utils: add lxc_drop_groups()

src/lxc/utils.c

@@ -1444,6 +1444,18 @@ bool lxc_switch_uid_gid(uid_t uid, gid_t gid)
 }
 
 /* Simple convenience function which enables uniform logging. */
+bool lxc_drop_groups(void)
+{
+	int ret;
+
+	ret = setgroups(0, NULL);
+	if (ret)
+		return log_error_errno(false, errno, "Failed to drop supplimentary groups");
+
+	NOTICE("Dropped supplimentary groups");
+	return ret == 0;
+}
+
 bool lxc_setgroups(int size, gid_t list[])
 {
 	if (setgroups(size, list) < 0) {

src/lxc/utils.h

@@ -157,6 +157,7 @@ __hidden extern bool task_blocks_signal(pid_t pid, int signal);
  */
 __hidden extern bool lxc_switch_uid_gid(uid_t uid, gid_t gid);
 __hidden extern bool lxc_setgroups(int size, gid_t list[]);
+__hidden extern bool lxc_drop_groups(void);
 
 /* Find an unused loop device and associate it with source. */
 __hidden extern int lxc_prepare_loop_dev(const char *source, char *loop_dev, int flags);