1/*
2 * Copyright (C) 2008 The Android Open Source Project
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *  * Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 *  * Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in
12 *    the documentation and/or other materials provided with the
13 *    distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
18 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
19 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
21 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
22 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
23 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
24 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
25 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26 * SUCH DAMAGE.
27 */
28
29#include "system_properties/context_node.h"
30
31#include <limits.h>
32#include <unistd.h>
33
34#include <async_safe/log.h>
35
36#include "system_properties/system_properties.h"
37
38// pthread_mutex_lock() calls into system_properties in the case of contention.
39// This creates a risk of dead lock if any system_properties functions
40// use pthread locks after system_property initialization.
41//
42// For this reason, the below three functions use a bionic Lock and static
43// allocation of memory for each filename.
44
45bool ContextNode::Open(bool access_rw, bool* fsetxattr_failed) {
46  lock_.lock();
47  if (pa_) {
48    lock_.unlock();
49    return true;
50  }
51
52  char filename[PROP_FILENAME_MAX];
53  int len = async_safe_format_buffer(filename, sizeof(filename), "%s/%s", filename_, context_);
54  if (len < 0 || len > PROP_FILENAME_MAX) {
55    lock_.unlock();
56    return false;
57  }
58
59  if (access_rw) {
60    pa_ = prop_area::map_prop_area_rw(filename, context_, fsetxattr_failed);
61  } else {
62    pa_ = prop_area::map_prop_area(filename);
63  }
64  lock_.unlock();
65  return pa_;
66}
67
68bool ContextNode::CheckAccessAndOpen() {
69  if (!pa_ && !no_access_) {
70    if (!CheckAccess() || !Open(false, nullptr)) {
71      no_access_ = true;
72    }
73  }
74  return pa_;
75}
76
77void ContextNode::ResetAccess() {
78  if (!CheckAccess()) {
79    Unmap();
80    no_access_ = true;
81  } else {
82    no_access_ = false;
83  }
84}
85
86bool ContextNode::CheckAccess() {
87  char filename[PROP_FILENAME_MAX];
88  int len = async_safe_format_buffer(filename, sizeof(filename), "%s/%s", filename_, context_);
89  if (len < 0 || len > PROP_FILENAME_MAX) {
90    return false;
91  }
92
93  return access(filename, R_OK) == 0;
94}
95
96void ContextNode::Unmap() {
97  prop_area::unmap_prop_area(&pa_);
98}
99