fix: handle overlay xattr opaque bit

Current behavior determines if a path is a whiteout if a overlay char
dev is present.

Additionally, also check the extended attrs.

Signed-off-by: Ramkumar Chinchani <rchincha@cisco.com>

oci/layer/generate.go

@@ -88,7 +88,7 @@ func GenerateLayer(path string, deltas []mtree.InodeDelta, opt *RepackOptions) (
 						return errors.Wrapf(err, "couldn't determine overlay whiteout for %s", fullPath)
 					}
 
-					whiteout, err := isOverlayWhiteout(fi)
+					whiteout, err := isOverlayWhiteout(fi, fullPath, tg.fsEval)
 					if err != nil {
 						return err
 					}
@@ -166,7 +166,7 @@ func GenerateInsertLayer(root string, target string, opaque bool, opt *RepackOpt
 			}
 
 			pathInTar := path.Join(target, curPath[len(root):])
-			whiteout, err := isOverlayWhiteout(info)
+			whiteout, err := isOverlayWhiteout(info, curPath, tg.fsEval)
 			if err != nil {
 				return err
 			}

oci/layer/tar_extract_linux_test.go

@@ -96,7 +96,7 @@ func TestUnpackEntryOverlayFSWhiteout(t *testing.T) {
 		t.Fatalf("failed to stat `file`: %v", err)
 	}
 
-	whiteout, err := isOverlayWhiteout(fi)
+	whiteout, err := isOverlayWhiteout(fi, filepath.Join(dir, "file"), te.fsEval)
 	if err != nil {
 		t.Fatalf("failed to check overlay whiteout: %v", err)
 	}

oci/layer/utils.go

@@ -25,6 +25,7 @@ import (
 
 	"github.com/apex/log"
 	rspec "github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/opencontainers/umoci/pkg/fseval"
 	"github.com/opencontainers/umoci/pkg/idtools"
 	"github.com/pkg/errors"
 	rootlesscontainers "github.com/rootless-containers/proto/go-proto"
@@ -230,7 +231,7 @@ func InnerErrno(err error) error {
 
 // isOverlayWhiteout returns true if the FileInfo represents an overlayfs style
 // whiteout (i.e. mknod c 0 0) and false otherwise.
-func isOverlayWhiteout(info os.FileInfo) (bool, error) {
+func isOverlayWhiteout(info os.FileInfo, fullPath string, fsEval fseval.FsEval) (bool, error) {
 	var major, minor uint32
 	switch stat := info.Sys().(type) {
 	case *unix.Stat_t:
@@ -243,6 +244,25 @@ func isOverlayWhiteout(info os.FileInfo) (bool, error) {
 		return false, errors.Errorf("[internal error] unknown stat info type %T", info.Sys())
 	}
 
-	return major == 0 && minor == 0 &&
-		info.Mode()&os.ModeCharDevice != 0, nil
+	if major == 0 && minor == 0 &&
+		info.Mode()&os.ModeCharDevice != 0 {
+		return true, nil
+	}
+
+	// also evaluate xattrs which may have opaque value set
+	attr, err := fsEval.Lgetxattr(fullPath, "user.overlay.opaque")
+	if err != nil {
+		v := errors.Cause(err)
+		if !errors.Is(err, os.ErrNotExist) && v != unix.EOPNOTSUPP && v != unix.ENODATA && v != unix.EPERM {
+			return false, errors.Errorf("[internal error] unknown stat info type %T", info.Sys())
+		}
+
+		return false, nil
+	}
+
+	if string(attr) == "y" {
+		return true, nil
+	}
+
+	return false, nil
 }