From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A5FDC001B0 for ; Mon, 3 Jul 2023 18:01:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230323AbjGCSBI (ORCPT ); Mon, 3 Jul 2023 14:01:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60436 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230028AbjGCSBF (ORCPT ); Mon, 3 Jul 2023 14:01:05 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B257FE62 for ; Mon, 3 Jul 2023 11:00:20 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1688407220; 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=VjXD9hgua/WyFNkzAf/5dqsBFSxFdg110zmVMs5EXro=; b=epjN2MyZYPvv9LQ1BfRtS79lY5bCK2BghCzBKtHEvoPskvVI9Yq9HtrAhEFIMQ7d+xKahZ 4yzOLKhR9w9KwvV32xGGWx1dzoOn/tQtSEkSQYk8IkFuD6nch4SAVFT3Yviar8xOoYg4zG jVeV+b6/aCPxZAb6WTbyxZvtwlMXsvM= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-190-6aNQgaaQNrOw4rSs3Du5HQ-1; Mon, 03 Jul 2023 14:00:14 -0400 X-MC-Unique: 6aNQgaaQNrOw4rSs3Du5HQ-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 23377858EED; Mon, 3 Jul 2023 18:00:14 +0000 (UTC) Received: from [10.22.17.92] (unknown [10.22.17.92]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9A78615230AE; Mon, 3 Jul 2023 18:00:13 +0000 (UTC) Message-ID: Date: Mon, 3 Jul 2023 14:00:13 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH v3 1/3] cpuset: Allow setscheduler regardless of manipulated task Content-Language: en-US To: =?UTF-8?Q?Michal_Koutn=c3=bd?= , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-kselftest@vger.kernel.org Cc: Zefan Li , Tejun Heo , Johannes Weiner , Shuah Khan References: <20230703172741.25392-1-mkoutny@suse.com> <20230703172741.25392-2-mkoutny@suse.com> From: Waiman Long In-Reply-To: <20230703172741.25392-2-mkoutny@suse.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/3/23 13:27, 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 when no effective change would happen. > 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()). > > Notice that foreign task's affinity may still be modified if the user > can modify destination cgroup's cpuset attributes > (update_tasks_cpumask() does no permissions check). The permissions > check could thus be skipped on v2 even when affinity changes. Stay > conservative in this patch though. > > [1] https://github.com/systemd/systemd/issues/18293#issuecomment-831205649 > > Signed-off-by: Michal Koutný > --- > kernel/cgroup/cpuset.c | 19 ++++++++++++++++--- > 1 file changed, 16 insertions(+), 3 deletions(-) > > diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c > index 58e6f18f01c1..0a9b860844ca 100644 > --- a/kernel/cgroup/cpuset.c > +++ b/kernel/cgroup/cpuset.c > @@ -2487,6 +2487,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset) > struct cgroup_subsys_state *css; > struct cpuset *cs, *oldcs; > struct task_struct *task; > + bool cpus_updated, mems_updated; > int ret; > > /* used later by cpuset_attach() */ > @@ -2501,13 +2502,25 @@ static int cpuset_can_attach(struct cgroup_taskset *tset) > if (ret) > goto out_unlock; > > + cpus_updated = !cpumask_equal(cs->effective_cpus, oldcs->effective_cpus); > + mems_updated = !nodes_equal(cs->effective_mems, oldcs->effective_mems); > + > cgroup_taskset_for_each(task, css, tset) { > ret = task_can_attach(task); > if (ret) > goto out_unlock; > - ret = security_task_setscheduler(task); > - if (ret) > - goto out_unlock; > + > + /* > + * Skip rights over task check in v2 when nothing changes, > + * migration permission derives from hierarchy ownership in > + * cgroup_procs_write_permission()). > + */ > + if (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) || > + (cpus_updated || mems_updated)) { > + ret = security_task_setscheduler(task); > + if (ret) > + goto out_unlock; > + } > > if (dl_task(task)) { > cs->nr_migrate_dl_tasks++; Reviewed-by: Waiman Long Thanks, Longman