From mboxrd@z Thu Jan  1 00:00:00 1970
From: Kees Cook <keescook@chromium.org>
Subject: Re: [PATCH net-next v6 01/11] bpf: Add eBPF program subtype and
 is_valid_subtype() verifier
Date: Tue, 18 Apr 2017 14:48:00 -0700
Message-ID: <CAGXu5j+vRGFvJZmjtAcT8Hi8B+Wz0e1b6VKYZHfQP_=DXzC4CQ@mail.gmail.com>
References: <20170328234650.19695-1-mic@digikod.net> <20170328234650.19695-2-mic@digikod.net>
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To: =?UTF-8?B?TWlja2HDq2wgU2FsYcO8bg==?= <mic@digikod.net>
Cc: LKML <linux-kernel@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>, Andy Lutomirski <luto@amacapital.net>, Arnaldo Carvalho de Melo <acme@kernel.org>, Casey Schaufler <casey@schaufler-ca.com>, Daniel Borkmann <daniel@iogearbox.net>, David Drysdale <drysdale@google.com>, "David S . Miller" <davem@davemloft.net>, "Eric W . Biederman" <ebiederm@xmission.com>, James Morris <james.l.morris@oracle.com>, Jann Horn <jann@thejh.net>, Jonathan Corbet <corbet@lwn.net>, Matthew Garrett <mjg59@srcf.ucam.org>, Michael Kerrisk <mtk.manpages@gmail.com>, Paul Moore <paul@paul-moore.com>, Sargun Dhillon <sargun@sargun.me>, "Serge E . Hallyn" <serge@hallyn.com>, Shuah Khan <shuah@kernel.org>, Tejun Heo <tj@kernel.org>, Thomas Graf <tgraf@suug.ch>, Will Drewry <wa>
List-Id: linux-api@vger.kernel.org

On Tue, Mar 28, 2017 at 4:46 PM, Micka=C3=ABl Sala=C3=BCn <mic@digikod.net>=
 wrote:
> The goal of the program subtype is to be able to have different static
> fine-grained verifications for a unique program type.
>
> The struct bpf_verifier_ops gets a new optional function:
> is_valid_subtype(). This new verifier is called at the beginning of the
> eBPF program verification to check if the (optional) program subtype is
> valid.
>
> For now, only Landlock eBPF programs are using a program subtype (see
> next commit) but this could be used by other program types in the future.
>
> Changes since v5:
> * use a prog_subtype pointer and make it future-proof
> * add subtype test
> * constify bpf_load_program()'s subtype argument
> * cleanup subtype initialization
> * rebase
>
> Changes since v4:
> * replace the "status" field with "version" (more generic)
> * replace the "access" field with "ability" (less confusing)
>
> Changes since v3:
> * remove the "origin" field
> * add an "option" field
> * cleanup comments
>
> Signed-off-by: Micka=C3=ABl Sala=C3=BCn <mic@digikod.net>
> Cc: Alexei Starovoitov <ast@kernel.org>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: David S. Miller <davem@davemloft.net>
> Link: https://lkml.kernel.org/r/20160827205559.GA43880@ast-mbp.thefaceboo=
k.com
> ---
> [...]
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index c35ebfe6d84d..3d07b10ade5e 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -843,6 +879,26 @@ static int bpf_prog_load(union bpf_attr *attr)
>         if (err < 0)
>                 goto free_prog;
>
> +       /* copy eBPF program subtype from user space */
> +       if (attr->prog_subtype) {
> +               __u32 size;
> +
> +               size =3D check_user_buf((void __user *)attr->prog_subtype=
,
> +                                     attr->prog_subtype_size,
> +                                     sizeof(prog->subtype));
> +               if (size < 0) {
> +                       err =3D size;
> +                       goto free_prog;
> +               }
> +               /* prog->subtype is __GFP_ZERO */
> +               if (copy_from_user(&prog->subtype,
> +                                  u64_to_user_ptr(attr->prog_subtype), s=
ize)
> +                                  !=3D 0)

It might be worth adding a comment here about how the ToCToU of the
check-then-copy doesn't matter in this case, since it's just a
future-proofing of bits, etc.

-Kees

--=20
Kees Cook
Pixel Security