audit: audit feature to set loginuid immutable

This adds a new 'audit_feature' bit which allows userspace to set it
such that the loginuid is absolutely immutable, even if you have
CAP_AUDIT_CONTROL.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Eric Paris <eparis@redhat.com>
diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
index 05e5e8f..e2f0d99 100644
--- a/include/uapi/linux/audit.h
+++ b/include/uapi/linux/audit.h
@@ -387,7 +387,8 @@
 };
 
 #define AUDIT_FEATURE_ONLY_UNSET_LOGINUID	0
-#define AUDIT_LAST_FEATURE			AUDIT_FEATURE_ONLY_UNSET_LOGINUID
+#define AUDIT_FEATURE_LOGINUID_IMMUTABLE	1
+#define AUDIT_LAST_FEATURE			AUDIT_FEATURE_LOGINUID_IMMUTABLE
 
 #define audit_feature_valid(x)		((x) >= 0 && (x) <= AUDIT_LAST_FEATURE)
 #define AUDIT_FEATURE_TO_MASK(x)	(1 << ((x) & 31)) /* mask for __u32 */