~azzar1/unity/add-show-desktop-key

/* 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"

/* Returns TRUE if the given uid is allowed to execute trampoline.

 * Only root or the web server should be allowed to execute.

 * This is determined by the whitelist allowed_uids in conf.h.

 */

int uid_allowed(int uid)

{

    int i;

    /* root is always allowed to execute trampoline */

    if (uid == 0)

        return 1;

    /* loop over all allowed_uids */

    for (i=(sizeof(allowed_uids)/sizeof(*allowed_uids))-1; i>=0; i--)

    {

        if (allowed_uids[i] == uid)

            return 1;

    }

    /* default to disallowing */

    return 0;

}

/* Turn the process into a daemon using the standard

 * 2-fork technique.

 */

void daemonize(void)

{

    pid_t pid, sid;

    /* already a daemon */

    if ( getppid() == 1 ) return;

    /* Fork off the parent process */

    pid = fork();

    if (pid < 0) {

        exit(1);

    }

    /* If we got a good PID, then we can exit the parent process. */

    if (pid > 0) {

        exit(0);

    }

    /* At this point we are executing as the child process */

    /* Change the file mode mask */

    umask(0);

    /* Create a new SID for the child process */

    sid = setsid();

    if (sid < 0) {

        exit(1);

    }

    /* Change the current working directory.  This prevents the current

       directory from being locked; hence not being able to remove it. */

    if ((chdir("/")) < 0) {

        exit(1);

    }

    /* Redirect standard files to /dev/null */

    freopen( "/dev/null", "r", stdin);

    freopen( "/dev/null", "w", stdout);

    freopen( "/dev/null", "w", stderr);

}

static void usage(const char* nm)

{

    fprintf(stderr,

        "usage: %s [-d] <uid> <jail> <cwd> <program> [args...]\n", nm);

    exit(1);

}

int main(int argc, char* const argv[])

{

    char* jailpath;

    char* work_dir;

    char* prog;

    char* const * args;

    int uid;

    int arg_num = 1;

    int daemon_mode = 0;

    /* Disallow execution from all users but the whitelisted ones, and root */

    if (!uid_allowed(getuid()))

    {

        fprintf(stderr, "only the web server may execute trampoline\n");

        exit(1);

    }

    /* Args check and usage */

    if (argc < 5)

    {

        usage(argv[0]);

    }

    if (strcmp(argv[arg_num], "-d") == 0)

    {

        if (argc < 6)

        {

            usage(argv[0]);

        }

        daemon_mode = 1;

        arg_num++;

    }

    uid = atoi(argv[arg_num++]);

    jailpath = argv[arg_num++];

    work_dir = argv[arg_num++];

    prog = argv[arg_num];

    args = argv + arg_num;

    /* Disallow suiding to the root user */

    if (uid == 0)

    {

        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

     */

    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(work_dir))

    {

        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);

    }

    if (daemon_mode)

    {

        daemonize();

    }

    /* 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(prog, args);

    /* XXX if (daemon_mode) use syslog? */

    /* nb exec won't return unless there was an error */

    perror("could not exec");

    return 1;

}