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=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 9A188C433E0 for ; Fri, 19 Jun 2020 15:46:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7138721532 for ; Fri, 19 Jun 2020 15:46:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592581616; bh=cxtuvjAdp9f4Te01/+BlbAfNdOyNnBZ251CMnNbZcN4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=ny5CxyjZz+M9RmFpbUwszOVkjX+lTPcln15z2AxTohvU+G1aDhvsIrT7n39a/CUDo kYXhxcU8bsiOQGkKzb2ErC1t1lMa6Wk53Ui96rwVJKHhX1qlzbKjjuhmBkRol7tPMu S2JzC5lXExoaRuzm5RY0Go5oUSlnQuo+mawxq+yA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405282AbgFSPqz (ORCPT ); Fri, 19 Jun 2020 11:46:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:58038 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2393474AbgFSP0T (ORCPT ); Fri, 19 Jun 2020 11:26:19 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0ABBD21582; Fri, 19 Jun 2020 15:26:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592580378; bh=cxtuvjAdp9f4Te01/+BlbAfNdOyNnBZ251CMnNbZcN4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DTkuR2ZecXRG5LHRT82s/Bhfvt7C8i0FT6G0FycwCrrhW1SF8WV1AdBFkoi9xDRD+ Ej31rRAkSibISWkvSMz4vzlz+YOZ457N/DcHICrxsitV2nKLET+IqwdpwOPJwHdKIw vMYOQOVCD16zimKS/YmpodOIw+Jpy6Csvgn+sHZI= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Coly Li , Jens Axboe , Sasha Levin Subject: [PATCH 5.7 227/376] bcache: fix refcount underflow in bcache_device_free() Date: Fri, 19 Jun 2020 16:32:25 +0200 Message-Id: <20200619141721.065966923@linuxfoundation.org> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20200619141710.350494719@linuxfoundation.org> References: <20200619141710.350494719@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Coly Li [ Upstream commit 86da9f736740eba602389908574dfbb0f517baa5 ] The problematic code piece in bcache_device_free() is, 785 static void bcache_device_free(struct bcache_device *d) 786 { 787 struct gendisk *disk = d->disk; [snipped] 799 if (disk) { 800 if (disk->flags & GENHD_FL_UP) 801 del_gendisk(disk); 802 803 if (disk->queue) 804 blk_cleanup_queue(disk->queue); 805 806 ida_simple_remove(&bcache_device_idx, 807 first_minor_to_idx(disk->first_minor)); 808 put_disk(disk); 809 } [snipped] 816 } At line 808, put_disk(disk) may encounter kobject refcount of 'disk' being underflow. Here is how to reproduce the issue, - Attche the backing device to a cache device and do random write to make the cache being dirty. - Stop the bcache device while the cache device has dirty data of the backing device. - Only register the backing device back, NOT register cache device. - The bcache device node /dev/bcache0 won't show up, because backing device waits for the cache device shows up for the missing dirty data. - Now echo 1 into /sys/fs/bcache/pendings_cleanup, to stop the pending backing device. - After the pending backing device stopped, use 'dmesg' to check kernel message, a use-after-free warning from KASA reported the refcount of kobject linked to the 'disk' is underflow. The dropping refcount at line 808 in the above code piece is added by add_disk(d->disk) in bch_cached_dev_run(). But in the above condition the cache device is not registered, bch_cached_dev_run() has no chance to be called and the refcount is not added. The put_disk() for a non- added refcount of gendisk kobject triggers a underflow warning. This patch checks whether GENHD_FL_UP is set in disk->flags, if it is not set then the bcache device was not added, don't call put_disk() and the the underflow issue can be avoided. Signed-off-by: Coly Li Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin --- drivers/md/bcache/super.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index d98354fa28e3..4d8bf731b118 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -797,7 +797,9 @@ static void bcache_device_free(struct bcache_device *d) bcache_device_detach(d); if (disk) { - if (disk->flags & GENHD_FL_UP) + bool disk_added = (disk->flags & GENHD_FL_UP) != 0; + + if (disk_added) del_gendisk(disk); if (disk->queue) @@ -805,7 +807,8 @@ static void bcache_device_free(struct bcache_device *d) ida_simple_remove(&bcache_device_idx, first_minor_to_idx(disk->first_minor)); - put_disk(disk); + if (disk_added) + put_disk(disk); } bioset_exit(&d->bio_split); -- 2.25.1