From e905172d17b74146447fcf81b7bd44d6e05030fb Mon Sep 17 00:00:00 2001
From: Ramkumar Chinchani <45800463+rchincha@users.noreply.github.com>
Date: Wed, 8 Nov 2023 14:07:59 -0800
Subject: [PATCH] fix: handle ancient empty docker layers (#522) (#538)

Earlier versions of docker images had empty layers of 1024 zero-valued
octets.

https://github.com/moby/moby/issues/20917#issuecomment-191901912

(cherry picked from commit f0f964216cb7dc1c5ec529ec49824e9a1879ef45)

Signed-off-by: Ramkumar Chinchani <rchincha@cisco.com>
---
 pkg/log/log.go          |  4 ++++
 pkg/overlay/metadata.go | 11 ++++++++++-
 pkg/stacker/base.go     |  6 +++++-
 pkg/types/layer_type.go |  4 +++-
 test/empty-layers.bats  | 25 +++++++++++++++++++++++++
 5 files changed, 47 insertions(+), 3 deletions(-)

diff --git a/pkg/log/log.go b/pkg/log/log.go
index 553383f0..c8a8c280 100644
--- a/pkg/log/log.go
+++ b/pkg/log/log.go
@@ -46,6 +46,10 @@ func Infof(msg string, v ...interface{}) {
 	addStackerLogSentinel(log.NewEntry(log.Log.(*log.Logger))).Infof(msg, v...)
 }
 
+func Warnf(msg string, v ...interface{}) {
+	addStackerLogSentinel(log.NewEntry(log.Log.(*log.Logger))).Warnf(msg, v...)
+}
+
 func Errorf(msg string, v ...interface{}) {
 	addStackerLogSentinel(log.NewEntry(log.Log.(*log.Logger))).Errorf(msg, v...)
 }
diff --git a/pkg/overlay/metadata.go b/pkg/overlay/metadata.go
index 2d5cbff7..d2bbcf0e 100644
--- a/pkg/overlay/metadata.go
+++ b/pkg/overlay/metadata.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"io/fs"
 	"os"
 	"path"
 
@@ -118,7 +119,15 @@ func (ovl overlayMetadata) lxcRootfsString(config types.StackerConfig, tag strin
 	for _, layer := range manifest.Layers {
 		contents := overlayPath(config, layer.Digest, "overlay")
 		if _, err := os.Stat(contents); err != nil {
-			return "", errors.Wrapf(err, "%s does not exist", contents)
+			if errors.Is(err, fs.ErrNotExist) {
+				// some docker layers may be empty tars, so ignore these
+				// https://github.com/moby/moby/issues/20917#issuecomment-191901912
+				log.Warnf("%s skipping empty tar layer", layer.Digest)
+
+				continue
+			}
+
+			return "", errors.Wrapf(err, "%s unable to stat", contents)
 		}
 		lowerdirs = append(lowerdirs, contents)
 	}
diff --git a/pkg/stacker/base.go b/pkg/stacker/base.go
index 20c5e63b..c85330ce 100644
--- a/pkg/stacker/base.go
+++ b/pkg/stacker/base.go
@@ -87,7 +87,11 @@ func SetupRootfs(o BaseLayerOpts) error {
 	case types.OCILayer:
 		fallthrough
 	case types.DockerLayer:
-		return setupContainersImageRootfs(o)
+		err := setupContainersImageRootfs(o)
+		if err != nil && errors.Is(err, types.ErrEmptyLayers) {
+			return o.Storage.SetupEmptyRootfs(o.Name)
+		}
+		return err
 	default:
 		return errors.Errorf("unknown layer type: %v", o.Layer.From.Type)
 	}
diff --git a/pkg/types/layer_type.go b/pkg/types/layer_type.go
index 6d1a1353..69e20a5b 100644
--- a/pkg/types/layer_type.go
+++ b/pkg/types/layer_type.go
@@ -10,6 +10,8 @@ import (
 	"stackerbuild.io/stacker/pkg/squashfs"
 )
 
+var ErrEmptyLayers = errors.New("empty layers")
+
 type LayerType struct {
 	Type   string
 	Verity squashfs.VerityMetadata
@@ -53,7 +55,7 @@ func NewLayerType(lt string, verity squashfs.VerityMetadata) (LayerType, error)
 
 func NewLayerTypeManifest(manifest ispec.Manifest) (LayerType, error) {
 	if len(manifest.Layers) == 0 {
-		return LayerType{}, errors.Errorf("no existing layers to determine layer type")
+		return NewLayerType("tar", squashfs.VerityMetadataMissing)
 	}
 
 	switch manifest.Layers[0].MediaType {
diff --git a/test/empty-layers.bats b/test/empty-layers.bats
index 940136fe..5e839af9 100644
--- a/test/empty-layers.bats
+++ b/test/empty-layers.bats
@@ -61,3 +61,28 @@ EOF
 
     [ "$layers0" = "$layers1" ]
 }
+
+@test "an image with empty layers" {
+  umoci init --layout oci
+  umoci new --image oci:emptylayer
+  chmod -R a+rw oci
+
+  cat > stacker.yaml <<EOF
+test_empty_layer:
+    from:
+        type: oci
+        url: oci:emptylayer
+EOF
+    stacker build
+}
+
+@test "a real-world docker image with empty/filler layer" {
+    cat > stacker.yaml <<EOF
+image:
+    from:
+        type: docker
+        url: docker://ghcr.io/project-stacker/grafana-oss:10.1.2-ubuntu
+EOF
+    stacker build
+}
+