On Fri, Sep 14, 2018 at 8:57 AM, Casey Schaufler <casey@xxxxxxxxxxxxxxxx> wrote: > On 9/13/2018 5:19 PM, Kees Cook wrote: >> We already have the minor LSMs that cannot change order. > > Are you saying that we don't have a mechanism to change > the order, or that they wouldn't work right in a different > order? Well, there's the capability module that has to be > first. I just meant their order is explicit in security.c. >> They aren't >> part of security= parsing either. > > True, but there's no reason now that we couldn't change that. > Except for capability. Hmm. Right, we have at least one that MUST be first (and must not be disabled). >> Should "blob-sharing" LSMs be like major LSMs or minor LSMs? > > I like the idea of changing the minor modules to do the full > registration process. That would make them all the same. > Except for capability. In any case, the "blob-sharing" LSMs > need to do the full registration process to account for their > blobs sizes, and that brings the "major" behavior along with it. I agree. I'm working on some clean-ups that I'll send out soon, though I'm worried about some of the various boot-time options... >> If someone is booting with "security=selinux,tomoyo" and then SARA >> lands upstream, does that person have to explicitly add "sara" to >> their boot args, since they're doing a non-default list of LSMs? > > Yes. security= is explicit. > >> (I actually prefer the answer being "yes" here, FWIW, I just want to >> nail down the expectations.) > > For now let's leave the minor (capability, yama, loadpin) as they are, > and require all new modules of any flavor to use full registration. I would even be fine to convert yama and loadpin. > We could consider something like > > security=$lsm # Stack with $lsm at priority 2 - Existing behavior > $lsm.stacked=N # Add $lsm to the stack at priority N. Delete if N == 0 > > It's OK to specify "selinux.stacked=2" and "sara.stacked=2". Which gets > called first is left up to the system to decide. Whatever the behavior is > gets documented. Capability will always be first and have priority 1. > It's OK to specify "smack.stacked=1". I'm less excited about this kind of stacking priority, but, whatever the case, I think my cleanups may help with whatever we decide. > The default stack is determined by CONFIG_SECURITY_$lsm_STACKED at > build time. CONFIG_SECURITY_$lsm_STACKED changes from a boolean to > an integer value to establish the default hook order. > > /sys/kernel/security/lsm reports the modules in hook call order. Didn't I send a patch to new-line terminate this list? I always get annoyed when I "cat" it. ;) > /sys/kernel/security/lsm-stack reports the list with the hook call priority > > capability:1,yama:1,selinux:1,sara:5,landlack:17 > > If stacking is not configured $lsm.stacked=0 is treated as security=none. > For other values of N $lsm.stacked=N is treated as security=$lsm. I feel like "order" is bad enough. Can we avoid adding "priority"? -Kees -- Kees Cook Pixel Security
