apparmor: make signal label match work 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

    signal send 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.
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/ipc.c

@@ -184,50 +184,34 @@ static void audit_signal_cb(struct audit_buffer *ab, void *va)
 			FLAGS_NONE, GFP_ATOMIC);
 }
 
-/* TODO: update to handle compound name&name2, conditionals */
-static void profile_match_signal(struct aa_profile *profile, const char *label,
-				 int signal, struct aa_perms *perms)
-{
-	unsigned int state;
-
-	/* TODO: secondary cache check <profile, profile, perm> */
-	state = aa_dfa_next(profile->policy.dfa,
-			    profile->policy.start[AA_CLASS_SIGNAL],
-			    signal);
-	state = aa_dfa_match(profile->policy.dfa, state, label);
-	aa_compute_perms(profile->policy.dfa, state, perms);
-}
-
 static int profile_signal_perm(struct aa_profile *profile,
-			       struct aa_profile *peer, u32 request,
+			       struct aa_label *peer, u32 request,
 			       struct common_audit_data *sa)
 {
 	struct aa_perms perms;
+	unsigned int state;
 
 	if (profile_unconfined(profile) ||
 	    !PROFILE_MEDIATES(profile, AA_CLASS_SIGNAL))
 		return 0;
 
-	aad(sa)->peer = &peer->label;
-	profile_match_signal(profile, peer->base.hname, aad(sa)->signal,
-			     &perms);
+	aad(sa)->peer = peer;
+	/* TODO: secondary cache check <profile, profile, perm> */
+	state = aa_dfa_next(profile->policy.dfa,
+			    profile->policy.start[AA_CLASS_SIGNAL],
+			    aad(sa)->signal);
+	aa_label_match(profile, peer, state, false, request, &perms);
 	aa_apply_modes_to_perms(profile, &perms);
 	return aa_check_perms(profile, &perms, request, sa, audit_signal_cb);
 }
 
-static int aa_signal_cross_perm(struct aa_profile *sender,
-				struct aa_profile *target,
-				struct common_audit_data *sa)
-{
-	return xcheck(profile_signal_perm(sender, target, MAY_WRITE, sa),
-		      profile_signal_perm(target, sender, MAY_READ, sa));
-}
-
 int aa_may_signal(struct aa_label *sender, struct aa_label *target, int sig)
 {
+	struct aa_profile *profile;
 	DEFINE_AUDIT_DATA(sa, LSM_AUDIT_DATA_NONE, OP_SIGNAL);
 
 	aad(&sa)->signal = map_signal_num(sig);
-	return xcheck_labels_profiles(sender, target, aa_signal_cross_perm,
-				      &sa);
+	return xcheck_labels(sender, target, profile,
+			profile_signal_perm(profile, target, MAY_WRITE, &sa),
+			profile_signal_perm(profile, sender, MAY_READ, &sa));
 }