I recently got hold of a tablet, mostly for reading PDFs on, but I realized that the preinstalled android OS didn’t let me have root access. Which is deeply immoral. I ought to be able to do what I want to the devices I buy. It took me ages to work out how to get root on it, so I have writen up the instructions in the hope that they might be useful to others on the internets.
Warning if you brick your device, don’t blame me. Caveat emptor and make a backup!
<p>I then found some <a href="http://www.androidtablets.net/forum/attachments/coby-generation-3-development/6435d1336095759-requesting-firmware-dumps-coby-generation-3-devices-coby_root3.zip">Coby rooting tools</a> on <a href="http://www.androidtablets.net/">androidtablets.net</a>. The basic approach is to use Saurik’s <a href="https://github.com/saurik/mempodroid">mempodroid</a> tool to exploit CVE-2012-0056. The main thing to suss out was to find a goot offset at which to place your shellcode. Someone on a forum somewhere had done that. I lost the link, so apologies for not crediting them. </p>
The only thing left to do was to create a nice script to automate the process. I cracked out vim and got typing.
echo Waiting for device...
echo Pushing files...
adb push data /data/local/tmp/
adb shell chmod 0777 /data/local/tmp/mempodroid
adb shell /data/local/tmp/mempodroid 0xd7cc 0xad27 sh /data/local/tmp/root.sh
I ran mempodroid from the commandline so that you would have something more interesting to look at.
./mempodroid 0xd7cc 0xad27 sh /data/local/tmp/root.sh
shell@android:/data/local/tmp $ su
And now we have root. Shortly afterwards I had Debian running which made me happy.
<h3>More about the Coby MID9742</h3>
So, now that I own my tablet properly, what do I make of it? I’ve found it to be adequate for reading PDFs, though it is a bit slow to render anything. I have only been using the built in software and things from the F-Droid free software repo, which means I can do encrypted browsing with tor, look at my calendar and all that shizzle. I’ve found the screen pretty good but the wireless to be awful. Battery life is a couple of hours max, which isn’t great, but is livable with. The tablet is pretty underpowered for doing anything much of interest — the effect being exaggerated by the sluggish wireless card. But it meets my requirement of being able to read PDFs and of being mostly powered by free as in freedom software.