Re: [patch 0/4] MAP_NOZERO v2 - VM_NOZERO/MAP_NOZERO early summer madness

Rik van Riel
2007-07-02T19:03:27Z

Andy Isaacson wrote:
> On Sat, Jun 30, 2007 at 08:21:52PM -0400, Kyle Moffett wrote:
>> That's why you'd need to call an LSM hook to get a unique identifier,
>> as the LSM would actually need to allocate identifiers for
>> equivalence classes. Secondly, processes may change labels as they
>> run, so you couldn't just call it once and cache the result, you
>> would need to call it for every freed page (or every re-use of a page).
>
> Davide's patch adds a owner_uid field to mm_struct. Assuming that turns
> into a "mm security equivalence class identifier", the LSM can simply
> update it when a label-change-event occurs. No need to call out to
> (potentially heavyweight!) LSM code in page allocation critical paths.
>
> I'm a bit concerned that tracking the equivalence classes will get
> expensive. I think you can end up with quadratic explosion in the worst
> case (every user using every permutation of LSM bits).

That should not happen. The default SELinux configuration
in Fedora (and Debian?) runs a few daemons in their own
restricted modes and has most of the system running in
unconfined_t, including the majority of user programs.

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