linux-kernel - Re: [PATCH] Yama: remove needless CONFIG_SECURITY_YAMA

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Date:	Tue, 21 Jul 2015 15:41:43 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Casey Schaufler <casey@...aufler-ca.com>
Cc:	Josh Boyer <jwboyer@...oraproject.org>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	James Morris <james.l.morris@...cle.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Yama: remove needless CONFIG_SECURITY_YAMA_STACKED

On Tue, Jul 21, 2015 at 1:56 PM, Casey Schaufler <casey@...aufler-ca.com> wrote:
> On 7/21/2015 1:09 PM, Josh Boyer wrote:
>> On Tue, Jul 21, 2015 at 3:48 PM, Casey Schaufler <casey@...aufler-ca.com> wrote:
>>> On 7/21/2015 12:09 PM, Kees Cook wrote:
>>>> Now that minor LSMs can cleanly stack with major LSMs, remove the unneeded
>>>> config for Yama to be made to explicitly stack. Just selecting the main
>>>> Yama CONFIG will allow it to work, regardless of the major LSM. Since
>>>> distros using Yama are already forcing it to stack, this is effectively
>>>> a no-op change.
>>> Today I can compile in all LSMs including Yama and pick the one I want.
>>> If we made your change it would be impossible to build in Yama and not
>>> use it. I suggest we hold off until after the security summit discussion
>> This is true, but it's also true regardless of stacking.  If Yama had
>> a CONFIG_SECURITY_YAMA_ENABLED (or whatever bikeshed color), then you
>> could enable Yama and not use it, yes?  It would also allow people to
>> default it as disabled, but then enable it at runtime via the
>> ptrace_scope sysctl.
>
> The way Kees proposed it you would *always* get Yama stacked with
> your other module if you compile Yama in. Thus, If I compile in
> SELinux and Yama I cannot run SELinux without Yama. Today, I can

Yama is entirely controllable from sysctl, so you could build it in
and set the ptrace_scope setting to 0 at boot. It's already being
built into distro kernels this way (via the STACKING config), so this
change is effectively no different.

> compile SELinux and Yama in but run only SELinux. My suggestion is
> to wait until we can specify the modules to use before we remove
> the kconfig option that provides that facility today.

I'm happy to wait, but I'm still going to send my other 2 "minor" LSMs
before LSS. :) Neither of them would be built into a kernel without
wanting their functionality, so they'll have the stack "always on"
semantics if their CONFIG is selected.

-Kees

-- 
Kees Cook
Chrome OS Security
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