init/util.cpp - third_party/android/platform/system/core - Git at Google

 /*
  * Copyright (C) 2008 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 "util.h"

 #include <ctype.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <pwd.h>
 #include <stdarg.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <time.h>
 #include <unistd.h>

 #include <thread>

 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/properties.h>
 #include <android-base/strings.h>
 #include <android-base/unique_fd.h>
 #include <cutils/sockets.h>
 #include <selinux/android.h>

 #if defined(__ANDROID__)
 #include "reboot_utils.h"
 #include "selinux.h"
 #else
 #include "host_init_stubs.h"
 #endif

 #ifdef _INIT_INIT_H
 #error "Do not include init.h in files used by ueventd; it will expose init's globals"
 #endif

 using android::base::boot_clock;
 using namespace std::literals::string_literals;

 namespace android {
 namespace init {

 const std::string kDefaultAndroidDtDir("/proc/device-tree/firmware/android/");

 // DecodeUid() - decodes and returns the given string, which can be either the
 // numeric or name representation, into the integer uid or gid.
 Result<uid_t> DecodeUid(const std::string& name) {
     if (isalpha(name[0])) {
         passwd* pwd = getpwnam(name.c_str());
         if (!pwd) return ErrnoError() << "getpwnam failed";

         return pwd->pw_uid;
     }

     errno = 0;
     uid_t result = static_cast<uid_t>(strtoul(name.c_str(), 0, 0));
     if (errno) return ErrnoError() << "strtoul failed";

     return result;
 }

 /*
  * CreateSocket - creates a Unix domain socket in ANDROID_SOCKET_DIR
  * ("/dev/socket") as dictated in init.rc. This socket is inherited by the
  * daemon. We communicate the file descriptor's value via the environment
  * variable ANDROID_SOCKET_ENV_PREFIX<name> ("ANDROID_SOCKET_foo").
  */
 int CreateSocket(const char* name, int type, bool passcred, mode_t perm, uid_t uid, gid_t gid,
                  const char* socketcon) {
     if (socketcon) {
         if (setsockcreatecon(socketcon) == -1) {
             PLOG(ERROR) << "setsockcreatecon(\"" << socketcon << "\") failed";
             return -1;
         }
     }

     android::base::unique_fd fd(socket(PF_UNIX, type, 0));
     if (fd < 0) {
         PLOG(ERROR) << "Failed to open socket '" << name << "'";
         return -1;
     }

     if (socketcon) setsockcreatecon(NULL);

     struct sockaddr_un addr;
     memset(&addr, 0 , sizeof(addr));
     addr.sun_family = AF_UNIX;
     snprintf(addr.sun_path, sizeof(addr.sun_path), ANDROID_SOCKET_DIR"/%s",
              name);

     if ((unlink(addr.sun_path) != 0) && (errno != ENOENT)) {
         PLOG(ERROR) << "Failed to unlink old socket '" << name << "'";
         return -1;
     }

     std::string secontext;
     if (SelabelLookupFileContext(addr.sun_path, S_IFSOCK, &secontext) && !secontext.empty()) {
         setfscreatecon(secontext.c_str());
     }

     if (passcred) {
         int on = 1;
         if (setsockopt(fd, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on))) {
             PLOG(ERROR) << "Failed to set SO_PASSCRED '" << name << "'";
             return -1;
         }
     }

     int ret = bind(fd, (struct sockaddr *) &addr, sizeof (addr));
     int savederrno = errno;

     if (!secontext.empty()) {
         setfscreatecon(nullptr);
     }

     if (ret) {
         errno = savederrno;
         PLOG(ERROR) << "Failed to bind socket '" << name << "'";
         goto out_unlink;
     }

     if (lchown(addr.sun_path, uid, gid)) {
         PLOG(ERROR) << "Failed to lchown socket '" << addr.sun_path << "'";
         goto out_unlink;
     }
     if (fchmodat(AT_FDCWD, addr.sun_path, perm, AT_SYMLINK_NOFOLLOW)) {
         PLOG(ERROR) << "Failed to fchmodat socket '" << addr.sun_path << "'";
         goto out_unlink;
     }

     LOG(INFO) << "Created socket '" << addr.sun_path << "'"
               << ", mode " << std::oct << perm << std::dec
               << ", user " << uid
               << ", group " << gid;

     return fd.release();

 out_unlink:
     unlink(addr.sun_path);
     return -1;
 }

 Result<std::string> ReadFile(const std::string& path) {
     android::base::unique_fd fd(
         TEMP_FAILURE_RETRY(open(path.c_str(), O_RDONLY | O_NOFOLLOW | O_CLOEXEC)));
     if (fd == -1) {
         return ErrnoError() << "open() failed";
     }

     // For security reasons, disallow world-writable
     // or group-writable files.
     struct stat sb;
     if (fstat(fd, &sb) == -1) {
         return ErrnoError() << "fstat failed()";
     }
     if ((sb.st_mode & (S_IWGRP | S_IWOTH)) != 0) {
         return Error() << "Skipping insecure file";
     }

     std::string content;
     if (!android::base::ReadFdToString(fd, &content)) {
         return ErrnoError() << "Unable to read file contents";
     }
     return content;
 }

 static int OpenFile(const std::string& path, int flags, mode_t mode) {
     std::string secontext;
     if (SelabelLookupFileContext(path, mode, &secontext) && !secontext.empty()) {
         setfscreatecon(secontext.c_str());
     }

     int rc = open(path.c_str(), flags, mode);

     if (!secontext.empty()) {
         int save_errno = errno;
         setfscreatecon(nullptr);
         errno = save_errno;
     }

     return rc;
 }

 Result<Success> WriteFile(const std::string& path, const std::string& content) {
     android::base::unique_fd fd(TEMP_FAILURE_RETRY(
         OpenFile(path, O_WRONLY | O_CREAT | O_NOFOLLOW | O_TRUNC | O_CLOEXEC, 0600)));
     if (fd == -1) {
         return ErrnoError() << "open() failed";
     }
     if (!android::base::WriteStringToFd(content, fd)) {
         return ErrnoError() << "Unable to write file contents";
     }
     return Success();
 }

 bool mkdir_recursive(const std::string& path, mode_t mode) {
     std::string::size_type slash = 0;
     while ((slash = path.find('/', slash + 1)) != std::string::npos) {
         auto directory = path.substr(0, slash);
         struct stat info;
         if (stat(directory.c_str(), &info) != 0) {
             auto ret = make_dir(directory, mode);
             if (!ret && errno != EEXIST) return false;
         }
     }
     auto ret = make_dir(path, mode);
     if (!ret && errno != EEXIST) return false;
     return true;
 }

 int wait_for_file(const char* filename, std::chrono::nanoseconds timeout) {
     android::base::Timer t;
     while (t.duration() < timeout) {
         struct stat sb;
         if (stat(filename, &sb) != -1) {
             LOG(INFO) << "wait for '" << filename << "' took " << t;
             return 0;
         }
         std::this_thread::sleep_for(10ms);
     }
     LOG(WARNING) << "wait for '" << filename << "' timed out and took " << t;
     return -1;
 }

 void import_kernel_cmdline(bool in_qemu,
                            const std::function<void(const std::string&, const std::string&, bool)>& fn) {
     std::string cmdline;
     android::base::ReadFileToString("/proc/cmdline", &cmdline);

     for (const auto& entry : android::base::Split(android::base::Trim(cmdline), " ")) {
         std::vector<std::string> pieces = android::base::Split(entry, "=");
         if (pieces.size() == 2) {
             fn(pieces[0], pieces[1], in_qemu);
         }
     }
 }

 bool make_dir(const std::string& path, mode_t mode) {
     std::string secontext;
     if (SelabelLookupFileContext(path, mode, &secontext) && !secontext.empty()) {
         setfscreatecon(secontext.c_str());
     }

     int rc = mkdir(path.c_str(), mode);

     if (!secontext.empty()) {
         int save_errno = errno;
         setfscreatecon(nullptr);
         errno = save_errno;
     }

     return rc == 0;
 }

 /*
  * Returns true is pathname is a directory
  */
 bool is_dir(const char* pathname) {
     struct stat info;
     if (stat(pathname, &info) == -1) {
         return false;
     }
     return S_ISDIR(info.st_mode);
 }

 bool expand_props(const std::string& src, std::string* dst) {
     const char* src_ptr = src.c_str();

     if (!dst) {
         return false;
     }

     /* - variables can either be $x.y or ${x.y}, in case they are only part
      *   of the string.
      * - will accept $$ as a literal $.
      * - no nested property expansion, i.e. ${foo.${bar}} is not supported,
      *   bad things will happen
      * - ${x.y:-default} will return default value if property empty.
      */
     while (*src_ptr) {
         const char* c;

         c = strchr(src_ptr, '$');
         if (!c) {
             dst->append(src_ptr);
             return true;
         }

         dst->append(src_ptr, c);
         c++;

         if (*c == '$') {
             dst->push_back(*(c++));
             src_ptr = c;
             continue;
         } else if (*c == '\0') {
             return true;
         }

         std::string prop_name;
         std::string def_val;
         if (*c == '{') {
             c++;
             const char* end = strchr(c, '}');
             if (!end) {
                 // failed to find closing brace, abort.
                 LOG(ERROR) << "unexpected end of string in '" << src << "', looking for }";
                 return false;
             }
             prop_name = std::string(c, end);
             c = end + 1;
             size_t def = prop_name.find(":-");
             if (def < prop_name.size()) {
                 def_val = prop_name.substr(def + 2);
                 prop_name = prop_name.substr(0, def);
             }
         } else {
             prop_name = c;
             LOG(ERROR) << "using deprecated syntax for specifying property '" << c << "', use ${name} instead";
             c += prop_name.size();
         }

         if (prop_name.empty()) {
             LOG(ERROR) << "invalid zero-length property name in '" << src << "'";
             return false;
         }

         std::string prop_val = android::base::GetProperty(prop_name, "");
         if (prop_val.empty()) {
             if (def_val.empty()) {
                 LOG(ERROR) << "property '" << prop_name << "' doesn't exist while expanding '" << src << "'";
                 return false;
             }
             prop_val = def_val;
         }

         dst->append(prop_val);
         src_ptr = c;
     }

     return true;
 }

 static std::string init_android_dt_dir() {
     // Use the standard procfs-based path by default
     std::string android_dt_dir = kDefaultAndroidDtDir;
     // The platform may specify a custom Android DT path in kernel cmdline
     import_kernel_cmdline(false,
                           [&](const std::string& key, const std::string& value, bool in_qemu) {
                               if (key == "androidboot.android_dt_dir") {
                                   android_dt_dir = value;
                               }
                           });
     LOG(INFO) << "Using Android DT directory " << android_dt_dir;
     return android_dt_dir;
 }

 // FIXME: The same logic is duplicated in system/core/fs_mgr/
 const std::string& get_android_dt_dir() {
     // Set once and saves time for subsequent calls to this function
     static const std::string kAndroidDtDir = init_android_dt_dir();
     return kAndroidDtDir;
 }

 // Reads the content of device tree file under the platform's Android DT directory.
 // Returns true if the read is success, false otherwise.
 bool read_android_dt_file(const std::string& sub_path, std::string* dt_content) {
     const std::string file_name = get_android_dt_dir() + sub_path;
     if (android::base::ReadFileToString(file_name, dt_content)) {
         if (!dt_content->empty()) {
             dt_content->pop_back();  // Trims the trailing '\0' out.
             return true;
         }
     }
     return false;
 }

 bool is_android_dt_value_expected(const std::string& sub_path, const std::string& expected_content) {
     std::string dt_content;
     if (read_android_dt_file(sub_path, &dt_content)) {
         if (dt_content == expected_content) {
             return true;
         }
     }
     return false;
 }

 bool IsLegalPropertyName(const std::string& name) {
     size_t namelen = name.size();

     if (namelen < 1) return false;
     if (name[0] == '.') return false;
     if (name[namelen - 1] == '.') return false;

     /* Only allow alphanumeric, plus '.', '-', '@', ':', or '_' */
     /* Don't allow ".." to appear in a property name */
     for (size_t i = 0; i < namelen; i++) {
         if (name[i] == '.') {
             // i=0 is guaranteed to never have a dot. See above.
             if (name[i - 1] == '.') return false;
             continue;
         }
         if (name[i] == '_' || name[i] == '-' || name[i] == '@' || name[i] == ':') continue;
         if (name[i] >= 'a' && name[i] <= 'z') continue;
         if (name[i] >= 'A' && name[i] <= 'Z') continue;
         if (name[i] >= '0' && name[i] <= '9') continue;
         return false;
     }

     return true;
 }

 static void InitAborter(const char* abort_message) {
     // When init forks, it continues to use this aborter for LOG(FATAL), but we want children to
     // simply abort instead of trying to reboot the system.
     if (getpid() != 1) {
         android::base::DefaultAborter(abort_message);
         return;
     }

     InitFatalReboot();
 }

 // The kernel opens /dev/console and uses that fd for stdin/stdout/stderr if there is a serial
 // console enabled and no initramfs, otherwise it does not provide any fds for stdin/stdout/stderr.
 // SetStdioToDevNull() is used to close these existing fds if they exist and replace them with
 // /dev/null regardless.
 //
 // In the case that these fds are provided by the kernel, the exec of second stage init causes an
 // SELinux denial as it does not have access to /dev/console.  In the case that they are not
 // provided, exec of any further process is potentially dangerous as the first fd's opened by that
 // process will take the stdin/stdout/stderr fileno's, which can cause issues if printf(), etc is
 // then used by that process.
 //
 // Lastly, simply calling SetStdioToDevNull() in first stage init is not enough, since first
 // stage init still runs in kernel context, future child processes will not have permissions to
 // access any fds that it opens, including the one opened below for /dev/null.  Therefore,
 // SetStdioToDevNull() must be called again in second stage init.
 void SetStdioToDevNull(char** argv) {
     // Make stdin/stdout/stderr all point to /dev/null.
     int fd = open("/dev/null", O_RDWR);
     if (fd == -1) {
         int saved_errno = errno;
         android::base::InitLogging(argv, &android::base::KernelLogger, InitAborter);
         errno = saved_errno;
         PLOG(FATAL) << "Couldn't open /dev/null";
     }
     dup2(fd, STDIN_FILENO);
     dup2(fd, STDOUT_FILENO);
     dup2(fd, STDERR_FILENO);
     if (fd > STDERR_FILENO) close(fd);
 }

 void InitKernelLogging(char** argv) {
     SetFatalRebootTarget();
     android::base::InitLogging(argv, &android::base::KernelLogger, InitAborter);
 }

 bool IsRecoveryMode() {
     return access("/system/bin/recovery", F_OK) == 0;
 }

 }  // namespace init
 }  // namespace android
	/*
	* Copyright (C) 2008 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 "util.h"

	#include <ctype.h>
	#include <errno.h>
	#include <fcntl.h>
	#include <pwd.h>
	#include <stdarg.h>
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	#include <sys/socket.h>
	#include <sys/un.h>
	#include <time.h>
	#include <unistd.h>

	#include <thread>

	#include <android-base/file.h>
	#include <android-base/logging.h>
	#include <android-base/properties.h>
	#include <android-base/strings.h>
	#include <android-base/unique_fd.h>
	#include <cutils/sockets.h>
	#include <selinux/android.h>

	#if defined(__ANDROID__)
	#include "reboot_utils.h"
	#include "selinux.h"
	#else
	#include "host_init_stubs.h"
	#endif

	#ifdef _INIT_INIT_H
	#error "Do not include init.h in files used by ueventd; it will expose init's globals"
	#endif

	using android::base::boot_clock;
	using namespace std::literals::string_literals;

	namespace android {
	namespace init {

	const std::string kDefaultAndroidDtDir("/proc/device-tree/firmware/android/");

	// DecodeUid() - decodes and returns the given string, which can be either the
	// numeric or name representation, into the integer uid or gid.
	Result<uid_t> DecodeUid(const std::string& name) {
	if (isalpha(name[0])) {
	passwd* pwd = getpwnam(name.c_str());
	if (!pwd) return ErrnoError() << "getpwnam failed";

	return pwd->pw_uid;
	}

	errno = 0;
	uid_t result = static_cast<uid_t>(strtoul(name.c_str(), 0, 0));
	if (errno) return ErrnoError() << "strtoul failed";

	return result;
	}

	/*
	* CreateSocket - creates a Unix domain socket in ANDROID_SOCKET_DIR
	* ("/dev/socket") as dictated in init.rc. This socket is inherited by the
	* daemon. We communicate the file descriptor's value via the environment
	* variable ANDROID_SOCKET_ENV_PREFIX<name> ("ANDROID_SOCKET_foo").
	*/
	int CreateSocket(const char* name, int type, bool passcred, mode_t perm, uid_t uid, gid_t gid,
	const char* socketcon) {
	if (socketcon) {
	if (setsockcreatecon(socketcon) == -1) {
	PLOG(ERROR) << "setsockcreatecon(\"" << socketcon << "\") failed";
	return -1;
	}
	}

	android::base::unique_fd fd(socket(PF_UNIX, type, 0));
	if (fd < 0) {
	PLOG(ERROR) << "Failed to open socket '" << name << "'";
	return -1;
	}

	if (socketcon) setsockcreatecon(NULL);

	struct sockaddr_un addr;
	memset(&addr, 0 , sizeof(addr));
	addr.sun_family = AF_UNIX;
	snprintf(addr.sun_path, sizeof(addr.sun_path), ANDROID_SOCKET_DIR"/%s",
	name);

	if ((unlink(addr.sun_path) != 0) && (errno != ENOENT)) {
	PLOG(ERROR) << "Failed to unlink old socket '" << name << "'";
	return -1;
	}

	std::string secontext;
	if (SelabelLookupFileContext(addr.sun_path, S_IFSOCK, &secontext) && !secontext.empty()) {
	setfscreatecon(secontext.c_str());
	}

	if (passcred) {
	int on = 1;
	if (setsockopt(fd, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on))) {
	PLOG(ERROR) << "Failed to set SO_PASSCRED '" << name << "'";
	return -1;
	}
	}

	int ret = bind(fd, (struct sockaddr *) &addr, sizeof (addr));
	int savederrno = errno;

	if (!secontext.empty()) {
	setfscreatecon(nullptr);
	}

	if (ret) {
	errno = savederrno;
	PLOG(ERROR) << "Failed to bind socket '" << name << "'";
	goto out_unlink;
	}

	if (lchown(addr.sun_path, uid, gid)) {
	PLOG(ERROR) << "Failed to lchown socket '" << addr.sun_path << "'";
	goto out_unlink;
	}
	if (fchmodat(AT_FDCWD, addr.sun_path, perm, AT_SYMLINK_NOFOLLOW)) {
	PLOG(ERROR) << "Failed to fchmodat socket '" << addr.sun_path << "'";
	goto out_unlink;
	}

	LOG(INFO) << "Created socket '" << addr.sun_path << "'"
	<< ", mode " << std::oct << perm << std::dec
	<< ", user " << uid
	<< ", group " << gid;

	return fd.release();

	out_unlink:
	unlink(addr.sun_path);
	return -1;
	}

	Result<std::string> ReadFile(const std::string& path) {
	android::base::unique_fd fd(
	TEMP_FAILURE_RETRY(open(path.c_str(), O_RDONLY \| O_NOFOLLOW \| O_CLOEXEC)));
	if (fd == -1) {
	return ErrnoError() << "open() failed";
	}

	// For security reasons, disallow world-writable
	// or group-writable files.
	struct stat sb;
	if (fstat(fd, &sb) == -1) {
	return ErrnoError() << "fstat failed()";
	}
	if ((sb.st_mode & (S_IWGRP \| S_IWOTH)) != 0) {
	return Error() << "Skipping insecure file";
	}

	std::string content;
	if (!android::base::ReadFdToString(fd, &content)) {
	return ErrnoError() << "Unable to read file contents";
	}
	return content;
	}

	static int OpenFile(const std::string& path, int flags, mode_t mode) {
	std::string secontext;
	if (SelabelLookupFileContext(path, mode, &secontext) && !secontext.empty()) {
	setfscreatecon(secontext.c_str());
	}

	int rc = open(path.c_str(), flags, mode);

	if (!secontext.empty()) {
	int save_errno = errno;
	setfscreatecon(nullptr);
	errno = save_errno;
	}

	return rc;
	}

	Result<Success> WriteFile(const std::string& path, const std::string& content) {
	android::base::unique_fd fd(TEMP_FAILURE_RETRY(
	OpenFile(path, O_WRONLY \| O_CREAT \| O_NOFOLLOW \| O_TRUNC \| O_CLOEXEC, 0600)));
	if (fd == -1) {
	return ErrnoError() << "open() failed";
	}
	if (!android::base::WriteStringToFd(content, fd)) {
	return ErrnoError() << "Unable to write file contents";
	}
	return Success();
	}

	bool mkdir_recursive(const std::string& path, mode_t mode) {
	std::string::size_type slash = 0;
	while ((slash = path.find('/', slash + 1)) != std::string::npos) {
	auto directory = path.substr(0, slash);
	struct stat info;
	if (stat(directory.c_str(), &info) != 0) {
	auto ret = make_dir(directory, mode);
	if (!ret && errno != EEXIST) return false;
	}
	}
	auto ret = make_dir(path, mode);
	if (!ret && errno != EEXIST) return false;
	return true;
	}

	int wait_for_file(const char* filename, std::chrono::nanoseconds timeout) {
	android::base::Timer t;
	while (t.duration() < timeout) {
	struct stat sb;
	if (stat(filename, &sb) != -1) {
	LOG(INFO) << "wait for '" << filename << "' took " << t;
	return 0;
	}
	std::this_thread::sleep_for(10ms);
	}
	LOG(WARNING) << "wait for '" << filename << "' timed out and took " << t;
	return -1;
	}

	void import_kernel_cmdline(bool in_qemu,
	const std::function<void(const std::string&, const std::string&, bool)>& fn) {
	std::string cmdline;
	android::base::ReadFileToString("/proc/cmdline", &cmdline);

	for (const auto& entry : android::base::Split(android::base::Trim(cmdline), " ")) {
	std::vector<std::string> pieces = android::base::Split(entry, "=");
	if (pieces.size() == 2) {
	fn(pieces[0], pieces[1], in_qemu);
	}
	}
	}

	bool make_dir(const std::string& path, mode_t mode) {
	std::string secontext;
	if (SelabelLookupFileContext(path, mode, &secontext) && !secontext.empty()) {
	setfscreatecon(secontext.c_str());
	}

	int rc = mkdir(path.c_str(), mode);

	if (!secontext.empty()) {
	int save_errno = errno;
	setfscreatecon(nullptr);
	errno = save_errno;
	}

	return rc == 0;
	}

	/*
	* Returns true is pathname is a directory
	*/
	bool is_dir(const char* pathname) {
	struct stat info;
	if (stat(pathname, &info) == -1) {
	return false;
	}
	return S_ISDIR(info.st_mode);
	}

	bool expand_props(const std::string& src, std::string* dst) {
	const char* src_ptr = src.c_str();

	if (!dst) {
	return false;
	}

	/* - variables can either be $x.y or ${x.y}, in case they are only part
	* of the string.
	* - will accept $$ as a literal $.
	* - no nested property expansion, i.e. ${foo.${bar}} is not supported,
	* bad things will happen
	* - ${x.y:-default} will return default value if property empty.
	*/
	while (*src_ptr) {
	const char* c;

	c = strchr(src_ptr, '$');
	if (!c) {
	dst->append(src_ptr);
	return true;
	}

	dst->append(src_ptr, c);
	c++;

	if (*c == '$') {
	dst->push_back(*(c++));
	src_ptr = c;
	continue;
	} else if (*c == '\0') {
	return true;
	}

	std::string prop_name;
	std::string def_val;
	if (*c == '{') {
	c++;
	const char* end = strchr(c, '}');
	if (!end) {
	// failed to find closing brace, abort.
	LOG(ERROR) << "unexpected end of string in '" << src << "', looking for }";
	return false;
	}
	prop_name = std::string(c, end);
	c = end + 1;
	size_t def = prop_name.find(":-");
	if (def < prop_name.size()) {
	def_val = prop_name.substr(def + 2);
	prop_name = prop_name.substr(0, def);
	}
	} else {
	prop_name = c;
	LOG(ERROR) << "using deprecated syntax for specifying property '" << c << "', use ${name} instead";
	c += prop_name.size();
	}

	if (prop_name.empty()) {
	LOG(ERROR) << "invalid zero-length property name in '" << src << "'";
	return false;
	}

	std::string prop_val = android::base::GetProperty(prop_name, "");
	if (prop_val.empty()) {
	if (def_val.empty()) {
	LOG(ERROR) << "property '" << prop_name << "' doesn't exist while expanding '" << src << "'";
	return false;
	}
	prop_val = def_val;
	}

	dst->append(prop_val);
	src_ptr = c;
	}

	return true;
	}

	static std::string init_android_dt_dir() {
	// Use the standard procfs-based path by default
	std::string android_dt_dir = kDefaultAndroidDtDir;
	// The platform may specify a custom Android DT path in kernel cmdline
	import_kernel_cmdline(false,
	[&](const std::string& key, const std::string& value, bool in_qemu) {
	if (key == "androidboot.android_dt_dir") {
	android_dt_dir = value;
	}
	});
	LOG(INFO) << "Using Android DT directory " << android_dt_dir;
	return android_dt_dir;
	}

	// FIXME: The same logic is duplicated in system/core/fs_mgr/
	const std::string& get_android_dt_dir() {
	// Set once and saves time for subsequent calls to this function
	static const std::string kAndroidDtDir = init_android_dt_dir();
	return kAndroidDtDir;
	}

	// Reads the content of device tree file under the platform's Android DT directory.
	// Returns true if the read is success, false otherwise.
	bool read_android_dt_file(const std::string& sub_path, std::string* dt_content) {
	const std::string file_name = get_android_dt_dir() + sub_path;
	if (android::base::ReadFileToString(file_name, dt_content)) {
	if (!dt_content->empty()) {
	dt_content->pop_back(); // Trims the trailing '\0' out.
	return true;
	}
	}
	return false;
	}

	bool is_android_dt_value_expected(const std::string& sub_path, const std::string& expected_content) {
	std::string dt_content;
	if (read_android_dt_file(sub_path, &dt_content)) {
	if (dt_content == expected_content) {
	return true;
	}
	}
	return false;
	}

	bool IsLegalPropertyName(const std::string& name) {
	size_t namelen = name.size();

	if (namelen < 1) return false;
	if (name[0] == '.') return false;
	if (name[namelen - 1] == '.') return false;

	/* Only allow alphanumeric, plus '.', '-', '@', ':', or '_' */
	/* Don't allow ".." to appear in a property name */
	for (size_t i = 0; i < namelen; i++) {
	if (name[i] == '.') {
	// i=0 is guaranteed to never have a dot. See above.
	if (name[i - 1] == '.') return false;
	continue;
	}
	if (name[i] == '_' \|\| name[i] == '-' \|\| name[i] == '@' \|\| name[i] == ':') continue;
	if (name[i] >= 'a' && name[i] <= 'z') continue;
	if (name[i] >= 'A' && name[i] <= 'Z') continue;
	if (name[i] >= '0' && name[i] <= '9') continue;
	return false;
	}

	return true;
	}

	static void InitAborter(const char* abort_message) {
	// When init forks, it continues to use this aborter for LOG(FATAL), but we want children to
	// simply abort instead of trying to reboot the system.
	if (getpid() != 1) {
	android::base::DefaultAborter(abort_message);
	return;
	}

	InitFatalReboot();
	}

	// The kernel opens /dev/console and uses that fd for stdin/stdout/stderr if there is a serial
	// console enabled and no initramfs, otherwise it does not provide any fds for stdin/stdout/stderr.
	// SetStdioToDevNull() is used to close these existing fds if they exist and replace them with
	// /dev/null regardless.
	//
	// In the case that these fds are provided by the kernel, the exec of second stage init causes an
	// SELinux denial as it does not have access to /dev/console. In the case that they are not
	// provided, exec of any further process is potentially dangerous as the first fd's opened by that
	// process will take the stdin/stdout/stderr fileno's, which can cause issues if printf(), etc is
	// then used by that process.
	//
	// Lastly, simply calling SetStdioToDevNull() in first stage init is not enough, since first
	// stage init still runs in kernel context, future child processes will not have permissions to
	// access any fds that it opens, including the one opened below for /dev/null. Therefore,
	// SetStdioToDevNull() must be called again in second stage init.
	void SetStdioToDevNull(char** argv) {
	// Make stdin/stdout/stderr all point to /dev/null.
	int fd = open("/dev/null", O_RDWR);
	if (fd == -1) {
	int saved_errno = errno;
	android::base::InitLogging(argv, &android::base::KernelLogger, InitAborter);
	errno = saved_errno;
	PLOG(FATAL) << "Couldn't open /dev/null";
	}
	dup2(fd, STDIN_FILENO);
	dup2(fd, STDOUT_FILENO);
	dup2(fd, STDERR_FILENO);
	if (fd > STDERR_FILENO) close(fd);
	}

	void InitKernelLogging(char** argv) {
	SetFatalRebootTarget();
	android::base::InitLogging(argv, &android::base::KernelLogger, InitAborter);
	}

	bool IsRecoveryMode() {
	return access("/system/bin/recovery", F_OK) == 0;
	}

	} // namespace init
	} // namespace android