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From:   KP Singh <kpsingh@chromium.org>
Date:   Mon, 16 Nov 2020 23:48:43 +0100
Message-ID: <CACYkzJ6U3PNZ0w5ryeWbyTi0NfSLg241iHMHz-b8mrDdsgfkfw@mail.gmail.com>
Subject: Re: [PATCH bpf-next 1/2] bpf: Add bpf_lsm_set_bprm_opts helper
To:     Daniel Borkmann <daniel@iogearbox.net>
Cc:     open list <linux-kernel@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Paul Turner <pjt@google.com>,
        Pauline Middelink <middelin@google.com>
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[...]

> >
> > +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.

- 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,
> > +};
> > +