chrootarchive: don't create parent dirs outside of chroot

If chroot is used with a special root directory then create
destination directory within chroot. This works automatically
already due to extractor creating parent paths and is only
used currently with cp where parent paths are actually required
and error will be shown to user before reaching this point.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>
(cherry picked from commit 52d285184068998c22632bfb869f6294b5613a58)
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
(cherry picked from commit 80f1169eca587305759829e626cebd2a434664f6)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

pkg/chrootarchive/archive.go

@@ -73,13 +73,17 @@ func untarHandler(tarArchive io.Reader, dest string, options *archive.TarOptions
 		options.ExcludePatterns = []string{}
 	}
 
-	idMapping := idtools.NewIDMappingsFromMaps(options.UIDMaps, options.GIDMaps)
-	rootIDs := idMapping.RootPair()
+	// If dest is inside a root then directory is created within chroot by extractor.
+	// This case is only currently used by cp.
+	if dest == root {
+		idMapping := idtools.NewIDMappingsFromMaps(options.UIDMaps, options.GIDMaps)
+		rootIDs := idMapping.RootPair()
 
-	dest = filepath.Clean(dest)
-	if _, err := os.Stat(dest); os.IsNotExist(err) {
-		if err := idtools.MkdirAllAndChownNew(dest, 0755, rootIDs); err != nil {
-			return err
+		dest = filepath.Clean(dest)
+		if _, err := os.Stat(dest); os.IsNotExist(err) {
+			if err := idtools.MkdirAllAndChownNew(dest, 0755, rootIDs); err != nil {
+				return err
+			}
 		}
 	}