archive, rootless: use user.* instead of trusted.*

unprivileged users cannot use the trusted.* xattrs.  Since for
rootless we always mount overlay with userxattr, we can just check if
running in rootless mode and use user.* instead of trusted.*.

Closes: https://github.com/containers/podman/issues/9936

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/archive/archive.go

@@ -20,6 +20,7 @@ import (
 	"github.com/containers/storage/pkg/pools"
 	"github.com/containers/storage/pkg/promise"
 	"github.com/containers/storage/pkg/system"
+	"github.com/containers/storage/pkg/unshare"
 	gzip "github.com/klauspost/pgzip"
 	rsystem "github.com/opencontainers/runc/libcontainer/system"
 	"github.com/pkg/errors"
@@ -1489,3 +1490,14 @@ func TarPath(uidmap []idtools.IDMap, gidmap []idtools.IDMap) func(path string) (
 		})
 	}
 }
+
+// GetOverlayXattrName returns the xattr used by the overlay driver with the
+// given name.
+// It uses the trusted.overlay prefix when running as root, and user.overlay
+// in rootless mode.
+func GetOverlayXattrName(name string) string {
+	if unshare.IsRootless() {
+		return fmt.Sprintf("user.overlay.%s", name)
+	}
+	return fmt.Sprintf("trusted.overlay.%s", name)
+}

pkg/archive/archive_linux.go

@@ -12,6 +12,10 @@ import (
 	"golang.org/x/sys/unix"
 )
 
+func getOverlayOpaqueXattrName() string {
+	return GetOverlayXattrName("opaque")
+}
+
 func GetWhiteoutConverter(format WhiteoutFormat, data interface{}) TarWhiteoutConverter {
 	if format == OverlayWhiteoutFormat {
 		if rolayers, ok := data.([]string); ok && len(rolayers) > 0 {
@@ -39,13 +43,13 @@ func (o overlayWhiteoutConverter) ConvertWrite(hdr *tar.Header, path string, fi
 
 	if fi.Mode()&os.ModeDir != 0 {
 		// convert opaque dirs to AUFS format by writing an empty file with the whiteout prefix
-		opaque, err := system.Lgetxattr(path, "trusted.overlay.opaque")
+		opaque, err := system.Lgetxattr(path, getOverlayOpaqueXattrName())
 		if err != nil {
 			return nil, err
 		}
 		if len(opaque) == 1 && opaque[0] == 'y' {
 			if hdr.Xattrs != nil {
-				delete(hdr.Xattrs, "trusted.overlay.opaque")
+				delete(hdr.Xattrs, getOverlayOpaqueXattrName())
 			}
 			// If there are no lower layers, then it can't have been deleted in this layer.
 			if len(o.rolayers) == 0 {
@@ -114,7 +118,7 @@ func (overlayWhiteoutConverter) ConvertReadWithHandler(hdr *tar.Header, path str
 
 	// if a directory is marked as opaque by the AUFS special file, we need to translate that to overlay
 	if base == WhiteoutOpaqueDir {
-		err := handler.Setxattr(dir, "trusted.overlay.opaque", []byte{'y'})
+		err := handler.Setxattr(dir, getOverlayOpaqueXattrName(), []byte{'y'})
 		// don't write the file itself
 		return false, err
 	}

pkg/archive/archive_linux_test.go

@@ -26,7 +26,7 @@ func setupOverlayTestDir(t *testing.T, src string) {
 	err := os.Mkdir(filepath.Join(src, "d1"), 0700)
 	require.NoError(t, err)
 
-	err = system.Lsetxattr(filepath.Join(src, "d1"), "trusted.overlay.opaque", []byte("y"), 0)
+	err = system.Lsetxattr(filepath.Join(src, "d1"), getOverlayOpaqueXattrName(), []byte("y"), 0)
 	require.NoError(t, err)
 
 	err = ioutil.WriteFile(filepath.Join(src, "d1", "f1"), []byte{}, 0600)
@@ -36,7 +36,7 @@ func setupOverlayTestDir(t *testing.T, src string) {
 	err = os.Mkdir(filepath.Join(src, "d2"), 0750)
 	require.NoError(t, err)
 
-	err = system.Lsetxattr(filepath.Join(src, "d2"), "trusted.overlay.opaque", []byte("y"), 0)
+	err = system.Lsetxattr(filepath.Join(src, "d2"), getOverlayOpaqueXattrName(), []byte("y"), 0)
 	require.NoError(t, err)
 
 	err = ioutil.WriteFile(filepath.Join(src, "d2", "f1"), []byte{}, 0660)
@@ -60,7 +60,7 @@ func setupOverlayLowerDir(t *testing.T, lower string) {
 }
 
 func checkOpaqueness(t *testing.T, path string, opaque string) {
-	xattrOpaque, err := system.Lgetxattr(path, "trusted.overlay.opaque")
+	xattrOpaque, err := system.Lgetxattr(path, getOverlayOpaqueXattrName())
 	require.NoError(t, err)
 
 	if string(xattrOpaque) != opaque {

pkg/archive/changes_linux.go

@@ -349,7 +349,7 @@ func overlayDeletedFile(layers []string, root, path string, fi os.FileInfo) (str
 		return "", nil
 	}
 	// If the directory isn't marked as opaque, then it's just a normal directory.
-	opaque, err := system.Lgetxattr(filepath.Join(root, path), "trusted.overlay.opaque")
+	opaque, err := system.Lgetxattr(filepath.Join(root, path), getOverlayOpaqueXattrName())
 	if err != nil {
 		return "", err
 	}