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      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 
     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 
     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 
     77 void ContextNode::ResetAccess() {
     78   if (!CheckAccess()) {
     79     Unmap();
     80     no_access_ = true;
     81   } else {
     82     no_access_ = false;
     83   }
     84 }
     85 
     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 
     96 void ContextNode::Unmap() {
     97   prop_area::unmap_prop_area(&pa_);
     98 }
     99