linux-kernel - Re: [PATCH bpf-next 1/2] bpf: Add bpf_lsm_set_bprm

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Date:   Mon, 16 Nov 2020 23:52:45 +0100
From:   KP Singh <kpsingh@...omium.org>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Paul Turner <pjt@...gle.com>,
        Pauline Middelink <middelin@...gle.com>
Subject: Re: [PATCH bpf-next 1/2] bpf: Add bpf_lsm_set_bprm_opts helper

On Mon, Nov 16, 2020 at 11:48 PM KP Singh <kpsingh@...omium.org> wrote:
>
> [...]
>
> > >
> > > +BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
> > > +{
> >
> > This should also reject invalid flags. I'd rather change this helper from RET_VOID
> > to RET_INTEGER and throw -EINVAL for everything other than BPF_LSM_F_BPRM_SECUREEXEC
> > passed in here including zero so it can be extended in future.
>
> Sounds good, I added:
>
>  enum {
>         BPF_LSM_F_BPRM_SECUREEXEC       = (1ULL << 0),
> +       /* Mask for all the currently supported BPRM options */
> +       BPF_LSM_F_BRPM_OPTS_MASK        = 0x1ULL,
>  };
>
> changed the return type to RET_INTEGER as suggested checking for
> invalid flags as:
>
>  BPF_CALL_2(bpf_lsm_set_bprm_opts, struct linux_binprm *, bprm, u64, flags)
>  {
> +
> +       if (flags & !BPF_LSM_F_BRPM_OPTS_MASK)
> +               return -EINVAL;
>
> Do let me know if this is okay and I can spin up a v2 with these changes.

Oops this should have been:

      if (flags & ~BPF_LSM_F_BRPM_OPTS_MASK)
               return -EINVAL;

>
> - KP
>
> >
> > > +     bprm->secureexec = (flags & BPF_LSM_F_BPRM_SECUREEXEC);
> > > +     return 0;
> > > +}
> > > +
> > > +BTF_ID_LIST_SINGLE(bpf_lsm_set_bprm_opts_btf_ids, struct, linux_binprm)
> > > +
> > > +const static struct bpf_func_proto bpf_lsm_set_bprm_opts_proto = {
> > > +     .func           = bpf_lsm_set_bprm_opts,
> > > +     .gpl_only       = false,
> > > +     .ret_type       = RET_VOID,
> > > +     .arg1_type      = ARG_PTR_TO_BTF_ID,
> > > +     .arg1_btf_id    = &bpf_lsm_set_bprm_opts_btf_ids[0],
> > > +     .arg2_type      = ARG_ANYTHING,
> > > +};
> > > +