apparmor: fix nnp subset test for unconfined

The subset test is not taking into account the unconfined exception
which will cause profile transitions in the stacked confinement
case to fail when no_new_privs is applied.

This fixes a regression introduced in the fix for
https://bugs.launchpad.net/bugs/1839037

BugLink: https://bugs.launchpad.net/bugs/1844186
Signed-off-by: John Johansen <[e-mail]>

security/apparmor/domain.c

···
 	 * aways results in a further reduction of permissions.
 	 */
 	if ((bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS) &&
-	    !unconfined(label) && !aa_label_is_subset(new, ctx->nnp)) {
+	    !unconfined(label) &&
+	    !aa_label_is_unconfined_subset(new, ctx->nnp)) {
 		error = -EPERM;
 		info = "no new privs";
 		goto audit;
···
 		 * reduce restrictions.
 		 */
 		if (task_no_new_privs(current) && !unconfined(label) &&
-		    !aa_label_is_subset(new, ctx->nnp)) {
+		    !aa_label_is_unconfined_subset(new, ctx->nnp)) {
 			/* not an apparmor denial per se, so don't log it */
 			AA_DEBUG("no_new_privs - change_hat denied");
 			error = -EPERM;
···
 		 * reduce restrictions.
 		 */
 		if (task_no_new_privs(current) && !unconfined(label) &&
-		    !aa_label_is_subset(previous, ctx->nnp)) {
+		    !aa_label_is_unconfined_subset(previous, ctx->nnp)) {
 			/* not an apparmor denial per se, so don't log it */
 			AA_DEBUG("no_new_privs - change_hat denied");
 			error = -EPERM;
···
 		 * reduce restrictions.
 		 */
 		if (task_no_new_privs(current) && !unconfined(label) &&
-		    !aa_label_is_subset(new, ctx->nnp)) {
+		    !aa_label_is_unconfined_subset(new, ctx->nnp)) {
 			/* not an apparmor denial per se, so don't log it */
 			AA_DEBUG("no_new_privs - change_hat denied");
 			error = -EPERM;

security/apparmor/include/label.h

···
 struct aa_label *aa_label_alloc(int size, struct aa_proxy *proxy, gfp_t gfp);
 
 bool aa_label_is_subset(struct aa_label *set, struct aa_label *sub);
+bool aa_label_is_unconfined_subset(struct aa_label *set, struct aa_label *sub);
 struct aa_profile *__aa_label_next_not_in_set(struct label_it *I,
 					     struct aa_label *set,
 					     struct aa_label *sub);

security/apparmor/label.c

···
 	return __aa_label_next_not_in_set(&i, set, sub) == NULL;
 }
 
+/**
+ * aa_label_is_unconfined_subset - test if @sub is a subset of @set
+ * @set: label to test against
+ * @sub: label to test if is subset of @set
+ *
+ * This checks for subset but taking into account unconfined. IF
+ * @sub contains an unconfined profile that does not have a matching
+ * unconfined in @set then this will not cause the test to fail.
+ * Conversely we don't care about an unconfined in @set that is not in
+ * @sub
+ *
+ * Returns: true if @sub is special_subset of @set
+ *     else false
+ */
+bool aa_label_is_unconfined_subset(struct aa_label *set, struct aa_label *sub)
+{
+	struct label_it i = { };
+	struct aa_profile *p;
+
+	AA_BUG(!set);
+	AA_BUG(!sub);
+
+	if (sub == set)
+		return true;
+
+	do {
+		p = __aa_label_next_not_in_set(&i, set, sub);
+		if (p && !profile_unconfined(p))
+			break;
+	} while (p);
+
+	return p == NULL;
+}
 
 
 /**