https://github.com/shadow-maint/shadow/issues/32

Anyway, we use su from util-linux.

--- src/su.c.orig	2016-12-01 20:41:50.000000000 +0100
+++ src/su.c	2017-02-26 17:36:32.291904996 +0100
@@ -373,8 +373,8 @@
 		              stderr);
 		(void) kill (-pid_child, caught);
 
-		snprintf (kill_msg, _(" ...killed.\n"));
-		snprintf (wait_msg, _(" ...waiting for child to terminate.\n"));
+		snprintf (kill_msg, sizeof kill_msg, _(" ...killed.\n"));
+		snprintf (wait_msg, sizeof wait_msg, _(" ...waiting for child to terminate.\n"));
 
 		(void) signal (SIGALRM, kill_child);
 		(void) alarm (2);