netdev - Re: [PATCH bpf-next v9 05/10] bpf: implement BPF_PROG_QUERY for BPF_LSM

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Date:   Fri, 17 Jun 2022 11:28:21 -0700
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org
Subject: Re: [PATCH bpf-next v9 05/10] bpf: implement BPF_PROG_QUERY for BPF_LSM_CGROUP

On Thu, Jun 16, 2022 at 5:58 PM Martin KaFai Lau <kafai@...com> wrote:
>
> On Fri, Jun 10, 2022 at 09:57:58AM -0700, Stanislav Fomichev wrote:
> > diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> > index ba402d50e130..c869317479ec 100644
> > --- a/kernel/bpf/cgroup.c
> > +++ b/kernel/bpf/cgroup.c
> > @@ -1029,57 +1029,92 @@ static int cgroup_bpf_detach(struct cgroup *cgrp, struct bpf_prog *prog,
> >  static int __cgroup_bpf_query(struct cgroup *cgrp, const union bpf_attr *attr,
> >                             union bpf_attr __user *uattr)
> >  {
> > +     __u32 __user *prog_attach_flags = u64_to_user_ptr(attr->query.prog_attach_flags);
> >       __u32 __user *prog_ids = u64_to_user_ptr(attr->query.prog_ids);
> >       enum bpf_attach_type type = attr->query.attach_type;
> > +     enum cgroup_bpf_attach_type from_atype, to_atype;
> >       enum cgroup_bpf_attach_type atype;
> >       struct bpf_prog_array *effective;
> >       struct hlist_head *progs;
> >       struct bpf_prog *prog;
> >       int cnt, ret = 0, i;
> > +     int total_cnt = 0;
> >       u32 flags;
> >
> > -     atype = to_cgroup_bpf_attach_type(type);
> > -     if (atype < 0)
> > -             return -EINVAL;
> > +     if (type == BPF_LSM_CGROUP) {
> > +             if (attr->query.prog_cnt && prog_ids && !prog_attach_flags)
> > +                     return -EINVAL;
> >
> > -     progs = &cgrp->bpf.progs[atype];
> > -     flags = cgrp->bpf.flags[atype];
> > +             from_atype = CGROUP_LSM_START;
> > +             to_atype = CGROUP_LSM_END;
> > +             flags = 0;
> > +     } else {
> > +             from_atype = to_cgroup_bpf_attach_type(type);
> > +             if (from_atype < 0)
> > +                     return -EINVAL;
> > +             to_atype = from_atype;
> > +             flags = cgrp->bpf.flags[from_atype];
> > +     }
> >
> > -     effective = rcu_dereference_protected(cgrp->bpf.effective[atype],
> > -                                           lockdep_is_held(&cgroup_mutex));
> > +     for (atype = from_atype; atype <= to_atype; atype++) {
> > +             progs = &cgrp->bpf.progs[atype];
> nit. Move the 'progs = ...' into the 'else {}' case below.
>
> >
> > -     if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE)
> > -             cnt = bpf_prog_array_length(effective);
> > -     else
> > -             cnt = prog_list_length(progs);
> > +             if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE) {
> > +                     effective = rcu_dereference_protected(cgrp->bpf.effective[atype],
> > +                                                           lockdep_is_held(&cgroup_mutex));
> > +                     total_cnt += bpf_prog_array_length(effective);
> > +             } else {
> > +                     total_cnt += prog_list_length(progs);
> > +             }
> > +     }
> >
> >       if (copy_to_user(&uattr->query.attach_flags, &flags, sizeof(flags)))
> >               return -EFAULT;
> > -     if (copy_to_user(&uattr->query.prog_cnt, &cnt, sizeof(cnt)))
> > +     if (copy_to_user(&uattr->query.prog_cnt, &total_cnt, sizeof(total_cnt)))
> >               return -EFAULT;
> > -     if (attr->query.prog_cnt == 0 || !prog_ids || !cnt)
> > +     if (attr->query.prog_cnt == 0 || !prog_ids || !total_cnt)
> >               /* return early if user requested only program count + flags */
> >               return 0;
> > -     if (attr->query.prog_cnt < cnt) {
> > -             cnt = attr->query.prog_cnt;
> > +
> > +     if (attr->query.prog_cnt < total_cnt) {
> > +             total_cnt = attr->query.prog_cnt;
> >               ret = -ENOSPC;
> >       }
> >
> > -     if (attr->query.query_flags & BPF_F_QUERY_EFFECTIVE) {
> > -             return bpf_prog_array_copy_to_user(effective, prog_ids, cnt);
> > -     } else {
> > -             struct bpf_prog_list *pl;
> > -             u32 id;
> > +     for (atype = from_atype; atype <= to_atype && total_cnt; atype++) {
> > +             progs = &cgrp->bpf.progs[atype];
> same here.
>
> > +             flags = cgrp->bpf.flags[atype];
> and the 'flags = ...' can be moved to 'if (prog_attach_flags) {}'
>
> Others lgtm.
>
> Reviewed-by: Martin KaFai Lau <kafai@...com>

Everything makes sense, will do, thanks!

Maybe we should also move "struct hlist_head *progs;" closer to the
places where we use them? Same for "struct bpf_prog *prog;" which
seems to be used only in one place.