On 9/13/2018 4:51 PM, Kees Cook wrote:

On Thu, Sep 13, 2018 at 4:32 PM, John Johansen
[off-list ref] wrote:

quoted

On 09/13/2018 04:06 PM, Kees Cook wrote:

quoted

- what order should any stacking happen? Makefile? security=?

Preferably not. For the single LSM we have the ability to choose the default LSM, ideally we let the distro decide in the Kconfig and the user with security=...

I can't find a non-crazy way to do this in Kconfig. Right now, if I
threw out all the _DEFAULT stuff, I could do:

config SECURITY_SELINUX_ENABLED
        bool "SELinux LSM enabled at boot time"
        depends on SECURITY_SELINUX
        depends on !SECURITY_APPARMOR_ENABLED && !SECURITY_SMACK_ENABLED
        default SECURITY_SELINUX

config SECURITY_SMACK_ENABLED
        bool "SMACK LSM enabled at boot time"
        depends on SECURITY_SMACK
        depends on !SECURITY_APPARMOR_ENABLED && !SECURITY_SELINUX_ENABLED
        default SECURITY_SMACK

config SECURITY_APPARMOR_ENABLED
        bool "AppArmor LSM enabled at boot time"
        depends on SECURITY_APPARMOR
        depends on !SECURITY_SMACK_ENABLED && !SECURITY_SELINUX_ENABLED
        default SECURITY_APPARMOR

config SECURITY_TOMOYO_ENABLED
        bool "TOMOYO LSM enabled at boot time"
        depends on SECURITY_TOMOYO
        default y if !SECURITY_SELINUX_ENABLED &&
!SECURITY_SMACK_ENABLED && !SECURITY_APPARMOR_ENABLED

config DEFAULT_SECURITY
        string
        default "selinux" if SECURITY_SELINUX_ENABLED
        default "smack" if SECURITY_SMACK_ENABLED
        default "apparmor" if SECURITY_APPARMOR_ENABLED
        default "tomoyo" if SECURITY_TOMOYO_ENABLED

(As before CONFIG_DEFAULT_SECURITY basically means the effective
"security=" contents. Reminder than Kconfig default are "first match",
so tomoyo would only happen if all others are not enabled by default.)

But this doesn't provide a way for Kconfig to declare the ordering of
TOMOYO followed by SELinux. If we just declare ordering is a function
of the Makefile, then the above would work as expected. The
"conflicting major LSM" could be specified on "security=" and stacked
could be enabled with $lsm.enable=1 (or disabled).

So, before we can really make a decision, I think we have to decide:
should ordering be arbitrary for even this level of stacking?

Do we have a case where it matters? I know that I could write a
module that would have issues if one hook got called and another
didn't because because a precursor module hook failed. I don't
think that any of the existing modules have this problem.