apparmor: fix ptrace label match when matching stacked labels

Given a label with a profile stack of
  A//&B or A//&C ...

A ptrace rule should be able to specify a generic trace pattern with
a rule like

  ptrace trace A//&**,

however this is failing because while the correct label match routine
is called, it is being done post label decomposition so it is always
being done against a profile instead of the stacked label.

To fix this refactor the cross check to pass the full peer label in to
the label_match.

Fixes: 290f458a4f ("apparmor: allow ptrace checks to be finer grained than just capability")
Cc: Stable <stable@vger.kernel.org>
Reported-by: Matthew Garrett <mjg59@google.com>
Tested-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/include/perms.h

@@ -133,6 +133,9 @@ extern struct aa_perms allperms;
 #define xcheck_labels_profiles(L1, L2, FN, args...)		\
 	xcheck_ns_labels((L1), (L2), xcheck_ns_profile_label, (FN), args)
 
+#define xcheck_labels(L1, L2, P, FN1, FN2)			\
+	xcheck(fn_for_each((L1), (P), (FN1)), fn_for_each((L2), (P), (FN2)))
+
 
 void aa_perm_mask_to_str(char *str, const char *chrs, u32 mask);
 void aa_audit_perm_names(struct audit_buffer *ab, const char **names, u32 mask);