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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham 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 22FACC3A5A2 for ; Fri, 23 Aug 2019 09:52:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ECFAF20850 for ; Fri, 23 Aug 2019 09:52:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389584AbfHWJw5 (ORCPT ); Fri, 23 Aug 2019 05:52:57 -0400 Received: from szxga06-in.huawei.com ([45.249.212.32]:59716 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2389081AbfHWJw4 (ORCPT ); Fri, 23 Aug 2019 05:52:56 -0400 Received: from DGGEMS407-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id 7FCA2C279BE7A2BE504B; Fri, 23 Aug 2019 17:37:04 +0800 (CST) Received: from [127.0.0.1] (10.133.205.80) by DGGEMS407-HUB.china.huawei.com (10.3.19.207) with Microsoft SMTP Server id 14.3.439.0; Fri, 23 Aug 2019 17:36:55 +0800 Subject: Re: [PATCH v3] tun: fix use-after-free when register netdev failed To: Jason Wang References: <1566221479-16094-1-git-send-email-yangyingliang@huawei.com> <20190819.182522.414877916903078544.davem@davemloft.net> <5D5E3133.2070108@huawei.com> <5D5E90C3.50306@huawei.com> <1676209666.10068041.1566529505528.JavaMail.zimbra@redhat.com> CC: David Miller , , eric dumazet , xiyou wangcong , From: Yang Yingliang Message-ID: <5D5FB3B6.5080800@huawei.com> Date: Fri, 23 Aug 2019 17:36:54 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <1676209666.10068041.1566529505528.JavaMail.zimbra@redhat.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.133.205.80] X-CFilter-Loop: Reflected Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2019/8/23 11:05, Jason Wang wrote: > ----- Original Message ----- >> >> On 2019/8/22 14:07, Yang Yingliang wrote: >>> >>> On 2019/8/22 10:13, Jason Wang wrote: >>>> On 2019/8/20 上午10:28, Jason Wang wrote: >>>>> On 2019/8/20 上午9:25, David Miller wrote: >>>>>> From: Yang Yingliang >>>>>> Date: Mon, 19 Aug 2019 21:31:19 +0800 >>>>>> >>>>>>> Call tun_attach() after register_netdevice() to make sure tfile->tun >>>>>>> is not published until the netdevice is registered. So the read/write >>>>>>> thread can not use the tun pointer that may freed by free_netdev(). >>>>>>> (The tun and dev pointer are allocated by alloc_netdev_mqs(), they >>>>>>> can >>>>>>> be freed by netdev_freemem().) >>>>>> register_netdevice() must always be the last operation in the order of >>>>>> network device setup. >>>>>> >>>>>> At the point register_netdevice() is called, the device is visible >>>>>> globally >>>>>> and therefore all of it's software state must be fully initialized and >>>>>> ready for us. >>>>>> >>>>>> You're going to have to find another solution to these problems. >>>>> >>>>> The device is loosely coupled with sockets/queues. Each side is >>>>> allowed to be go away without caring the other side. So in this >>>>> case, there's a small window that network stack think the device has >>>>> one queue but actually not, the code can then safely drop them. >>>>> Maybe it's ok here with some comments? >>>>> >>>>> Or if not, we can try to hold the device before tun_attach and drop >>>>> it after register_netdevice(). >>>> >>>> Hi Yang: >>>> >>>> I think maybe we can try to hold refcnt instead of playing real num >>>> queues here. Do you want to post a V4? >>> I think the refcnt can prevent freeing the memory in this case. >>> When register_netdevice() failed, free_netdev() will be called directly, >>> dev->pcpu_refcnt and dev are freed without checking refcnt of dev. >> How about using patch-v1 that using a flag to check whether the device >> registered successfully. >> > As I said, it lacks sufficient locks or barriers. To be clear, I meant > something like (compile-test only): > > diff --git a/drivers/net/tun.c b/drivers/net/tun.c > index db16d7a13e00..e52678f9f049 100644 > --- a/drivers/net/tun.c > +++ b/drivers/net/tun.c > @@ -2828,6 +2828,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr) > (ifr->ifr_flags & TUN_FEATURES); > > INIT_LIST_HEAD(&tun->disabled); > + dev_hold(dev); > err = tun_attach(tun, file, false, ifr->ifr_flags & IFF_NAPI, > ifr->ifr_flags & IFF_NAPI_FRAGS); > if (err < 0) > @@ -2836,6 +2837,7 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr) > err = register_netdevice(tun->dev); > if (err < 0) > goto err_detach; > + dev_put(dev); > } > > netif_carrier_on(tun->dev); > @@ -2852,11 +2854,13 @@ static int tun_set_iff(struct net *net, struct file *file, struct ifreq *ifr) > return 0; > > err_detach: > + dev_put(dev); > tun_detach_all(dev); > /* register_netdevice() already called tun_free_netdev() */ > goto err_free_dev; > > err_free_flow: > + dev_put(dev); > tun_flow_uninit(tun); > security_tun_dev_free_security(tun->security); > err_free_stat: > > What's your thought? The dev pointer are freed without checking the refcount in free_netdev() called by err_free_dev path, so I don't understand how the refcount protects this pointer. Thanks, Yang > > Thanks > > . >