On Tue, Jan 31, 2023 at 04:49:44PM +0100, Roberto Sassu wrote: > On Mon, 2023-01-30 at 14:57 -0800, Fan Wu wrote: > > From: Deven Bowers <deven.desai@xxxxxxxxxxxxxxxxxxx> > > > > IPE must have a centralized function to evaluate incoming callers > > against IPE's policy. This iteration of the policy against the rules > > for that specific caller is known as the evaluation loop. > > Not sure if you check the properties at every access. > > >From my previous comments (also for previous versions of the patches) > you could evaluate the property once, by calling the respective > functions in the other subsystems. > > Then, you reserve space in the security blob for inodes and superblocks > to cache the decision. The format could be a policy sequence number, to > ensure that the cache is valid only for the current policy, and a bit > for every hook you enforce. Thanks for raising this idea. I agree that if the property evaluation leads to a performance issue, it will be better to cache the evaluation result. But for this version, all the property evaluations are simple, so it is just as fast as accessing a cache. Also, for the initial version we prefer to keep the patch as minimal as possible. If the policy evolved to be super complex and the evaluation becomes a bottleneck, cache support will absolutely be the right way we will go. -Fan > > Also, currently you rely on the fact that the properties you defined > are immutable and the immutability is guaranteed by the other > subsystems, so no write can occur. > > But if you remove this limitation, the immutability is not guaranteed > anymore by the other subsystems (for example if a file is in an ext4 > filesystem), the LSM needs to take extra care to ensure that the > properties are still verified. This would be required for example if > IPE is used in conjuction with DIGLIM. > > In my opinion, IPE value would increase if the generic enforcement > mechanism is property-agnostic. > > Roberto >
