init/devices.cpp - LeafOS-Project/android_system_core - Gitiles

 /*
  * 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 <filesystem>
 #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 <libdm/dm.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::Split;
 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 FindDmDevice(const Uevent& uevent, std::string* name, std::string* uuid) {
     if (!StartsWith(uevent.path, "/devices/virtual/block/dm-")) return false;
     if (uevent.action == "remove") return false;  // Avoid error spam from ioctl

     dev_t dev = makedev(uevent.major, uevent.minor);

     auto& dm = android::dm::DeviceMapper::Instance();
     return dm.GetDeviceNameAndUuid(dev, name, uuid);
 }

 Permissions::Permissions(const std::string& name, mode_t perm, uid_t uid, gid_t gid,
                          bool no_fnm_pathname)
     : name_(name),
       perm_(perm),
       uid_(uid),
       gid_(gid),
       prefix_(false),
       wildcard_(false),
       no_fnm_pathname_(no_fnm_pathname) {
     // 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(), no_fnm_pathname_ ? 0 : 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";
         }
     }
 }

 std::string DeviceHandler::GetPartitionNameForDevice(const std::string& query_device) {
     static const auto partition_map = [] {
         std::vector<std::pair<std::string, std::string>> partition_map;
         auto parser = [&partition_map](const std::string& key, const std::string& value) {
             if (key != "androidboot.partition_map") {
                 return;
             }
             for (const auto& map : Split(value, ";")) {
                 auto map_pieces = Split(map, ",");
                 if (map_pieces.size() != 2) {
                     LOG(ERROR) << "Expected a comma separated device,partition mapping, but found '"
                                << map << "'";
                     continue;
                 }
                 partition_map.emplace_back(map_pieces[0], map_pieces[1]);
             }
         };
         ImportKernelCmdline(parser);
         ImportBootconfig(parser);
         return partition_map;
     }();

     for (const auto& [device, partition] : partition_map) {
         if (query_device == device) {
             return partition;
         }
     }
     return {};
 }

 // 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" ||
              subsystem_link_path == sysfs_mount_point_ + "/bus/amba")) {
             // 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());
     }

     gid_t new_group = -1;

     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 and the file mode to handle cases when
      * it was created with the wrong context and file mode 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";
         }

         struct stat s;
         if (stat(path.c_str(), &s) == 0) {
             if (gid != s.st_gid) {
                 new_group = gid;
             }
         if (mode != s.st_mode) {
             if (chmod(path.c_str(), mode) != 0) {
                 PLOG(ERROR) << "Cannot chmod " << path << " to " << mode;
             }
         }
         } else {
             PLOG(ERROR) << "Cannot stat " << path;
         }
     }

 out:
     if (chown(path.c_str(), uid, new_group) < 0) {
         PLOG(ERROR) << "Cannot chown " << path << " " << uid << " " << new_group;
     }
     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;
     std::string uuid;

     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 (FindDmDevice(uevent, &partition, &uuid)) {
         std::vector<std::string> symlinks = {"/dev/block/mapper/" + partition};
         if (!uuid.empty()) {
             symlinks.emplace_back("/dev/block/mapper/by-uuid/" + uuid);
         }
         return symlinks;
     } 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 partition_name = GetPartitionNameForDevice(uevent.device_name);
         if (!partition_name.empty()) {
             links.emplace_back("/dev/block/by-name/" + partition_name);
         }
     }

     std::string model;
     if (ReadFileToString("/sys/class/block/" + uevent.device_name + "/queue/zoned", &model) &&
         !StartsWith(model, "none")) {
         links.emplace_back("/dev/block/by-name/zoned_device");
     }

     auto last_slash = uevent.path.rfind('/');
     links.emplace_back(link_path + "/" + uevent.path.substr(last_slash + 1));

     return links;
 }

 static void RemoveDeviceMapperLinks(const std::string& devpath) {
     std::vector<std::string> dirs = {
             "/dev/block/mapper",
             "/dev/block/mapper/by-uuid",
     };
     for (const auto& dir : dirs) {
         if (access(dir.c_str(), F_OK) != 0) continue;

         std::unique_ptr<DIR, decltype(&closedir)> dh(opendir(dir.c_str()), closedir);
         if (!dh) {
             PLOG(ERROR) << "Failed to open directory " << dir;
             continue;
         }

         struct dirent* dp;
         std::string link_path;
         while ((dp = readdir(dh.get())) != nullptr) {
             if (dp->d_type != DT_LNK) continue;

             auto path = dir + "/" + dp->d_name;
             if (Readlink(path, &link_path) && link_path == devpath) {
                 unlink(path.c_str());
             }
         }
     }
 }

 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);
     }

     // Handle device-mapper nodes.
     // On kernels <= 5.10, the "add" event is fired on DM_DEV_CREATE, but does not contain name
     // information until DM_TABLE_LOAD - thus, we wait for a "change" event.
     // On kernels >= 5.15, the "add" event is fired on DM_TABLE_LOAD, followed by a "change"
     // event.
     if (action == "add" || (action == "change" && StartsWith(devpath, "/dev/block/dm-"))) {
         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") {
         if (StartsWith(devpath, "/dev/block/dm-")) {
             RemoveDeviceMapperLinks(devpath);
         }
         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::HandleAshmemUevent(const Uevent& uevent) {
     if (uevent.device_name == "ashmem") {
         static const std::string boot_id_path = "/proc/sys/kernel/random/boot_id";
         std::string boot_id;
         if (!ReadFileToString(boot_id_path, &boot_id)) {
             PLOG(ERROR) << "Cannot duplicate ashmem device node. Failed to read " << boot_id_path;
             return;
         };
         boot_id = Trim(boot_id);

         Uevent dup_ashmem_uevent = uevent;
         dup_ashmem_uevent.device_name += boot_id;
         dup_ashmem_uevent.path += boot_id;
         HandleUevent(dup_ashmem_uevent);
     }
 }

 void DeviceHandler::HandleUevent(const Uevent& uevent) {
   if (uevent.action == "add" || uevent.action == "change" ||
       uevent.action == "bind" || 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 if (uevent.subsystem == "misc" && StartsWith(uevent.device_name, "dm-user/")) {
         devpath = "/dev/dm-user/" + uevent.device_name.substr(8);
     } else {
         devpath = "/dev/" + Basename(uevent.path);
     }

     mkdir_recursive(Dirname(devpath), 0755);

     HandleDevice(uevent.action, devpath, block, uevent.major, uevent.minor, links);

     // Duplicate /dev/ashmem device and name it /dev/ashmem<boot_id>.
     // TODO(b/111903542): remove once all users of /dev/ashmem are migrated to libcutils API.
     HandleAshmemUevent(uevent);
 }

 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
	/*
	* 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 <filesystem>
	#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 <libdm/dm.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::Split;
	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 FindDmDevice(const Uevent& uevent, std::string* name, std::string* uuid) {
	if (!StartsWith(uevent.path, "/devices/virtual/block/dm-")) return false;
	if (uevent.action == "remove") return false; // Avoid error spam from ioctl

	dev_t dev = makedev(uevent.major, uevent.minor);

	auto& dm = android::dm::DeviceMapper::Instance();
	return dm.GetDeviceNameAndUuid(dev, name, uuid);
	}

	Permissions::Permissions(const std::string& name, mode_t perm, uid_t uid, gid_t gid,
	bool no_fnm_pathname)
	: name_(name),
	perm_(perm),
	uid_(uid),
	gid_(gid),
	prefix_(false),
	wildcard_(false),
	no_fnm_pathname_(no_fnm_pathname) {
	// 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(), no_fnm_pathname_ ? 0 : 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";
	}
	}
	}

	std::string DeviceHandler::GetPartitionNameForDevice(const std::string& query_device) {
	static const auto partition_map = [] {
	std::vector<std::pair<std::string, std::string>> partition_map;
	auto parser = [&partition_map](const std::string& key, const std::string& value) {
	if (key != "androidboot.partition_map") {
	return;
	}
	for (const auto& map : Split(value, ";")) {
	auto map_pieces = Split(map, ",");
	if (map_pieces.size() != 2) {
	LOG(ERROR) << "Expected a comma separated device,partition mapping, but found '"
	<< map << "'";
	continue;
	}
	partition_map.emplace_back(map_pieces[0], map_pieces[1]);
	}
	};
	ImportKernelCmdline(parser);
	ImportBootconfig(parser);
	return partition_map;
	}();

	for (const auto& [device, partition] : partition_map) {
	if (query_device == device) {
	return partition;
	}
	}
	return {};
	}

	// 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" \|\|
	subsystem_link_path == sysfs_mount_point_ + "/bus/amba")) {
	// 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());
	}

	gid_t new_group = -1;

	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 and the file mode to handle cases when
	* it was created with the wrong context and file mode 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";
	}

	struct stat s;
	if (stat(path.c_str(), &s) == 0) {
	if (gid != s.st_gid) {
	new_group = gid;
	}
	if (mode != s.st_mode) {
	if (chmod(path.c_str(), mode) != 0) {
	PLOG(ERROR) << "Cannot chmod " << path << " to " << mode;
	}
	}
	} else {
	PLOG(ERROR) << "Cannot stat " << path;
	}
	}

	out:
	if (chown(path.c_str(), uid, new_group) < 0) {
	PLOG(ERROR) << "Cannot chown " << path << " " << uid << " " << new_group;
	}
	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;
	std::string uuid;

	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 (FindDmDevice(uevent, &partition, &uuid)) {
	std::vector<std::string> symlinks = {"/dev/block/mapper/" + partition};
	if (!uuid.empty()) {
	symlinks.emplace_back("/dev/block/mapper/by-uuid/" + uuid);
	}
	return symlinks;
	} 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 partition_name = GetPartitionNameForDevice(uevent.device_name);
	if (!partition_name.empty()) {
	links.emplace_back("/dev/block/by-name/" + partition_name);
	}
	}

	std::string model;
	if (ReadFileToString("/sys/class/block/" + uevent.device_name + "/queue/zoned", &model) &&
	!StartsWith(model, "none")) {
	links.emplace_back("/dev/block/by-name/zoned_device");
	}

	auto last_slash = uevent.path.rfind('/');
	links.emplace_back(link_path + "/" + uevent.path.substr(last_slash + 1));

	return links;
	}

	static void RemoveDeviceMapperLinks(const std::string& devpath) {
	std::vector<std::string> dirs = {
	"/dev/block/mapper",
	"/dev/block/mapper/by-uuid",
	};
	for (const auto& dir : dirs) {
	if (access(dir.c_str(), F_OK) != 0) continue;

	std::unique_ptr<DIR, decltype(&closedir)> dh(opendir(dir.c_str()), closedir);
	if (!dh) {
	PLOG(ERROR) << "Failed to open directory " << dir;
	continue;
	}

	struct dirent* dp;
	std::string link_path;
	while ((dp = readdir(dh.get())) != nullptr) {
	if (dp->d_type != DT_LNK) continue;

	auto path = dir + "/" + dp->d_name;
	if (Readlink(path, &link_path) && link_path == devpath) {
	unlink(path.c_str());
	}
	}
	}
	}

	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);
	}

	// Handle device-mapper nodes.
	// On kernels <= 5.10, the "add" event is fired on DM_DEV_CREATE, but does not contain name
	// information until DM_TABLE_LOAD - thus, we wait for a "change" event.
	// On kernels >= 5.15, the "add" event is fired on DM_TABLE_LOAD, followed by a "change"
	// event.
	if (action == "add" \|\| (action == "change" && StartsWith(devpath, "/dev/block/dm-"))) {
	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") {
	if (StartsWith(devpath, "/dev/block/dm-")) {
	RemoveDeviceMapperLinks(devpath);
	}
	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::HandleAshmemUevent(const Uevent& uevent) {
	if (uevent.device_name == "ashmem") {
	static const std::string boot_id_path = "/proc/sys/kernel/random/boot_id";
	std::string boot_id;
	if (!ReadFileToString(boot_id_path, &boot_id)) {
	PLOG(ERROR) << "Cannot duplicate ashmem device node. Failed to read " << boot_id_path;
	return;
	};
	boot_id = Trim(boot_id);

	Uevent dup_ashmem_uevent = uevent;
	dup_ashmem_uevent.device_name += boot_id;
	dup_ashmem_uevent.path += boot_id;
	HandleUevent(dup_ashmem_uevent);
	}
	}

	void DeviceHandler::HandleUevent(const Uevent& uevent) {
	if (uevent.action == "add" \|\| uevent.action == "change" \|\|
	uevent.action == "bind" \|\| 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 if (uevent.subsystem == "misc" && StartsWith(uevent.device_name, "dm-user/")) {
	devpath = "/dev/dm-user/" + uevent.device_name.substr(8);
	} else {
	devpath = "/dev/" + Basename(uevent.path);
	}

	mkdir_recursive(Dirname(devpath), 0755);

	HandleDevice(uevent.action, devpath, block, uevent.major, uevent.minor, links);

	// Duplicate /dev/ashmem device and name it /dev/ashmem<boot_id>.
	// TODO(b/111903542): remove once all users of /dev/ashmem are migrated to libcutils API.
	HandleAshmemUevent(uevent);
	}

	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