Messages in this thread | | | Date | Thu, 29 Jun 2023 08:11:33 -0400 | Subject | Re: [PATCH 1/3] cpuset: Allow setscheduler regardless of manipulated task | From | Waiman Long <> |
| |
On 6/29/23 05:11, Michal Koutný wrote: > When we migrate a task between two cgroups, one of the checks is a > verification whether we can modify task's scheduler settings > (cap_task_setscheduler()). > > An implicit migration occurs also when enabling a controller on the > unified hierarchy (think of parent to child migration). The > aforementioned check may be problematic if the caller of the migration > (enabling a controller) has no permissions over migrated tasks. > For instance, a user's cgroup that ends up running a process of a > different user. Although cgroup permissions are configured favorably, > the enablement fails due to the foreign process [1]. > > Change the behavior by relaxing the permissions check on the unified > hierarchy (or in v2 mode). This is in accordance with unified hierarchy > attachment behavior when permissions of the source to target cgroups are > decisive whereas the migrated task is opaque (as opposed to more > restrictive check in __cgroup1_procs_write()).
The is_in_v2_mode() check is for supporting the v2 mode in cgroup v1. However, there is no controller enabling in v1. So I think you should just use cgroup_subsys_on_dfl(cpuset_cgrp_subsys) as the v2 check if your focus is just to prevent problem when enabling cpuset controller.
> > [1] https://github.com/systemd/systemd/issues/18293#issuecomment-831205649 > > Signed-off-by: Michal Koutný <mkoutny@suse.com> > --- > kernel/cgroup/cpuset.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index e4ca2dd2b764..3b5f87a9a150 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -2495,6 +2495,13 @@ static int cpuset_can_attach(struct cgroup_taskset *tset) > ret = task_can_attach(task, cs->effective_cpus); > if (ret) > goto out_unlock; > + > + /* > + * Skip rights over task check in v2, migration permission derives > + * from hierarchy ownership in cgroup_procs_write_permission()). > + */ > + if (is_in_v2_mode()) > + continue; > ret = security_task_setscheduler(task); > if (ret) > goto out_unlock;
This change will likely conflict with the latest cpuset change on tracking # of dl tasks in a cpuset. You will have to, at least, move the dl task check before the security_task_setscheduler() check.
Another fact about cpuset controller enabling is that both cpus_allowed and mems_allowed are empty at that point. You may also add these checks as a preconditions for disabling the security_task_setscheduler check.
Cheers, Longman
| |