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 X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3228BC433E0 for ; Sat, 20 Jun 2020 01:00:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1874F2166E for ; Sat, 20 Jun 2020 01:00:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731207AbgFTBAp (ORCPT ); Fri, 19 Jun 2020 21:00:45 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:59384 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1730293AbgFTBAn (ORCPT ); Fri, 19 Jun 2020 21:00:43 -0400 Received: from DGGEMS414-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 7725E667664D272F94E0; Sat, 20 Jun 2020 09:00:41 +0800 (CST) Received: from [10.166.213.22] (10.166.213.22) by smtp.huawei.com (10.3.19.214) with Microsoft SMTP Server (TLS) id 14.3.487.0; Sat, 20 Jun 2020 09:00:40 +0800 Subject: Re: [Patch net] cgroup: fix cgroup_sk_alloc() for sk_clone_lock() To: Roman Gushchin CC: Cong Wang , Linux Kernel Network Developers , Cameron Berkenpas , Peter Geis , Lu Fengqi , =?UTF-8?Q?Dani=c3=abl_Sonck?= , Daniel Borkmann , Tejun Heo References: <20200616180352.18602-1-xiyou.wangcong@gmail.com> <141629e1-55b5-34b1-b2ab-bab6b68f0671@huawei.com> <20200618193611.GE24694@carbon.DHCP.thefacebook.com> <4f17229e-1843-5bfc-ea2f-67ebaa9056da@huawei.com> <20200620005115.GE237539@carbon.dhcp.thefacebook.com> From: Zefan Li Message-ID: Date: Sat, 20 Jun 2020 09:00:40 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200620005115.GE237539@carbon.dhcp.thefacebook.com> Content-Type: text/plain; charset="gbk" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.166.213.22] X-CFilter-Loop: Reflected Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2020/6/20 8:51, Roman Gushchin wrote: > On Fri, Jun 19, 2020 at 02:40:19PM +0800, Zefan Li wrote: >> On 2020/6/19 5:09, Cong Wang wrote: >>> On Thu, Jun 18, 2020 at 12:36 PM Roman Gushchin wrote: >>>> >>>> On Thu, Jun 18, 2020 at 12:19:13PM -0700, Cong Wang wrote: >>>>> On Wed, Jun 17, 2020 at 6:44 PM Zefan Li wrote: >>>>>> >>>>>> Cc: Roman Gushchin >>>>>> >>>>>> Thanks for fixing this. >>>>>> >>>>>> On 2020/6/17 2:03, Cong Wang wrote: >>>>>>> When we clone a socket in sk_clone_lock(), its sk_cgrp_data is >>>>>>> copied, so the cgroup refcnt must be taken too. And, unlike the >>>>>>> sk_alloc() path, sock_update_netprioidx() is not called here. >>>>>>> Therefore, it is safe and necessary to grab the cgroup refcnt >>>>>>> even when cgroup_sk_alloc is disabled. >>>>>>> >>>>>>> sk_clone_lock() is in BH context anyway, the in_interrupt() >>>>>>> would terminate this function if called there. And for sk_alloc() >>>>>>> skcd->val is always zero. So it's safe to factor out the code >>>>>>> to make it more readable. >>>>>>> >>>>>>> Fixes: 090e28b229af92dc5b ("netprio_cgroup: Fix unlimited memory leak of v2 cgroups") >>>>>> >>>>>> but I don't think the bug was introduced by this commit, because there >>>>>> are already calls to cgroup_sk_alloc_disable() in write_priomap() and >>>>>> write_classid(), which can be triggered by writing to ifpriomap or >>>>>> classid in cgroupfs. This commit just made it much easier to happen >>>>>> with systemd invovled. >>>>>> >>>>>> I think it's 4bfc0bb2c60e2f4c ("bpf: decouple the lifetime of cgroup_bpf from cgroup itself"), >>>>>> which added cgroup_bpf_get() in cgroup_sk_alloc(). >>>>> >>>>> Good point. >>>>> >>>>> I take a deeper look, it looks like commit d979a39d7242e06 >>>>> is the one to blame, because it is the first commit that began to >>>>> hold cgroup refcnt in cgroup_sk_alloc(). >>>> >>>> I agree, ut seems that the issue is not related to bpf and probably >>>> can be reproduced without CONFIG_CGROUP_BPF. d979a39d7242e06 indeed >>>> seems closer to the origin. >>> >>> Yeah, I will update the Fixes tag and send V2. >>> >> >> Commit d979a39d7242e06 looks innocent to me. With this commit when cgroup_sk_alloc >> is disabled and then a socket is cloned the cgroup refcnt will not be incremented, >> but this is fine, because when the socket is to be freed: >> >> sk_prot_free() >> cgroup_sk_free() >> cgroup_put(sock_cgroup_ptr(skcd)) == cgroup_put(&cgrp_dfl_root.cgrp) >> >> cgroup_put() does nothing for the default root cgroup, so nothing bad will happen. >> >> but cgroup_bpf_put() will decrement the bpf refcnt while this refcnt were not incremented >> as cgroup_sk_alloc has already been disabled. That's why I think it's 4bfc0bb2c60e2f4c >> that needs to be fixed. > > Hm, does it mean that the problem always happens with the root cgroup? > >>>From the stacktrace provided by Peter it looks like that the problem > is bpf-related, but the original patch says nothing about it. > > So from the test above it sounds like the problem is that we're trying > to release root's cgroup_bpf, which is a bad idea, I totally agree. > Is this the problem? I think so, though I'm not familiar with the bfp cgroup code. > If so, we might wanna fix it in a different way, > just checking if (!(css->flags & CSS_NO_REF)) in cgroup_bpf_put() > like in cgroup_put(). It feels more reliable to me. > Yeah I also have this idea in my mind.