115 lines
3.5 KiB
C
115 lines
3.5 KiB
C
/* mcron.c -- Run the mcron program.
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*
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* Copyright (C) 2015 Mathieu Lirzin
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* Copyright (C) 2003, 2014 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
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* two plus one reasons why we need to do this, and one very unfortunate
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* consequence.
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*
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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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*
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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 ...!#'' idiosyncracies shows up in process listings in a way that
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* is difficult to determine what program is actually running.
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*
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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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*
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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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*/
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#include <libguile.h>
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#include <signal.h>
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#include <stdlib.h>
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#include <string.h>
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/* Handle the signal and exit. All signals that mcron handles will produce
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* the same behavior so we don't need to use the signal value in the
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* implementation. */
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static void
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react_to_terminal_signal (int signal)
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{
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scm_c_eval_string ("(delete-run-file)");
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exit (1);
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}
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/* Set up all the signal handlers as required by the cron personality. This
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* is necessary to perform the signal processing in C because the sigaction
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* function won't work when called from Guile; this function is called from
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* the Guile universe. */
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static 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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/* Launch the Mcron Guile main program. */
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static void
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inner_main (void *closure, int argc, char **argv)
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{
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scm_set_current_module (scm_c_resolve_module ("mcron main"));
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scm_c_define_gsubr ("c-set-cron-signals", 0, 0, 0, set_cron_signals);
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scm_c_eval_string ("(main)");
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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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