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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 A7849C433E1 for ; Mon, 8 Jun 2020 23:30:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8491920775 for ; Mon, 8 Jun 2020 23:30:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591659042; bh=FR0GBdXZRS3MESMaSu9Hju37YGFee3H+3/6KHSvEvTA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=uA8ojN5vDEWKGoJjJ9IGX1ZPqgLhmJuvrYIpZsx8IApRfoRFXYtY5GprH5WiffU7Z MMQHXTGKH+2iKdbJoj8e+nTodI9ESwoNdIHyue6S/gpBWpPTKU5ytxFzgC0UoP/R/u E86/Zw4sfv36WUfhiBFS3K/euhakvoeJ7AQvUQfE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731996AbgFHXal (ORCPT ); Mon, 8 Jun 2020 19:30:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:50844 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731648AbgFHXYl (ORCPT ); Mon, 8 Jun 2020 19:24:41 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 7D93120842; Mon, 8 Jun 2020 23:24:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591658680; bh=FR0GBdXZRS3MESMaSu9Hju37YGFee3H+3/6KHSvEvTA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=YXQRbD3QG+I8fZQyXPqAhzRmYviW4VPltqdN2vY1i8laMnz9J0Zskmw1NLDSKhwgY crZoG08RtZ9fUwPB+9QUNJMeTQGyEis53qhYkXm7RxX+/70Kn5ydLR7Sbj6BGF37jv bpjEcK3cqQ3tlvOyMI8Ma6h95HlvvDesRSF1fvLo= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Coly Li , Jens Axboe , Sasha Levin , linux-bcache@vger.kernel.org Subject: [PATCH AUTOSEL 4.19 091/106] bcache: fix refcount underflow in bcache_device_free() Date: Mon, 8 Jun 2020 19:22:23 -0400 Message-Id: <20200608232238.3368589-91-sashal@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200608232238.3368589-1-sashal@kernel.org> References: <20200608232238.3368589-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore 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 5b5cbfadd003..68ebc2759c2e 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -775,7 +775,9 @@ 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) @@ -783,7 +785,8 @@ 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