Index: mate-screensaver-1.19.0/src/setuid.c
# (vdanen) drops setgid calls to work with tcb auth
===================================================================
--- mate-screensaver-1.19.0/src/setuid.c
+++ mate-screensaver-1.19.0/src/setuid.c	2017-10-29 00:50:28.732394364 +0300
@@ -77,11 +77,13 @@
 	if (setgroups (1, &gid) < 0)
 		sgs_errno = errno ? errno : -1;
 
-	errno = 0;
+#if 0
+ 	errno = 0;
 	if (setgid (gid) != 0)
 		gid_errno = errno ? errno : -1;
 
-	errno = 0;
+#endif
+ 	errno = 0;
 	if (setuid (uid) != 0)
 		uid_errno = errno ? errno : -1;
 
@@ -207,7 +209,7 @@
 			*orig_uid = uid_gid_string (euid, egid);
 		}
 
-		if (uid != euid || gid != egid)
+		if (euid == (uid_t) 0 && (uid != euid || gid != egid))
 		{
 #ifdef HAVE_BSDAUTH /* we need to setgid auth to run the bsd_auth(3) login_* helpers */
 			struct group *authg = getgrnam("auth");