ima: use dynamically allocated hash storage

For each inode in the IMA policy, an iint is allocated.  To support
larger hash digests, the iint digest size changed from 20 bytes to
the maximum supported hash digest size.  Instead of allocating the
maximum size, which most likely is not needed, this patch dynamically
allocates the needed hash storage.

Changelog:
- fix krealloc bug

Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

security/integrity/ima/ima_appraise.c

@@ -45,10 +45,10 @@ int ima_must_appraise(struct inode *inode, int mask, enum ima_hooks func)
 static int ima_fix_xattr(struct dentry *dentry,
 			 struct integrity_iint_cache *iint)
 {
-	iint->ima_hash.type = IMA_XATTR_DIGEST;
+	iint->ima_hash->type = IMA_XATTR_DIGEST;
 	return __vfs_setxattr_noperm(dentry, XATTR_NAME_IMA,
-				     &iint->ima_hash.type,
-				     1 + iint->ima_hash.length, 0);
+				     &iint->ima_hash->type,
+				     1 + iint->ima_hash->length, 0);
 }
 
 /* Return specific func appraised cached result */
@@ -186,13 +186,13 @@ int ima_appraise_measurement(int func, struct integrity_iint_cache *iint,
 			status = INTEGRITY_FAIL;
 			break;
 		}
-		if (xattr_len - 1 >= iint->ima_hash.length)
+		if (xattr_len - 1 >= iint->ima_hash->length)
 			/* xattr length may be longer. md5 hash in previous
 			   version occupied 20 bytes in xattr, instead of 16
 			 */
 			rc = memcmp(xattr_value->digest,
-				    iint->ima_hash.digest,
-				    iint->ima_hash.length);
+				    iint->ima_hash->digest,
+				    iint->ima_hash->length);
 		else
 			rc = -EINVAL;
 		if (rc) {
@@ -206,8 +206,8 @@ int ima_appraise_measurement(int func, struct integrity_iint_cache *iint,
 		iint->flags |= IMA_DIGSIG;
 		rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
 					     (const char *)xattr_value, rc,
-					     iint->ima_hash.digest,
-					     iint->ima_hash.length);
+					     iint->ima_hash->digest,
+					     iint->ima_hash->length);
 		if (rc == -EOPNOTSUPP) {
 			status = INTEGRITY_UNKNOWN;
 		} else if (rc) {