nscd: Deallocate existing user names in file parser

This avoids a theoretical memory leak (theoretical because it depends on
multiple server-user/stat-user directives in the configuration file).

ChangeLog

@@ -1,3 +1,8 @@
+2018-08-14  Florian Weimer  <[email protected]>
+
+	* nscd/nscd_conf.c (nscd_parse_file): Deallocate old storage for
+	server_user, stat_user.
+
 2018-08-13  Joseph Myers  <[email protected]>
 
 	* sysdeps/unix/sysv/linux/syscall-names.list: Update kernel

nscd/nscd_conf.c

@@ -190,14 +190,18 @@ nscd_parse_file (const char *fname, struct database_dyn dbs[lastdb])
 	  if (!arg1)
 	    error (0, 0, _("Must specify user name for server-user option"));
 	  else
-	    server_user = xstrdup (arg1);
+	    {
+	      free ((char *) server_user);
+	      server_user = xstrdup (arg1);
+	    }
 	}
       else if (strcmp (entry, "stat-user") == 0)
 	{
 	  if (arg1 == NULL)
 	    error (0, 0, _("Must specify user name for stat-user option"));
 	  else
 	    {
+	      free ((char *) stat_user);
 	      stat_user = xstrdup (arg1);
 
 	      struct passwd *pw = getpwnam (stat_user);