LXR linux/security/root

   1/*
   2 * Root Plug sample LSM module
   3 *
   4 * Originally written for a Linux Journal.
   5 *
   6 * Copyright (C) 2002 Greg Kroah-Hartman <greg@kroah.com>
   7 *
   8 * Prevents any programs running with egid == 0 if a specific USB device
   9 * is not present in the system.  Yes, it can be gotten around, but is a
  10 * nice starting point for people to play with, and learn the LSM
  11 * interface.
  12 *
  13 * If you want to turn this into something with a semblance of security,
  14 * you need to hook the task_* functions also.
  15 *
  16 * See http://www.linuxjournal.com/article.php?sid=6279 for more information
  17 * about this code.
  18 *
  19 *      This program is free software; you can redistribute it and/or
  20 *      modify it under the terms of the GNU General Public License as
  21 *      published by the Free Software Foundation, version 2 of the
  22 *      License.
  23 */
  24
  25#include <linux/module.h>
  26#include <linux/kernel.h>
  27#include <linux/init.h>
  28#include <linux/security.h>
  29#include <linux/usb.h>
  30
  31/* flag to keep track of how we were registered */
  32static int secondary;
  33
  34/* default is a generic type of usb to serial converter */
  35static int vendor_id = 0x0557;
  36static int product_id = 0x2008;
  37
  38module_param(vendor_id, uint, 0400);
  39MODULE_PARM_DESC(vendor_id, "USB Vendor ID of device to look for");
  40
  41module_param(product_id, uint, 0400);
  42MODULE_PARM_DESC(product_id, "USB Product ID of device to look for");
  43
  44/* should we print out debug messages */
  45static int debug = 0;
  46
  47module_param(debug, bool, 0600);
  48MODULE_PARM_DESC(debug, "Debug enabled or not");
  49
  50#if defined(CONFIG_SECURITY_ROOTPLUG_MODULE)
  51#define MY_NAME THIS_MODULE->name
  52#else
  53#define MY_NAME "root_plug"
  54#endif
  55
  56#define root_dbg(fmt, arg...)                                   \
  57        do {                                                    \
  58                if (debug)                                      \
  59                        printk(KERN_DEBUG "%s: %s: " fmt ,      \
  60                                MY_NAME , __FUNCTION__ ,        \
  61                                ## arg);                        \
  62        } while (0)
  63
  64static int rootplug_bprm_check_security (struct linux_binprm *bprm)
  65{
  66        struct usb_device *dev;
  67
  68        root_dbg("file %s, e_uid = %d, e_gid = %d\n",
  69                 bprm->filename, bprm->e_uid, bprm->e_gid);
  70
  71        if (bprm->e_gid == 0) {
  72                dev = usb_find_device(vendor_id, product_id);
  73                if (!dev) {
  74                        root_dbg("e_gid = 0, and device not found, "
  75                                 "task not allowed to run...\n");
  76                        return -EPERM;
  77                }
  78                usb_put_dev(dev);
  79        }
  80
  81        return 0;
  82}
  83
  84static struct security_operations rootplug_security_ops = {
  85        /* Use the capability functions for some of the hooks */
  86        .ptrace =                       cap_ptrace,
  87        .capget =                       cap_capget,
  88        .capset_check =                 cap_capset_check,
  89        .capset_set =                   cap_capset_set,
  90        .capable =                      cap_capable,
  91
  92        .bprm_apply_creds =             cap_bprm_apply_creds,
  93        .bprm_set_security =            cap_bprm_set_security,
  94
  95        .task_post_setuid =             cap_task_post_setuid,
  96        .task_reparent_to_init =        cap_task_reparent_to_init,
  97
  98        .bprm_check_security =          rootplug_bprm_check_security,
  99};
 100
 101static int __init rootplug_init (void)
 102{
 103        /* register ourselves with the security framework */
 104        if (register_security (&rootplug_security_ops)) {
 105                printk (KERN_INFO 
 106                        "Failure registering Root Plug module with the kernel\n");
 107                /* try registering with primary module */
 108                if (mod_reg_security (MY_NAME, &rootplug_security_ops)) {
 109                        printk (KERN_INFO "Failure registering Root Plug "
 110                                " module with primary security module.\n");
 111                        return -EINVAL;
 112                }
 113                secondary = 1;
 114        }
 115        printk (KERN_INFO "Root Plug module initialized, "
 116                "vendor_id = %4.4x, product id = %4.4x\n", vendor_id, product_id);
 117        return 0;
 118}
 119
 120static void __exit rootplug_exit (void)
 121{
 122        /* remove ourselves from the security framework */
 123        if (secondary) {
 124                if (mod_unreg_security (MY_NAME, &rootplug_security_ops))
 125                        printk (KERN_INFO "Failure unregistering Root Plug "
 126                                " module with primary module.\n");
 127        } else { 
 128                if (unregister_security (&rootplug_security_ops)) {
 129                        printk (KERN_INFO "Failure unregistering Root Plug "
 130                                "module with the kernel\n");
 131                }
 132        }
 133        printk (KERN_INFO "Root Plug module removed\n");
 134}
 135
 136security_initcall (rootplug_init);
 137module_exit (rootplug_exit);
 138
 139MODULE_DESCRIPTION("Root Plug sample LSM module, written for Linux Journal article");
 140MODULE_LICENSE("GPL");
 141
 142