mz851: keep reproducible output a consistent dockerv2 manifest

integration/dockerfiles/Dockerfile_test_issue_mz851

@@ -0,0 +1,16 @@
+# mz851: building an OCI base with --reproducible and
+# FF_KANIKO_REPRODUCIBLE_PRESERVE_BASE_LAYERS flipped the output to a docker
+# schema2 manifest while keeping the OCI base layer descriptors verbatim. The
+# resulting docker manifest carrying OCI layer media types is malformed and
+# breaks strict readers like dockle.
+#
+# Breaks on v1.28.0 behind FF_KANIKO_REPRODUCIBLE_PRESERVE_BASE_LAYERS. The
+# cause is mutate.Canonical rebuilding the image on an empty (docker) base, so
+# --reproducible alone already rewrites to docker, and ReplaceBase then splices
+# the pristine OCI base layers back on top of that docker manifest.
+#
+# Pin an OCI base and add one RUN so kaniko produces a layer of its own. With
+# the fix the preserved base layers are relabeled so the output manifest,
+# config, and every layer are consistently dockerv2.
+FROM debian:12.10@sha256:6bc30d909583f38600edd6609e29eb3fb284ab8affce8d0389f332fc91c2dd91
+RUN echo 'hi' > /root/hi.txt

integration/images.go

@@ -499,6 +499,7 @@ func NewDockerFileBuilder() *DockerFileBuilder {
 	d.TestReproducibleDockerfiles = map[string]struct{}{
 		"Dockerfile_test_copy_reproducible": {},
 		"Dockerfile_test_issue_mz731":       {},
+		"Dockerfile_test_issue_mz851":       {},
 	}
 	return &d
 }

integration/integration_test.go

@@ -976,7 +976,11 @@ func TestReproducible(t *testing.T) {
 			t.Fatalf("build %s -> %s: %v", dockerfile, ref, err)
 		}
 	}
-	const baseRef = "alpine@sha256:5ce5f501c457015c4b91f91a15ac69157d9b06f1a75cf9107bf2b62e0843983a"
+	baseRefs := map[string]string{
+		"Dockerfile_test_copy_reproducible": "alpine@sha256:5ce5f501c457015c4b91f91a15ac69157d9b06f1a75cf9107bf2b62e0843983a",
+		"Dockerfile_test_issue_mz731":       "alpine@sha256:5ce5f501c457015c4b91f91a15ac69157d9b06f1a75cf9107bf2b62e0843983a",
+		"Dockerfile_test_issue_mz851":       "debian@sha256:6bc30d909583f38600edd6609e29eb3fb284ab8affce8d0389f332fc91c2dd91",
+	}
 	for dockerfile := range imageBuilder.TestReproducibleDockerfiles {
 		if match, _ := filepath.Match(config.dockerfilesPattern, dockerfile); !match {
 			continue
@@ -991,7 +995,7 @@ func TestReproducible(t *testing.T) {
 			containerDiff(t, ref0, ref1)
 
 			// mz731: make sure the inherited base layers were not mutated.
-			base := layerDigests(t, baseRef)
+			base := layerDigests(t, baseRefs[dockerfile])
 			kaniko := layerDigests(t, ref0)
 			testutil.CheckDeepEqual(t, base, kaniko[:len(base)])
 		})

pkg/executor/build.go

@@ -1306,6 +1306,10 @@ func DoBuild(opts *config.KanikoOptions) (image v1.Image, retErr error) {
 			if len(opts.Annotations) > 0 {
 				sourceImage = mutate.Annotations(sourceImage, opts.Annotations).(v1.Image)
 			}
+			err = image_util.AssertConsistentMediaType(sourceImage)
+			if err != nil {
+				return nil, err
+			}
 			pushImage = sourceImage
 		}
 		if stage.Final {

pkg/image/transform.go

@@ -18,12 +18,15 @@ package image
 
 import (
 	"encoding/json"
+	"strings"
 
 	v1 "github.com/google/go-containerregistry/pkg/v1"
 	"github.com/google/go-containerregistry/pkg/v1/empty"
 	"github.com/google/go-containerregistry/pkg/v1/mutate"
 	"github.com/google/go-containerregistry/pkg/v1/partial"
+	"github.com/google/go-containerregistry/pkg/v1/types"
 	"github.com/osscontainertools/kaniko/pkg/util"
+	"github.com/sirupsen/logrus"
 )
 
 // ReplaceBase returns img with its first len(base.Layers()) layers and first
@@ -77,7 +80,21 @@ func ReplaceBase(img, base v1.Image) (v1.Image, error) {
 		}
 		if !h.EmptyLayer {
 			if li < len(baseLayers) {
-				a.Layer = baseLayers[li]
+				mt, err := baseLayers[li].MediaType()
+				if err != nil {
+					return nil, err
+				}
+				switch mt {
+				case types.DockerLayer, types.DockerUncompressedLayer, types.DockerForeignLayer:
+					a.Layer = baseLayers[li]
+				case types.OCILayer:
+					a.Layer = &mediaTypeLayer{Layer: baseLayers[li], mediaType: types.DockerLayer}
+				case types.OCIUncompressedLayer:
+					a.Layer = &mediaTypeLayer{Layer: baseLayers[li], mediaType: types.DockerUncompressedLayer}
+				default:
+					logrus.Warnf("not preserving base layers: base image has %s layers, incompatible with a reproducible dockerv2 image", mt)
+					return img, nil
+				}
 			} else {
 				a.Layer = imgLayers[li]
 			}
@@ -100,6 +117,39 @@ func ReplaceBase(img, base v1.Image) (v1.Image, error) {
 	return mutate.ConfigFile(stacked, finalCfg)
 }
 
+type mediaTypeLayer struct {
+	v1.Layer
+	mediaType types.MediaType
+}
+
+func (l *mediaTypeLayer) MediaType() (types.MediaType, error) {
+	return l.mediaType, nil
+}
+
+func AssertConsistentMediaType(img v1.Image) error {
+	man, err := img.Manifest()
+	if err != nil {
+		return err
+	}
+	oci, docker := false, false
+	classify := func(mt types.MediaType) {
+		s := string(mt)
+		switch {
+		case strings.Contains(s, types.OCIVendorPrefix):
+			oci = true
+		case strings.Contains(s, types.DockerVendorPrefix):
+			docker = true
+		}
+	}
+	classify(man.MediaType)
+	classify(man.Config.MediaType)
+	for _, l := range man.Layers {
+		classify(l.MediaType)
+	}
+	util.Assert("image.consistent-media-type", !(oci && docker), "manifest mixes OCI and docker media types")
+	return nil
+}
+
 // WithoutAnnotations returns an image whose manifest has no annotations.
 // mutate.Annotations only merges into existing annotations and cannot delete
 // keys, so we wrap the image to intercept Manifest and RawManifest instead.