linux-kernel - Re: [PATCH v2 bpf-next 3/4] bpf: Introduce path iterator

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: <CAEf4Bzbm=mnRM=PYBLDTogrb+bNk2TnTj-kGr3=oFNEyQm8hKw@mail.gmail.com>
Date: Tue, 3 Jun 2025 14:44:56 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Song Liu <song@...nel.org>
Cc: 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, jack@...e.cz, kpsingh@...nel.org, 
	mattbobrowski@...gle.com, amir73il@...il.com, repnop@...gle.com, 
	jlayton@...nel.org, josef@...icpanda.com, mic@...ikod.net, gnoack@...gle.com, 
	m@...wtm.org
Subject: Re: [PATCH v2 bpf-next 3/4] bpf: Introduce path iterator

On Tue, Jun 3, 2025 at 2:09 PM Song Liu <song@...nel.org> wrote:
>
> On Tue, Jun 3, 2025 at 11:40 AM Andrii Nakryiko
> <andrii.nakryiko@...il.com> wrote:
> [...]
> > > +__bpf_kfunc struct path *bpf_iter_path_next(struct bpf_iter_path *it)
> > > +{
> > > +       struct bpf_iter_path_kern *kit = (void *)it;
> > > +       struct path root = {};
> > > +
> > > +       if (!path_walk_parent(&kit->path, &root))
> > > +               return NULL;
> > > +       return &kit->path;
> > > +}
> > > +
> > > +__bpf_kfunc void bpf_iter_path_destroy(struct bpf_iter_path *it)
> > > +{
> > > +       struct bpf_iter_path_kern *kit = (void *)it;
> > > +
> > > +       path_put(&kit->path);
> >
> > note, destroy() will be called even if construction of iterator fails
> > or we exhausted iterator. So you need to make sure that you have
> > bpf_iter_path state where you can detect that there is no path present
> > and skip path_put().
>
> In bpf_iter_path_next(), when path_walk_parent() returns false, we
> still hold reference to kit->path, then _destroy() will release it. So we
> should be fine, no?

you still need to handle iterators that failed to be initialized,
though? And one can argue that if path_walk_parent() returns false, we
need to put that last path before returning NULL, no?

>
> Thanks,
> Song
>
> >
> > > +}
> > > +
> > > +__bpf_kfunc_end_defs();
> > > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > > index a7d6e0c5928b..45b45cdfb223 100644
> > > --- a/kernel/bpf/verifier.c
> > > +++ b/kernel/bpf/verifier.c
> > > @@ -7036,6 +7036,10 @@ BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct socket) {
> > >         struct sock *sk;
> > >  };
> > >
> > > +BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct path) {
> > > +       struct dentry *dentry;
> > > +};
> > > +
> > >  static bool type_is_rcu(struct bpf_verifier_env *env,
> > >                         struct bpf_reg_state *reg,
> > >                         const char *field_name, u32 btf_id)
> > > @@ -7076,6 +7080,7 @@ static bool type_is_trusted_or_null(struct bpf_verifier_env *env,
> > >                                     const char *field_name, u32 btf_id)
> > >  {
> > >         BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct socket));
> > > +       BTF_TYPE_EMIT(BTF_TYPE_SAFE_TRUSTED_OR_NULL(struct path));
> > >
> > >         return btf_nested_type_is_trusted(&env->log, reg, field_name, btf_id,
> > >                                           "__safe_trusted_or_null");
> > > --
> > > 2.47.1
> > >
> >