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/* IVLE - Informatics Virtual Learning Environment
* Copyright (C) 2007-2008 The University of Melbourne
*
* This program 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 2 of the License, or
* (at your option) any later version.
*
* This program 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 this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
* Program: Trampoline
* Author: Tom Conway, Matt Giuca
* Date: 20/12/2007
*
* This program runs a given program in a given working dir.
* First, it chroots to a jail path and setuids to a given user ID.
* This is intented to provide a safe execution environment for arbitrary
* programs and scripts.
*
* Scripts (such as Python programs) should be executed by supplying
* "/usr/bin/python" as the program, and the script as the first argument.
*
* Usage: trampoline uid jail-path working-path program [args...]
* Must run as root. Will safely setuid to the supplied uid, checking that it
* is not root. Recommended that the file is set up as follows:
* sudo chown root:root trampoline; sudo chroot +s trampoline
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/* conf.h is admin-configured by the setup process.
* It defines jail_base.
*/
#include "conf.h"
/* Argument names */
#define ARG_UID 1
#define ARG_JAILPATH 2
#define ARG_CWD 3
#define ARG_PROG 4
#define MIN_ARGC 5
#define UID_ROOT 0
int main(int argc, char* const argv[])
{
char* jailpath;
int uid;
/* Args check and usage */
if (argc < MIN_ARGC)
{
fprintf(stderr, "usage: %s <uid> <jail> <cwd> <program> [args...]\n",
argv[0]);
exit(EXIT_FAILURE);
}
/* Disallow suiding to the root user */
uid = atoi(argv[ARG_UID]);
if (uid == UID_ROOT)
{
fprintf(stderr, "cannot set up a jail as root\n");
exit(1);
}
/* Jail path must:
* Be non-empty
* Start with a '/'
* Not contain "/.."
* Begin with jail_base
*/
jailpath = argv[ARG_JAILPATH];
if (strlen(jailpath) < 1 || jailpath[0] != '/'
|| strstr(jailpath, "/..")
|| strncmp(jailpath, jail_base, strlen(jail_base)))
{
fprintf(stderr, "bad jail path: %s\n", jailpath);
exit(1);
}
/* chroot into the jail.
* Henceforth this process, and its children, cannot see anything above
* jailpath. */
if (chroot(jailpath))
{
perror("could not chroot");
exit(1);
}
/* chdir into the specified working directory */
if (chdir(argv[ARG_CWD]))
{
perror("could not chdir");
exit(1);
}
/* setuid to the given user ID.
* Henceforth we will be running as this user instead of root.
*/
if (setuid(uid))
{
perror("could not setuid");
exit(1);
}
/* exec (replace this process with the a new instance of the target
* program). Pass along all the arguments.
* Note that for script execution, the "program" will be the interpreter,
* and the first argument will be the script. */
execv(argv[ARG_PROG], argv + ARG_PROG);
/* nb exec won't return unless there was an error */
perror("could not exec");
return EXIT_FAILURE;
}
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