DM-Verity has an (undocumented) mode where no salt is used. This was
never handled directly by the DM-Verity code, instead working due to the
fact that calling crypto_shash_update() with a zero length data is an
implicit noop.
This is no longer the case now that we have switched to
crypto_ahash_update(). Fix the issue by introducing explicit handling
of the no salt use case to DM-Verity.
Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com> Reported-by: Marian Csontos <mcsontos@redhat.com> Fixes: 32b85f0 ("dm verity: switch to using asynchronous hash crypto API") Tested-by: Milan Broz <gmazyland@gmail.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>