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Diffstat (limited to 'mcron.c')
| -rw-r--r-- | mcron.c | 102 |
1 files changed, 102 insertions, 0 deletions
@@ -0,0 +1,102 @@ +/* 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; +} |