sshd.c

C＋＋编写

/*
 * Author: Tatu Ylonen <[e-mail]>
 * Copyright (c) 1995 Tatu Ylonen <[e-mail]>, 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"
RCSID("$OpenBSD: sshd.c,v 1.263 2003/02/16 17:09:57 markus Exp $");

#include <openssl/dh.h>
#include <openssl/bn.h>
#include <openssl/md5.h>
#include <openssl/rand.h>

#include "ssh.h"
#include "ssh1.h"
#include "ssh2.h"
#include "xmalloc.h"
#include "rsa.h"
#include "sshpty.h"
#include "packet.h"
#include "mpaux.h"
#include "log.h"
#include "servconf.h"
#include "uidswap.h"
#include "compat.h"
#include "buffer.h"
#include "cipher.h"
#include "kex.h"
#include "key.h"
#include "dh.h"
#include "myproposal.h"
#include "authfile.h"
#include "pathnames.h"
#include "atomicio.h"
#include "canohost.h"
#include "auth.h"
#include "misc.h"
#include "dispatch.h"
#include "channels.h"
#include "session.h"
#include "monitor_mm.h"
#include "monitor.h"
#include "monitor_wrap.h"
#include "monitor_fdpass.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

extern char *__progname;

/* Server configuration options. */
ServerOptions options;

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

/*
 * Flag indicating whether IPv4 or IPv6.  This can be set on the command line.
 * Default value is AF_UNSPEC means both IPv4 and IPv6.
 */
int IPv4or6 = AF_UNSPEC;

/*
 * 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;

/*
 * 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;

/* for rekeying XXX fixme */
Kex *xxx_kex;

/*
 * 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 {
	Key	*server_key;		/* ephemeral server key */
	Key	*ssh1_host_key;		/* ssh1 host key */
	Key	**host_keys;		/* all private host keys */
	int	have_ssh1_key;
	int	have_ssh2_key;
	u_char	ssh1_cookie[SSH_SESSION_KEY_LENGTH];
} sensitive_data;

/*
 * Flag indicating whether the RSA server key needs to be regenerated.
 * Is set in the SIGALRM handler and cleared when the key is regenerated.
 */
static volatile sig_atomic_t key_do_regen = 0;

/* 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;
int session_id2_len = 0;

/* record remote hostname or ip */
u_int utmp_len = MAXHOSTNAMELEN;

/* 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;
struct monitor *pmonitor;

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

static void do_ssh1_kex(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).
 */
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)
{
	log("Received SIGHUP; restarting.");
	close_listen_socks();
	close_startup_pipes();
	execv(saved_argv[0], saved_argv);
	log("RESTART FAILED: av[0]='%.100s', error: %.100s.", saved_argv[0],
	    strerror(errno));
	exit(1);
}

/*
 * Generic signal handler for terminating signals in the master daemon.
 */
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.
 */
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.
 */
static void
grace_alarm_handler(int sig)
{
	/* XXX no idea how fix this signal handler */

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

/*
 * 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.
 */
static void
generate_ephemeral_server_key(void)
{
	u_int32_t rnd = 0;
	int i;

	verbose("Generating %s%d bit RSA key.",
	    sensitive_data.server_key ? "new " : "", options.server_key_bits);
	if (sensitive_data.server_key != NULL)
		key_free(sensitive_data.server_key);
	sensitive_data.server_key = key_generate(KEY_RSA1,
	    options.server_key_bits);
	verbose("RSA key generation complete.");

	for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
		if (i % 4 == 0)
			rnd = arc4random();
		sensitive_data.ssh1_cookie[i] = rnd & 0xff;
		rnd >>= 8;
	}
	arc4random_stir();
}

static void
key_regeneration_alarm(int sig)
{
	int save_errno = errno;

	signal(SIGALRM, SIG_DFL);
	errno = save_errno;
	key_do_regen = 1;
}

static void
sshd_exchange_identification(int sock_in, int sock_out)
{
	int i, mismatch;
	int remote_major, remote_minor;
	int major, 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. */

	if ((options.protocol & SSH_PROTO_1) &&
	    (options.protocol & SSH_PROTO_2)) {
		major = PROTOCOL_MAJOR_1;
		minor = 99;
	} else if (options.protocol & SSH_PROTO_2) {
		major = PROTOCOL_MAJOR_2;
		minor = PROTOCOL_MINOR_2;
	} else {
		major = PROTOCOL_MAJOR_1;
		minor = PROTOCOL_MINOR_1;
	}
	snprintf(buf, sizeof buf, "SSH-%d.%d-%.100s\n", major, minor, SSH_VERSION);
	server_version_string = xstrdup(buf);

	if (client_version_string == NULL) {
		/* Send our protocol version identification. */
		if (atomicio(write, sock_out, server_version_string,
		    strlen(server_version_string))
		    != strlen(server_version_string)) {
			log("Could not write ident string to %s", get_remote_ipaddr());
			fatal_cleanup();
		}

		/* 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) {
				log("Did not receive identification string from %s",
				    get_remote_ipaddr());
				fatal_cleanup();
			}
			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(write, sock_out, s, strlen(s));
		close(sock_in);
		close(sock_out);
		log("Bad protocol version identification '%.100s' from %s",
		    client_version_string, get_remote_ipaddr());
		fatal_cleanup();
	}
	debug("Client protocol version %d.%d; client software version %.100s",
	    remote_major, remote_minor, remote_version);

	compat_datafellows(remote_version);

	if (datafellows & SSH_BUG_PROBE) {
		log("probed from %s with %s.  Don't panic.",
		    get_remote_ipaddr(), client_version_string);
		fatal_cleanup();
	}

	if (datafellows & SSH_BUG_SCANNER) {
		log("scanned from %s with %s.  Don't panic.",
		    get_remote_ipaddr(), client_version_string);
		fatal_cleanup();
	}

	mismatch = 0;
	switch (remote_major) {
	case 1:
		if (remote_minor == 99) {
			if (options.protocol & SSH_PROTO_2)
				enable_compat20();
			else
				mismatch = 1;
			break;
		}
		if (!(options.protocol & SSH_PROTO_1)) {
			mismatch = 1;
			break;
		}
		if (remote_minor < 3) {
			packet_disconnect("Your ssh version is too old and "
			    "is no longer supported.  Please install a newer version.");
		} else if (remote_minor == 3) {
			/* note that this disables agent-forwarding */