From a9261d4125c97ce8624e9941b75dee1b43ad5df9 Mon Sep 17 00:00:00 2001

Patch-mainline: v5.1

References: bsc#1134973

Git-commit: a9261d4125c97ce8624e9941b75dee1b43ad5df9

From: Anand Jain <anand.jain@oracle.com>

Date: Mon, 15 Oct 2018 10:45:17 +0800

Subject: [PATCH] btrfs: harden agaist duplicate fsid on scanned devices

It's not that impossible to imagine that a device OR a btrfs image is

copied just by using the dd or the cp command. Which in case both the

copies of the btrfs will have the same fsid. If on the system with

automount enabled, the copied FS gets scanned.

We have a known bug in btrfs, that we let the device path be changed

after the device has been mounted. So using this loop hole the new

copied device would appears as if its mounted immediately after it's

been copied.

For example:

Initially.. /dev/mmcblk0p4 is mounted as /

  $ lsblk

  NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT

  mmcblk0     179:0    0 29.2G  0 disk

  |-mmcblk0p4 179:4    0    4G  0 part /

  |-mmcblk0p2 179:2    0  500M  0 part /boot

  |-mmcblk0p3 179:3    0  256M  0 part [SWAP]

  `-mmcblk0p1 179:1    0  256M  0 part /boot/efi

  $ btrfs fi show

     Label: none  uuid: 07892354-ddaa-4443-90ea-f76a06accaba

     Total devices 1 FS bytes used 1.40GiB

     devid    1 size 4.00GiB used 3.00GiB path /dev/mmcblk0p4

Copy mmcblk0 to sda

  $ dd if=/dev/mmcblk0 of=/dev/sda

And immediately after the copy completes the change in the device

superblock is notified which the automount scans using btrfs device scan

and the new device sda becomes the mounted root device.

  $ lsblk

  NAME        MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT

  sda           8:0    1 14.9G  0 disk

  |-sda4        8:4    1    4G  0 part /

  |-sda2        8:2    1  500M  0 part

  |-sda3        8:3    1  256M  0 part

  `-sda1        8:1    1  256M  0 part

  mmcblk0     179:0    0 29.2G  0 disk

  |-mmcblk0p4 179:4    0    4G  0 part

  |-mmcblk0p2 179:2    0  500M  0 part /boot

  |-mmcblk0p3 179:3    0  256M  0 part [SWAP]

  `-mmcblk0p1 179:1    0  256M  0 part /boot/efi

  $ btrfs fi show /

    Label: none  uuid: 07892354-ddaa-4443-90ea-f76a06accaba

    Total devices 1 FS bytes used 1.40GiB

    devid    1 size 4.00GiB used 3.00GiB path /dev/sda4

The bug is quite nasty that you can't either unmount /dev/sda4 or

/dev/mmcblk0p4. And the problem does not get solved until you take sda

out of the system on to another system to change its fsid using the

'btrfstune -u' command.

Signed-off-by: Anand Jain <anand.jain@oracle.com>

Reviewed-by: David Sterba <dsterba@suse.com>

Signed-off-by: David Sterba <dsterba@suse.com>

Signed-off-by: Qu Wenruo <wqu@suse.com>

---

 fs/btrfs/volumes.c |   29 +++++++++++++++++++++++++++++

 1 file changed, 29 insertions(+)

--- a/fs/btrfs/volumes.c

+++ b/fs/btrfs/volumes.c

@@ -641,6 +641,35 @@ static noinline int device_list_add(cons

 			return PTR_ERR(device);

 		}

+		/*

+		 * We are going to replace the device path for a given devid,

+		 * make sure it's the same device if the device is mounted

+		 */

+		if (device->bdev) {

+			struct block_device *path_bdev;

+

+			path_bdev = lookup_bdev(path);

+			if (IS_ERR(path_bdev)) {

+				mutex_unlock(&fs_devices->device_list_mutex);

+				return PTR_ERR(path_bdev);

+			}

+

+			if (device->bdev != path_bdev) {

+				bdput(path_bdev);

+				mutex_unlock(&fs_devices->device_list_mutex);

+				btrfs_warn_in_rcu(device->fs_info,

+			"duplicate device fsid:devid for %pU:%llu old:%s new:%s",

+					disk_super->fsid, devid,

+					rcu_str_deref(device->name), path);

+				return -EEXIST;

+			}

+			bdput(path_bdev);

+			btrfs_info_in_rcu(device->fs_info,

+				"device fsid %pU devid %llu moved old:%s new:%s",

+				disk_super->fsid, devid,

+				rcu_str_deref(device->name), path);

+		}

+

 		name = rcu_string_strdup(path, GFP_NOFS);

 		if (!name) {

 			kfree(device);