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,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 489BDC433DF for ; Fri, 19 Jun 2020 06:40:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 28E46206FA for ; Fri, 19 Jun 2020 06:40:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728851AbgFSGk0 (ORCPT ); Fri, 19 Jun 2020 02:40:26 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:58636 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725820AbgFSGkZ (ORCPT ); Fri, 19 Jun 2020 02:40:25 -0400 Received: from DGGEMS408-HUB.china.huawei.com (unknown [172.30.72.60]) by Forcepoint Email with ESMTP id 38FB89D1086A39C5E1FF; Fri, 19 Jun 2020 14:40:23 +0800 (CST) Received: from [10.166.213.22] (10.166.213.22) by smtp.huawei.com (10.3.19.208) with Microsoft SMTP Server (TLS) id 14.3.487.0; Fri, 19 Jun 2020 14:40:20 +0800 Subject: Re: [Patch net] cgroup: fix cgroup_sk_alloc() for sk_clone_lock() To: Cong Wang , Roman Gushchin CC: 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> From: Zefan Li Message-ID: <4f17229e-1843-5bfc-ea2f-67ebaa9056da@huawei.com> Date: Fri, 19 Jun 2020 14:40:19 +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: Content-Type: text/plain; charset="utf-8" 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 2020/6/19 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. >> >> Btw, based on the number of reported-by tags it seems that there was >> a real issue which the patch is fixing. Maybe you'll a couple of words >> about how it reveals itself in the real life? > > I still have no idea how exactly this is triggered. According to the > people who reported this bug, they just need to wait for some hours > to trigger. So I am not sure what to add here, just the stack trace? > > Thanks. > . >