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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 13080C47E4E for ; Thu, 15 Jul 2021 10:48:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F0C4161380 for ; Thu, 15 Jul 2021 10:48:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241680AbhGOKuz (ORCPT ); Thu, 15 Jul 2021 06:50:55 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:11423 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232055AbhGOKuy (ORCPT ); Thu, 15 Jul 2021 06:50:54 -0400 Received: from dggemv704-chm.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4GQWGJ3wr1zcdHc; Thu, 15 Jul 2021 18:44:40 +0800 (CST) Received: from dggpemm500005.china.huawei.com (7.185.36.74) by dggemv704-chm.china.huawei.com (10.3.19.47) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Thu, 15 Jul 2021 18:47:55 +0800 Received: from [10.69.30.204] (10.69.30.204) by dggpemm500005.china.huawei.com (7.185.36.74) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2176.2; Thu, 15 Jul 2021 18:47:55 +0800 Subject: Re: [PATCH 1/1 v2] skbuff: Fix a potential race while recycling page_pool packets To: Ilias Apalodimas CC: Networking , Alexander Duyck , "David S. Miller" , "Jakub Kicinski" , Alexander Lobakin , "Jonathan Lemon" , Willem de Bruijn , Miaohe Lin , Guillaume Nault , "Cong Wang" , Jesper Dangaard Brouer , Matteo Croce , open list References: <20210709062943.101532-1-ilias.apalodimas@linaro.org> From: Yunsheng Lin Message-ID: <401f10b2-3b92-a3f9-f01e-df2e190c8ff3@huawei.com> Date: Thu, 15 Jul 2021 18:47:55 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.69.30.204] X-ClientProxiedBy: dggeme714-chm.china.huawei.com (10.1.199.110) To dggpemm500005.china.huawei.com (7.185.36.74) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021/7/15 18:38, Ilias Apalodimas wrote: > On Thu, 15 Jul 2021 at 13:00, Ilias Apalodimas > wrote: >> >> On Thu, 15 Jul 2021 at 07:01, Yunsheng Lin wrote: >>> >>> On 2021/7/9 14:29, Ilias Apalodimas wrote: >>>> As Alexander points out, when we are trying to recycle a cloned/expanded >>>> SKB we might trigger a race. The recycling code relies on the >>>> pp_recycle bit to trigger, which we carry over to cloned SKBs. >>>> If that cloned SKB gets expanded or if we get references to the frags, >>>> call skbb_release_data() and overwrite skb->head, we are creating separate >>>> instances accessing the same page frags. Since the skb_release_data() >>>> will first try to recycle the frags, there's a potential race between >>>> the original and cloned SKB, since both will have the pp_recycle bit set. >>>> >>>> Fix this by explicitly those SKBs not recyclable. >>>> The atomic_sub_return effectively limits us to a single release case, >>>> and when we are calling skb_release_data we are also releasing the >>>> option to perform the recycling, or releasing the pages from the page pool. >>>> >>>> Fixes: 6a5bcd84e886 ("page_pool: Allow drivers to hint on SKB recycling") >>>> Reported-by: Alexander Duyck >>>> Suggested-by: Alexander Duyck >>>> Signed-off-by: Ilias Apalodimas >>>> --- >>>> Changes since v1: >>>> - Set the recycle bit to 0 during skb_release_data instead of the >>>> individual fucntions triggering the issue, in order to catch all >>>> cases >>>> net/core/skbuff.c | 4 +++- >>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/net/core/skbuff.c b/net/core/skbuff.c >>>> index 12aabcda6db2..f91f09a824be 100644 >>>> --- a/net/core/skbuff.c >>>> +++ b/net/core/skbuff.c >>>> @@ -663,7 +663,7 @@ static void skb_release_data(struct sk_buff *skb) >>>> if (skb->cloned && >>>> atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1, >>>> &shinfo->dataref)) >>>> - return; >>>> + goto exit; >>> >>> Is it possible this patch may break the head frag page for the original skb, >>> supposing it's head frag page is from the page pool and below change clears >>> the pp_recycle for original skb, causing a page leaking for the page pool? >>> >> >> So this would leak eventually dma mapping if the skb is cloned (and >> the dataref is now +1) and we are freeing the original skb first? >> > > Apologies for the noise, my description was not complete. > The case you are thinking is clone an SKB and then expand the original? Yes. It seems we might need different pp_recycle bit for head frag and data frag. > > thanks > /Ilias > > >>>> >>>> skb_zcopy_clear(skb, true); >>>> >>>> @@ -674,6 +674,8 @@ static void skb_release_data(struct sk_buff *skb) >>>> kfree_skb_list(shinfo->frag_list); >>>> >>>> skb_free_head(skb); >>>> +exit: >>>> + skb->pp_recycle = 0; >>>> } >>>> >>>> /* >>>> > . >