                                options.log_level = SYSLOG_LEVEL_DEBUG1;
                        } else {
                                if (options.log_level < SYSLOG_LEVEL_DEBUG3) {
                                        debug_flag++;
                                        options.log_level++;
                                }
                        }
                        break;
                case 'V':
                        fprintf(stderr, "%s, %s\n",
                            SSH_RELEASE,
#ifdef WITH_OPENSSL
                            SSLeay_version(SSLEAY_VERSION)
#else
                            "without OpenSSL"
#endif
                        );
                        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 (options.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)) {
                                options.stdio_forward_host = fwd.listen_host;
                                options.stdio_forward_port = fwd.listen_port;
                                free(fwd.connect_host);
                        } else {
                                fprintf(stderr,
                                    "Bad stdio forwarding specification '%s'\n",
                                    optarg);
                                exit(255);
                        }
                        options.request_tty = REQUEST_TTY_NO;
                        no_shell_flag = 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 == '+' ?
                            optarg + 1 : optarg)) {
                                /* SSH2 only */
                                free(options.ciphers);
                                options.ciphers = xstrdup(optarg);
                                options.cipher = SSH_CIPHER_INVALID;
                                break;
                        }
                        /* 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 = xstrdup("3des-cbc");
                        else if (options.cipher == SSH_CIPHER_BLOWFISH)
                                options.ciphers = xstrdup("blowfish-cbc");
                        else
                                options.ciphers = xstrdup(KEX_CLIENT_ENCRYPT);
                        break;
                case 'm':
                        if (mac_valid(optarg)) {
                                free(options.macs);
                                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;
                        options.request_tty = REQUEST_TTY_NO;
                        break;
                case 'T':
                        options.request_tty = REQUEST_TTY_NO;
                        break;
                case 'o':
                        line = xstrdup(optarg);
                        if (process_config_line(&options, pw,
                            host ? host : "", host ? host : "", line,
                            "command-line", 0, NULL, SSHCONF_USERCONF) != 0)
                                exit(255);
                        free(line);
                        break;
                case 's':
                        subsystem_flag = 1;
                        break;
                case 'S':
                        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 = xstrdup(++cp);
                } else
                        host = xstrdup(*av);
                if (ac > 1) {
                        optind = optreset = 1;
                        goto again;
                }
                ac--, av++;
        }

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

        host_arg = xstrdup(host);

#ifdef WITH_OPENSSL
        OpenSSL_add_all_algorithms();
        ERR_load_crypto_strings();
#endif

        /* 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. */
                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.");

        /*
         * Initialize "log" output.  Since we are the client all output
         * goes to stderr unless otherwise specified by -y or -E.
         */
        if (use_syslog && logfile != NULL)
                fatal("Can't specify both -y and -E");
        if (logfile != NULL)
                log_redirect_stderr_to(logfile);
        log_init(argv0,
            options.log_level == -1 ? SYSLOG_LEVEL_INFO : options.log_level,
            SYSLOG_FACILITY_USER, !use_syslog);

        if (debug_flag)
                logit("%s, %s", SSH_RELEASE,
#ifdef WITH_OPENSSL
                    SSLeay_version(SSLEAY_VERSION)
#else
                    "without OpenSSL"
#endif
                );

        /* Parse the configuration files */
        process_config_files(host_arg, pw, 0);

        /* Hostname canonicalisation needs a few options filled. */
        fill_default_options_for_canonicalization(&options);

        /* If the user has replaced the hostname then take it into use now */
        if (options.hostname != NULL) {
                /* NB. Please keep in sync with readconf.c:match_cfg_line() */
                cp = percent_expand(options.hostname,
                    "h", host, (char *)NULL);
                free(host);
                host = cp;
                free(options.hostname);
                options.hostname = xstrdup(host);
        }

        /* If canonicalization requested then try to apply it */
        lowercase(host);
        if (options.canonicalize_hostname != SSH_CANONICALISE_NO)
                addrs = resolve_canonicalize(&host, options.port);

        /*
         * If CanonicalizePermittedCNAMEs have been specified but
         * other canonicalization did not happen (by not being requested
         * or by failing with fallback) then the hostname may still be changed
         * as a result of CNAME following. 
         *
         * Try to resolve the bare hostname name using the system resolver's
         * usual search rules and then apply the CNAME follow rules.
         *
         * Skip the lookup if a ProxyCommand is being used unless the user
         * has specifically requested canonicalisation for this case via
         * CanonicalizeHostname=always
         */
        direct = option_clear_or_none(options.proxy_command) &&
            options.jump_host == NULL;
        if (addrs == NULL && options.num_permitted_cnames != 0 && (direct ||
            options.canonicalize_hostname == SSH_CANONICALISE_ALWAYS)) {
                if ((addrs = resolve_host(host, options.port,
                    option_clear_or_none(options.proxy_command),
                    cname, sizeof(cname))) == NULL) {
                        /* Don't fatal proxied host names not in the DNS */
                        if (option_clear_or_none(options.proxy_command))
                                cleanup_exit(255); /* logged in resolve_host */
                } else
                        check_follow_cname(direct, &host, cname);
        }

        /*
         * If canonicalisation is enabled then re-parse the configuration
         * files as new stanzas may match.
         */
        if (options.canonicalize_hostname != 0) {
                debug("Re-reading configuration after hostname "
                    "canonicalisation");
                free(options.hostname);
                options.hostname = xstrdup(host);
                process_config_files(host_arg, pw, 1);
                /*
                 * Address resolution happens early with canonicalisation
                 * enabled and the port number may have changed since, so
                 * reset it in address list
                 */
                if (addrs != NULL && options.port > 0)
                        set_addrinfo_port(addrs, options.port);
        }

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

        /*
         * If ProxyJump option specified, then construct a ProxyCommand now.
         */
        if (options.jump_host != NULL) {
                char port_s[8];

                /* Consistency check */
                if (options.proxy_command != NULL)
                        fatal("inconsistent options: ProxyCommand+ProxyJump");
                /* Never use FD passing for ProxyJump */
                options.proxy_use_fdpass = 0;
                snprintf(port_s, sizeof(port_s), "%d", options.jump_port);
                xasprintf(&options.proxy_command,
                    "ssh%s%s%s%s%s%s%s%s%s%.*s -W %%h:%%p %s",
                    /* Optional "-l user" argument if jump_user set */
                    options.jump_user == NULL ? "" : " -l ",
                    options.jump_user == NULL ? "" : options.jump_user,
                    /* Optional "-p port" argument if jump_port set */
                    options.jump_port <= 0 ? "" : " -p ",
                    options.jump_port <= 0 ? "" : port_s,
                    /* Optional additional jump hosts ",..." */
                    options.jump_extra == NULL ? "" : " -J ",
                    options.jump_extra == NULL ? "" : options.jump_extra,
                    /* Optional "-F" argumment if -F specified */
                    config == NULL ? "" : " -F ",
                    config == NULL ? "" : config,
                    /* Optional "-v" arguments if -v set */
                    debug_flag ? " -" : "",
                    debug_flag, "vvv",
                    /* Mandatory hostname */
                    options.jump_host);
                debug("Setting implicit ProxyCommand from ProxyJump: %s",
                    options.proxy_command);
        }

        if (options.port == 0)
                options.port = default_ssh_port();
        channel_set_af(options.address_family);

        /* Tidy and check options */
        if (options.host_key_alias != NULL)
                lowercase(options.host_key_alias);
        if (options.proxy_command != NULL &&
            strcmp(options.proxy_command, "-") == 0 &&
            options.proxy_use_fdpass)
                fatal("ProxyCommand=- and ProxyUseFDPass are incompatible");
        if (options.control_persist &&
            options.update_hostkeys == SSH_UPDATE_HOSTKEYS_ASK) {
                debug("UpdateHostKeys=ask is incompatible with ControlPersist; "
                    "disabling");
                options.update_hostkeys = 0;
        }
        if (options.connection_attempts <= 0)
                fatal("Invalid number of ConnectionAttempts");
#ifndef HAVE_CYGWIN
        if (original_effective_uid != 0)
                options.use_privileged_port = 0;
#endif

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

        if (options.request_tty == REQUEST_TTY_YES ||
            options.request_tty == REQUEST_TTY_FORCE)
                tty_flag = 1;

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

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

        seed_rng();

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

        if (gethostname(thishost, sizeof(thishost)) == -1)
                fatal("gethostname: %s", strerror(errno));
        strlcpy(shorthost, thishost, sizeof(shorthost));
        shorthost[strcspn(thishost, ".")] = '\0';
        snprintf(portstr, sizeof(portstr), "%d", options.port);
        snprintf(uidstr, sizeof(uidstr), "%d", pw->pw_uid);

        if ((md = ssh_digest_start(SSH_DIGEST_SHA1)) == NULL ||
            ssh_digest_update(md, thishost, strlen(thishost)) < 0 ||
            ssh_digest_update(md, host, strlen(host)) < 0 ||
            ssh_digest_update(md, portstr, strlen(portstr)) < 0 ||
            ssh_digest_update(md, options.user, strlen(options.user)) < 0 ||
            ssh_digest_final(md, conn_hash, sizeof(conn_hash)) < 0)
                fatal("%s: mux digest failed", __func__);
        ssh_digest_free(md);
        conn_hash_hex = tohex(conn_hash, ssh_digest_bytes(SSH_DIGEST_SHA1));

        if (options.local_command != NULL) {
                debug3("expanding LocalCommand: %s", options.local_command);
                cp = options.local_command;
                options.local_command = percent_expand(cp,
                    "C", conn_hash_hex,
                    "L", shorthost,
                    "d", pw->pw_dir,
                    "h", host,
                    "l", thishost,
                    "n", host_arg,
                    "p", portstr,
                    "r", options.user,
                    "u", pw->pw_name,
                    (char *)NULL);
                debug3("expanded LocalCommand: %s", options.local_command);
                free(cp);
        }

        if (options.control_path != NULL) {
                cp = tilde_expand_filename(options.control_path,
                    original_real_uid);
                free(options.control_path);
                options.control_path = percent_expand(cp,
                    "C", conn_hash_hex,
                    "L", shorthost,
                    "h", host,
                    "l", thishost,
                    "n", host_arg,
                    "p", portstr,
                    "r", options.user,
                    "u", pw->pw_name,
                    "i", uidstr,
                    (char *)NULL);
                free(cp);
        }
        free(conn_hash_hex);

        if (config_test) {
                dump_client_config(&options, host);
                exit(0);
        }

        if (muxclient_command != 0 && options.control_path == NULL)
                fatal("No ControlPath specified for \"-O\" command");
        if (options.control_path != NULL)
                muxclient(options.control_path);

        /*
         * If hostname canonicalisation was not enabled, then we may not
         * have yet resolved the hostname. Do so now.
         */
        if (addrs == NULL && options.proxy_command == NULL) {
                debug2("resolving \"%s\" port %d", host, options.port);
                if ((addrs = resolve_host(host, options.port, 1,
                    cname, sizeof(cname))) == NULL)
                        cleanup_exit(255); /* resolve_host logs the error */
        }

        timeout_ms = options.connection_timeout * 1000;

        /* Open a connection to the remote host. */
        if (ssh_connect(host, addrs, &hostaddr, options.port,
            options.address_family, options.connection_attempts,
            &timeout_ms, options.tcp_keep_alive,
            options.use_privileged_port) != 0)
                exit(255);

        if (addrs != NULL)
                freeaddrinfo(addrs);

        packet_set_timeout(options.server_alive_interval,
            options.server_alive_count_max);

        ssh = active_state; /* XXX */

        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 = 9;
                sensitive_data.keys = xcalloc(sensitive_data.nkeys,
                    sizeof(Key));
                for (i = 0; i < sensitive_data.nkeys; i++)
                        sensitive_data.keys[i] = NULL;

                PRIV_START;
#if WITH_SSH1
                sensitive_data.keys[0] = key_load_private_type(KEY_RSA1,
                    _PATH_HOST_KEY_FILE, "", NULL, NULL);
#endif
#ifdef OPENSSL_HAS_ECC
                sensitive_data.keys[1] = key_load_private_cert(KEY_ECDSA,
                    _PATH_HOST_ECDSA_KEY_FILE, "", NULL);
#endif
                sensitive_data.keys[2] = key_load_private_cert(KEY_ED25519,
                    _PATH_HOST_ED25519_KEY_FILE, "", NULL);
                sensitive_data.keys[3] = key_load_private_cert(KEY_RSA,
                    _PATH_HOST_RSA_KEY_FILE, "", NULL);
                sensitive_data.keys[4] = key_load_private_cert(KEY_DSA,
                    _PATH_HOST_DSA_KEY_FILE, "", NULL);
#ifdef OPENSSL_HAS_ECC
                sensitive_data.keys[5] = key_load_private_type(KEY_ECDSA,
                    _PATH_HOST_ECDSA_KEY_FILE, "", NULL, NULL);
#endif
                sensitive_data.keys[6] = key_load_private_type(KEY_ED25519,
                    _PATH_HOST_ED25519_KEY_FILE, "", NULL, NULL);
                sensitive_data.keys[7] = key_load_private_type(KEY_RSA,
                    _PATH_HOST_RSA_KEY_FILE, "", NULL, NULL);
                sensitive_data.keys[8] = key_load_private_type(KEY_DSA,
                    _PATH_HOST_DSA_KEY_FILE, "", NULL, NULL);
                PRIV_END;

                if (options.hostbased_authentication == 1 &&
                    sensitive_data.keys[0] == NULL &&
                    sensitive_data.keys[5] == NULL &&
                    sensitive_data.keys[6] == NULL &&
                    sensitive_data.keys[7] == NULL &&
                    sensitive_data.keys[8] == NULL) {
#ifdef OPENSSL_HAS_ECC
                        sensitive_data.keys[1] = key_load_cert(
                            _PATH_HOST_ECDSA_KEY_FILE);
#endif
                        sensitive_data.keys[2] = key_load_cert(
                            _PATH_HOST_ED25519_KEY_FILE);
                        sensitive_data.keys[3] = key_load_cert(
                            _PATH_HOST_RSA_KEY_FILE);
                        sensitive_data.keys[4] = key_load_cert(
                            _PATH_HOST_DSA_KEY_FILE);
#ifdef OPENSSL_HAS_ECC
                        sensitive_data.keys[5] = key_load_public(
                            _PATH_HOST_ECDSA_KEY_FILE, NULL);
#endif
                        sensitive_data.keys[6] = key_load_public(
                            _PATH_HOST_ED25519_KEY_FILE, NULL);
                        sensitive_data.keys[7] = key_load_public(
                            _PATH_HOST_RSA_KEY_FILE, NULL);
                        sensitive_data.keys[8] = key_load_public(
                            _PATH_HOST_DSA_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.
         */
        if (config == NULL) {
                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) {
#ifdef WITH_SELINUX
                        ssh_selinux_setfscreatecon(buf);
#endif
                        if (mkdir(buf, 0700) < 0)
                                error("Could not create directory '%.200s'.",
                                    buf);
#ifdef WITH_SELINUX
                        ssh_selinux_setfscreatecon(NULL);
#endif
                }
        }
        /* load options.identity_files */
        load_public_identity_files();

        /* optionally set the SSH_AUTHSOCKET_ENV_NAME varibale */
        if (options.identity_agent &&
            strcmp(options.identity_agent, SSH_AUTHSOCKET_ENV_NAME) != 0) {
                if (strcmp(options.identity_agent, "none") == 0) {
                        unsetenv(SSH_AUTHSOCKET_ENV_NAME);
                } else {
                        p = tilde_expand_filename(options.identity_agent,
                            original_real_uid);
                        cp = percent_expand(p, "d", pw->pw_dir,
                            "u", pw->pw_name, "l", thishost, "h", host,
                            "r", options.user, (char *)NULL);
                        setenv(SSH_AUTHSOCKET_ENV_NAME, cp, 1);
                        free(cp);
                        free(p);
                }
        }

        /* Expand ~ in known host file names. */
        tilde_expand_paths(options.system_hostfiles,
            options.num_system_hostfiles);
        tilde_expand_paths(options.user_hostfiles, options.num_user_hostfiles);

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

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

        if (packet_connection_is_on_socket()) {
                verbose("Authenticated to %s ([%s]:%d).", host,
                    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
        } else {
                verbose("Authenticated to %s (via proxy).", host);
        }

        /* 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;
                        }
                }
                free(sensitive_data.keys);
        }
        for (i = 0; i < options.num_identity_files; i++) {
                free(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;
                }
        }
        for (i = 0; i < options.num_certificate_files; i++) {
                free(options.certificate_files[i]);
                options.certificate_files[i] = NULL;
        }

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

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

        /* Kill ProxyCommand if it is running. */
        ssh_kill_proxy_command();

        return exit_status;
}

static void
control_persist_detach(void)
{
        pid_t pid;
        int devnull, keep_stderr;

        debug("%s: backgrounding master process", __func__);

        /*
         * master (current process) into the background, and make the
         * foreground process a client of the backgrounded master.
         */
        switch ((pid = fork())) {
        case -1:
                fatal("%s: fork: %s", __func__, strerror(errno));
        case 0:
                /* Child: master process continues mainloop */
                break;
        default:
                /* Parent: set up mux slave to connect to backgrounded master */
                debug2("%s: background process is %ld", __func__, (long)pid);
                stdin_null_flag = ostdin_null_flag;
                options.request_tty = orequest_tty;
                tty_flag = otty_flag;
                close(muxserver_sock);
                muxserver_sock = -1;
                options.control_master = SSHCTL_MASTER_NO;
                muxclient(options.control_path);
                /* muxclient() doesn't return on success. */
                fatal("Failed to connect to new control master");
        }
        if ((devnull = open(_PATH_DEVNULL, O_RDWR)) == -1) {
                error("%s: open(\"/dev/null\"): %s", __func__,
                    strerror(errno));
        } else {
                keep_stderr = log_is_on_stderr() && debug_flag;
                if (dup2(devnull, STDIN_FILENO) == -1 ||
                    dup2(devnull, STDOUT_FILENO) == -1 ||
                    (!keep_stderr && dup2(devnull, STDERR_FILENO) == -1))
                        error("%s: dup2: %s", __func__, strerror(errno));
                if (devnull > STDERR_FILENO)
                        close(devnull);
        }
        daemon(1, 1);
        setproctitle("%s [mux]", options.control_path);
}

/* Do fork() after authentication. Used by "ssh -f" */
static void
fork_postauth(void)
{
        if (need_controlpersist_detach)
                control_persist_detach();
        debug("forking to background");
        fork_after_authentication_flag = 0;
        if (daemon(1, 1) < 0)
                fatal("daemon() failed: %.200s", strerror(errno));
}

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

        /* XXX verbose() on failure? */
        debug("remote forward %s for: listen %s%s%d, connect %s:%d",
            type == SSH2_MSG_REQUEST_SUCCESS ? "success" : "failure",
            rfwd->listen_path ? rfwd->listen_path :
            rfwd->listen_host ? rfwd->listen_host : "",
            (rfwd->listen_path || rfwd->listen_host) ? ":" : "",
            rfwd->listen_port, rfwd->connect_path ? rfwd->connect_path :
            rfwd->connect_host, rfwd->connect_port);
        if (rfwd->listen_path == NULL && rfwd->listen_port == 0) {
                if (type == SSH2_MSG_REQUEST_SUCCESS) {
                        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);
                        channel_update_permitted_opens(rfwd->handle,
                            rfwd->allocated_port);
                } else {
                        channel_update_permitted_opens(rfwd->handle, -1);
                }
        }
        
        if (type == SSH2_MSG_REQUEST_FAILURE) {
                if (options.exit_on_forward_failure) {
                        if (rfwd->listen_path != NULL)
                                fatal("Error: remote port forwarding failed "
                                    "for listen path %s", rfwd->listen_path);
                        else
                                fatal("Error: remote port forwarding failed "
                                    "for listen port %d", rfwd->listen_port);
                } else {
                        if (rfwd->listen_path != NULL)
                                logit("Warning: remote port forwarding failed "
                                    "for listen path %s", rfwd->listen_path);
                        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_postauth();
        }
}

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

static void
ssh_stdio_confirm(int id, int success, void *arg)
{
        if (!success)
                fatal("stdio forwarding failed");
}

static void
ssh_init_stdio_forwarding(void)
{
        Channel *c;
        int in, out;

        if (options.stdio_forward_host == NULL)
                return;
        if (!compat20)
                fatal("stdio forwarding require Protocol 2");

        debug3("%s: %s:%d", __func__, options.stdio_forward_host,
            options.stdio_forward_port);

        if ((in = dup(STDIN_FILENO)) < 0 ||
            (out = dup(STDOUT_FILENO)) < 0)
                fatal("channel_connect_stdio_fwd: dup() in/out failed");
        if ((c = channel_connect_stdio_fwd(options.stdio_forward_host,
            options.stdio_forward_port, in, out)) == NULL)
                fatal("%s: channel_connect_stdio_fwd failed", __func__);
        channel_register_cleanup(c->self, client_cleanup_stdio_fwd, 0);
        channel_register_open_confirm(c->self, ssh_stdio_confirm, NULL);
}

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

        /* 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_path != NULL) ?
                    options.local_forwards[i].listen_path :
                    (options.local_forwards[i].listen_host == NULL) ?
                    (options.fwd_opts.gateway_ports ? "*" : "LOCALHOST") :
                    options.local_forwards[i].listen_host,
                    options.local_forwards[i].listen_port,
                    (options.local_forwards[i].connect_path != NULL) ?
                    options.local_forwards[i].connect_path :
                    options.local_forwards[i].connect_host,
                    options.local_forwards[i].connect_port);
                success += channel_setup_local_fwd_listener(
                    &options.local_forwards[i], &options.fwd_opts);
        }
        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_path != NULL) ?
                    options.remote_forwards[i].listen_path :
                    (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_path != NULL) ?
                    options.remote_forwards[i].connect_path :
                    options.remote_forwards[i].connect_host,
                    options.remote_forwards[i].connect_port);
                options.remote_forwards[i].handle =
                    channel_request_remote_forwarding(
                    &options.remote_forwards[i]);
                if (options.remote_forwards[i].handle < 0) {
                        if (options.exit_on_forward_failure)
                                fatal("Could not request remote forwarding.");
                        else
                                logit("Warning: Could not request remote "
                                    "forwarding.");
                } else {
                        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)
{
        int r;

        if (options.forward_agent) {
                /* Clear agent forwarding if we don't have an agent. */
                if ((r = ssh_get_authentication_socket(NULL)) != 0) {
                        options.forward_agent = 0;
                        if (r != SSH_ERR_AGENT_NOT_PRESENT)
                                debug("ssh_get_authentication_socket: %s",
                                    ssh_err(r));
                }
        }
}

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

        /* 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 (display == NULL && options.forward_x11)
                debug("X11 forwarding requested but DISPLAY not set");
        if (options.forward_x11 && client_x11_get_proto(display,
            options.xauth_location, options.forward_x11_trusted,
            options.forward_x11_timeout, &proto, &data) == 0) {
                /* Request forwarding with authentication spoofing. */
                debug("Requesting X11 forwarding with authentication "
                    "spoofing.");
                x11_request_forwarding_with_spoofing(0, display, proto,
                    data, 0);
                /* 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,
            options.ip_qos_interactive, options.ip_qos_bulk);

        /* 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_stdio_forwarding();
        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) {
                if (options.exit_on_forward_failure &&
                    options.num_remote_forwards > 0) {
                        debug("deferring postauth fork until remote forward "
                            "confirmation received");
                } else
                        fork_postauth();
        }

        /*
         * 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;
        char *proto = NULL, *data = NULL;

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

        display = getenv("DISPLAY");
        if (display == NULL && options.forward_x11)
                debug("X11 forwarding requested but DISPLAY not set");
        if (options.forward_x11 && client_x11_get_proto(display,
            options.xauth_location, options.forward_x11_trusted,
            options.forward_x11_timeout, &proto, &data) == 0) {
                /* Request forwarding with authentication spoofing. */
                debug("Requesting X11 forwarding with authentication "
                    "spoofing.");
                x11_request_forwarding_with_spoofing(id, display, proto,
                    data, 1);
                client_expect_confirm(id, "X11 forwarding", CONFIRM_WARN);
                /* XXX exit_on_forward_failure */
                interactive = 1;
        }

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

        /* Tell the packet module whether this is an interactive session. */
        packet_set_interactive(interactive,
            options.ip_qos_interactive, options.ip_qos_bulk);

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

/* 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 */
        if (!options.control_persist)
                ssh_init_stdio_forwarding();
        ssh_init_forwarding();

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

        /*
         * If we are in control persist mode and have a working mux listen
         * socket, then prepare to background ourselves and have a foreground
         * client attach as a control slave.
         * NB. we must save copies of the flags that we override for
         * the backgrounding, since we defer attachment of the slave until
         * after the connection is fully established (in particular,
         * async rfwd replies have been received for ExitOnForwardFailure).
         */
        if (options.control_persist && muxserver_sock != -1) {
                ostdin_null_flag = stdin_null_flag;
                ono_shell_flag = no_shell_flag;
                orequest_tty = options.request_tty;
                otty_flag = tty_flag;
                stdin_null_flag = 1;
                no_shell_flag = 1;
                tty_flag = 0;
                if (!fork_after_authentication_flag)
                        need_controlpersist_detach = 1;
                fork_after_authentication_flag = 1;
        }
        /*
         * ControlPersist mux listen socket setup failed, attempt the
         * stdio forward setup that we skipped earlier.
         */
        if (options.control_persist && muxserver_sock == -1)
                ssh_init_stdio_forwarding();

        if (!no_shell_flag || (datafellows & SSH_BUG_DUMMYCHAN))
                id = ssh_session2_open();
        else {
                packet_set_interactive(
                    options.control_master == SSHCTL_MASTER_NO,
                    options.ip_qos_interactive, options.ip_qos_bulk);
        }

        /* 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);

        /*
         * 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) {
                if (options.exit_on_forward_failure &&
                    options.num_remote_forwards > 0) {
                        debug("deferring postauth fork until remote forward "
                            "confirmation received");
                } else
                        fork_postauth();
        }

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

/* Loads all IdentityFile and CertificateFile keys */
static void
load_public_identity_files(void)
{
        char *filename, *cp, thishost[NI_MAXHOST];
        char *pwdir = NULL, *pwname = NULL;
        Key *public;
        struct passwd *pw;
        int i;
        u_int n_ids, n_certs;
        char *identity_files[SSH_MAX_IDENTITY_FILES];
        Key *identity_keys[SSH_MAX_IDENTITY_FILES];
        char *certificate_files[SSH_MAX_CERTIFICATE_FILES];
        struct sshkey *certificates[SSH_MAX_CERTIFICATE_FILES];
#ifdef ENABLE_PKCS11
        Key **keys;
        int nkeys;
#endif /* PKCS11 */

        n_ids = n_certs = 0;
        memset(identity_files, 0, sizeof(identity_files));
        memset(identity_keys, 0, sizeof(identity_keys));
        memset(certificate_files, 0, sizeof(certificate_files));
        memset(certificates, 0, sizeof(certificates));

#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++;
                }
                free(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 ||
                    strcasecmp(options.identity_files[i], "none") == 0) {
                        free(options.identity_files[i]);
                        options.identity_files[i] = NULL;
                        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);
                free(cp);
                public = key_load_public(filename, NULL);
                debug("identity file %s type %d", filename,
                    public ? public->type : -1);
                free(options.identity_files[i]);
                identity_files[n_ids] = filename;
                identity_keys[n_ids] = public;

                if (++n_ids >= SSH_MAX_IDENTITY_FILES)
                        continue;

                /*
                 * If no certificates have been explicitly listed then try
                 * to add the default certificate variant too.
                 */
                if (options.num_certificate_files != 0)
                        continue;
                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) {
                        free(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);
                        free(cp);
                        continue;
                }
                identity_keys[n_ids] = public;
                identity_files[n_ids] = cp;
                n_ids++;
        }

        if (options.num_certificate_files > SSH_MAX_CERTIFICATE_FILES)
                fatal("%s: too many certificates", __func__);
        for (i = 0; i < options.num_certificate_files; i++) {
                cp = tilde_expand_filename(options.certificate_files[i],
                    original_real_uid);
                filename = percent_expand(cp, "d", pwdir,
                    "u", pwname, "l", thishost, "h", host,
                    "r", options.user, (char *)NULL);
                free(cp);

                public = key_load_public(filename, NULL);
                debug("certificate file %s type %d", filename,
                    public ? public->type : -1);
                free(options.certificate_files[i]);
                options.certificate_files[i] = NULL;
                if (public == NULL) {
                        free(filename);
                        continue;
                }
                if (!key_is_cert(public)) {
                        debug("%s: key %s type %s is not a certificate",
                            __func__, filename, key_type(public));
                        key_free(public);
                        free(filename);
                        continue;
                }
                certificate_files[n_certs] = filename;
                certificates[n_certs] = public;
                ++n_certs;
        }

        options.num_identity_files = n_ids;
        memcpy(options.identity_files, identity_files, sizeof(identity_files));
        memcpy(options.identity_keys, identity_keys, sizeof(identity_keys));

        options.num_certificate_files = n_certs;
        memcpy(options.certificate_files,
            certificate_files, sizeof(certificate_files));
        memcpy(options.certificates, certificates, sizeof(certificates));

        explicit_bzero(pwname, strlen(pwname));
        free(pwname);
        explicit_bzero(pwdir, strlen(pwdir));
        free(pwdir);
}

static void
main_sigchld_handler(int sig)
{
        int save_errno = errno;
        pid_t pid;
        int status;

        while ((pid = waitpid(-1, &status, WNOHANG)) > 0 ||
            (pid < 0 && errno == EINTR))
                ;

        signal(sig, main_sigchld_handler);
        errno = save_errno;
}