linux-kernel - Re: [PATCH v3 bpf-next 1/5] namei: Introduce new helper function path_walk

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAPhsuW6jZxRBEgz00KV4SasiMhBGyMHoP5dMktoyCOeMbJwmgg@mail.gmail.com>
Date: Wed, 11 Jun 2025 09:31:26 -0700
From: Song Liu <song@...nel.org>
To: Mickaël Salaün <mic@...ikod.net>
Cc: NeilBrown <neil@...wn.name>, Jan Kara <jack@...e.cz>, bpf@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-security-module@...r.kernel.org, kernel-team@...a.com, 
	andrii@...nel.org, eddyz87@...il.com, ast@...nel.org, daniel@...earbox.net, 
	martin.lau@...ux.dev, viro@...iv.linux.org.uk, brauner@...nel.org, 
	kpsingh@...nel.org, mattbobrowski@...gle.com, amir73il@...il.com, 
	repnop@...gle.com, jlayton@...nel.org, josef@...icpanda.com, 
	gnoack@...gle.com, m@...wtm.org
Subject: Re: [PATCH v3 bpf-next 1/5] namei: Introduce new helper function path_walk_parent()

On Wed, Jun 11, 2025 at 8:42 AM Mickaël Salaün <mic@...ikod.net> wrote:
[...]
> > We can probably call this __path_walk_parent() and make it static.
> >
> > Then we can add an exported path_walk_parent() that calls
> > __path_walk_parent() and adds extra logic.
> >
> > If this looks good to folks, I can draft v4 based on this idea.
>
> This looks good but it would be better if we could also do a full path
> walk within RCU when possible.

I think we will need some callback mechanism for this. Something like:

for_each_parents(starting_path, root, callback_fn, cb_data, bool try_rcu) {
   if (!try_rcu)
      goto ref_walk;

   __read_seqcount_begin();
    /* rcu walk parents, from starting_path until root */
   walk_rcu(starting_path, root, path) {
    callback_fn(path, cb_data);
  }
  if (!read_seqcount_retry())
    return xxx;  /* successful rcu walk */

ref_walk:
  /* ref walk parents, from starting_path until root */
   walk(starting_path, root, path) {
    callback_fn(path, cb_data);
  }
  return xxx;
}

Personally, I don't like this version very much, because the callback
mechanism is not very flexible, and it is tricky to use it in BPF LSM.

Thanks,
Song