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/kernel.h>
  26 #include <linux/init.h>
  27 #include <linux/security.h>
  28 #include <linux/usb.h>
  29 #include <linux/moduleparam.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_param(product_id, uint, 0400);
  40
  41 /* should we print out debug messages */
  42 static int debug = 0;
  43
  44 module_param(debug, bool, 0600);
  45
  46 #define MY_NAME "root_plug"
  47
  48 #define root_dbg(fmt, arg...)                                   \
  49         do {                                                    \
  50                 if (debug)                                      \
  51                         printk(KERN_DEBUG "%s: %s: " fmt ,      \
  52                                 MY_NAME , __func__ ,    \
  53                                 ## arg);                        \
  54         } while (0)
  55
  56 static int rootplug_bprm_check_security (struct linux_binprm *bprm)
  57 {
  58         struct usb_device *dev;
  59
  60         root_dbg("file %s, e_uid = %d, e_gid = %d\n",
  61                  bprm->filename, bprm->e_uid, bprm->e_gid);
  62
  63         if (bprm->e_gid == 0) {
  64                 dev = usb_find_device(vendor_id, product_id);
  65                 if (!dev) {
  66                         root_dbg("e_gid = 0, and device not found, "
  67                                  "task not allowed to run...\n");
  68                         return -EPERM;
  69                 }
  70                 usb_put_dev(dev);
  71         }
  72
  73         return 0;
  74 }
  75
  76 static struct security_operations rootplug_security_ops = {
  77         /* Use the capability functions for some of the hooks */
  78         .ptrace =                       cap_ptrace,
  79         .capget =                       cap_capget,
  80         .capset_check =                 cap_capset_check,
  81         .capset_set =                   cap_capset_set,
  82         .capable =                      cap_capable,
  83
  84         .bprm_apply_creds =             cap_bprm_apply_creds,
  85         .bprm_set_security =            cap_bprm_set_security,
  86
  87         .task_post_setuid =             cap_task_post_setuid,
  88         .task_reparent_to_init =        cap_task_reparent_to_init,
  89
  90         .bprm_check_security =          rootplug_bprm_check_security,
  91 };
  92
  93 static int __init rootplug_init (void)
  94 {
  95         /* register ourselves with the security framework */
  96         if (register_security (&rootplug_security_ops)) {
  97                 printk (KERN_INFO
  98                         "Failure registering Root Plug module with the kernel\n");
  99                 /* try registering with primary module */
 100                 if (mod_reg_security (MY_NAME, &rootplug_security_ops)) {
 101                         printk (KERN_INFO "Failure registering Root Plug "
 102                                 " module with primary security module.\n");
 103                         return -EINVAL;
 104                 }
 105                 secondary = 1;
 106         }
 107         printk (KERN_INFO "Root Plug module initialized, "
 108                 "vendor_id = %4.4x, product id = %4.4x\n", vendor_id, product_id);
 109         return 0;
 110 }
 111
 112 security_initcall (rootplug_init);