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/* mcron - run jobs at scheduled times
Copyright (C) 2015, 2016 Mathieu Lirzin
Copyright (C) 2003, 2014 Dale Mellor
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/>. */
/* This C code represents the thinnest possible wrapper around the Guile code
which constitutes all the functionality of the mcron program. There are
two plus one reasons why we need to do this, and one very unfortunate
consequence.
* Firstly, SUID does not work on an executable script. In the end, it is
the execution of the translator, in our case guile, which determines the
effective user, and it is not wise to make the system guile installation
SUID root!
* Secondly, executable scripts show up in ugly ways in listings of the
system process table. Guile in particular, with its multi-line
#! ...\ \n -s ...!#
idiosyncracies shows up in process listings in a way that is difficult
to determine what program is actually running.
* A third reason for the C wrapper which might be mentioned is that a
security-conscious system administrator can choose to only install a
binary, thus removing the possibility of a user studying a guile script
and working out ways of hacking it to his own ends, or worse still
finding a way to modify it to his own ends.
* Unfortunately, running the guile script from inside a C program means
that the sigaction function does not work. Instead, it is necessary to
perform the signal processing in C. */
#include <libguile.h>
#include <signal.h>
#include <string.h>
/* This is a function designed to be installed as a signal handler, for
signals which are supposed to initiate shutdown of this program. It calls
the scheme procedure (see mcron.scm for details) to do all the work, and
then exits. */
void
react_to_terminal_signal (int sig)
{
scm_c_eval_string ("(delete-run-file)");
exit (1);
}
/* This is a function designed to be callable from scheme, and sets up all the
signal handlers required by the cron personality. */
SCM
set_cron_signals ()
{
static struct sigaction sa;
memset (&sa, 0, sizeof (sa));
sa.sa_handler = react_to_terminal_signal;
sigaction (SIGTERM, &sa, 0);
sigaction (SIGINT, &sa, 0);
sigaction (SIGQUIT, &sa, 0);
sigaction (SIGHUP, &sa, 0);
return SCM_BOOL_T;
}
/* The effective main function (i.e. the one that actually does some work).
We register the function above with the guile system, and then execute the
mcron guile program. */
void
inner_main (void *closure, int argc, char **argv)
{
scm_set_current_module (scm_c_resolve_module ("mcron main"));
scm_c_define_gsubr ("c-set-cron-signals", 0, 0, 0, set_cron_signals);
scm_c_eval_string ("(main)");
}
/* The real main function. Does nothing but start up the guile subsystem. */
int
main (int argc, char **argv)
{
setenv ("GUILE_LOAD_PATH", GUILE_LOAD_PATH, 1);
scm_boot_guile (argc, argv, inner_main, 0);
return 0;
}
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