Re: [PATCH 11/13] ovl: use is_subdir() for testing if one thing is a subdir of another

[Jeff Layton <jlayton@kernel.org>]

On Wed, 2026-02-04 at 15:57 +1100, NeilBrown wrote:
> From: NeilBrown <neil@brown.name>
> 
> Rather than using lock_rename(), use the more obvious is_subdir() for
> ensuring that neither upper nor workdir contain the other.
> Also be explicit in the comment that the two directories cannot be the
> same.
> 
> As this is a point-it-time sanity check and does not provide any
> on-going guarantees, the removal of locking does not introduce any
> interesting races.
> 
> Signed-off-by: NeilBrown <neil@brown.name>
> ---
>  fs/overlayfs/super.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
> 
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index ba9146f22a2c..2fd3e0aee50e 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -451,18 +451,13 @@ static int ovl_lower_dir(const char *name, const struct path *path,
>  	return 0;
>  }
>  
> -/* Workdir should not be subdir of upperdir and vice versa */
> +/*
> + * Workdir should not be subdir of upperdir and vice versa, and
> + * they should not be the same.
> + */
>  static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
>  {
> -	bool ok = false;
> -
> -	if (workdir != upperdir) {
> -		struct dentry *trap = lock_rename(workdir, upperdir);
> -		if (!IS_ERR(trap))
> -			unlock_rename(workdir, upperdir);
> -		ok = (trap == NULL);
> -	}
> -	return ok;
> +	return !is_subdir(workdir, upperdir) && !is_subdir(upperdir, workdir);
>  }
>  
>  static int ovl_setup_trap(struct super_block *sb, struct dentry *dir,

Reviewed-by: Jeff Layton <jlayton@kernel.org>