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 /* default is a generic type of usb to serial converter */
  32 static int vendor_id = 0x0557;
  33 static int product_id = 0x2008;
  34
  35 module_param(vendor_id, uint, 0400);
  36 module_param(product_id, uint, 0400);
  37
  38 /* should we print out debug messages */
  39 static int debug = 0;
  40
  41 module_param(debug, bool, 0600);
  42
  43 #define MY_NAME "root_plug"
  44
  45 #define root_dbg(fmt, arg...)                                   \
  46         do {                                                    \
  47                 if (debug)                                      \
  48                         printk(KERN_DEBUG "%s: %s: " fmt ,      \
  49                                 MY_NAME , __func__ ,    \
  50                                 ## arg);                        \
  51         } while (0)
  52
  53 static int rootplug_bprm_check_security (struct linux_binprm *bprm)
  54 {
  55         struct usb_device *dev;
  56
  57         root_dbg("file %s, e_uid = %d, e_gid = %d\n",
  58                  bprm->filename, bprm->cred->euid, bprm->cred->egid);
  59
  60         if (bprm->cred->egid == 0) {
  61                 dev = usb_find_device(vendor_id, product_id);
  62                 if (!dev) {
  63                         root_dbg("e_gid = 0, and device not found, "
  64                                  "task not allowed to run...\n");
  65                         return -EPERM;
  66                 }
  67                 usb_put_dev(dev);
  68         }
  69
  70         return 0;
  71 }
  72
  73 static struct security_operations rootplug_security_ops = {
  74         /* Use the capability functions for some of the hooks */
  75         .ptrace_may_access =            cap_ptrace_may_access,
  76         .ptrace_traceme =               cap_ptrace_traceme,
  77         .capget =                       cap_capget,
  78         .capset =                       cap_capset,
  79         .capable =                      cap_capable,
  80
  81         .bprm_set_creds =               cap_bprm_set_creds,
  82
  83         .task_fix_setuid =              cap_task_fix_setuid,
  84         .task_prctl =                   cap_task_prctl,
  85
  86         .bprm_check_security =          rootplug_bprm_check_security,
  87 };
  88
  89 static int __init rootplug_init (void)
  90 {
  91         /* register ourselves with the security framework */
  92         if (register_security (&rootplug_security_ops)) {
  93                 printk (KERN_INFO
  94                         "Failure registering Root Plug module with the kernel\n");
  95                         return -EINVAL;
  96         }
  97         printk (KERN_INFO "Root Plug module initialized, "
  98                 "vendor_id = %4.4x, product id = %4.4x\n", vendor_id, product_id);
  99         return 0;
 100 }
 101
 102 security_initcall (rootplug_init);