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

Amir Goldstein
2026-02-05T09:37:31Z

On Wed, Feb 4, 2026 at 6:09 AM NeilBrown <neilb@ownmail.net> 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>

Looks reasonable

Reviewed-by: Amir Goldstein <amir73il@gmail.com>

> ---
> 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,
> --
> 2.50.0.107.gf914562f5916.dirty
>