Re: [PATCH PLACEHOLDER 1/3] fs/exec: "always_unprivileged" patch

[Will Drewry]

On Thu, Jan 12, 2012 at 7:11 PM, Andrew Lutomirski <luto@xxxxxxx> wrote:
> (Also, preventing dropping of privileges will probably make a patch
> more complicted -- I'll have to find and update all the places that
> allow dropping privileges.)

An alternative approach might be that the restricted bit drops all
privileges that allows privilege changes in either direction.  E.g.,
- set restricted bit
-- adds a check anywhere MNT_NOSUID is
-- sets securebit to SECURE_NOROOT|..LOCKED
-- drops CAP_SETUID, CAP_DAC_OVERRIDE, ...
-- set the caps bounding set to the minimum the restricted bit allows

That may deviate from the intent (by re-using caps), but it could keep some
of the privilege transition checking code the same.

Just a thought,
will
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