Skip the /kaniko directory when copying root

This commit adds the skip option for otiai10.Copy to skip the /kaniko
directory when the root is being copied. The files under /kaniko dir
should be ignored and thus this shall not cause any loss of information.

fixes: #2033

integration/dockerfiles/Dockerfile_test_copy_root_multistage

@@ -0,0 +1,9 @@
+FROM debian:10.13 as base
+COPY . .
+
+FROM scratch as second
+ENV foopath context/foo
+COPY --from=0 $foopath context/b* /foo/
+
+FROM second as third
+COPY --from=base / /new/foo

pkg/executor/copy_multistage_test.go

@@ -82,6 +82,7 @@ COPY --from=first copied/bam.txt output/`
 		testutil.CheckDeepEqual(t, 1, len(files))
 		testutil.CheckDeepEqual(t, files[0].Name(), "bam.txt")
 	})
+
 	t.Run("copy directory across multistage into a directory", func(t *testing.T) {
 		testDir, fn := setupMultistageTests(t)
 		defer fn()
@@ -117,6 +118,40 @@ COPY --from=first copied another`
 		//testutil.CheckDeepEqual(t, linkName, "bam.txt")
 	})
 
+	t.Run("copy root across multistage", func(t *testing.T) {
+		testDir, fn := setupMultistageTests(t)
+		defer fn()
+		dockerFile := `
+FROM scratch as first
+COPY foo copied
+ENV test test
+
+From scratch as second
+COPY --from=first / output/`
+		ioutil.WriteFile(filepath.Join(testDir, "workspace", "Dockerfile"), []byte(dockerFile), 0755)
+		opts := &config.KanikoOptions{
+			DockerfilePath: filepath.Join(testDir, "workspace", "Dockerfile"),
+			SrcContext:     filepath.Join(testDir, "workspace"),
+			SnapshotMode:   constants.SnapshotModeFull,
+		}
+		_, err := DoBuild(opts)
+		testutil.CheckNoError(t, err)
+
+		filesUnderRoot, err := ioutil.ReadDir(filepath.Join(testDir, "output/"))
+		if err != nil {
+			t.Fatal(err)
+		}
+		testutil.CheckDeepEqual(t, 3, len(filesUnderRoot))
+
+		files, err := ioutil.ReadDir(filepath.Join(testDir, "output/workspace/foo"))
+		if err != nil {
+			t.Fatal(err)
+		}
+		testutil.CheckDeepEqual(t, 2, len(files))
+		testutil.CheckDeepEqual(t, "bam.link", files[0].Name())
+		testutil.CheckDeepEqual(t, "bam.txt", files[1].Name())
+	})
+
 }
 
 func setupMultistageTests(t *testing.T) (string, func()) {

pkg/util/fs_util.go

@@ -81,6 +81,13 @@ var ignorelist = append([]IgnoreListEntry{}, defaultIgnoreList...)
 
 var volumes = []string{}
 
+// skipKanikoDir opts to skip the '/kaniko' dir for otiai10.copy which should be ignored in root
+var skipKanikoDir = otiai10Cpy.Options{
+	Skip: func(info os.FileInfo, src, dest string) (bool, error) {
+		return strings.HasSuffix(src, "/kaniko"), nil
+	},
+}
+
 type FileContext struct {
 	Root          string
 	ExcludedFiles []string
@@ -956,7 +963,7 @@ func CopyFileOrSymlink(src string, destDir string, root string) error {
 		}
 		return os.Symlink(link, destFile)
 	}
-	if err := otiai10Cpy.Copy(src, destFile); err != nil {
+	if err := otiai10Cpy.Copy(src, destFile, skipKanikoDir); err != nil {
 		return errors.Wrap(err, "copying file")
 	}
 	if err := CopyOwnership(src, destDir, root); err != nil {