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
Open(bool access_rw,bool * fsetxattr_failed)45 bool 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
CheckAccessAndOpen()68 bool ContextNode::CheckAccessAndOpen() {
69 if (!pa_ && !no_access_) {
70 if (!CheckAccess() || !Open(false, nullptr)) {
71 no_access_ = true;
72 }
73 }
74 return pa_;
75 }
76
ResetAccess()77 void ContextNode::ResetAccess() {
78 if (!CheckAccess()) {
79 Unmap();
80 no_access_ = true;
81 } else {
82 no_access_ = false;
83 }
84 }
85
CheckAccess()86 bool 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
Unmap()96 void ContextNode::Unmap() {
97 prop_area::unmap_prop_area(&pa_);
98 }
99