linux-kernel - Re: [PATCH security-next v4 23/32] selinux: Remove boot parameter

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Message-ID: <cc2ff677-a45e-e171-7a71-7d8e202bcabd@tycho.nsa.gov>
Date:   Tue, 2 Oct 2018 14:33:35 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Kees Cook <keescook@...omium.org>,
        Jordan Glover <Golden_Miller83@...tonmail.ch>
Cc:     Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
        Casey Schaufler <casey@...aufler-ca.com>,
        John Johansen <john.johansen@...onical.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        "Schaufler, Casey" <casey.schaufler@...el.com>,
        linux-security-module <linux-security-module@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH security-next v4 23/32] selinux: Remove boot parameter

On 10/02/2018 12:54 PM, Kees Cook wrote:
> On Tue, Oct 2, 2018 at 9:33 AM, Jordan Glover
> <Golden_Miller83@...tonmail.ch> wrote:
>> It's always documented as: "selinux=1 security=selinux" so security= should
>> still do the job and selinux=1 become no-op, no?
> 
> The v3 patch set worked this way, yes. (The per-LSM enable defaults
> were set by the LSM. Only in the case of "lsm.disable=selinux" would
> the above stop working.)
> 
> John did not like the separation of having two CONFIG and two
> bootparams mixing the controls. The v3 resolution rules were:
> 
> SECURITY_SELINUX_BOOTPARAM_VALUE overrides CONFIG_LSM_ENABLE.
> SECURITY_APPARMOR_BOOTPARAM_VALUE overrides CONFIG_LSM_ENABLE.
> selinux= overrides SECURITY_SELINUX_BOOTPARAM_VALUE.
> apparmor.enabled= overrides SECURITY_APPARMOR_BOOTPARAM_VALUE.
> apparmor= overrides apparmor.enabled=.
> lsm.enable= overrides selinux=.
> lsm.enable= overrides apparmor=.
> lsm.disable= overrides lsm.enable=.
> major LSM _omission_ from security= (if present) overrides lsm.enable.
> 
> v4 removed the per-LSM boot params and CONFIGs at John's request, but
> Paul and Stephen don't want this for SELinux.
> 
> The pieces for reducing conflict with CONFIG_LSM_ENABLE and
> lsm.{enable,disable}= were:
> 
> 1- Remove SECURITY_APPARMOR_BOOTPARAM_VALUE.
> 2- Remove apparmor= and apparmor.enabled=.
> 3- Remove SECURITY_SELINUX_BOOTPARAM_VALUE.
> 4- Remove selinux=.
> 
> v4 used all of 1-4 above. SELinux says "4" cannot happen as it's too
> commonly used. Would 3 be okay for SELinux?

Let's say a user/packager/distro has been building kernels for the past 
14 years (*) with a config that has SECURITY_SELINUX_BOOTPARAM_VALUE=0, 
and now they build a new kernel that includes these patches using that 
same config.  Won't SELinux be enabled by default because 
SECURITY_SELINUX_BOOTPARAM_VALUE is now ignored and LSM_ENABLE defaults 
to all?  Is it ok to require them to specify a new config option to 
preserve old behavior?

(*) how long this config option has been around

> 
> John, with 4 not happening, do you prefer to not have 2 happen?
> 
> With CONFIGs removed, then the boot time defaults are controlled by
> CONFIG_LSM_ENABLE, but the boot params continue to work as before.
> Only the use of the new lsm.enable= and lsm.disable= would override
> the per-LSM boot params. This would clean up the build-time CONFIG
> weirdness, and leave the existing boot params as before (putting us
> functionally in between the v3 and v4 series).
> 
> -Kees
>