On Tue, May 02, 2017 at 12:02:23PM +0100, Daniel P. Berrange wrote:
If we are encoding a block of data that is 16 bytes in length, we cannot leave it as 16 bytes, we must pad it out to the next block boundary, 32 bytes. Without this padding, the decoder will incorrectly treat the last byte of plain text as the padding length, as it can't distinguish padded from non-padded data.
The problem exhibited itself when using a 16 byte passphrase for a LUKS volume
$ virsh secret-set-value 55806c7d-8e93-456f-829b-607d8c198367 \ $(echo -n 1234567812345678 | base64) Secret value set
$ virsh start demo error: Failed to start domain demo error: internal error: process exited while connecting to monitor: >>>>>>>>>>Len 16 2017-05-02T10:35:40.016390Z qemu-system-x86_64: -object \ secret,id=virtio-disk1-luks-secret0,data=SEtNi5vDUeyseMKHwc1c1Q==,\ keyid=masterKey0,iv=zm7apUB1A6dPcH53VW960Q==,format=base64: \ Incorrect number of padding bytes (56) found on decrypted data
Notice how the padding '56' corresponds to the ordinal value of the character '8'.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com> ---
ACK Erik