ima: fix buffer overrun in ima_eventdigest_init_common

commit 923168a0 upstream.

Function ima_eventdigest_init() calls ima_eventdigest_init_common()
with HASH_ALGO__LAST which is then used to access the array
hash_digest_size[] leading to buffer overrun. Have a conditional
statement to handle this.

Fixes: 9fab303a ("ima: fix violation measurement list record")
Signed-off-by: Samasth Norway Ananda <samasth.norway.ananda@oracle.com>
Tested-by: Enrico Bravi (PhD at polito.it) <enrico.bravi@huawei.com>
Cc: stable@vger.kernel.org # 5.19+
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>