Constellation allows insecure use of LUKS2 persistent storage partitions

Constellation is the first Confidential Kubernetes. The Constellation CVM image uses LUKS2-encrypted volumes for persistent storage. When opening an encrypted storage device, the CVM uses the libcryptsetup function crypt_activate_by_passhrase. If the VM is successful in opening the partition with the disk encryption key, it treats the volume as confidential. However, due to the unsafe handling of null keyslot algorithms in the cryptsetup 2.8.1, it is possible that the opened volume is not encrypted at all. Cryptsetup prior to version 2.8.1 does not report an error when processing LUKS2-formatted disks that use the cipher_null-ecb algorithm in the keyslot encryption field. This vulnerability is fixed in 2.24.0.