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/config.h>
  26 #include <linux/module.h>
  27 #include <linux/kernel.h>
  28 #include <linux/init.h>
  29 #include <linux/security.h>
  30 #include <linux/usb.h>
  31
  32 /* flag to keep track of how we were registered */
  33 static int secondary;
  34
  35 /* default is a generic type of usb to serial converter */
  36 static int vendor_id = 0x0557;
  37 static int product_id = 0x2008;
  38
  39 module_param(vendor_id, uint, 0400);
  40 MODULE_PARM_DESC(vendor_id, "USB Vendor ID of device to look for");
  41
  42 module_param(product_id, uint, 0400);
  43 MODULE_PARM_DESC(product_id, "USB Product ID of device to look for");
  44
  45 /* should we print out debug messages */
  46 static int debug = 0;
  47
  48 module_param(debug, bool, 0600);
  49 MODULE_PARM_DESC(debug, "Debug enabled or not");
  50
  51 #if defined(CONFIG_SECURITY_ROOTPLUG_MODULE)
  52 #define MY_NAME THIS_MODULE->name
  53 #else
  54 #define MY_NAME "root_plug"
  55 #endif
  56
  57 #define root_dbg(fmt, arg...)                                   \
  58         do {                                                    \
  59                 if (debug)                                      \
  60                         printk(KERN_DEBUG "%s: %s: " fmt ,      \
  61                                 MY_NAME , __FUNCTION__ ,        \
  62                                 ## arg);                        \
  63         } while (0)
  64
  65 static int rootplug_bprm_check_security (struct linux_binprm *bprm)
  66 {
  67         struct usb_device *dev;
  68
  69         root_dbg("file %s, e_uid = %d, e_gid = %d\n",
  70                  bprm->filename, bprm->e_uid, bprm->e_gid);
  71
  72         if (bprm->e_gid == 0) {
  73                 dev = usb_find_device(vendor_id, product_id);
  74                 if (!dev) {
  75                         root_dbg("e_gid = 0, and device not found, "
  76                                  "task not allowed to run...\n");
  77                         return -EPERM;
  78                 }
  79                 usb_put_dev(dev);
  80         }
  81
  82         return 0;
  83 }
  84
  85 static struct security_operations rootplug_security_ops = {
  86         /* Use the capability functions for some of the hooks */
  87         .ptrace =                       cap_ptrace,
  88         .capget =                       cap_capget,
  89         .capset_check =                 cap_capset_check,
  90         .capset_set =                   cap_capset_set,
  91         .capable =                      cap_capable,
  92
  93         .bprm_apply_creds =             cap_bprm_apply_creds,
  94         .bprm_set_security =            cap_bprm_set_security,
  95
  96         .task_post_setuid =             cap_task_post_setuid,
  97         .task_reparent_to_init =        cap_task_reparent_to_init,
  98
  99         .bprm_check_security =          rootplug_bprm_check_security,
 100 };
 101
 102 static int __init rootplug_init (void)
 103 {
 104         /* register ourselves with the security framework */
 105         if (register_security (&rootplug_security_ops)) {
 106                 printk (KERN_INFO
 107                         "Failure registering Root Plug module with the kernel\n");
 108                 /* try registering with primary module */
 109                 if (mod_reg_security (MY_NAME, &rootplug_security_ops)) {
 110                         printk (KERN_INFO "Failure registering Root Plug "
 111                                 " module with primary security module.\n");
 112                         return -EINVAL;
 113                 }
 114                 secondary = 1;
 115         }
 116         printk (KERN_INFO "Root Plug module initialized, "
 117                 "vendor_id = %4.4x, product id = %4.4x\n", vendor_id, product_id);
 118         return 0;
 119 }
 120
 121 static void __exit rootplug_exit (void)
 122 {
 123         /* remove ourselves from the security framework */
 124         if (secondary) {
 125                 if (mod_unreg_security (MY_NAME, &rootplug_security_ops))
 126                         printk (KERN_INFO "Failure unregistering Root Plug "
 127                                 " module with primary module.\n");
 128         } else {
 129                 if (unregister_security (&rootplug_security_ops)) {
 130                         printk (KERN_INFO "Failure unregistering Root Plug "
 131                                 "module with the kernel\n");
 132                 }
 133         }
 134         printk (KERN_INFO "Root Plug module removed\n");
 135 }
 136
 137 security_initcall (rootplug_init);
 138 module_exit (rootplug_exit);
 139
 140 MODULE_DESCRIPTION("Root Plug sample LSM module, written for Linux Journal article");
 141 MODULE_LICENSE("GPL");
 142