Wednesday, June 3, 2009

Hacking Ignite-UX's expert recovery mode to scrub disks offline


SAN arrays can be scrubbed independently (remember dilx?) but internal disks are more complicated to do. Many suggestions I've seen in the ITRC forums consist of logging into HP-UX, then wipe the disks using "dd /dev/zero" or similar tools. From my experience, this is risky. I used to do this over 10 years ago when decomissioning workstations, and the operating system eventually stopped working while the disks were scrubbing, leaving no proof that the they had indeed been wiped completely.

With a Proliant, no problem. Just boot up a Linux live CD such as System Rescue CD and it will come with a scrubber. Case closed. But with an Integrity server, it's more complicated as there aren't Linux live CDs available. Maybe with some elbow grease I could make one with CentOS but I don't know Linux enough to take on the challenge.

The Ignite-UX expert recovery mode

Ignite-UX comes with a rarely-used mode named "Expert Recovery" which puts on a RAM disk many tools you need to recover an unbootable system. Instead, we'll use the expert recovery shell to actually wipe out disks! While we could compile a statically-linked open source scrubbing tool such as diskscrub, to save time we'll bring in mediainit(1m) which, since the March 2009 release of 11.31, has a new scrubbing option. Since the man page does not describe precisely the algorithm used, I checked what mediainit actually writes, and from my findings, it follows the DoD 5520.22-M standard which consists of writing one character, the complement, then a random character. It should be enough for most people... but for classified stuff, nothing beats a drill press.


a/ Start by putting a working mediainit under /var/opt/ignite/scrub on your Ignite server. It has to come from a March 2009 11.31 release, as it's the earliest to support scrubbing. You'll also need to add the libpthread library since mediainit has a dependency on this library, and it's not included in the expert recovery environment.

ignite-server# mkdir /var/opt/ignite/scrub
ignite-server# cp /usr/bin/mediainit /var/opt/ignite/scrub
ignite-server# cp /usr/lib/hpux32/ /var/opt/ignite/scrub

b/ Ignite the server you want to wipe out. Igniting is beyond the scope of this howto, I personally use dbprofile and lanboot at the EFI to do this. If you are given choices between igniting 11.23 or 11.31, choose 11.31. Of course, if you're on a K class or some other older hardware that doesn't support 11.31, you're out of luck. Stop here, and try to compile diskscrub to add it to your 11.23 or 11.11 Ignite server.

Obtaining size of AUTO (226 bytes)
Downloading file AUTO (226 bytes)
1. target OS is B.11.23 IA
2. target OS is B.11.31 IA
3. Exit Boot Loader

Choose an operating system to install that your hardware supports: 2

c/ When you get to the Welcome to Ignite-UX screen, choose Run an Expert Recovery Shell. Configure your network and click OK. A RAM disk will be created, and some useful commands will be pulled from the Ignite Server. You'll be presented with a menu, where you must choose X - exit to shell.


s. Search for a file
b. Reboot
l. Load a file
r. Recover an unbootable HP-UX system
x. Exit to shell

This menu is for listing and loading the tools contained on the core media.
Once a tool is loaded, it may be run from the shell. Some tools require other
files to be present in order to successfully execute.

Select one of the above: x

Type 'menu' to return to the menu environment. Do not use 'exit'.


d/ mediainit and libpthread are missing from the environment, so they must be pulled from the Ignite server. To do this, we'll use tftp which is the protocol used to download software from the Ignite server.

First get mediainit and put it in /usr/bin:

# cd /usr/bin
# tftp ignite_server_ip_address
tftp> get /var/opt/ignite/scrub/mediainit
Received 88405 bytes in 0.0 seconds
tftp> quit
# chmod 755 /usr/bin/mediainit

Then get and put it in /usr/lib/hpux32:

# cd /usr/lib/hpux32
# tftp ignite_server_ip_address
tftp> get /var/opt/ignite/scrub/
Received 1521497 bytes in 0.6 seconds
tftp> quit

e/ You're done! You now have downloaded a workable scrubber in the Expert Recovery Shell.

# /usr/bin/mediainit
usage: mediainit [-vrn] [-f fmt_optn] [-i interleave] [-p partition_size] pathname
usage: mediainit -S [-t scrub_count] [-c scrub_character] special_file

f/ The last step is identifying your disk devices under /dev/rdsk, and wipe them using the -S option:

# /usr/bin/mediainit -S /dev/rdsk/c0t0d0
WARNING: You have invoked the disk scrub option.
Using this option will completely destroy the data
on the specified disk. All the signals except SIGINT(ctrl-c)
will be disabled during disk scrub.
Are you SURE you want to proceed? (y/n) y

Disk scrub:PASS 1

Disk scrub:PASS 2

Disk scrub:PASS 3
mediainit: Disk scrubbing successful

With these default options, mediainit will write these hex characters in order to follow the DoD spec: First '0x30', then '0x66' , finally '0xc6'. 66 is the complement of 30, while c6 is the "random" character which is actually hard coded in mediainit. It's actually more interesting to use -S alone rather than with the -c (scrub character) and -t (number of times to scrub) options since these two options do not alternate between different characters and you must reinvoke mediainit manually to change them.

Good luck


Anonymous said...

First '0x30', then '0x66' , finally '0xc6'. 66 is the complement of 30, while c6 is the "random" character

Wouldn't the complement of 0x30 be 0xCF?

0x30 = 0011 0000
0xCF = 1100 1111
0x66 = 0110 0110

Anonymous said...

Also the "diskscrub" utility has been ported to hp-ux.
It supports multiple wipe patterns.
You could put that onto your Ignite/UX boot server as per the example you gave.
of course you can also put that binary into your miniramdisk image so it'll be immediately available.