slsm: treat empty optional arguments as non-existent

Gets rid of a special case in slsm_serialize_subtree.

security/slsm/tree.c

@@ -237,20 +237,13 @@ ssize_t slsm_serialize_subtree(struct slsm_str *buf, struct slsm_str *path_buf,
 		return ret;
 
 	for (i = 0; i < t->rules_used; i++) {
-		ret = slsm_str_append(buf, "p=%s%cm=%u%cf=%u%c",
+		ret = slsm_str_append(buf, "p=%s%ca=%s%cm=%u%cf=%u%c",
 				path_buf->buf, '\0',
+				t->rules[i].app, '\0',
 				t->rules[i].perms.mode, '\0',
 				t->rules[i].perms.flags, '\0');
 		if (ret)
 			return ret;
-
-		// TODO: get rid of this special case by handling a=\0 in the parser
-		if (t->rules[i].app) {
-			buf->used--; // remove second trailing null byte
-			ret = slsm_str_append(buf, "a=%s%c", t->rules[i].app, '\0');
-			if (ret)
-				return ret;
-		}
 	}
 
 	// exclude null for the recursive calls
@@ -501,7 +494,8 @@ insert:
 				mode_str);
 		return error;
 	}
-	if (flags_str && (error = kstrtouint(flags_str, 10, &r.perms.flags))) {
+	if (flags_str && *flags_str
+			&& (error = kstrtouint(flags_str, 10, &r.perms.flags))) {
 		printk(KERN_ERR "slsm_insert_rule: format error: flags not a number: %s\n",
 				flags_str);
 		return error;
@@ -511,7 +505,7 @@ insert:
 	if (!path_components)
 		return -ENOMEM;
 
-	if (app) {
+	if (app && *app) {
 		r.app = kstrdup(app, GFP_KERNEL);
 		if (!r.app) {
 			kfree(path_components);