From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from szxga04-in.huawei.com (szxga04-in.huawei.com [45.249.212.190]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AC7A6381D4; Wed, 14 Aug 2024 08:10:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=45.249.212.190 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723623006; cv=none; b=bH6CPzXjAMgj6e6pOmzRssGTkhUXHwxqrXwlzOct+lKrVvobQ5rFv6IADKu+7QQCev4JWFfDWUhrW+0QKcxfyp7g5Cavyal9E69yd7IAZXDaQ+MXFAMPpRqEODMWV1Tu6MBReiUCMQqyOq/pR4J1JXbIBVQMgr3zd8IDaZMPZ3g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723623006; c=relaxed/simple; bh=qXAfBeVt1rlHSXfZpWFX1g81HBiDbsqPNxF5fCeW5cg=; h=Message-ID:Date:MIME-Version:Subject:To:CC:References:From: In-Reply-To:Content-Type; b=tn2slte3bw81/d89Fo69KTq8Dgcj1wLdLEDOQW8rIXnGKFBZO5jIG3RtvEjISpOrjy7WKRanAFR4HKHOPtgB8oK3F5OfSLVP+3L9q4IAvsCYBJ3SxtNtEihXwq34h8KpmZUYY8txBI2kOp8guuuUSvmMPFBvEJLqFXig4r+H1Ns= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=45.249.212.190 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.19.163.44]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4WkLQY1dFXz2Cm85; Wed, 14 Aug 2024 16:05:09 +0800 (CST) Received: from kwepemd100013.china.huawei.com (unknown [7.221.188.163]) by mail.maildlp.com (Postfix) with ESMTPS id 1782B1402E1; Wed, 14 Aug 2024 16:10:01 +0800 (CST) Received: from [10.67.109.79] (10.67.109.79) by kwepemd100013.china.huawei.com (7.221.188.163) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1258.34; Wed, 14 Aug 2024 16:10:00 +0800 Message-ID: Date: Wed, 14 Aug 2024 16:09:59 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH -next 2/2] cgroup: Disallow delegatee to write all interfaces outsize of cgroup ns To: Tejun Heo , =?UTF-8?Q?Michal_Koutn=C3=BD?= CC: , , , , References: <20240812073746.3070616-1-chenridong@huawei.com> <20240812073746.3070616-3-chenridong@huawei.com> Content-Language: en-US From: chenridong In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To kwepemd100013.china.huawei.com (7.221.188.163) On 2024/8/14 3:02, Tejun Heo wrote: > Hello, > > On Mon, Aug 12, 2024 at 06:57:06PM +0200, Michal Koutný wrote: > ... >> You could also have increased the ancestral limit (if there was any) >> echo max > dlgt_grp_ns/pids.max // similarly allowed >> >> If you're a root (or otherwise have sufficient permissions) and you can >> _see_ an ancestral cgroup, you can write to its attributes according to >> permissions. Thus the delegation works via cgroup ns (in)visibility but >> cgroup ns root is visible on both sides of the boundary hence the extra >> check. > > Yeah, the intended usage scenario w/ NS delegation is that the delegatee > won't be able to see the ancetral cgroups beyond the delegation point. Chen, > is this from an actual usecase? If so, can you describe what's going on? > > Thanks. > 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? Thanks, Ridong