security/root_plug.c

   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 */
  32 static int secondary;
  33
  34 /* default is a generic type of usb to serial converter */
  35 static int vendor_id = 0x0557;
  36 static int product_id = 0x2008;
  37
  38 module_param(vendor_id, uint, 0400);
  39 MODULE_PARM_DESC(vendor_id, "USB Vendor ID of device to look for");
  40
  41 module_param(product_id, uint, 0400);
  42 MODULE_PARM_DESC(product_id, "USB Product ID of device to look for");
  43
  44 /* should we print out debug messages */
  45 static int debug = 0;
  46
  47 module_param(debug, bool, 0600);
  48 MODULE_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
  64 static 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
  84 static 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
 101 static 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
 120 static 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
 136 security_initcall (rootplug_init);
 137 module_exit (rootplug_exit);
 138
 139 MODULE_DESCRIPTION("Root Plug sample LSM module, written for Linux Journal article");
 140 MODULE_LICENSE("GPL");
 141