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=-18.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_RED, USER_AGENT_GIT 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 BD448C4332B for ; Mon, 28 Dec 2020 14:48:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8F86520867 for ; Mon, 28 Dec 2020 14:48:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2439280AbgL1Osk (ORCPT ); Mon, 28 Dec 2020 09:48:40 -0500 Received: from mail.kernel.org ([198.145.29.99]:57788 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2441675AbgL1OWM (ORCPT ); Mon, 28 Dec 2020 09:22:12 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 2E80F229C4; Mon, 28 Dec 2020 14:21:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1609165291; bh=gDMSkKdkI6DuwgGljiqXB6oVSHWFOZH1OMuzsX0sd3U=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=TxcLn54tm+T52zNvjH3fXEpVmF24GHvwZZu6s0f7CPjngvyU1AkLf8097kMuG0bFr PgTWwyK/xP2MkaF0ekyWSa0vcSbB/aifXweFlE3Y+bolRfRmL1ICDY086tvzPMX5pL AwyCT0a9zqAcIpnSMOaQ+lnFLdS6EK6LBOGSnAS8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Muchun Song , Roman Gushchin , Shakeel Butt , Johannes Weiner , Michal Hocko , Vladimir Davydov , Joonsoo Kim , Yafang Shao , Chris Down , Christian Brauner , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 5.10 450/717] mm: memcg/slab: fix use after free in obj_cgroup_charge Date: Mon, 28 Dec 2020 13:47:28 +0100 Message-Id: <20201228125042.539219061@linuxfoundation.org> X-Mailer: git-send-email 2.29.2 In-Reply-To: <20201228125020.963311703@linuxfoundation.org> References: <20201228125020.963311703@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Muchun Song [ Upstream commit eefbfa7fd678805b38a46293e78543f98f353d3e ] The rcu_read_lock/unlock only can guarantee that the memcg will not be freed, but it cannot guarantee the success of css_get to memcg. If the whole process of a cgroup offlining is completed between reading a objcg->memcg pointer and bumping the css reference on another CPU, and there are exactly 0 external references to this memory cgroup (how we get to the obj_cgroup_charge() then?), css_get() can change the ref counter from 0 back to 1. Link: https://lkml.kernel.org/r/20201028035013.99711-2-songmuchun@bytedance.com Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API") Signed-off-by: Muchun Song Acked-by: Roman Gushchin Reviewed-by: Shakeel Butt Cc: Johannes Weiner Cc: Michal Hocko Cc: Vladimir Davydov Cc: Joonsoo Kim Cc: Yafang Shao Cc: Chris Down Cc: Christian Brauner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- mm/memcontrol.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 74b85077f89ad..a717728cc7b4a 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -3247,8 +3247,10 @@ int obj_cgroup_charge(struct obj_cgroup *objcg, gfp_t gfp, size_t size) * independently later. */ rcu_read_lock(); +retry: memcg = obj_cgroup_memcg(objcg); - css_get(&memcg->css); + if (unlikely(!css_tryget(&memcg->css))) + goto retry; rcu_read_unlock(); nr_pages = size >> PAGE_SHIFT; -- 2.27.0