Re: [PATCH 18/21] nullfs: refuse leases and delegations

[Jeff Layton <jlayton@kernel.org>]

On Fri, 2026-10-02 at 15:52 +0200, Christian Brauner wrote:
> Refuse leases and delegations on nullfs as well. generic_setlease()
> grants read leases and directory delegations on directories, so the
> owner of the shared inode, or anyone with CAP_LEASE, could put one on
> the directory that stands in for every unmounted mount and F_GETLEASE
> and F_GETDELEG would show it to every other holder. Nothing on nullfs
> ever changes, so a lease on it would never be broken and never tell
> anyone anything.
> 
> Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
> ---
>  fs/nullfs.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/nullfs.c b/fs/nullfs.c
> index d90c71f5eece..f76b87cf1841 100644
> --- a/fs/nullfs.c
> +++ b/fs/nullfs.c
> @@ -28,6 +28,13 @@ static int nullfs_nolock(struct file *file, int cmd, struct file_lock *fl)
>  	return -ENOLCK;
>  }
>  
> +/* and no leases or delegations */
> +static int nullfs_nolease(struct file *file, int arg, struct file_lease **flp,
> +			  void **priv)
> +{
> +	return -EINVAL;
> +}
> +
>  /* what libfs gives an empty directory, plus the refusal of file locks */
>  static const struct file_operations nullfs_dir_operations = {
>  	.llseek		= nullfs_dir_llseek,
> @@ -36,6 +43,7 @@ static const struct file_operations nullfs_dir_operations = {
>  	.fsync		= noop_fsync,
>  	.lock		= nullfs_nolock,
>  	.flock		= nullfs_nolock,
> +	.setlease	= nullfs_nolease,
>  };
>  
>  static int nullfs_fs_fill_super(struct super_block *s, struct fs_context *fc)

I don't think this patch is necessary. Commit 2b10994be716 made it so
that filesystems with a NULL ->setlease pointer already return -EINVAL.
-- 
Jeff Layton <jlayton@kernel.org>