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 8A11AC47E48 for ; Thu, 15 Jul 2021 04:01:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 702FD610C7 for ; Thu, 15 Jul 2021 04:01:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231607AbhGOEDy (ORCPT ); Thu, 15 Jul 2021 00:03:54 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:6932 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231439AbhGOEDw (ORCPT ); Thu, 15 Jul 2021 00:03:52 -0400 Received: from dggemv703-chm.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4GQLDN0J0hz7tvt; Thu, 15 Jul 2021 11:57:24 +0800 (CST) Received: from dggpemm500005.china.huawei.com (7.185.36.74) by dggemv703-chm.china.huawei.com (10.3.19.46) 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 12:00:58 +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 12:00:57 +0800 Subject: Re: [PATCH 1/1 v2] skbuff: Fix a potential race while recycling page_pool packets To: Ilias Apalodimas , CC: 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 , References: <20210709062943.101532-1-ilias.apalodimas@linaro.org> From: Yunsheng Lin Message-ID: Date: Thu, 15 Jul 2021 12:00:57 +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: <20210709062943.101532-1-ilias.apalodimas@linaro.org> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.69.30.204] X-ClientProxiedBy: dggeme702-chm.china.huawei.com (10.1.199.98) 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 2021/7/9 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? > > 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; > } > > /* >