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gerrit.omnirom.org / android_bionic / 12ba7e51d9c4f6d8c1fa5627f638b291520a7025 / . / libc / bionic / system_properties.cpp
blob: 0f684316a864cfc2278c0040a147f756b777f75f [file] [log] [blame]
/*
* 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 <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <poll.h>
#include <stdatomic.h>
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <new>
#include <linux/xattr.h>
#include <netinet/in.h>
#include <sys/mman.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/un.h>
#include <sys/xattr.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_lock.h"
#include "private/bionic_macros.h"
#include "private/libc_logging.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);
};
class prop_area {
public:
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);
}
const prop_info *find(const char *name);
bool add(const char *name, unsigned int namelen,
const char *value, unsigned int valuelen);
bool foreach(void (*propfn)(const prop_info *pi, void *cookie), void *cookie);
atomic_uint_least32_t *serial() { return &serial_; }
uint32_t magic() const { return magic_; }
uint32_t version() const { return version_; }
private:
void *allocate_obj(const size_t size, uint_least32_t *const off);
prop_bt *new_prop_bt(const char *name, uint8_t namelen, uint_least32_t *const off);
prop_info *new_prop_info(const char *name, uint8_t namelen,
const char *value, uint8_t valuelen,
uint_least32_t *const off);
void *to_prop_obj(uint_least32_t off);
prop_bt *to_prop_bt(atomic_uint_least32_t *off_p);
prop_info *to_prop_info(atomic_uint_least32_t *off_p);
prop_bt *root_node();
prop_bt *find_prop_bt(prop_bt *const bt, const char *name,
uint8_t namelen, bool alloc_if_needed);
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);
bool foreach_property(prop_bt *const trie,
void (*propfn)(const prop_info *pi, void *cookie),
void *cookie);
uint32_t bytes_used_;
atomic_uint_least32_t serial_;
uint32_t magic_;
uint32_t version_;
uint32_t reserved_[28];
char data_[0];
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;
explicit find_nth_cookie(uint32_t n) : count(0), n(n), pi(NULL) {
}
};
static char property_filename[PROP_FILENAME_MAX] = PROP_FILENAME;
static bool compat_mode = false;
static size_t pa_data_size;
static size_t pa_size;
static bool initialized = false;
// 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 prop_area* map_prop_area_rw(const char* filename, const char* context,
bool* fsetxattr_failed) {
/* dev is a tmpfs that we can use to carve a shared workspace
* out of, so let's do that...
*/
const int fd = open(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 nullptr;
}
if (context) {
if (fsetxattr(fd, XATTR_NAME_SELINUX, context, strlen(context) + 1, 0) != 0) {
__libc_format_log(ANDROID_LOG_ERROR, "libc",
"fsetxattr failed to set context (%s) for \"%s\"", context, filename);
/*
* fsetxattr() will fail during system properties tests due to selinux policy.
* We do not want to create a custom policy for the tester, so we will continue in
* this function but set a flag that an error has occurred.
* Init, which is the only daemon that should ever call this function will abort
* when this error occurs.
* Otherwise, the tester will ignore it and continue, albeit without any selinux
* property separation.
*/
if (fsetxattr_failed) {
*fsetxattr_failed = true;
}
}
}
if (ftruncate(fd, PA_SIZE) < 0) {
close(fd);
return nullptr;
}
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 nullptr;
}
prop_area *pa = new(memory_area) prop_area(PROP_AREA_MAGIC, PROP_AREA_VERSION);
close(fd);
return pa;
}
static prop_area* map_fd_ro(const int fd) {
struct stat fd_stat;
if (fstat(fd, &fd_stat) < 0) {
return nullptr;
}
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 nullptr;
}
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 nullptr;
}
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 nullptr;
}
if (pa->version() == PROP_AREA_VERSION_COMPAT) {
compat_mode = true;
}
return pa;
}
static prop_area* map_prop_area(const char* filename, bool is_legacy) {
int fd = open(filename, O_CLOEXEC | O_NOFOLLOW | O_RDONLY);
bool close_fd = true;
if (fd == -1 && errno == ENOENT && is_legacy) {
/*
* 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.
* Only do this for the legacy prop file, secured prop files
* do not have a backup
*/
fd = get_fd_from_env();
close_fd = false;
}
if (fd < 0) {
return nullptr;
}
prop_area* map_result = map_fd_ro(fd);
if (close_fd) {
close(fd);
}
return map_result;
}
void *prop_area::allocate_obj(const size_t size, uint_least32_t *const off)
{
const size_t aligned = BIONIC_ALIGN(size, sizeof(uint_least32_t));
if (bytes_used_ + aligned > pa_data_size) {
return NULL;
}
*off = bytes_used_;
bytes_used_ += aligned;
return data_ + *off;
}
prop_bt *prop_area::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;
}
prop_info *prop_area::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;
}
void *prop_area::to_prop_obj(uint_least32_t off)
{
if (off > pa_data_size)
return NULL;
return (data_ + off);
}
inline prop_bt *prop_area::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));
}
inline prop_info *prop_area::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));
}
inline prop_bt *prop_area::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);
}
prop_bt *prop_area::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(&current->left, memory_order_relaxed);
if (left_offset != 0) {
current = to_prop_bt(&current->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(&current->left, new_offset, memory_order_release);
}
return new_bt;
}
} else {
uint_least32_t right_offset = atomic_load_explicit(&current->right, memory_order_relaxed);
if (right_offset != 0) {
current = to_prop_bt(&current->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(&current->right, new_offset, memory_order_release);
}
return new_bt;
}
}
}
}
const prop_info *prop_area::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(&current->children, memory_order_relaxed);
if (children_offset != 0) {
root = to_prop_bt(&current->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(&current->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(&current->prop, memory_order_relaxed);
if (prop_offset != 0) {
return to_prop_info(&current->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(&current->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++;
}
bool prop_area::foreach_property(prop_bt *const trie,
void (*propfn)(const prop_info *pi, void *cookie), void *cookie)
{
if (!trie)
return false;
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 false;
}
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 false;
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 false;
}
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 false;
}
return true;
}
const prop_info *prop_area::find(const char *name) {
return find_property(root_node(), name, strlen(name), nullptr, 0, false);
}
bool prop_area::add(const char *name, unsigned int namelen,
const char *value, unsigned int valuelen) {
return find_property(root_node(), name, namelen, value, valuelen, true);
}
bool prop_area::foreach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
return foreach_property(root_node(), propfn, cookie);
}
class context_node {
public:
context_node(context_node* next, const char* context, prop_area* pa)
: next(next), context_(strdup(context)), pa_(pa), no_access_(false) {
lock_.init(false);
}
~context_node() {
unmap();
free(context_);
}
bool open(bool access_rw, bool* fsetxattr_failed);
bool check_access_and_open();
void reset_access();
const char* context() const { return context_; }
prop_area* pa() { return pa_; }
context_node* next;
private:
bool check_access();
void unmap();
Lock lock_;
char* context_;
prop_area* pa_;
bool no_access_;
};
struct prefix_node {
prefix_node(struct prefix_node* next, const char* prefix, context_node* context)
: prefix(strdup(prefix)), prefix_len(strlen(prefix)), context(context), next(next) {
}
~prefix_node() {
free(prefix);
}
char* prefix;
const size_t prefix_len;
context_node* context;
struct prefix_node* next;
};
template <typename List, typename... Args>
static inline void list_add(List** list, Args... args) {
*list = new List(*list, args...);
}
static void list_add_after_len(prefix_node** list, const char* prefix, context_node* context) {
size_t prefix_len = strlen(prefix);
auto next_list = list;
while (*next_list) {
if ((*next_list)->prefix_len < prefix_len || (*next_list)->prefix[0] == '*') {
list_add(next_list, prefix, context);
return;
}
next_list = &(*next_list)->next;
}
list_add(next_list, prefix, context);
}
template <typename List, typename Func>
static void list_foreach(List* list, Func func) {
while (list) {
func(list);
list = list->next;
}
}
template <typename List, typename Func>
static List* list_find(List* list, Func func) {
while (list) {
if (func(list)) {
return list;
}
list = list->next;
}
return nullptr;
}
template <typename List>
static void list_free(List** list) {
while (*list) {
auto old_list = *list;
*list = old_list->next;
delete old_list;
}
}
static prefix_node* prefixes = nullptr;
static context_node* contexts = nullptr;
/*
* 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 context_node::open(bool access_rw, bool* fsetxattr_failed) {
lock_.lock();
if (pa_) {
lock_.unlock();
return true;
}
char filename[PROP_FILENAME_MAX];
int len = __libc_format_buffer(filename, sizeof(filename), "%s/%s",
property_filename, context_);
if (len < 0 || len > PROP_FILENAME_MAX) {
lock_.unlock();
return false;
}
if (access_rw) {
pa_ = map_prop_area_rw(filename, context_, fsetxattr_failed);
} else {
pa_ = map_prop_area(filename, false);
}
lock_.unlock();
return pa_;
}
bool context_node::check_access_and_open() {
if (!pa_ && !no_access_) {
if (!check_access() || !open(false, nullptr)) {
no_access_ = true;
}
}
return pa_;
}
void context_node::reset_access() {
if (!check_access()) {
unmap();
no_access_ = true;
} else {
no_access_ = false;
}
}
bool context_node::check_access() {
char filename[PROP_FILENAME_MAX];
int len = __libc_format_buffer(filename, sizeof(filename), "%s/%s",
property_filename, context_);
if (len < 0 || len > PROP_FILENAME_MAX) {
return false;
}
return access(filename, R_OK) == 0;
}
void context_node::unmap() {
if (!pa_) {
return;
}
munmap(pa_, pa_size);
if (pa_ == __system_property_area__) {
__system_property_area__ = nullptr;
}
pa_ = nullptr;
}
static bool map_system_property_area(bool access_rw, bool* fsetxattr_failed) {
char filename[PROP_FILENAME_MAX];
int len = __libc_format_buffer(filename, sizeof(filename),
"%s/properties_serial", property_filename);
if (len < 0 || len > PROP_FILENAME_MAX) {
__system_property_area__ = nullptr;
return false;
}
if (access_rw) {
__system_property_area__ =
map_prop_area_rw(filename, "u:object_r:properties_serial:s0", fsetxattr_failed);
} else {
__system_property_area__ = map_prop_area(filename, false);
}
return __system_property_area__;
}
static prop_area* get_prop_area_for_name(const char* name) {
auto entry = list_find(prefixes, [name](prefix_node* l) {
return l->prefix[0] == '*' || !strncmp(l->prefix, name, l->prefix_len);
});
if (!entry) {
return nullptr;
}
auto cnode = entry->context;
if (!cnode->pa()) {
/*
* We explicitly do not check no_access_ in this case because unlike the
* case of foreach(), we want to generate an selinux audit for each
* non-permitted property access in this function.
*/
cnode->open(false, nullptr);
}
return cnode->pa();
}
/*
* The below two functions are duplicated from label_support.c in libselinux.
* TODO: Find a location suitable for these functions such that both libc and
* libselinux can share a common source file.
*/
/*
* The read_spec_entries and read_spec_entry functions may be used to
* replace sscanf to read entries from spec files. The file and
* property services now use these.
*/
/* Read an entry from a spec file (e.g. file_contexts) */
static inline int read_spec_entry(char **entry, char **ptr, int *len)
{
*entry = NULL;
char *tmp_buf = NULL;
while (isspace(**ptr) && **ptr != '\0')
(*ptr)++;
tmp_buf = *ptr;
*len = 0;
while (!isspace(**ptr) && **ptr != '\0') {
(*ptr)++;
(*len)++;
}
if (*len) {
*entry = strndup(tmp_buf, *len);
if (!*entry)
return -1;
}
return 0;
}
/*
* line_buf - Buffer containing the spec entries .
* num_args - The number of spec parameter entries to process.
* ... - A 'char **spec_entry' for each parameter.
* returns - The number of items processed.
*
* This function calls read_spec_entry() to do the actual string processing.
*/
static int read_spec_entries(char *line_buf, int num_args, ...)
{
char **spec_entry, *buf_p;
int len, rc, items, entry_len = 0;
va_list ap;
len = strlen(line_buf);
if (line_buf[len - 1] == '\n')
line_buf[len - 1] = '\0';
else
/* Handle case if line not \n terminated by bumping
* the len for the check below (as the line is NUL
* terminated by getline(3)) */
len++;
buf_p = line_buf;
while (isspace(*buf_p))
buf_p++;
/* Skip comment lines and empty lines. */
if (*buf_p == '#' || *buf_p == '\0')
return 0;
/* Process the spec file entries */
va_start(ap, num_args);
items = 0;
while (items < num_args) {
spec_entry = va_arg(ap, char **);
if (len - 1 == buf_p - line_buf) {
va_end(ap);
return items;
}
rc = read_spec_entry(spec_entry, &buf_p, &entry_len);
if (rc < 0) {
va_end(ap);
return rc;
}
if (entry_len)
items++;
}
va_end(ap);
return items;
}
static bool initialize_properties() {
FILE* file = fopen("/property_contexts", "re");
if (!file) {
return false;
}
char* buffer = nullptr;
size_t line_len;
char* prop_prefix = nullptr;
char* context = nullptr;
while (getline(&buffer, &line_len, file) > 0) {
int items = read_spec_entries(buffer, 2, &prop_prefix, &context);
if (items <= 0) {
continue;
}
if (items == 1) {
free(prop_prefix);
continue;
}
/*
* init uses ctl.* properties as an IPC mechanism and does not write them
* to a property file, therefore we do not need to create property files
* to store them.
*/
if (!strncmp(prop_prefix, "ctl.", 4)) {
free(prop_prefix);
free(context);
continue;
}
auto old_context = list_find(
contexts, [context](context_node* l) { return !strcmp(l->context(), context); });
if (old_context) {
list_add_after_len(&prefixes, prop_prefix, old_context);
} else {
list_add(&contexts, context, nullptr);
list_add_after_len(&prefixes, prop_prefix, contexts);
}
free(prop_prefix);
free(context);
}
free(buffer);
fclose(file);
return true;
}
static bool is_dir(const char* pathname) {
struct stat info;
if (stat(pathname, &info) == -1) {
return false;
}
return S_ISDIR(info.st_mode);
}
static void free_and_unmap_contexts() {
list_free(&prefixes);
list_free(&contexts);
if (__system_property_area__) {
munmap(__system_property_area__, pa_size);
__system_property_area__ = nullptr;
}
}
int __system_properties_init()
{
if (initialized) {
list_foreach(contexts, [](context_node* l) { l->reset_access(); });
return 0;
}
if (is_dir(property_filename)) {
if (!initialize_properties()) {
return -1;
}
if (!map_system_property_area(false, nullptr)) {
free_and_unmap_contexts();
return -1;
}
} else {
__system_property_area__ = map_prop_area(property_filename, true);
if (!__system_property_area__) {
return -1;
}
list_add(&contexts, "legacy_system_prop_area", __system_property_area__);
list_add_after_len(&prefixes, "*", contexts);
}
initialized = true;
return 0;
}
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()
{
free_and_unmap_contexts();
mkdir(property_filename, S_IRWXU | S_IRGRP | S_IXGRP | S_IROTH | S_IXOTH);
if (!initialize_properties()) {
return -1;
}
bool open_failed = false;
bool fsetxattr_failed = false;
list_foreach(contexts, [&fsetxattr_failed, &open_failed](context_node* l) {
if (!l->open(true, &fsetxattr_failed)) {
open_failed = true;
}
});
if (open_failed || !map_system_property_area(true, &fsetxattr_failed)) {
free_and_unmap_contexts();
return -1;
}
initialized = true;
return fsetxattr_failed ? -2 : 0;
}
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 (!__system_property_area__) {
return nullptr;
}
if (__predict_false(compat_mode)) {
return __system_property_find_compat(name);
}
prop_area* pa = get_prop_area_for_name(name);
if (!pa) {
__libc_format_log(ANDROID_LOG_ERROR, "libc", "Access denied finding property \"%s\"", name);
return nullptr;
}
return pa->find(name);
}
// 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)
{
if (len >= PROP_VALUE_MAX)
return -1;
prop_area* pa = __system_property_area__;
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);
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)
{
if (namelen >= PROP_NAME_MAX)
return -1;
if (valuelen >= PROP_VALUE_MAX)
return -1;
if (namelen < 1)
return -1;
if (!__system_property_area__) {
return -1;
}
prop_area* pa = get_prop_area_for_name(name);
if (!pa) {
__libc_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(
__system_property_area__->serial(),
atomic_load_explicit(__system_property_area__->serial(), memory_order_relaxed) + 1,
memory_order_release);
__futex_wake(__system_property_area__->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;
if (!pa) {
return 0;
}
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 (!__system_property_area__) {
return -1;
}
if (__predict_false(compat_mode)) {
return __system_property_foreach_compat(propfn, cookie);
}
list_foreach(contexts, [propfn, cookie](context_node* l) {
if (l->check_access_and_open()) {
l->pa()->foreach(propfn, cookie);
}
});
return 0;
}