120 lines
3.8 KiB
C
120 lines
3.8 KiB
C
/* -*-c-*- */
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/*
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* Copyright (C) 2003 Dale Mellor
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*
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* This file is part of GNU mcron.
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*
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* GNU mcron is free software: you can redistribute it and/or modify it under
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* the terms of the GNU General Public License as published by the Free
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* Software Foundation, either version 3 of the License, or (at your option)
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* any later version.
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*
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* GNU mcron is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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* more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with GNU mcron. If not, see <http://www.gnu.org/licenses/>.
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*/
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/*
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This C code represents the thinnest possible wrapper around the Guile code
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which constitutes all the functionality of the mcron program. There are two
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plus one reasons why we need to do this, and one very unfortunate
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consequence.
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Firstly, SUID does not work on an executable script. In the end, it is
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the execution of the translator, in our case guile, which determines the
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effective user, and it is not wise to make the system guile installation
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SUID root!
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Secondly, executable scripts show up in ugly ways in listings of the
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system process table. Guile in particular, with its multi-line
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#! ...\ \n -s ...!#
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idiosyncracies shows up in process listings in a way that is difficult
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to determine what program is actually running.
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A third reason for the C wrapper which might be mentioned is that a
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security-conscious system administrator can choose to only install a
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binary, thus removing the possibility of a user studying a guile script
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and working out ways of hacking it to his own ends, or worse still
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finding a way to modify it to his own ends.
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Unfortunately, running the guile script from inside a C program means
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that the sigaction function does not work. Instead, it is necessary to
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perform the signal processing in C.
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The guile code itself is substituted for the GU1LE_PROGRAM_GOES_HERE (sic)
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token by the makefile, which processes the scheme to make it look like one
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big string.
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*/
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#include <string.h>
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#include <signal.h>
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#include <libguile.h>
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/* This is a function designed to be installed as a signal handler, for signals
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which are supposed to initiate shutdown of this program. It calls the scheme
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procedure (see mcron.scm for details) to do all the work, and then exits. */
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void
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react_to_terminal_signal (int sig)
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{
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scm_eval_string (scm_take0str ("(delete-run-file)") );
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exit (1);
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}
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/* This is a function designed to be callable from scheme, and sets up all the
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signal handlers required by the cron personality. */
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SCM
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set_cron_signals ()
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{
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static struct sigaction sa;
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memset (&sa, 0, sizeof (sa));
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sa.sa_handler = react_to_terminal_signal;
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sigaction (SIGTERM, &sa, 0);
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sigaction (SIGINT, &sa, 0);
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sigaction (SIGQUIT, &sa, 0);
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sigaction (SIGHUP, &sa, 0);
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return SCM_BOOL_T;
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}
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/* The effective main function (i.e. the one that actually does some work). We
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register the function above with the guile system, and then execute the mcron
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guile program. */
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void
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inner_main ()
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{
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scm_c_define_gsubr ("c-set-cron-signals", 0, 0, 0, set_cron_signals);
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scm_eval_string (scm_take0str (
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GUILE_PROGRAM_GOES_HERE
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) );
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}
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/* The real main function. Does nothing but start up the guile subsystem. */
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int
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main (int argc, char **argv)
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{
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setenv ("GUILE_LOAD_PATH", GUILE_LOAD_PATH, 1);
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scm_boot_guile (argc, argv, inner_main, 0);
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return 0;
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}
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