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;; Copyright (C) 2003 Dale Mellor
;;
;; This program is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.
;;
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;;
;; You should have received a copy of the GNU General Public License
;; along with this program; if not, write to the Free Software
;; Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
;; USA.
;; Apart from the collecting of options and the handling of --help and --version
;; (which are done in the mcron.scm file), this file provides all the
;; functionality of the crontab personality. It is designed to be loaded and run
;; once, and then the calling program can exit and the crontab program will have
;; completed its function.
;; Procedure to communicate with running cron daemon that a user has modified
;; his crontab. The user name is placed in /var/cron/update, and the process
;; whose PID is held in /var/run/cron.pid is sent a SIGHUP.
(define (hit-server user-name)
(catch #t (lambda ()
(let ((server-pid (with-input-from-file "/var/run/cron.pid"
(lambda () (string->number (read-line))))))
(catch #t (lambda ()
(with-output-to-file "/var/cron/update" (lambda ()
(display user-name)(newline))))
(lambda (key . args)
(display "Cannot write to /var/cron/update.\n")
(primitive-exit 14)))
(kill server-pid SIGHUP)))
(lambda (key . args)
(display "Warning: a cron daemon is not running.\n"))))
;; Procedure to scan a file containing one user name per line (such as
;; /var/cron/allow and /var/cron/deny), and determine if the given name is in
;; there. The procedure returns #t, #f, or '() if the file does not exist.
(define (in-access-file? file name)
(catch #t (lambda ()
(with-input-from-file file (lambda ()
(let loop ((input (read-line)))
(if (eof-object? input)
#f
(if (string=? input name)
#t
(loop (read-line))))))))
(lambda (key . args) '())))
;; This program should have been installed SUID root. Here we get the passwd
;; entry for the real user who is running this program.
(define crontab-real-user (passwd:name (getpw (getuid))))
;; If the real user is not allowed to use crontab due to the /var/cron/allow
;; and/or /var/cron/deny files, bomb out now.
(if (or (eq? (in-access-file? "/var/cron/allow" crontab-real-user) #f)
(eq? (in-access-file? "/var/cron/deny" crontab-real-user) #t))
(begin
(display "Access denied by system operator.\n")
(primitive-exit 6)))
;; Iff the real user is root, he can use the -u option to access files of
;; another user.
(define crontab-user (option-ref options 'user crontab-real-user))
;; So now we know which crontab file we will be manipulating.
(define crontab-file (string-append "/var/cron/tabs/" crontab-user))
;; Check that no more than one of the mutually exclusive options are being used.
(if (> (+ (if (option-ref options 'edit #f) 1 0)
(if (option-ref options 'list #f) 1 0)
(if (option-ref options 'remove #f) 1 0))
1)
(begin
(display "crontab: Only one of options -e, -l or -r can be used.\n")
(primitive-exit 7)))
;; Check that a non-root user is trying to read someone else's files.
(if (and (not (eqv? (getuid) 0))
(option-ref options 'user #f))
(begin (display "crontab: Only root can use the -u option.\n")
(primitive-exit 8)))
;; There are four possible sub-personalities to the crontab personality: list,
;; remove, edit and replace (when the user uses no options but supplies file
;; names on the command line).
(cond
;; In the list personality, we simply open the crontab and copy it
;; character-by-character to the standard output. If anything goes wrong, it
;; can only mean that this user does not have a crontab file.
((option-ref options 'list #f)
(catch #t (lambda ()
(with-input-from-file crontab-file (lambda ()
(do ((input (read-char) (read-char)))
((eof-object? input))
(display input)))))
(lambda (key . args)
(display (string-append "No crontab for "
crontab-user
" exists.\n")))))
;; In the edit personality, we determine the name of a temporary file and an
;; editor command, copy an existing crontab file (if it is there) to the
;; temporary file, making sure the ownership is set so the real user can edit
;; it; once the editor returns we try to read the file to check that it is
;; parseable (but do nothing more with the configuration), and if it is okay
;; (this program is still running!) we move the temporary file to the real
;; crontab, wake the cron daemon up, and remove the temporary file.
((option-ref options 'edit #f)
(let ((temp-file (string-append "/tmp/crontab." (number->string (getpid))))
(editor (cond ((getenv "VISUAL") (getenv "VISUAL"))
((getenv "EDITOR") (getenv "EDITOR"))
(else "vi"))))
(catch #t (lambda () (copy-file crontab-file temp-file))
(lambda (key . args) (with-output-to-file temp-file noop)))
(chown temp-file (getuid) (getgid))
(system (string-append editor " " temp-file))
(read-vixie-file temp-file)
(copy-file temp-file crontab-file)
(delete-file temp-file)
(hit-server crontab-user)))
;; In the remove personality we simply make an effort to delete the crontab and
;; wake the daemon. No worries if this fails.
((option-ref options 'remove #f)
(catch #t (lambda () (delete-file crontab-file)
(hit-server crontab-user))
noop))
;; In the case of the replace personality we loop over all the arguments on the
;; command line, and for each one parse the file to make sure it is parseable
;; (but subsequently ignore the configuration), and all being well we copy it
;; to the crontab location; we deal with the standard input in the same way but
;; different. :-) In either case the server is woken so that it will read the
;; newly installed crontab.
((not (null? (option-ref options '() '())))
(let ((input-file (car (option-ref options '() '()))))
(if (string=? input-file "-")
(let ((input-string (stdin->string)))
(read-vixie-port (open-input-string input-string))
(with-output-to-file crontab-file (lambda ()
(display input-string))))
(begin
(read-vixie-file input-file)
(copy-file input-file crontab-file))))
(hit-server crontab-user))
;; The user is being silly. The message here is identical to the one Vixie cron
;; used to put out, for total compatibility.
(else
(display "crontab: usage error: file name must be specified for replace.\n")
(primitive-exit 15)))
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