AppArmor: Abstract use of cred security blob

Don't use the cred->security pointer directly.
Provide a helper function that provides the security blob pointer.

Signed-off-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
[kees: adjusted for ordered init series]
Signed-off-by: Kees Cook <keescook@chromium.org>

security/apparmor/include/cred.h

@@ -23,8 +23,22 @@
 #include "policy_ns.h"
 #include "task.h"
 
-#define cred_label(X) ((X)->security)
+static inline struct aa_label *cred_label(const struct cred *cred)
+{
+	struct aa_label **blob = cred->security;
 
+	AA_BUG(!blob);
+	return *blob;
+}
+
+static inline void set_cred_label(const struct cred *cred,
+				  struct aa_label *label)
+{
+	struct aa_label **blob = cred->security;
+
+	AA_BUG(!blob);
+	*blob = label;
+}
 
 /**
  * aa_cred_raw_label - obtain cred's label