[PATCH v1 00/22] LSM: Full security module stacking

[Casey Schaufler]

On 8/14/2018 10:05 AM, Sargun Dhillon wrote:
> On Mon, Jul 16, 2018 at 10:53 AM, Casey Schaufler
> <casey at schaufler-ca.com> wrote:
>> LSM: Full security module stacking
>>
>> I'm calling this v1 not because it's the first version
>> I've put out but because it's the first version I'm getting
>> serious external pressure to get upstream.
> Awesome work, I'm glad that this is getting further.

It's following the 90/90 rule pretty closely. The first
90% of the work took 90% of the time, and the last 10% is
taking the other 90% of the time.

>> The blob management part (through "LSM: Sharing of security blobs")
>> is ready for prime-time. These changes move the management of
>> security blobs out of the security modules and into the security
>> module infrastructure. With this change the proposed S.A.R.A,
>> LandLock and PTAGS security modules could co-exist with any of
>> the existing "major" security modules. The changes reduce some
>> code duplication.
>>
>> Beyond the blob management there's a bit of clean-up.
>> Mounting filesystems had to be changed so that options
>> a security module doesn't recognize won't be considered
>> a fatal error. The mount infrastructure is somewhat
>> more complex than one might assume.
>>
> Casey,
> Do you think you can break out 1 into its own patch? It seems like
> that'd be valuable to everyone.

Yes, I think that is a good idea. Landlock, S.A.R.A. and a couple
other security modules could be added upstream if this part of the
work was available. It would not provide everything needed to stack
all the existing modules. I believe there is concern that if this
much went upstream the work on finishing what's required to make
everything work might be abandoned.

> What's your thought here if we ever introduce dynamic security
> modules? It's nice that we now have a way around rolling back blobs if
> one fails, but what if a new module was activated, would we just
> resize the slab cache?

Making the blob size dynamic at run time makes the blob management
more complicated because you have to keep track of the modules in
play when the blob was allocated, and pay attention to that when hooks
are called. It's a lot simpler if you don't let blobs get smaller,
but still requires more bookkeeping than if the size is static. It
is completely doable. I have played with it a bit. There are performance
implications.