/* * 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/system_properties.h" #include <errno.h> #include <stdatomic.h> #include <stdlib.h> #include <string.h> #include <sys/stat.h> #include <sys/types.h> #include <unistd.h> #include <new> #include <async_safe/log.h> #include "private/ErrnoRestorer.h" #include "private/bionic_futex.h" #include "system_properties/context_node.h" #include "system_properties/prop_area.h" #include "system_properties/prop_info.h" #define SERIAL_DIRTY(serial) ((serial)&1) #define SERIAL_VALUE_LEN(serial) ((serial) >> 24) static bool is_dir(const char* pathname) { struct stat info; if (stat(pathname, &info) == -1) { return false; } return S_ISDIR(info.st_mode); } bool SystemProperties::Init(const char* filename) { // This is called from __libc_init_common, and should leave errno at 0 (http://b/37248982). ErrnoRestorer errno_restorer; if (initialized_) { /* resetprop remove */ // contexts_->ResetAccess(); return true; } if (strlen(filename) >= PROP_FILENAME_MAX) { return false; } strcpy(property_filename_, filename); if (is_dir(property_filename_)) { if (access("/dev/__properties__/property_info", R_OK) == 0) { contexts_ = new (contexts_data_) ContextsSerialized(); if (!contexts_->Initialize(false, property_filename_, nullptr)) { return false; } } else { contexts_ = new (contexts_data_) ContextsSplit(); if (!contexts_->Initialize(false, property_filename_, nullptr)) { return false; } } } else { contexts_ = new (contexts_data_) ContextsPreSplit(); if (!contexts_->Initialize(false, property_filename_, nullptr)) { return false; } } initialized_ = true; return true; } bool SystemProperties::AreaInit(const char* filename, bool* fsetxattr_failed) { if (strlen(filename) >= PROP_FILENAME_MAX) { return false; } strcpy(property_filename_, filename); contexts_ = new (contexts_data_) ContextsSerialized(); if (!contexts_->Initialize(true, property_filename_, fsetxattr_failed)) { return false; } initialized_ = true; return true; } uint32_t SystemProperties::AreaSerial() { if (!initialized_) { return -1; } prop_area* pa = contexts_->GetSerialPropArea(); if (!pa) { return -1; } // Make sure this read fulfilled before __system_property_serial return atomic_load_explicit(pa->serial(), memory_order_acquire); } const prop_info* SystemProperties::Find(const char* name) { if (!initialized_) { return nullptr; } prop_area* pa = contexts_->GetPropAreaForName(name); if (!pa) { async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Access denied finding property \"%s\"", name); return nullptr; } return pa->find(name); } static bool is_read_only(const char* name) { return strncmp(name, "ro.", 3) == 0; } int SystemProperties::Read(const prop_info* pi, char* name, char* value) { while (true) { uint32_t serial = Serial(pi); // acquire semantics size_t len = SERIAL_VALUE_LEN(serial); memcpy(value, pi->value, len + 1); // TODO: Fix the synchronization scheme here. // There is no fully supported way to implement this kind // of synchronization in C++11, since the memcpy races with // updates to pi, and the data being accessed is not atomic. // The following fence is unintuitive, but would be the // correct one if memcpy used memory_order_relaxed atomic accesses. // In practice it seems unlikely that the generated code would // would be any different, so this should be OK. atomic_thread_fence(memory_order_acquire); if (serial == load_const_atomic(&(pi->serial), memory_order_relaxed)) { if (name != nullptr) { size_t namelen = strlcpy(name, pi->name, PROP_NAME_MAX); if (namelen >= PROP_NAME_MAX) { async_safe_format_log(ANDROID_LOG_ERROR, "libc", "The property name length for \"%s\" is >= %d;" " please use __system_property_read_callback" " to read this property. (the name is truncated to \"%s\")", pi->name, PROP_NAME_MAX - 1, name); } } if (is_read_only(pi->name) && pi->is_long()) { async_safe_format_log( ANDROID_LOG_ERROR, "libc", "The property \"%s\" has a value with length %zu that is too large for" " __system_property_get()/__system_property_read(); use" " __system_property_read_callback() instead.", pi->name, strlen(pi->long_value())); } return len; } } } void SystemProperties::ReadCallback(const prop_info* pi, void (*callback)(void* cookie, const char* name, const char* value, uint32_t serial), void* cookie) { // Read only properties don't need to copy the value to a temporary buffer, since it can never // change. if (is_read_only(pi->name)) { uint32_t serial = Serial(pi); if (pi->is_long()) { callback(cookie, pi->name, pi->long_value(), serial); } else { callback(cookie, pi->name, pi->value, serial); } return; } while (true) { uint32_t serial = Serial(pi); // acquire semantics size_t len = SERIAL_VALUE_LEN(serial); char value_buf[len + 1]; memcpy(value_buf, pi->value, len); value_buf[len] = '\0'; // TODO: see todo in Read function atomic_thread_fence(memory_order_acquire); if (serial == load_const_atomic(&(pi->serial), memory_order_relaxed)) { callback(cookie, pi->name, value_buf, serial); return; } } } int SystemProperties::Get(const char* name, char* value) { const prop_info* pi = Find(name); if (pi != nullptr) { return Read(pi, nullptr, value); } else { value[0] = 0; return 0; } } int SystemProperties::Update(prop_info* pi, const char* value, unsigned int len) { if (len >= PROP_VALUE_MAX) { return -1; } if (!initialized_) { return -1; } prop_area* pa = contexts_->GetSerialPropArea(); if (!pa) { return -1; } uint32_t serial = atomic_load_explicit(&pi->serial, memory_order_relaxed); serial |= 1; atomic_store_explicit(&pi->serial, serial, memory_order_relaxed); // The memcpy call here also races. Again pretend it // used memory_order_relaxed atomics, and use the analogous // counterintuitive fence. atomic_thread_fence(memory_order_release); strlcpy(pi->value, value, len + 1); atomic_store_explicit(&pi->serial, (len << 24) | ((serial + 1) & 0xffffff), memory_order_release); __futex_wake(&pi->serial, INT32_MAX); atomic_store_explicit(pa->serial(), atomic_load_explicit(pa->serial(), memory_order_relaxed) + 1, memory_order_release); __futex_wake(pa->serial(), INT32_MAX); return 0; } int SystemProperties::Add(const char* name, unsigned int namelen, const char* value, unsigned int valuelen) { if (valuelen >= PROP_VALUE_MAX && !is_read_only(name)) { return -1; } if (namelen < 1) { return -1; } if (!initialized_) { return -1; } prop_area* serial_pa = contexts_->GetSerialPropArea(); if (serial_pa == nullptr) { return -1; } prop_area* pa = contexts_->GetPropAreaForName(name); if (!pa) { async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Access denied adding property \"%s\"", name); return -1; } bool ret = pa->add(name, namelen, value, valuelen); if (!ret) { return -1; } // There is only a single mutator, but we want to make sure that // updates are visible to a reader waiting for the update. atomic_store_explicit(serial_pa->serial(), atomic_load_explicit(serial_pa->serial(), memory_order_relaxed) + 1, memory_order_release); __futex_wake(serial_pa->serial(), INT32_MAX); return 0; } int SystemProperties::Delete(const char *name) { if (!initialized_) { return -1; } prop_area* serial_pa = contexts_->GetSerialPropArea(); if (serial_pa == nullptr) { return -1; } prop_area* pa = contexts_->GetPropAreaForName(name); if (!pa) { async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Access denied adding property \"%s\"", name); return -1; } bool ret = pa->del(name); if (!ret) { return -1; } // There is only a single mutator, but we want to make sure that // updates are visible to a reader waiting for the update. atomic_store_explicit(serial_pa->serial(), atomic_load_explicit(serial_pa->serial(), memory_order_relaxed) + 1, memory_order_release); __futex_wake(serial_pa->serial(), INT32_MAX); return 0; } // Wait for non-locked serial, and retrieve it with acquire semantics. uint32_t SystemProperties::Serial(const prop_info* pi) { uint32_t serial = load_const_atomic(&pi->serial, memory_order_acquire); while (SERIAL_DIRTY(serial)) { __futex_wait(const_cast<_Atomic(uint_least32_t)*>(&pi->serial), serial, nullptr); serial = load_const_atomic(&pi->serial, memory_order_acquire); } return serial; } uint32_t SystemProperties::WaitAny(uint32_t old_serial) { uint32_t new_serial; Wait(nullptr, old_serial, &new_serial, nullptr); return new_serial; } bool SystemProperties::Wait(const prop_info* pi, uint32_t old_serial, uint32_t* new_serial_ptr, const timespec* relative_timeout) { // Are we waiting on the global serial or a specific serial? atomic_uint_least32_t* serial_ptr; if (pi == nullptr) { if (!initialized_) { return -1; } prop_area* serial_pa = contexts_->GetSerialPropArea(); if (serial_pa == nullptr) { return -1; } serial_ptr = serial_pa->serial(); } else { serial_ptr = const_cast<atomic_uint_least32_t*>(&pi->serial); } uint32_t new_serial; do { int rc; if ((rc = __futex_wait(serial_ptr, old_serial, relative_timeout)) != 0 && rc == -ETIMEDOUT) { return false; } new_serial = load_const_atomic(serial_ptr, memory_order_acquire); } while (new_serial == old_serial); *new_serial_ptr = new_serial; return true; } const prop_info* SystemProperties::FindNth(unsigned n) { struct find_nth { const uint32_t sought; uint32_t current; const prop_info* result; explicit find_nth(uint32_t n) : sought(n), current(0), result(nullptr) { } static void fn(const prop_info* pi, void* ptr) { find_nth* self = reinterpret_cast<find_nth*>(ptr); if (self->current++ == self->sought) self->result = pi; } } state(n); Foreach(find_nth::fn, &state); return state.result; } int SystemProperties::Foreach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) { if (!initialized_) { return -1; } contexts_->ForEach(propfn, cookie); return 0; }