Boris managed to create a device capable of changing its maj:min without altering its device path.
Only multi-devices can be scanned. A device that gets scanned and remains in the Btrfs kernel cache might end up with an incorrect maj:min.
Despite the tempfsid feature patch did not introduce this bug, it could lead to issues if the above multi-device is converted to a single device with a stale maj:min. Subsequently, attempting to mount the same device with the correct maj:min might mistake it for another device with the same fsid, potentially resulting in wrongly auto-enabling the tempfsid feature.
To address this, this patch validates the device's maj:min at the time of device open and updates it if it has changed since the last scan.
CC: stable@vger.kernel.org # 6.7+ Fixes: a5b8a5f9f835 ("btrfs: support cloned-device mount capability") Reported-by: Boris Burkov boris@bur.io Co-developed-by: Boris Burkov boris@bur.io Signed-off-by: Anand Jain anand.jain@oracle.com --- v2: Drop using lookup_bdev() instead, get it from device->bdev->bd_dev.
v1: https://lore.kernel.org/linux-btrfs/752b8526be21d984e0ee58c7f66d312664ff5ac5...
fs/btrfs/volumes.c | 10 ++++++++++ 1 file changed, 10 insertions(+)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index e49935a54da0..c318640b4472 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -692,6 +692,16 @@ static int btrfs_open_one_device(struct btrfs_fs_devices *fs_devices, device->bdev = bdev_handle->bdev; clear_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state);
+ if (device->devt != device->bdev->bd_dev) { + btrfs_warn(NULL, + "device %s maj:min changed from %d:%d to %d:%d", + device->name->str, MAJOR(device->devt), + MINOR(device->devt), MAJOR(device->bdev->bd_dev), + MINOR(device->bdev->bd_dev)); + + device->devt = device->bdev->bd_dev; + } + fs_devices->open_devices++; if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state) && device->devid != BTRFS_DEV_REPLACE_DEVID) {