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Merge system-wide Vixie cron updates.

Browse source 
I don't believe that anyone should be running system-wide cron processes these
days (the attack surface is rather large), but should use separate per-user or
per-service mcron daemon processes.  But mcron is advertised as a drop-in
Vixie replacement, so we should do what we can to make it safe in this use
case.

I've performed a basic vetting of the changes against vandalism, but haven't
verified the correctness of the code or done any checking; the changes are
being accepted on the basis that almost anything is an improvement on what
currently exists.
This commit is contained in:
Dale Mellor 2023-03-18 14:18:17 +00:00
commit 0fe4d2cc95
Signed by: khleedril
GPG key ID: CA471FD501618A49
8 changed files with 333 additions and 154 deletions
Download patch file Download diff file Expand all files Collapse all files

53
Makefile.am
View file

@ -27,10 +27,17 @@ noinst_SCRIPTS =
if MULTI_USER
bin_SCRIPTS += bin/crontab
sbin_SCRIPTS = bin/cron
libexec_SCRIPTS = bin/crontab-access-real
sbin_PROGRAMS = bin/crontab-access
else
noinst_SCRIPTS += bin/cron bin/crontab
noinst_SCRIPTS += bin/cron bin/crontab bin/crontab-access-real
noinst_PROGRAMS = bin/crontab-access
endif
# The dynamic linker should detect that it's being run for a setuid program,
# but we take no chances.
bin_crontab_access_LDFLAGS = -static
# wrapper to be used in the build environment and for running tests.
noinst_SCRIPTS += pre-inst-env
@ -68,6 +75,7 @@ pkgscriptdir = $(pkgmoduledir)/scripts
dist_pkgscript_DATA = \
src/mcron/scripts/cron.scm \
src/mcron/scripts/crontab.scm \
src/mcron/scripts/crontab-access.scm \
src/mcron/scripts/mcron.scm
pkgscriptgodir = $(pkgmodulegodir)/scripts
@ -77,7 +85,13 @@ compiled_modules = \
$(pkgmodulego_DATA) \
$(pkgscriptgo_DATA)
CLEANFILES = $(compiled_modules) bin/crontab bin/cron bin/mcron
CLEANFILES = $(compiled_modules) \
bin/crontab \
bin/crontab-access \
src/crontab-access.c \
bin/crontab-access-real \
bin/cron \
bin/mcron
DISTCLEANFILES = src/mcron/config.scm
# Unset 'GUILE_LOAD_COMPILED_PATH' altogether while compiling. Otherwise, if
@ -100,10 +114,9 @@ DISTCLEANFILES = src/mcron/config.scm
--warn=format --warn=unbound-variable --warn=arity-mismatch \
--target="$(host)" --output="$@" "$<" $(devnull_verbose)
bin/% : src/%.in Makefile
$(AM_V_GEN)$(MKDIR_P) bin ; \
sed -e 's,%PREFIX%,${prefix},g' \
do_subst = sed -e 's,%PREFIX%,${prefix},g' \
-e 's,%sbindir%,${sbindir},g' \
-e 's,%libexecdir%,${libexecdir},g' \
-e 's,%modsrcdir%,${guilesitedir},g' \
-e 's,%modbuilddir%,${guilesitegodir},g' \
-e 's,%localstatedir%,${localstatedir},g' \
@ -114,8 +127,17 @@ bin/% : src/%.in Makefile
-e 's,%PACKAGE_BUGREPORT%,@PACKAGE_BUGREPORT@,g' \
-e 's,%PACKAGE_NAME%,@PACKAGE_NAME@,g' \
-e 's,%PACKAGE_URL%,@PACKAGE_URL@,g' \
-e 's,%GUILE%,$(GUILE),g' \
$< > $@ ; \
-e 's,%GUILE%,$(GUILE),g'
src/mcron/config.scm: src/mcron/config.scm.in Makefile
$(AM_V_GEN)$(do_subst) $< > $@
src/crontab-access.c: src/crontab-access.c.in Makefile
$(AM_V_GEN)$(do_subst) $< > $@
bin/% : src/%.in Makefile
$(AM_V_GEN)$(MKDIR_P) bin ; \
$(do_subst) $< > $@ ; \
chmod a+x $@
@ -153,6 +175,8 @@ EXTRA_DIST = \
HACKING \
src/cron.in \
src/crontab.in \
src/crontab-access-real.in \
src/crontab-access.c.in \
src/mcron.in \
tests/init.sh \
$(TESTS)
@ -166,10 +190,10 @@ transform_exe = s/$(EXEEXT)$$//;$(transform);s/$$/$(EXEEXT)/
install-exec-hook:
if MULTI_USER
tcrontab=`echo crontab | sed '$(transform_exe)'`; \
chmod u+s $(DESTDIR)$(bindir)/$${tcrontab}
tcron=`echo cron | sed '$(transform_exe)'`; \
chmod u+s $(DESTDIR)$(sbindir)/$${tcron}
tcrontab=`echo crontab | sed '$(transform_exe)'`;
tcrontab_access=`echo crontab-access | sed '$(transform_exe)'`; \
chmod u+s $(DESTDIR)$(sbindir)/$${tcrontab_access}
tcron=`echo cron | sed '$(transform_exe)'`;
endif
tmcron=`echo mcron | sed '$(transform_exe)'`;
@ -178,8 +202,9 @@ installcheck-local:
tmcron=`echo mcron | sed '$(transform_exe)'`; \
test -e $(DESTDIR)$(bindir)/$${tmcron}
if MULTI_USER
tcrontab=`echo crontab | sed '$(transform_exe)'`; \
test -u $(DESTDIR)$(bindir)/$${tcrontab}
tcrontab=`echo crontab | sed '$(transform_exe)'`;
tcrontab_access=`echo crontab | sed '$(transform_exe)'`; \
test -u $(DESTDIR)$(bindir)/$${tcrontab_access}
tcron=`echo cron | sed '$(transform_exe)'`; \
test -e $(DESTDIR)$(sbindir)/$${tcron}
else !MULTI_USER

10
configure.ac
View file

@ -65,6 +65,14 @@ AC_ARG_ENABLE([multi-user],
[Don't Install legacy cron and crontab programs])],
[enable_multi_user="$enableval"],
[enable_multi_user="yes"])
dnl Not possible to run this conditionally?
AC_PROG_CC
dnl AS_IF([test "x$enable_multi_user" = xyes],
dnl [# Need a C compiler to compile setuid wrapper
dnl AC_PROG_CC]
dnl fi
AM_CONDITIONAL([MULTI_USER], [test "x$enable_multi_user" = xyes])
# Configure the various files that mcron uses at runtime.
@ -127,5 +135,5 @@ AC_CONFIG_FILES([pre-inst-env:build-aux/pre-inst-env.in],
[chmod +x pre-inst-env])
AC_CONFIG_FILES([doc/config.texi
Makefile
src/mcron/config.scm])
src/mcron/config.scm.in])
AC_OUTPUT

45
src/crontab-access-real.in Normal file
View file

@ -0,0 +1,45 @@
#!%GUILE% --no-auto-compile
-*- scheme -*-
!#
;;;; crontab -- run jobs at scheduled times
;;; Copyright © 2003, 2020 Dale Mellor <mcron-lsfnyl@rdmp.org>
;;; Copyright © 2015, 2016, 2018 Mathieu Lirzin <mthl@gnu.org>
;;;
;;; This file is part of GNU Mcron.
;;;
;;; GNU Mcron 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 3 of the License, or
;;; (at your option) any later version.
;;;
;;; GNU Mcron 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 GNU Mcron. If not, see <http://www.gnu.org/licenses/>.
(unless (getenv "MCRON_UNINSTALLED")
(set! %load-path (cons "%modsrcdir%" %load-path))
(set! %load-compiled-path (cons "%modbuilddir%" %load-compiled-path)))
(use-modules (mcron scripts crontab)
(mcron command-line-processor))
(process-command-line (command-line)
application "crontab"
version "%VERSION%"
usage "[-u user] { -R | -l | -r }"
help-preamble "the default operation is to list."
option (--user= -u "the user whose files are to be manipulated")
option (--replace -R "replace this userʼs crontab via stdin")
option (--list -l "list this userʼs crontab")
option (--remove -r "delete the userʼs crontab")
bug-address "%PACKAGE_BUGREPORT%"
copyright "2003, 2016, 2020 Free Software Foundation, Inc."
license GPLv3)
((@ (mcron scripts crontab-access) main) --user --replace --list --remove)

10
src/crontab-access.c.in Normal file
View file

@ -0,0 +1,10 @@
#include <unistd.h>
int main(int argc, char **argv)
{
char *envp = NULL;
execve("%libexecdir%/crontab-access-real",
argv, &envp);
/* Should not get here! */
return 1;
}

1
src/mcron/config.scm.in → src/mcron/config.scm.in.in
View file

@ -26,6 +26,7 @@
(define-public config-package-url "@PACKAGE_URL@")
(define-public config-sendmail "@SENDMAIL@")
(define-public config-sbin-dir "%sbindir%")
(define-public config-spool-dir "@CONFIG_SPOOL_DIR@")
(define-public config-socket-file "@CONFIG_SOCKET_FILE@")
(define-public config-allow-file "@CONFIG_ALLOW_FILE@")

2
src/mcron/scripts/cron.scm
View file

@ -147,7 +147,7 @@ option.\n")
(delete-file config-socket-file))
noop)
(exit EXIT_FAILURE))))
'(SIGTERM SIGINT SIGQUIT SIGHUP))
(list SIGTERM SIGINT SIGQUIT SIGHUP))
;; We can now write the PID file.
(with-output-to-file config-pid-file

121
src/mcron/scripts/crontab-access.scm Normal file
View file

@ -0,0 +1,121 @@
;;;; crontab -- edit user's cron tabs
;;; Copyright © 2003, 2004 Dale Mellor <>
;;; Copyright © 2016 Mathieu Lirzin <mthl@gnu.org>
;;;
;;; This file is part of GNU Mcron.
;;;
;;; GNU Mcron 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 3 of the License, or
;;; (at your option) any later version.
;;;
;;; GNU Mcron 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 GNU Mcron. If not, see <http://www.gnu.org/licenses/>.
(define-module (mcron scripts crontab-access)
#:use-module (ice-9 rdelim)
#:use-module (mcron config)
#:use-module (mcron utils)
#:use-module (mcron vixie-specification)
#:export (main))
(define (hit-server user-name)
"Tell the running cron daemon that the user corresponding to
USER-NAME has modified his crontab. USER-NAME is written to the
'/var/cron/socket' UNIX socket."
(catch #t
(lambda ()
(let ((socket (socket AF_UNIX SOCK_STREAM 0)))
(connect socket AF_UNIX config-socket-file)
(display user-name socket)
(close socket)))
(lambda (key . args)
(display "Warning: a cron daemon is not running.\n"))))
(define (in-access-file? file name)
"Scan FILE which should contain one user name per line (such as
'/var/cron/allow' and '/var/cron/deny'). Return #t if NAME is in there, and
#f otherwise. If FILE cannot be opened, a value that is neither #t nor #f
is returned."
(catch #t
(lambda ()
(with-input-from-file file
(lambda ()
(let loop ((input (read-line)))
(cond ((eof-object? input)
#f)
((string=? input name)
#t)
(else
(loop (read-line))))))))
(const '())))
(define (main --user --replace --list --remove)
(when config-debug (debug-enable 'backtrace))
(let ((crontab-real-user
;; This program should have been installed SUID root. Here we get
;; the passwd entry for the real user who is running this program.
(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? config-allow-file crontab-real-user) #f)
(eq? (in-access-file? config-deny-file crontab-real-user) #t))
(mcron-error 6 "Access denied by system operator."))
;; Check that no more than one of the mutually exclusive options are
;; being used.
(when (< 1 (+ (if --list 1 0) (if --remove 1 0) (if --replace 1 0)))
(mcron-error 7 "Only one of options -l, -r or -R can be used."))
;; Check that a non-root user is trying to read someone else's files.
(when (and (not (zero? (getuid))) --user)
(mcron-error 8 "Only root can use the -u option."))
;; Crontabs being written should not have global or group access.
(umask #o077)
(letrec* ( ;; Iff the --user option is given, the crontab-user may be
;; different from the real user.
(crontab-user (or --user crontab-real-user))
;; So now we know which crontab file we will be manipulating.
(crontab-file
(string-append config-spool-dir "/" crontab-user)))
;; There are three possible actions: list, remove, and replace (via
;; stdin).
(cond
;; In the remove personality we simply make an effort to delete the
;; crontab and wake the daemon. No worries if this fails.
(--remove (catch #t (λ () (delete-file crontab-file)
(hit-server crontab-user))
noop))
;; Read crontab from stdin, verify it, replace it, wake daemon.
(--replace
(let ((input-string (read-string)))
(catch-mcron-error
(read-vixie-port (open-input-string input-string))
(unless (file-exists? config-spool-dir)
(mkdir config-spool-dir #o700))
(with-output-to-file crontab-file
(λ () (display input-string))))
(hit-server crontab-user)))
;; 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.
(else ;; --list or no action specified
(catch #t
(λ ()
(with-input-from-file crontab-file
(λ ()
(do ((input (read-char) (read-char)))
((eof-object? input))
(display input)))))
(λ (key . args)
(mcron-error 17 "No crontab for " crontab-user " exists.\n"))))))))

201
src/mcron/scripts/crontab.scm
View file

@ -19,26 +19,12 @@
(define-module (mcron scripts crontab)
#:use-module (ice-9 rdelim)
#:use-module (srfi srfi-1)
#:use-module (mcron config)
#:use-module (mcron utils)
#:use-module (mcron vixie-specification)
#:export (main))
(define (hit-server user-name)
"Tell the running cron daemon that the user corresponding to
USER-NAME has modified his crontab. USER-NAME is written to the
'/var/cron/socket' UNIX socket."
(catch #t
(lambda ()
(let ((socket (socket AF_UNIX SOCK_STREAM 0)))
(connect socket AF_UNIX config-socket-file)
(display user-name socket)
(close socket)))
(lambda (key . args)
(display "Warning: a cron daemon is not running.\n"))))
;; Display the prompt and wait for user to type his choice. Return #t if the
;; answer begins with 'y' or 'Y', return #f if it begins with 'n' or 'N',
;; otherwise ask again.
@ -56,23 +42,6 @@ USER-NAME has modified his crontab. USER-NAME is written to the
(define (in-access-file? file name)
"Scan FILE which should contain one user name per line (such as
'/var/cron/allow' and '/var/cron/deny'). Return #t if NAME is in there, and
#f otherwise. if FILE cannot be opened, a error is signaled."
(catch #t
(lambda ()
(with-input-from-file file
(lambda ()
(let loop ((input (read-line)))
(cond ((eof-object? input)
#f)
((string=? input name)
#t)
(else
(loop (read-line))))))))
(const '())))
;;;
;;; Entry point.
@ -80,117 +49,117 @@ USER-NAME has modified his crontab. USER-NAME is written to the
(define (main --user --edit --list --remove files)
(when config-debug (debug-enable 'backtrace))
(let ((crontab-real-user
;; This program should have been installed SUID root. Here we get
;; the passwd entry for the real user who is running this program.
(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? config-allow-file crontab-real-user) #f)
(eq? (in-access-file? config-deny-file crontab-real-user) #t))
(mcron-error 6 "Access denied by system operator."))
;; Check that no more than one of the mutually exclusive options are
;; being used.
(when (< 1 (+ (if --edit 1 0) (if --list 1 0) (if --remove 1 0)))
(mcron-error 7 "Only one of options -e, -l or -r can be used."))
;; Check that a non-root user is trying to read someone else's files.
;; This will be enforced in the setuid helper 'crontab-access', but good
;; to let the user know early.
(when (and (not (zero? (getuid))) --user)
(mcron-error 8 "Only root can use the -u option."))
(letrec* (;; Iff the --user option is given, the crontab-user may be
;; different from the real user.
(crontab-user (or --user crontab-real-user))
;; So now we know which crontab file we will be manipulating.
(crontab-file
(string-append config-spool-dir "/" crontab-user)))
;; Crontabs being edited should not be global or group-readable.
(umask #o077)
(let ((user-args (if --user (list "-u" --user) '())))
(define (usable-crontab-access? filename)
(and=> (stat filename #f)
(λ (st)
(or (zero? (getuid))
(and (not (zero? (logand #o4000 (stat:mode st))))
(zero? (stat:uid st))
(access? filename X_OK))))))
(define crontab-access
(find usable-crontab-access?
(map (λ (f) (string-append f "/crontab-access"))
(cons config-sbin-dir
(or (and=> (getenv "PATH") parse-path)
'())))))
(define (exec-crontab-access . args)
(catch #t
(λ ()
(apply execlp crontab-access crontab-access
(append user-args args))
(mcron-error 18 "Couldn't execute `crontab-access'."))
(λ args
(apply mcron-error 18 "Couldn't execute `crontab-access'." args))))
(define (crontab-access-dup2 srcs dsts closes . args)
(let ((pid (primitive-fork)))
(cond
((zero? pid)
(for-each dup2 srcs dsts)
(for-each close-fdes closes)
(apply exec-crontab-access args))
(else
(waitpid pid)))))
(define (try-replace file)
(call-with-input-file file
(λ (port)
(crontab-access-dup2 (list (fileno port)) '(0) '() "-R"))))
(unless crontab-access
(mcron-error 18 "Couldn't find a usable `crontab-access'."))
;; 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.
(--list
(catch #t
(λ ()
(with-input-from-file crontab-file
(λ ()
(do ((input (read-char) (read-char)))
((eof-object? input))
(display input)))))
(λ (key . args)
(display (string-append "No crontab for "
crontab-user
" exists.\n")))))
(--list (exec-crontab-access "-l"))
(--remove (exec-crontab-access "-r"))
;; 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. If the parse fails,
;; we give user a choice of editing the file again or quitting the
;; program and losing all changes made.
;; 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, once the editor returns we try to replace any
;; existing crontab file. If this fails, we give user a choice of
;; editing the file again or quitting the program and losing all changes
;; made.
(--edit
(let ((temp-file (string-append config-tmp-dir
(let* ((template (string-append config-tmp-dir
"/crontab."
(number->string (getpid)))))
(catch #t
(λ () (copy-file crontab-file temp-file))
(λ (key . args) (with-output-to-file temp-file noop)))
(chown temp-file (getuid) (getgid))
(number->string (getpid))
".XXXXXX"))
(temp-file (call-with-port (mkstemp template "w")
(λ (port)
(crontab-access-dup2 (list (fileno port)) '(1)
'(2) "-l")
(chmod port #o600)
(port-filename port)))))
(define (exit/cleanup status)
(false-if-exception (delete-file temp-file))
(primitive-exit status))
(let retry ()
(system (string-append
(catch #t
(λ () (system (string-append
(or (getenv "VISUAL") (getenv "EDITOR") "vi")
" "
temp-file))
(catch 'mcron-error
(λ () (read-vixie-file temp-file))
(λ (key exit-code . msg)
(apply mcron-error 0 msg)
temp-file)))
(λ _ (exit/cleanup 1)))
(case (status:exit-val (cdr (try-replace temp-file)))
((9 10 11)
(if (get-yes-no "Edit again?")
(retry)
(begin
(mcron-error 0 "Crontab not changed")
(primitive-exit 0))))))
(copy-file temp-file crontab-file)
(delete-file temp-file)
(hit-server crontab-user)))
(exit/cleanup 0))))
(else => exit/cleanup)))))
;; In the remove personality we simply make an effort to delete the
;; crontab and wake the daemon. No worries if this fails.
(--remove (catch #t (λ () (delete-file crontab-file)
(hit-server crontab-user))
noop))
;; XXX: This comment is wrong.
;; 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.
;; Replace crontab with given file or stdin. If it is a file, it must
;; be opened here and not in the setuid helper, to prevent accessing
;; unauthorized files.
((not (null? files))
(let ((input-file (car files)))
(catch-mcron-error
(if (string=? input-file "-")
(let ((input-string (read-string)))
(read-vixie-port (open-input-string input-string))
(with-output-to-file crontab-file
(λ () (display input-string))))
(begin
(read-vixie-file input-file)
(copy-file input-file crontab-file))))
(hit-server crontab-user)))
(unless (string=? input-file "-")
(dup2 (fileno (open-file input-file "r")) 0))
(exec-crontab-access "-R")))
;; The user is being silly. The message here is identical to the one
;; Vixie cron used to put out, for total compatibility.
(else (mcron-error 15
"usage error: file name must be specified for replace."))))))
"usage error: file name must be specified for replace.")))))