cosign: allow identity matching for keyless verification

Add `.spec.verify.matchOIDCIdentity` to OCIRepository and HelmChart. It allows specifying regular expressions to match against the subject and issuer of the certificate related to the artifact signature. Its used only if the artifact was signed using Cosign keyless signing. Signed-off-by: Sanskar Jaiswal <[email protected]>
fluxcd · Oct 10, 2023 · a96c5be · a96c5be
1 parent 3cf4fdf
commit a96c5be
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Showing 11 changed files with 523 additions and 13 deletions.
diff --git a/api/v1beta2/ocirepository_types.go b/api/v1beta2/ocirepository_types.go
@@ -190,6 +190,28 @@ type OCIRepositoryVerification struct {
 	// trusted public keys.
 	// +optional
 	SecretRef *meta.LocalObjectReference `json:"secretRef,omitempty"`
+
+	// MatchOIDCIdentity specifies the identity matching criteria to use
+	// while verifying an OCI artifact which was signed using Cosign keyless
+	// signing. The artifact's identity is deemed to be verified if any of the
+	// specified matchers match against the identity.
+	// +optional
+	MatchOIDCIdentity []OIDCIdentityMatch `json:"matchOIDCIdentity,omitempty"`
+}
+
+// OIDCIdentityMatch specifies options for verifying the certificate identity,
+// i.e. the issuer and the subject of the certificate.
+type OIDCIdentityMatch struct {
+	// Issuer specifies the regex pattern to match against to verify
+	// the OIDC issuer in the Fulcio certificate. The pattern must be a
+	// valid Go regular expression.
+	// +required
+	Issuer string `json:"issuer"`
+	// Subject specifies the regex pattern to match against to verify
+	// the identity subject in the Fulcio certificate. The pattern must
+	// be a valid Go regular expression.
+	// +required
+	Subject string `json:"subject"`
 }
 
 // OCIRepositoryStatus defines the observed state of OCIRepository

diff --git a/api/v1beta2/zz_generated.deepcopy.go b/api/v1beta2/zz_generated.deepcopy.go
diff --git a/config/crd/bases/source.toolkit.fluxcd.io_helmcharts.yaml b/config/crd/bases/source.toolkit.fluxcd.io_helmcharts.yaml
@@ -411,6 +411,32 @@ spec:
                   Chart dependencies, which are not bundled in the umbrella chart
                   artifact, are not verified.
                 properties:
+                  matchOIDCIdentity:
+                    description: MatchOIDCIdentity specifies the identity matching
+                      criteria to use while verifying an OCI artifact which was signed
+                      using Cosign keyless signing. The artifact's identity is deemed
+                      to be verified if any of the specified matchers match against
+                      the identity.
+                    items:
+                      description: OIDCIdentityMatch specifies options for verifying
+                        the certificate identity, i.e. the issuer and the subject
+                        of the certificate.
+                      properties:
+                        issuer:
+                          description: Issuer specifies the regex pattern to match
+                            against to verify the OIDC issuer in the Fulcio certificate.
+                            The pattern must be a valid Go regular expression.
+                          type: string
+                        subject:
+                          description: Subject specifies the regex pattern to match
+                            against to verify the identity subject in the Fulcio certificate.
+                            The pattern must be a valid Go regular expression.
+                          type: string
+                      required:
+                      - issuer
+                      - subject
+                      type: object
+                    type: array
                   provider:
                     default: cosign
                     description: Provider specifies the technology used to sign the

diff --git a/config/crd/bases/source.toolkit.fluxcd.io_ocirepositories.yaml b/config/crd/bases/source.toolkit.fluxcd.io_ocirepositories.yaml
@@ -164,6 +164,32 @@ spec:
                   public keys used to verify the signature and specifies which provider
                   to use to check whether OCI image is authentic.
                 properties:
+                  matchOIDCIdentity:
+                    description: MatchOIDCIdentity specifies the identity matching
+                      criteria to use while verifying an OCI artifact which was signed
+                      using Cosign keyless signing. The artifact's identity is deemed
+                      to be verified if any of the specified matchers match against
+                      the identity.
+                    items:
+                      description: OIDCIdentityMatch specifies options for verifying
+                        the certificate identity, i.e. the issuer and the subject
+                        of the certificate.
+                      properties:
+                        issuer:
+                          description: Issuer specifies the regex pattern to match
+                            against to verify the OIDC issuer in the Fulcio certificate.
+                            The pattern must be a valid Go regular expression.
+                          type: string
+                        subject:
+                          description: Subject specifies the regex pattern to match
+                            against to verify the identity subject in the Fulcio certificate.
+                            The pattern must be a valid Go regular expression.
+                          type: string
+                      required:
+                      - issuer
+                      - subject
+                      type: object
+                    type: array
                   provider:
                     default: cosign
                     description: Provider specifies the technology used to sign the

diff --git a/docs/api/v1beta2/source.md b/docs/api/v1beta2/source.md
@@ -3295,6 +3295,71 @@ github.com/fluxcd/pkg/apis/meta.LocalObjectReference
 trusted public keys.</p>
 </td>
 </tr>
+<tr>
+<td>
+<code>matchOIDCIdentity</code><br>
+<em>
+<a href="#source.toolkit.fluxcd.io/v1beta2.OIDCIdentityMatch">
+[]OIDCIdentityMatch
+</a>
+</em>
+</td>
+<td>
+<em>(Optional)</em>
+<p>MatchOIDCIdentity specifies the identity matching criteria to use
+while verifying an OCI artifact which was signed using Cosign keyless
+signing. The artifact&rsquo;s identity is deemed to be verified if any of the
+specified matchers match against the identity.</p>
+</td>
+</tr>
+</tbody>
+</table>
+</div>
+</div>
+<h3 id="source.toolkit.fluxcd.io/v1beta2.OIDCIdentityMatch">OIDCIdentityMatch
+</h3>
+<p>
+(<em>Appears on:</em>
+<a href="#source.toolkit.fluxcd.io/v1beta2.OCIRepositoryVerification">OCIRepositoryVerification</a>)
+</p>
+<p>OIDCIdentityMatch specifies options for verifying the certificate identity,
+i.e. the issuer and the subject of the certificate.</p>
+<div class="md-typeset__scrollwrap">
+<div class="md-typeset__table">
+<table>
+<thead>
+<tr>
+<th>Field</th>
+<th>Description</th>
+</tr>
+</thead>
+<tbody>
+<tr>
+<td>
+<code>issuer</code><br>
+<em>
+string
+</em>
+</td>
+<td>
+<p>Issuer specifies the regex pattern to match against to verify
+the OIDC issuer in the Fulcio certificate. The pattern must be a
+valid Go regular expression.</p>
+</td>
+</tr>
+<tr>
+<td>
+<code>subject</code><br>
+<em>
+string
+</em>
+</td>
+<td>
+<p>Subject specifies the regex pattern to match against to verify
+the identity subject in the Fulcio certificate. The pattern must
+be a valid Go regular expression.</p>
+</td>
+</tr>
 </tbody>
 </table>
 </div>

diff --git a/internal/controller/helmchart_controller.go b/internal/controller/helmchart_controller.go
@@ -29,6 +29,7 @@ import (
 
 	"github.com/google/go-containerregistry/pkg/v1/remote"
 	"github.com/opencontainers/go-digest"
+	"github.com/sigstore/cosign/v2/pkg/cosign"
 	helmgetter "helm.sh/helm/v3/pkg/getter"
 	helmreg "helm.sh/helm/v3/pkg/registry"
 	helmrepo "helm.sh/helm/v3/pkg/repo"
@@ -1338,6 +1339,15 @@ func (r *HelmChartReconciler) makeVerifiers(ctx context.Context, obj *helmv1.Hel
 		}
 
 		// if no secret is provided, add a keyless verifier
+		var identities []cosign.Identity
+		for _, match := range obj.Spec.Verify.MatchOIDCIdentity {
+			identities = append(identities, cosign.Identity{
+				IssuerRegExp:  match.Issuer,
+				SubjectRegExp: match.Subject,
+			})
+		}
+		defaultCosignOciOpts = append(defaultCosignOciOpts, soci.WithIdentities(identities))
+
 		verifier, err := soci.NewCosignVerifier(ctx, defaultCosignOciOpts...)
 		if err != nil {
 			return nil, err

diff --git a/internal/controller/helmchart_controller_test.go b/internal/controller/helmchart_controller_test.go
@@ -59,6 +59,7 @@ import (
 
 	sourcev1 "github.com/fluxcd/source-controller/api/v1"
 	helmv1 "github.com/fluxcd/source-controller/api/v1beta2"
+	ociv1 "github.com/fluxcd/source-controller/api/v1beta2"
 	serror "github.com/fluxcd/source-controller/internal/error"
 	"github.com/fluxcd/source-controller/internal/helm/chart"
 	"github.com/fluxcd/source-controller/internal/helm/chart/secureloader"
@@ -2533,6 +2534,160 @@ func TestHelmChartReconciler_reconcileSourceFromOCI_authStrategy(t *testing.T) {
 	}
 }
 
+func TestHelmChartRepository_reconcileSource_verifyOCISourceSignature_keyless(t *testing.T) {
+	tests := []struct {
+		name             string
+		version          string
+		want             sreconcile.Result
+		wantErr          bool
+		wantErrMsg       string
+		beforeFunc       func(obj *helmv1.HelmChart)
+		assertConditions []metav1.Condition
+		revision         string
+	}{
+		{
+			name:    "signed image with no identity matching specified should pass verification",
+			version: "6.5.1",
+			want:    sreconcile.ResultSuccess,
+			assertConditions: []metav1.Condition{
+				*conditions.TrueCondition(sourcev1.SourceVerifiedCondition, meta.SucceededReason, "verified signature of version <version>"),
+				*conditions.TrueCondition(meta.ReconcilingCondition, meta.ProgressingReason, "building artifact: pulled '<name>' chart with version '<version>'"),
+				*conditions.UnknownCondition(meta.ReadyCondition, meta.ProgressingReason, "building artifact: pulled '<name>' chart with version '<version>'"),
+			},
+			revision: "6.5.1@sha256:af589b918022cd8d85a4543312d28170c2e894ccab8484050ff4bdefdde30b4e",
+		},
+		{
+			name:    "signed image with correct subject and issuer should pass verification",
+			version: "6.5.1",
+			want:    sreconcile.ResultSuccess,
+			beforeFunc: func(obj *helmv1.HelmChart) {
+				obj.Spec.Verify.MatchOIDCIdentity = []ociv1.OIDCIdentityMatch{
+					{
+
+						Subject: "^https://github.com/stefanprodan/podinfo.*$",
+						Issuer:  "^https://token.actions.githubusercontent.com$",
+					},
+				}
+			},
+			assertConditions: []metav1.Condition{
+				*conditions.TrueCondition(sourcev1.SourceVerifiedCondition, meta.SucceededReason, "verified signature of version <version>"),
+				*conditions.TrueCondition(meta.ReconcilingCondition, meta.ProgressingReason, "building artifact: pulled '<name>' chart with version '<version>'"),
+				*conditions.UnknownCondition(meta.ReadyCondition, meta.ProgressingReason, "building artifact: pulled '<name>' chart with version '<version>'"),
+			},
+			revision: "6.5.1@sha256:af589b918022cd8d85a4543312d28170c2e894ccab8484050ff4bdefdde30b4e",
+		},
+		{
+			name:    "signed image with incorrect subject and issuer should not pass verification",
+			version: "6.5.1",
+			wantErr: true,
+			want:    sreconcile.ResultEmpty,
+			beforeFunc: func(obj *helmv1.HelmChart) {
+				obj.Spec.Verify.MatchOIDCIdentity = []ociv1.OIDCIdentityMatch{
+					{
+						Subject: "intruder",
+						Issuer:  "^https://honeypot.com$",
+					},
+				}
+			},
+			assertConditions: []metav1.Condition{
+				*conditions.TrueCondition(sourcev1.BuildFailedCondition, "ChartVerificationError", "chart verification error: failed to verify <url>: no matching signatures: none of the expected identities matched what was in the certificate"),
+				*conditions.FalseCondition(sourcev1.SourceVerifiedCondition, sourcev1.VerificationError, "chart verification error: failed to verify <url>: no matching signatures"),
+			},
+			revision: "6.5.1@sha256:af589b918022cd8d85a4543312d28170c2e894ccab8484050ff4bdefdde30b4e",
+		},
+		{
+			name:    "unsigned image should not pass verification",
+			version: "6.1.0",
+			wantErr: true,
+			want:    sreconcile.ResultEmpty,
+			assertConditions: []metav1.Condition{
+				*conditions.TrueCondition(sourcev1.BuildFailedCondition, "ChartVerificationError", "chart verification error: failed to verify <url>: no matching signatures"),
+				*conditions.FalseCondition(sourcev1.SourceVerifiedCondition, sourcev1.VerificationError, "chart verification error: failed to verify <url>: no matching signatures"),
+			},
+			revision: "6.1.0@sha256:642383f56ccb529e3f658d40312d01b58d9bc6caeef653da43e58d1afe88982a",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			g := NewWithT(t)
+
+			clientBuilder := fakeclient.NewClientBuilder()
+
+			repository := &helmv1.HelmRepository{
+				ObjectMeta: metav1.ObjectMeta{
+					GenerateName: "helmrepository-",
+				},
+				Spec: helmv1.HelmRepositorySpec{
+					URL:      "oci://ghcr.io/stefanprodan/charts",
+					Timeout:  &metav1.Duration{Duration: timeout},
+					Provider: helmv1.GenericOCIProvider,
+					Type:     helmv1.HelmRepositoryTypeOCI,
+				},
+			}
+			clientBuilder.WithObjects(repository)
+
+			r := &HelmChartReconciler{
+				Client:                  clientBuilder.Build(),
+				EventRecorder:           record.NewFakeRecorder(32),
+				Getters:                 testGetters,
+				Storage:                 testStorage,
+				RegistryClientGenerator: registry.ClientGenerator,
+				patchOptions:            getPatchOptions(helmChartReadyCondition.Owned, "sc"),
+			}
+
+			obj := &helmv1.HelmChart{
+				ObjectMeta: metav1.ObjectMeta{
+					GenerateName: "helmchart-",
+				},
+				Spec: helmv1.HelmChartSpec{
+					SourceRef: helmv1.LocalHelmChartSourceReference{
+						Kind: helmv1.HelmRepositoryKind,
+						Name: repository.Name,
+					},
+					Version: tt.version,
+					Chart:   "podinfo",
+					Verify: &helmv1.OCIRepositoryVerification{
+						Provider: "cosign",
+					},
+				},
+			}
+			chartUrl := fmt.Sprintf("%s/%s:%s", repository.Spec.URL, obj.Spec.Chart, obj.Spec.Version)
+
+			assertConditions := tt.assertConditions
+			for k := range assertConditions {
+				assertConditions[k].Message = strings.ReplaceAll(assertConditions[k].Message, "<name>", obj.Spec.Chart)
+				assertConditions[k].Message = strings.ReplaceAll(assertConditions[k].Message, "<version>", obj.Spec.Version)
+				assertConditions[k].Message = strings.ReplaceAll(assertConditions[k].Message, "<url>", chartUrl)
+				assertConditions[k].Message = strings.ReplaceAll(assertConditions[k].Message, "<provider>", "cosign")
+			}
+
+			if tt.beforeFunc != nil {
+				tt.beforeFunc(obj)
+			}
+
+			g.Expect(r.Client.Create(ctx, obj)).ToNot(HaveOccurred())
+			defer func() {
+				g.Expect(r.Client.Delete(ctx, obj)).ToNot(HaveOccurred())
+			}()
+
+			sp := patch.NewSerialPatcher(obj, r.Client)
+
+			var b chart.Build
+			got, err := r.reconcileSource(ctx, sp, obj, &b)
+			if tt.wantErr {
+				tt.wantErrMsg = strings.ReplaceAll(tt.wantErrMsg, "<url>", chartUrl)
+				g.Expect(err).ToNot(BeNil())
+				g.Expect(err.Error()).To(ContainSubstring(tt.wantErrMsg))
+			} else {
+				g.Expect(err).ToNot(HaveOccurred())
+			}
+			g.Expect(got).To(Equal(tt.want))
+			g.Expect(obj.Status.Conditions).To(conditions.MatchConditions(tt.assertConditions))
+		})
+	}
+}
+
 func TestHelmChartReconciler_reconcileSourceFromOCI_verifySignature(t *testing.T) {
 	g := NewWithT(t)