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/*
* Copyright (C) 2007 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "devices.h"
#include <errno.h>
#include <fnmatch.h>
#include <sys/sysmacros.h>
#include <unistd.h>
#include <chrono>
#include <map>
#include <memory>
#include <string>
#include <thread>
#include <android-base/chrono_utils.h>
#include <android-base/file.h>
#include <android-base/logging.h>
#include <android-base/stringprintf.h>
#include <android-base/strings.h>
#include <private/android_filesystem_config.h>
#include <selinux/android.h>
#include <selinux/selinux.h>
#include "selabel.h"
#include "util.h"
using namespace std::chrono_literals;
using android::base::Basename;
using android::base::Dirname;
using android::base::ReadFileToString;
using android::base::Readlink;
using android::base::Realpath;
using android::base::StartsWith;
using android::base::StringPrintf;
using android::base::Trim;
namespace android {
namespace init {
/* Given a path that may start with a PCI device, populate the supplied buffer
* with the PCI domain/bus number and the peripheral ID and return 0.
* If it doesn't start with a PCI device, or there is some error, return -1 */
static bool FindPciDevicePrefix(const std::string& path, std::string* result) {
result->clear();
if (!StartsWith(path, "/devices/pci")) return false;
/* Beginning of the prefix is the initial "pci" after "/devices/" */
std::string::size_type start = 9;
/* End of the prefix is two path '/' later, capturing the domain/bus number
* and the peripheral ID. Example: pci0000:00/0000:00:1f.2 */
auto end = path.find('/', start);
if (end == std::string::npos) return false;
end = path.find('/', end + 1);
if (end == std::string::npos) return false;
auto length = end - start;
if (length <= 4) {
// The minimum string that will get to this check is 'pci/', which is malformed,
// so return false
return false;
}
*result = path.substr(start, length);
return true;
}
/* Given a path that may start with a virtual block device, populate
* the supplied buffer with the virtual block device ID and return 0.
* If it doesn't start with a virtual block device, or there is some
* error, return -1 */
static bool FindVbdDevicePrefix(const std::string& path, std::string* result) {
result->clear();
if (!StartsWith(path, "/devices/vbd-")) return false;
/* Beginning of the prefix is the initial "vbd-" after "/devices/" */
std::string::size_type start = 13;
/* End of the prefix is one path '/' later, capturing the
virtual block device ID. Example: 768 */
auto end = path.find('/', start);
if (end == std::string::npos) return false;
auto length = end - start;
if (length == 0) return false;
*result = path.substr(start, length);
return true;
}
// Given a path that may start with a virtual dm block device, populate
// the supplied buffer with the dm module's instantiated name.
// If it doesn't start with a virtual block device, or there is some
// error, return false.
static bool FindDmDevicePartition(const std::string& path, std::string* result) {
result->clear();
if (!StartsWith(path, "/devices/virtual/block/dm-")) return false;
if (getpid() == 1) return false; // first_stage_init has no sepolicy needs
static std::map<std::string, std::string> cache;
// wait_for_file will not work, the content is also delayed ...
for (android::base::Timer t; t.duration() < 200ms; std::this_thread::sleep_for(10ms)) {
if (ReadFileToString("/sys" + path + "/dm/name", result) && !result->empty()) {
// Got it, set cache with result, when node arrives
cache[path] = *result = Trim(*result);
return true;
}
}
auto it = cache.find(path);
if ((it == cache.end()) || (it->second.empty())) return false;
// Return cached results, when node goes away
*result = it->second;
return true;
}
Permissions::Permissions(const std::string& name, mode_t perm, uid_t uid, gid_t gid)
: name_(name), perm_(perm), uid_(uid), gid_(gid), prefix_(false), wildcard_(false) {
// Set 'prefix_' or 'wildcard_' based on the below cases:
//
// 1) No '*' in 'name' -> Neither are set and Match() checks a given path for strict
// equality with 'name'
//
// 2) '*' only appears as the last character in 'name' -> 'prefix'_ is set to true and
// Match() checks if 'name' is a prefix of a given path.
//
// 3) '*' appears elsewhere -> 'wildcard_' is set to true and Match() uses fnmatch()
// with FNM_PATHNAME to compare 'name' to a given path.
auto wildcard_position = name_.find('*');
if (wildcard_position != std::string::npos) {
if (wildcard_position == name_.length() - 1) {
prefix_ = true;
name_.pop_back();
} else {
wildcard_ = true;
}
}
}
bool Permissions::Match(const std::string& path) const {
if (prefix_) return StartsWith(path, name_);
if (wildcard_) return fnmatch(name_.c_str(), path.c_str(), FNM_PATHNAME) == 0;
return path == name_;
}
bool SysfsPermissions::MatchWithSubsystem(const std::string& path,
const std::string& subsystem) const {
std::string path_basename = Basename(path);
if (name().find(subsystem) != std::string::npos) {
if (Match("/sys/class/" + subsystem + "/" + path_basename)) return true;
if (Match("/sys/bus/" + subsystem + "/devices/" + path_basename)) return true;
}
return Match(path);
}
void SysfsPermissions::SetPermissions(const std::string& path) const {
std::string attribute_file = path + "/" + attribute_;
LOG(VERBOSE) << "fixup " << attribute_file << " " << uid() << " " << gid() << " " << std::oct
<< perm();
if (access(attribute_file.c_str(), F_OK) == 0) {
if (chown(attribute_file.c_str(), uid(), gid()) != 0) {
PLOG(ERROR) << "chown(" << attribute_file << ", " << uid() << ", " << gid()
<< ") failed";
}
if (chmod(attribute_file.c_str(), perm()) != 0) {
PLOG(ERROR) << "chmod(" << attribute_file << ", " << perm() << ") failed";
}
}
}
// Given a path that may start with a platform device, find the parent platform device by finding a
// parent directory with a 'subsystem' symlink that points to the platform bus.
// If it doesn't start with a platform device, return false
bool DeviceHandler::FindPlatformDevice(std::string path, std::string* platform_device_path) const {
platform_device_path->clear();
// Uevents don't contain the mount point, so we need to add it here.
path.insert(0, sysfs_mount_point_);
std::string directory = Dirname(path);
while (directory != "/" && directory != ".") {
std::string subsystem_link_path;
if (Realpath(directory + "/subsystem", &subsystem_link_path) &&
subsystem_link_path == sysfs_mount_point_ + "/bus/platform") {
// We need to remove the mount point that we added above before returning.
directory.erase(0, sysfs_mount_point_.size());
*platform_device_path = directory;
return true;
}
auto last_slash = path.rfind('/');
if (last_slash == std::string::npos) return false;
path.erase(last_slash);
directory = Dirname(path);
}
return false;
}
void DeviceHandler::FixupSysPermissions(const std::string& upath,
const std::string& subsystem) const {
// upaths omit the "/sys" that paths in this list
// contain, so we prepend it...
std::string path = "/sys" + upath;
for (const auto& s : sysfs_permissions_) {
if (s.MatchWithSubsystem(path, subsystem)) s.SetPermissions(path);
}
if (!skip_restorecon_ && access(path.c_str(), F_OK) == 0) {
LOG(VERBOSE) << "restorecon_recursive: " << path;
if (selinux_android_restorecon(path.c_str(), SELINUX_ANDROID_RESTORECON_RECURSE) != 0) {
PLOG(ERROR) << "selinux_android_restorecon(" << path << ") failed";
}
}
}
std::tuple<mode_t, uid_t, gid_t> DeviceHandler::GetDevicePermissions(
const std::string& path, const std::vector<std::string>& links) const {
// Search the perms list in reverse so that ueventd.$hardware can override ueventd.rc.
for (auto it = dev_permissions_.crbegin(); it != dev_permissions_.crend(); ++it) {
if (it->Match(path) || std::any_of(links.cbegin(), links.cend(),
[it](const auto& link) { return it->Match(link); })) {
return {it->perm(), it->uid(), it->gid()};
}
}
/* Default if nothing found. */
return {0600, 0, 0};
}
void DeviceHandler::MakeDevice(const std::string& path, bool block, int major, int minor,
const std::vector<std::string>& links) const {
auto[mode, uid, gid] = GetDevicePermissions(path, links);
mode |= (block ? S_IFBLK : S_IFCHR);
std::string secontext;
if (!SelabelLookupFileContextBestMatch(path, links, mode, &secontext)) {
PLOG(ERROR) << "Device '" << path << "' not created; cannot find SELinux label";
return;
}
if (!secontext.empty()) {
setfscreatecon(secontext.c_str());
}
dev_t dev = makedev(major, minor);
/* Temporarily change egid to avoid race condition setting the gid of the
* device node. Unforunately changing the euid would prevent creation of
* some device nodes, so the uid has to be set with chown() and is still
* racy. Fixing the gid race at least fixed the issue with system_server
* opening dynamic input devices under the AID_INPUT gid. */
if (setegid(gid)) {
PLOG(ERROR) << "setegid(" << gid << ") for " << path << " device failed";
goto out;
}
/* If the node already exists update its SELinux label to handle cases when
* it was created with the wrong context during coldboot procedure. */
if (mknod(path.c_str(), mode, dev) && (errno == EEXIST) && !secontext.empty()) {
char* fcon = nullptr;
int rc = lgetfilecon(path.c_str(), &fcon);
if (rc < 0) {
PLOG(ERROR) << "Cannot get SELinux label on '" << path << "' device";
goto out;
}
bool different = fcon != secontext;
freecon(fcon);
if (different && lsetfilecon(path.c_str(), secontext.c_str())) {
PLOG(ERROR) << "Cannot set '" << secontext << "' SELinux label on '" << path
<< "' device";
}
}
out:
chown(path.c_str(), uid, -1);
if (setegid(AID_ROOT)) {
PLOG(FATAL) << "setegid(AID_ROOT) failed";
}
if (!secontext.empty()) {
setfscreatecon(nullptr);
}
}
// replaces any unacceptable characters with '_', the
// length of the resulting string is equal to the input string
void SanitizePartitionName(std::string* string) {
const char* accept =
"abcdefghijklmnopqrstuvwxyz"
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"0123456789"
"_-.";
if (!string) return;
std::string::size_type pos = 0;
while ((pos = string->find_first_not_of(accept, pos)) != std::string::npos) {
(*string)[pos] = '_';
}
}
std::vector<std::string> DeviceHandler::GetBlockDeviceSymlinks(const Uevent& uevent) const {
std::string device;
std::string type;
std::string partition;
if (FindPlatformDevice(uevent.path, &device)) {
// Skip /devices/platform or /devices/ if present
static const std::string devices_platform_prefix = "/devices/platform/";
static const std::string devices_prefix = "/devices/";
if (StartsWith(device, devices_platform_prefix)) {
device = device.substr(devices_platform_prefix.length());
} else if (StartsWith(device, devices_prefix)) {
device = device.substr(devices_prefix.length());
}
type = "platform";
} else if (FindPciDevicePrefix(uevent.path, &device)) {
type = "pci";
} else if (FindVbdDevicePrefix(uevent.path, &device)) {
type = "vbd";
} else if (FindDmDevicePartition(uevent.path, &partition)) {
return {"/dev/block/mapper/" + partition};
} else {
return {};
}
std::vector<std::string> links;
LOG(VERBOSE) << "found " << type << " device " << device;
auto link_path = "/dev/block/" + type + "/" + device;
bool is_boot_device = boot_devices_.find(device) != boot_devices_.end();
if (!uevent.partition_name.empty()) {
std::string partition_name_sanitized(uevent.partition_name);
SanitizePartitionName(&partition_name_sanitized);
if (partition_name_sanitized != uevent.partition_name) {
LOG(VERBOSE) << "Linking partition '" << uevent.partition_name << "' as '"
<< partition_name_sanitized << "'";
}
links.emplace_back(link_path + "/by-name/" + partition_name_sanitized);
// Adds symlink: /dev/block/by-name/<partition_name>.
if (is_boot_device) {
links.emplace_back("/dev/block/by-name/" + partition_name_sanitized);
}
} else if (is_boot_device) {
// If we don't have a partition name but we are a partition on a boot device, create a
// symlink of /dev/block/by-name/<device_name> for symmetry.
links.emplace_back("/dev/block/by-name/" + uevent.device_name);
}
auto last_slash = uevent.path.rfind('/');
links.emplace_back(link_path + "/" + uevent.path.substr(last_slash + 1));
return links;
}
void DeviceHandler::HandleDevice(const std::string& action, const std::string& devpath, bool block,
int major, int minor, const std::vector<std::string>& links) const {
if (action == "add") {
MakeDevice(devpath, block, major, minor, links);
for (const auto& link : links) {
if (!mkdir_recursive(Dirname(link), 0755)) {
PLOG(ERROR) << "Failed to create directory " << Dirname(link);
}
if (symlink(devpath.c_str(), link.c_str())) {
if (errno != EEXIST) {
PLOG(ERROR) << "Failed to symlink " << devpath << " to " << link;
} else if (std::string link_path;
Readlink(link, &link_path) && link_path != devpath) {
PLOG(ERROR) << "Failed to symlink " << devpath << " to " << link
<< ", which already links to: " << link_path;
}
}
}
}
if (action == "remove") {
for (const auto& link : links) {
std::string link_path;
if (Readlink(link, &link_path) && link_path == devpath) {
unlink(link.c_str());
}
}
unlink(devpath.c_str());
}
}
void DeviceHandler::HandleUevent(const Uevent& uevent) {
if (uevent.action == "add" || uevent.action == "change" || uevent.action == "online") {
FixupSysPermissions(uevent.path, uevent.subsystem);
}
// if it's not a /dev device, nothing to do
if (uevent.major < 0 || uevent.minor < 0) return;
std::string devpath;
std::vector<std::string> links;
bool block = false;
if (uevent.subsystem == "block") {
block = true;
devpath = "/dev/block/" + Basename(uevent.path);
if (StartsWith(uevent.path, "/devices")) {
links = GetBlockDeviceSymlinks(uevent);
}
} else if (const auto subsystem =
std::find(subsystems_.cbegin(), subsystems_.cend(), uevent.subsystem);
subsystem != subsystems_.cend()) {
devpath = subsystem->ParseDevPath(uevent);
} else if (uevent.subsystem == "usb") {
if (!uevent.device_name.empty()) {
devpath = "/dev/" + uevent.device_name;
} else {
// This imitates the file system that would be created
// if we were using devfs instead.
// Minors are broken up into groups of 128, starting at "001"
int bus_id = uevent.minor / 128 + 1;
int device_id = uevent.minor % 128 + 1;
devpath = StringPrintf("/dev/bus/usb/%03d/%03d", bus_id, device_id);
}
} else if (StartsWith(uevent.subsystem, "usb")) {
// ignore other USB events
return;
} else {
devpath = "/dev/" + Basename(uevent.path);
}
mkdir_recursive(Dirname(devpath), 0755);
HandleDevice(uevent.action, devpath, block, uevent.major, uevent.minor, links);
}
void DeviceHandler::ColdbootDone() {
skip_restorecon_ = false;
}
DeviceHandler::DeviceHandler(std::vector<Permissions> dev_permissions,
std::vector<SysfsPermissions> sysfs_permissions,
std::vector<Subsystem> subsystems, std::set<std::string> boot_devices,
bool skip_restorecon)
: dev_permissions_(std::move(dev_permissions)),
sysfs_permissions_(std::move(sysfs_permissions)),
subsystems_(std::move(subsystems)),
boot_devices_(std::move(boot_devices)),
skip_restorecon_(skip_restorecon),
sysfs_mount_point_("/sys") {}
DeviceHandler::DeviceHandler()
: DeviceHandler(std::vector<Permissions>{}, std::vector<SysfsPermissions>{},
std::vector<Subsystem>{}, std::set<std::string>{}, false) {}
} // namespace init
} // namespace android