linux-kernel - Re: [PATCH 4/4] binfmt_elf: Elf executable signature verification

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Date:	Mon, 18 Mar 2013 16:23:11 -0400
From:	Josh Boyer <jwboyer@...il.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, zohar@...ux.vnet.ibm.com,
	dmitry.kasatkin@...el.com, akpm@...ux-foundation.org,
	ebiederm@...ssion.com
Subject: Re: [PATCH 4/4] binfmt_elf: Elf executable signature verification

On Fri, Mar 15, 2013 at 4:35 PM, Vivek Goyal <vgoyal@...hat.com> wrote:
> Do elf executable signature verification (if one is present). If signature
> is present, it should be valid. Validly signed files are given a capability
> CAP_SIGNED.
>
> If file is unsigned, it can execute but it does not get the capability
> CAP_SIGNED.
>
> This is work in progress. This patch is just an RFC to show how one
> can go about making use of IMA APIs for executable signature
> verification.
>
> Signed-off-by: Vivek Goyal <vgoyal@...hat.com>
> ---
>  fs/Kconfig.binfmt |   12 ++++++++++++
>  fs/binfmt_elf.c   |   44 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 56 insertions(+), 0 deletions(-)
>
> diff --git a/fs/Kconfig.binfmt b/fs/Kconfig.binfmt
> index 0efd152..cbb1d4a 100644
> --- a/fs/Kconfig.binfmt
> +++ b/fs/Kconfig.binfmt
> @@ -23,6 +23,18 @@ config BINFMT_ELF
>           ld.so (check the file <file:Documentation/Changes> for location and
>           latest version).
>
> +config BINFMT_ELF_SIG
> +       bool "ELF binary signature verification"
> +       depends on BINFMT_ELF
> +       select INTEGRITY
> +       select INTEGRITY_SIGNATURE
> +       select INTEGRITY_ASYMMETRIC_KEYS
> +       select IMA
> +       select IMA_APPRAISE
> +       default n
> +       ---help---
> +         Check ELF binary signature verfication.
> +

I haven't reviewed the whole patch set, but this caught my eye.  There
are a couple things wrong with it.

1) The help text isn't helpful.  It could definitely be more verbose and
should probably point to something in Documentation/ that describes what
this whole thing is.

2) The select mechanism is horrible.  I would really like to see this
option use "depends on" instead of select given that you're selecting in
a whole subsystem that people probably aren't going to have already
enabled.

josh
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