linux-kernel - [PATCH 3.12 60/86] block: fix del_gendisk() vs blkdev

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Message-Id: <963657adc76fd455d019d804a82749325a392011.1493888632.git.jslaby@suse.cz>
Date:   Thu,  4 May 2017 11:04:25 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     stable@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>,
        Jan Kara <jack@...e.cz>, Jens Axboe <axboe@...com>,
        Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 60/86] block: fix del_gendisk() vs blkdev_ioctl crash

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

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

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@...e.cz>
Cc: Jens Axboe <axboe@...com>
Reported-by: Robert Hu <robert.hu@...el.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 block/genhd.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/block/genhd.c b/block/genhd.c
index 38d4ba122a43..037cf3e8f1bd 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);
-- 
2.12.2