ima: define ima_max_digest_data struct without a flexible array variable

To support larger hash digests in the 'iint' cache, instead of defining
the 'digest' field as the maximum digest size, the 'digest' field was
defined as a flexible array variable.  The "ima_digest_data" struct was
wrapped inside a local structure with the maximum digest size.  But
before adding the record to the iint cache, memory for the exact digest
size was dynamically allocated.

The original reason for defining the 'digest' field as a flexible array
variable is still valid for the 'iint' cache use case.  Instead of
wrapping the 'ima_digest_data' struct in a local structure define
'ima_max_digest_data' struct.

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

security/integrity/integrity.h

@@ -15,6 +15,7 @@
 #include <linux/types.h>
 #include <linux/integrity.h>
 #include <crypto/sha1.h>
+#include <crypto/hash.h>
 #include <linux/key.h>
 #include <linux/audit.h>
 
@@ -110,6 +111,15 @@ struct ima_digest_data {
 	u8 digest[];
 } __packed;
 
+/*
+ * Instead of wrapping the ima_digest_data struct inside a local structure
+ * with the maximum hash size, define ima_max_digest_data struct.
+ */
+struct ima_max_digest_data {
+	struct ima_digest_data hdr;
+	u8 digest[HASH_MAX_DIGESTSIZE];
+} __packed;
+
 /*
  * signature format v2 - for using with asymmetric keys
  */