path: root/usr.bin/ssh/sshd.c

/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Created: Fri Mar 17 17:09:28 1995 ylo
 * 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.
 */

#include "includes.h"
RCSID("$Id: sshd.c,v 1.67 1999/12/06 12:10:12 deraadt Exp $");

#include "xmalloc.h"
#include "rsa.h"
#include "ssh.h"
#include "pty.h"
#include "packet.h"
#include "buffer.h"
#include "cipher.h"
#include "mpaux.h"
#include "servconf.h"
#include "uidswap.h"
#include "compat.h"

#ifdef LIBWRAP
#include <tcpd.h>
#include <syslog.h>
int allow_severity = LOG_INFO;
int deny_severity = LOG_WARNING;
#endif /* LIBWRAP */

#ifndef O_NOCTTY
#define O_NOCTTY	0
#endif

/* Local Xauthority file. */
static char *xauthfile = NULL;

/* Server configuration options. */
ServerOptions options;

/* Name of the server configuration file. */
char *config_file_name = 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 is being started from inetd. */
int inetd_flag = 0;

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

/* argv[0] without path. */
char *av0;

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

/*
 * This is set to the socket that the server is listening; this is used in
 * the SIGHUP signal handler.
 */
int listen_sock;

/*
 * 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;

/* Flags set in auth-rsa from authorized_keys flags.  These are set in auth-rsa.c. */
int no_port_forwarding_flag = 0;
int no_agent_forwarding_flag = 0;
int no_x11_forwarding_flag = 0;
int no_pty_flag = 0;

/* RSA authentication "command=" option. */
char *forced_command = NULL;

/* RSA authentication "environment=" options. */
struct envstring *custom_environment = NULL;

/* Session id for the current session. */
unsigned char session_id[16];

/*
 * 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 {
	RSA *private_key;	 /* Private part of server key. */
	RSA *host_key;		 /* Private part of host key. */
} sensitive_data;

/*
 * Flag indicating whether the current session key has been used.  This flag
 * is set whenever the key is used, and cleared when the key is regenerated.
 */
int key_used = 0;

/* This is set to true when SIGHUP is received. */
int received_sighup = 0;

/* Public side of the server key.  This value is regenerated regularly with
   the private key. */
RSA *public_key;

/* Prototypes for various functions defined later in this file. */
void do_connection();
void do_authentication(char *user);
void do_authloop(struct passwd * pw);
void do_fake_authloop(char *user);
void do_authenticated(struct passwd * pw);
void do_exec_pty(const char *command, int ptyfd, int ttyfd,
	         const char *ttyname, struct passwd * pw, const char *term,
	         const char *display, const char *auth_proto,
	         const char *auth_data);
void do_exec_no_pty(const char *command, struct passwd * pw,
	            const char *display, const char *auth_proto,
	            const char *auth_data);
void do_child(const char *command, struct passwd * pw, const char *term,
	      const char *display, const char *auth_proto,
	      const char *auth_data, const char *ttyname);

/*
 * 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).
 */
void 
sighup_handler(int sig)
{
	received_sighup = 1;
	signal(SIGHUP, sighup_handler);
}

/*
 * Called from the main program after receiving SIGHUP.
 * Restarts the server.
 */
void 
sighup_restart()
{
	log("Received SIGHUP; restarting.");
	close(listen_sock);
	execv(saved_argv[0], saved_argv);
	log("RESTART FAILED: av0='%s', error: %s.", av0, strerror(errno));
	exit(1);
}

/*
 * Generic signal handler for terminating signals in the master daemon.
 * These close the listen socket; not closing it seems to cause "Address
 * already in use" problems on some machines, which is inconvenient.
 */
void 
sigterm_handler(int sig)
{
	log("Received signal %d; terminating.", sig);
	close(listen_sock);
	exit(255);
}

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

	while (waitpid(-1, &status, WNOHANG) > 0)
		;

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

/*
 * Signal handler for the alarm after the login grace period has expired.
 */
void 
grace_alarm_handler(int sig)
{
	/* Close the connection. */
	packet_close();

	/* Log error and exit. */
	fatal("Timeout before authentication for %s.", get_remote_ipaddr());
}

/*
 * convert ssh auth msg type into description
 */
char *
get_authname(int type)
{
	switch (type) {
	case SSH_CMSG_AUTH_PASSWORD:
		return "password";
	case SSH_CMSG_AUTH_RSA:
		return "rsa";
	case SSH_CMSG_AUTH_RHOSTS_RSA:
		return "rhosts-rsa";
	case SSH_CMSG_AUTH_RHOSTS:
		return "rhosts";
#ifdef KRB4
	case SSH_CMSG_AUTH_KERBEROS:
		return "kerberos";
#endif
#ifdef SKEY
	case SSH_CMSG_AUTH_TIS_RESPONSE:
		return "s/key";
#endif
	}
	fatal("get_authname: unknown auth %d: internal error", type);
	return NULL;
}

/*
 * Signal handler for the key regeneration alarm.  Note that this
 * alarm only occurs in the daemon waiting for connections, and it does not
 * do anything with the private key or random state before forking.
 * Thus there should be no concurrency control/asynchronous execution
 * problems.
 */
void 
key_regeneration_alarm(int sig)
{
	int save_errno = errno;

	/* Check if we should generate a new key. */
	if (key_used) {
		/* This should really be done in the background. */
		log("Generating new %d bit RSA key.", options.server_key_bits);

		if (sensitive_data.private_key != NULL)
			RSA_free(sensitive_data.private_key);
		sensitive_data.private_key = RSA_new();

		if (public_key != NULL)
			RSA_free(public_key);
		public_key = RSA_new();

		rsa_generate_key(sensitive_data.private_key, public_key,
				 options.server_key_bits);
		arc4random_stir();
		key_used = 0;
		log("RSA key generation complete.");
	}
	/* Reschedule the alarm. */
	signal(SIGALRM, key_regeneration_alarm);
	alarm(options.key_regeneration_time);
	errno = save_errno;
}

/*
 * Main program for the daemon.
 */
int
main(int ac, char **av)
{
	extern char *optarg;
	extern int optind;
	int opt, aux, sock_in, sock_out, newsock, i, pid, on = 1;
	int remote_major, remote_minor;
	int silentrsa = 0;
	struct sockaddr_in sin;
	char buf[100];			/* Must not be larger than remote_version. */
	char remote_version[100];	/* Must be at least as big as buf. */
	const char *remote_ip;
	int remote_port;
	char *comment;
	FILE *f;
	struct linger linger;

	/* Save argv[0]. */
	saved_argv = av;
	if (strchr(av[0], '/'))
		av0 = strrchr(av[0], '/') + 1;
	else
		av0 = av[0];

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

	/* Parse command-line arguments. */
	while ((opt = getopt(ac, av, "f:p:b:k:h:g:V:diqQ")) != EOF) {
		switch (opt) {
		case 'f':
			config_file_name = optarg;
			break;
		case 'd':
			debug_flag = 1;
			options.log_level = SYSLOG_LEVEL_DEBUG;
			break;
		case 'i':
			inetd_flag = 1;
			break;
		case 'Q':
			silentrsa = 1;
			break;
		case 'q':
			options.log_level = SYSLOG_LEVEL_QUIET;
			break;
		case 'b':
			options.server_key_bits = atoi(optarg);
			break;
		case 'p':
			options.port = atoi(optarg);
			break;
		case 'g':
			options.login_grace_time = atoi(optarg);
			break;
		case 'k':
			options.key_regeneration_time = atoi(optarg);
			break;
		case 'h':
			options.host_key_file = optarg;
			break;
		case 'V':
			client_version_string = optarg;
			/* only makes sense with inetd_flag, i.e. no listen() */
			inetd_flag = 1;
			break;
		case '?':
		default:
			fprintf(stderr, "sshd version %s\n", SSH_VERSION);
			fprintf(stderr, "Usage: %s [options]\n", av0);
			fprintf(stderr, "Options:\n");
			fprintf(stderr, "  -f file    Configuration file (default %s)\n", SERVER_CONFIG_FILE);
			fprintf(stderr, "  -d         Debugging mode\n");
			fprintf(stderr, "  -i         Started from inetd\n");
			fprintf(stderr, "  -q         Quiet (no logging)\n");
			fprintf(stderr, "  -p port    Listen on the specified port (default: 22)\n");
			fprintf(stderr, "  -k seconds Regenerate server key every this many seconds (default: 3600)\n");
			fprintf(stderr, "  -g seconds Grace period for authentication (default: 300)\n");
			fprintf(stderr, "  -b bits    Size of server RSA key (default: 768 bits)\n");
			fprintf(stderr, "  -h file    File from which to read host key (default: %s)\n",
				HOST_KEY_FILE);
			exit(1);
		}
	}

	/* check if RSA support exists */
	if (rsa_alive() == 0) {
		if (silentrsa == 0)
			printf("sshd: no RSA support in libssl and libcrypto -- exiting.  See ssl(8)\n");
		log("no RSA support in libssl and libcrypto -- exiting.  See ssl(8)");
		exit(1);
	}
	/* Read server configuration options from the configuration file. */
	read_server_config(&options, config_file_name);

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

	/* Check certain values for sanity. */
	if (options.server_key_bits < 512 ||
	    options.server_key_bits > 32768) {
		fprintf(stderr, "Bad server key size.\n");
		exit(1);
	}
	if (options.port < 1 || options.port > 65535) {
		fprintf(stderr, "Bad port number.\n");
		exit(1);
	}
	/* Check that there are no remaining arguments. */
	if (optind < ac) {
		fprintf(stderr, "Extra argument %s.\n", av[optind]);
		exit(1);
	}
	/* Force logging to stderr while loading the private host key
	   unless started from inetd */
	log_init(av0, options.log_level, options.log_facility, !inetd_flag);

	debug("sshd version %.100s", SSH_VERSION);

	sensitive_data.host_key = RSA_new();
	errno = 0;
	/* Load the host key.  It must have empty passphrase. */
	if (!load_private_key(options.host_key_file, "",
			      sensitive_data.host_key, &comment)) {
		error("Could not load host key: %.200s: %.100s",
		      options.host_key_file, strerror(errno));
		exit(1);
	}
	xfree(comment);

	/* Initialize the log (it is reinitialized below in case we
	   forked). */
	if (debug_flag && !inetd_flag)
		log_stderr = 1;
	log_init(av0, options.log_level, options.log_facility, log_stderr);

	/* If not in debugging mode, and not started from inetd,
	   disconnect from the controlling terminal, and fork.  The
	   original process exits. */
	if (!debug_flag && !inetd_flag) {
#ifdef TIOCNOTTY
		int fd;
#endif /* TIOCNOTTY */
		if (daemon(0, 0) < 0)
			fatal("daemon() failed: %.200s", strerror(errno));

		/* Disconnect from the controlling tty. */
#ifdef TIOCNOTTY
		fd = open("/dev/tty", O_RDWR | O_NOCTTY);
		if (fd >= 0) {
			(void) ioctl(fd, TIOCNOTTY, NULL);
			close(fd);
		}
#endif /* TIOCNOTTY */
	}
	/* Reinitialize the log (because of the fork above). */
	log_init(av0, options.log_level, options.log_facility, log_stderr);

	/* Check that server and host key lengths differ sufficiently.
	   This is necessary to make double encryption work with rsaref.
	   Oh, I hate software patents. I dont know if this can go? Niels */
	if (options.server_key_bits >
	BN_num_bits(sensitive_data.host_key->n) - SSH_KEY_BITS_RESERVED &&
	    options.server_key_bits <
	BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) {
		options.server_key_bits =
			BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED;
		debug("Forcing server key to %d bits to make it differ from host key.",
		      options.server_key_bits);
	}
	/* Do not display messages to stdout in RSA code. */
	rsa_set_verbose(0);

	/* Initialize the random number generator. */
	arc4random_stir();

	/* Chdir to the root directory so that the current disk can be
	   unmounted if desired. */
	chdir("/");

	/* Close connection cleanly after attack. */
	cipher_attack_detected = packet_disconnect;

	/* Start listening for a socket, unless started from inetd. */
	if (inetd_flag) {
		int s1, s2;
		s1 = dup(0);	/* Make sure descriptors 0, 1, and 2 are in use. */
		s2 = dup(s1);
		sock_in = dup(0);
		sock_out = dup(1);
		/* 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. */
		debug("inetd sockets after dupping: %d, %d", sock_in, sock_out);

		public_key = RSA_new();
		sensitive_data.private_key = RSA_new();

		log("Generating %d bit RSA key.", options.server_key_bits);
		rsa_generate_key(sensitive_data.private_key, public_key,
				 options.server_key_bits);
		arc4random_stir();
		log("RSA key generation complete.");
	} else {
		/* Create socket for listening. */
		listen_sock = socket(AF_INET, SOCK_STREAM, 0);
		if (listen_sock < 0)
			fatal("socket: %.100s", strerror(errno));

		/* Set socket options.  We try to make the port reusable
		   and have it close as fast as possible without waiting
		   in unnecessary wait states on close. */
		setsockopt(listen_sock, SOL_SOCKET, SO_REUSEADDR, (void *) &on,
			   sizeof(on));
		linger.l_onoff = 1;
		linger.l_linger = 5;
		setsockopt(listen_sock, SOL_SOCKET, SO_LINGER, (void *) &linger,
			   sizeof(linger));

		memset(&sin, 0, sizeof(sin));
		sin.sin_family = AF_INET;
		sin.sin_addr = options.listen_addr;
		sin.sin_port = htons(options.port);

		if (bind(listen_sock, (struct sockaddr *) & sin, sizeof(sin)) < 0) {
			error("bind: %.100s", strerror(errno));
			shutdown(listen_sock, SHUT_RDWR);
			close(listen_sock);
			fatal("Bind to port %d failed.", options.port);
		}
		if (!debug_flag) {
			/*
			 * Record our pid in /etc/sshd_pid to make it easier
			 * to kill the correct sshd.  We don\'t want to do
			 * this before the bind above because the bind will
			 * fail if there already is a daemon, and this will
			 * overwrite any old pid in the file.
			 */
			f = fopen(SSH_DAEMON_PID_FILE, "w");
			if (f) {
				fprintf(f, "%u\n", (unsigned int) getpid());
				fclose(f);
			}
		}

		log("Server listening on port %d.", options.port);
		if (listen(listen_sock, 5) < 0)
			fatal("listen: %.100s", strerror(errno));

		public_key = RSA_new();
		sensitive_data.private_key = RSA_new();

		log("Generating %d bit RSA key.", options.server_key_bits);
		rsa_generate_key(sensitive_data.private_key, public_key,
				 options.server_key_bits);
		arc4random_stir();
		log("RSA key generation complete.");

		/* Schedule server key regeneration alarm. */
		signal(SIGALRM, key_regeneration_alarm);
		alarm(options.key_regeneration_time);

		/* Arrange to restart on SIGHUP.  The handler needs listen_sock. */
		signal(SIGHUP, sighup_handler);
		signal(SIGTERM, sigterm_handler);
		signal(SIGQUIT, sigterm_handler);

		/* Arrange SIGCHLD to be caught. */
		signal(SIGCHLD, main_sigchld_handler);

		/*
		 * Stay listening for connections until the system crashes or
		 * the daemon is killed with a signal.
		 */
		for (;;) {
			if (received_sighup)
				sighup_restart();
			/* Wait in accept until there is a connection. */
			aux = sizeof(sin);
			newsock = accept(listen_sock, (struct sockaddr *) & sin, &aux);
			if (received_sighup)
				sighup_restart();
			if (newsock < 0) {
				if (errno == EINTR)
					continue;
				error("accept: %.100s", strerror(errno));
				continue;
			}
			/*
			 * 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_sock);
				sock_in = newsock;
				sock_out = newsock;
				pid = getpid();
				break;
			} else {
				/*
				 * Normal production daemon.  Fork, and have
				 * the child process the connection. The
				 * parent continues listening.
				 */
				if ((pid = fork()) == 0) {
					/*
					 * Child.  Close the listening socket, and start using the
					 * accepted socket.  Reinitialize logging (since our pid has
					 * changed).  We break out of the loop to handle the connection.
					 */
					close(listen_sock);
					sock_in = newsock;
					sock_out = newsock;
					log_init(av0, options.log_level, options.log_facility, log_stderr);
					break;
				}
			}

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

			/* Mark that the key has been used (it was "given" to the child). */
			key_used = 1;

			arc4random_stir();

			/* Close the new socket (the child is now taking care of it). */
			close(newsock);
		}
	}

	/* This is the child processing a new connection. */

	/*
	 * 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);

	/*
	 * Set socket options for the connection.  We want the socket to
	 * close as fast as possible without waiting for anything.  If the
	 * connection is not a socket, these will do nothing.
	 */
	/* setsockopt(sock_in, SOL_SOCKET, SO_REUSEADDR, (void *)&on, sizeof(on)); */
	linger.l_onoff = 1;
	linger.l_linger = 5;
	setsockopt(sock_in, SOL_SOCKET, SO_LINGER, (void *) &linger, sizeof(linger));

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

	remote_port = get_remote_port();
	remote_ip = get_remote_ipaddr();

	/* Check whether logins are denied from this host. */
#ifdef LIBWRAP
	{
		struct request_info req;

		request_init(&req, RQ_DAEMON, av0, RQ_FILE, sock_in, NULL);
		fromhost(&req);

		if (!hosts_access(&req)) {
			close(sock_in);
			close(sock_out);
			refuse(&req);
		}
		verbose("Connection from %.500s port %d", eval_client(&req), remote_port);
	}
#else
	/* Log the connection. */
	verbose("Connection from %.500s port %d", remote_ip, remote_port);
#endif /* LIBWRAP */

	/*
	 * 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);

	if (client_version_string != NULL) {
		/* we are exec'ed by sshd2, so skip exchange of protocol version */
		strlcpy(buf, client_version_string, sizeof(buf));
	} else {
		/* Send our protocol version identification. */
		snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n",
			 PROTOCOL_MAJOR, PROTOCOL_MINOR, SSH_VERSION);
		if (write(sock_out, buf, strlen(buf)) != strlen(buf))
			fatal("Could not write ident string to %s.", get_remote_ipaddr());

		/* Read other side\'s version identification. */
		for (i = 0; i < sizeof(buf) - 1; i++) {
			if (read(sock_in, &buf[i], 1) != 1)
				fatal("Did not receive ident string from %s.", get_remote_ipaddr());
			if (buf[i] == '\r') {
				buf[i] = '\n';
				buf[i + 1] = 0;
				break;
			}
			if (buf[i] == '\n') {
				/* buf[i] == '\n' */
				buf[i + 1] = 0;
				break;
			}
		}
		buf[sizeof(buf) - 1] = 0;
	}

	/*
	 * Check that the versions match.  In future this might accept
	 * several versions and set appropriate flags to handle them.
	 */
	if (sscanf(buf, "SSH-%d.%d-%[^\n]\n", &remote_major, &remote_minor,
		   remote_version) != 3) {
		const char *s = "Protocol mismatch.\n";
		(void) write(sock_out, s, strlen(s));
		close(sock_in);
		close(sock_out);
		fatal("Bad protocol version identification '%.100s' from %s",
		      buf, get_remote_ipaddr());
	}
	debug("Client protocol version %d.%d; client software version %.100s",
	      remote_major, remote_minor, remote_version);
	if (remote_major != PROTOCOL_MAJOR) {
		const char *s = "Protocol major versions differ.\n";
		(void) write(sock_out, s, strlen(s));
		close(sock_in);
		close(sock_out);
		fatal("Protocol major versions differ for %s: %d vs. %d",
		      get_remote_ipaddr(),
		      PROTOCOL_MAJOR, remote_major);
	}
	/* Check that the client has sufficiently high software version. */
	if (remote_major == 1 && remote_minor < 3)
		packet_disconnect("Your ssh version is too old and is no longer supported.  Please install a newer version.");

	if (remote_major == 1 && remote_minor == 3) {
		enable_compat13();
		if (strcmp(remote_version, "OpenSSH-1.1") != 0) {
			debug("Agent forwarding disabled, remote version is not compatible.");
			no_agent_forwarding_flag = 1;
		}
	}
	/*
	 * Check that the connection comes from a privileged port.  Rhosts-
	 * and Rhosts-RSA-Authentication only make sense from priviledged
	 * programs.  Of course, if the intruder has root access on his local
	 * machine, he can connect from any port.  So do not use these
	 * authentication methods from machines that you do not trust.
	 */
	if (remote_port >= IPPORT_RESERVED ||
	    remote_port < IPPORT_RESERVED / 2) {
		options.rhosts_authentication = 0;
		options.rhosts_rsa_authentication = 0;
	}
	packet_set_nonblocking();

	/* Handle the connection. */
	do_connection();

#ifdef KRB4
	/* Cleanup user's ticket cache file. */
	if (options.kerberos_ticket_cleanup)
		(void) dest_tkt();
#endif /* KRB4 */

	/* Cleanup user's local Xauthority file. */
	if (xauthfile)
		unlink(xauthfile);

	/* The connection has been terminated. */
	verbose("Closing connection to %.100s", remote_ip);
	packet_close();
	exit(0);
}

/*
 * Process an incoming connection.  Protocol version identifiers have already
 * been exchanged.  This sends server key and performs the key exchange.
 * Server and host keys will no longer be needed after this functions.
 */
void
do_connection()
{
	int i, len;
	BIGNUM *session_key_int;
	unsigned char session_key[SSH_SESSION_KEY_LENGTH];
	unsigned char check_bytes[8];
	char *user;
	unsigned int cipher_type, auth_mask, protocol_flags;
	int plen, slen;
	u_int32_t rand = 0;

	/*
	 * Generate check bytes that the client must send back in the user
	 * packet in order for it to be accepted; this is used to defy ip
	 * spoofing attacks.  Note that this only works against somebody
	 * doing IP spoofing from a remote machine; any machine on the local
	 * network can still see outgoing packets and catch the random
	 * cookie.  This only affects rhosts authentication, and this is one
	 * of the reasons why it is inherently insecure.
	 */
	for (i = 0; i < 8; i++) {
		if (i % 4 == 0)
			rand = arc4random();
		check_bytes[i] = rand & 0xff;
		rand >>= 8;
	}

	/*
	 * Send our public key.  We include in the packet 64 bits of random
	 * data that must be matched in the reply in order to prevent IP
	 * spoofing.
	 */
	packet_start(SSH_SMSG_PUBLIC_KEY);
	for (i = 0; i < 8; i++)
		packet_put_char(check_bytes[i]);

	/* Store our public server RSA key. */
	packet_put_int(BN_num_bits(public_key->n));
	packet_put_bignum(public_key->e);
	packet_put_bignum(public_key->n);

	/* Store our public host RSA key. */
	packet_put_int(BN_num_bits(sensitive_data.host_key->n));
	packet_put_bignum(sensitive_data.host_key->e);
	packet_put_bignum(sensitive_data.host_key->n);

	/* Put protocol flags. */
	packet_put_int(SSH_PROTOFLAG_HOST_IN_FWD_OPEN);

	/* Declare which ciphers we support. */
	packet_put_int(cipher_mask());

	/* Declare supported authentication types. */
	auth_mask = 0;
	if (options.rhosts_authentication)
		auth_mask |= 1 << SSH_AUTH_RHOSTS;
	if (options.rhosts_rsa_authentication)
		auth_mask |= 1 << SSH_AUTH_RHOSTS_RSA;
	if (options.rsa_authentication)
		auth_mask |= 1 << SSH_AUTH_RSA;
#ifdef KRB4
	if (options.kerberos_authentication)
		auth_mask |= 1 << SSH_AUTH_KERBEROS;
#endif
#ifdef AFS
	if (options.kerberos_tgt_passing)
		auth_mask |= 1 << SSH_PASS_KERBEROS_TGT;
	if (options.afs_token_passing)
		auth_mask |= 1 << SSH_PASS_AFS_TOKEN;
#endif
#ifdef SKEY
	if (options.skey_authentication == 1)
		auth_mask |= 1 << SSH_AUTH_TIS;
#endif
	if (options.password_authentication)
		auth_mask |= 1 << SSH_AUTH_PASSWORD;
	packet_put_int(auth_mask);

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

	debug("Sent %d bit public key and %d bit host key.",
	      BN_num_bits(public_key->n), BN_num_bits(sensitive_data.host_key->n));

	/* Read clients reply (cipher type and session key). */
	packet_read_expect(&plen, SSH_CMSG_SESSION_KEY);

	/* Get cipher type. */
	cipher_type = packet_get_char();

	/* Get check bytes from the packet.  These must match those we
	   sent earlier with the public key packet. */
	for (i = 0; i < 8; i++)
		if (check_bytes[i] != packet_get_char())
			packet_disconnect("IP Spoofing check bytes do not match.");

	debug("Encryption type: %.200s", cipher_name(cipher_type));

	/* Get the encrypted integer. */
	session_key_int = BN_new();
	packet_get_bignum(session_key_int, &slen);

	protocol_flags = packet_get_int();
	packet_set_protocol_flags(protocol_flags);

	packet_integrity_check(plen, 1 + 8 + slen + 4, SSH_CMSG_SESSION_KEY);

	/*
	 * Decrypt it using our private server key and private host key (key
	 * with larger modulus first).
	 */
	if (BN_cmp(sensitive_data.private_key->n, sensitive_data.host_key->n) > 0) {
		/* Private key has bigger modulus. */
		if (BN_num_bits(sensitive_data.private_key->n) <
		    BN_num_bits(sensitive_data.host_key->n) + SSH_KEY_BITS_RESERVED) {
			fatal("do_connection: %s: private_key %d < host_key %d + SSH_KEY_BITS_RESERVED %d",
			      get_remote_ipaddr(),
			      BN_num_bits(sensitive_data.private_key->n),
			      BN_num_bits(sensitive_data.host_key->n),
			      SSH_KEY_BITS_RESERVED);
		}
		rsa_private_decrypt(session_key_int, session_key_int,
				    sensitive_data.private_key);
		rsa_private_decrypt(session_key_int, session_key_int,
				    sensitive_data.host_key);
	} else {
		/* Host key has bigger modulus (or they are equal). */
		if (BN_num_bits(sensitive_data.host_key->n) <
		    BN_num_bits(sensitive_data.private_key->n) + SSH_KEY_BITS_RESERVED) {
			fatal("do_connection: %s: host_key %d < private_key %d + SSH_KEY_BITS_RESERVED %d",
			      get_remote_ipaddr(),
			      BN_num_bits(sensitive_data.host_key->n),
			      BN_num_bits(sensitive_data.private_key->n),
			      SSH_KEY_BITS_RESERVED);
		}
		rsa_private_decrypt(session_key_int, session_key_int,
				    sensitive_data.host_key);
		rsa_private_decrypt(session_key_int, session_key_int,
				    sensitive_data.private_key);
	}

	compute_session_id(session_id, check_bytes,
			   sensitive_data.host_key->n,
			   sensitive_data.private_key->n);

	/*
	 * Extract session key from the decrypted integer.  The key is in the
	 * least significant 256 bits of the integer; the first byte of the
	 * key is in the highest bits.
	 */
	BN_mask_bits(session_key_int, sizeof(session_key) * 8);
	len = BN_num_bytes(session_key_int);
	if (len < 0 || len > sizeof(session_key))
		fatal("do_connection: bad len from %s: session_key_int %d > sizeof(session_key) %d",
		      get_remote_ipaddr(),
		      len, sizeof(session_key));
	memset(session_key, 0, sizeof(session_key));
	BN_bn2bin(session_key_int, session_key + sizeof(session_key) - len);

	/* Xor the first 16 bytes of the session key with the session id. */
	for (i = 0; i < 16; i++)
		session_key[i] ^= session_id[i];

	/* Destroy the decrypted integer.  It is no longer needed. */
	BN_clear_free(session_key_int);

	/* Set the session key.  From this on all communications will be encrypted. */
	packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, cipher_type);

	/* Destroy our copy of the session key.  It is no longer needed. */
	memset(session_key, 0, sizeof(session_key));

	debug("Received session key; encryption turned on.");

	/* Send an acknowledgement packet.  Note that this packet is sent encrypted. */
	packet_start(SSH_SMSG_SUCCESS);
	packet_send();
	packet_write_wait();

	/* Get the name of the user that we wish to log in as. */
	packet_read_expect(&plen, SSH_CMSG_USER);

	/* Get the user name. */
	{
		int ulen;
		user = packet_get_string(&ulen);
		packet_integrity_check(plen, (4 + ulen), SSH_CMSG_USER);
	}

	/* Destroy the private and public keys.  They will no longer be needed. */
	RSA_free(public_key);
	RSA_free(sensitive_data.private_key);
	RSA_free(sensitive_data.host_key);

	setproctitle("%s", user);
	/* Do the authentication. */
	do_authentication(user);
}

/*
 * Check if the user is allowed to log in via ssh. If user is listed in
 * DenyUsers or user's primary group is listed in DenyGroups, false will
 * be returned. If AllowUsers isn't empty and user isn't listed there, or
 * if AllowGroups isn't empty and user isn't listed there, false will be
 * returned. Otherwise true is returned.
 * XXX This function should also check if user has a valid shell
 */
static int
allowed_user(struct passwd * pw)
{
	struct group *grp;
	int i;

	/* Shouldn't be called if pw is NULL, but better safe than sorry... */
	if (!pw)
		return 0;

	/* XXX Should check for valid login shell */

	/* Return false if user is listed in DenyUsers */
	if (options.num_deny_users > 0) {
		if (!pw->pw_name)
			return 0;
		for (i = 0; i < options.num_deny_users; i++)
			if (match_pattern(pw->pw_name, options.deny_users[i]))
				return 0;
	}
	/* Return false if AllowUsers isn't empty and user isn't listed there */
	if (options.num_allow_users > 0) {
		if (!pw->pw_name)
			return 0;
		for (i = 0; i < options.num_allow_users; i++)
			if (match_pattern(pw->pw_name, options.allow_users[i]))
				break;
		/* i < options.num_allow_users iff we break for loop */
		if (i >= options.num_allow_users)
			return 0;
	}
	/* Get the primary group name if we need it. Return false if it fails */
	if (options.num_deny_groups > 0 || options.num_allow_groups > 0) {
		grp = getgrgid(pw->pw_gid);
		if (!grp)
			return 0;

		/* Return false if user's group is listed in DenyGroups */
		if (options.num_deny_groups > 0) {
			if (!grp->gr_name)
				return 0;
			for (i = 0; i < options.num_deny_groups; i++)
				if (match_pattern(grp->gr_name, options.deny_groups[i]))
					return 0;
		}
		/*
		 * Return false if AllowGroups isn't empty and user's group
		 * isn't listed there
		 */
		if (options.num_allow_groups > 0) {
			if (!grp->gr_name)
				return 0;
			for (i = 0; i < options.num_allow_groups; i++)
				if (match_pattern(grp->gr_name, options.allow_groups[i]))
					break;
			/* i < options.num_allow_groups iff we break for
			   loop */
			if (i >= options.num_allow_groups)
				return 0;
		}
	}
	/* We found no reason not to let this user try to log on... */
	return 1;
}

/*
 * Performs authentication of an incoming connection.  Session key has already
 * been exchanged and encryption is enabled.  User is the user name to log
 * in as (received from the client).
 */
void
do_authentication(char *user)
{
	struct passwd *pw, pwcopy;

#ifdef AFS
	/* If machine has AFS, set process authentication group. */
	if (k_hasafs()) {
		k_setpag();
		k_unlog();
	}
#endif /* AFS */

	/* Verify that the user is a valid user. */
	pw = getpwnam(user);
	if (!pw || !allowed_user(pw))
		do_fake_authloop(user);

	/* Take a copy of the returned structure. */
	memset(&pwcopy, 0, sizeof(pwcopy));
	pwcopy.pw_name = xstrdup(pw->pw_name);
	pwcopy.pw_passwd = xstrdup(pw->pw_passwd);
	pwcopy.pw_uid = pw->pw_uid;
	pwcopy.pw_gid = pw->pw_gid;
	pwcopy.pw_dir = xstrdup(pw->pw_dir);
	pwcopy.pw_shell = xstrdup(pw->pw_shell);
	pw = &pwcopy;

	/*
	 * If we are not running as root, the user must have the same uid as
	 * the server.
	 */
	if (getuid() != 0 && pw->pw_uid != getuid())
		packet_disconnect("Cannot change user when server not running as root.");

	debug("Attempting authentication for %.100s.", user);

	/* If the user has no password, accept authentication immediately. */
	if (options.password_authentication &&
#ifdef KRB4
	    (!options.kerberos_authentication || options.kerberos_or_local_passwd) &&
#endif /* KRB4 */
	    auth_password(pw, "")) {
		/* Authentication with empty password succeeded. */
		log("Login for user %s from %.100s, accepted without authentication.",
		    pw->pw_name, get_remote_ipaddr());
	} else {
		/* Loop until the user has been authenticated or the
		   connection is closed, do_authloop() returns only if
		   authentication is successfull */
		do_authloop(pw);
	}

	/* Check if the user is logging in as root and root logins are disallowed. */
	if (pw->pw_uid == 0 && !options.permit_root_login) {
		if (forced_command)
			log("Root login accepted for forced command.");
		else
			packet_disconnect("ROOT LOGIN REFUSED FROM %.200s",
					  get_canonical_hostname());
	}
	/* The user has been authenticated and accepted. */
	packet_start(SSH_SMSG_SUCCESS);
	packet_send();
	packet_write_wait();

	/* Perform session preparation. */
	do_authenticated(pw);
}

#define AUTH_FAIL_MAX 6
#define AUTH_FAIL_LOG (AUTH_FAIL_MAX/2)
#define AUTH_FAIL_MSG "Too many authentication failures for %.100s"

/*
 * read packets and try to authenticate local user *pw.
 * return if authentication is successfull
 */
void
do_authloop(struct passwd * pw)
{
	int attempt = 0;
	unsigned int bits;
	BIGNUM *client_host_key_e, *client_host_key_n;
	BIGNUM *n;
	char *client_user, *password;
	char user[1024];
	int plen, dlen, nlen, ulen, elen;
	int type = 0;
	void (*authlog) (const char *fmt,...) = verbose;

	/* Indicate that authentication is needed. */
	packet_start(SSH_SMSG_FAILURE);
	packet_send();
	packet_write_wait();

	for (attempt = 1;; attempt++) {
		int authenticated = 0;
		strlcpy(user, "", sizeof user);

		/* Get a packet from the client. */
		type = packet_read(&plen);

		/* Process the packet. */
		switch (type) {
#ifdef AFS
		case SSH_CMSG_HAVE_KERBEROS_TGT:
			if (!options.kerberos_tgt_passing) {
				/* packet_get_all(); */
				verbose("Kerberos tgt passing disabled.");
				break;
			} else {
				/* Accept Kerberos tgt. */
				char *tgt = packet_get_string(&dlen);
				packet_integrity_check(plen, 4 + dlen, type);
				if (!auth_kerberos_tgt(pw, tgt))
					verbose("Kerberos tgt REFUSED for %s", pw->pw_name);
				xfree(tgt);
			}
			continue;

		case SSH_CMSG_HAVE_AFS_TOKEN:
			if (!options.afs_token_passing || !k_hasafs()) {
				/* packet_get_all(); */
				verbose("AFS token passing disabled.");
				break;
			} else {
				/* Accept AFS token. */
				char *token_string = packet_get_string(&dlen);
				packet_integrity_check(plen, 4 + dlen, type);
				if (!auth_afs_token(pw, token_string))
					verbose("AFS token REFUSED for %s", pw->pw_name);
				xfree(token_string);
			}
			continue;
#endif /* AFS */
#ifdef KRB4
		case SSH_CMSG_AUTH_KERBEROS:
			if (!options.kerberos_authentication) {
				/* packet_get_all(); */
				verbose("Kerberos authentication disabled.");
				break;
			} else {
				/* Try Kerberos v4 authentication. */
				KTEXT_ST auth;
				char *tkt_user = NULL;
				char *kdata = packet_get_string((unsigned int *) &auth.length);
				packet_integrity_check(plen, 4 + auth.length, type);

				if (auth.length < MAX_KTXT_LEN)
					memcpy(auth.dat, kdata, auth.length);
				xfree(kdata);

				authenticated = auth_krb4(pw->pw_name, &auth, &tkt_user);

				if (authenticated) {
					snprintf(user, sizeof user, " tktuser %s", tkt_user);
					xfree(tkt_user);
				}
			}
			break;
#endif /* KRB4 */

		case SSH_CMSG_AUTH_RHOSTS:
			if (!options.rhosts_authentication) {
				verbose("Rhosts authentication disabled.");
				break;
			}
			/*
			 * Get client user name.  Note that we just have to
			 * trust the client; this is one reason why rhosts
			 * authentication is insecure. (Another is
			 * IP-spoofing on a local network.)
			 */
			client_user = packet_get_string(&ulen);
			packet_integrity_check(plen, 4 + ulen, type);

			/* Try to authenticate using /etc/hosts.equiv and
			   .rhosts. */
			authenticated = auth_rhosts(pw, client_user);

			snprintf(user, sizeof user, " ruser %s", client_user);
			xfree(client_user);
			break;

		case SSH_CMSG_AUTH_RHOSTS_RSA:
			if (!options.rhosts_rsa_authentication) {
				verbose("Rhosts with RSA authentication disabled.");
				break;
			}
			/*
			 * Get client user name.  Note that we just have to
			 * trust the client; root on the client machine can
			 * claim to be any user.
			 */
			client_user = packet_get_string(&ulen);

			/* Get the client host key. */
			client_host_key_e = BN_new();
			client_host_key_n = BN_new();
			bits = packet_get_int();
			packet_get_bignum(client_host_key_e, &elen);
			packet_get_bignum(client_host_key_n, &nlen);

			if (bits != BN_num_bits(client_host_key_n))
				error("Warning: keysize mismatch for client_host_key: "
				      "actual %d, announced %d", BN_num_bits(client_host_key_n), bits);
			packet_integrity_check(plen, (4 + ulen) + 4 + elen + nlen, type);

			authenticated = auth_rhosts_rsa(pw, client_user,
				   client_host_key_e, client_host_key_n);
			BN_clear_free(client_host_key_e);
			BN_clear_free(client_host_key_n);

			snprintf(user, sizeof user, " ruser %s", client_user);
			xfree(client_user);
			break;

		case SSH_CMSG_AUTH_RSA:
			if (!options.rsa_authentication) {
				verbose("RSA authentication disabled.");
				break;
			}
			/* RSA authentication requested. */
			n = BN_new();
			packet_get_bignum(n, &nlen);
			packet_integrity_check(plen, nlen, type);
			authenticated = auth_rsa(pw, n);
			BN_clear_free(n);
			break;

		case SSH_CMSG_AUTH_PASSWORD:
			if (!options.password_authentication) {
				verbose("Password authentication disabled.");
				break;
			}
			/*
			 * Read user password.  It is in plain text, but was
			 * transmitted over the encrypted channel so it is
			 * not visible to an outside observer.
			 */
			password = packet_get_string(&dlen);
			packet_integrity_check(plen, 4 + dlen, type);

			/* Try authentication with the password. */
			authenticated = auth_password(pw, password);

			memset(password, 0, strlen(password));
			xfree(password);
			break;

#ifdef SKEY
		case SSH_CMSG_AUTH_TIS:
			debug("rcvd SSH_CMSG_AUTH_TIS");
			if (options.skey_authentication == 1) {
				char *skeyinfo = skey_keyinfo(pw->pw_name);
				if (skeyinfo == NULL) {
					debug("generating fake skeyinfo for %.100s.", pw->pw_name);
					skeyinfo = skey_fake_keyinfo(pw->pw_name);
				}
				if (skeyinfo != NULL) {
					/* we send our s/key- in tis-challenge messages */
					debug("sending challenge '%s'", skeyinfo);
					packet_start(SSH_SMSG_AUTH_TIS_CHALLENGE);
					packet_put_string(skeyinfo, strlen(skeyinfo));
					packet_send();
					packet_write_wait();
					continue;
				}
			}
			break;
		case SSH_CMSG_AUTH_TIS_RESPONSE:
			debug("rcvd SSH_CMSG_AUTH_TIS_RESPONSE");
			if (options.skey_authentication == 1) {
				char *response = packet_get_string(&dlen);
				debug("skey response == '%s'", response);
				packet_integrity_check(plen, 4 + dlen, type);
				authenticated = (skey_haskey(pw->pw_name) == 0 &&
						 skey_passcheck(pw->pw_name, response) != -1);
				xfree(response);
			}
			break;
#else
		case SSH_CMSG_AUTH_TIS:
			/* TIS Authentication is unsupported */
			log("TIS authentication unsupported.");
			break;
#endif

		default:
			/*
			 * Any unknown messages will be ignored (and failure
			 * returned) during authentication.
			 */
			log("Unknown message during authentication: type %d", type);
			break;
		}

		/* Raise logging level */
		if (authenticated ||
		    attempt == AUTH_FAIL_LOG ||
		    type == SSH_CMSG_AUTH_PASSWORD)
			authlog = log;

		authlog("%s %s for %.200s from %.200s port %d%s",
			authenticated ? "Accepted" : "Failed",
			get_authname(type),
			pw->pw_uid == 0 ? "ROOT" : pw->pw_name,
			get_remote_ipaddr(),
			get_remote_port(),
			user);

		if (authenticated)
			return;

		if (attempt > AUTH_FAIL_MAX)
			packet_disconnect(AUTH_FAIL_MSG, pw->pw_name);

		/* Send a message indicating that the authentication attempt failed. */
		packet_start(SSH_SMSG_FAILURE);
		packet_send();
		packet_write_wait();
	}
}

/*
 * The user does not exist or access is denied,
 * but fake indication that authentication is needed.
 */
void
do_fake_authloop(char *user)
{
	int attempt = 0;

	log("Faking authloop for illegal user %.200s from %.200s port %d",
	    user,
	    get_remote_ipaddr(),
	    get_remote_port());

	/* Indicate that authentication is needed. */
	packet_start(SSH_SMSG_FAILURE);
	packet_send();
	packet_write_wait();

	/*
	 * Keep reading packets, and always respond with a failure.  This is
	 * to avoid disclosing whether such a user really exists.
	 */
	for (attempt = 1;; attempt++) {
		/* Read a packet.  This will not return if the client disconnects. */
		int plen;
		int type = packet_read(&plen);
#ifdef SKEY
		int dlen;
		char *password, *skeyinfo;
		if (options.password_authentication &&
		    options.skey_authentication == 1 &&
		    type == SSH_CMSG_AUTH_PASSWORD &&
		    (password = packet_get_string(&dlen)) != NULL &&
		    dlen == 5 &&
		    strncasecmp(password, "s/key", 5) == 0 &&
		    (skeyinfo = skey_fake_keyinfo(user)) != NULL) {
			/* Send a fake s/key challenge. */
			packet_send_debug(skeyinfo);
		}
#endif
		if (attempt > AUTH_FAIL_MAX)
			packet_disconnect(AUTH_FAIL_MSG, user);

		/*
		 * Send failure.  This should be indistinguishable from a
		 * failed authentication.
		 */
		packet_start(SSH_SMSG_FAILURE);
		packet_send();
		packet_write_wait();
	}
	/* NOTREACHED */
	abort();
}


/*
 * Remove local Xauthority file.
 */
static void
xauthfile_cleanup_proc(void *ignore)
{
	debug("xauthfile_cleanup_proc called");

	if (xauthfile != NULL) {
		unlink(xauthfile);
		xfree(xauthfile);
		xauthfile = NULL;
	}
}

/*
 * Prepares for an interactive session.  This is called after the user has
 * been successfully authenticated.  During this message exchange, pseudo
 * terminals are allocated, X11, TCP/IP, and authentication agent forwardings
 * are requested, etc.
 */
void 
do_authenticated(struct passwd * pw)
{
	int type;
	int compression_level = 0, enable_compression_after_reply = 0;
	int have_pty = 0, ptyfd = -1, ttyfd = -1, xauthfd = -1;
	int row, col, xpixel, ypixel, screen;
	char ttyname[64];
	char *command, *term = NULL, *display = NULL, *proto = NULL,
	*data = NULL;
	struct group *grp;
	gid_t tty_gid;
	mode_t tty_mode;
	int n_bytes;

	/*
	 * Cancel the alarm we set to limit the time taken for
	 * authentication.
	 */
	alarm(0);

	/*
	 * Inform the channel mechanism that we are the server side and that
	 * the client may request to connect to any port at all. (The user
	 * could do it anyway, and we wouldn\'t know what is permitted except
	 * by the client telling us, so we can equally well trust the client
	 * not to request anything bogus.)
	 */
	channel_permit_all_opens();

	/*
	 * We stay in this loop until the client requests to execute a shell
	 * or a command.
	 */
	while (1) {
		int plen, dlen;

		/* Get a packet from the client. */
		type = packet_read(&plen);

		/* Process the packet. */
		switch (type) {
		case SSH_CMSG_REQUEST_COMPRESSION:
			packet_integrity_check(plen, 4, type);
			compression_level = packet_get_int();
			if (compression_level < 1 || compression_level > 9) {
				packet_send_debug("Received illegal compression level %d.",
						  compression_level);
				goto fail;
			}
			/* Enable compression after we have responded with SUCCESS. */
			enable_compression_after_reply = 1;
			break;

		case SSH_CMSG_REQUEST_PTY:
			if (no_pty_flag) {
				debug("Allocating a pty not permitted for this authentication.");
				goto fail;
			}
			if (have_pty)
				packet_disconnect("Protocol error: you already have a pty.");

			debug("Allocating pty.");

			/* Allocate a pty and open it. */
			if (!pty_allocate(&ptyfd, &ttyfd, ttyname,
			    sizeof(ttyname))) {
				error("Failed to allocate pty.");
				goto fail;
			}
			/* Determine the group to make the owner of the tty. */
			grp = getgrnam("tty");
			if (grp) {
				tty_gid = grp->gr_gid;
				tty_mode = S_IRUSR | S_IWUSR | S_IWGRP;
			} else {
				tty_gid = pw->pw_gid;
				tty_mode = S_IRUSR | S_IWUSR | S_IWGRP | S_IWOTH;
			}

			/* Change ownership of the tty. */
			if (chown(ttyname, pw->pw_uid, tty_gid) < 0)
				fatal("chown(%.100s, %d, %d) failed: %.100s",
				      ttyname, pw->pw_uid, tty_gid, strerror(errno));
			if (chmod(ttyname, tty_mode) < 0)
				fatal("chmod(%.100s, 0%o) failed: %.100s",
				      ttyname, tty_mode, strerror(errno));

			/* Get TERM from the packet.  Note that the value may be of arbitrary length. */
			term = packet_get_string(&dlen);
			packet_integrity_check(dlen, strlen(term), type);
			/* packet_integrity_check(plen, 4 + dlen + 4*4 + n_bytes, type); */
			/* Remaining bytes */
			n_bytes = plen - (4 + dlen + 4 * 4);

			if (strcmp(term, "") == 0)
				term = NULL;

			/* Get window size from the packet. */
			row = packet_get_int();
			col = packet_get_int();
			xpixel = packet_get_int();
			ypixel = packet_get_int();
			pty_change_window_size(ptyfd, row, col, xpixel, ypixel);

			/* Get tty modes from the packet. */
			tty_parse_modes(ttyfd, &n_bytes);
			packet_integrity_check(plen, 4 + dlen + 4 * 4 + n_bytes, type);

			/* Indicate that we now have a pty. */
			have_pty = 1;
			break;

		case SSH_CMSG_X11_REQUEST_FORWARDING:
			if (!options.x11_forwarding) {
				packet_send_debug("X11 forwarding disabled in server configuration file.");
				goto fail;
			}
#ifdef XAUTH_PATH
			if (no_x11_forwarding_flag) {
				packet_send_debug("X11 forwarding not permitted for this authentication.");
				goto fail;
			}
			debug("Received request for X11 forwarding with auth spoofing.");
			if (display)
				packet_disconnect("Protocol error: X11 display already set.");
			{
				int proto_len, data_len;
				proto = packet_get_string(&proto_len);
				data = packet_get_string(&data_len);
				packet_integrity_check(plen, 4 + proto_len + 4 + data_len + 4, type);
			}
			if (packet_get_protocol_flags() & SSH_PROTOFLAG_SCREEN_NUMBER)
				screen = packet_get_int();
			else
				screen = 0;
			display = x11_create_display_inet(screen);
			if (!display)
				goto fail;

			/* Setup to always have a local .Xauthority. */
			xauthfile = xmalloc(MAXPATHLEN);
			snprintf(xauthfile, MAXPATHLEN, "/tmp/XauthXXXXXX");

			if ((xauthfd = mkstemp(xauthfile)) != -1) {
				fchown(xauthfd, pw->pw_uid, pw->pw_gid);
				close(xauthfd);
				fatal_add_cleanup(xauthfile_cleanup_proc, NULL);
			} else {
				xfree(xauthfile);
				xauthfile = NULL;
			}
			break;
#else /* XAUTH_PATH */
			packet_send_debug("No xauth program; cannot forward with spoofing.");
			goto fail;
#endif /* XAUTH_PATH */

		case SSH_CMSG_AGENT_REQUEST_FORWARDING:
			if (no_agent_forwarding_flag) {
				debug("Authentication agent forwarding not permitted for this authentication.");
				goto fail;
			}
			debug("Received authentication agent forwarding request.");
			auth_input_request_forwarding(pw);
			break;

		case SSH_CMSG_PORT_FORWARD_REQUEST:
			if (no_port_forwarding_flag) {
				debug("Port forwarding not permitted for this authentication.");
				goto fail;
			}
			debug("Received TCP/IP port forwarding request.");
			channel_input_port_forward_request(pw->pw_uid == 0);
			break;

		case SSH_CMSG_MAX_PACKET_SIZE:
			if (packet_set_maxsize(packet_get_int()) < 0)
				goto fail;
			break;

		case SSH_CMSG_EXEC_SHELL:
			/* Set interactive/non-interactive mode. */
			packet_set_interactive(have_pty || display != NULL,
					       options.keepalives);

			if (forced_command != NULL)
				goto do_forced_command;
			debug("Forking shell.");
			packet_integrity_check(plen, 0, type);
			if (have_pty)
				do_exec_pty(NULL, ptyfd, ttyfd, ttyname, pw, term, display, proto, data);
			else
				do_exec_no_pty(NULL, pw, display, proto, data);
			return;

		case SSH_CMSG_EXEC_CMD:
			/* Set interactive/non-interactive mode. */
			packet_set_interactive(have_pty || display != NULL,
					       options.keepalives);

			if (forced_command != NULL)
				goto do_forced_command;
			/* Get command from the packet. */
			{
				int dlen;
				command = packet_get_string(&dlen);
				debug("Executing command '%.500s'", command);
				packet_integrity_check(plen, 4 + dlen, type);
			}
			if (have_pty)
				do_exec_pty(command, ptyfd, ttyfd, ttyname, pw, term, display, proto, data);
			else
				do_exec_no_pty(command, pw, display, proto, data);
			xfree(command);
			return;

		default:
			/*
			 * Any unknown messages in this phase are ignored,
			 * and a failure message is returned.
			 */
			log("Unknown packet type received after authentication: %d", type);
			goto fail;
		}

		/* The request was successfully processed. */
		packet_start(SSH_SMSG_SUCCESS);
		packet_send();
		packet_write_wait();

		/* Enable compression now that we have replied if appropriate. */
		if (enable_compression_after_reply) {
			enable_compression_after_reply = 0;
			packet_start_compression(compression_level);
		}
		continue;

fail:
		/* The request failed. */
		packet_start(SSH_SMSG_FAILURE);
		packet_send();
		packet_write_wait();
		continue;

do_forced_command:
		/*
		 * There is a forced command specified for this login.
		 * Execute it.
		 */
		debug("Executing forced command: %.900s", forced_command);
		if (have_pty)
			do_exec_pty(forced_command, ptyfd, ttyfd, ttyname, pw, term, display, proto, data);
		else
			do_exec_no_pty(forced_command, pw, display, proto, data);
		return;
	}
}

/*
 * This is called to fork and execute a command when we have no tty.  This
 * will call do_child from the child, and server_loop from the parent after
 * setting up file descriptors and such.
 */
void 
do_exec_no_pty(const char *command, struct passwd * pw,
	       const char *display, const char *auth_proto,
	       const char *auth_data)
{
	int pid;

#ifdef USE_PIPES
	int pin[2], pout[2], perr[2];
	/* Allocate pipes for communicating with the program. */
	if (pipe(pin) < 0 || pipe(pout) < 0 || pipe(perr) < 0)
		packet_disconnect("Could not create pipes: %.100s",
				  strerror(errno));
#else /* USE_PIPES */
	int inout[2], err[2];
	/* Uses socket pairs to communicate with the program. */
	if (socketpair(AF_UNIX, SOCK_STREAM, 0, inout) < 0 ||
	    socketpair(AF_UNIX, SOCK_STREAM, 0, err) < 0)
		packet_disconnect("Could not create socket pairs: %.100s",
				  strerror(errno));
#endif /* USE_PIPES */

	setproctitle("%s@notty", pw->pw_name);

	/* Fork the child. */
	if ((pid = fork()) == 0) {
		/* Child.  Reinitialize the log since the pid has changed. */
		log_init(av0, options.log_level, options.log_facility, log_stderr);

		/*
		 * Create a new session and process group since the 4.4BSD
		 * setlogin() affects the entire process group.
		 */
		if (setsid() < 0)
			error("setsid failed: %.100s", strerror(errno));

#ifdef USE_PIPES
		/*
		 * Redirect stdin.  We close the parent side of the socket
		 * pair, and make the child side the standard input.
		 */
		close(pin[1]);
		if (dup2(pin[0], 0) < 0)
			perror("dup2 stdin");
		close(pin[0]);

		/* Redirect stdout. */
		close(pout[0]);
		if (dup2(pout[1], 1) < 0)
			perror("dup2 stdout");
		close(pout[1]);

		/* Redirect stderr. */
		close(perr[0]);
		if (dup2(perr[1], 2) < 0)
			perror("dup2 stderr");
		close(perr[1]);
#else /* USE_PIPES */
		/*
		 * Redirect stdin, stdout, and stderr.  Stdin and stdout will
		 * use the same socket, as some programs (particularly rdist)
		 * seem to depend on it.
		 */
		close(inout[1]);
		close(err[1]);
		if (dup2(inout[0], 0) < 0)	/* stdin */
			perror("dup2 stdin");
		if (dup2(inout[0], 1) < 0)	/* stdout.  Note: same socket as stdin. */
			perror("dup2 stdout");
		if (dup2(err[0], 2) < 0)	/* stderr */
			perror("dup2 stderr");
#endif /* USE_PIPES */

		/* Do processing for the child (exec command etc). */
		do_child(command, pw, NULL, display, auth_proto, auth_data, NULL);
		/* NOTREACHED */
	}
	if (pid < 0)
		packet_disconnect("fork failed: %.100s", strerror(errno));
#ifdef USE_PIPES
	/* We are the parent.  Close the child sides of the pipes. */
	close(pin[0]);
	close(pout[1]);
	close(perr[1]);

	/* Enter the interactive session. */
	server_loop(pid, pin[1], pout[0], perr[0]);
	/* server_loop has closed pin[1], pout[1], and perr[1]. */
#else /* USE_PIPES */
	/* We are the parent.  Close the child sides of the socket pairs. */
	close(inout[0]);
	close(err[0]);

	/*
	 * Enter the interactive session.  Note: server_loop must be able to
	 * handle the case that fdin and fdout are the same.
	 */
	server_loop(pid, inout[1], inout[1], err[1]);
	/* server_loop has closed inout[1] and err[1]. */
#endif /* USE_PIPES */
}

struct pty_cleanup_context {
	const char *ttyname;
	int pid;
};

/*
 * Function to perform cleanup if we get aborted abnormally (e.g., due to a
 * dropped connection).
 */
void 
pty_cleanup_proc(void *context)
{
	struct pty_cleanup_context *cu = context;

	debug("pty_cleanup_proc called");

	/* Record that the user has logged out. */
	record_logout(cu->pid, cu->ttyname);

	/* Release the pseudo-tty. */
	pty_release(cu->ttyname);
}

/*
 * This is called to fork and execute a command when we have a tty.  This
 * will call do_child from the child, and server_loop from the parent after
 * setting up file descriptors, controlling tty, updating wtmp, utmp,
 * lastlog, and other such operations.
 */
void 
do_exec_pty(const char *command, int ptyfd, int ttyfd,
	    const char *ttyname, struct passwd * pw, const char *term,
	    const char *display, const char *auth_proto,
	    const char *auth_data)
{
	int pid, fdout;
	const char *hostname;
	time_t last_login_time;
	char buf[100], *time_string;
	FILE *f;
	char line[256];
	struct stat st;
	int quiet_login;
	struct sockaddr_in from;
	int fromlen;
	struct pty_cleanup_context cleanup_context;

	/* Get remote host name. */
	hostname = get_canonical_hostname();

	/*
	 * Get the time when the user last logged in.  Buf will be set to
	 * contain the hostname the last login was from.
	 */
	if (!options.use_login) {
		last_login_time = get_last_login_time(pw->pw_uid, pw->pw_name,
						      buf, sizeof(buf));
	}
	setproctitle("%s@%s", pw->pw_name, strrchr(ttyname, '/') + 1);

	/* Fork the child. */
	if ((pid = fork()) == 0) {
		pid = getpid();

		/* Child.  Reinitialize the log because the pid has
		   changed. */
		log_init(av0, options.log_level, options.log_facility, log_stderr);

		/* Close the master side of the pseudo tty. */
		close(ptyfd);

		/* Make the pseudo tty our controlling tty. */
		pty_make_controlling_tty(&ttyfd, ttyname);

		/* Redirect stdin from the pseudo tty. */
		if (dup2(ttyfd, fileno(stdin)) < 0)
			error("dup2 stdin failed: %.100s", strerror(errno));

		/* Redirect stdout to the pseudo tty. */
		if (dup2(ttyfd, fileno(stdout)) < 0)
			error("dup2 stdin failed: %.100s", strerror(errno));

		/* Redirect stderr to the pseudo tty. */
		if (dup2(ttyfd, fileno(stderr)) < 0)
			error("dup2 stdin failed: %.100s", strerror(errno));

		/* Close the extra descriptor for the pseudo tty. */
		close(ttyfd);

		/*
		 * Get IP address of client.  This is needed because we want
		 * to record where the user logged in from.  If the
		 * connection is not a socket, let the ip address be 0.0.0.0.
		 */
		memset(&from, 0, sizeof(from));
		if (packet_get_connection_in() == packet_get_connection_out()) {
			fromlen = sizeof(from);
			if (getpeername(packet_get_connection_in(),
			     (struct sockaddr *) & from, &fromlen) < 0) {
				debug("getpeername: %.100s", strerror(errno));
				fatal_cleanup();
			}
		}
		/* Record that there was a login on that terminal. */
		record_login(pid, ttyname, pw->pw_name, pw->pw_uid, hostname,
			     &from);

		/* Check if .hushlogin exists. */
		snprintf(line, sizeof line, "%.200s/.hushlogin", pw->pw_dir);
		quiet_login = stat(line, &st) >= 0;

		/*
		 * If the user has logged in before, display the time of last
		 * login. However, don't display anything extra if a command
		 * has been specified (so that ssh can be used to execute
		 * commands on a remote machine without users knowing they
		 * are going to another machine). Login(1) will do this for
		 * us as well, so check if login(1) is used
		 */
		if (command == NULL && last_login_time != 0 && !quiet_login &&
		    !options.use_login) {
			/* Convert the date to a string. */
			time_string = ctime(&last_login_time);
			/* Remove the trailing newline. */
			if (strchr(time_string, '\n'))
				*strchr(time_string, '\n') = 0;
			/* Display the last login time.  Host if displayed
			   if known. */
			if (strcmp(buf, "") == 0)
				printf("Last login: %s\r\n", time_string);
			else
				printf("Last login: %s from %s\r\n", time_string, buf);
		}
		/*
		 * Print /etc/motd unless a command was specified or printing
		 * it was disabled in server options or login(1) will be
		 * used.  Note that some machines appear to print it in
		 * /etc/profile or similar.
		 */
		if (command == NULL && options.print_motd && !quiet_login &&
		    !options.use_login) {
			/* Print /etc/motd if it exists. */
			f = fopen("/etc/motd", "r");
			if (f) {
				while (fgets(line, sizeof(line), f))
					fputs(line, stdout);
				fclose(f);
			}
		}
		/* Do common processing for the child, such as execing the command. */
		do_child(command, pw, term, display, auth_proto, auth_data, ttyname);
		/* NOTREACHED */
	}
	if (pid < 0)
		packet_disconnect("fork failed: %.100s", strerror(errno));
	/* Parent.  Close the slave side of the pseudo tty. */
	close(ttyfd);

	/*
	 * Create another descriptor of the pty master side for use as the
	 * standard input.  We could use the original descriptor, but this
	 * simplifies code in server_loop.  The descriptor is bidirectional.
	 */
	fdout = dup(ptyfd);
	if (fdout < 0)
		packet_disconnect("dup failed: %.100s", strerror(errno));

	/*
	 * Add a cleanup function to clear the utmp entry and record logout
	 * time in case we call fatal() (e.g., the connection gets closed).
	 */
	cleanup_context.pid = pid;
	cleanup_context.ttyname = ttyname;
	fatal_add_cleanup(pty_cleanup_proc, (void *) &cleanup_context);

	/* Enter interactive session. */
	server_loop(pid, ptyfd, fdout, -1);
	/* server_loop has not closed ptyfd and fdout. */

	/* Cancel the cleanup function. */
	fatal_remove_cleanup(pty_cleanup_proc, (void *) &cleanup_context);

	/* Record that the user has logged out. */
	record_logout(pid, ttyname);

	/* Release the pseudo-tty. */
	pty_release(ttyname);

	/*
	 * Close the server side of the socket pairs.  We must do this after
	 * the pty cleanup, so that another process doesn't get this pty
	 * while we're still cleaning up.
	 */
	close(ptyfd);
	close(fdout);
}

/*
 * Sets the value of the given variable in the environment.  If the variable
 * already exists, its value is overriden.
 */
void 
child_set_env(char ***envp, unsigned int *envsizep, const char *name,
	      const char *value)
{
	unsigned int i, namelen;
	char **env;

	/*
	 * Find the slot where the value should be stored.  If the variable
	 * already exists, we reuse the slot; otherwise we append a new slot
	 * at the end of the array, expanding if necessary.
	 */
	env = *envp;
	namelen = strlen(name);
	for (i = 0; env[i]; i++)
		if (strncmp(env[i], name, namelen) == 0 && env[i][namelen] == '=')
			break;
	if (env[i]) {
		/* Reuse the slot. */
		xfree(env[i]);
	} else {
		/* New variable.  Expand if necessary. */
		if (i >= (*envsizep) - 1) {
			(*envsizep) += 50;
			env = (*envp) = xrealloc(env, (*envsizep) * sizeof(char *));
		}
		/* Need to set the NULL pointer at end of array beyond the new slot. */
		env[i + 1] = NULL;
	}

	/* Allocate space and format the variable in the appropriate slot. */
	env[i] = xmalloc(strlen(name) + 1 + strlen(value) + 1);
	snprintf(env[i], strlen(name) + 1 + strlen(value) + 1, "%s=%s", name, value);
}

/*
 * Reads environment variables from the given file and adds/overrides them
 * into the environment.  If the file does not exist, this does nothing.
 * Otherwise, it must consist of empty lines, comments (line starts with '#')
 * and assignments of the form name=value.  No other forms are allowed.
 */
void 
read_environment_file(char ***env, unsigned int *envsize,
		      const char *filename)
{
	FILE *f;
	char buf[4096];
	char *cp, *value;

	f = fopen(filename, "r");
	if (!f)
		return;

	while (fgets(buf, sizeof(buf), f)) {
		for (cp = buf; *cp == ' ' || *cp == '\t'; cp++)
			;
		if (!*cp || *cp == '#' || *cp == '\n')
			continue;
		if (strchr(cp, '\n'))
			*strchr(cp, '\n') = '\0';
		value = strchr(cp, '=');
		if (value == NULL) {
			fprintf(stderr, "Bad line in %.100s: %.200s\n", filename, buf);
			continue;
		}
		/* Replace the equals sign by nul, and advance value to the value string. */
		*value = '\0';
		value++;
		child_set_env(env, envsize, cp, value);
	}
	fclose(f);
}

/*
 * Performs common processing for the child, such as setting up the
 * environment, closing extra file descriptors, setting the user and group
 * ids, and executing the command or shell.
 */
void 
do_child(const char *command, struct passwd * pw, const char *term,
	 const char *display, const char *auth_proto,
	 const char *auth_data, const char *ttyname)
{
	const char *shell, *cp = NULL;
	char buf[256];
	FILE *f;
	unsigned int envsize, i;
	char **env;
	extern char **environ;
	struct stat st;
	char *argv[10];

	f = fopen("/etc/nologin", "r");
	if (f) {
		/* /etc/nologin exists.  Print its contents and exit. */
		while (fgets(buf, sizeof(buf), f))
			fputs(buf, stderr);
		fclose(f);
		if (pw->pw_uid != 0)
			exit(254);
	}
	/* Set login name in the kernel. */
	if (setlogin(pw->pw_name) < 0)
		error("setlogin failed: %s", strerror(errno));

	/* Set uid, gid, and groups. */
	/* Login(1) does this as well, and it needs uid 0 for the "-h"
	   switch, so we let login(1) to this for us. */
	if (!options.use_login) {
		if (getuid() == 0 || geteuid() == 0) {
			if (setgid(pw->pw_gid) < 0) {
				perror("setgid");
				exit(1);
			}
			/* Initialize the group list. */
			if (initgroups(pw->pw_name, pw->pw_gid) < 0) {
				perror("initgroups");
				exit(1);
			}
			endgrent();

			/* Permanently switch to the desired uid. */
			permanently_set_uid(pw->pw_uid);
		}
		if (getuid() != pw->pw_uid || geteuid() != pw->pw_uid)
			fatal("Failed to set uids to %d.", (int) pw->pw_uid);
	}
	/*
	 * Get the shell from the password data.  An empty shell field is
	 * legal, and means /bin/sh.
	 */
	shell = (pw->pw_shell[0] == '\0') ? _PATH_BSHELL : pw->pw_shell;

#ifdef AFS
	/* Try to get AFS tokens for the local cell. */
	if (k_hasafs()) {
		char cell[64];

		if (k_afs_cell_of_file(pw->pw_dir, cell, sizeof(cell)) == 0)
			krb_afslog(cell, 0);

		krb_afslog(0, 0);
	}
#endif /* AFS */

	/* Initialize the environment. */
	envsize = 100;
	env = xmalloc(envsize * sizeof(char *));
	env[0] = NULL;

	if (!options.use_login) {
		/* Set basic environment. */
		child_set_env(&env, &envsize, "USER", pw->pw_name);
		child_set_env(&env, &envsize, "LOGNAME", pw->pw_name);
		child_set_env(&env, &envsize, "HOME", pw->pw_dir);
		child_set_env(&env, &envsize, "PATH", _PATH_STDPATH);

		snprintf(buf, sizeof buf, "%.200s/%.50s",
			 _PATH_MAILDIR, pw->pw_name);
		child_set_env(&env, &envsize, "MAIL", buf);

		/* Normal systems set SHELL by default. */
		child_set_env(&env, &envsize, "SHELL", shell);
	}
	if (getenv("TZ"))
		child_set_env(&env, &envsize, "TZ", getenv("TZ"));

	/* Set custom environment options from RSA authentication. */
	while (custom_environment) {
		struct envstring *ce = custom_environment;
		char *s = ce->s;
		int i;
		for (i = 0; s[i] != '=' && s[i]; i++);
		if (s[i] == '=') {
			s[i] = 0;
			child_set_env(&env, &envsize, s, s + i + 1);
		}
		custom_environment = ce->next;
		xfree(ce->s);
		xfree(ce);
	}

	snprintf(buf, sizeof buf, "%.50s %d %d",
		 get_remote_ipaddr(), get_remote_port(), options.port);
	child_set_env(&env, &envsize, "SSH_CLIENT", buf);

	if (ttyname)
		child_set_env(&env, &envsize, "SSH_TTY", ttyname);
	if (term)
		child_set_env(&env, &envsize, "TERM", term);
	if (display)
		child_set_env(&env, &envsize, "DISPLAY", display);

#ifdef KRB4
	{
		extern char *ticket;

		if (ticket)
			child_set_env(&env, &envsize, "KRBTKFILE", ticket);
	}
#endif /* KRB4 */

	if (xauthfile)
		child_set_env(&env, &envsize, "XAUTHORITY", xauthfile);
	if (auth_get_socket_name() != NULL)
		child_set_env(&env, &envsize, SSH_AUTHSOCKET_ENV_NAME,
			      auth_get_socket_name());

	/* read $HOME/.ssh/environment. */
	if (!options.use_login) {
		snprintf(buf, sizeof buf, "%.200s/.ssh/environment", pw->pw_dir);
		read_environment_file(&env, &envsize, buf);
	}
	if (debug_flag) {
		/* dump the environment */
		fprintf(stderr, "Environment:\n");
		for (i = 0; env[i]; i++)
			fprintf(stderr, "  %.200s\n", env[i]);
	}
	/*
	 * Close the connection descriptors; note that this is the child, and
	 * the server will still have the socket open, and it is important
	 * that we do not shutdown it.  Note that the descriptors cannot be
	 * closed before building the environment, as we call
	 * get_remote_ipaddr there.
	 */
	if (packet_get_connection_in() == packet_get_connection_out())
		close(packet_get_connection_in());
	else {
		close(packet_get_connection_in());
		close(packet_get_connection_out());
	}
	/*
	 * Close all descriptors related to channels.  They will still remain
	 * open in the parent.
	 */
	/* XXX better use close-on-exec? -markus */
	channel_close_all();

	/*
	 * Close any extra file descriptors.  Note that there may still be
	 * descriptors left by system functions.  They will be closed later.
	 */
	endpwent();
	endhostent();

	/*
	 * Close any extra open file descriptors so that we don\'t have them
	 * hanging around in clients.  Note that we want to do this after
	 * initgroups, because at least on Solaris 2.3 it leaves file
	 * descriptors open.
	 */
	for (i = 3; i < 64; i++)
		close(i);

	/* Change current directory to the user\'s home directory. */
	if (chdir(pw->pw_dir) < 0)
		fprintf(stderr, "Could not chdir to home directory %s: %s\n",
			pw->pw_dir, strerror(errno));

	/*
	 * Must take new environment into use so that .ssh/rc, /etc/sshrc and
	 * xauth are run in the proper environment.
	 */
	environ = env;

	/*
	 * Run $HOME/.ssh/rc, /etc/sshrc, or xauth (whichever is found first
	 * in this order).
	 */
	if (!options.use_login) {
		if (stat(SSH_USER_RC, &st) >= 0) {
			if (debug_flag)
				fprintf(stderr, "Running /bin/sh %s\n", SSH_USER_RC);

			f = popen("/bin/sh " SSH_USER_RC, "w");
			if (f) {
				if (auth_proto != NULL && auth_data != NULL)
					fprintf(f, "%s %s\n", auth_proto, auth_data);
				pclose(f);
			} else
				fprintf(stderr, "Could not run %s\n", SSH_USER_RC);
		} else if (stat(SSH_SYSTEM_RC, &st) >= 0) {
			if (debug_flag)
				fprintf(stderr, "Running /bin/sh %s\n", SSH_SYSTEM_RC);

			f = popen("/bin/sh " SSH_SYSTEM_RC, "w");
			if (f) {
				if (auth_proto != NULL && auth_data != NULL)
					fprintf(f, "%s %s\n", auth_proto, auth_data);
				pclose(f);
			} else
				fprintf(stderr, "Could not run %s\n", SSH_SYSTEM_RC);
		}
#ifdef XAUTH_PATH
		else {
			/* Add authority data to .Xauthority if appropriate. */
			if (auth_proto != NULL && auth_data != NULL) {
				if (debug_flag)
					fprintf(stderr, "Running %.100s add %.100s %.100s %.100s\n",
						XAUTH_PATH, display, auth_proto, auth_data);

				f = popen(XAUTH_PATH " -q -", "w");
				if (f) {
					fprintf(f, "add %s %s %s\n", display, auth_proto, auth_data);
					fclose(f);
				} else
					fprintf(stderr, "Could not run %s -q -\n", XAUTH_PATH);
			}
		}
#endif /* XAUTH_PATH */

		/* Get the last component of the shell name. */
		cp = strrchr(shell, '/');
		if (cp)
			cp++;
		else
			cp = shell;
	}
	/*
	 * If we have no command, execute the shell.  In this case, the shell
	 * name to be passed in argv[0] is preceded by '-' to indicate that
	 * this is a login shell.
	 */
	if (!command) {
		if (!options.use_login) {
			char buf[256];

			/*
			 * Check for mail if we have a tty and it was enabled
			 * in server options.
			 */
			if (ttyname && options.check_mail) {
				char *mailbox;
				struct stat mailstat;
				mailbox = getenv("MAIL");
				if (mailbox != NULL) {
					if (stat(mailbox, &mailstat) != 0 || mailstat.st_size == 0)
						printf("No mail.\n");
					else if (mailstat.st_mtime < mailstat.st_atime)
						printf("You have mail.\n");
					else
						printf("You have new mail.\n");
				}
			}
			/* Start the shell.  Set initial character to '-'. */
			buf[0] = '-';
			strncpy(buf + 1, cp, sizeof(buf) - 1);
			buf[sizeof(buf) - 1] = 0;

			/* Execute the shell. */
			argv[0] = buf;
			argv[1] = NULL;
			execve(shell, argv, env);

			/* Executing the shell failed. */
			perror(shell);
			exit(1);

		} else {
			/* Launch login(1). */

			execl("/usr/bin/login", "login", "-h", get_remote_ipaddr(),
			      "-p", "-f", "--", pw->pw_name, NULL);

			/* Login couldn't be executed, die. */

			perror("login");
			exit(1);
		}
	}
	/*
	 * Execute the command using the user's shell.  This uses the -c
	 * option to execute the command.
	 */
	argv[0] = (char *) cp;
	argv[1] = "-c";
	argv[2] = (char *) command;
	argv[3] = NULL;
	execve(shell, argv, env);
	perror(shell);
	exit(1);
}