sshd.c

C＋＋编写

			enable_compat13();
		}
		break;
	case 2:
		if (options.protocol & SSH_PROTO_2) {
			enable_compat20();
			break;
		}
		/* FALLTHROUGH */
	default:
		mismatch = 1;
		break;
	}
	chop(server_version_string);
	debug("Local version string %.200s", server_version_string);

	if (mismatch) {
		s = "Protocol major versions differ.\n";
		(void) atomicio(write, sock_out, s, strlen(s));
		close(sock_in);
		close(sock_out);
		log("Protocol major versions differ for %s: %.200s vs. %.200s",
		    get_remote_ipaddr(),
		    server_version_string, client_version_string);
		fatal_cleanup();
	}
}

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

	if (sensitive_data.server_key) {
		key_free(sensitive_data.server_key);
		sensitive_data.server_key = NULL;
	}
	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;
		}
	}
	sensitive_data.ssh1_host_key = NULL;
	memset(sensitive_data.ssh1_cookie, 0, SSH_SESSION_KEY_LENGTH);
}

/* Demote private to public keys for network child */
void
demote_sensitive_data(void)
{
	Key *tmp;
	int i;

	if (sensitive_data.server_key) {
		tmp = key_demote(sensitive_data.server_key);
		key_free(sensitive_data.server_key);
		sensitive_data.server_key = tmp;
	}

	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;
			if (tmp->type == KEY_RSA1)
				sensitive_data.ssh1_host_key = tmp;
		}
	}

	/* We do not clear ssh1_host key and cookie.  XXX - Okay Niels? */
}

static void
privsep_preauth_child(void)
{
	u_int32_t rnd[256];
	gid_t gidset[1];
	struct passwd *pw;
	int i;

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

	for (i = 0; i < 256; i++)
		rnd[i] = arc4random();
	RAND_seed(rnd, sizeof(rnd));

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

	if ((pw = getpwnam(SSH_PRIVSEP_USER)) == NULL)
		fatal("Privilege separation user %s does not exist",
		    SSH_PRIVSEP_USER);
	memset(pw->pw_passwd, 0, strlen(pw->pw_passwd));
	endpwent();

	/* 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)pw->pw_uid,
	    (u_int)pw->pw_gid);
#if 0
	/* XXX not ready, to heavy after chroot */
	do_setusercontext(pw);
#else
	gidset[0] = pw->pw_gid;
	if (setgid(pw->pw_gid) < 0)
		fatal("setgid failed for %u", pw->pw_gid );
	if (setgroups(1, gidset) < 0)
		fatal("setgroups: %.100s", strerror(errno));
	permanently_set_uid(pw);
#endif
}

static Authctxt *
privsep_preauth(void)
{
	Authctxt *authctxt = NULL;
	int status;
	pid_t pid;

	/* 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 = &xxx_kex;

	pid = fork();
	if (pid == -1) {
		fatal("fork of unprivileged child failed");
	} else if (pid != 0) {
		fatal_remove_cleanup((void (*) (void *)) packet_close, NULL);

		debug2("Network child is on pid %ld", (long)pid);

		close(pmonitor->m_recvfd);
		authctxt = monitor_child_preauth(pmonitor);
		close(pmonitor->m_sendfd);

		/* Sync memory */
		monitor_sync(pmonitor);

		/* Wait for the child's exit status */
		while (waitpid(pid, &status, 0) < 0)
			if (errno != EINTR)
				break;

		/* Reinstall, since the child has finished */
		fatal_add_cleanup((void (*) (void *)) packet_close, NULL);

		return (authctxt);
	} else {
		/* child */

		close(pmonitor->m_sendfd);

		/* Demote the child */
		if (getuid() == 0 || geteuid() == 0)
			privsep_preauth_child();
		setproctitle("%s", "[net]");
	}
	return (NULL);
}

static void
privsep_postauth(Authctxt *authctxt)
{
	extern Authctxt *x_authctxt;

	/* XXX - Remote port forwarding */
	x_authctxt = authctxt;

	if (authctxt->pw->pw_uid == 0 || options.use_login) {
		/* File descriptor passing is broken or root login */
		monitor_apply_keystate(pmonitor);
		use_privsep = 0;
		return;
	}

	/* Authentication complete */
	alarm(0);
	if (startup_pipe != -1) {
		close(startup_pipe);
		startup_pipe = -1;
	}

	/* 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) {
		fatal_remove_cleanup((void (*) (void *)) packet_close, NULL);

		debug2("User child is on pid %ld", (long)pmonitor->m_pid);
		close(pmonitor->m_recvfd);
		monitor_child_postauth(pmonitor);

		/* NEVERREACHED */
		exit(0);
	}

	close(pmonitor->m_sendfd);

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

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

	/* It is safe now to apply the key state */
	monitor_apply_keystate(pmonitor);
}

static char *
list_hostkey_types(void)
{
	Buffer b;
	char *p;
	int i;

	buffer_init(&b);
	for (i = 0; i < options.num_host_key_files; i++) {
		Key *key = sensitive_data.host_keys[i];
		if (key == NULL)
			continue;
		switch (key->type) {
		case KEY_RSA:
		case KEY_DSA:
			if (buffer_len(&b) > 0)
				buffer_append(&b, ",", 1);
			p = key_ssh_name(key);
			buffer_append(&b, p, strlen(p));
			break;
		}
	}
	buffer_append(&b, "\0", 1);
	p = xstrdup(buffer_ptr(&b));
	buffer_free(&b);
	debug("list_hostkey_types: %s", p);
	return p;
}

Key *
get_hostkey_by_type(int type)
{
	int i;

	for (i = 0; i < options.num_host_key_files; i++) {
		Key *key = sensitive_data.host_keys[i];
		if (key != NULL && key->type == type)
			return key;
	}
	return NULL;
}

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

int
get_hostkey_index(Key *key)
{
	int i;

	for (i = 0; i < options.num_host_key_files; i++) {
		if (key == sensitive_data.host_keys[i])
			return (i);
	}
	return (-1);
}

/*
 * 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)
{
	double 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 /= (double) (options.max_startups - options.max_startups_begin);
	p += options.max_startups_rate;
	p /= 100.0;
	r = arc4random() / (double) UINT_MAX;

	debug("drop_connection: p %g, r %g", p, r);
	return (r < p) ? 1 : 0;
}

static void
usage(void)
{
	fprintf(stderr, "sshd version %s\n", SSH_VERSION);
	fprintf(stderr, "Usage: %s [options]\n", __progname);
	fprintf(stderr, "Options:\n");
	fprintf(stderr, "  -f file    Configuration file (default %s)\n", _PATH_SERVER_CONFIG_FILE);
	fprintf(stderr, "  -d         Debugging mode (multiple -d means more debugging)\n");
	fprintf(stderr, "  -i         Started from inetd\n");
	fprintf(stderr, "  -D         Do not fork into daemon mode\n");
	fprintf(stderr, "  -t         Only test configuration file and keys\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: 600)\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",
	    _PATH_HOST_KEY_FILE);
	fprintf(stderr, "  -u len     Maximum hostname length for utmp recording\n");
	fprintf(stderr, "  -4         Use IPv4 only\n");
	fprintf(stderr, "  -6         Use IPv6 only\n");
	fprintf(stderr, "  -o option  Process the option as if it was read from a configuration file.\n");
	exit(1);
}

/*
 * Main program for the daemon.
 */
int
main(int ac, char **av)
{
	extern char *optarg;
	extern int optind;
	int opt, sock_in = 0, sock_out = 0, newsock, j, i, fdsetsz, on = 1;
	pid_t pid;
	socklen_t fromlen;
	fd_set *fdset;
	struct sockaddr_storage from;
	const char *remote_ip;
	int remote_port;
	FILE *f;
	struct addrinfo *ai;
	char ntop[NI_MAXHOST], strport[NI_MAXSERV];
	int listen_sock, maxfd;
	int startup_p[2];
	int startups = 0;
	Authctxt *authctxt;
	Key *key;
	int ret, key_used = 0;

	/* Save argv. */
	saved_argv = av;

	/* 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:u:o:dDeiqtQ46")) != -1) {
		switch (opt) {
		case '4':
			IPv4or6 = AF_INET;
			break;
		case '6':
			IPv4or6 = AF_INET6;
			break;
		case 'f':
			config_file_name = optarg;
			break;
		case 'd':
			if (0 == debug_flag) {
				debug_flag = 1;
				options.log_level = SYSLOG_LEVEL_DEBUG1;
			} else if (options.log_level < SYSLOG_LEVEL_DEBUG3) {
				options.log_level++;
			} else {
				fprintf(stderr, "Too high debugging level.\n");
				exit(1);
			}
			break;
		case 'D':
			no_daemon_flag = 1;
			break;
		case 'e':
			log_stderr = 1;
			break;
		case 'i':
			inetd_flag = 1;
			break;
		case 'Q':
			/* ignored */
			break;
		case 'q':
			options.log_level = SYSLOG_LEVEL_QUIET;
			break;
		case 'b':
			options.server_key_bits = atoi(optarg);
			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':
			if ((options.key_regeneration_time = convtime(optarg)) == -1) {
				fprintf(stderr, "Invalid key regeneration interval.\n");
				exit(1);
			}
			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++] = optarg;
			break;
		case 'V':
			client_version_string = optarg;
			/* only makes sense with inetd_flag, i.e. no listen() */
			inetd_flag = 1;