From a9261d4125c97ce8624e9941b75dee1b43ad5df9 Mon Sep 17 00:00:00 2001 From: Anand Jain 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 Reviewed-by: David Sterba Signed-off-by: David Sterba --- fs/btrfs/volumes.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 29fc8a09dd2e..fc9a3d8f6238 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -857,6 +857,35 @@ static noinline struct btrfs_device *device_list_add(const char *path, return ERR_PTR(-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) { mutex_unlock(&fs_devices->device_list_mutex); -- 2.30.2