ima: added policy support for 'security.ima' type

The 'security.ima' extended attribute may contain either the file data's
hash or a digital signature.  This patch adds support for requiring a
specific extended attribute type.  It extends the IMA policy with a new
keyword 'appraise_type=imasig'.  (Default is hash.)

Changelog v2:
- Fixed Documentation/ABI/testing/ima_policy option syntax
Changelog v1:
- Differentiate between 'required' vs. 'actual' extended attribute

Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
index cd00ba3..3cdd787 100644
--- a/security/integrity/ima/ima_main.c
+++ b/security/integrity/ima/ima_main.c
@@ -169,6 +169,7 @@
 	 * (IMA_MEASURE, IMA_MEASURED, IMA_APPRAISE, IMA_APPRAISED,
 	 *  IMA_AUDIT, IMA_AUDITED) */
 	iint->flags |= action;
+	action &= IMA_DO_MASK;
 	action &= ~((iint->flags & IMA_DONE_MASK) >> 1);
 
 	/* Nothing to do, just return existing appraised status */