Magisk/native/jni/external/systemproperties/context_node.cpp

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/*
* Copyright (C) 2008 The Android Open Source Project
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include "system_properties/context_node.h"
#include <limits.h>
#include <unistd.h>
#include <async_safe/log.h>
#include "system_properties/system_properties.h"
// pthread_mutex_lock() calls into system_properties in the case of contention.
// This creates a risk of dead lock if any system_properties functions
// use pthread locks after system_property initialization.
//
// For this reason, the below three functions use a bionic Lock and static
// allocation of memory for each filename.
bool ContextNode::Open(bool access_rw, bool* fsetxattr_failed) {
lock_.lock();
if (pa_) {
lock_.unlock();
return true;
}
char filename[PROP_FILENAME_MAX];
int len = async_safe_format_buffer(filename, sizeof(filename), "%s/%s", filename_, context_);
if (len < 0 || len >= PROP_FILENAME_MAX) {
lock_.unlock();
return false;
}
if (access_rw) {
pa_ = prop_area::map_prop_area_rw(filename, context_, fsetxattr_failed);
} else {
pa_ = prop_area::map_prop_area(filename);
}
lock_.unlock();
return pa_;
}
bool ContextNode::CheckAccessAndOpen() {
if (!pa_ && !no_access_) {
if (!CheckAccess() || !Open(false, nullptr)) {
no_access_ = true;
}
}
return pa_;
}
void ContextNode::ResetAccess() {
if (!CheckAccess()) {
Unmap();
no_access_ = true;
} else {
no_access_ = false;
}
}
bool ContextNode::CheckAccess() {
char filename[PROP_FILENAME_MAX];
int len = async_safe_format_buffer(filename, sizeof(filename), "%s/%s", filename_, context_);
if (len < 0 || len >= PROP_FILENAME_MAX) {
return false;
}
return access(filename, R_OK) == 0;
}
void ContextNode::Unmap() {
prop_area::unmap_prop_area(&pa_);
}