/*
* 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 <new>
#include <stdatomic.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
#include <stddef.h>
#include <errno.h>
#include <poll.h>
#include <fcntl.h>
#include <stdbool.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/select.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <netinet/in.h>
#define _REALLY_INCLUDE_SYS__SYSTEM_PROPERTIES_H_
#include <sys/_system_properties.h>
#include <sys/system_properties.h>
#include "private/bionic_futex.h"
#include "private/bionic_macros.h"
static const char property_service_socket[] = "/dev/socket/" PROP_SERVICE_NAME;
/*
* Properties are stored in a hybrid trie/binary tree structure.
* Each property's name is delimited at '.' characters, and the tokens are put
* into a trie structure. Siblings at each level of the trie are stored in a
* binary tree. For instance, "ro.secure"="1" could be stored as follows:
*
* +-----+ children +----+ children +--------+
* | |-------------->| ro |-------------->| secure |
* +-----+ +----+ +--------+
* / \ / |
* left / \ right left / | prop +===========+
* v v v +-------->| ro.secure |
* +-----+ +-----+ +-----+ +-----------+
* | net | | sys | | com | | 1 |
* +-----+ +-----+ +-----+ +===========+
*/
// Represents a node in the trie.
struct prop_bt {
uint8_t namelen;
uint8_t reserved[3];
// The property trie is updated only by the init process (single threaded) which provides
// property service. And it can be read by multiple threads at the same time.
// As the property trie is not protected by locks, we use atomic_uint_least32_t types for the
// left, right, children "pointers" in the trie node. To make sure readers who see the
// change of "pointers" can also notice the change of prop_bt structure contents pointed by
// the "pointers", we always use release-consume ordering pair when accessing these "pointers".
// prop "points" to prop_info structure if there is a propery associated with the trie node.
// Its situation is similar to the left, right, children "pointers". So we use
// atomic_uint_least32_t and release-consume ordering to protect it as well.
// We should also avoid rereading these fields redundantly, since not
// all processor implementations ensure that multiple loads from the
// same field are carried out in the right order.
atomic_uint_least32_t prop;
atomic_uint_least32_t left;
atomic_uint_least32_t right;
atomic_uint_least32_t children;
char name[0];
prop_bt(const char *name, const uint8_t name_length) {
this->namelen = name_length;
memcpy(this->name, name, name_length);
this->name[name_length] = '\0';
}
private:
DISALLOW_COPY_AND_ASSIGN(prop_bt);
};
struct prop_area {
uint32_t bytes_used;
atomic_uint_least32_t serial;
uint32_t magic;
uint32_t version;
uint32_t reserved[28];
char data[0];
prop_area(const uint32_t magic, const uint32_t version) :
magic(magic), version(version) {
atomic_init(&serial, 0);
memset(reserved, 0, sizeof(reserved));
// Allocate enough space for the root node.
bytes_used = sizeof(prop_bt);
}
private:
DISALLOW_COPY_AND_ASSIGN(prop_area);
};
struct prop_info {
atomic_uint_least32_t serial;
char value[PROP_VALUE_MAX];
char name[0];
prop_info(const char *name, const uint8_t namelen, const char *value,
const uint8_t valuelen) {
memcpy(this->name, name, namelen);
this->name[namelen] = '\0';
atomic_init(&this->serial, valuelen << 24);
memcpy(this->value, value, valuelen);
this->value[valuelen] = '\0';
}
private:
DISALLOW_COPY_AND_ASSIGN(prop_info);
};
struct find_nth_cookie {
uint32_t count;
const uint32_t n;
const prop_info *pi;
find_nth_cookie(uint32_t n) : count(0), n(n), pi(NULL) {
}
};
static char property_filename[PATH_MAX] = PROP_FILENAME;
static bool compat_mode = false;
static size_t pa_data_size;
static size_t pa_size;
// NOTE: This isn't static because system_properties_compat.c
// requires it.
prop_area *__system_property_area__ = NULL;
static int get_fd_from_env(void)
{
// This environment variable consistes of two decimal integer
// values separated by a ",". The first value is a file descriptor
// and the second is the size of the system properties area. The
// size is currently unused.
char *env = getenv("ANDROID_PROPERTY_WORKSPACE");
if (!env) {
return -1;
}
return atoi(env);
}
static int map_prop_area_rw()
{
/* dev is a tmpfs that we can use to carve a shared workspace
* out of, so let's do that...
*/
const int fd = open(property_filename,
O_RDWR | O_CREAT | O_NOFOLLOW | O_CLOEXEC | O_EXCL, 0444);
if (fd < 0) {
if (errno == EACCES) {
/* for consistency with the case where the process has already
* mapped the page in and segfaults when trying to write to it
*/
abort();
}
return -1;
}
if (ftruncate(fd, PA_SIZE) < 0) {
close(fd);
return -1;
}
pa_size = PA_SIZE;
pa_data_size = pa_size - sizeof(prop_area);
compat_mode = false;
void *const memory_area = mmap(NULL, pa_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (memory_area == MAP_FAILED) {
close(fd);
return -1;
}
prop_area *pa = new(memory_area) prop_area(PROP_AREA_MAGIC, PROP_AREA_VERSION);
/* plug into the lib property services */
__system_property_area__ = pa;
close(fd);
return 0;
}
static int map_fd_ro(const int fd) {
struct stat fd_stat;
if (fstat(fd, &fd_stat) < 0) {
return -1;
}
if ((fd_stat.st_uid != 0)
|| (fd_stat.st_gid != 0)
|| ((fd_stat.st_mode & (S_IWGRP | S_IWOTH)) != 0)
|| (fd_stat.st_size < static_cast<off_t>(sizeof(prop_area))) ) {
return -1;
}
pa_size = fd_stat.st_size;
pa_data_size = pa_size - sizeof(prop_area);
void* const map_result = mmap(NULL, pa_size, PROT_READ, MAP_SHARED, fd, 0);
if (map_result == MAP_FAILED) {
return -1;
}
prop_area* pa = reinterpret_cast<prop_area*>(map_result);
if ((pa->magic != PROP_AREA_MAGIC) || (pa->version != PROP_AREA_VERSION &&
pa->version != PROP_AREA_VERSION_COMPAT)) {
munmap(pa, pa_size);
return -1;
}
if (pa->version == PROP_AREA_VERSION_COMPAT) {
compat_mode = true;
}
__system_property_area__ = pa;
return 0;
}
static int map_prop_area()
{
int fd = open(property_filename, O_CLOEXEC | O_NOFOLLOW | O_RDONLY);
bool close_fd = true;
if (fd == -1 && errno == ENOENT) {
/*
* For backwards compatibility, if the file doesn't
* exist, we use the environment to get the file descriptor.
* For security reasons, we only use this backup if the kernel
* returns ENOENT. We don't want to use the backup if the kernel
* returns other errors such as ENOMEM or ENFILE, since it
* might be possible for an external program to trigger this
* condition.
*/
fd = get_fd_from_env();
close_fd = false;
}
if (fd < 0) {
return -1;
}
const int map_result = map_fd_ro(fd);
if (close_fd) {
close(fd);
}
return map_result;
}
static void *allocate_obj(const size_t size, uint_least32_t *const off)
{
prop_area *pa = __system_property_area__;
const size_t aligned = BIONIC_ALIGN(size, sizeof(uint_least32_t));
if (pa->bytes_used + aligned > pa_data_size) {
return NULL;
}
*off = pa->bytes_used;
pa->bytes_used += aligned;
return pa->data + *off;
}
static prop_bt *new_prop_bt(const char *name, uint8_t namelen, uint_least32_t *const off)
{
uint_least32_t new_offset;
void *const p = allocate_obj(sizeof(prop_bt) + namelen + 1, &new_offset);
if (p != NULL) {
prop_bt* bt = new(p) prop_bt(name, namelen);
*off = new_offset;
return bt;
}
return NULL;
}
static prop_info *new_prop_info(const char *name, uint8_t namelen,
const char *value, uint8_t valuelen, uint_least32_t *const off)
{
uint_least32_t new_offset;
void* const p = allocate_obj(sizeof(prop_info) + namelen + 1, &new_offset);
if (p != NULL) {
prop_info* info = new(p) prop_info(name, namelen, value, valuelen);
*off = new_offset;
return info;
}
return NULL;
}
static void *to_prop_obj(uint_least32_t off)
{
if (off > pa_data_size)
return NULL;
if (!__system_property_area__)
return NULL;
return (__system_property_area__->data + off);
}
static inline prop_bt *to_prop_bt(atomic_uint_least32_t* off_p) {
uint_least32_t off = atomic_load_explicit(off_p, memory_order_consume);
return reinterpret_cast<prop_bt*>(to_prop_obj(off));
}
static inline prop_info *to_prop_info(atomic_uint_least32_t* off_p) {
uint_least32_t off = atomic_load_explicit(off_p, memory_order_consume);
return reinterpret_cast<prop_info*>(to_prop_obj(off));
}
static inline prop_bt *root_node()
{
return reinterpret_cast<prop_bt*>(to_prop_obj(0));
}
static int cmp_prop_name(const char *one, uint8_t one_len, const char *two,
uint8_t two_len)
{
if (one_len < two_len)
return -1;
else if (one_len > two_len)
return 1;
else
return strncmp(one, two, one_len);
}
static prop_bt *find_prop_bt(prop_bt *const bt, const char *name,
uint8_t namelen, bool alloc_if_needed)
{
prop_bt* current = bt;
while (true) {
if (!current) {
return NULL;
}
const int ret = cmp_prop_name(name, namelen, current->name, current->namelen);
if (ret == 0) {
return current;
}
if (ret < 0) {
uint_least32_t left_offset = atomic_load_explicit(¤t->left, memory_order_relaxed);
if (left_offset != 0) {
current = to_prop_bt(¤t->left);
} else {
if (!alloc_if_needed) {
return NULL;
}
uint_least32_t new_offset;
prop_bt* new_bt = new_prop_bt(name, namelen, &new_offset);
if (new_bt) {
atomic_store_explicit(¤t->left, new_offset, memory_order_release);
}
return new_bt;
}
} else {
uint_least32_t right_offset = atomic_load_explicit(¤t->right, memory_order_relaxed);
if (right_offset != 0) {
current = to_prop_bt(¤t->right);
} else {
if (!alloc_if_needed) {
return NULL;
}
uint_least32_t new_offset;
prop_bt* new_bt = new_prop_bt(name, namelen, &new_offset);
if (new_bt) {
atomic_store_explicit(¤t->right, new_offset, memory_order_release);
}
return new_bt;
}
}
}
}
static const prop_info *find_property(prop_bt *const trie, const char *name,
uint8_t namelen, const char *value, uint8_t valuelen,
bool alloc_if_needed)
{
if (!trie) return NULL;
const char *remaining_name = name;
prop_bt* current = trie;
while (true) {
const char *sep = strchr(remaining_name, '.');
const bool want_subtree = (sep != NULL);
const uint8_t substr_size = (want_subtree) ?
sep - remaining_name : strlen(remaining_name);
if (!substr_size) {
return NULL;
}
prop_bt* root = NULL;
uint_least32_t children_offset = atomic_load_explicit(¤t->children, memory_order_relaxed);
if (children_offset != 0) {
root = to_prop_bt(¤t->children);
} else if (alloc_if_needed) {
uint_least32_t new_offset;
root = new_prop_bt(remaining_name, substr_size, &new_offset);
if (root) {
atomic_store_explicit(¤t->children, new_offset, memory_order_release);
}
}
if (!root) {
return NULL;
}
current = find_prop_bt(root, remaining_name, substr_size, alloc_if_needed);
if (!current) {
return NULL;
}
if (!want_subtree)
break;
remaining_name = sep + 1;
}
uint_least32_t prop_offset = atomic_load_explicit(¤t->prop, memory_order_relaxed);
if (prop_offset != 0) {
return to_prop_info(¤t->prop);
} else if (alloc_if_needed) {
uint_least32_t new_offset;
prop_info* new_info = new_prop_info(name, namelen, value, valuelen, &new_offset);
if (new_info) {
atomic_store_explicit(¤t->prop, new_offset, memory_order_release);
}
return new_info;
} else {
return NULL;
}
}
static int send_prop_msg(const prop_msg *msg)
{
const int fd = socket(AF_LOCAL, SOCK_STREAM | SOCK_CLOEXEC, 0);
if (fd == -1) {
return -1;
}
const size_t namelen = strlen(property_service_socket);
sockaddr_un addr;
memset(&addr, 0, sizeof(addr));
strlcpy(addr.sun_path, property_service_socket, sizeof(addr.sun_path));
addr.sun_family = AF_LOCAL;
socklen_t alen = namelen + offsetof(sockaddr_un, sun_path) + 1;
if (TEMP_FAILURE_RETRY(connect(fd, reinterpret_cast<sockaddr*>(&addr), alen)) < 0) {
close(fd);
return -1;
}
const int num_bytes = TEMP_FAILURE_RETRY(send(fd, msg, sizeof(prop_msg), 0));
int result = -1;
if (num_bytes == sizeof(prop_msg)) {
// We successfully wrote to the property server but now we
// wait for the property server to finish its work. It
// acknowledges its completion by closing the socket so we
// poll here (on nothing), waiting for the socket to close.
// If you 'adb shell setprop foo bar' you'll see the POLLHUP
// once the socket closes. Out of paranoia we cap our poll
// at 250 ms.
pollfd pollfds[1];
pollfds[0].fd = fd;
pollfds[0].events = 0;
const int poll_result = TEMP_FAILURE_RETRY(poll(pollfds, 1, 250 /* ms */));
if (poll_result == 1 && (pollfds[0].revents & POLLHUP) != 0) {
result = 0;
} else {
// Ignore the timeout and treat it like a success anyway.
// The init process is single-threaded and its property
// service is sometimes slow to respond (perhaps it's off
// starting a child process or something) and thus this
// times out and the caller thinks it failed, even though
// it's still getting around to it. So we fake it here,
// mostly for ctl.* properties, but we do try and wait 250
// ms so callers who do read-after-write can reliably see
// what they've written. Most of the time.
// TODO: fix the system properties design.
result = 0;
}
}
close(fd);
return result;
}
static void find_nth_fn(const prop_info *pi, void *ptr)
{
find_nth_cookie *cookie = reinterpret_cast<find_nth_cookie*>(ptr);
if (cookie->n == cookie->count)
cookie->pi = pi;
cookie->count++;
}
static int foreach_property(prop_bt *const trie,
void (*propfn)(const prop_info *pi, void *cookie), void *cookie)
{
if (!trie)
return -1;
uint_least32_t left_offset = atomic_load_explicit(&trie->left, memory_order_relaxed);
if (left_offset != 0) {
const int err = foreach_property(to_prop_bt(&trie->left), propfn, cookie);
if (err < 0)
return -1;
}
uint_least32_t prop_offset = atomic_load_explicit(&trie->prop, memory_order_relaxed);
if (prop_offset != 0) {
prop_info *info = to_prop_info(&trie->prop);
if (!info)
return -1;
propfn(info, cookie);
}
uint_least32_t children_offset = atomic_load_explicit(&trie->children, memory_order_relaxed);
if (children_offset != 0) {
const int err = foreach_property(to_prop_bt(&trie->children), propfn, cookie);
if (err < 0)
return -1;
}
uint_least32_t right_offset = atomic_load_explicit(&trie->right, memory_order_relaxed);
if (right_offset != 0) {
const int err = foreach_property(to_prop_bt(&trie->right), propfn, cookie);
if (err < 0)
return -1;
}
return 0;
}
int __system_properties_init()
{
return map_prop_area();
}
int __system_property_set_filename(const char *filename)
{
size_t len = strlen(filename);
if (len >= sizeof(property_filename))
return -1;
strcpy(property_filename, filename);
return 0;
}
int __system_property_area_init()
{
return map_prop_area_rw();
}
unsigned int __system_property_area_serial()
{
prop_area *pa = __system_property_area__;
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 *__system_property_find(const char *name)
{
if (__predict_false(compat_mode)) {
return __system_property_find_compat(name);
}
return find_property(root_node(), name, strlen(name), NULL, 0, false);
}
// The C11 standard doesn't allow atomic loads from const fields,
// though C++11 does. Fudge it until standards get straightened out.
static inline uint_least32_t load_const_atomic(const atomic_uint_least32_t* s,
memory_order mo) {
atomic_uint_least32_t* non_const_s = const_cast<atomic_uint_least32_t*>(s);
return atomic_load_explicit(non_const_s, mo);
}
int __system_property_read(const prop_info *pi, char *name, char *value)
{
if (__predict_false(compat_mode)) {
return __system_property_read_compat(pi, name, value);
}
while (true) {
uint32_t serial = __system_property_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 != 0) {
strcpy(name, pi->name);
}
return len;
}
}
}
int __system_property_get(const char *name, char *value)
{
const prop_info *pi = __system_property_find(name);
if (pi != 0) {
return __system_property_read(pi, 0, value);
} else {
value[0] = 0;
return 0;
}
}
int __system_property_set(const char *key, const char *value)
{
if (key == 0) return -1;
if (value == 0) value = "";
if (strlen(key) >= PROP_NAME_MAX) return -1;
if (strlen(value) >= PROP_VALUE_MAX) return -1;
prop_msg msg;
memset(&msg, 0, sizeof msg);
msg.cmd = PROP_MSG_SETPROP;
strlcpy(msg.name, key, sizeof msg.name);
strlcpy(msg.value, value, sizeof msg.value);
const int err = send_prop_msg(&msg);
if (err < 0) {
return err;
}
return 0;
}
int __system_property_update(prop_info *pi, const char *value, unsigned int len)
{
prop_area *pa = __system_property_area__;
if (len >= PROP_VALUE_MAX)
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);
memcpy(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 __system_property_add(const char *name, unsigned int namelen,
const char *value, unsigned int valuelen)
{
prop_area *pa = __system_property_area__;
const prop_info *pi;
if (namelen >= PROP_NAME_MAX)
return -1;
if (valuelen >= PROP_VALUE_MAX)
return -1;
if (namelen < 1)
return -1;
pi = find_property(root_node(), name, namelen, value, valuelen, true);
if (!pi)
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(
&pa->serial,
atomic_load_explicit(&pa->serial, memory_order_relaxed) + 1,
memory_order_release);
__futex_wake(&pa->serial, INT32_MAX);
return 0;
}
// Wait for non-locked serial, and retrieve it with acquire semantics.
unsigned int __system_property_serial(const prop_info *pi)
{
uint32_t serial = load_const_atomic(&pi->serial, memory_order_acquire);
while (SERIAL_DIRTY(serial)) {
__futex_wait(const_cast<volatile void *>(
reinterpret_cast<const void *>(&pi->serial)),
serial, NULL);
serial = load_const_atomic(&pi->serial, memory_order_acquire);
}
return serial;
}
unsigned int __system_property_wait_any(unsigned int serial)
{
prop_area *pa = __system_property_area__;
uint32_t my_serial;
do {
__futex_wait(&pa->serial, serial, NULL);
my_serial = atomic_load_explicit(&pa->serial, memory_order_acquire);
} while (my_serial == serial);
return my_serial;
}
const prop_info *__system_property_find_nth(unsigned n)
{
find_nth_cookie cookie(n);
const int err = __system_property_foreach(find_nth_fn, &cookie);
if (err < 0) {
return NULL;
}
return cookie.pi;
}
int __system_property_foreach(void (*propfn)(const prop_info *pi, void *cookie),
void *cookie)
{
if (__predict_false(compat_mode)) {
return __system_property_foreach_compat(propfn, cookie);
}
return foreach_property(root_node(), propfn, cookie);
}