LSM: shrink sizeof LSM specific portion of common_audit_data

Linus found that the gigantic size of the common audit data caused a big
perf hit on something as simple as running stat() in a loop.  This patch
requires LSMs to declare the LSM specific portion separately rather than
doing it in a union.  Thus each LSM can be responsible for shrinking their
portion and don't have to pay a penalty just because other LSMs have a
bigger space requirement.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

security/selinux/include/avc.h

@@ -46,6 +46,22 @@ struct avc_cache_stats {
 	unsigned int frees;
 };
 
+struct selinux_audit_data {
+	u32 ssid;
+	u32 tsid;
+	u16 tclass;
+	u32 requested;
+	u32 audited;
+	u32 denied;
+	/*
+	 * auditdeny is a bit tricky and unintuitive.  See the
+	 * comments in avc.c for it's meaning and usage.
+	 */
+	u32 auditdeny;
+	struct av_decision *avd;
+	int result;
+};
+
 /*
  * AVC operations
  */