Fix for rebase omitting os/arch config properties (#751) (#752)

* Quick fix for missing `os` and `architecture` config properties, required by config spec [1]

* Also include unspec'd `os.version` property which is required for Windows images to run on Windows containers [2]

This implementation takes these three properties from newBase, which most accurately defines the newly rebased image's os/architecture. If the properties were taken from original, it would prevent reuse of de-facto ABI-compatible top layers with differing old and new base images (i.e. data-only top layers rebased from amd64 to arm, Windows os.version upgrades).

This does not address additional, optional config properties that are currently being omitted during rebase such as `author` and `created`.

Fixes [#751]

[1]: https://github.com/opencontainers/image-spec/blob/master/config.md#properties
[2]: https://docs.microsoft.com/en-us/virtualization/windowscontainers/deploy-containers/version-compatibility#matching-container-host-version-with-container-image-versions

Signed-off-by: Micah Young <ymicah@vmware.com>

pkg/v1/mutate/rebase.go

@@ -60,23 +60,42 @@ func Rebase(orig, oldBase, newBase v1.Image) (v1.Image, error) {
 		return nil, fmt.Errorf("failed to get config for original: %v", err)
 	}
 
+	newConfig, err := newBase.ConfigFile()
+	if err != nil {
+		return nil, fmt.Errorf("could not get config for new base: %v", err)
+	}
+
 	// Stitch together an image that contains:
 	// - original image's config
+	// - new base image's os/arch properties
 	// - new base image's layers + top of original image's layers
 	// - new base image's history + top of original image's history
 	rebasedImage, err := Config(empty.Image, *origConfig.Config.DeepCopy())
 	if err != nil {
 		return nil, fmt.Errorf("failed to create empty image with original config: %v", err)
 	}
+
+	// Add new config properties from existing images.
+	rebasedConfig, err := rebasedImage.ConfigFile()
+	if err != nil {
+		return nil, fmt.Errorf("could not get config for rebased image: %v", err)
+	}
+	// OS/Arch properties from new base
+	rebasedConfig.Architecture = newConfig.Architecture
+	rebasedConfig.OS = newConfig.OS
+	rebasedConfig.OSVersion = newConfig.OSVersion
+
+	// Apply config properties to rebased.
+	rebasedImage, err = ConfigFile(rebasedImage, rebasedConfig)
+	if err != nil {
+		return nil, fmt.Errorf("failed to replace config for rebased image: %v", err)
+	}
+
 	// Get new base layers and config for history.
 	newBaseLayers, err := newBase.Layers()
 	if err != nil {
 		return nil, fmt.Errorf("could not get new base layers for new base: %v", err)
 	}
-	newConfig, err := newBase.ConfigFile()
-	if err != nil {
-		return nil, fmt.Errorf("could not get config for new base: %v", err)
-	}
 	// Add new base layers.
 	rebasedImage, err = Append(rebasedImage, createAddendums(0, 0, newConfig.History, newBaseLayers)...)
 	if err != nil {

pkg/v1/mutate/rebase_test.go

@@ -97,6 +97,20 @@ func TestRebase(t *testing.T) {
 	t.Log("New base:")
 	newBaseLayerDigests := layerDigests(t, newBase)
 
+	// Add config file os/arch property fields
+	newBaseConfigFile, err := newBase.ConfigFile()
+	if err != nil {
+		t.Fatalf("newBase.ConfigFile: %v", err)
+	}
+	newBaseConfigFile.Architecture = "arm"
+	newBaseConfigFile.OS = "windows"
+	newBaseConfigFile.OSVersion = "10.0.17763.1339"
+
+	newBase, err = mutate.ConfigFile(newBase, newBaseConfigFile)
+	if err != nil {
+		t.Fatalf("ConfigFile (newBase): %v", err)
+	}
+
 	// Rebase original image onto new base.
 	rebased, err := mutate.Rebase(orig, oldBase, newBase)
 	if err != nil {
@@ -151,4 +165,15 @@ func TestRebase(t *testing.T) {
 			t.Errorf("Layer %d mismatch, got %q, want %q", i, got, want)
 		}
 	}
+
+	// Compare ConfigFile property fields copied from new base.
+	if rebasedConfig.Architecture != newBaseConfig.Architecture {
+		t.Errorf("ConfigFile property Architecture mismatch, got %q, want %q", rebasedConfig.Architecture, newBaseConfig.Architecture)
+	}
+	if rebasedConfig.OS != newBaseConfig.OS {
+		t.Errorf("ConfigFile property OS mismatch, got %q, want %q", rebasedConfig.OS, newBaseConfig.OS)
+	}
+	if rebasedConfig.OSVersion != newBaseConfig.OSVersion {
+		t.Errorf("ConfigFile property OSVersion mismatch, got %q, want %q", rebasedConfig.OSVersion, newBaseConfig.OSVersion)
+	}
 }