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    SubjectRe: [PATCH security-next v4 23/32] selinux: Remove boot parameter
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    On 10/3/18 4:55 PM, Kees Cook wrote:
    > On Wed, Oct 3, 2018 at 2:34 PM, James Morris <jmorris@namei.org> wrote:
    >> On Wed, 3 Oct 2018, Kees Cook wrote:
    >>
    >>> On Wed, Oct 3, 2018 at 11:28 AM, James Morris <jmorris@namei.org> wrote:
    >>>> On Wed, 3 Oct 2018, Kees Cook wrote:
    >>>>
    >>>>> On Wed, Oct 3, 2018 at 11:17 AM, James Morris <jmorris@namei.org> wrote:
    >>>>>> On Tue, 2 Oct 2018, John Johansen wrote:
    >>>>>>> To me a list like
    >>>>>>> lsm.enable=X,Y,Z
    >>>>>>
    >>>>>> What about even simpler:
    >>>>>>
    >>>>>> lsm=selinux,!apparmor,yama
    >>>>>
    >>>>> We're going to have lsm.order=, so I'd like to keep it with a dot
    >>>>> separator (this makes it more like module parameters, too). You want
    >>>>> to mix enable/disable in the same string? That implies you'd want
    >>>>> implicit enabling (i.e. it complements the builtin enabling), which is
    >>>>> opposite from what John wanted.
    >>>>>
    >>>>
    >>>> Why can't this be the order as well?
    >>>
    >>> That was covered extensively in the earlier threads. It boils down to
    >>> making sure we do not create a pattern of leaving LSMs disabled by
    >>> default when they are added to the kernel. The v1 series used
    >>> security= like this:
    >>>
    >>> + security= [SECURITY] An ordered comma-separated list of
    >>> + security modules to attempt to enable at boot. If
    >>> + this boot parameter is not specified, only the
    >>> + security modules asking for initialization will be
    >>> + enabled (see CONFIG_DEFAULT_SECURITY). Duplicate
    >>> + or invalid security modules will be ignored. The
    >>> + capability module is always loaded first, without
    >>> + regard to this parameter.
    >>>
    >>> This meant booting "security=apparmor" would disable all the other
    >>> LSMs, which wasn't friendly at all. So "security=" was left alone (to
    >>> leave it to only select the "major" LSM: all major LSMs not matching
    >>> "security=" would be disabled). So I proposed "lsm.order=" to specify
    >>> the order things were going to be initialized in, but to avoid kernels
    >>> booting with newly added LSMs forced-off due to not being listed in
    >>> "lsm.order=", it had to have implicit fall-back for unlisted LSMs.
    >>> (i.e. anything missing from lsm.order would then follow their order in
    >>> CONFIG_LSM_ORDER, and anything missing there would fall back to
    >>> link-time ordering.) However, then the objection was raised that this
    >>> didn't provide a way to explicitly disable an LSM. So I proposed
    >>> lsm.enable/disable, and John argued for CONFIG_LSM_ENABLE over
    >>> CONFIG_LSM_DISABLE.
    >>
    >> Ok, but it may end up being clearer, simpler, and thus more secure to just
    >> have a single way to configure LSM.
    >>
    >> For example:
    >>
    >> - All LSMs which are built are NOT enabled by default
    >>
    >> - You specify enablement and order via a Kconfig:
    >>
    >> CONFIG_LSM="selinux,yama"
    >>
    >> - This can be entirely overridden by a boot param:
    >>
    >> lsm="apparmor,landlock"
    >
    > This doesn't work with how SELinux and AppArmor do their bootparams,
    > unfortunately. (And Paul and Stephen have expressed that the
    > documented selinux on/off must continue to work.) For example, let's
    > say you've built an Ubuntu kernel with:
    >
    > CONFIG_SELINUX=y
    > ...
    > CONFIG_LSM="yama,apparmor"
    >
    > (i.e. you want SELinux available, but not enabled, so it's left out of
    > CONFIG_LSM)
    >
    > Then someone boots the system with:
    >
    > selinux=1 security=selinux
    >
    > In what order does selinux get initialized relative to yama?
    > (apparmor, flagged as a "legacy major", would have been disabled by
    > the "security=" not matching it.)
    >

    To me, "security=selinux" means SELinux and nothing else, so I think that
    all of these params are inviting a lot of confusion.

    Sorry, I don't have a good answer for this.

    >
    > The LSM order needs to be defined externally to enablement because
    > something may become enabled when not listed in the order.
    >
    > Now, maybe I misunderstood your earlier suggestion, and what you meant
    > was to do something like:
    >
    > CONFIG_LSM="yama,apparmor,!selinux"
    >
    > to mean "put selinux here in the order, but don't enable it". Then the
    > problem becomes what happens to an LSM that has been built in but not
    > listed in CONFIG_LSM?
    >
    > Related to that, this means that when new LSMs are added, they will
    > need to be added to any custom CONFIG_LSM= or lsm= parameters. If
    > that's really how we have to go, I'll accept it, but I think it's a
    > bit unfriendly. :P
    >
    > Another reason I don't like it is because it requires users to know
    > about all the LSMs to make changes. One LSM can't be added/removed
    > without specifying ALL of the LSMs. (i.e. there is no trivial way to
    > enable/disable a single LSM without it growing its own enable/disable
    > code as in SELinux/AppArmor. I'd hoped to make that easier for both
    > users and developers.) Again, I can live with it, but I think it's
    > unfriendly.
    >
    > I just want to have a direct I can go that meets all the requirements.
    > :) I'm fine to ignore my sense of aesthetics if everyone can agree on
    > the code.


    --
    ~Randy

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