coordinator: implement history with fs store backend

coordinator/history/fsstore.go

@@ -0,0 +1,56 @@
+// Copyright 2024 Edgeless Systems GmbH
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package history
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io/fs"
+	"path/filepath"
+	"sync"
+
+	"github.com/spf13/afero"
+)
+
+type fsStore struct {
+	fs  *afero.Afero
+	mux sync.RWMutex
+}
+
+func newPVStore(fs *afero.Afero) *fsStore {
+	return &fsStore{fs: fs}
+}
+
+func (s *fsStore) Get(key string) ([]byte, error) {
+	s.mux.RLock()
+	defer s.mux.RUnlock()
+	return s.fs.ReadFile(key)
+}
+
+func (s *fsStore) Set(key string, value []byte) error {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+	if err := s.fs.MkdirAll(filepath.Base(key), 0o755); err != nil {
+		return fmt.Errorf("creating directory for %q: %w", key, err)
+	}
+	return s.fs.WriteFile(key, value, 0o644)
+}
+
+func (s *fsStore) CompareAndSwap(key string, oldVal, newVal []byte) error {
+	s.mux.Lock()
+	defer s.mux.Unlock()
+	current, err := s.fs.ReadFile(key)
+	// Treat non-existing file as empty to allow initial set.
+	if err != nil && !(errors.Is(err, fs.ErrNotExist) && len(oldVal) == 0) {
+		return err
+	}
+	if !bytes.Equal(current, oldVal) {
+		return fmt.Errorf("object %q has changed since last read", key)
+	}
+	if err := s.fs.MkdirAll(filepath.Base(key), 0o755); err != nil {
+		return fmt.Errorf("creating directory for %q: %w", key, err)
+	}
+	return s.fs.WriteFile(key, newVal, 0o644)
+}

coordinator/history/history.go

@@ -0,0 +1,231 @@
+// Copyright 2024 Edgeless Systems GmbH
+// SPDX-License-Identifier: AGPL-3.0-only
+
+package history
+
+import (
+	"bytes"
+	"crypto/ecdsa"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"hash"
+
+	"github.com/spf13/afero"
+)
+
+const (
+	hashSize = 32 // byte, History.hashFun().Size()
+	histPath = "/mnt/state/history"
+)
+
+// History is the history of the Coordinator.
+type History struct {
+	store      store
+	hashFun    func() hash.Hash
+	signingKey *ecdsa.PrivateKey
+}
+
+// New creates a new History with the given signing key.
+func New() (*History, error) {
+	osFS := afero.NewOsFs()
+	if err := osFS.MkdirAll(histPath, 0o755); err != nil {
+		return nil, fmt.Errorf("creating history directory: %w", err)
+	}
+	h := &History{
+		store:   newPVStore(&afero.Afero{Fs: afero.NewBasePathFs(osFS, histPath)}),
+		hashFun: sha256.New,
+	}
+	if hashSize != h.hashFun().Size() {
+		return nil, errors.New("mismatch between hashSize and hash function size")
+	}
+	return h, nil
+}
+
+// ConfigureSigningKey sets the signing key for validation and signing of the protected history parts.
+func (h *History) ConfigureSigningKey(signingKey *ecdsa.PrivateKey) {
+	h.signingKey = signingKey
+}
+
+// GetManifest returns the manifest for the given hash.
+func (h *History) GetManifest(hash [hashSize]byte) ([]byte, error) {
+	return h.getContentaddressed("manifests/%s", hash)
+}
+
+// SetManifest sets the manifest and returns its hash.
+func (h *History) SetManifest(manifest []byte) ([hashSize]byte, error) {
+	return h.setContentaddressed("manifests/%s", manifest)
+}
+
+// GetPolicy returns the policy for the given hash.
+func (h *History) GetPolicy(hash [hashSize]byte) ([]byte, error) {
+	return h.getContentaddressed("policies/%s", hash)
+}
+
+// SetPolicy sets the policy and returns its hash.
+func (h *History) SetPolicy(policy []byte) ([hashSize]byte, error) {
+	return h.setContentaddressed("policies/%s", policy)
+}
+
+// GetTransition returns the transition for the given hash.
+func (h *History) GetTransition(hash [hashSize]byte) (*Transition, error) {
+	transitionBytes, err := h.getContentaddressed("transitions/%s", hash)
+	if err != nil {
+		return nil, err
+	}
+	var transition Transition
+	if err := transition.unmarshalBinary(transitionBytes); err != nil {
+		return nil, fmt.Errorf("unmarshaling transition: %w", err)
+	}
+	return &transition, nil
+}
+
+// SetTransition sets the transition and returns its hash.
+func (h *History) SetTransition(transition *Transition) ([hashSize]byte, error) {
+	return h.setContentaddressed("transitions/%s", transition.marshalBinary())
+}
+
+// GetLatest returns the verified transition for the given hash.
+func (h *History) GetLatest() (*LatestTransition, error) {
+	if h.signingKey == nil {
+		return nil, errors.New("signing key not configured")
+	}
+	transitionBytes, err := h.store.Get("transitions/latest")
+	if err != nil {
+		return nil, fmt.Errorf("getting latest transition: %w", err)
+	}
+	var latestTransition LatestTransition
+	if err := latestTransition.unmarshalBinary(transitionBytes); err != nil {
+		return nil, fmt.Errorf("unmarshaling latest transition: %w", err)
+	}
+	if err := latestTransition.verify(&h.signingKey.PublicKey); err != nil {
+		return nil, fmt.Errorf("verifying latest transition: %w", err)
+	}
+	return &latestTransition, nil
+}
+
+// SetLatest signs and sets the latest transition if the current latest is equal to oldT.
+func (h *History) SetLatest(oldT, newT *LatestTransition) error {
+	if h.signingKey == nil {
+		return errors.New("signing key not configured")
+	}
+	if err := newT.sign(h.signingKey); err != nil {
+		return fmt.Errorf("signing latest transition: %w", err)
+	}
+	if err := h.store.CompareAndSwap("transitions/latest", oldT.marshalBinary(), newT.marshalBinary()); err != nil {
+		return fmt.Errorf("setting latest transition: %w", err)
+	}
+	return nil
+}
+
+func (h *History) getContentaddressed(pathFmt string, hash [hashSize]byte) ([]byte, error) {
+	hashStr := hex.EncodeToString(hash[:])
+	data, err := h.store.Get(fmt.Sprintf(pathFmt, hashStr))
+	if err != nil {
+		return nil, err
+	}
+	dataHash := h.hash(data)
+	if !bytes.Equal(hash[:], dataHash[:]) {
+		return nil, HashMismatchError{Expected: hash[:], Actual: dataHash[:]}
+	}
+	return data, nil
+}
+
+func (h *History) setContentaddressed(pathFmt string, data []byte) ([hashSize]byte, error) {
+	hash := h.hash(data)
+	hashStr := hex.EncodeToString(hash[:])
+	if err := h.store.Set(fmt.Sprintf(pathFmt, hashStr), data); err != nil {
+		return [hashSize]byte{}, err
+	}
+	return hash, nil
+}
+
+func (h *History) hash(in []byte) [hashSize]byte {
+	hf := h.hashFun()
+	_, _ = hf.Write(in) // Hash.Write never returns an error.
+	sum := hf.Sum(nil)
+	var hash [hashSize]byte
+	copy(hash[:], sum) // Correct len of sum enforced in constructor.
+	return hash
+}
+
+// Transition is a transition between two manifests.
+type Transition struct {
+	ManifestHash           [hashSize]byte
+	PreviousTransitionHash [hashSize]byte
+}
+
+func (t *Transition) unmarshalBinary(data []byte) error {
+	if len(data) != 2*hashSize {
+		return fmt.Errorf("transition has invalid length %d, expected %d", len(data), 2*hashSize)
+	}
+	copy(t.ManifestHash[:], data[:hashSize])
+	copy(t.PreviousTransitionHash[:], data[hashSize:])
+	return nil
+}
+
+func (t *Transition) marshalBinary() []byte {
+	data := make([]byte, 2*hashSize)
+	copy(data[:hashSize], t.ManifestHash[:])
+	copy(data[hashSize:], t.PreviousTransitionHash[:])
+	return data
+}
+
+// LatestTransition is the latest transition signed by the Coordinator.
+type LatestTransition struct {
+	TransitionHash [hashSize]byte
+	signature      []byte
+}
+
+func (l *LatestTransition) unmarshalBinary(data []byte) error {
+	if len(data) <= hashSize {
+		return errors.New("latest transition has invalid length")
+	}
+	sigLen := len(data) - hashSize
+	l.signature = make([]byte, sigLen)
+	copy(l.TransitionHash[:], data[:hashSize])
+	copy(l.signature, data[hashSize:])
+	return nil
+}
+
+func (l *LatestTransition) marshalBinary() []byte {
+	if l == nil {
+		return []byte{}
+	}
+	data := make([]byte, hashSize+len(l.signature))
+	copy(data[:hashSize], l.TransitionHash[:])
+	copy(data[hashSize:], l.signature)
+	return data
+}
+
+func (l *LatestTransition) sign(key *ecdsa.PrivateKey) error {
+	var err error
+	l.signature, err = ecdsa.SignASN1(rand.Reader, key, l.TransitionHash[:])
+	return err
+}
+
+func (l *LatestTransition) verify(key *ecdsa.PublicKey) error {
+	if !ecdsa.VerifyASN1(key, l.TransitionHash[:], l.signature) {
+		return errors.New("latest transition signature is invalid")
+	}
+	return nil
+}
+
+// HashMismatchError is returned when a hash does not match the expected value.
+// This can occur when content addressed storage has been corrupted.
+type HashMismatchError struct {
+	Expected []byte
+	Actual   []byte
+}
+
+func (e HashMismatchError) Error() string {
+	return fmt.Sprintf("hash mismatch: expected %x, got %x", e.Expected, e.Actual)
+}
+
+type store interface {
+	Get(key string) ([]byte, error)
+	Set(key string, value []byte) error
+	CompareAndSwap(key string, oldVal, newVal []byte) error
+}