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SubjectRe: Patch "btrfs: harden agaist duplicate fsid on scanned devices" has been added to the 4.14-stable tree
On Sat, Feb 09, 2019 at 12:28:20PM -0500, Sasha Levin wrote:
> This is a note to let you know that I've just added the patch titled
>
> btrfs: harden agaist duplicate fsid on scanned devices
>
> to the 4.14-stable tree which can be found at:
> http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
>
> The filename of the patch is:
> btrfs-harden-agaist-duplicate-fsid-on-scanned-device.patch
> and it can be found in the queue-4.14 subdirectory.
>
> If you, or anyone else, feels it should not be added to the stable tree,
> please let <stable@vger.kernel.org> know about it.
>
>
>
> commit 2590f717cfd952f726597e4ebf0800154be5e5f5
> Author: Anand Jain <anand.jain@oracle.com>
> Date: Mon Oct 15 10:45:17 2018 +0800
>
> btrfs: harden agaist duplicate fsid on scanned devices
>
> [ Upstream commit a9261d4125c97ce8624e9941b75dee1b43ad5df9 ]
>
> 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: Sasha Levin <sashal@kernel.org>
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 9663b6aa2a56..1e8d216720a2 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -696,6 +696,35 @@ static noinline int device_list_add(const char *path,
> return -EEXIST;
> }
>
> + /*
> + * 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 ERR_CAST(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 ERR_PTR(-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)
> return -ENOMEM;

This patch causes a build warning:

../fs/btrfs/volumes.c:709:12: warning: returning ‘void *’ from a function with return type ‘int’ makes integer from pointer without a cast [-Wint-conversion]
return ERR_CAST(path_bdev);
^~~~~~~~~~~~~~~~~~~
../fs/btrfs/volumes.c:719:12: warning: returning ‘void *’ from a function with return type ‘int’ makes integer from pointer without a cast [-Wint-conversion]
return ERR_PTR(-EEXIST);
^~~~~~~~~~~~~~~~

and it's correct, the code is should not do this. I'll drop this
patch now.

thanks,

greg k-h

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