When su is invoked with command line arguments for the shell (e.g. "su
- -c 'cmd'"), set argv[0] in the shell to "-su" or "-<basename>" (as
determined by the SU_NAME option in /etc/login.defs).  This is
necessary to make Bash compiled with the NON_INTERACTIVE_LOGIN_SHELLS
option to read startup files.  It is also consistent with the
behaviour of `su' in coreutils, and with the case where there are no
arguments ("su -").

diff -ru -x '*~' shadow-4.1.4.2-orig/src/su.c shadow-4.1.4.2/src/su.c
--- shadow-4.1.4.2-orig/src/su.c	2009-07-23 22:38:56.000000000 +0200
+++ shadow-4.1.4.2/src/su.c	2010-06-04 13:02:24.000000000 +0200
@@ -983,7 +983,7 @@
 		 * Use the shell and create an argv
 		 * with the rest of the command line included.
 		 */
-		argv[-1] = shellstr;
+		argv[-1] = cp;
 #ifndef USE_PAM
 		execve_shell (shellstr, &argv[-1], environ);
 		err = errno;