init/subcontext.cpp - android-core - Git at Google

 /*
  * 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.
  */

 #include "subcontext.h"

 #include <fcntl.h>
 #include <poll.h>
 #include <sys/socket.h>
 #include <unistd.h>

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

 #include "action.h"
 #include "selinux.h"
 #include "system/core/init/subcontext.pb.h"
 #include "util.h"

 using android::base::GetBoolProperty;
 using android::base::GetExecutablePath;
 using android::base::Join;
 using android::base::Socketpair;
 using android::base::Split;
 using android::base::StartsWith;
 using android::base::unique_fd;

 namespace android {
 namespace init {

 const std::string kInitContext = "u:r:init:s0";
 const std::string kVendorContext = "u:r:vendor_init:s0";

 namespace {

 constexpr size_t kBufferSize = 4096;

 Result<std::string> ReadMessage(int socket) {
     char buffer[kBufferSize] = {};
     auto result = TEMP_FAILURE_RETRY(recv(socket, buffer, sizeof(buffer), 0));
     if (result <= 0) {
         return ErrnoError();
     }
     return std::string(buffer, result);
 }

 template <typename T>
 Result<Success> SendMessage(int socket, const T& message) {
     std::string message_string;
     if (!message.SerializeToString(&message_string)) {
         return Error() << "Unable to serialize message";
     }

     if (message_string.size() > kBufferSize) {
         return Error() << "Serialized message too long to send";
     }

     if (auto result =
             TEMP_FAILURE_RETRY(send(socket, message_string.c_str(), message_string.size(), 0));
         result != static_cast<long>(message_string.size())) {
         return ErrnoError() << "send() failed to send message contents";
     }
     return Success();
 }

 class SubcontextProcess {
   public:
     SubcontextProcess(const KeywordFunctionMap* function_map, std::string context, int init_fd)
         : function_map_(function_map), context_(std::move(context)), init_fd_(init_fd){};
     void MainLoop();

   private:
     void RunCommand(const SubcontextCommand::ExecuteCommand& execute_command,
                     SubcontextReply::ResultMessage* result_message) const;

     const KeywordFunctionMap* function_map_;
     const std::string context_;
     const int init_fd_;
 };

 void SubcontextProcess::RunCommand(const SubcontextCommand::ExecuteCommand& execute_command,
                                    SubcontextReply::ResultMessage* result_message) const {
     // Need to use ArraySplice instead of this code.
     auto args = std::vector<std::string>();
     for (const auto& string : execute_command.args()) {
         args.emplace_back(string);
     }

     auto map_result = function_map_->FindFunction(args);
     Result<Success> result;
     if (!map_result) {
         result = Error() << "Cannot find command: " << map_result.error();
     } else {
         result = RunBuiltinFunction(map_result->second, args, context_);
     }

     if (result) {
         result_message->set_success(true);
     } else {
         result_message->set_success(false);
         result_message->set_error_string(result.error_string());
         result_message->set_error_errno(result.error_errno());
     }
 }

 void SubcontextProcess::MainLoop() {
     pollfd ufd[1];
     ufd[0].events = POLLIN;
     ufd[0].fd = init_fd_;

     while (true) {
         ufd[0].revents = 0;
         int nr = TEMP_FAILURE_RETRY(poll(ufd, arraysize(ufd), -1));
         if (nr == 0) continue;
         if (nr < 0) {
             PLOG(FATAL) << "poll() of subcontext socket failed, continuing";
         }

         auto init_message = ReadMessage(init_fd_);
         if (!init_message) {
             LOG(FATAL) << "Could not read message from init: " << init_message.error();
         }

         auto subcontext_command = SubcontextCommand();
         if (!subcontext_command.ParseFromString(*init_message)) {
             LOG(FATAL) << "Unable to parse message from init";
         }

         auto reply = SubcontextReply();
         switch (subcontext_command.command_case()) {
             case SubcontextCommand::kExecuteCommand: {
                 RunCommand(subcontext_command.execute_command(), reply.mutable_result());
                 break;
             }
             default:
                 LOG(FATAL) << "Unknown message type from init: "
                            << subcontext_command.command_case();
         }

         if (auto result = SendMessage(init_fd_, reply); !result) {
             LOG(FATAL) << "Failed to send message to init: " << result.error();
         }
     }
 }

 }  // namespace

 int SubcontextMain(int argc, char** argv, const KeywordFunctionMap* function_map) {
     if (argc < 4) LOG(FATAL) << "Fewer than 4 args specified to subcontext (" << argc << ")";

     auto context = std::string(argv[2]);
     auto init_fd = std::atoi(argv[3]);

     SelabelInitialize();
     auto subcontext_process = SubcontextProcess(function_map, context, init_fd);
     subcontext_process.MainLoop();
     return 0;
 }

 void Subcontext::Fork() {
     unique_fd subcontext_socket;
     if (!Socketpair(AF_UNIX, SOCK_SEQPACKET | SOCK_CLOEXEC, 0, &socket_, &subcontext_socket)) {
         LOG(FATAL) << "Could not create socket pair to communicate to subcontext";
         return;
     }

     auto result = fork();

     if (result == -1) {
         LOG(FATAL) << "Could not fork subcontext";
     } else if (result == 0) {
         socket_.reset();

         // We explicitly do not use O_CLOEXEC here, such that we can reference this FD by number
         // in the subcontext process after we exec.
         int child_fd = dup(subcontext_socket);
         if (child_fd < 0) {
             PLOG(FATAL) << "Could not dup child_fd";
         }

         if (setexeccon(context_.c_str()) < 0) {
             PLOG(FATAL) << "Could not set execcon for '" << context_ << "'";
         }

         auto init_path = GetExecutablePath();
         auto child_fd_string = std::to_string(child_fd);
         const char* args[] = {init_path.c_str(), "subcontext", context_.c_str(),
                               child_fd_string.c_str(), nullptr};
         execv(init_path.data(), const_cast<char**>(args));

         PLOG(FATAL) << "Could not execv subcontext init";
     } else {
         subcontext_socket.reset();
         pid_ = result;
         LOG(INFO) << "Forked subcontext for '" << context_ << "' with pid " << pid_;
     }
 }

 void Subcontext::Restart() {
     LOG(ERROR) << "Restarting subcontext '" << context_ << "'";
     if (pid_) {
         kill(pid_, SIGKILL);
     }
     pid_ = 0;
     socket_.reset();
     Fork();
 }

 Result<Success> Subcontext::Execute(const std::vector<std::string>& args) {
     auto subcontext_command = SubcontextCommand();
     std::copy(
         args.begin(), args.end(),
         RepeatedPtrFieldBackInserter(subcontext_command.mutable_execute_command()->mutable_args()));

     if (auto result = SendMessage(socket_, subcontext_command); !result) {
         Restart();
         return ErrnoError() << "Failed to send message to subcontext";
     }

     auto subcontext_message = ReadMessage(socket_);
     if (!subcontext_message) {
         Restart();
         return Error() << "Failed to receive result from subcontext: " << subcontext_message.error();
     }

     auto subcontext_reply = SubcontextReply();
     if (!subcontext_reply.ParseFromString(*subcontext_message)) {
         Restart();
         return Error() << "Unable to parse message from subcontext";
     }

     switch (subcontext_reply.reply_case()) {
         case SubcontextReply::kResult: {
             auto result = subcontext_reply.result();
             if (result.success()) {
                 return Success();
             } else {
                 return ResultError(result.error_string(), result.error_errno());
             }
         }
         default:
             return Error() << "Unknown message type from subcontext: "
                            << subcontext_reply.reply_case();
     }
 }

 static std::vector<Subcontext> subcontexts;

 std::vector<Subcontext>* InitializeSubcontexts() {
     if (GetBoolProperty("ro.init.subcontexts_enabled", false)) {
         static const char* const paths_and_secontexts[][2] = {
             {"/vendor", kVendorContext.c_str()},
         };
         for (const auto& [path_prefix, secontext] : paths_and_secontexts) {
             subcontexts.emplace_back(path_prefix, secontext);
         }
     }
     return &subcontexts;
 }

 bool SubcontextChildReap(pid_t pid) {
     for (auto& subcontext : subcontexts) {
         if (subcontext.pid() == pid) {
             subcontext.Restart();
             return true;
         }
     }
     return false;
 }

 }  // 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.
	*/

	#include "subcontext.h"

	#include <fcntl.h>
	#include <poll.h>
	#include <sys/socket.h>
	#include <unistd.h>

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

	#include "action.h"
	#include "selinux.h"
	#include "system/core/init/subcontext.pb.h"
	#include "util.h"

	using android::base::GetBoolProperty;
	using android::base::GetExecutablePath;
	using android::base::Join;
	using android::base::Socketpair;
	using android::base::Split;
	using android::base::StartsWith;
	using android::base::unique_fd;

	namespace android {
	namespace init {

	const std::string kInitContext = "u:r:init:s0";
	const std::string kVendorContext = "u:r:vendor_init:s0";

	namespace {

	constexpr size_t kBufferSize = 4096;

	Result<std::string> ReadMessage(int socket) {
	char buffer[kBufferSize] = {};
	auto result = TEMP_FAILURE_RETRY(recv(socket, buffer, sizeof(buffer), 0));
	if (result <= 0) {
	return ErrnoError();
	}
	return std::string(buffer, result);
	}

	template <typename T>
	Result<Success> SendMessage(int socket, const T& message) {
	std::string message_string;
	if (!message.SerializeToString(&message_string)) {
	return Error() << "Unable to serialize message";
	}

	if (message_string.size() > kBufferSize) {
	return Error() << "Serialized message too long to send";
	}

	if (auto result =
	TEMP_FAILURE_RETRY(send(socket, message_string.c_str(), message_string.size(), 0));
	result != static_cast<long>(message_string.size())) {
	return ErrnoError() << "send() failed to send message contents";
	}
	return Success();
	}

	class SubcontextProcess {
	public:
	SubcontextProcess(const KeywordFunctionMap* function_map, std::string context, int init_fd)
	: function_map_(function_map), context_(std::move(context)), init_fd_(init_fd){};
	void MainLoop();

	private:
	void RunCommand(const SubcontextCommand::ExecuteCommand& execute_command,
	SubcontextReply::ResultMessage* result_message) const;

	const KeywordFunctionMap* function_map_;
	const std::string context_;
	const int init_fd_;
	};

	void SubcontextProcess::RunCommand(const SubcontextCommand::ExecuteCommand& execute_command,
	SubcontextReply::ResultMessage* result_message) const {
	// Need to use ArraySplice instead of this code.
	auto args = std::vector<std::string>();
	for (const auto& string : execute_command.args()) {
	args.emplace_back(string);
	}

	auto map_result = function_map_->FindFunction(args);
	Result<Success> result;
	if (!map_result) {
	result = Error() << "Cannot find command: " << map_result.error();
	} else {
	result = RunBuiltinFunction(map_result->second, args, context_);
	}

	if (result) {
	result_message->set_success(true);
	} else {
	result_message->set_success(false);
	result_message->set_error_string(result.error_string());
	result_message->set_error_errno(result.error_errno());
	}
	}

	void SubcontextProcess::MainLoop() {
	pollfd ufd[1];
	ufd[0].events = POLLIN;
	ufd[0].fd = init_fd_;

	while (true) {
	ufd[0].revents = 0;
	int nr = TEMP_FAILURE_RETRY(poll(ufd, arraysize(ufd), -1));
	if (nr == 0) continue;
	if (nr < 0) {
	PLOG(FATAL) << "poll() of subcontext socket failed, continuing";
	}

	auto init_message = ReadMessage(init_fd_);
	if (!init_message) {
	LOG(FATAL) << "Could not read message from init: " << init_message.error();
	}

	auto subcontext_command = SubcontextCommand();
	if (!subcontext_command.ParseFromString(*init_message)) {
	LOG(FATAL) << "Unable to parse message from init";
	}

	auto reply = SubcontextReply();
	switch (subcontext_command.command_case()) {
	case SubcontextCommand::kExecuteCommand: {
	RunCommand(subcontext_command.execute_command(), reply.mutable_result());
	break;
	}
	default:
	LOG(FATAL) << "Unknown message type from init: "
	<< subcontext_command.command_case();
	}

	if (auto result = SendMessage(init_fd_, reply); !result) {
	LOG(FATAL) << "Failed to send message to init: " << result.error();
	}
	}
	}

	} // namespace

	int SubcontextMain(int argc, char** argv, const KeywordFunctionMap* function_map) {
	if (argc < 4) LOG(FATAL) << "Fewer than 4 args specified to subcontext (" << argc << ")";

	auto context = std::string(argv[2]);
	auto init_fd = std::atoi(argv[3]);

	SelabelInitialize();
	auto subcontext_process = SubcontextProcess(function_map, context, init_fd);
	subcontext_process.MainLoop();
	return 0;
	}

	void Subcontext::Fork() {
	unique_fd subcontext_socket;
	if (!Socketpair(AF_UNIX, SOCK_SEQPACKET \| SOCK_CLOEXEC, 0, &socket_, &subcontext_socket)) {
	LOG(FATAL) << "Could not create socket pair to communicate to subcontext";
	return;
	}

	auto result = fork();

	if (result == -1) {
	LOG(FATAL) << "Could not fork subcontext";
	} else if (result == 0) {
	socket_.reset();

	// We explicitly do not use O_CLOEXEC here, such that we can reference this FD by number
	// in the subcontext process after we exec.
	int child_fd = dup(subcontext_socket);
	if (child_fd < 0) {
	PLOG(FATAL) << "Could not dup child_fd";
	}

	if (setexeccon(context_.c_str()) < 0) {
	PLOG(FATAL) << "Could not set execcon for '" << context_ << "'";
	}

	auto init_path = GetExecutablePath();
	auto child_fd_string = std::to_string(child_fd);
	const char* args[] = {init_path.c_str(), "subcontext", context_.c_str(),
	child_fd_string.c_str(), nullptr};
	execv(init_path.data(), const_cast<char**>(args));

	PLOG(FATAL) << "Could not execv subcontext init";
	} else {
	subcontext_socket.reset();
	pid_ = result;
	LOG(INFO) << "Forked subcontext for '" << context_ << "' with pid " << pid_;
	}
	}

	void Subcontext::Restart() {
	LOG(ERROR) << "Restarting subcontext '" << context_ << "'";
	if (pid_) {
	kill(pid_, SIGKILL);
	}
	pid_ = 0;
	socket_.reset();
	Fork();
	}

	Result<Success> Subcontext::Execute(const std::vector<std::string>& args) {
	auto subcontext_command = SubcontextCommand();
	std::copy(
	args.begin(), args.end(),
	RepeatedPtrFieldBackInserter(subcontext_command.mutable_execute_command()->mutable_args()));

	if (auto result = SendMessage(socket_, subcontext_command); !result) {
	Restart();
	return ErrnoError() << "Failed to send message to subcontext";
	}

	auto subcontext_message = ReadMessage(socket_);
	if (!subcontext_message) {
	Restart();
	return Error() << "Failed to receive result from subcontext: " << subcontext_message.error();
	}

	auto subcontext_reply = SubcontextReply();
	if (!subcontext_reply.ParseFromString(*subcontext_message)) {
	Restart();
	return Error() << "Unable to parse message from subcontext";
	}

	switch (subcontext_reply.reply_case()) {
	case SubcontextReply::kResult: {
	auto result = subcontext_reply.result();
	if (result.success()) {
	return Success();
	} else {
	return ResultError(result.error_string(), result.error_errno());
	}
	}
	default:
	return Error() << "Unknown message type from subcontext: "
	<< subcontext_reply.reply_case();
	}
	}

	static std::vector<Subcontext> subcontexts;

	std::vector<Subcontext>* InitializeSubcontexts() {
	if (GetBoolProperty("ro.init.subcontexts_enabled", false)) {
	static const char* const paths_and_secontexts[][2] = {
	{"/vendor", kVendorContext.c_str()},
	};
	for (const auto& [path_prefix, secontext] : paths_and_secontexts) {
	subcontexts.emplace_back(path_prefix, secontext);
	}
	}
	return &subcontexts;
	}

	bool SubcontextChildReap(pid_t pid) {
	for (auto& subcontext : subcontexts) {
	if (subcontext.pid() == pid) {
	subcontext.Restart();
	return true;
	}
	}
	return false;
	}

	} // namespace init
	} // namespace android