Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1752643AbdFSTm7 (ORCPT <rfc822;robin@linux-mips.org> + 2 others);
        Mon, 19 Jun 2017 15:42:59 -0400
Received: from wtarreau.pck.nerim.net ([62.212.114.60]:51743 "EHLO 1wt.eu"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751795AbdFSSdu (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 19 Jun 2017 14:33:50 -0400
From: Willy Tarreau <w@1wt.eu>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        linux@roeck-us.net
Cc: Dan Williams <dan.j.williams@intel.com>, Jan Kara <jack@suse.cz>,
        Jens Axboe <axboe@fb.com>, Willy Tarreau <w@1wt.eu>
Subject: [PATCH 3.10 015/268] block: fix del_gendisk() vs blkdev_ioctl crash
Date: Mon, 19 Jun 2017 20:28:34 +0200
Message-Id: <1497897167-14556-16-git-send-email-w@1wt.eu>
X-Mailer: git-send-email 2.8.0.rc2.1.gbe9624a
In-Reply-To: <1497897167-14556-1-git-send-email-w@1wt.eu>
References: <1497897167-14556-1-git-send-email-w@1wt.eu>
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Return-Path: <linux-kernel-owner@vger.kernel.org>

From: Dan Williams <dan.j.williams@intel.com>

commit ac34f15e0c6d2fd58480052b6985f6991fb53bcc upstream.

When tearing down a block device early in its lifetime, userspace may
still be performing discovery actions like blkdev_ioctl() to re-read
partitions.

The nvdimm_revalidate_disk() implementation depends on
disk->driverfs_dev to be valid at entry.  However, it is set to NULL in
del_gendisk() and fatally this is happening *before* the disk device is
deleted from userspace view.

There's no reason for del_gendisk() to clear ->driverfs_dev.  That
device is the parent of the disk.  It is guaranteed to not be freed
until the disk, as a child, drops its ->parent reference.

We could also fix this issue locally in nvdimm_revalidate_disk() by
using disk_to_dev(disk)->parent, but lets fix it globally since
->driverfs_dev follows the lifetime of the parent.  Longer term we
should probably just add a @parent parameter to add_disk(), and stop
carrying this pointer in the gendisk.

 BUG: unable to handle kernel NULL pointer dereference at           (null)
 IP: [<ffffffffa00340a8>] nvdimm_revalidate_disk+0x18/0x90 [libnvdimm]
 CPU: 2 PID: 538 Comm: systemd-udevd Tainted: G           O    4.4.0-rc5 #2257
 [..]
 Call Trace:
  [<ffffffff8143e5c7>] rescan_partitions+0x87/0x2c0
  [<ffffffff810f37f9>] ? __lock_is_held+0x49/0x70
  [<ffffffff81438c62>] __blkdev_reread_part+0x72/0xb0
  [<ffffffff81438cc5>] blkdev_reread_part+0x25/0x40
  [<ffffffff8143982d>] blkdev_ioctl+0x4fd/0x9c0
  [<ffffffff811246c9>] ? current_kernel_time64+0x69/0xd0
  [<ffffffff812916dd>] block_ioctl+0x3d/0x50
  [<ffffffff81264c38>] do_vfs_ioctl+0x308/0x560
  [<ffffffff8115dbd1>] ? __audit_syscall_entry+0xb1/0x100
  [<ffffffff810031d6>] ? do_audit_syscall_entry+0x66/0x70
  [<ffffffff81264f09>] SyS_ioctl+0x79/0x90
  [<ffffffff81902672>] entry_SYSCALL_64_fastpath+0x12/0x76

Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@fb.com>
Reported-by: Robert Hu <robert.hu@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Willy Tarreau <w@1wt.eu>
---
 block/genhd.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/block/genhd.c b/block/genhd.c
index 7af2f6a..afd8206 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -662,7 +662,6 @@ void del_gendisk(struct gendisk *disk)
 
 	kobject_put(disk->part0.holder_dir);
 	kobject_put(disk->slave_dir);
-	disk->driverfs_dev = NULL;
 	if (!sysfs_deprecated)
 		sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk)));
 	pm_runtime_set_memalloc_noio(disk_to_dev(disk), false);
-- 
2.8.0.rc2.1.gbe9624a