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Message-ID: <CAGXu5j+vRGFvJZmjtAcT8Hi8B+Wz0e1b6VKYZHfQP_=DXzC4CQ@mail.gmail.com>
Date: Tue, 18 Apr 2017 14:48:00 -0700
From: Kees Cook <keescook@...omium.org>
To: Mickaël Salaün <mic@...ikod.net>
Cc: LKML <linux-kernel@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
Andy Lutomirski <luto@...capital.net>, Arnaldo Carvalho de Melo <acme@...nel.org>,
Casey Schaufler <casey@...aufler-ca.com>, Daniel Borkmann <daniel@...earbox.net>,
David Drysdale <drysdale@...gle.com>, "David S . Miller" <davem@...emloft.net>,
"Eric W . Biederman" <ebiederm@...ssion.com>, James Morris <james.l.morris@...cle.com>,
Jann Horn <jann@...jh.net>, Jonathan Corbet <corbet@....net>, Matthew Garrett <mjg59@...f.ucam.org>,
Michael Kerrisk <mtk.manpages@...il.com>, Paul Moore <paul@...l-moore.com>,
Sargun Dhillon <sargun@...gun.me>, "Serge E . Hallyn" <serge@...lyn.com>, Shuah Khan <shuah@...nel.org>,
Tejun Heo <tj@...nel.org>, Thomas Graf <tgraf@...g.ch>, Will Drewry <wad@...omium.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Linux API <linux-api@...r.kernel.org>,
linux-security-module <linux-security-module@...r.kernel.org>,
Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v6 01/11] bpf: Add eBPF program subtype and
is_valid_subtype() verifier
On Tue, Mar 28, 2017 at 4:46 PM, Mickaël Salaün <mic@...ikod.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: Mickaël Salaün <mic@...ikod.net>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: David S. Miller <davem@...emloft.net>
> Link: https://lkml.kernel.org/r/20160827205559.GA43880@ast-mbp.thefacebook.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 = check_user_buf((void __user *)attr->prog_subtype,
> + attr->prog_subtype_size,
> + sizeof(prog->subtype));
> + if (size < 0) {
> + err = size;
> + goto free_prog;
> + }
> + /* prog->subtype is __GFP_ZERO */
> + if (copy_from_user(&prog->subtype,
> + u64_to_user_ptr(attr->prog_subtype), size)
> + != 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
--
Kees Cook
Pixel Security
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