From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH 1/3] cpuset: Allow setscheduler regardless of manipulated task Date: Thu, 29 Jun 2023 08:11:33 -0400 Message-ID: <15c607d9-c1fa-ca11-d675-8f2b3a6fd15b@redhat.com> References: <20230629091146.28801-1-mkoutny@suse.com> <20230629091146.28801-2-mkoutny@suse.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1688040700; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=iUMXrX97pfVEXgUti557n3bGMAKPy8ETXJCsvtuqbtI=; b=Cjmq1SOGJJuoaldEXYcOisxPFuhLY3diXOlUw1Xfw0ZZVYIiuWU/K7TGFzoWgJEeqgxWCt QZaeFb/DeBeXzWU5s7gtSaWEka4354nVp1lG8mXRiWM6rqx4lzGW49xsaDbRl3gvMDYXGR RYDa9+dZY53f1hwqK3U2fh8FDxidD+o= Content-Language: en-US In-Reply-To: <20230629091146.28801-2-mkoutny-IBi9RG/b67k@public.gmane.org> List-ID: Content-Type: text/plain; charset="utf-8"; format="flowed" To: =?UTF-8?Q?Michal_Koutn=c3=bd?= , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kselftest-u79uwXL29TY76Z2rM5mHXA@public.gmane.org Cc: Zefan Li , Tejun Heo , Johannes Weiner , Shuah Khan 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 > --- > 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