Re: [PATCH v2] btrfs: validate device maj:min during open

[Christoph Hellwig <hch@infradead.org>]

On Fri, Mar 08, 2024 at 09:34:03PM +0530, Anand Jain wrote:
> > bdev_open_by_path.  bdev_open_by_path bdev_open_by_path calls
> > lookup_bdev to translate the path to a dev_t and then calls
> > bdev_open_by_dev on the dev_t, which stored the passes in dev_t in
> > bdev->bd_dev.  I see absolutely no way how this check could ever
> > trigger.
> > 
> 
> Prior to this patch, the device->devt value of the device could become
> stale, as it might not have been updated since the last scan of the
> device. During this interval, the device could have undergone changes
> to its devt.

How can it become stale here? btrfs_open_one_device exits early
if device->bdev is set, so you set up a new device->bdev and
stash the just opened bdev there.  The dev_t of an existing
struct block_device never changes, so it must match the one
in the btrfs_device that was just initialized from it.