Re: Potential issues (security and otherwise) with the current cgroup-bpf API

On Mon, Dec 19, 2016 at 05:56:24PM -0800, Andy Lutomirski wrote:

quoted

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Huh?  My example in the original email attaches a program in a
sub-hierarchy.  Are you saying that 4.11 could make that example stop
working?

Are you suggesting sub-cgroups should not be allowed to override the filter of a parent cgroup?

Yes, exactly.  I think there are two sensible behaviors:

a) sub-cgroups cannot have a filter at all of the parent has a filter.
(This is the "punt" approach -- it lets different semantics be
assigned later without breaking userspace.)

b) sub-cgroups can have a filter if a parent does, too.  The semantics
are that the sub-cgroup filter runs first and all side-effects occur.
If that filter says "reject" then ancestor filters are skipped.  If
that filter says "accept", then the ancestor filter is run and its
side-effects happen as well.  (And so on, all the way up to the root.)

So from what I understand the proposed cgroup is not in fact
hierarchical at all.

@TJ, I thought you were enforcing all new cgroups to be properly
hierarchical, that would very much include this one.