[XFRM]: Fix OOPSes in xfrm_audit_log().

Make sure that this function is called correctly, and
add BUG() checking to ensure the arguments are sane.

Based upon a patch by Joy Latten.

Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index a24f385..c394b41 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -1997,9 +1997,14 @@
 	if (audit_enabled == 0)
 		return;
 
+	BUG_ON((type == AUDIT_MAC_IPSEC_ADDSA ||
+		type == AUDIT_MAC_IPSEC_DELSA) && !x);
+	BUG_ON((type == AUDIT_MAC_IPSEC_ADDSPD ||
+		type == AUDIT_MAC_IPSEC_DELSPD) && !xp);
+
 	audit_buf = audit_log_start(current->audit_context, GFP_ATOMIC, type);
 	if (audit_buf == NULL)
-	return;
+		return;
 
 	switch(type) {
 	case AUDIT_MAC_IPSEC_ADDSA: