Commit 9f7eb840 authored Mar 01, 2024 by Anand Jain Committed by David Sterba Mar 26, 2024

btrfs: validate device maj:min during open



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 temp-fsid 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 temp-fsid 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: a5b8a5f9 ("btrfs: support cloned-device mount capability")
Reported-by: Boris Burkov <boris@bur.io>
Co-developed-by: Boris Burkov <boris@bur.io>
Reviewed-by: Boris Burkov <boris@bur.io&gt;#>
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 1ec17ef5

fs/btrfs/volumes.c

+10 −0

Original line number	Diff line number	Diff line
		@@ -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) {