Re: [PATCH bpf-next 2/4] landlock: Use path_parent()

[Song Liu]

On Sat, May 31, 2025 at 6:51 AM Tingmao Wang <m@xxxxxxxxxx> wrote:
[...]
> I'm not sure if the original behavior was intentional, but since this
> technically counts as a functional changes, just pointing this out.

Thanks for pointing it out! I think it is possible to keep current
behavior. Or we can change the behavior and state that clearly
in the commit log. Mickaël, WDYT?

>
> Also I'm slightly worried about the performance overhead of doing
> path_connected for every hop in the iteration (but ultimately it's
> Mickaël's call).  At least for Landlock, I think if we want to block all

Maybe we need a flag to path_parent (or path_walk_parent) so
that we only check for path_connected when necessary.

Thanks,
Song

> access to disconnected files, as long as we eventually realize we have
> been disconnected (by doing the "if dentry == path.mnt" check once when we
> reach root), and in that case deny access, we should be good.
>
>
> > @@ -918,12 +915,15 @@ static bool is_access_to_paths_allowed(
> >                               allowed_parent1 = true;
> >                               allowed_parent2 = true;
> >                       }
> > +                     goto walk_done;
> > +             case PATH_PARENT_SAME_MOUNT:
> >                       break;
> > +             default:
> > +                     WARN_ON_ONCE(1);
> > +                     goto walk_done;
> >               }
> > -             parent_dentry = dget_parent(walker_path.dentry);
> > -             dput(walker_path.dentry);
> > -             walker_path.dentry = parent_dentry;
> >       }
> > +walk_done:
> >       path_put(&walker_path);
> >
> >       if (!allowed_parent1) {
>