Permission denied reading /dev/block/mmcblk0p4 as root

I will list my main objective first, dependencies after. If there is a better path to my goal, please show me the way.... * I want to [install Lollipop](http://www.android.gs/update-htc-one-s-to-android-5-1-1-lollipop-with-resurrection-remix-5-4-4-custom-rom/) on my HTC One S. *(Or a later version, if one is compatible with the One S, Google Play Services included.)* * For this I need [HBOOT 2.16](https://forum.xda-developers.com/htc-one-s/general/guide-how-to-install-hboot-2-16-time-t2898605) * For this I need [S-OFF](https://forum.xda-developers.com/showthread.php?t=2155135) * For this I need [Super cid: 11111111](https://forum.xda-developers.com/showthread.php?t=1671643) (Phew, what a hassle!) I am working up from the bottom of this list: the instructions for Super cid begin adb shell su dd if=/dev/block/mmcblk0p4 of=/sdcard/mmcblk0p4 This gives me a permission denied error. Here is the full contents of the shell: #> adb shell shell@ville:/ $ su 255|shell@ville:/ $ dd if=/dev/block/mmcblk0p4 of=/sdcard/mmcblk0p4 /dev/block/mmcblk0p4: cannot open for read: Permission denied 1|shell@ville:/ $ ls -al /dev/block/mmcblk0p4 brw------- root root 179, 4 2017-02-28 20:35 mmcblk0p4 shell@ville:/ $ I find it odd that su seems to change the user to 255 and the failure of dd seems to change the user to 1, but what do I know? Why is this permission error happening and how do I fix it? The phone currently runs Cyanogenmod.