I'm leaving this post here for posterity's sake, but an easier root method is now available at:
The package may be downloaded at http://vulnfactory.org/public/motochopper.zip
As promised, this post describes how to root the Atrix HD Jelly Bean build. This should also work on other Motorola 4.1.2 builds (Razr/Razr Maxx, Razr HD, Razr M, etc.).
The exploit requires setting up a special Samba share and mounting this share on your phone using the File Manager app. I apologize that this process may seem involved for some of you, and request that members of this community help each other out if some of you are having problems completing the procedure. I'm not able to provide individual tech support to every user who wants to root this phone.
The following instructions require a working Linux installation. The following instructions are for Ubuntu. If you don't want to install Ubuntu permanently on your machine, I suggest using a LiveCD installation. Instructions on setting this up are described here:
Once you're booted into Ubuntu, open a terminal. Create a new directory for your Samba share:
Next, install the samba package:
sudo apt-get install samba
Edit the configuration file for samba:
sudo gedit /etc/samba/smb.conf
Add the following lines to the end of the configuration file and save your changes:
path = /tmp/share
available = yes
valid users = guest
read only = yes
browsable = yes
public = yes
Close the text editor once you've saved your changes.
Next, create a user for the Samba share by typing in the terminal:
sudo useradd guest -m -G users
Set a password for the new user. Remember this password:
Provide a password here and press enter. You won't see the characters you're typing, so be careful.
Next, set a password on the share. Use the same password you just provided:
sudo smbpasswd -a guest
Type the password you created before and press enter.
Next, restart the Samba server:
Finally, download and prepare the required files to the Samba share:
At this point, you'll need to know the IP address of your Linux host, which you can get by running "ifconfig" from your terminal (it should be of the form "192.168.x.x").
Next, move over to your Android device. Ensure you have enabled USB Debugging Mode (under Settings -> Development Settings). Ensure your device is connected via Wifi.
Open the "File Manager" app, and select "Remote storage". Click "Add storage", and fill in fields as follows:
Host IP address: [your Linux machine's IP address]
Domain name: WORKGROUP
Shared folder name: share
Password: [the password you created above]
At this point, the phone will mount your Linux share. To complete the process, plug in your phone via USB to your Linux machine, and type the following in your Linux terminal:
sudo /tmp/share/adb kill-server
sudo /tmp/share/adb shell /storage/rfs0/pwn
If it's successful, this should print "[+] Rooting complete!".
Finally, install Supersu by typing the following in the terminal:
sudo /tmp/share/adb install /tmp/share/eu.chainfire.supersu.apk
Congratulations, enjoy your rooted device.
I can't stress this enough: I can't provide individualized tech support for everyone on this forum. Please help each other.
TTLayland has been successfully rooted using this technique and has volunteered to help. If you get stuck and can't find support on these forums, feel free to email him at ttlayland (at) gmail (dot) com.