payload_consumer/filesystem_verifier_action.cc - android_system_update_engine - Gitiles

 //
 // Copyright (C) 2012 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 "update_engine/payload_consumer/filesystem_verifier_action.h"

 #include <errno.h>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>

 #include <algorithm>
 #include <cstdlib>
 #include <memory>
 #include <string>
 #include <utility>

 #include <base/bind.h>
 #include <base/strings/string_util.h>
 #include <brillo/data_encoding.h>
 #include <brillo/message_loops/message_loop.h>
 #include <brillo/secure_blob.h>
 #include <brillo/streams/file_stream.h>

 #include "payload_generator/delta_diff_generator.h"
 #include "update_engine/common/utils.h"
 #include "update_engine/payload_consumer/file_descriptor.h"

 using brillo::data_encoding::Base64Encode;
 using std::string;

 // On a partition with verity enabled, we expect to see the following format:
 // ===================================================
 //              Normal Filesystem Data
 // (this should take most of the space, like over 90%)
 // ===================================================
 //                  Hash tree
 //         ~0.8% (e.g. 16M for 2GB image)
 // ===================================================
 //                  FEC data
 //                    ~0.8%
 // ===================================================
 //                   Footer
 //                     4K
 // ===================================================

 // For OTA that doesn't do on device verity computation, hash tree and fec data
 // are written during DownloadAction as a regular InstallOp, so no special
 // handling needed, we can just read the entire partition in 1 go.

 // Verity enabled case: Only Normal FS data is written during download action.
 // When hasing the entire partition, we will need to build the hash tree, write
 // it to disk, then build FEC, and write it to disk. Therefore, it is important
 // that we finish writing hash tree before we attempt to read & hash it. The
 // same principal applies to FEC data.

 // |verity_writer_| handles building and
 // writing of FEC/HashTree, we just need to be careful when reading.
 // Specifically, we must stop at beginning of Hash tree, let |verity_writer_|
 // write both hash tree and FEC, then continue reading the remaining part of
 // partition.

 namespace chromeos_update_engine {

 namespace {
 const off_t kReadFileBufferSize = 128 * 1024;
 }  // namespace

 void FilesystemVerifierAction::PerformAction() {
   // Will tell the ActionProcessor we've failed if we return.
   ScopedActionCompleter abort_action_completer(processor_, this);

   if (!HasInputObject()) {
     LOG(ERROR) << "FilesystemVerifierAction missing input object.";
     return;
   }
   install_plan_ = GetInputObject();

   if (install_plan_.partitions.empty()) {
     LOG(INFO) << "No partitions to verify.";
     if (HasOutputPipe())
       SetOutputObject(install_plan_);
     abort_action_completer.set_code(ErrorCode::kSuccess);
     return;
   }
   install_plan_.Dump();
   StartPartitionHashing();
   abort_action_completer.set_should_complete(false);
 }

 void FilesystemVerifierAction::TerminateProcessing() {
   brillo::MessageLoop::current()->CancelTask(pending_task_id_);
   cancelled_ = true;
   Cleanup(ErrorCode::kSuccess);  // error code is ignored if canceled_ is true.
 }

 void FilesystemVerifierAction::Cleanup(ErrorCode code) {
   partition_fd_.reset();
   // This memory is not used anymore.
   buffer_.clear();

   if (cancelled_)
     return;
   if (code == ErrorCode::kSuccess && HasOutputPipe())
     SetOutputObject(install_plan_);
   UpdateProgress(1.0);
   processor_->ActionComplete(this, code);
 }

 void FilesystemVerifierAction::UpdateProgress(double progress) {
   if (delegate_ != nullptr) {
     delegate_->OnVerifyProgressUpdate(progress);
   }
 }

 bool FilesystemVerifierAction::InitializeFdVABC() {
   const InstallPlan::Partition& partition =
       install_plan_.partitions[partition_index_];

   // FilesystemVerifierAction need the read_fd_.
   partition_fd_ =
       dynamic_control_->OpenCowFd(partition.name, partition.source_path, true);
   if (!partition_fd_) {
     LOG(ERROR) << "OpenCowReader(" << partition.name << ", "
                << partition.source_path << ") failed.";
     return false;
   }
   partition_size_ = partition.target_size;
   return true;
 }

 bool FilesystemVerifierAction::InitializeFd(const std::string& part_path) {
   partition_fd_ = FileDescriptorPtr(new EintrSafeFileDescriptor());
   const bool write_verity = ShouldWriteVerity();
   int flags = write_verity ? O_RDWR : O_RDONLY;
   if (!utils::SetBlockDeviceReadOnly(part_path, !write_verity)) {
     LOG(WARNING) << "Failed to set block device " << part_path << " as "
                  << (write_verity ? "writable" : "readonly");
   }
   if (!partition_fd_->Open(part_path.c_str(), flags)) {
     LOG(ERROR) << "Unable to open " << part_path << " for reading.";
     return false;
   }
   return true;
 }

 void FilesystemVerifierAction::StartPartitionHashing() {
   if (partition_index_ == install_plan_.partitions.size()) {
     if (!install_plan_.untouched_dynamic_partitions.empty()) {
       LOG(INFO) << "Verifying extents of untouched dynamic partitions ["
                 << base::JoinString(install_plan_.untouched_dynamic_partitions,
                                     ", ")
                 << "]";
       if (!dynamic_control_->VerifyExtentsForUntouchedPartitions(
               install_plan_.source_slot,
               install_plan_.target_slot,
               install_plan_.untouched_dynamic_partitions)) {
         Cleanup(ErrorCode::kFilesystemVerifierError);
         return;
       }
     }

     Cleanup(ErrorCode::kSuccess);
     return;
   }
   const InstallPlan::Partition& partition =
       install_plan_.partitions[partition_index_];
   string part_path;
   switch (verifier_step_) {
     case VerifierStep::kVerifySourceHash:
       part_path = partition.source_path;
       partition_size_ = partition.source_size;
       break;
     case VerifierStep::kVerifyTargetHash:
       part_path = partition.target_path;
       partition_size_ = partition.target_size;
       break;
   }

   LOG(INFO) << "Hashing partition " << partition_index_ << " ("
             << partition.name << ") on device " << part_path;
   auto success = false;
   if (dynamic_control_->UpdateUsesSnapshotCompression() &&
       verifier_step_ == VerifierStep::kVerifyTargetHash &&
       dynamic_control_->IsDynamicPartition(partition.name,
                                            install_plan_.target_slot)) {
     success = InitializeFdVABC();
   } else {
     if (part_path.empty()) {
       if (partition_size_ == 0) {
         LOG(INFO) << "Skip hashing partition " << partition_index_ << " ("
                   << partition.name << ") because size is 0.";
         partition_index_++;
         StartPartitionHashing();
         return;
       }
       LOG(ERROR) << "Cannot hash partition " << partition_index_ << " ("
                  << partition.name
                  << ") because its device path cannot be determined.";
       Cleanup(ErrorCode::kFilesystemVerifierError);
       return;
     }
     success = InitializeFd(part_path);
   }
   if (!success) {
     Cleanup(ErrorCode::kFilesystemVerifierError);
     return;
   }
   buffer_.resize(kReadFileBufferSize);
   hasher_ = std::make_unique<HashCalculator>();

   offset_ = 0;
   filesystem_data_end_ = partition_size_;
   CHECK_LE(partition.hash_tree_offset, partition.fec_offset)
       << " Hash tree is expected to come before FEC data";
   if (partition.hash_tree_offset != 0) {
     filesystem_data_end_ = partition.hash_tree_offset;
   } else if (partition.fec_offset != 0) {
     filesystem_data_end_ = partition.fec_offset;
   }
   if (ShouldWriteVerity()) {
     if (!verity_writer_->Init(partition)) {
       LOG(INFO) << "Verity writes enabled on partition " << partition.name;
       Cleanup(ErrorCode::kVerityCalculationError);
       return;
     }
   } else {
     LOG(INFO) << "Verity writes disabled on partition " << partition.name;
   }

   // Start the first read.
   ScheduleFileSystemRead();
 }

 bool FilesystemVerifierAction::ShouldWriteVerity() {
   const InstallPlan::Partition& partition =
       install_plan_.partitions[partition_index_];
   return verifier_step_ == VerifierStep::kVerifyTargetHash &&
          install_plan_.write_verity &&
          (partition.hash_tree_size > 0 || partition.fec_size > 0);
 }

 void FilesystemVerifierAction::ReadVerityAndFooter() {
   if (ShouldWriteVerity()) {
     if (!verity_writer_->Finalize(partition_fd_, partition_fd_)) {
       LOG(ERROR) << "Failed to write hashtree/FEC data.";
       Cleanup(ErrorCode::kFilesystemVerifierError);
       return;
     }
   }
   // Since we handed our |read_fd_| to verity_writer_ during |Finalize()|
   // call, fd's position could have been changed. Re-seek.
   partition_fd_->Seek(filesystem_data_end_, SEEK_SET);
   auto bytes_to_read = partition_size_ - filesystem_data_end_;
   while (bytes_to_read > 0) {
     const auto read_size = std::min<size_t>(buffer_.size(), bytes_to_read);
     auto bytes_read = partition_fd_->Read(buffer_.data(), read_size);
     if (bytes_read <= 0) {
       PLOG(ERROR) << "Failed to read hash tree " << bytes_read;
       Cleanup(ErrorCode::kFilesystemVerifierError);
       return;
     }
     if (!hasher_->Update(buffer_.data(), bytes_read)) {
       LOG(ERROR) << "Unable to update the hash.";
       Cleanup(ErrorCode::kError);
       return;
     }
     bytes_to_read -= bytes_read;
   }
   FinishPartitionHashing();
 }

 void FilesystemVerifierAction::ScheduleFileSystemRead() {
   // We can only start reading anything past |hash_tree_offset| after we have
   // already read all the data blocks that the hash tree covers. The same
   // applies to FEC.

   size_t bytes_to_read = std::min(static_cast<uint64_t>(buffer_.size()),
                                   filesystem_data_end_ - offset_);
   if (!bytes_to_read) {
     ReadVerityAndFooter();
     return;
   }
   partition_fd_->Seek(offset_, SEEK_SET);
   auto bytes_read = partition_fd_->Read(buffer_.data(), bytes_to_read);
   if (bytes_read < 0) {
     LOG(ERROR) << "Unable to schedule an asynchronous read from the stream. "
                << bytes_read;
     Cleanup(ErrorCode::kError);
   } else {
     // We could just invoke |OnReadDoneCallback()|, it works. But |PostTask|
     // is used so that users can cancel updates.
     pending_task_id_ = brillo::MessageLoop::current()->PostTask(
         base::Bind(&FilesystemVerifierAction::OnReadDone,
                    base::Unretained(this),
                    bytes_read));
   }
 }

 void FilesystemVerifierAction::OnReadDone(size_t bytes_read) {
   if (cancelled_) {
     Cleanup(ErrorCode::kError);
     return;
   }
   if (bytes_read == 0) {
     LOG(ERROR) << "Failed to read the remaining " << partition_size_ - offset_
                << " bytes from partition "
                << install_plan_.partitions[partition_index_].name;
     Cleanup(ErrorCode::kFilesystemVerifierError);
     return;
   }

   if (!hasher_->Update(buffer_.data(), bytes_read)) {
     LOG(ERROR) << "Unable to update the hash.";
     Cleanup(ErrorCode::kError);
     return;
   }

   // WE don't consider sizes of each partition. Every partition
   // has the same length on progress bar.
   // TODO(zhangkelvin) Take sizes of each partition into account

   UpdateProgress(
       (static_cast<double>(offset_) / partition_size_ + partition_index_) /
       install_plan_.partitions.size());
   if (ShouldWriteVerity()) {
     if (!verity_writer_->Update(offset_, buffer_.data(), bytes_read)) {
       LOG(ERROR) << "Unable to update verity";
       Cleanup(ErrorCode::kVerityCalculationError);
       return;
     }
   }

   offset_ += bytes_read;
   if (offset_ == filesystem_data_end_) {
     ReadVerityAndFooter();
     return;
   }

   ScheduleFileSystemRead();
 }

 void FilesystemVerifierAction::FinishPartitionHashing() {
   if (!hasher_->Finalize()) {
     LOG(ERROR) << "Unable to finalize the hash.";
     Cleanup(ErrorCode::kError);
     return;
   }
   InstallPlan::Partition& partition =
       install_plan_.partitions[partition_index_];
   LOG(INFO) << "Hash of " << partition.name << ": "
             << Base64Encode(hasher_->raw_hash());

   switch (verifier_step_) {
     case VerifierStep::kVerifyTargetHash:
       if (partition.target_hash != hasher_->raw_hash()) {
         LOG(ERROR) << "New '" << partition.name
                    << "' partition verification failed.";
         if (partition.source_hash.empty()) {
           // No need to verify source if it is a full payload.
           Cleanup(ErrorCode::kNewRootfsVerificationError);
           return;
         }
         // If we have not verified source partition yet, now that the target
         // partition does not match, and it's not a full payload, we need to
         // switch to kVerifySourceHash step to check if it's because the
         // source partition does not match either.
         verifier_step_ = VerifierStep::kVerifySourceHash;
       } else {
         partition_index_++;
       }
       break;
     case VerifierStep::kVerifySourceHash:
       if (partition.source_hash != hasher_->raw_hash()) {
         LOG(ERROR) << "Old '" << partition.name
                    << "' partition verification failed.";
         LOG(ERROR) << "This is a server-side error due to mismatched delta"
                    << " update image!";
         LOG(ERROR) << "The delta I've been given contains a " << partition.name
                    << " delta update that must be applied over a "
                    << partition.name << " with a specific checksum, but the "
                    << partition.name
                    << " we're starting with doesn't have that checksum! This"
                       " means that the delta I've been given doesn't match my"
                       " existing system. The "
                    << partition.name << " partition I have has hash: "
                    << Base64Encode(hasher_->raw_hash())
                    << " but the update expected me to have "
                    << Base64Encode(partition.source_hash) << " .";
         LOG(INFO) << "To get the checksum of the " << partition.name
                   << " partition run this command: dd if="
                   << partition.source_path
                   << " bs=1M count=" << partition.source_size
                   << " iflag=count_bytes 2>/dev/null | openssl dgst -sha256 "
                      "-binary | openssl base64";
         LOG(INFO) << "To get the checksum of partitions in a bin file, "
                   << "run: .../src/scripts/sha256_partitions.sh .../file.bin";
         Cleanup(ErrorCode::kDownloadStateInitializationError);
         return;
       }
       // The action will skip kVerifySourceHash step if target partition hash
       // matches, if we are in this step, it means target hash does not match,
       // and now that the source partition hash matches, we should set the
       // error code to reflect the error in target partition. We only need to
       // verify the source partition which the target hash does not match, the
       // rest of the partitions don't matter.
       Cleanup(ErrorCode::kNewRootfsVerificationError);
       return;
   }
   // Start hashing the next partition, if any.
   hasher_.reset();
   buffer_.clear();
   if (partition_fd_) {
     partition_fd_.reset();
   }
   StartPartitionHashing();
 }

 }  // namespace chromeos_update_engine
	//
	// Copyright (C) 2012 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 "update_engine/payload_consumer/filesystem_verifier_action.h"

	#include <errno.h>
	#include <fcntl.h>
	#include <sys/stat.h>
	#include <sys/types.h>
	#include <unistd.h>

	#include <algorithm>
	#include <cstdlib>
	#include <memory>
	#include <string>
	#include <utility>

	#include <base/bind.h>
	#include <base/strings/string_util.h>
	#include <brillo/data_encoding.h>
	#include <brillo/message_loops/message_loop.h>
	#include <brillo/secure_blob.h>
	#include <brillo/streams/file_stream.h>

	#include "payload_generator/delta_diff_generator.h"
	#include "update_engine/common/utils.h"
	#include "update_engine/payload_consumer/file_descriptor.h"

	using brillo::data_encoding::Base64Encode;
	using std::string;

	// On a partition with verity enabled, we expect to see the following format:
	// ===================================================
	// Normal Filesystem Data
	// (this should take most of the space, like over 90%)
	// ===================================================
	// Hash tree
	// ~0.8% (e.g. 16M for 2GB image)
	// ===================================================
	// FEC data
	// ~0.8%
	// ===================================================
	// Footer
	// 4K
	// ===================================================

	// For OTA that doesn't do on device verity computation, hash tree and fec data
	// are written during DownloadAction as a regular InstallOp, so no special
	// handling needed, we can just read the entire partition in 1 go.

	// Verity enabled case: Only Normal FS data is written during download action.
	// When hasing the entire partition, we will need to build the hash tree, write
	// it to disk, then build FEC, and write it to disk. Therefore, it is important
	// that we finish writing hash tree before we attempt to read & hash it. The
	// same principal applies to FEC data.

	// \|verity_writer_\| handles building and
	// writing of FEC/HashTree, we just need to be careful when reading.
	// Specifically, we must stop at beginning of Hash tree, let \|verity_writer_\|
	// write both hash tree and FEC, then continue reading the remaining part of
	// partition.

	namespace chromeos_update_engine {

	namespace {
	const off_t kReadFileBufferSize = 128 * 1024;
	} // namespace

	void FilesystemVerifierAction::PerformAction() {
	// Will tell the ActionProcessor we've failed if we return.
	ScopedActionCompleter abort_action_completer(processor_, this);

	if (!HasInputObject()) {
	LOG(ERROR) << "FilesystemVerifierAction missing input object.";
	return;
	}
	install_plan_ = GetInputObject();

	if (install_plan_.partitions.empty()) {
	LOG(INFO) << "No partitions to verify.";
	if (HasOutputPipe())
	SetOutputObject(install_plan_);
	abort_action_completer.set_code(ErrorCode::kSuccess);
	return;
	}
	install_plan_.Dump();
	StartPartitionHashing();
	abort_action_completer.set_should_complete(false);
	}

	void FilesystemVerifierAction::TerminateProcessing() {
	brillo::MessageLoop::current()->CancelTask(pending_task_id_);
	cancelled_ = true;
	Cleanup(ErrorCode::kSuccess); // error code is ignored if canceled_ is true.
	}

	void FilesystemVerifierAction::Cleanup(ErrorCode code) {
	partition_fd_.reset();
	// This memory is not used anymore.
	buffer_.clear();

	if (cancelled_)
	return;
	if (code == ErrorCode::kSuccess && HasOutputPipe())
	SetOutputObject(install_plan_);
	UpdateProgress(1.0);
	processor_->ActionComplete(this, code);
	}

	void FilesystemVerifierAction::UpdateProgress(double progress) {
	if (delegate_ != nullptr) {
	delegate_->OnVerifyProgressUpdate(progress);
	}
	}

	bool FilesystemVerifierAction::InitializeFdVABC() {
	const InstallPlan::Partition& partition =
	install_plan_.partitions[partition_index_];

	// FilesystemVerifierAction need the read_fd_.
	partition_fd_ =
	dynamic_control_->OpenCowFd(partition.name, partition.source_path, true);
	if (!partition_fd_) {
	LOG(ERROR) << "OpenCowReader(" << partition.name << ", "
	<< partition.source_path << ") failed.";
	return false;
	}
	partition_size_ = partition.target_size;
	return true;
	}

	bool FilesystemVerifierAction::InitializeFd(const std::string& part_path) {
	partition_fd_ = FileDescriptorPtr(new EintrSafeFileDescriptor());
	const bool write_verity = ShouldWriteVerity();
	int flags = write_verity ? O_RDWR : O_RDONLY;
	if (!utils::SetBlockDeviceReadOnly(part_path, !write_verity)) {
	LOG(WARNING) << "Failed to set block device " << part_path << " as "
	<< (write_verity ? "writable" : "readonly");
	}
	if (!partition_fd_->Open(part_path.c_str(), flags)) {
	LOG(ERROR) << "Unable to open " << part_path << " for reading.";
	return false;
	}
	return true;
	}

	void FilesystemVerifierAction::StartPartitionHashing() {
	if (partition_index_ == install_plan_.partitions.size()) {
	if (!install_plan_.untouched_dynamic_partitions.empty()) {
	LOG(INFO) << "Verifying extents of untouched dynamic partitions ["
	<< base::JoinString(install_plan_.untouched_dynamic_partitions,
	", ")
	<< "]";
	if (!dynamic_control_->VerifyExtentsForUntouchedPartitions(
	install_plan_.source_slot,
	install_plan_.target_slot,
	install_plan_.untouched_dynamic_partitions)) {
	Cleanup(ErrorCode::kFilesystemVerifierError);
	return;
	}
	}

	Cleanup(ErrorCode::kSuccess);
	return;
	}
	const InstallPlan::Partition& partition =
	install_plan_.partitions[partition_index_];
	string part_path;
	switch (verifier_step_) {
	case VerifierStep::kVerifySourceHash:
	part_path = partition.source_path;
	partition_size_ = partition.source_size;
	break;
	case VerifierStep::kVerifyTargetHash:
	part_path = partition.target_path;
	partition_size_ = partition.target_size;
	break;
	}

	LOG(INFO) << "Hashing partition " << partition_index_ << " ("
	<< partition.name << ") on device " << part_path;
	auto success = false;
	if (dynamic_control_->UpdateUsesSnapshotCompression() &&
	verifier_step_ == VerifierStep::kVerifyTargetHash &&
	dynamic_control_->IsDynamicPartition(partition.name,
	install_plan_.target_slot)) {
	success = InitializeFdVABC();
	} else {
	if (part_path.empty()) {
	if (partition_size_ == 0) {
	LOG(INFO) << "Skip hashing partition " << partition_index_ << " ("
	<< partition.name << ") because size is 0.";
	partition_index_++;
	StartPartitionHashing();
	return;
	}
	LOG(ERROR) << "Cannot hash partition " << partition_index_ << " ("
	<< partition.name
	<< ") because its device path cannot be determined.";
	Cleanup(ErrorCode::kFilesystemVerifierError);
	return;
	}
	success = InitializeFd(part_path);
	}
	if (!success) {
	Cleanup(ErrorCode::kFilesystemVerifierError);
	return;
	}
	buffer_.resize(kReadFileBufferSize);
	hasher_ = std::make_unique<HashCalculator>();

	offset_ = 0;
	filesystem_data_end_ = partition_size_;
	CHECK_LE(partition.hash_tree_offset, partition.fec_offset)
	<< " Hash tree is expected to come before FEC data";
	if (partition.hash_tree_offset != 0) {
	filesystem_data_end_ = partition.hash_tree_offset;
	} else if (partition.fec_offset != 0) {
	filesystem_data_end_ = partition.fec_offset;
	}
	if (ShouldWriteVerity()) {
	if (!verity_writer_->Init(partition)) {
	LOG(INFO) << "Verity writes enabled on partition " << partition.name;
	Cleanup(ErrorCode::kVerityCalculationError);
	return;
	}
	} else {
	LOG(INFO) << "Verity writes disabled on partition " << partition.name;
	}

	// Start the first read.
	ScheduleFileSystemRead();
	}

	bool FilesystemVerifierAction::ShouldWriteVerity() {
	const InstallPlan::Partition& partition =
	install_plan_.partitions[partition_index_];
	return verifier_step_ == VerifierStep::kVerifyTargetHash &&
	install_plan_.write_verity &&
	(partition.hash_tree_size > 0 \|\| partition.fec_size > 0);
	}

	void FilesystemVerifierAction::ReadVerityAndFooter() {
	if (ShouldWriteVerity()) {
	if (!verity_writer_->Finalize(partition_fd_, partition_fd_)) {
	LOG(ERROR) << "Failed to write hashtree/FEC data.";
	Cleanup(ErrorCode::kFilesystemVerifierError);
	return;
	}
	}
	// Since we handed our \|read_fd_\| to verity_writer_ during \|Finalize()\|
	// call, fd's position could have been changed. Re-seek.
	partition_fd_->Seek(filesystem_data_end_, SEEK_SET);
	auto bytes_to_read = partition_size_ - filesystem_data_end_;
	while (bytes_to_read > 0) {
	const auto read_size = std::min<size_t>(buffer_.size(), bytes_to_read);
	auto bytes_read = partition_fd_->Read(buffer_.data(), read_size);
	if (bytes_read <= 0) {
	PLOG(ERROR) << "Failed to read hash tree " << bytes_read;
	Cleanup(ErrorCode::kFilesystemVerifierError);
	return;
	}
	if (!hasher_->Update(buffer_.data(), bytes_read)) {
	LOG(ERROR) << "Unable to update the hash.";
	Cleanup(ErrorCode::kError);
	return;
	}
	bytes_to_read -= bytes_read;
	}
	FinishPartitionHashing();
	}

	void FilesystemVerifierAction::ScheduleFileSystemRead() {
	// We can only start reading anything past \|hash_tree_offset\| after we have
	// already read all the data blocks that the hash tree covers. The same
	// applies to FEC.

	size_t bytes_to_read = std::min(static_cast<uint64_t>(buffer_.size()),
	filesystem_data_end_ - offset_);
	if (!bytes_to_read) {
	ReadVerityAndFooter();
	return;
	}
	partition_fd_->Seek(offset_, SEEK_SET);
	auto bytes_read = partition_fd_->Read(buffer_.data(), bytes_to_read);
	if (bytes_read < 0) {
	LOG(ERROR) << "Unable to schedule an asynchronous read from the stream. "
	<< bytes_read;
	Cleanup(ErrorCode::kError);
	} else {
	// We could just invoke \|OnReadDoneCallback()\|, it works. But \|PostTask\|
	// is used so that users can cancel updates.
	pending_task_id_ = brillo::MessageLoop::current()->PostTask(
	base::Bind(&FilesystemVerifierAction::OnReadDone,
	base::Unretained(this),
	bytes_read));
	}
	}

	void FilesystemVerifierAction::OnReadDone(size_t bytes_read) {
	if (cancelled_) {
	Cleanup(ErrorCode::kError);
	return;
	}
	if (bytes_read == 0) {
	LOG(ERROR) << "Failed to read the remaining " << partition_size_ - offset_
	<< " bytes from partition "
	<< install_plan_.partitions[partition_index_].name;
	Cleanup(ErrorCode::kFilesystemVerifierError);
	return;
	}

	if (!hasher_->Update(buffer_.data(), bytes_read)) {
	LOG(ERROR) << "Unable to update the hash.";
	Cleanup(ErrorCode::kError);
	return;
	}

	// WE don't consider sizes of each partition. Every partition
	// has the same length on progress bar.
	// TODO(zhangkelvin) Take sizes of each partition into account

	UpdateProgress(
	(static_cast<double>(offset_) / partition_size_ + partition_index_) /
	install_plan_.partitions.size());
	if (ShouldWriteVerity()) {
	if (!verity_writer_->Update(offset_, buffer_.data(), bytes_read)) {
	LOG(ERROR) << "Unable to update verity";
	Cleanup(ErrorCode::kVerityCalculationError);
	return;
	}
	}

	offset_ += bytes_read;
	if (offset_ == filesystem_data_end_) {
	ReadVerityAndFooter();
	return;
	}

	ScheduleFileSystemRead();
	}

	void FilesystemVerifierAction::FinishPartitionHashing() {
	if (!hasher_->Finalize()) {
	LOG(ERROR) << "Unable to finalize the hash.";
	Cleanup(ErrorCode::kError);
	return;
	}
	InstallPlan::Partition& partition =
	install_plan_.partitions[partition_index_];
	LOG(INFO) << "Hash of " << partition.name << ": "
	<< Base64Encode(hasher_->raw_hash());

	switch (verifier_step_) {
	case VerifierStep::kVerifyTargetHash:
	if (partition.target_hash != hasher_->raw_hash()) {
	LOG(ERROR) << "New '" << partition.name
	<< "' partition verification failed.";
	if (partition.source_hash.empty()) {
	// No need to verify source if it is a full payload.
	Cleanup(ErrorCode::kNewRootfsVerificationError);
	return;
	}
	// If we have not verified source partition yet, now that the target
	// partition does not match, and it's not a full payload, we need to
	// switch to kVerifySourceHash step to check if it's because the
	// source partition does not match either.
	verifier_step_ = VerifierStep::kVerifySourceHash;
	} else {
	partition_index_++;
	}
	break;
	case VerifierStep::kVerifySourceHash:
	if (partition.source_hash != hasher_->raw_hash()) {
	LOG(ERROR) << "Old '" << partition.name
	<< "' partition verification failed.";
	LOG(ERROR) << "This is a server-side error due to mismatched delta"
	<< " update image!";
	LOG(ERROR) << "The delta I've been given contains a " << partition.name
	<< " delta update that must be applied over a "
	<< partition.name << " with a specific checksum, but the "
	<< partition.name
	<< " we're starting with doesn't have that checksum! This"
	" means that the delta I've been given doesn't match my"
	" existing system. The "
	<< partition.name << " partition I have has hash: "
	<< Base64Encode(hasher_->raw_hash())
	<< " but the update expected me to have "
	<< Base64Encode(partition.source_hash) << " .";
	LOG(INFO) << "To get the checksum of the " << partition.name
	<< " partition run this command: dd if="
	<< partition.source_path
	<< " bs=1M count=" << partition.source_size
	<< " iflag=count_bytes 2>/dev/null \| openssl dgst -sha256 "
	"-binary \| openssl base64";
	LOG(INFO) << "To get the checksum of partitions in a bin file, "
	<< "run: .../src/scripts/sha256_partitions.sh .../file.bin";
	Cleanup(ErrorCode::kDownloadStateInitializationError);
	return;
	}
	// The action will skip kVerifySourceHash step if target partition hash
	// matches, if we are in this step, it means target hash does not match,
	// and now that the source partition hash matches, we should set the
	// error code to reflect the error in target partition. We only need to
	// verify the source partition which the target hash does not match, the
	// rest of the partitions don't matter.
	Cleanup(ErrorCode::kNewRootfsVerificationError);
	return;
	}
	// Start hashing the next partition, if any.
	hasher_.reset();
	buffer_.clear();
	if (partition_fd_) {
	partition_fd_.reset();
	}
	StartPartitionHashing();
	}

	} // namespace chromeos_update_engine