Remove --overlayfs-stale-read flag

It defaults to true and setting it to false can cause filesytem corruption.

PiperOrigin-RevId: 378518663

runsc/boot/fs.go

@@ -763,12 +763,10 @@ func (c *containerMounter) createRootMount(ctx context.Context, conf *config.Con
 	p9FS := mustFindFilesystem("9p")
 	opts := p9MountData(fd, conf.FileAccess, false /* vfs2 */)
 
-	if conf.OverlayfsStaleRead {
-		// We can't check for overlayfs here because sandbox is chroot'ed and gofer
-		// can only send mount options for specs.Mounts (specs.Root is missing
-		// Options field). So assume root is always on top of overlayfs.
-		opts = append(opts, "overlayfs_stale_read")
-	}
+	// We can't check for overlayfs here because sandbox is chroot'ed and gofer
+	// can only send mount options for specs.Mounts (specs.Root is missing
+	// Options field). So assume root is always on top of overlayfs.
+	opts = append(opts, "overlayfs_stale_read")
 
 	rootInode, err := p9FS.Mount(ctx, rootDevice, mf, strings.Join(opts, ","), nil)
 	if err != nil {

runsc/boot/vfs.go

@@ -210,12 +210,10 @@ func (c *containerMounter) createMountNamespaceVFS2(ctx context.Context, conf *c
 	fd := c.fds.remove()
 	data := p9MountData(fd, conf.FileAccess, true /* vfs2 */)
 
-	if conf.OverlayfsStaleRead {
-		// We can't check for overlayfs here because sandbox is chroot'ed and gofer
-		// can only send mount options for specs.Mounts (specs.Root is missing
-		// Options field). So assume root is always on top of overlayfs.
-		data = append(data, "overlayfs_stale_read")
-	}
+	// We can't check for overlayfs here because sandbox is chroot'ed and gofer
+	// can only send mount options for specs.Mounts (specs.Root is missing
+	// Options field). So assume root is always on top of overlayfs.
+	data = append(data, "overlayfs_stale_read")
 
 	log.Infof("Mounting root over 9P, ioFD: %d", fd)
 	opts := &vfs.MountOptions{

runsc/cmd/gofer.go

@@ -473,14 +473,12 @@ func adjustMountOptions(conf *config.Config, path string, opts []string) ([]stri
 	rv := make([]string, len(opts))
 	copy(rv, opts)
 
-	if conf.OverlayfsStaleRead {
-		statfs := unix.Statfs_t{}
-		if err := unix.Statfs(path, &statfs); err != nil {
-			return nil, err
-		}
-		if statfs.Type == unix.OVERLAYFS_SUPER_MAGIC {
-			rv = append(rv, "overlayfs_stale_read")
-		}
+	statfs := unix.Statfs_t{}
+	if err := unix.Statfs(path, &statfs); err != nil {
+		return nil, err
+	}
+	if statfs.Type == unix.OVERLAYFS_SUPER_MAGIC {
+		rv = append(rv, "overlayfs_stale_read")
 	}
 	return rv, nil
 }

runsc/config/config.go

@@ -151,12 +151,6 @@ type Config struct {
 	// ReferenceLeakMode sets reference leak check mode
 	ReferenceLeak refs.LeakMode `flag:"ref-leak-mode"`
 
-	// OverlayfsStaleRead instructs the sandbox to assume that the root mount
-	// is on a Linux overlayfs mount, which does not necessarily preserve
-	// coherence between read-only and subsequent writable file descriptors
-	// representing the "same" file.
-	OverlayfsStaleRead bool `flag:"overlayfs-stale-read"`
-
 	// CPUNumFromQuota sets CPU number count to available CPU quota, using
 	// least integer value greater than or equal to quota.
 	//

runsc/config/flags.go

@@ -72,7 +72,6 @@ func RegisterFlags() {
 		flag.Var(fileAccessTypePtr(FileAccessShared), "file-access-mounts", "specifies which filesystem validation to use for volumes other than the root mount: shared (default), exclusive.")
 		flag.Bool("overlay", false, "wrap filesystem mounts with writable overlay. All modifications are stored in memory inside the sandbox.")
 		flag.Bool("verity", false, "specifies whether a verity file system will be mounted.")
-		flag.Bool("overlayfs-stale-read", true, "assume root mount is an overlay filesystem")
 		flag.Bool("fsgofer-host-uds", false, "allow the gofer to mount Unix Domain Sockets.")
 		flag.Bool("vfs2", false, "enables VFSv2. This uses the new VFS layer that is faster than the previous one.")
 		flag.Bool("fuse", false, "TEST ONLY; use while FUSE in VFSv2 is landing. This allows the use of the new experimental FUSE filesystem.")