root/security/root_plug.c

DEFINITIONS

1. rootplug_bprm_check_security
2. rootplug_init

/*
 * Root Plug sample LSM module
 *
 * Originally written for a Linux Journal.
 *
 * Copyright (C) 2002 Greg Kroah-Hartman <greg@kroah.com>
 *
 * Prevents any programs running with egid == 0 if a specific USB device
 * is not present in the system.  Yes, it can be gotten around, but is a
 * nice starting point for people to play with, and learn the LSM
 * interface.
 *
 * If you want to turn this into something with a semblance of security,
 * you need to hook the task_* functions also.
 *
 * See http://www.linuxjournal.com/article.php?sid=6279 for more information
 * about this code.
 *
 *      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, version 2 of the
 *      License.
 */

#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/security.h>
#include <linux/usb.h>
#include <linux/moduleparam.h>

/* default is a generic type of usb to serial converter */
static int vendor_id = 0x0557;
static int product_id = 0x2008;

module_param(vendor_id, uint, 0400);
module_param(product_id, uint, 0400);

/* should we print out debug messages */
static int debug = 0;

module_param(debug, bool, 0600);

#define MY_NAME "root_plug"

#define root_dbg(fmt, arg...)                                   \
        do {                                                    \
                if (debug)                                      \
                        printk(KERN_DEBUG "%s: %s: " fmt ,      \
                                MY_NAME , __func__ ,    \
                                ## arg);                        \
        } while (0)

static int rootplug_bprm_check_security (struct linux_binprm *bprm)
{
        struct usb_device *dev;

        root_dbg("file %s, e_uid = %d, e_gid = %d\n",
                 bprm->filename, bprm->e_uid, bprm->e_gid);

        if (bprm->e_gid == 0) {
                dev = usb_find_device(vendor_id, product_id);
                if (!dev) {
                        root_dbg("e_gid = 0, and device not found, "
                                 "task not allowed to run...\n");
                        return -EPERM;
                }
                usb_put_dev(dev);
        }

        return 0;
}

static struct security_operations rootplug_security_ops = {
        /* Use the capability functions for some of the hooks */
        .ptrace_may_access =            cap_ptrace_may_access,
        .ptrace_traceme =               cap_ptrace_traceme,
        .capget =                       cap_capget,
        .capset_check =                 cap_capset_check,
        .capset_set =                   cap_capset_set,
        .capable =                      cap_capable,

        .bprm_apply_creds =             cap_bprm_apply_creds,
        .bprm_set_security =            cap_bprm_set_security,

        .task_post_setuid =             cap_task_post_setuid,
        .task_reparent_to_init =        cap_task_reparent_to_init,
        .task_prctl =                   cap_task_prctl,

        .bprm_check_security =          rootplug_bprm_check_security,
};

static int __init rootplug_init (void)
{
        /* register ourselves with the security framework */
        if (register_security (&rootplug_security_ops)) {
                printk (KERN_INFO 
                        "Failure registering Root Plug module with the kernel\n");
                        return -EINVAL;
        }
        printk (KERN_INFO "Root Plug module initialized, "
                "vendor_id = %4.4x, product id = %4.4x\n", vendor_id, product_id);
        return 0;
}

security_initcall (rootplug_init);