root cannot list files in /data

1|shell@maguro:/ # ls -l /system/xbin/ -rwxr-xr-x root shell 59816 2013-07-11 02:12 dexdump -rwsr-sr-x root root 67008 2013-10-08 17:24 su shell@maguro:/ # ls /data opendir failed, Permission denied The permissions on su are correct right? I get the hash prompt, but I can't list the files in /data (or do anything that requires superuser permissions). I don't have Superuser.apk installed, I don't want to install it because of that grant/deny access dialogue that pops up if you wipe the device. What does Superuser.apk do that I can't do when I unpack the *.img files?