busybox/loginutils/login.c

/* vi: set sw=4 ts=4: */
/*
 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
 */

#include <fcntl.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <syslog.h>
#include <termios.h>
#include <unistd.h>
#include <utmp.h>
#include <sys/resource.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <ctype.h>
#include <time.h>

#include "busybox.h"
#ifdef CONFIG_SELINUX
#include <selinux/selinux.h>  /* for is_selinux_enabled()  */
#include <selinux/get_context_list.h> /* for get_default_context() */
#include <selinux/flask.h> /* for security class definitions  */
#include <errno.h>
#endif

#ifdef CONFIG_FEATURE_UTMP
// import from utmp.c
static void checkutmp(int picky);
static void setutmp(const char *name, const char *line);
/* Stuff global to this file */
static struct utmp utent;
#endif

// login defines
#define TIMEOUT       60
#define EMPTY_USERNAME_COUNT    10
#define USERNAME_SIZE 32


static int check_nologin ( int amroot );

#if defined CONFIG_FEATURE_SECURETTY
static int check_tty ( const char *tty );

#else
static inline int check_tty ( const char *tty )  { return 1; }

#endif

static int is_my_tty ( const char *tty );
static int login_prompt ( char *buf_name );
static void motd ( void );


static void alarm_handler ( int sig ATTRIBUTE_UNUSED)
{
	fprintf (stderr, "\nLogin timed out after %d seconds.\n", TIMEOUT );
	exit ( EXIT_SUCCESS );
}


int login_main(int argc, char **argv)
{
	char tty[BUFSIZ];
	char full_tty[200];
	char fromhost[512];
	char username[USERNAME_SIZE];
	const char *tmp;
	int amroot;
	int flag;
	int failed;
	int count=0;
	struct passwd *pw, pw_copy;
#ifdef CONFIG_WHEEL_GROUP
	struct group *grp;
#endif
	int opt_preserve = 0;
	int opt_fflag = 0;
	char *opt_host = 0;
	int alarmstarted = 0;
#ifdef CONFIG_SELINUX
	security_context_t user_sid = NULL;
#endif

	username[0]=0;
	amroot = ( getuid ( ) == 0 );
	signal ( SIGALRM, alarm_handler );
	alarm ( TIMEOUT );
	alarmstarted = 1;

	while (( flag = getopt(argc, argv, "f:h:p")) != EOF ) {
		switch ( flag ) {
		case 'p':
			opt_preserve = 1;
			break;
		case 'f':
			/*
			 * username must be a separate token
			 * (-f root, *NOT* -froot). --marekm
			 */
			if ( optarg != argv[optind-1] )
				bb_show_usage( );

			if ( !amroot )		/* Auth bypass only if real UID is zero */
				bb_error_msg_and_die ( "-f permission denied" );

			safe_strncpy(username, optarg, USERNAME_SIZE);
			opt_fflag = 1;
			break;
		case 'h':
			opt_host = optarg;
			break;
		default:
			bb_show_usage( );
		}
	}

	if (optind < argc)             // user from command line (getty)
		safe_strncpy(username, argv[optind], USERNAME_SIZE);

	if ( !isatty ( 0 ) || !isatty ( 1 ) || !isatty ( 2 ))
		return EXIT_FAILURE;		/* Must be a terminal */

#ifdef CONFIG_FEATURE_UTMP
	checkutmp ( !amroot );
#endif

	tmp = ttyname ( 0 );
	if ( tmp && ( strncmp ( tmp, "/dev/", 5 ) == 0 ))
		safe_strncpy ( tty, tmp + 5, sizeof( tty ));
	else if ( tmp && *tmp == '/' )
		safe_strncpy ( tty, tmp, sizeof( tty ));
	else
		safe_strncpy ( tty, "UNKNOWN", sizeof( tty ));

#ifdef CONFIG_FEATURE_UTMP
	if ( amroot )
		memset ( utent.ut_host, 0, sizeof utent.ut_host );
#endif

	if ( opt_host ) {
#ifdef CONFIG_FEATURE_UTMP
		safe_strncpy ( utent.ut_host, opt_host, sizeof( utent. ut_host ));
#endif
		snprintf ( fromhost, sizeof( fromhost ) - 1, " on `%.100s' from `%.200s'", tty, opt_host );
	}
	else
		snprintf ( fromhost, sizeof( fromhost ) - 1, " on `%.100s'", tty );

	bb_setpgrp;

	openlog ( "login", LOG_PID | LOG_CONS | LOG_NOWAIT, LOG_AUTH );

	while ( 1 ) {
		failed = 0;

		if ( !username[0] )
			if(!login_prompt ( username ))
				return EXIT_FAILURE;

		if ( !alarmstarted && ( TIMEOUT > 0 )) {
			alarm ( TIMEOUT );
			alarmstarted = 1;
		}

		if (!( pw = getpwnam ( username ))) {
			pw_copy.pw_name   = "UNKNOWN";
			pw_copy.pw_passwd = "!";
			opt_fflag = 0;
			failed = 1;
		} else
			pw_copy = *pw;

		pw = &pw_copy;

		if (( pw-> pw_passwd [0] == '!' ) || ( pw-> pw_passwd[0] == '*' ))
			failed = 1;

		if ( opt_fflag ) {
			opt_fflag = 0;
			goto auth_ok;
		}

		if (!failed && ( pw-> pw_uid == 0 ) && ( !check_tty ( tty )))
			failed = 1;

		/* Don't check the password if password entry is empty (!) */
		if ( !pw-> pw_passwd[0] )
			goto auth_ok;

		/* authorization takes place here */
		if ( correct_password ( pw ))
			goto auth_ok;

		failed = 1;

auth_ok:
		if ( !failed)
			break;

		bb_do_delay(FAIL_DELAY);
		puts("Login incorrect");
		username[0] = 0;
		if ( ++count == 3 ) {
			syslog ( LOG_WARNING, "invalid password for `%s'%s\n", pw->pw_name, fromhost);
			return EXIT_FAILURE;
	}
	}

	alarm ( 0 );
	if ( check_nologin ( pw-> pw_uid == 0 ))
		return EXIT_FAILURE;

#ifdef CONFIG_FEATURE_UTMP
	setutmp ( username, tty );
#endif

	if ( *tty != '/' )
		snprintf ( full_tty, sizeof( full_tty ) - 1, "/dev/%s", tty);
	else
		safe_strncpy ( full_tty, tty, sizeof( full_tty ) - 1 );

#ifdef CONFIG_SELINUX
	if (is_selinux_enabled())
	{
		security_context_t old_tty_sid, new_tty_sid;

		if (get_default_context(username, NULL, &user_sid))
		{
			fprintf(stderr, "Unable to get SID for %s\n", username);
			exit(1);
		}
		if (getfilecon(full_tty, &old_tty_sid) < 0)
		{
			fprintf(stderr, "getfilecon(%.100s) failed: %.100s\n", full_tty, strerror(errno));
			return EXIT_FAILURE;
		}
		if (security_compute_relabel(user_sid, old_tty_sid, SECCLASS_CHR_FILE, &new_tty_sid) != 0)
		{
			fprintf(stderr, "security_change_sid(%.100s) failed: %.100s\n", full_tty, strerror(errno));
			return EXIT_FAILURE;
		}
		if(setfilecon(full_tty, new_tty_sid) != 0)
		{
			fprintf(stderr, "chsid(%.100s, %s) failed: %.100s\n", full_tty, new_tty_sid, strerror(errno));
			return EXIT_FAILURE;
		}
	}
#endif
	if ( !is_my_tty ( full_tty ))
		syslog ( LOG_ERR, "unable to determine TTY name, got %s\n", full_tty );

	/* Try these, but don't complain if they fail
	 * (for example when the root fs is read only) */
	chown ( full_tty, pw-> pw_uid, pw-> pw_gid );
	chmod ( full_tty, 0600 );

	if (ENABLE_LOGIN_SCRIPTS) {
		char *script = getenv("LOGIN_PRE_SUID_SCRIPT");
		if (script) {
			char *t_argv[2] = { script, NULL };
			switch(fork()) {
			case -1: break;
			case 0: /* child */
				xchdir("/");
				setenv("LOGIN_TTY", full_tty, 1);
				setenv("LOGIN_USER", pw->pw_name, 1);
				setenv("LOGIN_UID", utoa(pw->pw_uid), 1);
				setenv("LOGIN_GID", utoa(pw->pw_gid), 1);
				setenv("LOGIN_SHELL", pw->pw_shell, 1);
				execvp(script, t_argv);
				exit(1);
			default: /* parent */
				wait(NULL);
			}
		}
	}

	change_identity ( pw );
	tmp = pw-> pw_shell;
	if(!tmp || !*tmp)
		tmp = DEFAULT_SHELL;
	setup_environment ( tmp, 1, !opt_preserve, pw );

	motd ( );
	signal ( SIGALRM, SIG_DFL );	/* default alarm signal */

	if ( pw-> pw_uid == 0 )
		syslog ( LOG_INFO, "root login %s\n", fromhost );
#ifdef CONFIG_SELINUX
	/* well, a simple setexeccon() here would do the job as well,
	 * but let's play the game for now */
	set_current_security_context(user_sid);
#endif
	run_shell ( tmp, 1, 0, 0);	/* exec the shell finally. */

	return EXIT_FAILURE;
}



static int login_prompt ( char *buf_name )
{
	char buf [1024];
	char *sp, *ep;
	int i;

	for(i=0; i<EMPTY_USERNAME_COUNT; i++) {
		print_login_prompt();

		if ( !fgets ( buf, sizeof( buf ) - 1, stdin ))
			return 0;

		if ( !strchr ( buf, '\n' ))
			return 0;

		for ( sp = buf; isspace ( *sp ); sp++ ) { }
		for ( ep = sp; isgraph ( *ep ); ep++ ) { }

		*ep = 0;
		safe_strncpy(buf_name, sp, USERNAME_SIZE);
		if(buf_name[0])
			return 1;
	}
	return 0;
}


static int check_nologin ( int amroot )
{
	if ( access ( bb_path_nologin_file, F_OK ) == 0 ) {
		FILE *fp;
		int c;

		if (( fp = fopen ( bb_path_nologin_file, "r" ))) {
			while (( c = getc ( fp )) != EOF )
				putchar (( c == '\n' ) ? '\r' : c );

			fflush ( stdout );
			fclose ( fp );
		} else {
			puts ( "\r\nSystem closed for routine maintenance.\r" );
		}
		if ( !amroot )
			return 1;

		puts ( "\r\n[Disconnect bypassed -- root login allowed.]\r" );
	}
	return 0;
}

#ifdef CONFIG_FEATURE_SECURETTY

static int check_tty ( const char *tty )
{
	FILE *fp;
	int i;
	char buf[BUFSIZ];

	if (( fp = fopen ( bb_path_securetty_file, "r" ))) {
		while ( fgets ( buf, sizeof( buf ) - 1, fp )) {
			for ( i = strlen( buf ) - 1; i >= 0; --i ) {
				if ( !isspace ( buf[i] ))
					break;
			}
			buf[++i] = '\0';
			if (( buf [0] == '\0' ) || ( buf [0] == '#' ))
				continue;

			if ( strcmp ( buf, tty ) == 0 ) {
				fclose ( fp );
				return 1;
			}
		}
		fclose(fp);
		return 0;
	}
	/* A missing securetty file is not an error. */
	return 1;
}

#endif

/* returns 1 if true */
static int is_my_tty ( const char *tty )
{
	struct stat by_name, by_fd;

	if ( stat ( tty, &by_name ) || fstat ( 0, &by_fd ))
		return 0;

	if ( by_name. st_rdev != by_fd. st_rdev )
		return 0;
	else
		return 1;
}


static void motd (void)
{
	FILE *fp;
	int c;

	if (( fp = fopen ( bb_path_motd_file, "r" ))) {
		while (( c = getc ( fp )) != EOF )
			putchar ( c );
		fclose ( fp );
	}
}


#ifdef CONFIG_FEATURE_UTMP
// vv  Taken from tinylogin utmp.c  vv

#define	NO_UTENT \
	"No utmp entry.  You must exec \"login\" from the lowest level \"sh\""
#define	NO_TTY \
	"Unable to determine your tty name."

/*
 * checkutmp - see if utmp file is correct for this process
 *
 *	System V is very picky about the contents of the utmp file
 *	and requires that a slot for the current process exist.
 *	The utmp file is scanned for an entry with the same process
 *	ID.  If no entry exists the process exits with a message.
 *
 *	The "picky" flag is for network and other logins that may
 *	use special flags.  It allows the pid checks to be overridden.
 *	This means that getty should never invoke login with any
 *	command line flags.
 */

static void checkutmp(int picky)
{
	char *line;
	struct utmp *ut;
	pid_t pid = getpid();

	setutent();

	/* First, try to find a valid utmp entry for this process.  */
	while ((ut = getutent()))
		if (ut->ut_pid == pid && ut->ut_line[0] && ut->ut_id[0] &&
			(ut->ut_type == LOGIN_PROCESS || ut->ut_type == USER_PROCESS))
			break;

	/* If there is one, just use it, otherwise create a new one.  */
	if (ut) {
		utent = *ut;
	} else {
		time_t t_tmp;
		
		if (picky) {
			puts(NO_UTENT);
			exit(1);
		}
		line = ttyname(0);
		if (!line) {
			puts(NO_TTY);
			exit(1);
		}
		if (strncmp(line, "/dev/", 5) == 0)
			line += 5;
		memset(&utent, 0, sizeof utent);
		utent.ut_type = LOGIN_PROCESS;
		utent.ut_pid = pid;
		strncpy(utent.ut_line, line, sizeof utent.ut_line);
		/* XXX - assumes /dev/tty?? */
		strncpy(utent.ut_id, utent.ut_line + 3, sizeof utent.ut_id);
		strncpy(utent.ut_user, "LOGIN", sizeof utent.ut_user);
		t_tmp = (time_t)utent.ut_time;
		time(&t_tmp);
	}
}

/*
 * setutmp - put a USER_PROCESS entry in the utmp file
 *
 *	setutmp changes the type of the current utmp entry to
 *	USER_PROCESS.  the wtmp file will be updated as well.
 */

static void setutmp(const char *name, const char *line ATTRIBUTE_UNUSED)
{
	time_t t_tmp = (time_t)utent.ut_time;

	utent.ut_type = USER_PROCESS;
	strncpy(utent.ut_user, name, sizeof utent.ut_user);
	time(&t_tmp);
	/* other fields already filled in by checkutmp above */
	setutent();
	pututline(&utent);
	endutent();
#ifdef CONFIG_FEATURE_WTMP
	if (access(bb_path_wtmp_file, R_OK|W_OK) == -1) {
		close(creat(bb_path_wtmp_file, 0664));
	}
	updwtmp(bb_path_wtmp_file, &utent);
#endif
}
#endif /* CONFIG_FEATURE_UTMP */