Subject: Re: [PATCH] Yama: remove needless CONFIG_SECURITY_YAMA_STACKED
To: Kees Cook <keescook@chromium.org>
References: <20150721190946.GA5127@www.outflux.net>
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 <CAGXu5j+JzdMPxuh68xFZ3mrAmZgygLZU-+gp6psd0VFxNPY-nA@mail.gmail.com>
Cc: Josh Boyer <jwboyer@fedoraproject.org>,
        linux-security-module <linux-security-module@vger.kernel.org>,
        James Morris <james.l.morris@oracle.com>,
        "linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>,
        "Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>
From: Casey Schaufler <casey@schaufler-ca.com>
Message-ID: <55AEDDDE.6060809@schaufler-ca.com>
Date: Tue, 21 Jul 2015 17:03:42 -0700
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On 7/21/2015 3:41 PM, Kees Cook wrote:
> On Tue, Jul 21, 2015 at 1:56 PM, Casey Schaufler <casey@schaufler-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@schaufler-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.

Fair enough then. I'll withdraw my objection. One question comes
to mind, and that is how are you planning to order them? I put
Yama ahead of the "major" modules because that was how it had been
stacked previously. Let's assume that the capability module stays
in the first position. Are you planning to put your new modules
before Yama, before the "major" module(s) or at the end?

> -Kees
>

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