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[72.235.129.167]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2d3ac7ca35fsm2013998a91.9.2024.08.14.09.52.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 14 Aug 2024 09:52:41 -0700 (PDT) Sender: Tejun Heo Date: Wed, 14 Aug 2024 06:52:39 -1000 From: Tejun Heo To: chenridong Cc: Michal =?iso-8859-1?Q?Koutn=FD?= , lizefan.x@bytedance.com, hannes@cmpxchg.org, longman@redhat.com, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH -next 2/2] cgroup: Disallow delegatee to write all interfaces outsize of cgroup ns Message-ID: References: <20240812073746.3070616-1-chenridong@huawei.com> <20240812073746.3070616-3-chenridong@huawei.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Hello, On Wed, Aug 14, 2024 at 04:09:59PM +0800, chenridong wrote: ... > Hi，TJ， We plan to use delegation in cgroup-v2, so I am conducting some > tests. > As doc mentions 'Because the resource control interface files in a given > directory control the distribution of the parent's resources, the delegatee > shouldn't be allowed to write to them.' However I found a root can write > parent's file(cgroup.subtree_control) to change the resource limits(a > fraudulent method). I believe this could pose a risk in some scenarios where > a root enters a new cgroup ns without unmounting original cgroup system, and > it can break limitations. For instance, running a docker with --privileged, > could this be a risk? > > So I sent this patch to discuss whether this case should be addressed? That sounsd like a misconfiguration. cgroup NS doesn't make much sense if you don't limit the actual visibility. The interface is half broken in that situation anyway and if you're leaking filesystem visibility into a supposedly isolated container, relaxed resource limits aren't biggest of your problems. While the proposed change isn't necessarily a bad idea, it's a behavior change and I don't either modifying existing behavior or introducing a new mount flag is justified here. Maybe just update the documentation indicating that the ancestral cgroups shouldn't be visible in a delegated ns? Thanks. -- tejun