ovl: unprivieged mounts

Enable unprivileged user namespace mounts of overlayfs.  Overlayfs's
permission model (*) ensures that the mounter itself cannot gain additional
privileges by the act of creating an overlayfs mount.

This feature request is coming from the "rootless" container crowd.

(*) Documentation/filesystems/overlayfs.txt#Permission model

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 6366adf..2bd570c 100644 (file)
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -2096,6 +2096,7 @@ static struct dentry *ovl_mount(struct file_system_type *fs_type, int flags,
 static struct file_system_type ovl_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "overlay",
+       .fs_flags       = FS_USERNS_MOUNT,
        .mount          = ovl_mount,
        .kill_sb        = kill_anon_super,
 };