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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 51C9CC4332F for ; Sun, 11 Dec 2022 22:21:15 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DBD088E0003; Sun, 11 Dec 2022 17:21:14 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D6D4A8E0002; Sun, 11 Dec 2022 17:21:14 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C357F8E0003; Sun, 11 Dec 2022 17:21:14 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id B0FEE8E0002 for ; Sun, 11 Dec 2022 17:21:14 -0500 (EST) Received: from smtpin21.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 95C40808FA for ; Sun, 11 Dec 2022 22:21:14 +0000 (UTC) X-FDA: 80231447268.21.5EF6C42 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by imf17.hostedemail.com (Postfix) with ESMTP id 0701D40008 for ; Sun, 11 Dec 2022 22:21:11 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=LG2acMN2; spf=pass (imf17.hostedemail.com: domain of longman@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=longman@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1670797272; h=from:from:sender: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:dkim-signature; bh=+MsWk87quHbEwHCR1sVYteGgGZjHdGBkMWIDf/Jp0nk=; b=Fe4+yVcHRib1h/6lHsZtgDyZA2G28/oiNh33BhZrfbqqF2IwyVVuA/iRuPWO6gESRsMJUR 9Bv62lzvh2gVwR117FzrD2PYZjWQFELZ3dEx3KalpINekR7lGoD+DpNOhNrj615NBISOVp AMi+Ev2lo9up6A9A5wXa+j/o8YtKg10= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=LG2acMN2; spf=pass (imf17.hostedemail.com: domain of longman@redhat.com designates 170.10.133.124 as permitted sender) smtp.mailfrom=longman@redhat.com; dmarc=pass (policy=none) header.from=redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1670797272; a=rsa-sha256; cv=none; b=u9uToVolR4jNEUI9hmy5tZDsw773G/SjMdEpWrn4JRpQVBikxuY2jegxGKA8C9ov4SVeG6 Ek0LU70gkl9qYhcHCpYwTHztIPXQUtRAonNvLm33dpmWS847qyImf7z4MsQlXlsux/rx8+ hMv/5lT/oY0M8VBbHguh/HEKOFImZ68= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1670797271; 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=+MsWk87quHbEwHCR1sVYteGgGZjHdGBkMWIDf/Jp0nk=; b=LG2acMN2TQiHjgL/l0Q4UWV/5J9BfFbH+TdCh2PDalr6IjIFRlZSJ9Lv6KOxs2FsR2rCkr /UGr4e/tIvNhN+piok0ClULPu7bpfHDqWU5AAshheeOHEy43l+XvbkvVc0ld1WvztRxvBi HwRAs9YphhWubrgGIt6yU3pwYHyNw+o= 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-478-dS9F4qTYMZGQE_Cocb_m5Q-1; Sun, 11 Dec 2022 17:21:08 -0500 X-MC-Unique: dS9F4qTYMZGQE_Cocb_m5Q-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9496C101A56C; Sun, 11 Dec 2022 22:21:07 +0000 (UTC) Received: from llong.com (unknown [10.22.16.68]) by smtp.corp.redhat.com (Postfix) with ESMTP id 073EF1121331; Sun, 11 Dec 2022 22:21:06 +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-block v2 1/3] bdi, blk-cgroup: Fix potential UAF of blkcg Date: Sun, 11 Dec 2022 17:20:56 -0500 Message-Id: <20221211222058.2946830-2-longman@redhat.com> In-Reply-To: <20221211222058.2946830-1-longman@redhat.com> References: <20221211222058.2946830-1-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 10.11.54.3 X-Rspamd-Queue-Id: 0701D40008 X-Stat-Signature: x6jjkp99tk4ni4xxii51fkx6oso14p58 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1670797271-321244 X-HE-Meta: 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 css_tryget() in blkcg_destroy_blkgs() and issue a warning if css_tryget() fails. 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 | 8 ++++++++ mm/backing-dev.c | 8 ++++++-- 2 files changed, 14 insertions(+), 2 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 1bb939d3b793..21cc88349f21 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(!css_tryget(&blkcg->css))) + return; + might_sleep(); spin_lock_irq(&blkcg->lock); @@ -1110,6 +1117,7 @@ static void blkcg_destroy_blkgs(struct blkcg *blkcg) } spin_unlock_irq(&blkcg->lock); + css_put(&blkcg->css); } /** 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