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>
diff --git a/security/smack/smack.h b/security/smack/smack.h
index 2ad0065..ccba382 100644
--- a/security/smack/smack.h
+++ b/security/smack/smack.h
@@ -185,6 +185,15 @@
  */
 #define SMK_NUM_ACCESS_TYPE 5
 
+/* SMACK data */
+struct smack_audit_data {
+	const char *function;
+	char *subject;
+	char *object;
+	char *request;
+	int result;
+};
+
 /*
  * Smack audit data; is empty if CONFIG_AUDIT not set
  * to save some stack
@@ -192,6 +201,7 @@
 struct smk_audit_info {
 #ifdef CONFIG_AUDIT
 	struct common_audit_data a;
+	struct smack_audit_data sad;
 #endif
 };
 /*
@@ -311,7 +321,8 @@
 {
 	memset(a, 0, sizeof(*a));
 	a->a.type = type;
-	a->a.smack_audit_data.function = func;
+	a->a.smack_audit_data = &a->sad;
+	a->a.smack_audit_data->function = func;
 }
 
 static inline void smk_ad_setfield_u_tsk(struct smk_audit_info *a,