1 /*
2 * mmap based event notifications for SELinux
3 *
4 * Author: KaiGai Kohei <kaigai@ak.jp.nec.com>
5 *
6 * Copyright (C) 2010 NEC corporation
7 *
8 * This program is free software; you can redistribute it and/or modify
9 * it under the terms of the GNU General Public License version 2,
10 * as published by the Free Software Foundation.
11 */
12 #include <linux/kernel.h>
13 #include <linux/gfp.h>
14 #include <linux/mm.h>
15 #include <linux/mutex.h>
16 #include "avc.h"
17 #include "services.h"
18
19 /*
20 * The selinux_status_page shall be exposed to userspace applications
21 * using mmap interface on /selinux/status.
22 * It enables to notify applications a few events that will cause reset
23 * of userspace access vector without context switching.
24 *
25 * The selinux_kernel_status structure on the head of status page is
26 * protected from concurrent accesses using seqlock logic, so userspace
27 * application should reference the status page according to the seqlock
28 * logic.
29 *
30 * Typically, application checks status->sequence at the head of access
31 * control routine. If it is odd-number, kernel is updating the status,
32 * so please wait for a moment. If it is changed from the last sequence
33 * number, it means something happen, so application will reset userspace
34 * avc, if needed.
35 * In most cases, application shall confirm the kernel status is not
36 * changed without any system call invocations.
37 */
38 static struct page *selinux_status_page;
39 static DEFINE_MUTEX(selinux_status_lock);
40
41 /*
42 * selinux_kernel_status_page
43 *
44 * It returns a reference to selinux_status_page. If the status page is
45 * not allocated yet, it also tries to allocate it at the first time.
46 */
selinux_kernel_status_page(void)47 struct page *selinux_kernel_status_page(void)
48 {
49 struct selinux_kernel_status *status;
50 struct page *result = NULL;
51
52 mutex_lock(&selinux_status_lock);
53 if (!selinux_status_page) {
54 selinux_status_page = alloc_page(GFP_KERNEL|__GFP_ZERO);
55
56 if (selinux_status_page) {
57 status = page_address(selinux_status_page);
58
59 status->version = SELINUX_KERNEL_STATUS_VERSION;
60 status->sequence = 0;
61 status->enforcing = selinux_enforcing;
62 /*
63 * NOTE: the next policyload event shall set
64 * a positive value on the status->policyload,
65 * although it may not be 1, but never zero.
66 * So, application can know it was updated.
67 */
68 status->policyload = 0;
69 status->deny_unknown = !security_get_allow_unknown();
70 }
71 }
72 result = selinux_status_page;
73 mutex_unlock(&selinux_status_lock);
74
75 return result;
76 }
77
78 /*
79 * selinux_status_update_setenforce
80 *
81 * It updates status of the current enforcing/permissive mode.
82 */
selinux_status_update_setenforce(int enforcing)83 void selinux_status_update_setenforce(int enforcing)
84 {
85 struct selinux_kernel_status *status;
86
87 mutex_lock(&selinux_status_lock);
88 if (selinux_status_page) {
89 status = page_address(selinux_status_page);
90
91 status->sequence++;
92 smp_wmb();
93
94 status->enforcing = enforcing;
95
96 smp_wmb();
97 status->sequence++;
98 }
99 mutex_unlock(&selinux_status_lock);
100 }
101
102 /*
103 * selinux_status_update_policyload
104 *
105 * It updates status of the times of policy reloaded, and current
106 * setting of deny_unknown.
107 */
selinux_status_update_policyload(int seqno)108 void selinux_status_update_policyload(int seqno)
109 {
110 struct selinux_kernel_status *status;
111
112 mutex_lock(&selinux_status_lock);
113 if (selinux_status_page) {
114 status = page_address(selinux_status_page);
115
116 status->sequence++;
117 smp_wmb();
118
119 status->policyload = seqno;
120 status->deny_unknown = !security_get_allow_unknown();
121
122 smp_wmb();
123 status->sequence++;
124 }
125 mutex_unlock(&selinux_status_lock);
126 }
127