From patchwork Tue Nov 29 20:34:00 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 13059141 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 2AB92C4332F for ; Tue, 29 Nov 2022 20:35:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236387AbiK2UfX (ORCPT ); Tue, 29 Nov 2022 15:35:23 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40668 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236376AbiK2UfX (ORCPT ); Tue, 29 Nov 2022 15:35:23 -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 65DAF63B97 for ; Tue, 29 Nov 2022 12:34:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1669754070; 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; bh=nsMFyIcOKMdH8kGov88EPCbLbTICW8XLJaolwn8fdZQ=; b=PbrlCkmRV13K7Tlf2bNtM4huFyhOcEHKDNqY+K9wP1snZVx51QLwVQJp5aUkAbHH3lLPxc jgtNtXwP8KPM6XxxA5vyCJOSZtnilLFKLnBNOCvQRNnmmkOPjA7pBviKiflF5CZGKiy95m AR4yNJZlZrzm0DuH4A85TCidd7cFT1g= 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-445-SZGhVrRyO_-myQQoKno4yA-1; Tue, 29 Nov 2022 15:34:25 -0500 X-MC-Unique: SZGhVrRyO_-myQQoKno4yA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.rdu2.redhat.com [10.11.54.7]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 60622802314; Tue, 29 Nov 2022 20:34:23 +0000 (UTC) Received: from llong.com (unknown [10.22.17.30]) by smtp.corp.redhat.com (Postfix) with ESMTP id 696AE140EBF5; Tue, 29 Nov 2022 20:34:22 +0000 (UTC) From: Waiman Long To: Jens Axboe , Tejun Heo Cc: cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ming Lei , Andy Shevchenko , Andrew Morton , =?utf-8?q?Michal_Koutn=C3=BD?= , Hillf Danton , Chaitanya Kulkarni , Bart Van Assche , Josef Bacik , Waiman Long , Yi Zhang Subject: [PATCH-block v2] bdi, blk-cgroup: Fix potential UAF of blkcg Date: Tue, 29 Nov 2022 15:34:00 -0500 Message-Id: <20221129203400.1456100-1-longman@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 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. 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: [ 34.342395] [ 34.344510] blkcg_unpin_online+0x38/0x60 [ 34.348523] cgwb_release_workfn+0x6a/0x200 [ 34.352708] process_one_work+0x1e5/0x3b0 [ 34.356742] ? rescuer_thread+0x390/0x390 [ 34.360758] worker_thread+0x50/0x3a0 [ 34.364425] ? rescuer_thread+0x390/0x390 [ 34.368447] kthread+0xd9/0x100 [ 34.371592] ? kthread_complete_and_exit+0x20/0x20 [ 34.376386] ret_from_fork+0x22/0x30 [ 34.379982] This confirms that a potential UAF situation can happen. Fix that by delaying the css_put() until after the blkcg_unpin_online() call. Also use css_tryget() in blkcg_destroy_blkgs() and issue a warning if css_tryget() fails with no RCU read lock held. 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 --- block/blk-cgroup.c | 10 +++++++++- mm/backing-dev.c | 8 ++++++-- 2 files changed, 15 insertions(+), 3 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 57941d2a8ba3..904372bb96f1 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -1088,7 +1088,15 @@ static void blkcg_destroy_blkgs(struct blkcg *blkcg) might_sleep(); - css_get(&blkcg->css); + /* + * blkcg_destroy_blkgs() shouldn't be called with all the blkcg + * references gone and rcu_read_lock not held. + */ + if (!css_tryget(&blkcg->css)) { + WARN_ON_ONCE(!rcu_read_lock_held()); + return; + } + spin_lock_irq(&blkcg->lock); while (!hlist_empty(&blkcg->blkg_list)) { struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first, 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);