security/selinux/ss/status.c

   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  */
  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  */
  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  */
 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 }