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