init/selinux.cpp - platform/system/core - Gitiles

 /*
  * Copyright (C) 2017 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.
  */

 // This file contains the functions that initialize SELinux during boot as well as helper functions
 // for SELinux operation for init.

 // When the system boots, there is no SEPolicy present and init is running in the kernel domain.
 // Init loads the SEPolicy from the file system, restores the context of /init based on this
 // SEPolicy, and finally exec()'s itself to run in the proper domain.

 // The SEPolicy on Android comes in two variants: monolithic and split.

 // The monolithic policy variant is for legacy non-treble devices that contain a single SEPolicy
 // file located at /sepolicy and is directly loaded into the kernel SELinux subsystem.

 // The split policy is for supporting treble devices.  It splits the SEPolicy across files on
 // /system/etc/selinux (the 'plat' portion of the policy) and /vendor/etc/selinux (the 'nonplat'
 // portion of the policy).  This is necessary to allow the system image to be updated independently
 // of the vendor image, while maintaining contributions from both partitions in the SEPolicy.  This
 // is especially important for VTS testing, where the SEPolicy on the Google System Image may not be
 // identical to the system image shipped on a vendor's device.

 // The split SEPolicy is loaded as described below:
 // 1) There is a precompiled SEPolicy located at /vendor/etc/selinux/precompiled_sepolicy.
 //    Stored along with this file is the sha256 hash of the parts of the SEPolicy on /system that
 //    were used to compile this precompiled policy.  The system partition contains a similar sha256
 //    of the parts of the SEPolicy that it currently contains.  If these two hashes match, then the
 //    system loads this precompiled_sepolicy directly.
 // 2) If these hashes do not match, then /system has been updated out of sync with /vendor and the
 //    init needs to compile the SEPolicy.  /system contains the SEPolicy compiler, secilc, and it
 //    is used by the LoadSplitPolicy() function below to compile the SEPolicy to a temp directory
 //    and load it.  That function contains even more documentation with the specific implementation
 //    details of how the SEPolicy is compiled if needed.

 #include "selinux.h"

 #include <fcntl.h>
 #include <stdlib.h>
 #include <sys/wait.h>
 #include <unistd.h>

 #include <android-base/chrono_utils.h>
 #include <android-base/file.h>
 #include <android-base/logging.h>
 #include <android-base/unique_fd.h>
 #include <selinux/android.h>

 #include "log.h"
 #include "util.h"

 using android::base::Timer;
 using android::base::unique_fd;

 namespace android {
 namespace init {

 namespace {

 selabel_handle* sehandle = nullptr;

 enum EnforcingStatus { SELINUX_PERMISSIVE, SELINUX_ENFORCING };

 EnforcingStatus StatusFromCmdline() {
     EnforcingStatus status = SELINUX_ENFORCING;

     import_kernel_cmdline(false,
                           [&](const std::string& key, const std::string& value, bool in_qemu) {
                               if (key == "androidboot.selinux" && value == "permissive") {
                                   status = SELINUX_PERMISSIVE;
                               }
                           });

     return status;
 }

 bool IsEnforcing() {
     if (ALLOW_PERMISSIVE_SELINUX) {
         return StatusFromCmdline() == SELINUX_ENFORCING;
     }
     return true;
 }

 // Forks, executes the provided program in the child, and waits for the completion in the parent.
 // Child's stderr is captured and logged using LOG(ERROR).
 bool ForkExecveAndWaitForCompletion(const char* filename, char* const argv[]) {
     // Create a pipe used for redirecting child process's output.
     // * pipe_fds[0] is the FD the parent will use for reading.
     // * pipe_fds[1] is the FD the child will use for writing.
     int pipe_fds[2];
     if (pipe(pipe_fds) == -1) {
         PLOG(ERROR) << "Failed to create pipe";
         return false;
     }

     pid_t child_pid = fork();
     if (child_pid == -1) {
         PLOG(ERROR) << "Failed to fork for " << filename;
         return false;
     }

     if (child_pid == 0) {
         // fork succeeded -- this is executing in the child process

         // Close the pipe FD not used by this process
         TEMP_FAILURE_RETRY(close(pipe_fds[0]));

         // Redirect stderr to the pipe FD provided by the parent
         if (TEMP_FAILURE_RETRY(dup2(pipe_fds[1], STDERR_FILENO)) == -1) {
             PLOG(ERROR) << "Failed to redirect stderr of " << filename;
             _exit(127);
             return false;
         }
         TEMP_FAILURE_RETRY(close(pipe_fds[1]));

         if (execv(filename, argv) == -1) {
             PLOG(ERROR) << "Failed to execve " << filename;
             return false;
         }
         // Unreachable because execve will have succeeded and replaced this code
         // with child process's code.
         _exit(127);
         return false;
     } else {
         // fork succeeded -- this is executing in the original/parent process

         // Close the pipe FD not used by this process
         TEMP_FAILURE_RETRY(close(pipe_fds[1]));

         // Log the redirected output of the child process.
         // It's unfortunate that there's no standard way to obtain an istream for a file descriptor.
         // As a result, we're buffering all output and logging it in one go at the end of the
         // invocation, instead of logging it as it comes in.
         const int child_out_fd = pipe_fds[0];
         std::string child_output;
         if (!android::base::ReadFdToString(child_out_fd, &child_output)) {
             PLOG(ERROR) << "Failed to capture full output of " << filename;
         }
         TEMP_FAILURE_RETRY(close(child_out_fd));
         if (!child_output.empty()) {
             // Log captured output, line by line, because LOG expects to be invoked for each line
             std::istringstream in(child_output);
             std::string line;
             while (std::getline(in, line)) {
                 LOG(ERROR) << filename << ": " << line;
             }
         }

         // Wait for child to terminate
         int status;
         if (TEMP_FAILURE_RETRY(waitpid(child_pid, &status, 0)) != child_pid) {
             PLOG(ERROR) << "Failed to wait for " << filename;
             return false;
         }

         if (WIFEXITED(status)) {
             int status_code = WEXITSTATUS(status);
             if (status_code == 0) {
                 return true;
             } else {
                 LOG(ERROR) << filename << " exited with status " << status_code;
             }
         } else if (WIFSIGNALED(status)) {
             LOG(ERROR) << filename << " killed by signal " << WTERMSIG(status);
         } else if (WIFSTOPPED(status)) {
             LOG(ERROR) << filename << " stopped by signal " << WSTOPSIG(status);
         } else {
             LOG(ERROR) << "waitpid for " << filename << " returned unexpected status: " << status;
         }

         return false;
     }
 }

 bool ReadFirstLine(const char* file, std::string* line) {
     line->clear();

     std::string contents;
     if (!android::base::ReadFileToString(file, &contents, true /* follow symlinks */)) {
         return false;
     }
     std::istringstream in(contents);
     std::getline(in, *line);
     return true;
 }

 bool FindPrecompiledSplitPolicy(std::string* file) {
     file->clear();
     // If there is an odm partition, precompiled_sepolicy will be in
     // odm/etc/selinux. Otherwise it will be in vendor/etc/selinux.
     static constexpr const char vendor_precompiled_sepolicy[] =
         "/vendor/etc/selinux/precompiled_sepolicy";
     static constexpr const char odm_precompiled_sepolicy[] =
         "/odm/etc/selinux/precompiled_sepolicy";
     if (access(odm_precompiled_sepolicy, R_OK) == 0) {
         *file = odm_precompiled_sepolicy;
     } else if (access(vendor_precompiled_sepolicy, R_OK) == 0) {
         *file = vendor_precompiled_sepolicy;
     } else {
         PLOG(INFO) << "No precompiled sepolicy";
         return false;
     }
     std::string actual_plat_id;
     if (!ReadFirstLine("/system/etc/selinux/plat_and_mapping_sepolicy.cil.sha256", &actual_plat_id)) {
         PLOG(INFO) << "Failed to read "
                       "/system/etc/selinux/plat_and_mapping_sepolicy.cil.sha256";
         return false;
     }

     std::string precompiled_plat_id;
     std::string precompiled_sha256 = *file + ".plat_and_mapping.sha256";
     if (!ReadFirstLine(precompiled_sha256.c_str(), &precompiled_plat_id)) {
         PLOG(INFO) << "Failed to read " << precompiled_sha256;
         file->clear();
         return false;
     }
     if ((actual_plat_id.empty()) || (actual_plat_id != precompiled_plat_id)) {
         file->clear();
         return false;
     }
     return true;
 }

 bool GetVendorMappingVersion(std::string* plat_vers) {
     if (!ReadFirstLine("/vendor/etc/selinux/plat_sepolicy_vers.txt", plat_vers)) {
         PLOG(ERROR) << "Failed to read /vendor/etc/selinux/plat_sepolicy_vers.txt";
         return false;
     }
     if (plat_vers->empty()) {
         LOG(ERROR) << "No version present in plat_sepolicy_vers.txt";
         return false;
     }
     return true;
 }

 constexpr const char plat_policy_cil_file[] = "/system/etc/selinux/plat_sepolicy.cil";

 bool IsSplitPolicyDevice() {
     return access(plat_policy_cil_file, R_OK) != -1;
 }

 bool LoadSplitPolicy() {
     // IMPLEMENTATION NOTE: Split policy consists of three CIL files:
     // * platform -- policy needed due to logic contained in the system image,
     // * non-platform -- policy needed due to logic contained in the vendor image,
     // * mapping -- mapping policy which helps preserve forward-compatibility of non-platform policy
     //   with newer versions of platform policy.
     //
     // secilc is invoked to compile the above three policy files into a single monolithic policy
     // file. This file is then loaded into the kernel.

     // Load precompiled policy from vendor image, if a matching policy is found there. The policy
     // must match the platform policy on the system image.
     std::string precompiled_sepolicy_file;
     if (FindPrecompiledSplitPolicy(&precompiled_sepolicy_file)) {
         unique_fd fd(open(precompiled_sepolicy_file.c_str(), O_RDONLY | O_CLOEXEC | O_BINARY));
         if (fd != -1) {
             if (selinux_android_load_policy_from_fd(fd, precompiled_sepolicy_file.c_str()) < 0) {
                 LOG(ERROR) << "Failed to load SELinux policy from " << precompiled_sepolicy_file;
                 return false;
             }
             return true;
         }
     }
     // No suitable precompiled policy could be loaded

     LOG(INFO) << "Compiling SELinux policy";

     // Determine the highest policy language version supported by the kernel
     set_selinuxmnt("/sys/fs/selinux");
     int max_policy_version = security_policyvers();
     if (max_policy_version == -1) {
         PLOG(ERROR) << "Failed to determine highest policy version supported by kernel";
         return false;
     }

     // We store the output of the compilation on /dev because this is the most convenient tmpfs
     // storage mount available this early in the boot sequence.
     char compiled_sepolicy[] = "/dev/sepolicy.XXXXXX";
     unique_fd compiled_sepolicy_fd(mkostemp(compiled_sepolicy, O_CLOEXEC));
     if (compiled_sepolicy_fd < 0) {
         PLOG(ERROR) << "Failed to create temporary file " << compiled_sepolicy;
         return false;
     }

     // Determine which mapping file to include
     std::string vend_plat_vers;
     if (!GetVendorMappingVersion(&vend_plat_vers)) {
         return false;
     }
     std::string mapping_file("/system/etc/selinux/mapping/" + vend_plat_vers + ".cil");

     // vendor_sepolicy.cil and nonplat_declaration.cil are the new design to replace
     // nonplat_sepolicy.cil.
     std::string nonplat_declaration_cil_file("/vendor/etc/selinux/nonplat_declaration.cil");
     std::string vendor_policy_cil_file("/vendor/etc/selinux/vendor_sepolicy.cil");

     if (access(vendor_policy_cil_file.c_str(), F_OK) == -1) {
         // For backward compatibility.
         // TODO: remove this after no device is using nonplat_sepolicy.cil.
         vendor_policy_cil_file = "/vendor/etc/selinux/nonplat_sepolicy.cil";
         nonplat_declaration_cil_file.clear();
     } else if (access(nonplat_declaration_cil_file.c_str(), F_OK) == -1) {
         LOG(ERROR) << "Missing " << nonplat_declaration_cil_file;
         return false;
     }

     // odm_sepolicy.cil is default but optional.
     std::string odm_policy_cil_file("/odm/etc/selinux/odm_sepolicy.cil");
     if (access(odm_policy_cil_file.c_str(), F_OK) == -1) {
         odm_policy_cil_file.clear();
     }
     const std::string version_as_string = std::to_string(max_policy_version);

     // clang-format off
     std::vector<const char*> compile_args {
         "/system/bin/secilc",
         plat_policy_cil_file,
         "-m", "-M", "true", "-G", "-N",
         // Target the highest policy language version supported by the kernel
         "-c", version_as_string.c_str(),
         mapping_file.c_str(),
         "-o", compiled_sepolicy,
         // We don't care about file_contexts output by the compiler
         "-f", "/sys/fs/selinux/null",  // /dev/null is not yet available
     };
     // clang-format on

     if (!nonplat_declaration_cil_file.empty()) {
         compile_args.push_back(nonplat_declaration_cil_file.c_str());
     }
     if (!vendor_policy_cil_file.empty()) {
         compile_args.push_back(vendor_policy_cil_file.c_str());
     }
     if (!odm_policy_cil_file.empty()) {
         compile_args.push_back(odm_policy_cil_file.c_str());
     }
     compile_args.push_back(nullptr);

     if (!ForkExecveAndWaitForCompletion(compile_args[0], (char**)compile_args.data())) {
         unlink(compiled_sepolicy);
         return false;
     }
     unlink(compiled_sepolicy);

     LOG(INFO) << "Loading compiled SELinux policy";
     if (selinux_android_load_policy_from_fd(compiled_sepolicy_fd, compiled_sepolicy) < 0) {
         LOG(ERROR) << "Failed to load SELinux policy from " << compiled_sepolicy;
         return false;
     }

     return true;
 }

 bool LoadMonolithicPolicy() {
     LOG(VERBOSE) << "Loading SELinux policy from monolithic file";
     if (selinux_android_load_policy() < 0) {
         PLOG(ERROR) << "Failed to load monolithic SELinux policy";
         return false;
     }
     return true;
 }

 bool LoadPolicy() {
     return IsSplitPolicyDevice() ? LoadSplitPolicy() : LoadMonolithicPolicy();
 }

 }  // namespace

 void SelinuxInitialize() {
     Timer t;

     LOG(INFO) << "Loading SELinux policy";
     if (!LoadPolicy()) {
         LOG(FATAL) << "Unable to load SELinux policy";
     }

     bool kernel_enforcing = (security_getenforce() == 1);
     bool is_enforcing = IsEnforcing();
     if (kernel_enforcing != is_enforcing) {
         if (security_setenforce(is_enforcing)) {
             PLOG(FATAL) << "security_setenforce(%s) failed" << (is_enforcing ? "true" : "false");
         }
     }

     if (auto result = WriteFile("/sys/fs/selinux/checkreqprot", "0"); !result) {
         LOG(FATAL) << "Unable to write to /sys/fs/selinux/checkreqprot: " << result.error();
     }

     // init's first stage can't set properties, so pass the time to the second stage.
     setenv("INIT_SELINUX_TOOK", std::to_string(t.duration().count()).c_str(), 1);
 }

 // The files and directories that were created before initial sepolicy load or
 // files on ramdisk need to have their security context restored to the proper
 // value. This must happen before /dev is populated by ueventd.
 void SelinuxRestoreContext() {
     LOG(INFO) << "Running restorecon...";
     selinux_android_restorecon("/dev", 0);
     selinux_android_restorecon("/dev/kmsg", 0);
     if constexpr (WORLD_WRITABLE_KMSG) {
         selinux_android_restorecon("/dev/kmsg_debug", 0);
     }
     selinux_android_restorecon("/dev/socket", 0);
     selinux_android_restorecon("/dev/random", 0);
     selinux_android_restorecon("/dev/urandom", 0);
     selinux_android_restorecon("/dev/__properties__", 0);

     selinux_android_restorecon("/plat_file_contexts", 0);
     selinux_android_restorecon("/nonplat_file_contexts", 0);
     selinux_android_restorecon("/plat_property_contexts", 0);
     selinux_android_restorecon("/nonplat_property_contexts", 0);
     selinux_android_restorecon("/plat_seapp_contexts", 0);
     selinux_android_restorecon("/nonplat_seapp_contexts", 0);
     selinux_android_restorecon("/plat_service_contexts", 0);
     selinux_android_restorecon("/nonplat_service_contexts", 0);
     selinux_android_restorecon("/plat_hwservice_contexts", 0);
     selinux_android_restorecon("/nonplat_hwservice_contexts", 0);
     selinux_android_restorecon("/sepolicy", 0);
     selinux_android_restorecon("/vndservice_contexts", 0);

     selinux_android_restorecon("/dev/block", SELINUX_ANDROID_RESTORECON_RECURSE);
     selinux_android_restorecon("/dev/device-mapper", 0);

     selinux_android_restorecon("/sbin/mke2fs_static", 0);
     selinux_android_restorecon("/sbin/e2fsdroid_static", 0);
 }

 // This function sets up SELinux logging to be written to kmsg, to match init's logging.
 void SelinuxSetupKernelLogging() {
     selinux_callback cb;
     cb.func_log = selinux_klog_callback;
     selinux_set_callback(SELINUX_CB_LOG, cb);
 }

 // selinux_android_file_context_handle() takes on the order of 10+ms to run, so we want to cache
 // its value.  selinux_android_restorecon() also needs an sehandle for file context look up.  It
 // will create and store its own copy, but selinux_android_set_sehandle() can be used to provide
 // one, thus eliminating an extra call to selinux_android_file_context_handle().
 void SelabelInitialize() {
     sehandle = selinux_android_file_context_handle();
     selinux_android_set_sehandle(sehandle);
 }

 // A C++ wrapper around selabel_lookup() using the cached sehandle.
 // If sehandle is null, this returns success with an empty context.
 bool SelabelLookupFileContext(const std::string& key, int type, std::string* result) {
     result->clear();

     if (!sehandle) return true;

     char* context;
     if (selabel_lookup(sehandle, &context, key.c_str(), type) != 0) {
         return false;
     }
     *result = context;
     free(context);
     return true;
 }

 // A C++ wrapper around selabel_lookup_best_match() using the cached sehandle.
 // If sehandle is null, this returns success with an empty context.
 bool SelabelLookupFileContextBestMatch(const std::string& key,
                                        const std::vector<std::string>& aliases, int type,
                                        std::string* result) {
     result->clear();

     if (!sehandle) return true;

     std::vector<const char*> c_aliases;
     for (const auto& alias : aliases) {
         c_aliases.emplace_back(alias.c_str());
     }
     c_aliases.emplace_back(nullptr);

     char* context;
     if (selabel_lookup_best_match(sehandle, &context, key.c_str(), &c_aliases[0], type) != 0) {
         return false;
     }
     *result = context;
     free(context);
     return true;
 }

 }  // namespace init
 }  // namespace android
	/*
	* Copyright (C) 2017 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.
	*/

	// This file contains the functions that initialize SELinux during boot as well as helper functions
	// for SELinux operation for init.

	// When the system boots, there is no SEPolicy present and init is running in the kernel domain.
	// Init loads the SEPolicy from the file system, restores the context of /init based on this
	// SEPolicy, and finally exec()'s itself to run in the proper domain.

	// The SEPolicy on Android comes in two variants: monolithic and split.

	// The monolithic policy variant is for legacy non-treble devices that contain a single SEPolicy
	// file located at /sepolicy and is directly loaded into the kernel SELinux subsystem.

	// The split policy is for supporting treble devices. It splits the SEPolicy across files on
	// /system/etc/selinux (the 'plat' portion of the policy) and /vendor/etc/selinux (the 'nonplat'
	// portion of the policy). This is necessary to allow the system image to be updated independently
	// of the vendor image, while maintaining contributions from both partitions in the SEPolicy. This
	// is especially important for VTS testing, where the SEPolicy on the Google System Image may not be
	// identical to the system image shipped on a vendor's device.

	// The split SEPolicy is loaded as described below:
	// 1) There is a precompiled SEPolicy located at /vendor/etc/selinux/precompiled_sepolicy.
	// Stored along with this file is the sha256 hash of the parts of the SEPolicy on /system that
	// were used to compile this precompiled policy. The system partition contains a similar sha256
	// of the parts of the SEPolicy that it currently contains. If these two hashes match, then the
	// system loads this precompiled_sepolicy directly.
	// 2) If these hashes do not match, then /system has been updated out of sync with /vendor and the
	// init needs to compile the SEPolicy. /system contains the SEPolicy compiler, secilc, and it
	// is used by the LoadSplitPolicy() function below to compile the SEPolicy to a temp directory
	// and load it. That function contains even more documentation with the specific implementation
	// details of how the SEPolicy is compiled if needed.

	#include "selinux.h"

	#include <fcntl.h>
	#include <stdlib.h>
	#include <sys/wait.h>
	#include <unistd.h>

	#include <android-base/chrono_utils.h>
	#include <android-base/file.h>
	#include <android-base/logging.h>
	#include <android-base/unique_fd.h>
	#include <selinux/android.h>

	#include "log.h"
	#include "util.h"

	using android::base::Timer;
	using android::base::unique_fd;

	namespace android {
	namespace init {

	namespace {

	selabel_handle* sehandle = nullptr;

	enum EnforcingStatus { SELINUX_PERMISSIVE, SELINUX_ENFORCING };

	EnforcingStatus StatusFromCmdline() {
	EnforcingStatus status = SELINUX_ENFORCING;

	import_kernel_cmdline(false,
	[&](const std::string& key, const std::string& value, bool in_qemu) {
	if (key == "androidboot.selinux" && value == "permissive") {
	status = SELINUX_PERMISSIVE;
	}
	});

	return status;
	}

	bool IsEnforcing() {
	if (ALLOW_PERMISSIVE_SELINUX) {
	return StatusFromCmdline() == SELINUX_ENFORCING;
	}
	return true;
	}

	// Forks, executes the provided program in the child, and waits for the completion in the parent.
	// Child's stderr is captured and logged using LOG(ERROR).
	bool ForkExecveAndWaitForCompletion(const char* filename, char* const argv[]) {
	// Create a pipe used for redirecting child process's output.
	// * pipe_fds[0] is the FD the parent will use for reading.
	// * pipe_fds[1] is the FD the child will use for writing.
	int pipe_fds[2];
	if (pipe(pipe_fds) == -1) {
	PLOG(ERROR) << "Failed to create pipe";
	return false;
	}

	pid_t child_pid = fork();
	if (child_pid == -1) {
	PLOG(ERROR) << "Failed to fork for " << filename;
	return false;
	}

	if (child_pid == 0) {
	// fork succeeded -- this is executing in the child process

	// Close the pipe FD not used by this process
	TEMP_FAILURE_RETRY(close(pipe_fds[0]));

	// Redirect stderr to the pipe FD provided by the parent
	if (TEMP_FAILURE_RETRY(dup2(pipe_fds[1], STDERR_FILENO)) == -1) {
	PLOG(ERROR) << "Failed to redirect stderr of " << filename;
	_exit(127);
	return false;
	}
	TEMP_FAILURE_RETRY(close(pipe_fds[1]));

	if (execv(filename, argv) == -1) {
	PLOG(ERROR) << "Failed to execve " << filename;
	return false;
	}
	// Unreachable because execve will have succeeded and replaced this code
	// with child process's code.
	_exit(127);
	return false;
	} else {
	// fork succeeded -- this is executing in the original/parent process

	// Close the pipe FD not used by this process
	TEMP_FAILURE_RETRY(close(pipe_fds[1]));

	// Log the redirected output of the child process.
	// It's unfortunate that there's no standard way to obtain an istream for a file descriptor.
	// As a result, we're buffering all output and logging it in one go at the end of the
	// invocation, instead of logging it as it comes in.
	const int child_out_fd = pipe_fds[0];
	std::string child_output;
	if (!android::base::ReadFdToString(child_out_fd, &child_output)) {
	PLOG(ERROR) << "Failed to capture full output of " << filename;
	}
	TEMP_FAILURE_RETRY(close(child_out_fd));
	if (!child_output.empty()) {
	// Log captured output, line by line, because LOG expects to be invoked for each line
	std::istringstream in(child_output);
	std::string line;
	while (std::getline(in, line)) {
	LOG(ERROR) << filename << ": " << line;
	}
	}

	// Wait for child to terminate
	int status;
	if (TEMP_FAILURE_RETRY(waitpid(child_pid, &status, 0)) != child_pid) {
	PLOG(ERROR) << "Failed to wait for " << filename;
	return false;
	}

	if (WIFEXITED(status)) {
	int status_code = WEXITSTATUS(status);
	if (status_code == 0) {
	return true;
	} else {
	LOG(ERROR) << filename << " exited with status " << status_code;
	}
	} else if (WIFSIGNALED(status)) {
	LOG(ERROR) << filename << " killed by signal " << WTERMSIG(status);
	} else if (WIFSTOPPED(status)) {
	LOG(ERROR) << filename << " stopped by signal " << WSTOPSIG(status);
	} else {
	LOG(ERROR) << "waitpid for " << filename << " returned unexpected status: " << status;
	}

	return false;
	}
	}

	bool ReadFirstLine(const char* file, std::string* line) {
	line->clear();

	std::string contents;
	if (!android::base::ReadFileToString(file, &contents, true /* follow symlinks */)) {
	return false;
	}
	std::istringstream in(contents);
	std::getline(in, *line);
	return true;
	}

	bool FindPrecompiledSplitPolicy(std::string* file) {
	file->clear();
	// If there is an odm partition, precompiled_sepolicy will be in
	// odm/etc/selinux. Otherwise it will be in vendor/etc/selinux.
	static constexpr const char vendor_precompiled_sepolicy[] =
	"/vendor/etc/selinux/precompiled_sepolicy";
	static constexpr const char odm_precompiled_sepolicy[] =
	"/odm/etc/selinux/precompiled_sepolicy";
	if (access(odm_precompiled_sepolicy, R_OK) == 0) {
	*file = odm_precompiled_sepolicy;
	} else if (access(vendor_precompiled_sepolicy, R_OK) == 0) {
	*file = vendor_precompiled_sepolicy;
	} else {
	PLOG(INFO) << "No precompiled sepolicy";
	return false;
	}
	std::string actual_plat_id;
	if (!ReadFirstLine("/system/etc/selinux/plat_and_mapping_sepolicy.cil.sha256", &actual_plat_id)) {
	PLOG(INFO) << "Failed to read "
	"/system/etc/selinux/plat_and_mapping_sepolicy.cil.sha256";
	return false;
	}

	std::string precompiled_plat_id;
	std::string precompiled_sha256 = *file + ".plat_and_mapping.sha256";
	if (!ReadFirstLine(precompiled_sha256.c_str(), &precompiled_plat_id)) {
	PLOG(INFO) << "Failed to read " << precompiled_sha256;
	file->clear();
	return false;
	}
	if ((actual_plat_id.empty()) \|\| (actual_plat_id != precompiled_plat_id)) {
	file->clear();
	return false;
	}
	return true;
	}

	bool GetVendorMappingVersion(std::string* plat_vers) {
	if (!ReadFirstLine("/vendor/etc/selinux/plat_sepolicy_vers.txt", plat_vers)) {
	PLOG(ERROR) << "Failed to read /vendor/etc/selinux/plat_sepolicy_vers.txt";
	return false;
	}
	if (plat_vers->empty()) {
	LOG(ERROR) << "No version present in plat_sepolicy_vers.txt";
	return false;
	}
	return true;
	}

	constexpr const char plat_policy_cil_file[] = "/system/etc/selinux/plat_sepolicy.cil";

	bool IsSplitPolicyDevice() {
	return access(plat_policy_cil_file, R_OK) != -1;
	}

	bool LoadSplitPolicy() {
	// IMPLEMENTATION NOTE: Split policy consists of three CIL files:
	// * platform -- policy needed due to logic contained in the system image,
	// * non-platform -- policy needed due to logic contained in the vendor image,
	// * mapping -- mapping policy which helps preserve forward-compatibility of non-platform policy
	// with newer versions of platform policy.
	//
	// secilc is invoked to compile the above three policy files into a single monolithic policy
	// file. This file is then loaded into the kernel.

	// Load precompiled policy from vendor image, if a matching policy is found there. The policy
	// must match the platform policy on the system image.
	std::string precompiled_sepolicy_file;
	if (FindPrecompiledSplitPolicy(&precompiled_sepolicy_file)) {
	unique_fd fd(open(precompiled_sepolicy_file.c_str(), O_RDONLY \| O_CLOEXEC \| O_BINARY));
	if (fd != -1) {
	if (selinux_android_load_policy_from_fd(fd, precompiled_sepolicy_file.c_str()) < 0) {
	LOG(ERROR) << "Failed to load SELinux policy from " << precompiled_sepolicy_file;
	return false;
	}
	return true;
	}
	}
	// No suitable precompiled policy could be loaded

	LOG(INFO) << "Compiling SELinux policy";

	// Determine the highest policy language version supported by the kernel
	set_selinuxmnt("/sys/fs/selinux");
	int max_policy_version = security_policyvers();
	if (max_policy_version == -1) {
	PLOG(ERROR) << "Failed to determine highest policy version supported by kernel";
	return false;
	}

	// We store the output of the compilation on /dev because this is the most convenient tmpfs
	// storage mount available this early in the boot sequence.
	char compiled_sepolicy[] = "/dev/sepolicy.XXXXXX";
	unique_fd compiled_sepolicy_fd(mkostemp(compiled_sepolicy, O_CLOEXEC));
	if (compiled_sepolicy_fd < 0) {
	PLOG(ERROR) << "Failed to create temporary file " << compiled_sepolicy;
	return false;
	}

	// Determine which mapping file to include
	std::string vend_plat_vers;
	if (!GetVendorMappingVersion(&vend_plat_vers)) {
	return false;
	}
	std::string mapping_file("/system/etc/selinux/mapping/" + vend_plat_vers + ".cil");

	// vendor_sepolicy.cil and nonplat_declaration.cil are the new design to replace
	// nonplat_sepolicy.cil.
	std::string nonplat_declaration_cil_file("/vendor/etc/selinux/nonplat_declaration.cil");
	std::string vendor_policy_cil_file("/vendor/etc/selinux/vendor_sepolicy.cil");

	if (access(vendor_policy_cil_file.c_str(), F_OK) == -1) {
	// For backward compatibility.
	// TODO: remove this after no device is using nonplat_sepolicy.cil.
	vendor_policy_cil_file = "/vendor/etc/selinux/nonplat_sepolicy.cil";
	nonplat_declaration_cil_file.clear();
	} else if (access(nonplat_declaration_cil_file.c_str(), F_OK) == -1) {
	LOG(ERROR) << "Missing " << nonplat_declaration_cil_file;
	return false;
	}

	// odm_sepolicy.cil is default but optional.
	std::string odm_policy_cil_file("/odm/etc/selinux/odm_sepolicy.cil");
	if (access(odm_policy_cil_file.c_str(), F_OK) == -1) {
	odm_policy_cil_file.clear();
	}
	const std::string version_as_string = std::to_string(max_policy_version);

	// clang-format off
	std::vector<const char*> compile_args {
	"/system/bin/secilc",
	plat_policy_cil_file,
	"-m", "-M", "true", "-G", "-N",
	// Target the highest policy language version supported by the kernel
	"-c", version_as_string.c_str(),
	mapping_file.c_str(),
	"-o", compiled_sepolicy,
	// We don't care about file_contexts output by the compiler
	"-f", "/sys/fs/selinux/null", // /dev/null is not yet available
	};
	// clang-format on

	if (!nonplat_declaration_cil_file.empty()) {
	compile_args.push_back(nonplat_declaration_cil_file.c_str());
	}
	if (!vendor_policy_cil_file.empty()) {
	compile_args.push_back(vendor_policy_cil_file.c_str());
	}
	if (!odm_policy_cil_file.empty()) {
	compile_args.push_back(odm_policy_cil_file.c_str());
	}
	compile_args.push_back(nullptr);

	if (!ForkExecveAndWaitForCompletion(compile_args[0], (char**)compile_args.data())) {
	unlink(compiled_sepolicy);
	return false;
	}
	unlink(compiled_sepolicy);

	LOG(INFO) << "Loading compiled SELinux policy";
	if (selinux_android_load_policy_from_fd(compiled_sepolicy_fd, compiled_sepolicy) < 0) {
	LOG(ERROR) << "Failed to load SELinux policy from " << compiled_sepolicy;
	return false;
	}

	return true;
	}

	bool LoadMonolithicPolicy() {
	LOG(VERBOSE) << "Loading SELinux policy from monolithic file";
	if (selinux_android_load_policy() < 0) {
	PLOG(ERROR) << "Failed to load monolithic SELinux policy";
	return false;
	}
	return true;
	}

	bool LoadPolicy() {
	return IsSplitPolicyDevice() ? LoadSplitPolicy() : LoadMonolithicPolicy();
	}

	} // namespace

	void SelinuxInitialize() {
	Timer t;

	LOG(INFO) << "Loading SELinux policy";
	if (!LoadPolicy()) {
	LOG(FATAL) << "Unable to load SELinux policy";
	}

	bool kernel_enforcing = (security_getenforce() == 1);
	bool is_enforcing = IsEnforcing();
	if (kernel_enforcing != is_enforcing) {
	if (security_setenforce(is_enforcing)) {
	PLOG(FATAL) << "security_setenforce(%s) failed" << (is_enforcing ? "true" : "false");
	}
	}

	if (auto result = WriteFile("/sys/fs/selinux/checkreqprot", "0"); !result) {
	LOG(FATAL) << "Unable to write to /sys/fs/selinux/checkreqprot: " << result.error();
	}

	// init's first stage can't set properties, so pass the time to the second stage.
	setenv("INIT_SELINUX_TOOK", std::to_string(t.duration().count()).c_str(), 1);
	}

	// The files and directories that were created before initial sepolicy load or
	// files on ramdisk need to have their security context restored to the proper
	// value. This must happen before /dev is populated by ueventd.
	void SelinuxRestoreContext() {
	LOG(INFO) << "Running restorecon...";
	selinux_android_restorecon("/dev", 0);
	selinux_android_restorecon("/dev/kmsg", 0);
	if constexpr (WORLD_WRITABLE_KMSG) {
	selinux_android_restorecon("/dev/kmsg_debug", 0);
	}
	selinux_android_restorecon("/dev/socket", 0);
	selinux_android_restorecon("/dev/random", 0);
	selinux_android_restorecon("/dev/urandom", 0);
	selinux_android_restorecon("/dev/__properties__", 0);

	selinux_android_restorecon("/plat_file_contexts", 0);
	selinux_android_restorecon("/nonplat_file_contexts", 0);
	selinux_android_restorecon("/plat_property_contexts", 0);
	selinux_android_restorecon("/nonplat_property_contexts", 0);
	selinux_android_restorecon("/plat_seapp_contexts", 0);
	selinux_android_restorecon("/nonplat_seapp_contexts", 0);
	selinux_android_restorecon("/plat_service_contexts", 0);
	selinux_android_restorecon("/nonplat_service_contexts", 0);
	selinux_android_restorecon("/plat_hwservice_contexts", 0);
	selinux_android_restorecon("/nonplat_hwservice_contexts", 0);
	selinux_android_restorecon("/sepolicy", 0);
	selinux_android_restorecon("/vndservice_contexts", 0);

	selinux_android_restorecon("/dev/block", SELINUX_ANDROID_RESTORECON_RECURSE);
	selinux_android_restorecon("/dev/device-mapper", 0);

	selinux_android_restorecon("/sbin/mke2fs_static", 0);
	selinux_android_restorecon("/sbin/e2fsdroid_static", 0);
	}

	// This function sets up SELinux logging to be written to kmsg, to match init's logging.
	void SelinuxSetupKernelLogging() {
	selinux_callback cb;
	cb.func_log = selinux_klog_callback;
	selinux_set_callback(SELINUX_CB_LOG, cb);
	}

	// selinux_android_file_context_handle() takes on the order of 10+ms to run, so we want to cache
	// its value. selinux_android_restorecon() also needs an sehandle for file context look up. It
	// will create and store its own copy, but selinux_android_set_sehandle() can be used to provide
	// one, thus eliminating an extra call to selinux_android_file_context_handle().
	void SelabelInitialize() {
	sehandle = selinux_android_file_context_handle();
	selinux_android_set_sehandle(sehandle);
	}

	// A C++ wrapper around selabel_lookup() using the cached sehandle.
	// If sehandle is null, this returns success with an empty context.
	bool SelabelLookupFileContext(const std::string& key, int type, std::string* result) {
	result->clear();

	if (!sehandle) return true;

	char* context;
	if (selabel_lookup(sehandle, &context, key.c_str(), type) != 0) {
	return false;
	}
	*result = context;
	free(context);
	return true;
	}

	// A C++ wrapper around selabel_lookup_best_match() using the cached sehandle.
	// If sehandle is null, this returns success with an empty context.
	bool SelabelLookupFileContextBestMatch(const std::string& key,
	const std::vector<std::string>& aliases, int type,
	std::string* result) {
	result->clear();

	if (!sehandle) return true;

	std::vector<const char*> c_aliases;
	for (const auto& alias : aliases) {
	c_aliases.emplace_back(alias.c_str());
	}
	c_aliases.emplace_back(nullptr);

	char* context;
	if (selabel_lookup_best_match(sehandle, &context, key.c_str(), &c_aliases[0], type) != 0) {
	return false;
	}
	*result = context;
	free(context);
	return true;
	}

	} // namespace init
	} // namespace android