Merge pull request #124 from docker/feat-generate-vsa-policy-uri

feat: add `digest` and `downloadLocation` to VSA policy

README.md

@@ -345,7 +345,11 @@ The VSA can be signed and published to the registry using the signing functions
     "timeVerified": "2024-04-19T08:00:00.01Z",
     "resourceUri": "pkg:docker/example.org/example-image@1.0?platform=linux%2Famd64&digest=sha256%3A49f717386e5462e945232569a97a05831cb83bef8c3369be3bb7ea1793686960",
     "policy": {
-      "uri": "https://example.org/internal-policy/v1"
+      "uri": "https://example.org/internal-policy/v1",
+      "downloadLocation": "https://docker.github.io/tuf-staging/targets/docker/d71d6b8f49fcba1295b16f5394dd5863a14e4277eb663d66d8c48e392509afe0.policy.rego",
+      "digest": {
+        "sha256": "d71d6b8f49fcba1295b16f5394dd5863a14e4277eb663d66d8c48e392509afe0"
+      }
     },
     "verificationResult": "PASSED",
     "verifiedLevels": ["SLSA_BUILD_LEVEL_3"]

pkg/attest/verify.go

@@ -86,6 +86,8 @@ func toVerificationResult(p *policy.Policy, input *policy.Input, result *policy.
 		return nil, err
 	}
 
+	vsaPolicy := attestation.VSAPolicy{URI: result.Summary.PolicyURI, DownloadLocation: p.URI, Digest: p.Digest}
+
 	return &VerificationResult{
 		Policy:     p,
 		Outcome:    outcome,
@@ -103,7 +105,7 @@ func toVerificationResult(p *policy.Policy, input *policy.Input, result *policy.
 				},
 				TimeVerified:       time.Now().UTC().Format(time.RFC3339),
 				ResourceURI:        resourceURI,
-				Policy:             attestation.VSAPolicy{URI: result.Summary.PolicyURI},
+				Policy:             vsaPolicy,
 				VerificationResult: outcomeStr,
 				VerifiedLevels:     result.Summary.SLSALevels,
 			},

pkg/attest/verify_test.go

@@ -112,7 +112,9 @@ func TestVSA(t *testing.T) {
 	assert.Equal(t, "PASSED", attestationPredicate.VerificationResult)
 	assert.Equal(t, "docker-official-images", attestationPredicate.Verifier.ID)
 	assert.Equal(t, []string{"SLSA_BUILD_LEVEL_3"}, attestationPredicate.VerifiedLevels)
+	assert.Equal(t, PassPolicyDir+"/policy.rego", attestationPredicate.Policy.DownloadLocation)
 	assert.Equal(t, "https://docker.com/official/policy/v0.1", attestationPredicate.Policy.URI)
+	assert.Equal(t, map[string]string{"sha256": "d71d6b8f49fcba1295b16f5394dd5863a14e4277eb663d66d8c48e392509afe0"}, attestationPredicate.Policy.Digest)
 }
 
 func TestVerificationFailure(t *testing.T) {
@@ -162,7 +164,9 @@ func TestVerificationFailure(t *testing.T) {
 	assert.Equal(t, "FAILED", attestationPredicate.VerificationResult)
 	assert.Equal(t, "docker-official-images", attestationPredicate.Verifier.ID)
 	assert.Equal(t, []string{"SLSA_BUILD_LEVEL_3"}, attestationPredicate.VerifiedLevels)
+	assert.Equal(t, FailPolicyDir+"/policy.rego", attestationPredicate.Policy.DownloadLocation)
 	assert.Equal(t, "https://docker.com/official/policy/v0.1", attestationPredicate.Policy.URI)
+	assert.Equal(t, map[string]string{"sha256": "ad045e1bd7cd602d90196acf68f2c57d7b51565d59e6e30e30d94ae86aa16201"}, attestationPredicate.Policy.Digest)
 }
 
 func TestSignVerify(t *testing.T) {

pkg/attestation/vsa.go

@@ -16,7 +16,7 @@ type VSAPredicate struct {
 	TimeVerified       string                `json:"timeVerified"`
 	ResourceURI        string                `json:"resourceUri"`
 	Policy             VSAPolicy             `json:"policy"`
-	InputAttestations  []VSAInputAttestation `json:"inputAttestations"`
+	InputAttestations  []VSAInputAttestation `json:"inputAttestations,omitempty"`
 	VerificationResult string                `json:"verificationResult"`
 	VerifiedLevels     []string              `json:"verifiedLevels"`
 }
@@ -26,7 +26,9 @@ type VSAVerifier struct {
 }
 
 type VSAPolicy struct {
-	URI string `json:"uri"`
+	URI              string            `json:"uri,omitempty"`
+	Digest           map[string]string `json:"digest"`
+	DownloadLocation string            `json:"downloadLocation,omitempty"`
 }
 
 type VSAInputAttestation struct {

pkg/config/config.go

@@ -36,13 +36,13 @@ func LoadTUFMappings(tufClient tuf.Downloader, localTargetsDir string) (*PolicyM
 		return nil, fmt.Errorf("tuf client not set")
 	}
 	filename := MappingFilename
-	_, fileContents, err := tufClient.DownloadTarget(filename, filepath.Join(localTargetsDir, filename))
+	file, err := tufClient.DownloadTarget(filename, filepath.Join(localTargetsDir, filename))
 	if err != nil {
 		return nil, fmt.Errorf("failed to download policy mapping file %s: %w", filename, err)
 	}
 	mappings := &policyMappingsFile{}
 
-	err = yaml.Unmarshal(fileContents, mappings)
+	err = yaml.Unmarshal(file.Data, mappings)
 	if err != nil {
 		return nil, fmt.Errorf("failed to unmarshal policy mapping file %s: %w", filename, err)
 	}

pkg/mirror/targets.go

@@ -23,7 +23,7 @@ func (m *TUFMirror) GetTUFTargetMirrors() ([]*Image, error) {
 	targets := md.Targets[metadata.TARGETS].Signed.Targets
 	for _, t := range targets {
 		// download target file
-		_, data, err := m.TUFClient.DownloadTarget(t.Path, filepath.Join(m.tufPath, "download"))
+		file, err := m.TUFClient.DownloadTarget(t.Path, filepath.Join(m.tufPath, "download"))
 		if err != nil {
 			return nil, fmt.Errorf("failed to download target %s: %w", t.Path, err)
 		}
@@ -38,7 +38,7 @@ func (m *TUFMirror) GetTUFTargetMirrors() ([]*Image, error) {
 		}
 		name := hash.String() + "." + t.Path
 		ann := map[string]string{tufFileAnnotation: name}
-		layer := mutate.Addendum{Layer: static.NewLayer(data, tufTargetMediaType), Annotations: ann}
+		layer := mutate.Addendum{Layer: static.NewLayer(file.Data, tufTargetMediaType), Annotations: ann}
 		img, err = mutate.Append(img, layer)
 		if err != nil {
 			return nil, fmt.Errorf("failed to append role layer to image: %w", err)
@@ -69,7 +69,7 @@ func (m *TUFMirror) GetDelegatedTargetMirrors() ([]*Index, error) {
 		// for each target file, create an image with the target file as a layer
 		for _, target := range roleMeta.Signed.Targets {
 			// download target file
-			_, data, err := m.TUFClient.DownloadTarget(target.Path, filepath.Join(m.tufPath, "download"))
+			file, err := m.TUFClient.DownloadTarget(target.Path, filepath.Join(m.tufPath, "download"))
 			if err != nil {
 				return nil, fmt.Errorf("failed to download target %s: %w", target.Path, err)
 			}
@@ -89,7 +89,7 @@ func (m *TUFMirror) GetDelegatedTargetMirrors() ([]*Index, error) {
 			}
 			name := hash.String() + "." + filename
 			ann := map[string]string{tufFileAnnotation: name}
-			layer := mutate.Addendum{Layer: static.NewLayer(data, tufTargetMediaType), Annotations: ann}
+			layer := mutate.Addendum{Layer: static.NewLayer(file.Data, tufTargetMediaType), Annotations: ann}
 			img, err = mutate.Append(img, layer)
 			if err != nil {
 				return nil, fmt.Errorf("failed to append role layer to image: %w", err)

pkg/policy/policy.go

@@ -8,6 +8,7 @@ import (
 	"path/filepath"
 
 	"github.com/distribution/reference"
+	"github.com/docker/attest/internal/util"
 	"github.com/docker/attest/pkg/attestation"
 	"github.com/docker/attest/pkg/config"
 	"github.com/docker/attest/pkg/oci"
@@ -17,6 +18,8 @@ func resolveLocalPolicy(opts *Options, mapping *config.PolicyMapping, imageName
 	if opts.LocalPolicyDir == "" {
 		return nil, fmt.Errorf("local policy dir not set")
 	}
+	var URI string
+	var digest map[string]string
 	files := make([]*File, 0, len(mapping.Files))
 	for _, f := range mapping.Files {
 		filename := f.Path
@@ -29,10 +32,24 @@ func resolveLocalPolicy(opts *Options, mapping *config.PolicyMapping, imageName
 			Path:    filename,
 			Content: fileContents,
 		})
+		// if the file is a policy file, store the URI and digest
+		if filepath.Ext(filename) == ".rego" {
+			// TODO: support multiple rego files, need some way to identify the main policy file
+			if URI != "" {
+				return nil, fmt.Errorf("multiple policy files found in policy mapping")
+			}
+			URI = filePath
+			digest = map[string]string{"sha256": util.SHA256Hex(fileContents)}
+		}
+	}
+	if URI == "" {
+		return nil, fmt.Errorf("no policy file found in policy mapping")
 	}
 	policy := &Policy{
 		InputFiles: files,
 		Mapping:    mapping,
+		URI:        URI,
+		Digest:     digest,
 	}
 	if imageName != matchedName {
 		policy.ResolvedName = matchedName
@@ -41,21 +58,37 @@ func resolveLocalPolicy(opts *Options, mapping *config.PolicyMapping, imageName
 }
 
 func resolveTUFPolicy(opts *Options, mapping *config.PolicyMapping, imageName string, matchedName string) (*Policy, error) {
+	var URI string
+	var digest map[string]string
 	files := make([]*File, 0, len(mapping.Files))
 	for _, f := range mapping.Files {
 		filename := f.Path
-		_, fileContents, err := opts.TUFClient.DownloadTarget(filename, filepath.Join(opts.LocalTargetsDir, filename))
+		file, err := opts.TUFClient.DownloadTarget(filename, filepath.Join(opts.LocalTargetsDir, filename))
 		if err != nil {
 			return nil, fmt.Errorf("failed to download policy file %s: %w", filename, err)
 		}
 		files = append(files, &File{
 			Path:    filename,
-			Content: fileContents,
+			Content: file.Data,
 		})
+		// if the file is a policy file, store the URI and digest
+		if filepath.Ext(filename) == ".rego" {
+			// TODO: support multiple rego files, need some way to identify the main policy file
+			if URI != "" {
+				return nil, fmt.Errorf("multiple policy files found in policy mapping")
+			}
+			URI = file.TargetURI
+			digest = map[string]string{"sha256": file.Digest}
+		}
+	}
+	if URI == "" {
+		return nil, fmt.Errorf("no policy file found in policy mapping")
 	}
 	policy := &Policy{
 		InputFiles: files,
 		Mapping:    mapping,
+		URI:        URI,
+		Digest:     digest,
 	}
 	if imageName != matchedName {
 		policy.ResolvedName = matchedName

pkg/policy/policy_test.go

@@ -32,7 +32,7 @@ func loadAttestation(t *testing.T, path string) *attestation.Envelope {
 
 func TestRegoEvaluator_Evaluate(t *testing.T) {
 	ctx, _ := test.Setup(t)
-	errorStr := "failed to resolve policy by id: policy with id non-existent-policy-id not found"
+	resolveErrorStr := "failed to resolve policy by id: policy with id non-existent-policy-id not found"
 	TestDataPath := filepath.Join("..", "..", "test", "testdata")
 	ExampleAttestation := filepath.Join(TestDataPath, "example_attestation.json")
 
@@ -43,22 +43,23 @@ func TestRegoEvaluator_Evaluate(t *testing.T) {
 	}
 
 	testCases := []struct {
-		repo          string
+		repo            string
-		expectSuccess bool
+		expectSuccess   bool
-		isCanonical   bool
+		isCanonical     bool
-		resolver      attestation.Resolver
+		resolver        attestation.Resolver
-		policy        *policy.Options
+		policy          *policy.Options
-		policyID      string
+		policyID        string
-		errorStr      string
+		resolveErrorStr string
 	}{
 		{repo: "testdata/mock-tuf-allow", expectSuccess: true, isCanonical: false, resolver: defaultResolver},
 		{repo: "testdata/mock-tuf-allow", expectSuccess: true, isCanonical: false, resolver: defaultResolver, policyID: "docker-official-images"},
-		{repo: "testdata/mock-tuf-allow", expectSuccess: false, isCanonical: false, resolver: defaultResolver, policyID: "non-existent-policy-id", errorStr: errorStr},
+		{repo: "testdata/mock-tuf-allow", expectSuccess: false, isCanonical: false, resolver: defaultResolver, policyID: "non-existent-policy-id", resolveErrorStr: resolveErrorStr},
 		{repo: "testdata/mock-tuf-deny", expectSuccess: false, isCanonical: false, resolver: defaultResolver},
 		{repo: "testdata/mock-tuf-verify-sig", expectSuccess: true, isCanonical: false, resolver: defaultResolver},
 		{repo: "testdata/mock-tuf-wrong-key", expectSuccess: false, isCanonical: false, resolver: defaultResolver},
 		{repo: "testdata/mock-tuf-allow-canonical", expectSuccess: true, isCanonical: true, resolver: defaultResolver},
 		{repo: "testdata/mock-tuf-allow-canonical", expectSuccess: false, isCanonical: false, resolver: defaultResolver},
+		{repo: "testdata/mock-tuf-no-rego", expectSuccess: false, isCanonical: false, resolver: defaultResolver, resolveErrorStr: "no policy file found in policy mapping"},
 	}
 
 	for _, tc := range testCases {
@@ -86,9 +87,9 @@ func TestRegoEvaluator_Evaluate(t *testing.T) {
 			resolver, err := policy.CreateImageDetailsResolver(src)
 			require.NoError(t, err)
 			policy, err := policy.ResolvePolicy(ctx, resolver, tc.policy)
-			if tc.errorStr != "" {
+			if tc.resolveErrorStr != "" {
 				require.Error(t, err)
-				assert.Contains(t, err.Error(), tc.errorStr)
+				assert.Contains(t, err.Error(), tc.resolveErrorStr)
 				return
 			}
 			require.NoErrorf(t, err, "failed to resolve policy")

pkg/policy/testdata/mock-tuf-no-rego/doi/policy.yaml

@@ -0,0 +1 @@
+policy: "this is not rego"

pkg/policy/testdata/mock-tuf-no-rego/mapping.yaml

@@ -0,0 +1,11 @@
+# map repos to policies
+version: v1
+kind: policy-mapping
+policies:
+  - id: docker-official-images
+    description: Docker Official Images
+    files:
+      - path: doi/policy.yaml
+rules:
+  - pattern: "^docker[.]io/library/(.*)$"
+    policy-id: docker-official-images

pkg/policy/types.go

@@ -40,6 +40,8 @@ type Policy struct {
 	Query        string
 	Mapping      *config.PolicyMapping
 	ResolvedName string
+	URI          string
+	Digest       map[string]string
 }
 
 type Input struct {

pkg/tuf/example_registry_test.go

@@ -28,16 +28,13 @@ func ExampleNewClient_registry() {
 
 	// get trusted tuf metadata
 	trustedMetadata := registryClient.GetMetadata()
-	if err != nil {
-		panic(err)
-	}
 
 	// top-level target files
 	targets := trustedMetadata.Targets[metadata.TARGETS].Signed.Targets
 
 	for _, t := range targets {
 		// download target files
-		_, _, err := registryClient.DownloadTarget(t.Path, filepath.Join(tufOutputPath, "download"))
+		_, err := registryClient.DownloadTarget(t.Path, filepath.Join(tufOutputPath, "download"))
 		if err != nil {
 			panic(err)
 		}

pkg/tuf/mock.go

@@ -4,6 +4,8 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+
+	"github.com/docker/attest/internal/util"
 )
 
 type MockTufClient struct {
@@ -24,10 +26,11 @@ func NewMockTufClient(srcPath string, dstPath string) *MockTufClient {
 	}
 }
 
-func (dc *MockTufClient) DownloadTarget(target string, filePath string) (actualFilePath string, data []byte, err error) {
+func (dc *MockTufClient) DownloadTarget(target string, filePath string) (file *TargetFile, err error) {
-	src, err := os.Open(filepath.Join(dc.srcPath, target))
+	targetPath := filepath.Join(dc.srcPath, target)
+	src, err := os.Open(targetPath)
 	if err != nil {
-		return "", nil, err
+		return nil, err
 	}
 	defer src.Close()
 
@@ -40,11 +43,11 @@ func (dc *MockTufClient) DownloadTarget(target string, filePath string) (actualF
 
 	err = os.MkdirAll(filepath.Dir(dstFilePath), os.ModePerm)
 	if err != nil {
-		return "", nil, err
+		return nil, err
 	}
 	dst, err := os.Create(dstFilePath)
 	if err != nil {
-		return "", nil, err
+		return nil, err
 	}
 	defer dst.Close()
 
@@ -53,10 +56,10 @@ func (dc *MockTufClient) DownloadTarget(target string, filePath string) (actualF
 
 	b, err := io.ReadAll(tee)
 	if err != nil {
-		return "", nil, err
+		return nil, err
 	}
 
-	return dstFilePath, b, nil
+	return &TargetFile{ActualFilePath: dstFilePath, TargetURI: targetPath, Data: b, Digest: util.SHA256Hex(b)}, nil
 }
 
 type MockVersionChecker struct {

pkg/tuf/tuf.go

@@ -36,7 +36,7 @@ var (
 )
 
 type Downloader interface {
-	DownloadTarget(target, filePath string) (actualFilePath string, data []byte, err error)
+	DownloadTarget(target, filePath string) (file *TargetFile, err error)
 }
 
 type Client struct {
@@ -44,6 +44,13 @@ type Client struct {
 	cfg     *config.UpdaterConfig
 }
 
+type TargetFile struct {
+	ActualFilePath string
+	TargetURI      string
+	Digest         string
+	Data           []byte
+}
+
 // NewClient creates a new TUF client.
 func NewClient(initialRoot []byte, tufPath, metadataSource, targetsSource string, versionChecker VersionChecker) (*Client, error) {
 	var tufSource Source
@@ -119,40 +126,69 @@ func NewClient(initialRoot []byte, tufPath, metadataSource, targetsSource string
 	return client, nil
 }
 
+func (t *Client) generateTargetURI(target *metadata.TargetFiles, digest string) (string, error) {
+	switch fetcher := t.cfg.Fetcher.(type) {
+	case *RegistryFetcher:
+		return fmt.Sprintf("%s@sha256:%s", t.cfg.RemoteTargetsURL, digest), nil
+	case *fetcher.DefaultFetcher:
+		targetBaseURL := ensureTrailingSlash(t.cfg.RemoteTargetsURL)
+		targetRemotePath := target.Path
+		// if PrefixTargetsWithHash is set, we need to prefix the target name with the hash and handle subdirectories
+		// similar logic to https://github.com/theupdateframework/go-tuf/blob/f95222bdd22d2ac4e5b8ed6fe912b645e213c3b5/metadata/updater/updater.go#L227-L247
+		if t.cfg.PrefixTargetsWithHash {
+			baseName := filepath.Base(targetRemotePath)
+			dirName, ok := strings.CutSuffix(targetRemotePath, "/"+baseName)
+			if !ok {
+				// <hash>.<target-name>
+				targetRemotePath = fmt.Sprintf("%s.%s", digest, baseName)
+			} else {
+				// <dir-prefix>/<hash>.<target-name>
+				targetRemotePath = fmt.Sprintf("%s/%s.%s", dirName, digest, baseName)
+			}
+		}
+		return fmt.Sprintf("%s%s", targetBaseURL, targetRemotePath), nil
+	default:
+		return "", fmt.Errorf("unsupported fetcher type: %T", fetcher)
+	}
+}
+
 // DownloadTarget downloads the target file using Updater. The Updater gets the target
 // information, verifies if the target is already cached, and if it is not cached,
 // downloads the target file.
-func (t *Client) DownloadTarget(target string, filePath string) (actualFilePath string, data []byte, err error) {
+func (t *Client) DownloadTarget(target string, filePath string) (file *TargetFile, err error) {
 	// search if the desired target is available
 	targetInfo, err := t.updater.GetTargetInfo(target)
 	if err != nil {
-		return "", nil, err
+		return nil, err
 	}
 
 	// check if filePath exists and create the directory if it doesn't
 	if _, err := os.Stat(filepath.Dir(filePath)); os.IsNotExist(err) {
 		err = os.MkdirAll(filepath.Dir(filePath), os.ModePerm)
 		if err != nil {
-			return "", nil, fmt.Errorf("failed to create target download directory '%s': %w", filepath.Dir(filePath), err)
+			return nil, fmt.Errorf("failed to create target download directory '%s': %w", filepath.Dir(filePath), err)
 		}
 	}
 
 	// target is available, so let's see if the target is already present locally
-	actualFilePath, data, err = t.updater.FindCachedTarget(targetInfo, filePath)
+	actualFilePath, data, err := t.updater.FindCachedTarget(targetInfo, filePath)
 	if err != nil {
-		return "", nil, fmt.Errorf("failed while finding a cached target: %w", err)
+		return nil, fmt.Errorf("failed while finding a cached target: %w", err)
 	}
 	if data != nil {
-		return actualFilePath, data, err
+		digest := util.SHA256Hex(data)
+		uri, err := t.generateTargetURI(targetInfo, digest)
+		return &TargetFile{ActualFilePath: actualFilePath, TargetURI: uri, Data: data, Digest: digest}, err
 	}
 
 	// target is not present locally, so let's try to download it
 	actualFilePath, data, err = t.updater.DownloadTarget(targetInfo, filePath, "")
 	if err != nil {
-		return "", nil, fmt.Errorf("failed to download target file %s - %w", target, err)
+		return nil, fmt.Errorf("failed to download target file %s - %w", target, err)
 	}
-
+	digest := util.SHA256Hex(data)
-	return actualFilePath, data, err
+	uri, err := t.generateTargetURI(targetInfo, digest)
+	return &TargetFile{ActualFilePath: actualFilePath, TargetURI: uri, Data: data, Digest: digest}, err
 }
 
 func (t *Client) GetMetadata() trustedmetadata.TrustedMetadata {

pkg/tuf/tuf_test.go

@@ -122,14 +122,14 @@ func TestDownloadTarget(t *testing.T) {
 		targets := trustedMetadata.Targets[metadata.TARGETS].Signed.Targets
 		for _, target := range targets {
 			// download target files
-			_, _, err := tufClient.DownloadTarget(target.Path, filepath.Join(tufPath, "download"))
+			_, err := tufClient.DownloadTarget(target.Path, filepath.Join(tufPath, "download"))
 			assert.NoErrorf(t, err, "Failed to download target: %v", err)
 		}
 
 		// download delegated target
 		targetInfo, err := tufClient.updater.GetTargetInfo(delegatedTargetFile)
 		assert.NoError(t, err)
-		_, _, err = tufClient.DownloadTarget(targetInfo.Path, filepath.Join(tufPath, targetInfo.Path))
+		_, err = tufClient.DownloadTarget(targetInfo.Path, filepath.Join(tufPath, targetInfo.Path))
 		assert.NoError(t, err)
 	}
 }

pkg/tuf/version.go

@@ -67,11 +67,11 @@ func (vc *DefaultVersionChecker) CheckVersion(client Downloader) error {
 
 	// see https://github.com/Masterminds/semver/blob/v3.2.1/README.md#checking-version-constraints
 	// for more information on the expected format of the version constraints in the TUF repo
-	_, versionConstraintsBytes, err := client.DownloadTarget("version-constraints", "")
+	target, err := client.DownloadTarget("version-constraints", "")
 	if err != nil {
 		return fmt.Errorf("failed to download version-constraints: %w", err)
 	}
-	versionConstraints, err := semver.NewConstraint(string(versionConstraintsBytes))
+	versionConstraints, err := semver.NewConstraint(string(target.Data))
 	if err != nil {
 		return fmt.Errorf("failed to parse minimum version: %w", err)
 	}