Merge pull request #2069 from giuseppe/composefs-do-not-make-mount-vi…

…sible

composefs fixes

drivers/overlay/composefs.go

@@ -137,54 +137,62 @@ func hasACL(path string) (bool, error) {
 	return binary.LittleEndian.Uint32(flags)&LCFS_EROFS_FLAGS_HAS_ACL != 0, nil
 }
 
-func mountComposefsBlob(dataDir, mountPoint string) error {
+func openComposefsMount(dataDir string) (int, error) {
 	blobFile := getComposefsBlob(dataDir)
 	loop, err := loopback.AttachLoopDeviceRO(blobFile)
 	if err != nil {
-		return err
+		return -1, err
 	}
 	defer loop.Close()
 
 	hasACL, err := hasACL(blobFile)
 	if err != nil {
-		return err
+		return -1, err
 	}
 
 	fsfd, err := unix.Fsopen("erofs", 0)
 	if err != nil {
-		return fmt.Errorf("failed to open erofs filesystem: %w", err)
+		return -1, fmt.Errorf("failed to open erofs filesystem: %w", err)
 	}
 	defer unix.Close(fsfd)
 
 	if err := unix.FsconfigSetString(fsfd, "source", loop.Name()); err != nil {
-		return fmt.Errorf("failed to set source for erofs filesystem: %w", err)
+		return -1, fmt.Errorf("failed to set source for erofs filesystem: %w", err)
 	}
 
 	if err := unix.FsconfigSetFlag(fsfd, "ro"); err != nil {
-		return fmt.Errorf("failed to set erofs filesystem read-only: %w", err)
+		return -1, fmt.Errorf("failed to set erofs filesystem read-only: %w", err)
 	}
 
 	if !hasACL {
 		if err := unix.FsconfigSetFlag(fsfd, "noacl"); err != nil {
-			return fmt.Errorf("failed to set noacl for erofs filesystem: %w", err)
+			return -1, fmt.Errorf("failed to set noacl for erofs filesystem: %w", err)
 		}
 	}
 
 	if err := unix.FsconfigCreate(fsfd); err != nil {
 		buffer := make([]byte, 4096)
 		if n, _ := unix.Read(fsfd, buffer); n > 0 {
-			return fmt.Errorf("failed to create erofs filesystem: %s: %w", string(buffer[:n]), err)
+			return -1, fmt.Errorf("failed to create erofs filesystem: %s: %w", string(buffer[:n]), err)
 		}
-		return fmt.Errorf("failed to create erofs filesystem: %w", err)
+		return -1, fmt.Errorf("failed to create erofs filesystem: %w", err)
 	}
 
 	mfd, err := unix.Fsmount(fsfd, 0, unix.MOUNT_ATTR_RDONLY)
 	if err != nil {
 		buffer := make([]byte, 4096)
 		if n, _ := unix.Read(fsfd, buffer); n > 0 {
-			return fmt.Errorf("failed to mount erofs filesystem: %s: %w", string(buffer[:n]), err)
+			return -1, fmt.Errorf("failed to mount erofs filesystem: %s: %w", string(buffer[:n]), err)
 		}
-		return fmt.Errorf("failed to mount erofs filesystem: %w", err)
+		return -1, fmt.Errorf("failed to mount erofs filesystem: %w", err)
+	}
+	return mfd, nil
+}
+
+func mountComposefsBlob(dataDir, mountPoint string) error {
+	mfd, err := openComposefsMount(dataDir)
+	if err != nil {
+		return err
 	}
 	defer unix.Close(mfd)
 

drivers/overlay/overlay.go

@@ -1456,6 +1456,31 @@ func (d *Driver) get(id string, disableShifting bool, options graphdriver.MountO
 		return "", err
 	}
 
+	// user namespace requires this to move a directory from lower to upper.
+	rootUID, rootGID, err := idtools.GetRootUIDGID(options.UidMaps, options.GidMaps)
+	if err != nil {
+		return "", err
+	}
+
+	mergedDir := d.getMergedDir(id, dir, inAdditionalStore)
+	// Attempt to create the merged dir if it doesn't exist, but don't chown an already existing directory (it might be in an additional store)
+	if err := idtools.MkdirAllAndChownNew(mergedDir, 0o700, idtools.IDPair{UID: rootUID, GID: rootGID}); err != nil && !os.IsExist(err) {
+		return "", err
+	}
+
+	if count := d.ctr.Increment(mergedDir); count > 1 {
+		return mergedDir, nil
+	}
+	defer func() {
+		if retErr != nil {
+			if c := d.ctr.Decrement(mergedDir); c <= 0 {
+				if mntErr := unix.Unmount(mergedDir, 0); mntErr != nil {
+					logrus.Errorf("Unmounting %v: %v", mergedDir, mntErr)
+				}
+			}
+		}
+	}()
+
 	readWrite := !inAdditionalStore
 
 	if !d.SupportsShifting() || options.DisableShifting {
@@ -1575,7 +1600,7 @@ func (d *Driver) get(id string, disableShifting bool, options graphdriver.MountO
 			return "", fmt.Errorf("cannot mount a composefs layer as writeable")
 		}
 
-		dest := filepath.Join(composeFsLayersDir, fmt.Sprintf("%d", i))
+		dest := filepath.Join(composeFsLayersDir, strconv.Itoa(i))
 		if err := os.MkdirAll(dest, 0o700); err != nil {
 			return "", err
 		}
@@ -1683,12 +1708,6 @@ func (d *Driver) get(id string, disableShifting bool, options graphdriver.MountO
 		optsList = append(optsList, "metacopy=on", "redirect_dir=on")
 	}
 
-	// user namespace requires this to move a directory from lower to upper.
-	rootUID, rootGID, err := idtools.GetRootUIDGID(options.UidMaps, options.GidMaps)
-	if err != nil {
-		return "", err
-	}
-
 	if len(absLowers) == 0 {
 		absLowers = append(absLowers, path.Join(dir, "empty"))
 	}
@@ -1703,26 +1722,6 @@ func (d *Driver) get(id string, disableShifting bool, options graphdriver.MountO
 		}
 	}
 
-	mergedDir := d.getMergedDir(id, dir, inAdditionalStore)
-	// Attempt to create the merged dir only if it doesn't exist.
-	if err := fileutils.Exists(mergedDir); err != nil && os.IsNotExist(err) {
-		if err := idtools.MkdirAllAs(mergedDir, 0o700, rootUID, rootGID); err != nil && !os.IsExist(err) {
-			return "", err
-		}
-	}
-	if count := d.ctr.Increment(mergedDir); count > 1 {
-		return mergedDir, nil
-	}
-	defer func() {
-		if retErr != nil {
-			if c := d.ctr.Decrement(mergedDir); c <= 0 {
-				if mntErr := unix.Unmount(mergedDir, 0); mntErr != nil {
-					logrus.Errorf("Unmounting %v: %v", mergedDir, mntErr)
-				}
-			}
-		}
-	}()
-
 	workdir := path.Join(dir, "work")
 
 	if d.options.mountProgram == "" && unshare.IsRootless() {
@@ -2128,24 +2127,16 @@ func (d *Driver) DiffGetter(id string) (_ graphdriver.FileGetCloser, Err error)
 	for _, diffDir := range diffDirs {
 		// diffDir has the form $GRAPH_ROOT/overlay/$ID/diff, so grab the $ID from the parent directory
 		id := path.Base(path.Dir(diffDir))
-		composefsBlob := d.getComposefsData(id)
-		if fileutils.Exists(composefsBlob) != nil {
+		composefsData := d.getComposefsData(id)
+		if fileutils.Exists(composefsData) != nil {
 			// not a composefs layer, ignore it
 			continue
 		}
-		dir, err := os.MkdirTemp(d.runhome, "composefs-mnt")
-		if err != nil {
-			return nil, err
-		}
-		if err := mountComposefsBlob(composefsBlob, dir); err != nil {
-			return nil, err
-		}
-		fd, err := os.Open(dir)
+		fd, err := openComposefsMount(composefsData)
 		if err != nil {
 			return nil, err
 		}
-		composefsMounts[diffDir] = fd
-		_ = unix.Unmount(dir, unix.MNT_DETACH)
+		composefsMounts[diffDir] = os.NewFile(uintptr(fd), composefsData)
 	}
 	return &overlayFileGetter{diffDirs: diffDirs, composefsMounts: composefsMounts}, nil
 }

drivers/overlay/overlay_nocgo.go

@@ -7,6 +7,10 @@ import (
 	"fmt"
 )
 
+func openComposefsMount(dataDir string) (int, error) {
+	return 0, fmt.Errorf("composefs not supported on this build")
+}
+
 func getComposeFsHelper() (string, error) {
 	return "", fmt.Errorf("composefs not supported on this build")
 }