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Many Thanks, I will look into the Secure Pipelines and policy delivery / update options. Regards, Tim On 25/04/12 13:40, Stephen Smalley wrote:
On Wed, 2012-04-25 at 10:37 +0100, Tim Sheppard wrote:The other thing I need to be able to do is constrain a process to only permit it to change a context from c1 -> c2 (or label1 -> label2 in the general case). Is this possible to manage in a policy at all and if so is there any runtime flexibility over the rules that can be created to allow me to specify the only legal changes are c1 -> c2 -> c3 -> end for process1-1 and c1 -> c2 -> c3 -> c4-> c5 -> end for process1-2. Essentially, I need to be able to ensure that a process cannot change the security labelling to bypass a stage in the chain.That's more easily expressed via Type Enforcement (which supports intransitive relationships) than MLS. Type Enforcement is what is normally used for assured pipelines. Some people have instead modeled assured pipelines using MLS categories by using incomparable category sets on the input and output sides of each stage and clever configuration, but that's more complicated and less precise in its control of the information flow. With regard to runtime flexibility, there isn't presently a way to programmatically instantiate new domains and types; your application can only use ones that are already defined in the policy. So options might include: - Ship a policy module with your application that defines the maximal set of domains/types ever required for one of these pipelines, and then your application can just use the relevant subset for any given instance, or - Implement some kind of userspace daemon that runs with privilege (and thus can load policy) and accepts requests to instantiate new pipeline stage domains and types, generates new policy modules to define them, and loads them (I think maybe some folks from Tresys have done this in the past?). Or you could always extend SELinux to directly support such functionality, but that would be a larger project (and require a custom kernel).
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