inet6: only mark autoconf addresses tentative if detached

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

/* $OpenBSD: sshd.c,v 1.591 2022/09/17 10:34:29 djm Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * This program is the ssh daemon.  It listens for connections from clients,
 * and performs authentication, executes use commands or shell, and forwards
 * information to/from the application to the user client over an encrypted
 * connection.  This can also handle forwarding of X11, TCP/IP, and
 * authentication agent 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".
 *
 * SSH2 implementation:
 * Privilege Separation:
 *
 * Copyright (c) 2000, 2001, 2002 Markus Friedl.  All rights reserved.
 * Copyright (c) 2002 Niels Provos.  All rights reserved.
 *
 * 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>
#include <sys/ioctl.h>
#include <sys/socket.h>
#ifdef HAVE_SYS_STAT_H
# include <sys/stat.h>
#endif
#ifdef HAVE_SYS_TIME_H
# include <sys/time.h>
#endif
#include "openbsd-compat/sys-tree.h"
#include "openbsd-compat/sys-queue.h"
#include <sys/wait.h>

#include <errno.h>
#include <fcntl.h>
#include <netdb.h>
#ifdef HAVE_PATHS_H
#include <paths.h>
#endif
#include <grp.h>
#ifdef HAVE_POLL_H
#include <poll.h>
#endif
#include <pwd.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <limits.h>

#ifdef WITH_OPENSSL
#include <openssl/dh.h>
#include <openssl/bn.h>
#include <openssl/rand.h>
#include "openbsd-compat/openssl-compat.h"
#endif

#ifdef HAVE_SECUREWARE
#include <sys/security.h>
#include <prot.h>
#endif

#include "xmalloc.h"
#include "ssh.h"
#include "ssh2.h"
#include "sshpty.h"
#include "packet.h"
#include "log.h"
#include "sshbuf.h"
#include "misc.h"
#include "match.h"
#include "servconf.h"
#include "uidswap.h"
#include "compat.h"
#include "cipher.h"
#include "digest.h"
#include "sshkey.h"
#include "kex.h"
#include "myproposal.h"
#include "authfile.h"
#include "pathnames.h"
#include "atomicio.h"
#include "canohost.h"
#include "hostfile.h"
#include "auth.h"
#include "authfd.h"
#include "msg.h"
#include "dispatch.h"
#include "channels.h"
#include "session.h"
#include "monitor.h"
#ifdef GSSAPI
#include "ssh-gss.h"
#endif
#include "monitor_wrap.h"
#include "ssh-sandbox.h"
#include "auth-options.h"
#include "version.h"
#include "ssherr.h"
#include "sk-api.h"
#include "srclimit.h"
#include "dh.h"

/* Re-exec fds */
#define REEXEC_DEVCRYPTO_RESERVED_FD    (STDERR_FILENO + 1)
#define REEXEC_STARTUP_PIPE_FD          (STDERR_FILENO + 2)
#define REEXEC_CONFIG_PASS_FD           (STDERR_FILENO + 3)
#define REEXEC_MIN_FREE_FD              (STDERR_FILENO + 4)

extern char *__progname;

/* Server configuration options. */
ServerOptions options;

/* Name of the server configuration file. */
char *config_file_name = _PATH_SERVER_CONFIG_FILE;

/*
 * Debug mode flag.  This can be set on the command line.  If debug
 * mode is enabled, extra debugging output will be sent to the system
 * log, the daemon will not go to background, and will exit after processing
 * the first connection.
 */
int debug_flag = 0;

/*
 * Indicating that the daemon should only test the configuration and keys.
 * If test_flag > 1 ("-T" flag), then sshd will also dump the effective
 * configuration, optionally using connection information provided by the
 * "-C" flag.
 */
static int test_flag = 0;

/* Flag indicating that the daemon is being started from inetd. */
static int inetd_flag = 0;

/* Flag indicating that sshd should not detach and become a daemon. */
static int no_daemon_flag = 0;

/* debug goes to stderr unless inetd_flag is set */
static int log_stderr = 0;

/* Saved arguments to main(). */
static char **saved_argv;
static int saved_argc;

/* re-exec */
static int rexeced_flag = 0;
static int rexec_flag = 1;
static int rexec_argc = 0;
static char **rexec_argv;

/*
 * The sockets that the server is listening; this is used in the SIGHUP
 * signal handler.
 */
#define MAX_LISTEN_SOCKS        16
static int listen_socks[MAX_LISTEN_SOCKS];
static int num_listen_socks = 0;

/* Daemon's agent connection */
int auth_sock = -1;
static int have_agent = 0;

/*
 * Any really sensitive data in the application is contained in this
 * structure. The idea is that this structure could be locked into memory so
 * that the pages do not get written into swap.  However, there are some
 * problems. The private key contains BIGNUMs, and we do not (in principle)
 * have access to the internals of them, and locking just the structure is
 * not very useful.  Currently, memory locking is not implemented.
 */
struct {
        struct sshkey   **host_keys;            /* all private host keys */
        struct sshkey   **host_pubkeys;         /* all public host keys */
        struct sshkey   **host_certificates;    /* all public host certificates */
        int             have_ssh2_key;
} sensitive_data;

/* This is set to true when a signal is received. */
static volatile sig_atomic_t received_sighup = 0;
static volatile sig_atomic_t received_sigterm = 0;

/* record remote hostname or ip */
u_int utmp_len = HOST_NAME_MAX+1;

/*
 * startup_pipes/flags are used for tracking children of the listening sshd
 * process early in their lifespans. This tracking is needed for three things:
 *
 * 1) Implementing the MaxStartups limit of concurrent unauthenticated
 *    connections.
 * 2) Avoiding a race condition for SIGHUP processing, where child processes
 *    may have listen_socks open that could collide with main listener process
 *    after it restarts.
 * 3) Ensuring that rexec'd sshd processes have received their initial state
 *    from the parent listen process before handling SIGHUP.
 *
 * Child processes signal that they have completed closure of the listen_socks
 * and (if applicable) received their rexec state by sending a char over their
 * sock. Child processes signal that authentication has completed by closing
 * the sock (or by exiting).
 */
static int *startup_pipes = NULL;
static int *startup_flags = NULL;       /* Indicates child closed listener */
static int startup_pipe = -1;           /* in child */

/* variables used for privilege separation */
int use_privsep = -1;
struct monitor *pmonitor = NULL;
int privsep_is_preauth = 1;
static int privsep_chroot = 1;

/* global connection state and authentication contexts */
Authctxt *the_authctxt = NULL;
struct ssh *the_active_state;

/* global key/cert auth options. XXX move to permanent ssh->authctxt? */
struct sshauthopt *auth_opts = NULL;

/* sshd_config buffer */
struct sshbuf *cfg;

/* Included files from the configuration file */
struct include_list includes = TAILQ_HEAD_INITIALIZER(includes);

/* message to be displayed after login */
struct sshbuf *loginmsg;

/* Unprivileged user */
struct passwd *privsep_pw = NULL;

/* Prototypes for various functions defined later in this file. */
void destroy_sensitive_data(void);
void demote_sensitive_data(void);
static void do_ssh2_kex(struct ssh *);

static char *listener_proctitle;

/*
 * Close all listening sockets
 */
static void
close_listen_socks(void)
{
        int i;

        for (i = 0; i < num_listen_socks; i++)
                close(listen_socks[i]);
        num_listen_socks = 0;
}

static void
close_startup_pipes(void)
{
        int i;

        if (startup_pipes)
                for (i = 0; i < options.max_startups; i++)
                        if (startup_pipes[i] != -1)
                                close(startup_pipes[i]);
}

/*
 * Signal handler for SIGHUP.  Sshd execs itself when it receives SIGHUP;
 * the effect is to reread the configuration file (and to regenerate
 * the server key).
 */

/*ARGSUSED*/
static void
sighup_handler(int sig)
{
        received_sighup = 1;
}

/*
 * Called from the main program after receiving SIGHUP.
 * Restarts the server.
 */
static void
sighup_restart(void)
{
        logit("Received SIGHUP; restarting.");
        if (options.pid_file != NULL)
                unlink(options.pid_file);
        platform_pre_restart();
        close_listen_socks();
        close_startup_pipes();
        ssh_signal(SIGHUP, SIG_IGN); /* will be restored after exec */
        execv(saved_argv[0], saved_argv);
        logit("RESTART FAILED: av[0]='%.100s', error: %.100s.", saved_argv[0],
            strerror(errno));
        exit(1);
}

/*
 * Generic signal handler for terminating signals in the master daemon.
 */
/*ARGSUSED*/
static void
sigterm_handler(int sig)
{
        received_sigterm = sig;
}

/*
 * SIGCHLD handler.  This is called whenever a child dies.  This will then
 * reap any zombies left by exited children.
 */
/*ARGSUSED*/
static void
main_sigchld_handler(int sig)
{
        int save_errno = errno;
        pid_t pid;
        int status;

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

/*
 * Signal handler for the alarm after the login grace period has expired.
 */
/*ARGSUSED*/
static void
grace_alarm_handler(int sig)
{
        /*
         * Try to kill any processes that we have spawned, E.g. authorized
         * keys command helpers or privsep children.
         */
        if (getpgid(0) == getpid()) {
                ssh_signal(SIGTERM, SIG_IGN);
                kill(0, SIGTERM);
        }

        /* Log error and exit. */
        sigdie("Timeout before authentication for %s port %d",
            ssh_remote_ipaddr(the_active_state),
            ssh_remote_port(the_active_state));
}

/* Destroy the host and server keys.  They will no longer be needed. */
void
destroy_sensitive_data(void)
{
        u_int i;

        for (i = 0; i < options.num_host_key_files; i++) {
                if (sensitive_data.host_keys[i]) {
                        sshkey_free(sensitive_data.host_keys[i]);
                        sensitive_data.host_keys[i] = NULL;
                }
                if (sensitive_data.host_certificates[i]) {
                        sshkey_free(sensitive_data.host_certificates[i]);
                        sensitive_data.host_certificates[i] = NULL;
                }
        }
}

/* Demote private to public keys for network child */
void
demote_sensitive_data(void)
{
        struct sshkey *tmp;
        u_int i;
        int r;

        for (i = 0; i < options.num_host_key_files; i++) {
                if (sensitive_data.host_keys[i]) {
                        if ((r = sshkey_from_private(
                            sensitive_data.host_keys[i], &tmp)) != 0)
                                fatal_r(r, "could not demote host %s key",
                                    sshkey_type(sensitive_data.host_keys[i]));
                        sshkey_free(sensitive_data.host_keys[i]);
                        sensitive_data.host_keys[i] = tmp;
                }
                /* Certs do not need demotion */
        }
}

static void
reseed_prngs(void)
{
        u_int32_t rnd[256];

#ifdef WITH_OPENSSL
        RAND_poll();
#endif
        arc4random_stir(); /* noop on recent arc4random() implementations */
        arc4random_buf(rnd, sizeof(rnd)); /* let arc4random notice PID change */

#ifdef WITH_OPENSSL
        RAND_seed(rnd, sizeof(rnd));
        /* give libcrypto a chance to notice the PID change */
        if ((RAND_bytes((u_char *)rnd, 1)) != 1)
                fatal("%s: RAND_bytes failed", __func__);
#endif

        explicit_bzero(rnd, sizeof(rnd));
}

static void
privsep_preauth_child(void)
{
        gid_t gidset[1];

        /* Enable challenge-response authentication for privilege separation */
        privsep_challenge_enable();

#ifdef GSSAPI
        /* Cache supported mechanism OIDs for later use */
        ssh_gssapi_prepare_supported_oids();
#endif

        reseed_prngs();

        /* Demote the private keys to public keys. */
        demote_sensitive_data();

        /* Demote the child */
        if (privsep_chroot) {
                /* Change our root directory */
                if (chroot(_PATH_PRIVSEP_CHROOT_DIR) == -1)
                        fatal("chroot(\"%s\"): %s", _PATH_PRIVSEP_CHROOT_DIR,
                            strerror(errno));
                if (chdir("/") == -1)
                        fatal("chdir(\"/\"): %s", strerror(errno));

                /* Drop our privileges */
                debug3("privsep user:group %u:%u", (u_int)privsep_pw->pw_uid,
                    (u_int)privsep_pw->pw_gid);
                gidset[0] = privsep_pw->pw_gid;
                if (setgroups(1, gidset) == -1)
                        fatal("setgroups: %.100s", strerror(errno));
                permanently_set_uid(privsep_pw);
        }
}

static int
privsep_preauth(struct ssh *ssh)
{
        int status, r;
        pid_t pid;
        struct ssh_sandbox *box = NULL;

        /* Set up unprivileged child process to deal with network data */
        pmonitor = monitor_init();
        /* Store a pointer to the kex for later rekeying */
        pmonitor->m_pkex = &ssh->kex;

        if (use_privsep == PRIVSEP_ON)
                box = ssh_sandbox_init(pmonitor);
        pid = fork();
        if (pid == -1) {
                fatal("fork of unprivileged child failed");
        } else if (pid != 0) {
                debug2("Network child is on pid %ld", (long)pid);

                pmonitor->m_pid = pid;
                if (have_agent) {
                        r = ssh_get_authentication_socket(&auth_sock);
                        if (r != 0) {
                                error_r(r, "Could not get agent socket");
                                have_agent = 0;
                        }
                }
                if (box != NULL)
                        ssh_sandbox_parent_preauth(box, pid);
                monitor_child_preauth(ssh, pmonitor);

                /* Wait for the child's exit status */
                while (waitpid(pid, &status, 0) == -1) {
                        if (errno == EINTR)
                                continue;
                        pmonitor->m_pid = -1;
                        fatal_f("waitpid: %s", strerror(errno));
                }
                privsep_is_preauth = 0;
                pmonitor->m_pid = -1;
                if (WIFEXITED(status)) {
                        if (WEXITSTATUS(status) != 0)
                                fatal_f("preauth child exited with status %d",
                                    WEXITSTATUS(status));
                } else if (WIFSIGNALED(status))
                        fatal_f("preauth child terminated by signal %d",
                            WTERMSIG(status));
                if (box != NULL)
                        ssh_sandbox_parent_finish(box);
                return 1;
        } else {
                /* child */
                close(pmonitor->m_sendfd);
                close(pmonitor->m_log_recvfd);

                /* Arrange for logging to be sent to the monitor */
                set_log_handler(mm_log_handler, pmonitor);

                privsep_preauth_child();
                setproctitle("%s", "[net]");
                if (box != NULL)
                        ssh_sandbox_child(box);

                return 0;
        }
}

static void
privsep_postauth(struct ssh *ssh, Authctxt *authctxt)
{
#ifdef DISABLE_FD_PASSING
        if (1) {
#else
        if (authctxt->pw->pw_uid == 0) {
#endif
                /* File descriptor passing is broken or root login */
                use_privsep = 0;
                goto skip;
        }

        /* New socket pair */
        monitor_reinit(pmonitor);

        pmonitor->m_pid = fork();
        if (pmonitor->m_pid == -1)
                fatal("fork of unprivileged child failed");
        else if (pmonitor->m_pid != 0) {
                verbose("User child is on pid %ld", (long)pmonitor->m_pid);
                sshbuf_reset(loginmsg);
                monitor_clear_keystate(ssh, pmonitor);
                monitor_child_postauth(ssh, pmonitor);

                /* NEVERREACHED */
                exit(0);
        }

        /* child */

        close(pmonitor->m_sendfd);
        pmonitor->m_sendfd = -1;

        /* Demote the private keys to public keys. */
        demote_sensitive_data();

        reseed_prngs();

        /* Drop privileges */
        do_setusercontext(authctxt->pw);

 skip:
        /* It is safe now to apply the key state */
        monitor_apply_keystate(ssh, pmonitor);

        /*
         * Tell the packet layer that authentication was successful, since
         * this information is not part of the key state.
         */
        ssh_packet_set_authenticated(ssh);
}

static void
append_hostkey_type(struct sshbuf *b, const char *s)
{
        int r;

        if (match_pattern_list(s, options.hostkeyalgorithms, 0) != 1) {
                debug3_f("%s key not permitted by HostkeyAlgorithms", s);
                return;
        }
        if ((r = sshbuf_putf(b, "%s%s", sshbuf_len(b) > 0 ? "," : "", s)) != 0)
                fatal_fr(r, "sshbuf_putf");
}

static char *
list_hostkey_types(void)
{
        struct sshbuf *b;
        struct sshkey *key;
        char *ret;
        u_int i;

        if ((b = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        for (i = 0; i < options.num_host_key_files; i++) {
                key = sensitive_data.host_keys[i];
                if (key == NULL)
                        key = sensitive_data.host_pubkeys[i];
                if (key == NULL)
                        continue;
                switch (key->type) {
                case KEY_RSA:
                        /* for RSA we also support SHA2 signatures */
                        append_hostkey_type(b, "rsa-sha2-512");
                        append_hostkey_type(b, "rsa-sha2-256");
                        /* FALLTHROUGH */
                case KEY_DSA:
                case KEY_ECDSA:
                case KEY_ED25519:
                case KEY_ECDSA_SK:
                case KEY_ED25519_SK:
                case KEY_XMSS:
                        append_hostkey_type(b, sshkey_ssh_name(key));
                        break;
                }
                /* If the private key has a cert peer, then list that too */
                key = sensitive_data.host_certificates[i];
                if (key == NULL)
                        continue;
                switch (key->type) {
                case KEY_RSA_CERT:
                        /* for RSA we also support SHA2 signatures */
                        append_hostkey_type(b,
                            "rsa-sha2-512-cert-v01@openssh.com");
                        append_hostkey_type(b,
                            "rsa-sha2-256-cert-v01@openssh.com");
                        /* FALLTHROUGH */
                case KEY_DSA_CERT:
                case KEY_ECDSA_CERT:
                case KEY_ED25519_CERT:
                case KEY_ECDSA_SK_CERT:
                case KEY_ED25519_SK_CERT:
                case KEY_XMSS_CERT:
                        append_hostkey_type(b, sshkey_ssh_name(key));
                        break;
                }
        }
        if ((ret = sshbuf_dup_string(b)) == NULL)
                fatal_f("sshbuf_dup_string failed");
        sshbuf_free(b);
        debug_f("%s", ret);
        return ret;
}

static struct sshkey *
get_hostkey_by_type(int type, int nid, int need_private, struct ssh *ssh)
{
        u_int i;
        struct sshkey *key;

        for (i = 0; i < options.num_host_key_files; i++) {
                switch (type) {
                case KEY_RSA_CERT:
                case KEY_DSA_CERT:
                case KEY_ECDSA_CERT:
                case KEY_ED25519_CERT:
                case KEY_ECDSA_SK_CERT:
                case KEY_ED25519_SK_CERT:
                case KEY_XMSS_CERT:
                        key = sensitive_data.host_certificates[i];
                        break;
                default:
                        key = sensitive_data.host_keys[i];
                        if (key == NULL && !need_private)
                                key = sensitive_data.host_pubkeys[i];
                        break;
                }
                if (key == NULL || key->type != type)
                        continue;
                switch (type) {
                case KEY_ECDSA:
                case KEY_ECDSA_SK:
                case KEY_ECDSA_CERT:
                case KEY_ECDSA_SK_CERT:
                        if (key->ecdsa_nid != nid)
                                continue;
                        /* FALLTHROUGH */
                default:
                        return need_private ?
                            sensitive_data.host_keys[i] : key;
                }
        }
        return NULL;
}

struct sshkey *
get_hostkey_public_by_type(int type, int nid, struct ssh *ssh)
{
        return get_hostkey_by_type(type, nid, 0, ssh);
}

struct sshkey *
get_hostkey_private_by_type(int type, int nid, struct ssh *ssh)
{
        return get_hostkey_by_type(type, nid, 1, ssh);
}

struct sshkey *
get_hostkey_by_index(int ind)
{
        if (ind < 0 || (u_int)ind >= options.num_host_key_files)
                return (NULL);
        return (sensitive_data.host_keys[ind]);
}

struct sshkey *
get_hostkey_public_by_index(int ind, struct ssh *ssh)
{
        if (ind < 0 || (u_int)ind >= options.num_host_key_files)
                return (NULL);
        return (sensitive_data.host_pubkeys[ind]);
}

int
get_hostkey_index(struct sshkey *key, int compare, struct ssh *ssh)
{
        u_int i;

        for (i = 0; i < options.num_host_key_files; i++) {
                if (sshkey_is_cert(key)) {
                        if (key == sensitive_data.host_certificates[i] ||
                            (compare && sensitive_data.host_certificates[i] &&
                            sshkey_equal(key,
                            sensitive_data.host_certificates[i])))
                                return (i);
                } else {
                        if (key == sensitive_data.host_keys[i] ||
                            (compare && sensitive_data.host_keys[i] &&
                            sshkey_equal(key, sensitive_data.host_keys[i])))
                                return (i);
                        if (key == sensitive_data.host_pubkeys[i] ||
                            (compare && sensitive_data.host_pubkeys[i] &&
                            sshkey_equal(key, sensitive_data.host_pubkeys[i])))
                                return (i);
                }
        }
        return (-1);
}

/* Inform the client of all hostkeys */
static void
notify_hostkeys(struct ssh *ssh)
{
        struct sshbuf *buf;
        struct sshkey *key;
        u_int i, nkeys;
        int r;
        char *fp;

        /* Some clients cannot cope with the hostkeys message, skip those. */
        if (ssh->compat & SSH_BUG_HOSTKEYS)
                return;

        if ((buf = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new");
        for (i = nkeys = 0; i < options.num_host_key_files; i++) {
                key = get_hostkey_public_by_index(i, ssh);
                if (key == NULL || key->type == KEY_UNSPEC ||
                    sshkey_is_cert(key))
                        continue;
                fp = sshkey_fingerprint(key, options.fingerprint_hash,
                    SSH_FP_DEFAULT);
                debug3_f("key %d: %s %s", i, sshkey_ssh_name(key), fp);
                free(fp);
                if (nkeys == 0) {
                        /*
                         * Start building the request when we find the
                         * first usable key.
                         */
                        if ((r = sshpkt_start(ssh, SSH2_MSG_GLOBAL_REQUEST)) != 0 ||
                            (r = sshpkt_put_cstring(ssh, "hostkeys-00@openssh.com")) != 0 ||
                            (r = sshpkt_put_u8(ssh, 0)) != 0) /* want reply */
                                sshpkt_fatal(ssh, r, "%s: start request", __func__);
                }
                /* Append the key to the request */
                sshbuf_reset(buf);
                if ((r = sshkey_putb(key, buf)) != 0)
                        fatal_fr(r, "couldn't put hostkey %d", i);
                if ((r = sshpkt_put_stringb(ssh, buf)) != 0)
                        sshpkt_fatal(ssh, r, "%s: append key", __func__);
                nkeys++;
        }
        debug3_f("sent %u hostkeys", nkeys);
        if (nkeys == 0)
                fatal_f("no hostkeys");
        if ((r = sshpkt_send(ssh)) != 0)
                sshpkt_fatal(ssh, r, "%s: send", __func__);
        sshbuf_free(buf);
}

/*
 * returns 1 if connection should be dropped, 0 otherwise.
 * dropping starts at connection #max_startups_begin with a probability
 * of (max_startups_rate/100). the probability increases linearly until
 * all connections are dropped for startups > max_startups
 */
static int
should_drop_connection(int startups)
{
        int p, r;

        if (startups < options.max_startups_begin)
                return 0;
        if (startups >= options.max_startups)
                return 1;
        if (options.max_startups_rate == 100)
                return 1;

        p  = 100 - options.max_startups_rate;
        p *= startups - options.max_startups_begin;
        p /= options.max_startups - options.max_startups_begin;
        p += options.max_startups_rate;
        r = arc4random_uniform(100);

        debug_f("p %d, r %d", p, r);
        return (r < p) ? 1 : 0;
}

/*
 * Check whether connection should be accepted by MaxStartups.
 * Returns 0 if the connection is accepted. If the connection is refused,
 * returns 1 and attempts to send notification to client.
 * Logs when the MaxStartups condition is entered or exited, and periodically
 * while in that state.
 */
static int
drop_connection(int sock, int startups, int notify_pipe)
{
        char *laddr, *raddr;
        const char msg[] = "Exceeded MaxStartups\r\n";
        static time_t last_drop, first_drop;
        static u_int ndropped;
        LogLevel drop_level = SYSLOG_LEVEL_VERBOSE;
        time_t now;

        now = monotime();
        if (!should_drop_connection(startups) &&
            srclimit_check_allow(sock, notify_pipe) == 1) {
                if (last_drop != 0 &&
                    startups < options.max_startups_begin - 1) {
                        /* XXX maybe need better hysteresis here */
                        logit("exited MaxStartups throttling after %s, "
                            "%u connections dropped",
                            fmt_timeframe(now - first_drop), ndropped);
                        last_drop = 0;
                }
                return 0;
        }

#define SSHD_MAXSTARTUPS_LOG_INTERVAL   (5 * 60)
        if (last_drop == 0) {
                error("beginning MaxStartups throttling");
                drop_level = SYSLOG_LEVEL_INFO;
                first_drop = now;
                ndropped = 0;
        } else if (last_drop + SSHD_MAXSTARTUPS_LOG_INTERVAL < now) {
                /* Periodic logs */
                error("in MaxStartups throttling for %s, "
                    "%u connections dropped",
                    fmt_timeframe(now - first_drop), ndropped + 1);
                drop_level = SYSLOG_LEVEL_INFO;
        }
        last_drop = now;
        ndropped++;

        laddr = get_local_ipaddr(sock);
        raddr = get_peer_ipaddr(sock);
        do_log2(drop_level, "drop connection #%d from [%s]:%d on [%s]:%d "
            "past MaxStartups", startups, raddr, get_peer_port(sock),
            laddr, get_local_port(sock));
        free(laddr);
        free(raddr);
        /* best-effort notification to client */
        (void)write(sock, msg, sizeof(msg) - 1);
        return 1;
}

static void
usage(void)
{
        fprintf(stderr, "%s, %s\n", SSH_RELEASE, SSH_OPENSSL_VERSION);
        fprintf(stderr,
"usage: sshd [-46DdeiqTt] [-C connection_spec] [-c host_cert_file]\n"
"            [-E log_file] [-f config_file] [-g login_grace_time]\n"
"            [-h host_key_file] [-o option] [-p port] [-u len]\n"
        );
        exit(1);
}

static void
send_rexec_state(int fd, struct sshbuf *conf)
{
        struct sshbuf *m = NULL, *inc = NULL;
        struct include_item *item = NULL;
        int r;

        debug3_f("entering fd = %d config len %zu", fd,
            sshbuf_len(conf));

        if ((m = sshbuf_new()) == NULL || (inc = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");

        /* pack includes into a string */
        TAILQ_FOREACH(item, &includes, entry) {
                if ((r = sshbuf_put_cstring(inc, item->selector)) != 0 ||
                    (r = sshbuf_put_cstring(inc, item->filename)) != 0 ||
                    (r = sshbuf_put_stringb(inc, item->contents)) != 0)
                        fatal_fr(r, "compose includes");
        }

        /*
         * Protocol from reexec master to child:
         *      string  configuration
         *      string  included_files[] {
         *              string  selector
         *              string  filename
         *              string  contents
         *      }
         *      string  rng_seed (if required)
         */
        if ((r = sshbuf_put_stringb(m, conf)) != 0 ||
            (r = sshbuf_put_stringb(m, inc)) != 0)
                fatal_fr(r, "compose config");
#if defined(WITH_OPENSSL) && !defined(OPENSSL_PRNG_ONLY)
        rexec_send_rng_seed(m);
#endif
        if (ssh_msg_send(fd, 0, m) == -1)
                error_f("ssh_msg_send failed");

        sshbuf_free(m);
        sshbuf_free(inc);

        debug3_f("done");
}

static void
recv_rexec_state(int fd, struct sshbuf *conf)
{
        struct sshbuf *m, *inc;
        u_char *cp, ver;
        size_t len;
        int r;
        struct include_item *item;

        debug3_f("entering fd = %d", fd);

        if ((m = sshbuf_new()) == NULL || (inc = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if (ssh_msg_recv(fd, m) == -1)
                fatal_f("ssh_msg_recv failed");
        if ((r = sshbuf_get_u8(m, &ver)) != 0)
                fatal_fr(r, "parse version");
        if (ver != 0)
                fatal_f("rexec version mismatch");
        if ((r = sshbuf_get_string(m, &cp, &len)) != 0 ||
            (r = sshbuf_get_stringb(m, inc)) != 0)
                fatal_fr(r, "parse config");

#if defined(WITH_OPENSSL) && !defined(OPENSSL_PRNG_ONLY)
        rexec_recv_rng_seed(m);
#endif

        if (conf != NULL && (r = sshbuf_put(conf, cp, len)))
                fatal_fr(r, "sshbuf_put");

        while (sshbuf_len(inc) != 0) {
                item = xcalloc(1, sizeof(*item));
                if ((item->contents = sshbuf_new()) == NULL)
                        fatal_f("sshbuf_new failed");
                if ((r = sshbuf_get_cstring(inc, &item->selector, NULL)) != 0 ||
                    (r = sshbuf_get_cstring(inc, &item->filename, NULL)) != 0 ||
                    (r = sshbuf_get_stringb(inc, item->contents)) != 0)
                        fatal_fr(r, "parse includes");
                TAILQ_INSERT_TAIL(&includes, item, entry);
        }

        free(cp);
        sshbuf_free(m);

        debug3_f("done");
}

/* Accept a connection from inetd */
static void
server_accept_inetd(int *sock_in, int *sock_out)
{
        if (rexeced_flag) {
                close(REEXEC_CONFIG_PASS_FD);
                *sock_in = *sock_out = dup(STDIN_FILENO);
        } else {
                *sock_in = dup(STDIN_FILENO);
                *sock_out = dup(STDOUT_FILENO);
        }
        /*
         * We intentionally do not close the descriptors 0, 1, and 2
         * as our code for setting the descriptors won't work if
         * ttyfd happens to be one of those.
         */
        if (stdfd_devnull(1, 1, !log_stderr) == -1)
                error_f("stdfd_devnull failed");
        debug("inetd sockets after dupping: %d, %d", *sock_in, *sock_out);
}

/*
 * Listen for TCP connections
 */
static void
listen_on_addrs(struct listenaddr *la)
{
        int ret, listen_sock;
        struct addrinfo *ai;
        char ntop[NI_MAXHOST], strport[NI_MAXSERV];

        for (ai = la->addrs; ai; ai = ai->ai_next) {
                if (ai->ai_family != AF_INET && ai->ai_family != AF_INET6)
                        continue;
                if (num_listen_socks >= MAX_LISTEN_SOCKS)
                        fatal("Too many listen sockets. "
                            "Enlarge MAX_LISTEN_SOCKS");
                if ((ret = getnameinfo(ai->ai_addr, ai->ai_addrlen,
                    ntop, sizeof(ntop), strport, sizeof(strport),
                    NI_NUMERICHOST|NI_NUMERICSERV)) != 0) {
                        error("getnameinfo failed: %.100s",
                            ssh_gai_strerror(ret));
                        continue;
                }
                /* Create socket for listening. */
                listen_sock = socket(ai->ai_family, ai->ai_socktype,
                    ai->ai_protocol);
                if (listen_sock == -1) {
                        /* kernel may not support ipv6 */
                        verbose("socket: %.100s", strerror(errno));
                        continue;
                }
                if (set_nonblock(listen_sock) == -1) {
                        close(listen_sock);
                        continue;
                }
                if (fcntl(listen_sock, F_SETFD, FD_CLOEXEC) == -1) {
                        verbose("socket: CLOEXEC: %s", strerror(errno));
                        close(listen_sock);
                        continue;
                }
                /* Socket options */
                set_reuseaddr(listen_sock);
                if (la->rdomain != NULL &&
                    set_rdomain(listen_sock, la->rdomain) == -1) {
                        close(listen_sock);
                        continue;
                }

                /* Only communicate in IPv6 over AF_INET6 sockets. */
                if (ai->ai_family == AF_INET6)
                        sock_set_v6only(listen_sock);

                debug("Bind to port %s on %s.", strport, ntop);

                /* Bind the socket to the desired port. */
                if (bind(listen_sock, ai->ai_addr, ai->ai_addrlen) == -1) {
                        error("Bind to port %s on %s failed: %.200s.",
                            strport, ntop, strerror(errno));
                        close(listen_sock);
                        continue;
                }
                listen_socks[num_listen_socks] = listen_sock;
                num_listen_socks++;

                /* Start listening on the port. */
                if (listen(listen_sock, SSH_LISTEN_BACKLOG) == -1)
                        fatal("listen on [%s]:%s: %.100s",
                            ntop, strport, strerror(errno));
                logit("Server listening on %s port %s%s%s.",
                    ntop, strport,
                    la->rdomain == NULL ? "" : " rdomain ",
                    la->rdomain == NULL ? "" : la->rdomain);
        }
}

static void
server_listen(void)
{
        u_int i;

        /* Initialise per-source limit tracking. */
        srclimit_init(options.max_startups, options.per_source_max_startups,
            options.per_source_masklen_ipv4, options.per_source_masklen_ipv6);

        for (i = 0; i < options.num_listen_addrs; i++) {
                listen_on_addrs(&options.listen_addrs[i]);
                freeaddrinfo(options.listen_addrs[i].addrs);
                free(options.listen_addrs[i].rdomain);
                memset(&options.listen_addrs[i], 0,
                    sizeof(options.listen_addrs[i]));
        }
        free(options.listen_addrs);
        options.listen_addrs = NULL;
        options.num_listen_addrs = 0;

        if (!num_listen_socks)
                fatal("Cannot bind any address.");
}

/*
 * The main TCP accept loop. Note that, for the non-debug case, returns
 * from this function are in a forked subprocess.
 */
static void
server_accept_loop(int *sock_in, int *sock_out, int *newsock, int *config_s)
{
        struct pollfd *pfd = NULL;
        int i, j, ret, npfd;
        int ostartups = -1, startups = 0, listening = 0, lameduck = 0;
        int startup_p[2] = { -1 , -1 }, *startup_pollfd;
        char c = 0;
        struct sockaddr_storage from;
        socklen_t fromlen;
        pid_t pid;
        u_char rnd[256];
        sigset_t nsigset, osigset;

        /* pipes connected to unauthenticated child sshd processes */
        startup_pipes = xcalloc(options.max_startups, sizeof(int));
        startup_flags = xcalloc(options.max_startups, sizeof(int));
        startup_pollfd = xcalloc(options.max_startups, sizeof(int));
        for (i = 0; i < options.max_startups; i++)
                startup_pipes[i] = -1;

        /*
         * Prepare signal mask that we use to block signals that might set
         * received_sigterm or received_sighup, so that we are guaranteed
         * to immediately wake up the ppoll if a signal is received after
         * the flag is checked.
         */
        sigemptyset(&nsigset);
        sigaddset(&nsigset, SIGHUP);
        sigaddset(&nsigset, SIGCHLD);
        sigaddset(&nsigset, SIGTERM);
        sigaddset(&nsigset, SIGQUIT);

        /* sized for worst-case */
        pfd = xcalloc(num_listen_socks + options.max_startups,
            sizeof(struct pollfd));

        /*
         * Stay listening for connections until the system crashes or
         * the daemon is killed with a signal.
         */
        for (;;) {
                sigprocmask(SIG_BLOCK, &nsigset, &osigset);
                if (received_sigterm) {
                        logit("Received signal %d; terminating.",
                            (int) received_sigterm);
                        close_listen_socks();
                        if (options.pid_file != NULL)
                                unlink(options.pid_file);
                        exit(received_sigterm == SIGTERM ? 0 : 255);
                }
                if (ostartups != startups) {
                        setproctitle("%s [listener] %d of %d-%d startups",
                            listener_proctitle, startups,
                            options.max_startups_begin, options.max_startups);
                        ostartups = startups;
                }
                if (received_sighup) {
                        if (!lameduck) {
                                debug("Received SIGHUP; waiting for children");
                                close_listen_socks();
                                lameduck = 1;
                        }
                        if (listening <= 0) {
                                sigprocmask(SIG_SETMASK, &osigset, NULL);
                                sighup_restart();
                        }
                }

                for (i = 0; i < num_listen_socks; i++) {
                        pfd[i].fd = listen_socks[i];
                        pfd[i].events = POLLIN;
                }
                npfd = num_listen_socks;
                for (i = 0; i < options.max_startups; i++) {
                        startup_pollfd[i] = -1;
                        if (startup_pipes[i] != -1) {
                                pfd[npfd].fd = startup_pipes[i];
                                pfd[npfd].events = POLLIN;
                                startup_pollfd[i] = npfd++;
                        }
                }

                /* Wait until a connection arrives or a child exits. */
                ret = ppoll(pfd, npfd, NULL, &osigset);
                if (ret == -1 && errno != EINTR) {
                        error("ppoll: %.100s", strerror(errno));
                        if (errno == EINVAL)
                                cleanup_exit(1); /* can't recover */
                }
                sigprocmask(SIG_SETMASK, &osigset, NULL);
                if (ret == -1)
                        continue;

                for (i = 0; i < options.max_startups; i++) {
                        if (startup_pipes[i] == -1 ||
                            startup_pollfd[i] == -1 ||
                            !(pfd[startup_pollfd[i]].revents & (POLLIN|POLLHUP)))
                                continue;
                        switch (read(startup_pipes[i], &c, sizeof(c))) {
                        case -1:
                                if (errno == EINTR || errno == EAGAIN)
                                        continue;
                                if (errno != EPIPE) {
                                        error_f("startup pipe %d (fd=%d): "
                                            "read %s", i, startup_pipes[i],
                                            strerror(errno));
                                }
                                /* FALLTHROUGH */
                        case 0:
                                /* child exited or completed auth */
                                close(startup_pipes[i]);
                                srclimit_done(startup_pipes[i]);
                                startup_pipes[i] = -1;
                                startups--;
                                if (startup_flags[i])
                                        listening--;
                                break;
                        case 1:
                                /* child has finished preliminaries */
                                if (startup_flags[i]) {
                                        listening--;
                                        startup_flags[i] = 0;
                                }
                                break;
                        }
                }
                for (i = 0; i < num_listen_socks; i++) {
                        if (!(pfd[i].revents & POLLIN))
                                continue;
                        fromlen = sizeof(from);
                        *newsock = accept(listen_socks[i],
                            (struct sockaddr *)&from, &fromlen);
                        if (*newsock == -1) {
                                if (errno != EINTR && errno != EWOULDBLOCK &&
                                    errno != ECONNABORTED && errno != EAGAIN)
                                        error("accept: %.100s",
                                            strerror(errno));
                                if (errno == EMFILE || errno == ENFILE)
                                        usleep(100 * 1000);
                                continue;
                        }
                        if (unset_nonblock(*newsock) == -1) {
                                close(*newsock);
                                continue;
                        }
                        if (pipe(startup_p) == -1) {
                                error_f("pipe(startup_p): %s", strerror(errno));
                                close(*newsock);
                                continue;
                        }
                        if (drop_connection(*newsock, startups, startup_p[0])) {
                                close(*newsock);
                                close(startup_p[0]);
                                close(startup_p[1]);
                                continue;
                        }

                        if (rexec_flag && socketpair(AF_UNIX,
                            SOCK_STREAM, 0, config_s) == -1) {
                                error("reexec socketpair: %s",
                                    strerror(errno));
                                close(*newsock);
                                close(startup_p[0]);
                                close(startup_p[1]);
                                continue;
                        }

                        for (j = 0; j < options.max_startups; j++)
                                if (startup_pipes[j] == -1) {
                                        startup_pipes[j] = startup_p[0];
                                        startups++;
                                        startup_flags[j] = 1;
                                        break;
                                }

                        /*
                         * Got connection.  Fork a child to handle it, unless
                         * we are in debugging mode.
                         */
                        if (debug_flag) {
                                /*
                                 * In debugging mode.  Close the listening
                                 * socket, and start processing the
                                 * connection without forking.
                                 */
                                debug("Server will not fork when running in debugging mode.");
                                close_listen_socks();
                                *sock_in = *newsock;
                                *sock_out = *newsock;
                                close(startup_p[0]);
                                close(startup_p[1]);
                                startup_pipe = -1;
                                pid = getpid();
                                if (rexec_flag) {
                                        send_rexec_state(config_s[0], cfg);
                                        close(config_s[0]);
                                }
                                free(pfd);
                                return;
                        }

                        /*
                         * Normal production daemon.  Fork, and have
                         * the child process the connection. The
                         * parent continues listening.
                         */
                        platform_pre_fork();
                        listening++;
                        if ((pid = fork()) == 0) {
                                /*
                                 * Child.  Close the listening and
                                 * max_startup sockets.  Start using
                                 * the accepted socket. Reinitialize
                                 * logging (since our pid has changed).
                                 * We return from this function to handle
                                 * the connection.
                                 */
                                platform_post_fork_child();
                                startup_pipe = startup_p[1];
                                close_startup_pipes();
                                close_listen_socks();
                                *sock_in = *newsock;
                                *sock_out = *newsock;
                                log_init(__progname,
                                    options.log_level,
                                    options.log_facility,
                                    log_stderr);
                                if (rexec_flag)
                                        close(config_s[0]);
                                else {
                                        /*
                                         * Signal parent that the preliminaries
                                         * for this child are complete. For the
                                         * re-exec case, this happens after the
                                         * child has received the rexec state
                                         * from the server.
                                         */
                                        (void)atomicio(vwrite, startup_pipe,
                                            "\0", 1);
                                }
                                free(pfd);
                                return;
                        }

                        /* Parent.  Stay in the loop. */
                        platform_post_fork_parent(pid);
                        if (pid == -1)
                                error("fork: %.100s", strerror(errno));
                        else
                                debug("Forked child %ld.", (long)pid);

                        close(startup_p[1]);

                        if (rexec_flag) {
                                close(config_s[1]);
                                send_rexec_state(config_s[0], cfg);
                                close(config_s[0]);
                        }
                        close(*newsock);

                        /*
                         * Ensure that our random state differs
                         * from that of the child
                         */
                        arc4random_stir();
                        arc4random_buf(rnd, sizeof(rnd));
#ifdef WITH_OPENSSL
                        RAND_seed(rnd, sizeof(rnd));
                        if ((RAND_bytes((u_char *)rnd, 1)) != 1)
                                fatal("%s: RAND_bytes failed", __func__);
#endif
                        explicit_bzero(rnd, sizeof(rnd));
                }
        }
}

/*
 * If IP options are supported, make sure there are none (log and
 * return an error if any are found).  Basically we are worried about
 * source routing; it can be used to pretend you are somebody
 * (ip-address) you are not. That itself may be "almost acceptable"
 * under certain circumstances, but rhosts authentication is useless
 * if source routing is accepted. Notice also that if we just dropped
 * source routing here, the other side could use IP spoofing to do
 * rest of the interaction and could still bypass security.  So we
 * exit here if we detect any IP options.
 */
static void
check_ip_options(struct ssh *ssh)
{
#ifdef IP_OPTIONS
        int sock_in = ssh_packet_get_connection_in(ssh);
        struct sockaddr_storage from;
        u_char opts[200];
        socklen_t i, option_size = sizeof(opts), fromlen = sizeof(from);
        char text[sizeof(opts) * 3 + 1];

        memset(&from, 0, sizeof(from));
        if (getpeername(sock_in, (struct sockaddr *)&from,
            &fromlen) == -1)
                return;
        if (from.ss_family != AF_INET)
                return;
        /* XXX IPv6 options? */

        if (getsockopt(sock_in, IPPROTO_IP, IP_OPTIONS, opts,
            &option_size) >= 0 && option_size != 0) {
                text[0] = '\0';
                for (i = 0; i < option_size; i++)
                        snprintf(text + i*3, sizeof(text) - i*3,
                            " %2.2x", opts[i]);
                fatal("Connection from %.100s port %d with IP opts: %.800s",
                    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh), text);
        }
        return;
#endif /* IP_OPTIONS */
}

/* Set the routing domain for this process */
static void
set_process_rdomain(struct ssh *ssh, const char *name)
{
#if defined(HAVE_SYS_SET_PROCESS_RDOMAIN)
        if (name == NULL)
                return; /* default */

        if (strcmp(name, "%D") == 0) {
                /* "expands" to routing domain of connection */
                if ((name = ssh_packet_rdomain_in(ssh)) == NULL)
                        return;
        }
        /* NB. We don't pass 'ssh' to sys_set_process_rdomain() */
        return sys_set_process_rdomain(name);
#elif defined(__OpenBSD__)
        int rtable, ortable = getrtable();
        const char *errstr;

        if (name == NULL)
                return; /* default */

        if (strcmp(name, "%D") == 0) {
                /* "expands" to routing domain of connection */
                if ((name = ssh_packet_rdomain_in(ssh)) == NULL)
                        return;
        }

        rtable = (int)strtonum(name, 0, 255, &errstr);
        if (errstr != NULL) /* Shouldn't happen */
                fatal("Invalid routing domain \"%s\": %s", name, errstr);
        if (rtable != ortable && setrtable(rtable) != 0)
                fatal("Unable to set routing domain %d: %s",
                    rtable, strerror(errno));
        debug_f("set routing domain %d (was %d)", rtable, ortable);
#else /* defined(__OpenBSD__) */
        fatal("Unable to set routing domain: not supported in this platform");
#endif
}

static void
accumulate_host_timing_secret(struct sshbuf *server_cfg,
    struct sshkey *key)
{
        static struct ssh_digest_ctx *ctx;
        u_char *hash;
        size_t len;
        struct sshbuf *buf;
        int r;

        if (ctx == NULL && (ctx = ssh_digest_start(SSH_DIGEST_SHA512)) == NULL)
                fatal_f("ssh_digest_start");
        if (key == NULL) { /* finalize */
                /* add server config in case we are using agent for host keys */
                if (ssh_digest_update(ctx, sshbuf_ptr(server_cfg),
                    sshbuf_len(server_cfg)) != 0)
                        fatal_f("ssh_digest_update");
                len = ssh_digest_bytes(SSH_DIGEST_SHA512);
                hash = xmalloc(len);
                if (ssh_digest_final(ctx, hash, len) != 0)
                        fatal_f("ssh_digest_final");
                options.timing_secret = PEEK_U64(hash);
                freezero(hash, len);
                ssh_digest_free(ctx);
                ctx = NULL;
                return;
        }
        if ((buf = sshbuf_new()) == NULL)
                fatal_f("could not allocate buffer");
        if ((r = sshkey_private_serialize(key, buf)) != 0)
                fatal_fr(r, "decode key");
        if (ssh_digest_update(ctx, sshbuf_ptr(buf), sshbuf_len(buf)) != 0)
                fatal_f("ssh_digest_update");
        sshbuf_reset(buf);
        sshbuf_free(buf);
}

static char *
prepare_proctitle(int ac, char **av)
{
        char *ret = NULL;
        int i;

        for (i = 0; i < ac; i++)
                xextendf(&ret, " ", "%s", av[i]);
        return ret;
}

/*
 * Main program for the daemon.
 */
int
main(int ac, char **av)
{
        struct ssh *ssh = NULL;
        extern char *optarg;
        extern int optind;
        int r, opt, on = 1, already_daemon, remote_port;
        int sock_in = -1, sock_out = -1, newsock = -1;
        const char *remote_ip, *rdomain;
        char *fp, *line, *laddr, *logfile = NULL;
        int config_s[2] = { -1 , -1 };
        u_int i, j;
        u_int64_t ibytes, obytes;
        mode_t new_umask;
        struct sshkey *key;
        struct sshkey *pubkey;
        int keytype;
        Authctxt *authctxt;
        struct connection_info *connection_info = NULL;

#ifdef HAVE_SECUREWARE
        (void)set_auth_parameters(ac, av);
#endif
        __progname = ssh_get_progname(av[0]);

        /* Save argv. Duplicate so setproctitle emulation doesn't clobber it */
        saved_argc = ac;
        rexec_argc = ac;
        saved_argv = xcalloc(ac + 1, sizeof(*saved_argv));
        for (i = 0; (int)i < ac; i++)
                saved_argv[i] = xstrdup(av[i]);
        saved_argv[i] = NULL;

#ifndef HAVE_SETPROCTITLE
        /* Prepare for later setproctitle emulation */
        compat_init_setproctitle(ac, av);
        av = saved_argv;
#endif

        if (geteuid() == 0 && setgroups(0, NULL) == -1)
                debug("setgroups(): %.200s", strerror(errno));

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

        seed_rng();

        /* Initialize configuration options to their default values. */
        initialize_server_options(&options);

        /* Parse command-line arguments. */
        while ((opt = getopt(ac, av,
            "C:E:b:c:f:g:h:k:o:p:u:46DQRTdeiqrt")) != -1) {
                switch (opt) {
                case '4':
                        options.address_family = AF_INET;
                        break;
                case '6':
                        options.address_family = AF_INET6;
                        break;
                case 'f':
                        config_file_name = optarg;
                        break;
                case 'c':
                        servconf_add_hostcert("[command-line]", 0,
                            &options, optarg);
                        break;
                case 'd':
                        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;
                case 'D':
                        no_daemon_flag = 1;
                        break;
                case 'E':
                        logfile = optarg;
                        /* FALLTHROUGH */
                case 'e':
                        log_stderr = 1;
                        break;
                case 'i':
                        inetd_flag = 1;
                        break;
                case 'r':
                        rexec_flag = 0;
                        break;
                case 'R':
                        rexeced_flag = 1;
                        inetd_flag = 1;
                        break;
                case 'Q':
                        /* ignored */
                        break;
                case 'q':
                        options.log_level = SYSLOG_LEVEL_QUIET;
                        break;
                case 'b':
                        /* protocol 1, ignored */
                        break;
                case 'p':
                        options.ports_from_cmdline = 1;
                        if (options.num_ports >= MAX_PORTS) {
                                fprintf(stderr, "too many ports.\n");
                                exit(1);
                        }
                        options.ports[options.num_ports++] = a2port(optarg);
                        if (options.ports[options.num_ports-1] <= 0) {
                                fprintf(stderr, "Bad port number.\n");
                                exit(1);
                        }
                        break;
                case 'g':
                        if ((options.login_grace_time = convtime(optarg)) == -1) {
                                fprintf(stderr, "Invalid login grace time.\n");
                                exit(1);
                        }
                        break;
                case 'k':
                        /* protocol 1, ignored */
                        break;
                case 'h':
                        servconf_add_hostkey("[command-line]", 0,
                            &options, optarg, 1);
                        break;
                case 't':
                        test_flag = 1;
                        break;
                case 'T':
                        test_flag = 2;
                        break;
                case 'C':
                        connection_info = get_connection_info(ssh, 0, 0);
                        if (parse_server_match_testspec(connection_info,
                            optarg) == -1)
                                exit(1);
                        break;
                case 'u':
                        utmp_len = (u_int)strtonum(optarg, 0, HOST_NAME_MAX+1+1, NULL);
                        if (utmp_len > HOST_NAME_MAX+1) {
                                fprintf(stderr, "Invalid utmp length.\n");
                                exit(1);
                        }
                        break;
                case 'o':
                        line = xstrdup(optarg);
                        if (process_server_config_line(&options, line,
                            "command-line", 0, NULL, NULL, &includes) != 0)
                                exit(1);
                        free(line);
                        break;
                case '?':
                default:
                        usage();
                        break;
                }
        }
        if (rexeced_flag || inetd_flag)
                rexec_flag = 0;
        if (!test_flag && rexec_flag && !path_absolute(av[0]))
                fatal("sshd re-exec requires execution with an absolute path");
        if (rexeced_flag)
                closefrom(REEXEC_MIN_FREE_FD);
        else
                closefrom(REEXEC_DEVCRYPTO_RESERVED_FD);

        /* If requested, redirect the logs to the specified logfile. */
        if (logfile != NULL)
                log_redirect_stderr_to(logfile);
        /*
         * Force logging to stderr until we have loaded the private host
         * key (unless started from inetd)
         */
        log_init(__progname,
            options.log_level == SYSLOG_LEVEL_NOT_SET ?
            SYSLOG_LEVEL_INFO : options.log_level,
            options.log_facility == SYSLOG_FACILITY_NOT_SET ?
            SYSLOG_FACILITY_AUTH : options.log_facility,
            log_stderr || !inetd_flag || debug_flag);

        /*
         * Unset KRB5CCNAME, otherwise the user's session may inherit it from
         * root's environment
         */
        if (getenv("KRB5CCNAME") != NULL)
                (void) unsetenv("KRB5CCNAME");

        sensitive_data.have_ssh2_key = 0;

        /*
         * If we're not doing an extended test do not silently ignore connection
         * test params.
         */
        if (test_flag < 2 && connection_info != NULL)
                fatal("Config test connection parameter (-C) provided without "
                    "test mode (-T)");

        /* Fetch our configuration */
        if ((cfg = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        if (rexeced_flag) {
                setproctitle("%s", "[rexeced]");
                recv_rexec_state(REEXEC_CONFIG_PASS_FD, cfg);
                if (!debug_flag) {
                        startup_pipe = dup(REEXEC_STARTUP_PIPE_FD);
                        close(REEXEC_STARTUP_PIPE_FD);
                        /*
                         * Signal parent that this child is at a point where
                         * they can go away if they have a SIGHUP pending.
                         */
                        (void)atomicio(vwrite, startup_pipe, "\0", 1);
                }
        } else if (strcasecmp(config_file_name, "none") != 0)
                load_server_config(config_file_name, cfg);

        parse_server_config(&options, rexeced_flag ? "rexec" : config_file_name,
            cfg, &includes, NULL, rexeced_flag);

#ifdef WITH_OPENSSL
        if (options.moduli_file != NULL)
                dh_set_moduli_file(options.moduli_file);
#endif

        /* Fill in default values for those options not explicitly set. */
        fill_default_server_options(&options);

        /* Check that options are sensible */
        if (options.authorized_keys_command_user == NULL &&
            (options.authorized_keys_command != NULL &&
            strcasecmp(options.authorized_keys_command, "none") != 0))
                fatal("AuthorizedKeysCommand set without "
                    "AuthorizedKeysCommandUser");
        if (options.authorized_principals_command_user == NULL &&
            (options.authorized_principals_command != NULL &&
            strcasecmp(options.authorized_principals_command, "none") != 0))
                fatal("AuthorizedPrincipalsCommand set without "
                    "AuthorizedPrincipalsCommandUser");

        /*
         * Check whether there is any path through configured auth methods.
         * Unfortunately it is not possible to verify this generally before
         * daemonisation in the presence of Match block, but this catches
         * and warns for trivial misconfigurations that could break login.
         */
        if (options.num_auth_methods != 0) {
                for (i = 0; i < options.num_auth_methods; i++) {
                        if (auth2_methods_valid(options.auth_methods[i],
                            1) == 0)
                                break;
                }
                if (i >= options.num_auth_methods)
                        fatal("AuthenticationMethods cannot be satisfied by "
                            "enabled authentication methods");
        }

        /* Check that there are no remaining arguments. */
        if (optind < ac) {
                fprintf(stderr, "Extra argument %s.\n", av[optind]);
                exit(1);
        }

        debug("sshd version %s, %s", SSH_VERSION, SSH_OPENSSL_VERSION);

        /* Store privilege separation user for later use if required. */
        privsep_chroot = use_privsep && (getuid() == 0 || geteuid() == 0);
        if ((privsep_pw = getpwnam(SSH_PRIVSEP_USER)) == NULL) {
                if (privsep_chroot || options.kerberos_authentication)
                        fatal("Privilege separation user %s does not exist",
                            SSH_PRIVSEP_USER);
        } else {
                privsep_pw = pwcopy(privsep_pw);
                freezero(privsep_pw->pw_passwd, strlen(privsep_pw->pw_passwd));
                privsep_pw->pw_passwd = xstrdup("*");
        }
        endpwent();

        /* load host keys */
        sensitive_data.host_keys = xcalloc(options.num_host_key_files,
            sizeof(struct sshkey *));
        sensitive_data.host_pubkeys = xcalloc(options.num_host_key_files,
            sizeof(struct sshkey *));

        if (options.host_key_agent) {
                if (strcmp(options.host_key_agent, SSH_AUTHSOCKET_ENV_NAME))
                        setenv(SSH_AUTHSOCKET_ENV_NAME,
                            options.host_key_agent, 1);
                if ((r = ssh_get_authentication_socket(NULL)) == 0)
                        have_agent = 1;
                else
                        error_r(r, "Could not connect to agent \"%s\"",
                            options.host_key_agent);
        }

        for (i = 0; i < options.num_host_key_files; i++) {
                int ll = options.host_key_file_userprovided[i] ?
                    SYSLOG_LEVEL_ERROR : SYSLOG_LEVEL_DEBUG1;

                if (options.host_key_files[i] == NULL)
                        continue;
                if ((r = sshkey_load_private(options.host_key_files[i], "",
                    &key, NULL)) != 0 && r != SSH_ERR_SYSTEM_ERROR)
                        do_log2_r(r, ll, "Unable to load host key \"%s\"",
                            options.host_key_files[i]);
                if (sshkey_is_sk(key) &&
                    key->sk_flags & SSH_SK_USER_PRESENCE_REQD) {
                        debug("host key %s requires user presence, ignoring",
                            options.host_key_files[i]);
                        key->sk_flags &= ~SSH_SK_USER_PRESENCE_REQD;
                }
                if (r == 0 && key != NULL &&
                    (r = sshkey_shield_private(key)) != 0) {
                        do_log2_r(r, ll, "Unable to shield host key \"%s\"",
                            options.host_key_files[i]);
                        sshkey_free(key);
                        key = NULL;
                }
                if ((r = sshkey_load_public(options.host_key_files[i],
                    &pubkey, NULL)) != 0 && r != SSH_ERR_SYSTEM_ERROR)
                        do_log2_r(r, ll, "Unable to load host key \"%s\"",
                            options.host_key_files[i]);
                if (pubkey != NULL && key != NULL) {
                        if (!sshkey_equal(pubkey, key)) {
                                error("Public key for %s does not match "
                                    "private key", options.host_key_files[i]);
                                sshkey_free(pubkey);
                                pubkey = NULL;
                        }
                }
                if (pubkey == NULL && key != NULL) {
                        if ((r = sshkey_from_private(key, &pubkey)) != 0)
                                fatal_r(r, "Could not demote key: \"%s\"",
                                    options.host_key_files[i]);
                }
                if (pubkey != NULL && (r = sshkey_check_rsa_length(pubkey,
                    options.required_rsa_size)) != 0) {
                        error_fr(r, "Host key %s", options.host_key_files[i]);
                        sshkey_free(pubkey);
                        sshkey_free(key);
                        continue;
                }
                sensitive_data.host_keys[i] = key;
                sensitive_data.host_pubkeys[i] = pubkey;

                if (key == NULL && pubkey != NULL && have_agent) {
                        debug("will rely on agent for hostkey %s",
                            options.host_key_files[i]);
                        keytype = pubkey->type;
                } else if (key != NULL) {
                        keytype = key->type;
                        accumulate_host_timing_secret(cfg, key);
                } else {
                        do_log2(ll, "Unable to load host key: %s",
                            options.host_key_files[i]);
                        sensitive_data.host_keys[i] = NULL;
                        sensitive_data.host_pubkeys[i] = NULL;
                        continue;
                }

                switch (keytype) {
                case KEY_RSA:
                case KEY_DSA:
                case KEY_ECDSA:
                case KEY_ED25519:
                case KEY_ECDSA_SK:
                case KEY_ED25519_SK:
                case KEY_XMSS:
                        if (have_agent || key != NULL)
                                sensitive_data.have_ssh2_key = 1;
                        break;
                }
                if ((fp = sshkey_fingerprint(pubkey, options.fingerprint_hash,
                    SSH_FP_DEFAULT)) == NULL)
                        fatal("sshkey_fingerprint failed");
                debug("%s host key #%d: %s %s",
                    key ? "private" : "agent", i, sshkey_ssh_name(pubkey), fp);
                free(fp);
        }
        accumulate_host_timing_secret(cfg, NULL);
        if (!sensitive_data.have_ssh2_key) {
                logit("sshd: no hostkeys available -- exiting.");
                exit(1);
        }

        /*
         * Load certificates. They are stored in an array at identical
         * indices to the public keys that they relate to.
         */
        sensitive_data.host_certificates = xcalloc(options.num_host_key_files,
            sizeof(struct sshkey *));
        for (i = 0; i < options.num_host_key_files; i++)
                sensitive_data.host_certificates[i] = NULL;

        for (i = 0; i < options.num_host_cert_files; i++) {
                if (options.host_cert_files[i] == NULL)
                        continue;
                if ((r = sshkey_load_public(options.host_cert_files[i],
                    &key, NULL)) != 0) {
                        error_r(r, "Could not load host certificate \"%s\"",
                            options.host_cert_files[i]);
                        continue;
                }
                if (!sshkey_is_cert(key)) {
                        error("Certificate file is not a certificate: %s",
                            options.host_cert_files[i]);
                        sshkey_free(key);
                        continue;
                }
                /* Find matching private key */
                for (j = 0; j < options.num_host_key_files; j++) {
                        if (sshkey_equal_public(key,
                            sensitive_data.host_pubkeys[j])) {
                                sensitive_data.host_certificates[j] = key;
                                break;
                        }
                }
                if (j >= options.num_host_key_files) {
                        error("No matching private key for certificate: %s",
                            options.host_cert_files[i]);
                        sshkey_free(key);
                        continue;
                }
                sensitive_data.host_certificates[j] = key;
                debug("host certificate: #%u type %d %s", j, key->type,
                    sshkey_type(key));
        }

        if (privsep_chroot) {
                struct stat st;

                if ((stat(_PATH_PRIVSEP_CHROOT_DIR, &st) == -1) ||
                    (S_ISDIR(st.st_mode) == 0))
                        fatal("Missing privilege separation directory: %s",
                            _PATH_PRIVSEP_CHROOT_DIR);

#ifdef HAVE_CYGWIN
                if (check_ntsec(_PATH_PRIVSEP_CHROOT_DIR) &&
                    (st.st_uid != getuid () ||
                    (st.st_mode & (S_IWGRP|S_IWOTH)) != 0))
#else
                if (st.st_uid != 0 || (st.st_mode & (S_IWGRP|S_IWOTH)) != 0)
#endif
                        fatal("%s must be owned by root and not group or "
                            "world-writable.", _PATH_PRIVSEP_CHROOT_DIR);
        }

        if (test_flag > 1) {
                /*
                 * If no connection info was provided by -C then use
                 * use a blank one that will cause no predicate to match.
                 */
                if (connection_info == NULL)
                        connection_info = get_connection_info(ssh, 0, 0);
                connection_info->test = 1;
                parse_server_match_config(&options, &includes, connection_info);
                dump_config(&options);
        }

        /* Configuration looks good, so exit if in test mode. */
        if (test_flag)
                exit(0);

        /*
         * Clear out any supplemental groups we may have inherited.  This
         * prevents inadvertent creation of files with bad modes (in the
         * portable version at least, it's certainly possible for PAM
         * to create a file, and we can't control the code in every
         * module which might be used).
         */
        if (setgroups(0, NULL) < 0)
                debug("setgroups() failed: %.200s", strerror(errno));

        if (rexec_flag) {
                if (rexec_argc < 0)
                        fatal("rexec_argc %d < 0", rexec_argc);
                rexec_argv = xcalloc(rexec_argc + 2, sizeof(char *));
                for (i = 0; i < (u_int)rexec_argc; i++) {
                        debug("rexec_argv[%d]='%s'", i, saved_argv[i]);
                        rexec_argv[i] = saved_argv[i];
                }
                rexec_argv[rexec_argc] = "-R";
                rexec_argv[rexec_argc + 1] = NULL;
        }
        listener_proctitle = prepare_proctitle(ac, av);

        /* Ensure that umask disallows at least group and world write */
        new_umask = umask(0077) | 0022;
        (void) umask(new_umask);

        /* Initialize the log (it is reinitialized below in case we forked). */
        if (debug_flag && (!inetd_flag || rexeced_flag))
                log_stderr = 1;
        log_init(__progname, options.log_level,
            options.log_facility, log_stderr);
        for (i = 0; i < options.num_log_verbose; i++)
                log_verbose_add(options.log_verbose[i]);

        /*
         * If not in debugging mode, not started from inetd and not already
         * daemonized (eg re-exec via SIGHUP), disconnect from the controlling
         * terminal, and fork.  The original process exits.
         */
        already_daemon = daemonized();
        if (!(debug_flag || inetd_flag || no_daemon_flag || already_daemon)) {

                if (daemon(0, 0) == -1)
                        fatal("daemon() failed: %.200s", strerror(errno));

                disconnect_controlling_tty();
        }
        /* Reinitialize the log (because of the fork above). */
        log_init(__progname, options.log_level, options.log_facility, log_stderr);

        /*
         * Chdir to the root directory so that the current disk can be
         * unmounted if desired.
         */
        if (chdir("/") == -1)
                error("chdir(\"/\"): %s", strerror(errno));

        /* ignore SIGPIPE */
        ssh_signal(SIGPIPE, SIG_IGN);

        /* Get a connection, either from inetd or a listening TCP socket */
        if (inetd_flag) {
                server_accept_inetd(&sock_in, &sock_out);
        } else {
                platform_pre_listen();
                server_listen();

                ssh_signal(SIGHUP, sighup_handler);
                ssh_signal(SIGCHLD, main_sigchld_handler);
                ssh_signal(SIGTERM, sigterm_handler);
                ssh_signal(SIGQUIT, sigterm_handler);

                /*
                 * Write out the pid file after the sigterm handler
                 * is setup and the listen sockets are bound
                 */
                if (options.pid_file != NULL && !debug_flag) {
                        FILE *f = fopen(options.pid_file, "w");

                        if (f == NULL) {
                                error("Couldn't create pid file \"%s\": %s",
                                    options.pid_file, strerror(errno));
                        } else {
                                fprintf(f, "%ld\n", (long) getpid());
                                fclose(f);
                        }
                }

                /* Accept a connection and return in a forked child */
                server_accept_loop(&sock_in, &sock_out,
                    &newsock, config_s);
        }

        /* This is the child processing a new connection. */
        setproctitle("%s", "[accepted]");

        /*
         * Create a new session and process group since the 4.4BSD
         * setlogin() affects the entire process group.  We don't
         * want the child to be able to affect the parent.
         */
        if (!debug_flag && !inetd_flag && setsid() == -1)
                error("setsid: %.100s", strerror(errno));

        if (rexec_flag) {
                debug("rexec start in %d out %d newsock %d pipe %d sock %d",
                    sock_in, sock_out, newsock, startup_pipe, config_s[0]);
                dup2(newsock, STDIN_FILENO);
                dup2(STDIN_FILENO, STDOUT_FILENO);
                if (startup_pipe == -1)
                        close(REEXEC_STARTUP_PIPE_FD);
                else if (startup_pipe != REEXEC_STARTUP_PIPE_FD) {
                        dup2(startup_pipe, REEXEC_STARTUP_PIPE_FD);
                        close(startup_pipe);
                        startup_pipe = REEXEC_STARTUP_PIPE_FD;
                }

                dup2(config_s[1], REEXEC_CONFIG_PASS_FD);
                close(config_s[1]);

                ssh_signal(SIGHUP, SIG_IGN); /* avoid reset to SIG_DFL */
                execv(rexec_argv[0], rexec_argv);

                /* Reexec has failed, fall back and continue */
                error("rexec of %s failed: %s", rexec_argv[0], strerror(errno));
                recv_rexec_state(REEXEC_CONFIG_PASS_FD, NULL);
                log_init(__progname, options.log_level,
                    options.log_facility, log_stderr);

                /* Clean up fds */
                close(REEXEC_CONFIG_PASS_FD);
                newsock = sock_out = sock_in = dup(STDIN_FILENO);
                if (stdfd_devnull(1, 1, 0) == -1)
                        error_f("stdfd_devnull failed");
                debug("rexec cleanup in %d out %d newsock %d pipe %d sock %d",
                    sock_in, sock_out, newsock, startup_pipe, config_s[0]);
        }

        /* Executed child processes don't need these. */
        fcntl(sock_out, F_SETFD, FD_CLOEXEC);
        fcntl(sock_in, F_SETFD, FD_CLOEXEC);

        /* We will not restart on SIGHUP since it no longer makes sense. */
        ssh_signal(SIGALRM, SIG_DFL);
        ssh_signal(SIGHUP, SIG_DFL);
        ssh_signal(SIGTERM, SIG_DFL);
        ssh_signal(SIGQUIT, SIG_DFL);
        ssh_signal(SIGCHLD, SIG_DFL);
        ssh_signal(SIGINT, SIG_DFL);

        /*
         * Register our connection.  This turns encryption off because we do
         * not have a key.
         */
        if ((ssh = ssh_packet_set_connection(NULL, sock_in, sock_out)) == NULL)
                fatal("Unable to create connection");
        the_active_state = ssh;
        ssh_packet_set_server(ssh);

        check_ip_options(ssh);

        /* Prepare the channels layer */
        channel_init_channels(ssh);
        channel_set_af(ssh, options.address_family);
        process_permitopen(ssh, &options);

        /* Set SO_KEEPALIVE if requested. */
        if (options.tcp_keep_alive && ssh_packet_connection_is_on_socket(ssh) &&
            setsockopt(sock_in, SOL_SOCKET, SO_KEEPALIVE, &on, sizeof(on)) == -1)
                error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));

        if ((remote_port = ssh_remote_port(ssh)) < 0) {
                debug("ssh_remote_port failed");
                cleanup_exit(255);
        }

        if (options.routing_domain != NULL)
                set_process_rdomain(ssh, options.routing_domain);

        /*
         * The rest of the code depends on the fact that
         * ssh_remote_ipaddr() caches the remote ip, even if
         * the socket goes away.
         */
        remote_ip = ssh_remote_ipaddr(ssh);

#ifdef SSH_AUDIT_EVENTS
        audit_connection_from(remote_ip, remote_port);
#endif

        rdomain = ssh_packet_rdomain_in(ssh);

        /* Log the connection. */
        laddr = get_local_ipaddr(sock_in);
        verbose("Connection from %s port %d on %s port %d%s%s%s",
            remote_ip, remote_port, laddr,  ssh_local_port(ssh),
            rdomain == NULL ? "" : " rdomain \"",
            rdomain == NULL ? "" : rdomain,
            rdomain == NULL ? "" : "\"");
        free(laddr);

        /*
         * We don't want to listen forever unless the other side
         * successfully authenticates itself.  So we set up an alarm which is
         * cleared after successful authentication.  A limit of zero
         * indicates no limit. Note that we don't set the alarm in debugging
         * mode; it is just annoying to have the server exit just when you
         * are about to discover the bug.
         */
        ssh_signal(SIGALRM, grace_alarm_handler);
        if (!debug_flag)
                alarm(options.login_grace_time);

        if ((r = kex_exchange_identification(ssh, -1,
            options.version_addendum)) != 0)
                sshpkt_fatal(ssh, r, "banner exchange");

        ssh_packet_set_nonblocking(ssh);

        /* allocate authentication context */
        authctxt = xcalloc(1, sizeof(*authctxt));
        ssh->authctxt = authctxt;

        authctxt->loginmsg = loginmsg;

        /* XXX global for cleanup, access from other modules */
        the_authctxt = authctxt;

        /* Set default key authentication options */
        if ((auth_opts = sshauthopt_new_with_keys_defaults()) == NULL)
                fatal("allocation failed");

        /* prepare buffer to collect messages to display to user after login */
        if ((loginmsg = sshbuf_new()) == NULL)
                fatal_f("sshbuf_new failed");
        auth_debug_reset();

        if (use_privsep) {
                if (privsep_preauth(ssh) == 1)
                        goto authenticated;
        } else if (have_agent) {
                if ((r = ssh_get_authentication_socket(&auth_sock)) != 0) {
                        error_r(r, "Unable to get agent socket");
                        have_agent = 0;
                }
        }

        /* perform the key exchange */
        /* authenticate user and start session */
        do_ssh2_kex(ssh);
        do_authentication2(ssh);

        /*
         * If we use privilege separation, the unprivileged child transfers
         * the current keystate and exits
         */
        if (use_privsep) {
                mm_send_keystate(ssh, pmonitor);
                ssh_packet_clear_keys(ssh);
                exit(0);
        }

 authenticated:
        /*
         * Cancel the alarm we set to limit the time taken for
         * authentication.
         */
        alarm(0);
        ssh_signal(SIGALRM, SIG_DFL);
        authctxt->authenticated = 1;
        if (startup_pipe != -1) {
                close(startup_pipe);
                startup_pipe = -1;
        }

#ifdef SSH_AUDIT_EVENTS
        audit_event(ssh, SSH_AUTH_SUCCESS);
#endif

#ifdef GSSAPI
        if (options.gss_authentication) {
                temporarily_use_uid(authctxt->pw);
                ssh_gssapi_storecreds();
                restore_uid();
        }
#endif
#ifdef USE_PAM
        if (options.use_pam) {
                do_pam_setcred(1);
                do_pam_session(ssh);
        }
#endif

        /*
         * In privilege separation, we fork another child and prepare
         * file descriptor passing.
         */
        if (use_privsep) {
                privsep_postauth(ssh, authctxt);
                /* the monitor process [priv] will not return */
        }

        ssh_packet_set_timeout(ssh, options.client_alive_interval,
            options.client_alive_count_max);

        /* Try to send all our hostkeys to the client */
        notify_hostkeys(ssh);

        /* Start session. */
        do_authenticated(ssh, authctxt);

        /* The connection has been terminated. */
        ssh_packet_get_bytes(ssh, &ibytes, &obytes);
        verbose("Transferred: sent %llu, received %llu bytes",
            (unsigned long long)obytes, (unsigned long long)ibytes);

        verbose("Closing connection to %.500s port %d", remote_ip, remote_port);

#ifdef USE_PAM
        if (options.use_pam)
                finish_pam();
#endif /* USE_PAM */

#ifdef SSH_AUDIT_EVENTS
        PRIVSEP(audit_event(ssh, SSH_CONNECTION_CLOSE));
#endif

        ssh_packet_close(ssh);

        if (use_privsep)
                mm_terminate();

        exit(0);
}

int
sshd_hostkey_sign(struct ssh *ssh, struct sshkey *privkey,
    struct sshkey *pubkey, u_char **signature, size_t *slenp,
    const u_char *data, size_t dlen, const char *alg)
{
        int r;

        if (use_privsep) {
                if (privkey) {
                        if (mm_sshkey_sign(ssh, privkey, signature, slenp,
                            data, dlen, alg, options.sk_provider, NULL,
                            ssh->compat) < 0)
                                fatal_f("privkey sign failed");
                } else {
                        if (mm_sshkey_sign(ssh, pubkey, signature, slenp,
                            data, dlen, alg, options.sk_provider, NULL,
                            ssh->compat) < 0)
                                fatal_f("pubkey sign failed");
                }
        } else {
                if (privkey) {
                        if (sshkey_sign(privkey, signature, slenp, data, dlen,
                            alg, options.sk_provider, NULL, ssh->compat) < 0)
                                fatal_f("privkey sign failed");
                } else {
                        if ((r = ssh_agent_sign(auth_sock, pubkey,
                            signature, slenp, data, dlen, alg,
                            ssh->compat)) != 0) {
                                fatal_fr(r, "agent sign failed");
                        }
                }
        }
        return 0;
}

/* SSH2 key exchange */
static void
do_ssh2_kex(struct ssh *ssh)
{
        char *myproposal[PROPOSAL_MAX] = { KEX_SERVER };
        struct kex *kex;
        char *prop_kex = NULL, *prop_enc = NULL, *prop_hostkey = NULL;
        int r;

        myproposal[PROPOSAL_KEX_ALGS] = prop_kex = compat_kex_proposal(ssh,
            options.kex_algorithms);
        myproposal[PROPOSAL_ENC_ALGS_CTOS] =
            myproposal[PROPOSAL_ENC_ALGS_STOC] = prop_enc =
            compat_cipher_proposal(ssh, options.ciphers);
        myproposal[PROPOSAL_MAC_ALGS_CTOS] =
            myproposal[PROPOSAL_MAC_ALGS_STOC] = options.macs;

        if (options.compression == COMP_NONE) {
                myproposal[PROPOSAL_COMP_ALGS_CTOS] =
                    myproposal[PROPOSAL_COMP_ALGS_STOC] = "none";
        }

        if (options.rekey_limit || options.rekey_interval)
                ssh_packet_set_rekey_limits(ssh, options.rekey_limit,
                    options.rekey_interval);

        myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = prop_hostkey =
           compat_pkalg_proposal(ssh, list_hostkey_types());

        /* start key exchange */
        if ((r = kex_setup(ssh, myproposal)) != 0)
                fatal_r(r, "kex_setup");
        kex = ssh->kex;
#ifdef WITH_OPENSSL
        kex->kex[KEX_DH_GRP1_SHA1] = kex_gen_server;
        kex->kex[KEX_DH_GRP14_SHA1] = kex_gen_server;
        kex->kex[KEX_DH_GRP14_SHA256] = kex_gen_server;
        kex->kex[KEX_DH_GRP16_SHA512] = kex_gen_server;
        kex->kex[KEX_DH_GRP18_SHA512] = kex_gen_server;
        kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
        kex->kex[KEX_DH_GEX_SHA256] = kexgex_server;
# ifdef OPENSSL_HAS_ECC
        kex->kex[KEX_ECDH_SHA2] = kex_gen_server;
# endif
#endif
        kex->kex[KEX_C25519_SHA256] = kex_gen_server;
        kex->kex[KEX_KEM_SNTRUP761X25519_SHA512] = kex_gen_server;
        kex->load_host_public_key=&get_hostkey_public_by_type;
        kex->load_host_private_key=&get_hostkey_private_by_type;
        kex->host_key_index=&get_hostkey_index;
        kex->sign = sshd_hostkey_sign;

        ssh_dispatch_run_fatal(ssh, DISPATCH_BLOCK, &kex->done);

#ifdef DEBUG_KEXDH
        /* send 1st encrypted/maced/compressed message */
        if ((r = sshpkt_start(ssh, SSH2_MSG_IGNORE)) != 0 ||
            (r = sshpkt_put_cstring(ssh, "markus")) != 0 ||
            (r = sshpkt_send(ssh)) != 0 ||
            (r = ssh_packet_write_wait(ssh)) != 0)
                fatal_fr(r, "send test");
#endif
        free(prop_kex);
        free(prop_enc);
        free(prop_hostkey);
        debug("KEX done");
}

/* server specific fatal cleanup */
void
cleanup_exit(int i)
{
        if (the_active_state != NULL && the_authctxt != NULL) {
                do_cleanup(the_active_state, the_authctxt);
                if (use_privsep && privsep_is_preauth &&
                    pmonitor != NULL && pmonitor->m_pid > 1) {
                        debug("Killing privsep child %d", pmonitor->m_pid);
                        if (kill(pmonitor->m_pid, SIGKILL) != 0 &&
                            errno != ESRCH) {
                                error_f("kill(%d): %s", pmonitor->m_pid,
                                    strerror(errno));
                        }
                }
        }
#ifdef SSH_AUDIT_EVENTS
        /* done after do_cleanup so it can cancel the PAM auth 'thread' */
        if (the_active_state != NULL && (!use_privsep || mm_is_monitor()))
                audit_event(the_active_state, SSH_CONNECTION_ABANDON);
#endif
        _exit(i);
}