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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 */
33static int secondary;
34
35/* default is a generic type of usb to serial converter */
36static int vendor_id = 0x0557;
37static int product_id = 0x2008;
38
39module_param(vendor_id, uint, 0400);
40MODULE_PARM_DESC(vendor_id, "USB Vendor ID of device to look for");
41
42module_param(product_id, uint, 0400);
43MODULE_PARM_DESC(product_id, "USB Product ID of device to look for");
44
45/* should we print out debug messages */
46static int debug = 0;
47
48module_param(debug, bool, 0600);
49MODULE_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
65static 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
85static 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
102static 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
121static 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
137security_initcall (rootplug_init);
138module_exit (rootplug_exit);
139
140MODULE_DESCRIPTION("Root Plug sample LSM module, written for Linux Journal article");
141MODULE_LICENSE("GPL");
142