selinux: add _cleanup_ concepts to SELinux label allocation

src/basic/selinux-util.c

@@ -295,14 +295,20 @@ int mac_selinux_get_child_mls_label(int socket_fd, const char *exe, const char *
         return r;
 }
 
-void mac_selinux_free(char *label) {
+char* mac_selinux_free(char *label) {
 
 #ifdef HAVE_SELINUX
+        if (!label)
+                return NULL;
+
         if (!mac_selinux_use())
-                return;
+                return NULL;
+
 
         freecon((security_context_t) label);
 #endif
+
+        return NULL;
 }
 
 int mac_selinux_create_file_prepare(const char *path, mode_t mode) {

src/basic/selinux-util.h

@@ -24,6 +24,8 @@
 #include <sys/socket.h>
 #include <stdbool.h>
 
+#include "macro.h"
+
 bool mac_selinux_use(void);
 void mac_selinux_retest(void);
 
@@ -36,7 +38,7 @@ int mac_selinux_apply(const char *path, const char *label);
 int mac_selinux_get_create_label_from_exe(const char *exe, char **label);
 int mac_selinux_get_our_label(char **label);
 int mac_selinux_get_child_mls_label(int socket_fd, const char *exe, const char *exec_label, char **label);
-void mac_selinux_free(char *label);
+char* mac_selinux_free(char *label);
 
 int mac_selinux_create_file_prepare(const char *path, mode_t mode);
 void mac_selinux_create_file_clear(void);
@@ -45,3 +47,5 @@ int mac_selinux_create_socket_prepare(const char *label);
 void mac_selinux_create_socket_clear(void);
 
 int mac_selinux_bind(int fd, const struct sockaddr *addr, socklen_t addrlen);
+
+DEFINE_TRIVIAL_CLEANUP_FUNC(char*, mac_selinux_free);