Please apply this small patch to su to set PAM_RUSER.
Compiled and tested.

BTW pam_listfile core dumps if an argument passed to it does not contain
'=' .


--- sh-utils-2.0/src/su.c.old	Thu Feb 15 04:08:25 2001
+++ sh-utils-2.0/src/su.c	Thu Feb 15 04:08:35 2001
@@ -317,6 +317,8 @@
 correct_password (const struct passwd *pw)
 {
 #ifdef USE_PAM
+  struct passwd *caller;
+
   /* root always succeeds; this isn't an authentication question (no
    * extra privs are being granted) so it shouldn't authenticate with PAM.
    * However, we want to create the pam_handle so that proper credentials
@@ -331,6 +333,11 @@
 	exit(1);
   }

+  caller = getpwuid(getuid());
+  if (caller != NULL && caller->pw_name != NULL) {
+
retval = pam_set_item(pamh, PAM_RUSER, caller->pw_name);
+
PAM_BAIL_P;
+  }

   retval = pam_authenticate(pamh, 0);
   PAM_BAIL_P;