On 11/06/2017 10:23 PM, Serge E. Hallyn wrote:
> I think I definately prefer what I mentioned in the email to Boris.
> Basically a "permanent capability bounding set". The normal bounding
> set gets reset to a full set on every new user_ns creation. In this
> proposal, it would instead be set to the calling task's permanent
> capability set, which starts (at boot) full, and which privileged
> tasks can pull capabilities out of.
Actually, this may solve a similar problem I've been looking at. The
idea was basically at strategic points in the kernel (possibly LSM hook
sites, still evaluating, and probably syscall entry) validate that a
task has not "magically" acquired capabilities that it or parent
specifically said it cannot have and then take some action like say
killing it immediately. Using your terms, basically make the "permanent
capability set" a write-once privilege escalation defense. To handle the
0-day threat, perhaps make it writable but only with more "restrictive"
values.
-chrish
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