dm integrity: fix memory corruption when tag_size is less than digest size

It is possible to set up dm-integrity in such a way that the
"tag_size" parameter is less than the actual digest size. In this
situation, a part of the digest beyond tag_size is ignored.

In this case, dm-integrity would write beyond the end of the
ic->recalc_tags array and corrupt memory. The corruption happened in
integrity_recalc->integrity_sector_checksum->crypto_shash_final.

Fix this corruption by increasing the tags array so that it has enough
padding at the end to accomodate the loop in integrity_recalc() being
able to write a full digest size for the last member of the tags
array.

Cc: stable@vger.kernel.org # v4.19+
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>