linux-kernel - Re: [PATCH 2/3] binfmt_elf: Verify signature of signed elf binary

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Date:	Wed, 16 Jan 2013 15:16:13 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, pjones@...hat.com, hpa@...or.com,
	dhowells@...hat.com, jwboyer@...hat.com,
	Dmitry Kasatkin <dmitry.kasatkin@...el.com>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/3] binfmt_elf: Verify signature of signed elf binary

Vivek Goyal <vgoyal@...hat.com> writes:

> On Wed, Jan 16, 2013 at 05:35:23PM -0500, Mimi Zohar wrote:
>> On Tue, 2013-01-15 at 16:34 -0500, Vivek Goyal wrote:
>> > If a binary is signed, verify its signature. If signature is not valid, do
>> > not allow execution. If binary is not signed, execution is allowed
>> > unconditionally.
>> 
>> Basically you're building the policy into the executable.  Anyone can
>> rebuild the executable and, without signing it, install/replace an
>> existing one.  How is this safe?  The signature verification policy
>> needs to be defined independently of the executable.
>
> Upon signature verification this executable will also acquire a new
> capability(say CAP_SIGNED). And some of the services can be allowed only
> if process has that new capability. (TODO item)

Just a quick segway.  The ptrace problem is solved by existing
mechanisms if you have a capability that other binaries don't have.

Eric
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