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/* @(#)sysdep.c	3.49 3/25/89 15:31:55 */

/*
 *    Copyright (C) 1987, 1988 Ronald S. Karr and Landon Curt Noll
 * 
 * See the file COPYING, distributed with smail, for restriction
 * and warranty information.
 */

/*
 * sysdep.c:
 *	functions which may be operating system dependent.
 *
 *	external functions: time_stamp, get_arpa_date, get_local_year,
 *			    unix_date, compute_sender, getfullname,
 *			    fopen_as_user, lock_file, unlock_file,
 *			    compute_hostname, open_child, close_child,
 *			    close_all, scan_dir, fcntl_rd_lock
 */
#include <stdio.h>
#include <sys/types.h>
#include <pwd.h>
#include <ctype.h>
#include <sys/stat.h>
#include <errno.h>
#include "defs.h"
#include "smail.h"
#include "child.h"
#include "dys.h"
#include "log.h"
#include "exitcodes.h"

#ifndef DEPEND
# include "extern.h"
# include "debug.h"
#endif

#ifdef	UNIX_SYS5
# include <sys/param.h>
# include <fcntl.h>
#endif

#ifdef	HAVE_UNAME
# include <sys/utsname.h>
#endif

#if     defined(UNIX_BSD)
# include <sys/dir.h>
#else
# if	defined(UNIX_XENIX)
#  include <sys/ndir.h>
# else
#  if	defined(HAVE_READDIR)
#   include <dirent.h>
#   define direct dirent
#  else
#   include <sys/dir.h>
#  endif /* defined(HAVE_READDIR) */
# endif	/* not defined(UNIX_XENIX) */
#endif	/* not defined(UNIX_BSD) */

#ifdef	UNIX_BSD
# include <sys/time.h>
# include <sys/file.h>
#else
# include <time.h>
#endif

#if	!defined(UNIX_BSD) && !defined(UNIX_SYS5)
/* use this for ancient ftime() system call, as a last resort */
# include <sys/timeb.h>
#endif

/* functions local to this file */
static char *get_time_zone();
static void fullname_from_gcos();
static void check_stale();
static int lock_file_by_name();
static void unlock_file_by_name();

/* imported library functions */
extern long lseek();
extern long time();
extern char *getenv();
extern char *getlogin();
extern struct tm *gmtime();
extern struct tm *localtime();
extern char *ctime();
#ifndef	UNIX_SYS5
extern char *timezone();
#endif	/* UNIX_SYS5 */

/* define these, if they aren't already */
#ifndef O_RDONLY
# define O_RDONLY	0
#endif
#ifndef	O_WRONLY
# define O_WRONLY	1
#endif
#ifndef O_RDWR
# define O_RDWR		2
#endif

\f


/*
 * time_stamp - return a time stamp string in the form:
 *
 *	mm/dd/yy hh:mm:ss
 */
char *
time_stamp()
{
#ifdef GLOTZNET
    long clock = time((long *)0) - tzoffset * 3600;
#else /* GLOTZNET */
    long clock = time((long *)0);
#endif /* GLOTZNET */
    struct tm *ltm = localtime(&clock);
    static char timebuf[sizeof("mm/dd/yy hh:mm:ss")];

    (void) sprintf(timebuf, "%02d/%02d/%02d %02d:%02d:%02d",
		   ltm->tm_mon+1, ltm->tm_mday, ltm->tm_year,
		   ltm->tm_hour, ltm->tm_min, ltm->tm_sec);
    return timebuf;
}

/*
 * strings used by the date and time routines below
 */
static char *week_day[] = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
static char *months[] = {
    "Jan", "Feb", "Mar", "Apr", "May", "Jun",
    "Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
};

/*
 * get_local_year - get the year according to local time
 */
int
get_local_year()
{
	long stamp;		/* local time stamp in seconds form Epoch */

	/* return year */
#ifdef GLOTZNET
	stamp = time((long *)0) - tzoffset * 3600;
#else /* GLOTZNET */
	stamp = time((long *)0);
#endif /* GLOTZNET */
	return (localtime(&stamp))->tm_year+1900;
}

/*
 * get_arpa_date - return date in RFC822 format
 */
char *
get_arpa_date(clock)
    long clock;
{
#ifdef GLOTZNET
    struct tm *ltm;
    char *tz_name;
    static char timebuf[sizeof("ddd, dd mmm yy hh:mm tzn+hh:mm:ss")];

    clock -= tzoffset * 3600;
    ltm = localtime(&clock);
    tz_name = get_time_zone(ltm);
#else /* GLOTZNET */
    struct tm *ltm = localtime(&clock);
    char *tz_name = get_time_zone(ltm);
    static char timebuf[sizeof("ddd, dd mmm yy hh:mm tzn+hh:mm:ss")];
#endif /* GLOTZNET */

    if (tz_name == NULL) {
	tz_name = "GMT";
#ifdef GLOTZNET
	clock += tzoffset * 3600;
#endif /* GLOTZNET */
	ltm = gmtime(&clock);
    }
    (void) sprintf(timebuf, "%s, %d %s %02d %02d:%02d %s",
		   week_day[ltm->tm_wday], ltm->tm_mday,
		   months[ltm->tm_mon], ltm->tm_year,
		   ltm->tm_hour, ltm->tm_min, tz_name);
    return timebuf;
}

/*
 * get_time_zone - get the current timezone
 */
/* ARGSUSED */
static char *
get_time_zone(ltm)
    struct tm *ltm;
{
#ifdef	UNIX_BSD
    struct timeval tv;
    struct timezone tz;
    (void) gettimeofday(&tv, &tz);
#ifdef GLOTZNET
    tz.tz_minuteswest += tzoffset * 60;
    if (tznodst) ltm->tm_isdst = 0;
#endif /* GLOTZNET */
    return timezone(tz.tz_minuteswest, ltm->tm_isdst);
#else	/* not UNIX_BSD */
# ifdef UNIX_SYS5
    extern char *tzname[2];

    return tzname[ltm->tm_isdst];
# else	/* not UNIX_SYS5 */
    struct timeb timeb;

    /* try the V6/V7 system call for getting the time zone */
    (void) ftime(&timeb);
    return timezone(timeb.timezone, ltm->tm_isdst);
# endif	/* not UNIX_SYS5 */
#endif	/* not UNIX_BSD */
}

/*
 * unix_date - get the current date as suitable for a From_ line
 *
 * Use ctime format.
 */
char *
unix_date()
{
#ifdef GLOTZNET
    long clock = time((long *)0) - tzoffset * 3600;
#else /* GLOTZNET */
    long clock = time((long *)0);
#endif /* GLOTZNET */
    char *date = ctime(&clock);

    /*
     * XXX - ctime format is quite standard, so just but the nul in
     * the proper spot.
     */
    date[24] = '\0';			/* get rid of that \n */
    return date;
}

/*
 * compute_sender - compute the user running this program.
 *
 * We don't go through the passwd file cache, because the cache
 * doesn't keep the full name information.
 */
void
compute_sender()
{
    struct passwd *pw;
    struct passwd *getpwuid();	/* get a password file entry given uid */

    islocal = TRUE;			/* we can only compute local senders */
    if (sender = getlogin()) {
	register char *new_sender = xmalloc(strlen(sender) + 1);

	(void) strcpy(new_sender, sender);
	sender = new_sender;
	return;
    }
    if (pw = getpwuid(real_uid)) {
	sender = xmalloc((unsigned)(strlen(pw->pw_name)));
	(void) strcpy(sender, pw->pw_name);
	if (!sender_name == NULL) {
	    /*
	     * might as well compute the full name while we have the
	     * password entry on hand
	     */
	    fullname_from_gcos(pw->pw_gecos);
	}
	return;
    }
    sender = "postmaster";
    return;
}

/*
 * getfullname - get the full name of the sender
 *
 * The full name comes from the GCOS field in the password entry.
 */
void
getfullname()
{
    struct passwd *pw;
    struct passwd *getpwnam();	/* get a password entry given a username */

    if (islocal) {
	/* only possible for local senders */
	pw = getpwnam(sender);
	if (pw) {
	    fullname_from_gcos(pw->pw_gecos);
	}
    }
    return;
}

/*
 * fullname_from_gcos - fill in sender_name from the given gcos field
 *
 * (Modified to strip 0000-name(0000) USG junk - hargen@pdn 8/20/88
 */
static void
fullname_from_gcos(gecos)
    register char *gecos;
{
    struct str str;
    register struct str *sp = &str;	/* put full name here */
    char *cp;

    STR_INIT(sp);
    if (isdigit(*gecos) && (cp = index(gecos, '-')) != NULL)
	gecos = cp + 1;			/* skip USG-style 0000-Name junk */
    while (*gecos && *gecos != ',' && *gecos != '(') {
	/* name may end with a comma or USG-style (0000) junk */
	if (*gecos == '&') {		/* & means copy sender, capitalized */
	    STR_NEXT(sp, uppercase(sender[0]));
	    STR_CAT(sp, sender+1);
	} else {
	    STR_NEXT(sp, *gecos);
	}
	gecos++;
    }
    STR_NEXT(sp, '\0');
    STR_DONE(sp);
    sender_name = sp->p;
}

/*
 * fopen_as_user - call fopen(3s) within the context of a specific uid/gid
 *
 * given a uid and gid, fopen a file only if the given uid/gid would be
 * able to do so.  Also, for "a" and "w" types:  if the file did not
 * previously exist, the file will be owned by the uid/gid after having
 * being opened (if the mailer is running as root).
 *
 * return value and errno are set as a call to fopen(3s) would set them.
 *
 * NOTE: the mode argument is only required if type is "a" or "w".
 */
/*VARARGS5*/
FILE *
fopen_as_user(fn, type, check_path, uid, gid, mode)
    char *fn;				/* name of file to open */
    char *type;				/* mode for fopen ("r", "w" or "a") */
    int uid;				/* user id */
    int gid;				/* group id */
    int mode;				/* mode for creat() */
{
    struct stat dir_stat;		/* one for directories */
    struct stat file_stat;		/* one for the file */
    char *fn_build;			/* area for building test filenames */
    register char *fnp;			/* pointer for scanning fn */
    char *new_fnp;			/* pointer for scanning fn */
    register char *bp;			/* pointer to building fn_build */
    FILE *f;				/* opened file */
#ifdef	HAVE_SETEUID
    int fd;				/* file descriptor for opened file */
#endif

    /* reject non-root-based paths out of hand, though we shouldn't get any */
    if (fn[0] != '/') {
	write_log(LOG_SYS|LOG_PANIC,
		  "fopen_as_user: given non-root based path: %s",
		  fn);
	errno = EACCES;
	return NULL;
    }

#ifdef	HAVE_SETEUID
    /*
     * Under BSD, it is easy if we are running as root.  Just set the
     * effective ids to the passed uid and gid and call fopen.  Then
     * set the effective ids back to root.  Having independent seteuid
     * and setruid calls is great.
     *
     * NOTE:  we assume that setgroups(0, (int *)NULL) has been called
     *	      to clear out any groups that may erroneously allow access
     *	      to the file.
     */
    if (geteuid() == 0) {
	int save_gid = getegid();

	/* order here is, oddly enough, mildly important */
	(void) setegid(gid);
	(void) seteuid(uid);

	if (type[0] == 'a') {
	    fd = open(fn, O_WRONLY|O_APPEND|O_CREAT, mode);
	    if (fd < 0) {
		f = NULL;
	    } else {
		f = fdopen(fd, type);
	    }
	} else if (type[0] == 'w') {
	    fd = open(fn, O_WRONLY|O_CREAT|O_TRUNC, mode);
	    if (fd < 0) {
		f = NULL;
	    } else {
		f = fdopen(fd, type);
	    }
	} else {
	    f = fopen(fn, type);
	}

	/* and it is important, again, here */
	(void) seteuid(0);
	(void) setegid(save_gid);

	return f;
    }
#endif	/* HAVE_SETEUID */
    /*
     * now wasn't that nice and simple?  Well, now we get to do
     * it the long way.  We stat all of the directories to ensure
     * that search permission is allowed all the way down to the
     * file itself.  Then, if type is "w" or "a", we chmod the
     * file, if it did not already exist (creating only if the
     * directory allowed write access, of course).
     *
     * NOTE:  namei calls are not known to be cheap, though on a system
     *	      with a good namei cache, this may not be too bad.
     */
    if (check_path) {
	fnp = fn;
	bp = fn_build = xmalloc(strlen(fn));
	while (new_fnp = index(fnp, '/')) {
	    while (fnp <= new_fnp) {
		*bp++ = *fnp++;
	    }
	    bp[0] = '\0';
	    /* since the name ends in /, it can only match directories */
	    if (stat(fn_build, &dir_stat) < 0) {
		/* directory doesn't exist, or we can't access it */
		return NULL;
	    }
	    /*
	     * should probably use some #define somewhere.  However,
	     * the octal numbers below are permission mode bits.
	     */
	    if (! ((dir_stat.st_uid == uid && (dir_stat.st_mode & 0100)) ||
		   (dir_stat.st_gid == gid && (dir_stat.st_mode & 0010)) ||
		   (dir_stat.st_mode & 0001)) )
	    {
		errno = EACCES;
		return NULL;
	    }
	}
    }

    /* made it that far, stat the file, itself */
    if (stat(fn, &file_stat) >= 0) {
	/* file exists, make sure access is allowed, then open it */
	if (type[0] == 'r') {
	    /* check for read access */
	    if (! ((file_stat.st_uid == uid && (file_stat.st_mode & 0400)) ||
		   (file_stat.st_gid == gid && (file_stat.st_mode & 0040)) ||
		   (file_stat.st_mode & 0004)) )
	    {
		errno = EACCES;
		return NULL;
	    }
	} else {
	    /* check for write access */
	    if (! ((file_stat.st_uid == uid && (file_stat.st_mode & 0200)) ||
		   (file_stat.st_gid == gid && (file_stat.st_mode & 0020)) ||
		   (file_stat.st_mode & 0002)) )
	    {
		errno = EACCES;
		return NULL;
	    }
	}

	return fopen(fn, type);
    }

    /*
     * file does not exist, if type is "r", this is an error, otherwise
     * the directory must be writable to creat the file.
     */
    if (type[0] == 'r') {
	errno = EACCES;
	return NULL;
    }
    if (check_path) {
	if (! ((dir_stat.st_uid == uid && (dir_stat.st_mode & 0200)) ||
	       (dir_stat.st_gid == gid && (dir_stat.st_mode & 0020)) ||
	       (dir_stat.st_mode & 0002)) )
	{
	    errno = EACCES;
	    return NULL;
	}
    }

    /* now creat the file and chown and chmod it */
    f = fopen(fn, type);
    if (f == NULL) {
	return NULL;
    }
    /*
     * YAPTN - Yet Another Pass Through Namei()
     * The order here is significant for non-superusers under System V.
     */
    (void) chmod(fn, mode);
    (void) chown(fn, uid, gid);

    return f;
}

/*
 * lock_file - lock a user's mailbox or other mail file
 *
 * return SUCCEED or FAIL.
 */
#ifdef	lock_fd_wait
/*
 * under 4.3BSD and some 4.2+ operating systems, flock(2) is used
 * to lock mailboxes or other mail files.  FLOCK_MAILBOX should
 * be defined in os.h in this case.  We assume that the file
 * descriptor points to the beginning of the file.
 */
int
lock_file(fn, f)
    char *fn;				/* name of file */
    FILE *f;				/* open file */
{
    long offset;
    int success;

    if (! flock_mailbox) {
	/* use filename-based locking for mailbox files */
	return lock_file_by_name(fn);
    }

    offset = lseek(fileno(f), 0L, 1);
    (void) lseek(fileno(f), 0L, 0);
    success = lock_fd_wait(fileno(f));
    (void) lseek(fileno(f), offset, 0);
    if (success < 0) {
	/*
	 * This should never fail, but if it does, we will retry delivery
	 * at a later time.
	 */
	return FAIL;
    }
    return SUCCEED;
}

#else	/* not lock_fd_wait */

/*
 * if the lock_fd_wait macro is not available then we must always
 * use the V6-style file-locking.
 */
/*ARGSUSED*/
int
lock_file(fn, f)
    char *fn;				/* name of file */
    FILE *f;				/* open file */
{
    return lock_file_by_name(fn);
}

#endif	/* not lock_fd_wait */

/*
 * V7-style or Xenix-style locking.
 * As far as I know, all flavors of UN*X that do not use 4.3BSD style
 * locking use this method.
 *
 * To lock a file named fn, create a file named fn.lock (or for Xenix,
 * /tmp/basename.mlk) and stuff the pid into it.  If the file already
 * exisits, see if it is stale and remove it if so.  If it was stale,
 * sleep for FNLOCK_INTERVAL and try to lock it again.  Retry at most
 * FNLOCK_RETRIES times.  On non-BSD systems, locking will not be done
 * if the basename for the file is more than 12 chars.  The lenth
 * restriction does not apply to Xenix, because the basename is always
 * truncated to 10 chars, allowing sufficient space for the .mlk
 * suffix.
 *
 * on systems without O_EXCL for the open(2) call, creat is used
 * with a mode that does not allow writing.
 */
static int
lock_file_by_name(fn)
    char *fn;				/* name of file */
{
    int l_fd;				/* open lock file */
    char *l_fn;				/* lock file name */
    int retries;			/* remaining retries */
    char apid[BITS_PER_INT/3 + 1];	/* ASCII representation of pid */

    if (fn[0] != '/') {
	/*
	 * there should not be a way for the software to generate
	 * a filename that does not begin with /
	 */
	panic(EX_SOFTWARE, "lock_by_name: non-rooted filename: %s", fn);
	/*NOTREACHED*/
    }

    /*
     * will it be possible to create the lock file?  On BSD systems,
     * the open call will tell us if the filename is too long.  On
     * other systems, we need to check this ourselves before hand.
     */
#if	!defined(UNIX_BSD) && !defined(UNIX_XENIX)
    {
	char *p = rindex(fn, '/') + 1;

	/* allow at least enough room for a trailing .l */
	if (strlen(p) > DIRSIZ - 2) {
	    /*
	     * always succeed
	     */
	    return SUCCEED;
	}
    }
#endif	/* not UNIX_BSD and not UNIX_XENIX */

    /*
     * generate the lock filename
     */
#ifdef UNIX_XENIX
    {
	char *p = rindex(fn, '/') + 1;

	l_fn = xmalloc(sizeof("/tmp/.mlk") + 10);
	(void) sprintf(l_fn, "/tmp/%.10s.mlk", p);
    }
#else	/* not UNIX_XENIX */
    l_fn = xmalloc(strlen(fn) + sizeof(".lock"));
    (void) sprintf(l_fn, "%s.lock", fn);
#endif	/* not UNIX_XENIX */

    /*
     * try to create the lock file at most FNLOCK_RETRIES+1 times.
     * each time a lock fails, read a pid from the lock file and try
     * to remove the lock if that pid does not exist then sleep for
     * FNLOCK_INTERVAL and try again.
     */
    for (retries = fnlock_retries; retries-- >= 0; sleep(fnlock_interval)) {
#ifdef	O_EXCL
	l_fd = open(l_fn, O_WRONLY|O_CREAT|O_EXCL, fnlock_mode);
#else	/* O_EXCL */
	/*
	 * if we can't open for exclusive creat, we will have to
	 * use the creat call.
	 */
	l_fd = creat(l_fn, fnlock_mode & (~0222));
#endif	/* O_EXCL */
	if (l_fd < 0) {
	    /*
	     * examine why this failed
	     */
#ifdef	O_EXCL
	    /*
	     * open with O_EXCL returns this error if file exists
	     */
	    if (errno == EEXIST) {
		check_stale(l_fn);	/* remove stale lock files */
		continue;
	    }
#else	/* O_EXCL */
	    /*
	     * creat returns the ambiguous EACCES if the file exists
	     * and is not writable (the correct condition for a lock)
	     */
	    if (errno == EACCES) {
		check_stale(l_fn);
		continue;
	    }
#endif	/* O_EXCL */
	    /*
	     * some other reason is preventing us from writing
	     * the lock file, thus we won't bother retrying.
	     */
	    xfree(l_fn);
#ifdef	UNIX_BSD
	    if (errno == ENOENT) {
		/*
		 * this is what BSD seems to return on basename too
		 * long, so return SUCCEED in this case because
		 * locking is not possible.  Unfortunately this
		 * error does not uniquely identify the problem.
		 */
		return SUCCEED;
	    }
#endif	/* UNIX_BSD */
	    /*
	     * for anything else, something strange is preventing us
	     * creating the lock file.  FAIL for now, we will try
	     * again later.
	     */
	    return FAIL;
	}
	break;
    }
    xfree(l_fn);			/* don't need this any more */

    /*
     * none of the attempts to create the lock file succeeded
     */
    if (l_fd < 0) {
	return FAIL;
    }
    (void) sprintf(apid, "%d", getpid());
    (void) write(l_fd, apid, strlen(apid));
    (void) close(l_fd);

    return SUCCEED;
}

/*
 * check_stale - see if a lock file is stale.  If so, remove it.
 */
static void
check_stale(l_fn)
    char *l_fn;				/* name of lock file */
{
    char buf[50];
    int ct;
    int fd;
    int pid = 0;
    struct stat statbuf;

#ifdef O_RDONLY
    fd = open(l_fn, O_RDONLY);
#else
    fd = open(l_fn, 0);
#endif
    if (fd < 0) {
	DEBUG2(DBG_DRIVER_MID, "%s: cannot open lock file: %s",
	       l_fn, strerrno());
	return;				/* doesn't exist? */
    }

    for (;;) {
	ct = read(fd, buf, sizeof(buf) - 1);
	if (ct == 0) {
	    DEBUG1(DBG_DRIVER_MID, "%s: zero-length lock file ... ", l_fn);

	    /* sleep 30 seconds and see if new data comes in */
	    (void) sleep(30);

	    /* see if it has been removed */
	    (void) fstat(fd, &statbuf);

	    /* fine if it went away */
	    if (statbuf.st_nlink == 0) {
		DEBUG(DBG_DRIVER_MID, "lock file went away\n");
		(void) close(fd);
		return;
	    }

	    /* stale if still empty */
	    if (statbuf.st_size == 0) {
		if (statbuf.st_nlink > 0) {
		    /* unlink if it still exists */
		    (void) unlink(l_fn);
		}
		DEBUG(DBG_DRIVER_MID, "still empty, removed\n");
		(void) close(fd);
		return;
	    }
	}
	else {
#ifdef UNIX_XENIX
	    /* For Xenix, simple existence is quite enough. */
	    DEBUG1(DBG_DRIVER_MID, "%s: valid lock file\n", l_fn);
#else  /* !Xenix */
	    buf[ct] = '\0';
	    (void) sscanf(buf, "%d", &pid);
	    /* see if the pid exists */
	    if (kill(pid, 0) < 0 && errno == ESRCH) {
		/* process does not exist */
		(void) fstat(fd, &statbuf);
		if (statbuf.st_nlink > 0) {
		    /* remove the file if it still exists */
		    (void) unlink(l_fn);
		}
		DEBUG1(DBG_DRIVER_MID, "%s: stale lock file, removed\n",
					l_fn);
	    } else {
		DEBUG1(DBG_DRIVER_MID, "%s: valid lock file\n", l_fn);
	    }
#endif  /* !Xenix */
	    (void) close(fd);
	    return;
	}
    }
}

/*
 * unlock_file - unlock a user's mailbox or other mail file
 *
 * we do not check to make sure we unlocked the file.  What
 * could we do if an unlock failed?
 */
#ifdef	lock_fd_wait
/*
 * for 4.3BSD-style locking, just call flock to unlock the file
 */
void
unlock_file(fn, f)
    char *fn;				/* name of file */
    FILE *f;				/* open file */
{
    long offset;

    if (! flock_mailbox) {
	/* use the V6 locking protocol */
	unlock_file_by_name(fn);
	return;
    }
    offset = lseek(fileno(f), 0L, 1);
    (void) lseek(fileno(f), 0L, 0);	/* unlock from beginning to end */
    unlock_fd_wait(fileno(f));
    (void) lseek(fileno(f), offset, 0);
}
#else	/* not lock_fd_wait */
/*
 * flock not available, so always call the V6-style unlock function.
 */
/*ARGSUSED*/
void
unlock_file(fn, f)
    char *fn;				/* name of file */
    FILE *f;				/* open file */
{
    unlock_file_by_name(fn);
}
#endif	/* not lock_fd_wait */
/*
 * for V6-style locking remove the lock file.  Be careful to
 * make sure that the name passed to unlink(2) won't unlink
 * the main file (i.e., use the same checks for basename size
 * used in creating the lock file)
 */
static void
unlock_file_by_name(fn)
    char *fn;				/* name of file */
{
    char *l_fn;				/* lock file name */

    if (fn[0] != '/') {
	/*
	 * there should not be a way for the software to generate
	 * a filename that does not begin with /, however, the panic
	 * should have occured when lock_file was called.  We will
	 * check anyway, just to make us feel better.
	 */
	panic(EX_SOFTWARE, "unlock_file: non-rooted filename: %s", fn);
	/*NOTREACHED*/
    }

    /*
     * was it possible to create the lock file?  On BSD systems,
     * the unlink will fail if the lock file name is too long.  On
     * other systems, we need to check this ourselves before hand.
     */
#if	!defined(UNIX_BSD) && !defined(UNIX_XENIX)
    {
	char *p = rindex(fn, '/') + 1;

	/* allow at least enough room for a trailing .l */
	if (strlen(p) > DIRSIZ - 2) {
	    /*
	     * no lock file could have been created so don't try
	     * to remove one.
	     */
	    return;
	}
    }
#endif	/* not UNIX_BSD and not UNIX_XENIX */

    /*
     * generate the lock filename
     */
#ifdef UNIX_XENIX
    {
	char *p = rindex(fn, '/') + 1;

	l_fn = xmalloc(sizeof("/tmp/.mlk") + 10);
	(void) sprintf(l_fn, "/tmp/%.10s.mlk", p);
    }
#else	/* not UNIX_XENIX */
    l_fn = xmalloc(strlen(fn) + sizeof(".lock"));
    (void) sprintf(l_fn, "%s.lock", fn);
#endif	/* not UNIX_XENIX */

    /*
     * remove the lock file and clean up
     */
    (void) unlink(l_fn);
    xfree(l_fn);
}

/*
 * compute_hostname - compute the name of the local host
 *
 * return NULL if we are on an operating system that does not know about
 * hostnames.
 */
#ifdef	HAVE_GETHOSTNAME
char *
compute_hostname()
{
    register char *p;
    static char *hostname;
# ifdef	GETHOSTNAME_USE_PTR
    int len;
# endif

    /*
     * My man page says that 255 chars (plus nul byte) is the limit
     * on length of the local host name.  There appears to be no
     * #define for it in 4.2BSD.
     */
    hostname = xmalloc(256);
# ifdef GETHOSTNAME_USE_PTR
    len = 256;
    (void) gethostname(hostname, &len);
# else
    (void) gethostname(hostname, 256);
# endif
    /*
     * Some systems return the entire hostname, including the domain.
     * In this case, the primary hostname should be set to this name,
     * though for now, just truncate off the domain.
     */
    if ((p = index(hostname, '.')) != NULL) {
	*p = '\0';
    }

    /* though we don't need to continue wasting all that space */
    hostname = xrealloc(hostname, strlen(hostname) + 1);

    return hostname;
}
#else	/* not HAVE_GETHOSTNAME */

# ifdef	HAVE_UNAME
char *
compute_hostname()
{
    static struct utsname utsname;

    (void) uname(&utsname);
    /* Is the sysname tag used for something interesting? */
    return utsname.nodename;
}
# else	/* not HAVE_UNAME */
#  ifdef SITENAME_FILE
/* sitename is stored in a file */
char *
compute_hostname()
{
    static struct str hostname;
    static int inited = FALSE;
    register int c;
    FILE *f;

    if (inited) {
	return hostname.p;
    }
    inited = TRUE;
    STR_INIT(&hostname);

    f = fopen(SITENAME_FILE, "r");
    while ((c = getc(f)) != EOF && c != '\n') {
	STR_NEXT(&hostname, c);
    }
    STR_NEXT(&hostname, '\0');
    STR_DONE(&hostname);
    return hostname.p;
}
#  else	/* not SITENAME_FILE */
char *
compute_hostname()
{
    /*
     * perhaps we should call uuname -l rather than punting.
     */
    panic(EX_SOFTWARE,
	  "the local host name is not computable and is not configured");
    /*NOTREACHED*/
}
#  endif /* not SITENAME_FILE */
# endif	/* not HAVE_UNAME */
#endif	/* not HAVE_GETHOSTNAME */

\f


/*
 * open_child - create a child process and open pipes to it and exec
 *
 * open_child creates a child process, with possible read and write
 * pipes to the child process's stdin and stdout/stderr.  Setuid and
 * setgid are called in the child process to change the uid/gid to
 * whichever uid/gid are given to open_child.
 *
 * open_child does nothing with signals in the parent process.
 * Only signal behaviors modified by exec will be changed in the
 * child process.  If more complex signal behavior desired, call
 * with argv == NULL and handle signals and the exec in the caller
 * routine within the child process.
 *
 * inputs:
 *	argv	- a vector suitable for passing to execve.  argv[0] is
 *		  given as the program to exec.  If argv is NULL, then
 *		  do a return instead of an exec.  In this case as well,
 *		  never to a vfork(), always use fork().
 *	envp	- a vector of environment variables suitable for passing
 *		  to execve.  If envp is null and CHILD_MINENV is not
 *		  set in flags, then the parents environment will be
 *		  passed to the child.
 *	in	- a pointer to a FILE* variable.  If non-NULL, a pipe
 *		  is created, with the write-end returned in this
 *		  variable and with the read-end tied to the stdin of
 *		  the child process.
 *	out	- a pointer to a FILE* variable.  If non-NULL, a pipe
 *		  is created, with thre read-end returned in this
 *		  variable and with the write-end tied to the stdout
 *		  of the child process.
 *	errfd	- if errfd >= 0 then it sepecifies a file descriptor
 *		  to duplicate to the stdout and/or stderr of the
 *		  child.  If out != NULL, errfd is only dup'd to the
 *		  stderr.
 *	flags	- a bitmask of flags affecting open_child's operation.
 *		  Flags are:
 *
 *		CHILD_DUPERR	- duplicate stdout to stderr in the
 *				  child process.
 *		CHILD_DEVNULL	- open "/dev/null" and associate it
 *				  with stdin and/or stdout in the
 *				  child process, if no in and/or out
 *				  variable is specified.
 *		CHILD_RETRY	- retry fork() operation up to FORK_RETRIES
 *				  times at FORK_INTERVAL second intervals,
 *				  if fork returns EAGAIN.
 *		CHILD_MINENV	- give the child process a very minimal
 *				  environment.  This is overridden by giving
 *				  an explicit environment in envp.
 *		CHILD_NOCLOSE	- don't close file descriptors.  If this is
 *				  not set, close all file descriptors
 *				  other than stdin/stdout/stderr.
 *
 *	uid	- do a setuid(uid) in the child
 *	gid	- do a setgid(gid) in the child
 *
 * output:
 *	pid of child process, or 0 if in child process (only if argv==NULL).
 *	Return EOF if pipe() or fork() failed.
 */
int
open_child(argv, envp, in, out, errfd, flags, uid, gid)
    char **argv;			/* arg vector for execve */
    char **envp;			/* environment vector for execve */
    FILE **in;				/* make a stdin file pointer */
    FILE **out;				/* make a stdout file pointer */
    int errfd;				/* fd to use for stdout/stderr */
    int flags;				/* flags affecting operation */
    int uid;				/* user ID for child process */
    int gid;				/* group ID for child process */
{
    int stdin_fd[2];			/* fds from pipe(2) for child stdin */
    int stdout_fd[2];			/* fds from pipe(2) for child stdout */
    /* remember, fd[0] is the read descriptor, fd[1] is the write descriptor */
    int retries = FORK_RETRIES;		/* countdown of retries */
    int pid;				/* pid from fork() */
    static char *min_env[] = {
#ifdef	CHILD_ENVIRON
	CHILD_ENVIRON,
#else	/* CHILD_ENVIRON */
	"PATH=/bin:/usr/bin",
	"SHELL=/bin/sh",
	"HOME=/",
#endif	/* CHILD_ENVIRON */
#ifndef	UNIX_BSD
	NULL,				/* leave space for timezone */
#endif	/* UNIX_BSD */
	NULL,				/* end of environment */
    };

    if (in && pipe(stdin_fd) < 0) {
	return EOF;
    }
    if (out && pipe(stdout_fd) < 0) {
	/* free resources */
	(void) close(stdin_fd[0]);
	(void) close(stdin_fd[1]);
	return EOF;
    }

    /* keep trying to create a fork until we succeed or retries == 0 */
    while (
#ifdef	UNIX_BSD
	   (pid = (argv? vfork(): fork())) < 0 &&
#else	/* UNIX_BSD */
	   (pid = fork()) < 0 &&
#endif	/* UNIX_BSD */
	   errno == EAGAIN &&
	   --retries >= 0)
    {
	(void) sleep(FORK_INTERVAL);	/* sleep between retries */
    }
    if (pid < 0) {
	/* free resources */
	(void) close(stdin_fd[0]);
	(void) close(stdin_fd[1]);
	(void) close(stdout_fd[0]);
	(void) close(stdout_fd[1]);
	return EOF;
    }

    if (pid == 0) {
	/* in child process */

	/* close unnecessary file descriptors */
	if (in) {
	    (void) close(stdin_fd[1]);
	}
	if (out) {
	    (void) close(stdout_fd[0]);
	}

	/* if errfd == 0, watch out for the code below */
	if (errfd == 0 || errfd == 1) {
	    int new_errfd;

	    /* search for a descriptor we don't care about */
	    for (new_errfd = 3; new_errfd < 10; new_errfd++) {
		if (in && new_errfd == stdin_fd[0] ||
		    out && new_errfd == stdout_fd[1])
		{
		    continue;
		}
	    }
	    (void) dup2(errfd, new_errfd);
	    (void) close(errfd);
	    errfd = new_errfd;
	}
	if (in || (flags & CHILD_DEVNULL)) {
	    /*
	     * setup the child's stdin
	     */
	    if (in) {
		/* pipe from parent process */
		if (stdin_fd[0] != 0) {
		    (void) dup2(stdin_fd[0], 0);
		    (void) close(stdin_fd[0]);
		}
	    } else if (flags & CHILD_DEVNULL) {
		/*
		 * XXX - we rely on pipe() never returning 0 as the
		 *	 write file descriptor, or this could close
		 *	 stdout_fd[1], which would not be nice.
		 */
		/* open /dev/null as the stdin */
		(void) close(0);
		if (open("/dev/null", O_RDONLY) < 0) {
		    /* uggh! failed to open /dev/null, quit */
		    _exit(EX_OSFILE);
		}
	    }
	}

	if (out || errfd >= 0 || (flags & CHILD_DEVNULL)) {
	    /*
	     * setup the child's stdout
	     */
	    if (out) {
		/* pipe to parent process */
		if (stdout_fd[1] != 1) {
		    (void) dup2(stdout_fd[1], 1);
		    (void) close(stdout_fd[1]);
		}
	    } else if (errfd >= 0) {
		/* use the given fd for stdout */
		(void) dup2(errfd, 1);
	    } else if (flags & CHILD_DEVNULL) {
		/* open /dev/null as stdout */
		(void) close(1);
		if (open("/dev/null", O_WRONLY) < 0) {
		    /* uggh! failed to open /dev/null, quit */
		    _exit(EX_OSFILE);
		}
	    }
	}

	if (errfd >= 0) {
	    /* use this fd as the stderr */
	    if (errfd != 2) {
		(void) dup2(errfd, 2);
		(void) close(errfd);
	    }
	} else if (flags & CHILD_DUPERR) {
	    /* duplicate stdout to get the stderr */
	    (void) dup2(1, 2);
	} else {
	    (void) close(2);
	    if (open("/dev/null", O_WRONLY) < 0) {
		/* uggh! failed to open /dev/null, quit */
		_exit(EX_OSFILE);
	    }
	}

	/* close all unnecessary file descriptors */
	if ( !(flags & CHILD_NOCLOSE) ) {
	    close_all();
	}

	/* change uid and gid, if we can, don't bother to check */
	(void) setgid(gid);
	(void) setuid(uid);

	if (argv) {
	    /* execute the program */
	    if (envp) {
		(void) execve(argv[0], argv, envp);
	    } else if (flags & CHILD_MINENV) {
#if	!defined(UNIX_BSD)
		/* pass the TZ environment variable on non-BSD systems */
		char *tz = getenv("TZ");

		if (tz) {
		    char *tzenv = xmalloc(strlen(tz) + 4);

		    strcpy(tzenv, "TZ=");
		    strcat(tzenv, tz);
		    min_env[3] = tzenv;
		}
#endif	/* not UNIX_BSD */
		(void) execve(argv[0], argv, min_env);
	    } else {
		(void) execv(argv[0], argv);
	    }

	    /* Oh well, all this work and we can't even exec the file */
	    _exit(EX_OSFILE);
	}
    } else {
	/* in parent process */
	if (in) {
	    /* close the child stdin, return the write-channel */
	    (void) close(stdin_fd[0]);
	    *in = fdopen(stdin_fd[1], "w");
	}
	if (out) {
	    /* close the child stdout, return the read-channel */
	    (void) close(stdout_fd[1]);
	    *out = fdopen(stdout_fd[0], "r");
	}
    }

    return pid;
}

/*
 * close_child - close down the child process started with open_child.
 *
 * if non-zero file pointers are passed, the given files are closed.
 * Then, wait for the specified pid to exit and return its status.
 *
 * NOTE:  we do not keep the exit status of processes other than the
 *	  one we are waiting.  Thus, only one process should be open
 *	  at a time by open_child, unless the caller wishes to handle
 *	  the performing the waits itself.
 *
 * return EOF, on error, or exit status.
 */
int
close_child(in, out, pid)
    FILE *in;				/* pipe to child's stdin */
    FILE *out;				/* pipe to child's stdout */
    int pid;				/* pid of child process */
{
    int i;				/* return value from wait */
    int status;				/* status from wait */

    if (in) {
	(void) fclose(in);		/* close the pipe to stdin */
    }

    if (out) {
	(void) fclose(out);		/* close the pipe to stdout */
    }

    /* wait for the child process to die */
    while ((i = wait(&status)) != pid && i >= 0) ;

    if (i < 0) {
	/* failed to find the child process */
	return FAIL;
    }
    return status;			/* everything went okay */
}

/*
 * close_all - close all file descriptors other than 0, 1 and 2
 *
 * At several key points smail needs to know that no extra file descriptors
 * being used, such as when execing other processes (to ensure that
 * child processes cannot read or write protected information left open in
 * smail) and at startup (to prevent smail running out of file descriptors).
 */
void
close_all()
{
    register int i;

    for (i = 3;
	 /* so just how many file descriptors do we have? */
#ifdef	NOFILE
	 i < NOFILE;
#else
# ifdef	OPEN_MAX
	 i < OPEN_MAX;
# else
	 /* if neither of the above are defined, 20 shoule be right */
	 i < 20;
# endif
#endif
	 i++)
    {
	(void) close(i);
    }
}

#ifndef	HAVE_RENAME
/*
 * rename - emulate the BSD/System V.3 rename(2) system call
 *
 * This subroutine is not atomic, so functions which are worried about
 * consistency across system failures or in the face of multiple processes
 * should consider the situation when HAVE_RENAME is not defined.
 *
 * The errno returned will not always correspond to what would have
 * been produced by a true rename(2) system call.
 */
int
rename(from, to)
    char *from;				/* old file name */
    char *to;				/* new file name */
{
    if (unlink(to) && errno != ENOENT) {
	/* could not unlink `to', though it may exist */
	return -1;
    }

    if (link(from, to) < 0) {
	/* failed to link, however, an existing `to' file was removed */
	return -1;
    }

    if (unlink(from) < 0) {
	/* could not unlink, the file exists under two names */
	return -1;
    }
    return 0;
}
#endif	/* HAVE_RENAME */

#if !defined(HAVE_MKDIR)
/*
 * for OS's that lack a mkdir system call, call the mkdir program
 */
int
mkdir(dir, mode)
    char *dir;
    int mode;
{
    static char *mkdir_argv[] = {
	"/bin/mkdir",
	NULL,				/* space for directory name */
	NULL,
    };
    /* set the umask so that the directory will have the correct perms */
    int oumask = umask((~mode)&0777);
    int pid;

    mkdir_argv[1] = dir;

    /* start up the mkdir program */
    pid = open_child(mkdir_argv, (char **)NULL,
		     (FILE **)NULL, (FILE **)NULL, -1, CHILD_DEVNULL, 0, 0);

    (void) umask(oumask);

    return close_child((FILE *)NULL, (FILE *)NULL, pid);
}
#endif	/* !defined(HAVE_MKDIR) */

#ifndef	HAVE_DUP2
/*
 * dup2 - this provides the dup2 function as described by the Posix Draft
 *        for those sites which do not have it.
 *
 * Mark Colburn (mark@jhereg.mn.org)
 */
int
dup2(fildes, fildes2)
        int     fildes, fildes2;
{
        int     fid;

        if (fcntl(fildes, F_GETFL, 0) == -1)
                return(EBADF);
        if (fildes != fildes2)
                close(fildes2);
        fid = fcntl(fildes, F_DUPFD, fildes2);
        return(fid);
}
#endif	/* HAVE_DUP2 */

#ifndef HAVE_READDIR
/*
 * for OS's that lack the directory facilities, emulate
 */
struct direct_with_null {
    struct direct d;
    int trailing_null;			/* make sure name ends in a nul byte */
};

typedef FILE DIR;
#define opendir(dn)	(fopen(dn, "r"))
#define closedir(dn)	(fclose(dn))

static struct direct *
readdir(dirp)
    DIR *dirp;
{
    static struct direct_with_null ret;

    ret.trailing_null = 0;
    do {
	if (fread(&ret.d, sizeof(ret.d), 1, (FILE *)dirp) < 1) {
	    return NULL;
	}
    } while (ret.d.d_ino == 0);
    return &ret.d;
}
#endif	/* HAVE_READDIR */

/*
 * scan_dir - scan through a directory, looking for filenames
 *
 * if given a non-NULL directory argument, opens the directory and
 * returns the first file, or NULL if it contains no files.
 * successive calls, with a NULL argument, return successive files
 * in the directory.  On the call after the last directory, a NULL
 * is returned and the directory is closed.
 *
 * scan_dir returns static data which is reused on subsequent calls.
 */
char *
scan_dir(dn)
    char *dn;				/* directory name, or NULL */
{
    static DIR *dirp = NULL;		/* opened directory */
    struct direct *dp;			/* current directory entry */

    if (dn) {
	dirp = opendir(dn);
    }
    if (dirp == NULL) {
	return NULL;			/* no directory, so no entries */
    }
    dp = readdir(dirp);
    if (dp == NULL) {
	(void) closedir(dirp);
	return NULL;
    }

    return dp->d_name;
}

#ifdef	USE_FCNTL_RD_LOCK
/*
 * fcntl_rd_lock - get a shared lock using a System V-style fcntl.
 */
int
fcntl_rd_lock(fd)
    int fd;
{
    struct flock l;

    l.l_type = F_RDLCK;
    l.l_whence = 0;
    l.l_start = 0L;
    l.l_len = 0L;
    if (fcntl(fd, F_SETLKW, &l) < 0) {
	return FAIL;
    }
    return SUCCEED;
}
#endif
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