When using locations image data is not immutable

Bug https://bugs.launchpad.net/glance/+bug/1525915 points out that an image can be set back to queued which allows modifying the image bytes.

There is an alternative way to modify the bytes without having the image's status change from 'active'.

When using locations a location which may be directly modified can be used:

 $ glance --os-image-api-version 1 image-update --location http://example.com e2093a55-2aa2-454e-95b4-80a5a80f5043

In the above call http://example.com may be any domain/path which can be modified by the creator of the image.

Images whose locations have been added in this way have no checksum:

+------------------+--------------------------------------+
| Property | Value |
+------------------+--------------------------------------+
| checksum | None |
| container_format | bare |
| created_at | 2015-12-14T14:53:41.000000 |
| deleted | False |
| deleted_at | None |
| disk_format | raw |
| id | e2093a55-2aa2-454e-95b4-80a5a80f5043 |
| is_public | False |
| min_disk | 0 |
| min_ram | 0 |
| name | http2 |
| owner | 1358057831f74e66953dd6f283874d34 |
| protected | False |
| size | 1270 |
| status | active |
| updated_at | 2015-12-14T14:55:03.000000 |
| virtual_size | None |
+------------------+--------------------------------------+