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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E4A83C001B2 for ; Thu, 15 Dec 2022 03:32:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229560AbiLODcl (ORCPT ); Wed, 14 Dec 2022 22:32:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44380 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229670AbiLODci (ORCPT ); Wed, 14 Dec 2022 22:32:38 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8A7B523BD6 for ; Wed, 14 Dec 2022 19:31:54 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1671075113; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=JQg3oq06Uw+1wG32ld/l34XBIlmOl7KcZS/r8y8eH90=; b=BNOOOfQqNCwnIVq5uI1Gv6r+0NBA2km1aEquWDKmN4DNp7r+/v11I1OPj3bGw6cdDIQEpU 1TOr/FBSkY210y0yAYAfKtD9T9M8YrAaZcti41LBW9f7Z3YgU9izwICJ/C602IYdW44erP SBAdBBFAT/9pC3hP+W6Oj3Snax2UcRc= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-529-vK79Q7I0O6SEt1SJkCSsgA-1; Wed, 14 Dec 2022 22:31:45 -0500 X-MC-Unique: vK79Q7I0O6SEt1SJkCSsgA-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 35F9B811E9C; Thu, 15 Dec 2022 03:31:45 +0000 (UTC) Received: from llong.com (unknown [10.22.16.55]) by smtp.corp.redhat.com (Postfix) with ESMTP id A624640ED76E; Thu, 15 Dec 2022 03:31:44 +0000 (UTC) From: Waiman Long To: Jens Axboe , Tejun Heo , Josef Bacik , Zefan Li , Johannes Weiner , Andrew Morton Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, =?UTF-8?q?Michal=20Koutn=C3=BD?= , "Dennis Zhou (Facebook)" , Waiman Long , Yi Zhang Subject: [PATCH v4 1/2] bdi, blk-cgroup: Fix potential UAF of blkcg Date: Wed, 14 Dec 2022 22:31:31 -0500 Message-Id: <20221215033132.230023-2-longman@redhat.com> In-Reply-To: <20221215033132.230023-1-longman@redhat.com> References: <20221215033132.230023-1-longman@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org Commit 59b57717fff8 ("blkcg: delay blkg destruction until after writeback has finished") delayed call to blkcg_destroy_blkgs() to cgwb_release_workfn(). However, it is done after a css_put() of blkcg which may be the final put that causes the blkcg to be freed as RCU read lock isn't held. Another place where blkcg_destroy_blkgs() can be called indirectly via blkcg_unpin_online() is from the offline_css() function called from css_killed_work_fn(). Over there, the potentially final css_put() call is issued after offline_css(). By adding a css_tryget() into blkcg_destroy_blkgs() and warning its failure, the following stack trace was produced in a test system on bootup. [ 34.254240] RIP: 0010:blkcg_destroy_blkgs+0x16a/0x1a0 : [ 34.339943] Call Trace: [ 34.344510] blkcg_unpin_online+0x38/0x60 [ 34.348523] cgwb_release_workfn+0x6a/0x200 [ 34.352708] process_one_work+0x1e5/0x3b0 [ 34.360758] worker_thread+0x50/0x3a0 [ 34.368447] kthread+0xd9/0x100 [ 34.376386] ret_from_fork+0x22/0x30 This confirms that a potential UAF situation can really happen in cgwb_release_workfn(). Fix that by delaying the css_put() until after the blkcg_unpin_online() call. Also use percpu_ref_is_zero() in blkcg_destroy_blkgs() and issue a warning if reference count is zero. The reproducing system can no longer produce a warning with this patch. All the runnable block/0* tests including block/027 were run successfully without failure. Fixes: 59b57717fff8 ("blkcg: delay blkg destruction until after writeback has finished") Suggested-by: Michal Koutný Reported-by: Yi Zhang Signed-off-by: Waiman Long Acked-by: Tejun Heo --- block/blk-cgroup.c | 7 +++++++ mm/backing-dev.c | 8 ++++++-- 2 files changed, 13 insertions(+), 2 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 1bb939d3b793..ca28306aa1b1 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1084,6 +1084,13 @@ struct list_head *blkcg_get_cgwb_list(struct cgroup_subsys_state *css) */ static void blkcg_destroy_blkgs(struct blkcg *blkcg) { + /* + * blkcg_destroy_blkgs() shouldn't be called with all the blkcg + * references gone. + */ + if (WARN_ON_ONCE(percpu_ref_is_zero(&blkcg->css.refcnt))) + return; + might_sleep(); spin_lock_irq(&blkcg->lock); diff --git a/mm/backing-dev.c b/mm/backing-dev.c index c30419a5e119..36f75b072325 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -390,11 +390,15 @@ static void cgwb_release_workfn(struct work_struct *work) wb_shutdown(wb); css_put(wb->memcg_css); - css_put(wb->blkcg_css); mutex_unlock(&wb->bdi->cgwb_release_mutex); - /* triggers blkg destruction if no online users left */ + /* + * Triggers blkg destruction if no online users left + * The final blkcg css_put() has to be done after blkcg_unpin_online() + * to avoid use-after-free. + */ blkcg_unpin_online(wb->blkcg_css); + css_put(wb->blkcg_css); fprop_local_destroy_percpu(&wb->memcg_completions); -- 2.31.1