openssh/sshd.c

/* $OpenBSD: sshd.c,v 1.490 2017/05/31 08:09:45 markus 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>
#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 "rsa.h"
#include "sshpty.h"
#include "packet.h"
#include "log.h"
#include "buffer.h"
#include "misc.h"
#include "match.h"
#include "servconf.h"
#include "uidswap.h"
#include "compat.h"
#include "cipher.h"
#include "digest.h"
#include "key.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 "version.h"
#include "ssherr.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;

/* Flag indicating that the daemon should only test the configuration and keys. */
int test_flag = 0;

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

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

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

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

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

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

/*
 * the client's version string, passed by sshd2 in compat mode. if != NULL,
 * sshd will skip the version-number exchange
 */
char *client_version_string = NULL;
char *server_version_string = NULL;

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

/* session identifier, used by RSA-auth */
u_char session_id[16];

/* same for ssh2 */
u_char *session_id2 = NULL;
u_int session_id2_len = 0;

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

/* options.max_startup sized array of fd ints */
int *startup_pipes = NULL;
int startup_pipe;		/* 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 authentication context */
Authctxt *the_authctxt = NULL;

/* sshd_config buffer */
Buffer cfg;

/* message to be displayed after login */
Buffer 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(void);

/*
 * 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 = -1;
}

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)
{
	int save_errno = errno;

	received_sighup = 1;
	signal(SIGHUP, sighup_handler);
	errno = save_errno;
}

/*
 * 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();
	alarm(0);  /* alarm timer persists across exec */
	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 < 0 && errno == EINTR))
		;

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

/*
 * Signal handler for the alarm after the login grace period has expired.
 */
/*ARGSUSED*/
static void
grace_alarm_handler(int sig)
{
	if (use_privsep && pmonitor != NULL && pmonitor->m_pid > 0)
		kill(pmonitor->m_pid, SIGALRM);

	/*
	 * Try to kill any processes that we have spawned, E.g. authorized
	 * keys command helpers.
	 */
	if (getpgid(0) == getpid()) {
		signal(SIGTERM, SIG_IGN);
		kill(0, SIGTERM);
	}

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

static void
sshd_exchange_identification(struct ssh *ssh, int sock_in, int sock_out)
{
	u_int i;
	int remote_major, remote_minor;
	char *s;
	char buf[256];			/* Must not be larger than remote_version. */
	char remote_version[256];	/* Must be at least as big as buf. */

	xasprintf(&server_version_string, "SSH-%d.%d-%.100s%s%s\r\n",
	    PROTOCOL_MAJOR_2, PROTOCOL_MINOR_2, SSH_VERSION,
	    *options.version_addendum == '\0' ? "" : " ",
	    options.version_addendum);

	/* Send our protocol version identification. */
	if (atomicio(vwrite, sock_out, server_version_string,
	    strlen(server_version_string))
	    != strlen(server_version_string)) {
		logit("Could not write ident string to %s port %d",
		    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
		cleanup_exit(255);
	}

	/* Read other sides version identification. */
	memset(buf, 0, sizeof(buf));
	for (i = 0; i < sizeof(buf) - 1; i++) {
		if (atomicio(read, sock_in, &buf[i], 1) != 1) {
			logit("Did not receive identification string "
			    "from %s port %d",
			    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
			cleanup_exit(255);
		}
		if (buf[i] == '\r') {
			buf[i] = 0;
			/* Kludge for F-Secure Macintosh < 1.0.2 */
			if (i == 12 &&
			    strncmp(buf, "SSH-1.5-W1.0", 12) == 0)
				break;
			continue;
		}
		if (buf[i] == '\n') {
			buf[i] = 0;
			break;
		}
	}
	buf[sizeof(buf) - 1] = 0;
	client_version_string = xstrdup(buf);

	/*
	 * Check that the versions match.  In future this might accept
	 * several versions and set appropriate flags to handle them.
	 */
	if (sscanf(client_version_string, "SSH-%d.%d-%[^\n]\n",
	    &remote_major, &remote_minor, remote_version) != 3) {
		s = "Protocol mismatch.\n";
		(void) atomicio(vwrite, sock_out, s, strlen(s));
		logit("Bad protocol version identification '%.100s' "
		    "from %s port %d", client_version_string,
		    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh));
		close(sock_in);
		close(sock_out);
		cleanup_exit(255);
	}
	debug("Client protocol version %d.%d; client software version %.100s",
	    remote_major, remote_minor, remote_version);

	ssh->compat = compat_datafellows(remote_version);

	if ((ssh->compat & SSH_BUG_PROBE) != 0) {
		logit("probed from %s port %d with %s.  Don't panic.",
		    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
		    client_version_string);
		cleanup_exit(255);
	}
	if ((ssh->compat & SSH_BUG_SCANNER) != 0) {
		logit("scanned from %s port %d with %s.  Don't panic.",
		    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
		    client_version_string);
		cleanup_exit(255);
	}
	if ((ssh->compat & SSH_BUG_RSASIGMD5) != 0) {
		logit("Client version \"%.100s\" uses unsafe RSA signature "
		    "scheme; disabling use of RSA keys", remote_version);
	}
	if ((ssh->compat & SSH_BUG_DERIVEKEY) != 0) {
		fatal("Client version \"%.100s\" uses unsafe key agreement; "
		    "refusing connection", remote_version);
	}

	chop(server_version_string);
	debug("Local version string %.200s", server_version_string);

	if (remote_major != 2 ||
	    (remote_major == 1 && remote_minor != 99)) {
		s = "Protocol major versions differ.\n";
		(void) atomicio(vwrite, sock_out, s, strlen(s));
		close(sock_in);
		close(sock_out);
		logit("Protocol major versions differ for %s port %d: "
		    "%.200s vs. %.200s",
		    ssh_remote_ipaddr(ssh), ssh_remote_port(ssh),
		    server_version_string, client_version_string);
		cleanup_exit(255);
	}
}

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

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

	for (i = 0; i < options.num_host_key_files; i++) {
		if (sensitive_data.host_keys[i]) {
			tmp = key_demote(sensitive_data.host_keys[i]);
			key_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 */
	if (options.gss_authentication)
		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) < 0)
			fatal("setgroups: %.100s", strerror(errno));
		permanently_set_uid(privsep_pw);
	}
}

static int
privsep_preauth(Authctxt *authctxt)
{
	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 = &active_state->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("Could not get agent socket: %s",
				    ssh_err(r));
				have_agent = 0;
			}
		}
		if (box != NULL)
			ssh_sandbox_parent_preauth(box, pid);
		monitor_child_preauth(authctxt, pmonitor);

		/* Wait for the child's exit status */
		while (waitpid(pid, &status, 0) < 0) {
			if (errno == EINTR)
				continue;
			pmonitor->m_pid = -1;
			fatal("%s: waitpid: %s", __func__, strerror(errno));
		}
		privsep_is_preauth = 0;
		pmonitor->m_pid = -1;
		if (WIFEXITED(status)) {
			if (WEXITSTATUS(status) != 0)
				fatal("%s: preauth child exited with status %d",
				    __func__, WEXITSTATUS(status));
		} else if (WIFSIGNALED(status))
			fatal("%s: preauth child terminated by signal %d",
			    __func__, 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(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);
		buffer_clear(&loginmsg);
		monitor_clear_keystate(pmonitor);
		monitor_child_postauth(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(pmonitor);

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

static char *
list_hostkey_types(void)
{
	Buffer b;
	const char *p;
	char *ret;
	int i;
	struct sshkey *key;

	buffer_init(&b);
	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;
		/* Check that the key is accepted in HostkeyAlgorithms */
		if (match_pattern_list(sshkey_ssh_name(key),
		    options.hostkeyalgorithms, 0) != 1) {
			debug3("%s: %s key not permitted by HostkeyAlgorithms",
			    __func__, sshkey_ssh_name(key));
			continue;
		}
		switch (key->type) {
		case KEY_RSA:
		case KEY_DSA:
		case KEY_ECDSA:
		case KEY_ED25519:
			if (buffer_len(&b) > 0)
				buffer_append(&b, ",", 1);
			p = key_ssh_name(key);
			buffer_append(&b, p, strlen(p));

			/* for RSA we also support SHA2 signatures */
			if (key->type == KEY_RSA) {
				p = ",rsa-sha2-512,rsa-sha2-256";
				buffer_append(&b, p, strlen(p));
			}
			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:
		case KEY_DSA_CERT:
		case KEY_ECDSA_CERT:
		case KEY_ED25519_CERT:
			if (buffer_len(&b) > 0)
				buffer_append(&b, ",", 1);
			p = key_ssh_name(key);
			buffer_append(&b, p, strlen(p));
			break;
		}
	}
	if ((ret = sshbuf_dup_string(&b)) == NULL)
		fatal("%s: sshbuf_dup_string failed", __func__);
	buffer_free(&b);
	debug("list_hostkey_types: %s", ret);
	return ret;
}

static struct sshkey *
get_hostkey_by_type(int type, int nid, int need_private, struct ssh *ssh)
{
	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:
			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 &&
		    (key->type != KEY_ECDSA || key->ecdsa_nid == nid))
			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 || 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 || 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)
{
	int i;

	for (i = 0; i < options.num_host_key_files; i++) {
		if (key_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;
	int i, nkeys, r;
	char *fp;

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

	if ((buf = sshbuf_new()) == NULL)
		fatal("%s: sshbuf_new", __func__);
	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("%s: key %d: %s %s", __func__, i,
		    sshkey_ssh_name(key), fp);
		free(fp);
		if (nkeys == 0) {
			packet_start(SSH2_MSG_GLOBAL_REQUEST);
			packet_put_cstring("hostkeys-00@openssh.com");
			packet_put_char(0); /* want-reply */
		}
		sshbuf_reset(buf);
		if ((r = sshkey_putb(key, buf)) != 0)
			fatal("%s: couldn't put hostkey %d: %s",
			    __func__, i, ssh_err(r));
		packet_put_string(sshbuf_ptr(buf), sshbuf_len(buf));
		nkeys++;
	}
	debug3("%s: sent %d hostkeys", __func__, nkeys);
	if (nkeys == 0)
		fatal("%s: no hostkeys", __func__);
	packet_send();
	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
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("drop_connection: p %d, r %d", p, r);
	return (r < p) ? 1 : 0;
}

static void
usage(void)
{
	fprintf(stderr, "%s, %s\n",
	    SSH_RELEASE,
#ifdef WITH_OPENSSL
	    SSLeay_version(SSLEAY_VERSION)
#else
	    "without OpenSSL"
#endif
	);
	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;
	int r;

	debug3("%s: entering fd = %d config len %zu", __func__, fd,
	    sshbuf_len(conf));

	/*
	 * Protocol from reexec master to child:
	 *	string	configuration
	 *	string rngseed		(only if OpenSSL is not self-seeded)
	 */
	if ((m = sshbuf_new()) == NULL)
		fatal("%s: sshbuf_new failed", __func__);
	if ((r = sshbuf_put_stringb(m, conf)) != 0)
		fatal("%s: buffer error: %s", __func__, ssh_err(r));

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

	if (ssh_msg_send(fd, 0, m) == -1)
		fatal("%s: ssh_msg_send failed", __func__);

	sshbuf_free(m);

	debug3("%s: done", __func__);
}

static void
recv_rexec_state(int fd, Buffer *conf)
{
	Buffer m;
	char *cp;
	u_int len;

	debug3("%s: entering fd = %d", __func__, fd);

	buffer_init(&m);

	if (ssh_msg_recv(fd, &m) == -1)
		fatal("%s: ssh_msg_recv failed", __func__);
	if (buffer_get_char(&m) != 0)
		fatal("%s: rexec version mismatch", __func__);

	cp = buffer_get_string(&m, &len);
	if (conf != NULL)
		buffer_append(conf, cp, len);
	free(cp);

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

	buffer_free(&m);

	debug3("%s: done", __func__);
}

/* Accept a connection from inetd */
static void
server_accept_inetd(int *sock_in, int *sock_out)
{
	int fd;

	startup_pipe = -1;
	if (rexeced_flag) {
		close(REEXEC_CONFIG_PASS_FD);
		*sock_in = *sock_out = dup(STDIN_FILENO);
		if (!debug_flag) {
			startup_pipe = dup(REEXEC_STARTUP_PIPE_FD);
			close(REEXEC_STARTUP_PIPE_FD);
		}
	} 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 ((fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) {
		dup2(fd, STDIN_FILENO);
		dup2(fd, STDOUT_FILENO);
		if (!log_stderr)
			dup2(fd, STDERR_FILENO);
		if (fd > (log_stderr ? STDERR_FILENO : STDOUT_FILENO))
			close(fd);
	}
	debug("inetd sockets after dupping: %d, %d", *sock_in, *sock_out);
}

/*
 * Listen for TCP connections
 */
static void
server_listen(void)
{
	int ret, listen_sock, on = 1;
	struct addrinfo *ai;
	char ntop[NI_MAXHOST], strport[NI_MAXSERV];

	for (ai = options.listen_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 < 0) {
			/* 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;
		}
		/*
		 * Set socket options.
		 * Allow local port reuse in TIME_WAIT.
		 */
		if (setsockopt(listen_sock, SOL_SOCKET, SO_REUSEADDR,
		    &on, sizeof(on)) == -1)
			error("setsockopt SO_REUSEADDR: %s", strerror(errno));

		/* 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) < 0) {
			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) < 0)
			fatal("listen on [%s]:%s: %.100s",
			    ntop, strport, strerror(errno));
		logit("Server listening on %s port %s.", ntop, strport);
	}
	freeaddrinfo(options.listen_addrs);

	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)
{
	fd_set *fdset;
	int i, j, ret, maxfd;
	int startups = 0;
	int startup_p[2] = { -1 , -1 };
	struct sockaddr_storage from;
	socklen_t fromlen;
	pid_t pid;
	u_char rnd[256];

	/* setup fd set for accept */
	fdset = NULL;
	maxfd = 0;
	for (i = 0; i < num_listen_socks; i++)
		if (listen_socks[i] > maxfd)
			maxfd = listen_socks[i];
	/* pipes connected to unauthenticated childs */
	startup_pipes = xcalloc(options.max_startups, sizeof(int));
	for (i = 0; i < options.max_startups; i++)
		startup_pipes[i] = -1;

	/*
	 * Stay listening for connections until the system crashes or
	 * the daemon is killed with a signal.
	 */
	for (;;) {
		if (received_sighup)
			sighup_restart();
		free(fdset);
		fdset = xcalloc(howmany(maxfd + 1, NFDBITS),
		    sizeof(fd_mask));

		for (i = 0; i < num_listen_socks; i++)
			FD_SET(listen_socks[i], fdset);
		for (i = 0; i < options.max_startups; i++)
			if (startup_pipes[i] != -1)
				FD_SET(startup_pipes[i], fdset);

		/* Wait in select until there is a connection. */
		ret = select(maxfd+1, fdset, NULL, NULL, NULL);
		if (ret < 0 && errno != EINTR)
			error("select: %.100s", strerror(errno));
		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 (ret < 0)
			continue;

		for (i = 0; i < options.max_startups; i++)
			if (startup_pipes[i] != -1 &&
			    FD_ISSET(startup_pipes[i], fdset)) {
				/*
				 * the read end of the pipe is ready
				 * if the child has closed the pipe
				 * after successful authentication
				 * or if the child has died
				 */
				close(startup_pipes[i]);
				startup_pipes[i] = -1;
				startups--;
			}
		for (i = 0; i < num_listen_socks; i++) {
			if (!FD_ISSET(listen_socks[i], fdset))
				continue;
			fromlen = sizeof(from);
			*newsock = accept(listen_socks[i],
			    (struct sockaddr *)&from, &fromlen);
			if (*newsock < 0) {
				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 (drop_connection(startups) == 1) {
				char *laddr = get_local_ipaddr(*newsock);
				char *raddr = get_peer_ipaddr(*newsock);

				verbose("drop connection #%d from [%s]:%d "
				    "on [%s]:%d past MaxStartups", startups,
				    raddr, get_peer_port(*newsock),
				    laddr, get_local_port(*newsock));
				free(laddr);
				free(raddr);
				close(*newsock);
				continue;
			}
			if (pipe(startup_p) == -1) {
				close(*newsock);
				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];
					if (maxfd < startup_p[0])
						maxfd = startup_p[0];
					startups++;
					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]);
				}
				break;
			}

			/*
			 * Normal production daemon.  Fork, and have
			 * the child process the connection. The
			 * parent continues listening.
			 */
			platform_pre_fork();
			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 break out of the loop 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]);
				break;
			}

			/* Parent.  Stay in the loop. */
			platform_post_fork_parent(pid);
			if (pid < 0)
				error("fork: %.100s", strerror(errno));
			else
				debug("Forked child %ld.", (long)pid);

			close(startup_p[1]);

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

		/* child process check (or debug mode) */
		if (num_listen_socks < 0)
			break;
	}
}

/*
 * 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 autentication 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) < 0)
		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 */
}

/*
 * Main program for the daemon.
 */
int
main(int ac, char **av)
{
	struct ssh *ssh = NULL;
	extern char *optarg;
	extern int optind;
	int r, opt, i, j, on = 1, already_daemon;
	int sock_in = -1, sock_out = -1, newsock = -1;
	const char *remote_ip;
	int remote_port;
	char *fp, *line, *laddr, *logfile = NULL;
	int config_s[2] = { -1 , -1 };
	u_int n;
	u_int64_t ibytes, obytes;
	mode_t new_umask;
	struct sshkey *key;
	struct sshkey *pubkey;
	int keytype;
	Authctxt *authctxt;
	struct connection_info *connection_info = get_connection_info(0, 0);

	ssh_malloc_init();	/* must be called before any mallocs */

#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; 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();

	/* 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':
			if (options.num_host_cert_files >= MAX_HOSTCERTS) {
				fprintf(stderr, "too many host certificates.\n");
				exit(1);
			}
			options.host_cert_files[options.num_host_cert_files++] =
			   derelativise_path(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':
			if (options.num_host_key_files >= MAX_HOSTKEYS) {
				fprintf(stderr, "too many host keys.\n");
				exit(1);
			}
			options.host_key_files[options.num_host_key_files++] = 
			   derelativise_path(optarg);
			break;
		case 't':
			test_flag = 1;
			break;
		case 'T':
			test_flag = 2;
			break;
		case 'C':
			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) != 0)
				exit(1);
			free(line);
			break;
		case '?':
		default:
			usage();
			break;
		}
	}
	if (rexeced_flag || inetd_flag)
		rexec_flag = 0;
	if (!test_flag && (rexec_flag && (av[0] == NULL || *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);

#ifdef WITH_OPENSSL
	OpenSSL_add_all_algorithms();
#endif

	/* 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);

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

#ifdef _UNICOS
	/* Cray can define user privs drop all privs now!
	 * Not needed on PRIV_SU systems!
	 */
	drop_cray_privs();
#endif

	sensitive_data.have_ssh2_key = 0;

	/*
	 * If we're doing an extended config test, make sure we have all of
	 * the parameters we need.  If we're not doing an extended test,
	 * do not silently ignore connection test params.
	 */
	if (test_flag >= 2 && server_match_spec_complete(connection_info) == 0)
		fatal("user, host and addr are all required when testing "
		   "Match configs");
	if (test_flag < 2 && server_match_spec_complete(connection_info) >= 0)
		fatal("Config test connection parameter (-C) provided without "
		   "test mode (-T)");

	/* Fetch our configuration */
	buffer_init(&cfg);
	if (rexeced_flag)
		recv_rexec_state(REEXEC_CONFIG_PASS_FD, &cfg);
	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, NULL);

	seed_rng();

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

	/* challenge-response is implemented via keyboard interactive */
	if (options.challenge_response_authentication)
		options.kbd_interactive_authentication = 1;

	/* 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 (n = 0; n < options.num_auth_methods; n++) {
			if (auth2_methods_valid(options.auth_methods[n],
			    1) == 0)
				break;
		}
		if (n >= options.num_auth_methods)
			fatal("AuthenticationMethods cannot be satisfied by "
			    "enabled authentication methods");
	}

	/* set default channel AF */
	channel_set_af(options.address_family);

	/* 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,
#ifdef WITH_OPENSSL
	    SSLeay_version(SSLEAY_VERSION)
#else
	    "without OpenSSL"
#endif
	);

	/* 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 {
		explicit_bzero(privsep_pw->pw_passwd,
		    strlen(privsep_pw->pw_passwd));
		privsep_pw = pwcopy(privsep_pw);
		free(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("Could not connect to agent \"%s\": %s",
			    options.host_key_agent, ssh_err(r));
	}

	for (i = 0; i < options.num_host_key_files; i++) {
		if (options.host_key_files[i] == NULL)
			continue;
		key = key_load_private(options.host_key_files[i], "", NULL);
		pubkey = key_load_public(options.host_key_files[i], NULL);

		if (pubkey == NULL && key != NULL)
			pubkey = key_demote(key);
		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;
		} else {
			error("Could not 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:
			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);
	}
	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;
		key = key_load_public(options.host_cert_files[i], NULL);
		if (key == NULL) {
			error("Could not load host certificate: %s",
			    options.host_cert_files[i]);
			continue;
		}
		if (!key_is_cert(key)) {
			error("Certificate file is not a certificate: %s",
			    options.host_cert_files[i]);
			key_free(key);
			continue;
		}
		/* Find matching private key */
		for (j = 0; j < options.num_host_key_files; j++) {
			if (key_equal_public(key,
			    sensitive_data.host_keys[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]);
			key_free(key);
			continue;
		}
		sensitive_data.host_certificates[j] = key;
		debug("host certificate: #%d type %d %s", j, key->type,
		    key_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 (server_match_spec_complete(connection_info) == 1)
			parse_server_match_config(&options, 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) {
		rexec_argv = xcalloc(rexec_argc + 2, sizeof(char *));
		for (i = 0; i < 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;
	}

	/* 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);

	/*
	 * 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) < 0)
			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 */
	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();

		signal(SIGHUP, sighup_handler);
		signal(SIGCHLD, main_sigchld_handler);
		signal(SIGTERM, sigterm_handler);
		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 !defined(SSHD_ACQUIRES_CTTY)
	/*
	 * If setsid is called, on some platforms sshd will later acquire a
	 * controlling terminal which will result in "could not set
	 * controlling tty" errors.
	 */
	if (!debug_flag && !inetd_flag && setsid() < 0)
		error("setsid: %.100s", strerror(errno));
#endif

	if (rexec_flag) {
		int fd;

		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]);

		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 ((fd = open(_PATH_DEVNULL, O_RDWR, 0)) != -1) {
			dup2(fd, STDIN_FILENO);
			dup2(fd, STDOUT_FILENO);
			if (fd > STDERR_FILENO)
				close(fd);
		}
		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);

	/*
	 * Disable the key regeneration alarm.  We will not regenerate the
	 * key since we are no longer in a position to give it to anyone. We
	 * will not restart on SIGHUP since it no longer makes sense.
	 */
	alarm(0);
	signal(SIGALRM, SIG_DFL);
	signal(SIGHUP, SIG_DFL);
	signal(SIGTERM, SIG_DFL);
	signal(SIGQUIT, SIG_DFL);
	signal(SIGCHLD, SIG_DFL);
	signal(SIGINT, SIG_DFL);

	/*
	 * Register our connection.  This turns encryption off because we do
	 * not have a key.
	 */
	packet_set_connection(sock_in, sock_out);
	packet_set_server();
	ssh = active_state; /* XXX */
	check_ip_options(ssh);

	/* Set SO_KEEPALIVE if requested. */
	if (options.tcp_keep_alive && packet_connection_is_on_socket() &&
	    setsockopt(sock_in, SOL_SOCKET, SO_KEEPALIVE, &on, sizeof(on)) < 0)
		error("setsockopt SO_KEEPALIVE: %.100s", strerror(errno));

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

	/*
	 * 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

	/* Log the connection. */
	laddr = get_local_ipaddr(sock_in);
	verbose("Connection from %s port %d on %s port %d",
	    remote_ip, remote_port, laddr,  ssh_local_port(ssh));
	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.
	 */
	signal(SIGALRM, grace_alarm_handler);
	if (!debug_flag)
		alarm(options.login_grace_time);

	sshd_exchange_identification(ssh, sock_in, sock_out);
	packet_set_nonblocking();

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

	authctxt->loginmsg = &loginmsg;

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

	/* prepare buffer to collect messages to display to user after login */
	buffer_init(&loginmsg);
	auth_debug_reset();

	if (use_privsep) {
		if (privsep_preauth(authctxt) == 1)
			goto authenticated;
	} else if (have_agent) {
		if ((r = ssh_get_authentication_socket(&auth_sock)) != 0) {
			error("Unable to get agent socket: %s", ssh_err(r));
			have_agent = 0;
		}
	}

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

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

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

#ifdef SSH_AUDIT_EVENTS
	audit_event(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();
	}
#endif

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

	packet_set_timeout(options.client_alive_interval,
	    options.client_alive_count_max);

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

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

	/* The connection has been terminated. */
	packet_get_bytes(&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_CONNECTION_CLOSE));
#endif

	packet_close();

	if (use_privsep)
		mm_terminate();

	exit(0);
}

int
sshd_hostkey_sign(struct sshkey *privkey, struct sshkey *pubkey,
    u_char **signature, size_t *slen, const u_char *data, size_t dlen,
    const char *alg, u_int flag)
{
	int r;
	u_int xxx_slen, xxx_dlen = dlen;

	if (privkey) {
		if (PRIVSEP(key_sign(privkey, signature, &xxx_slen, data, xxx_dlen,
		    alg) < 0))
			fatal("%s: key_sign failed", __func__);
		if (slen)
			*slen = xxx_slen;
	} else if (use_privsep) {
		if (mm_key_sign(pubkey, signature, &xxx_slen, data, xxx_dlen,
		    alg) < 0)
			fatal("%s: pubkey_sign failed", __func__);
		if (slen)
			*slen = xxx_slen;
	} else {
		if ((r = ssh_agent_sign(auth_sock, pubkey, signature, slen,
		    data, dlen, alg, datafellows)) != 0)
			fatal("%s: ssh_agent_sign failed: %s",
			    __func__, ssh_err(r));
	}
	return 0;
}

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

	myproposal[PROPOSAL_KEX_ALGS] = compat_kex_proposal(
	    options.kex_algorithms);
	myproposal[PROPOSAL_ENC_ALGS_CTOS] = compat_cipher_proposal(
	    options.ciphers);
	myproposal[PROPOSAL_ENC_ALGS_STOC] = compat_cipher_proposal(
	    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)
		packet_set_rekey_limits(options.rekey_limit,
		    options.rekey_interval);

	myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = compat_pkalg_proposal(
	    list_hostkey_types());

	/* start key exchange */
	if ((r = kex_setup(active_state, myproposal)) != 0)
		fatal("kex_setup: %s", ssh_err(r));
	kex = active_state->kex;
#ifdef WITH_OPENSSL
	kex->kex[KEX_DH_GRP1_SHA1] = kexdh_server;
	kex->kex[KEX_DH_GRP14_SHA1] = kexdh_server;
	kex->kex[KEX_DH_GRP14_SHA256] = kexdh_server;
	kex->kex[KEX_DH_GRP16_SHA512] = kexdh_server;
	kex->kex[KEX_DH_GRP18_SHA512] = kexdh_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] = kexecdh_server;
# endif
#endif
	kex->kex[KEX_C25519_SHA256] = kexc25519_server;
	kex->server = 1;
	kex->client_version_string=client_version_string;
	kex->server_version_string=server_version_string;
	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(active_state, DISPATCH_BLOCK, &kex->done);

	session_id2 = kex->session_id;
	session_id2_len = kex->session_id_len;

#ifdef DEBUG_KEXDH
	/* send 1st encrypted/maced/compressed message */
	packet_start(SSH2_MSG_IGNORE);
	packet_put_cstring("markus");
	packet_send();
	packet_write_wait();
#endif
	debug("KEX done");
}

/* server specific fatal cleanup */
void
cleanup_exit(int i)
{
	if (the_authctxt) {
		do_cleanup(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("%s: kill(%d): %s", __func__,
				    pmonitor->m_pid, strerror(errno));
		}
	}
#ifdef SSH_AUDIT_EVENTS
	/* done after do_cleanup so it can cancel the PAM auth 'thread' */
	if (!use_privsep || mm_is_monitor())
		audit_event(SSH_CONNECTION_ABANDON);
#endif
	_exit(i);
}