On Tue, Jun 16, 2015 at 03:10:17PM -0400, Tejun Heo wrote: > +4-2. Common ancestor rule > + > +Let's say cgroups C0 and C1 have been delegated to user U0 who created > +C00, C01 under C0 and C10 under C1 as follows. > + > + ~~~~~~~~~~~~~ - C0 - C00 > + ~ cgroup ~ \ C01 > + ~ hierarchy ~ > + ~~~~~~~~~~~~~ - C1 - C10 > + > +C0 and C1 are separate entities in terms of resource distribution > +regardless of their relative positions in the hierarchy. The > +resources the processes under C0 are entitled to are controlled by > +C0's ancestors and may be completely different from C1. It's clear > +that the intention of delegating C0 to U0 is allowing U0 to organize > +the processes under C0 and further control the distribution of C0's > +resources. > + > +On traditional hierarchies, if a task has write access to "tasks" or > +"cgroup.procs" file of a cgroup and its uid agrees with the target, it > +can move the target to the cgroup. In the above example, U0 will not > +only be able to move processes in each sub-hierarchy but also across > +the two sub-hierarchies, effectively allowing it to violate the > +organizational and resource restrictions implied by the hierarchical > +structure above C0 and C1. > + > +On the unified hierarchy, to write to a "cgroup.procs" file, in > +addition to the usual write permission to the file and uid match, the > +writer must also have write acess to the "cgroup.procs" file of the > +common ancestor of the source and destination cgroups. This prevents > +delegatees from smuggling processes across disjoint sub-hierarchies.
I think this would be better as the first paragraph in 4.2, because it nicely explains and summarizes the rule and its reasoning; then follow up with detailed explanations and examples that corroborate the design choice. Otherwise, the patch looks good to me. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
