SSH

Breaking back into your network with the Synology Web UI

5 Comments / Misc Computers and Tech

Have you ever left town, or even just took a trip to the coffee shop, only to find that you’re locked out of your home network? Maybe you needed a file that you forgot to put in Dropbox, or felt paranoid and wanted to check on your security cameras, or you just wanted to stream music. I have…

The end of a long drive

Last night, I arrived at my hotel after a 4 hour drive only to find my VPN wasn’t working. I always VPN in to home, so that I can access my file server, my VMs, security cameras, what have you. I didn’t understand.. I was sure I had things set up right. You see, I recently had my Xfinity router replaced, and had to set it up to talk to my Asus N66U, but I was absolutely sure it was working. Almost sure. Well, I thought it was working…

So I tried SSHing in. No dice. Hmm.. Any web server ports I exposed? Guess not. Maybe port forwarding was messed up somewhere?

Ah HA! I could reach my wonderful Synology NAS’s web UI. If you haven’t used this thing, it’s like a full-on desktop environment with apps. It’s amazing. Only thing it’s really missing is a web browser for accessing the home network (get on this, guys!). After spending some time thinking about it, I devised a solution to get me back into my home network, with full VPN access (though, see the end of the story for what happened there).

Christian’s step-by-step guide to breaking in with Synology

No more stories for now.

To get started, I’m assuming you have three things:

  1. Remote access (with admin rights) to your Synology NAS’s web console.
  2. A Linux server somewhere both sides can log into remotely (other than your local machine, as I’m assuming yours isn’t publicly connected to the network).
  3. A local Linux or Mac with a web browser and ssh. You can make this work on Windows with Putty as well, but I’m not going into details on that. Just figure out SSH tunneling and replace step 7 below.

All set? Here’s what you do.

  1. Log into your NAS and go to Package Center. Click Settings -> Package Sources and add:
  2. Name: MissileHugger
    Location: http://packages.missilehugger.com/
  3. Install the “Web Console” package and run it from the start menu.
  4. Web Console doesn’t support interactive sessions with commands, so you’ll need to have some SSH key set up on your linux server’s authorized_keys, and have that key available to you. There’s also no multi-line paste, so you’ll need to copy this key through Web Console line-by-line:

    Locally:

    $ cat ~/.ssh/id_dsa

    On Web Console:

    $ echo "-----BEGIN DSA PRIVATE KEY-----" > id_dsa
$ echo "<first line of private key>" >> id_dsa
$ echo "<second line of private key>" >> id_dsa
$ ...
$ echo "-----END DSA PRIVATE KEY-----" >> id_dsa
$ chmod 600 id_dsa
  5. Establish a reverse tunnel to your Linux box, pointing to the web server you’re trying to reach (we’ll say 192.168.1.1 for your router).

    Remember that Web Console doesn’t support interactive sessions, or pseudo-terminal allocation, so we’ll need to tweak some stuff when calling ssh:

    $ ssh -o 'StrictHostKeyChecking no' -t -t -i id_dsa \
      -R 19980:192.168.1.1:80 youruser@yourlinuxserver

    The ‘StrictHostKeyChecking no’ is to get around not having any way to verify a host key from Web Console, and the two -t parameters (yes, two) forces TTY allocation regardless of the shell.

  6. If all went well, your Linux server should locally have a port 19980 that reaches your web server. Verify this by logging in and typing: 
    $ lynx http://localhost:19980
  7. On your local machine, set up a tunnel to connect port 19980 on your machine to port 19980 on your Linux server. 
    $ ssh -L 19980:yourlinuxserver:19980 youruser@yourlinuxserver
  8. You should now be able to reach your router. Try it! Open your favorite browser and go to http://localhost:19980
  9. Clean up. Delete your id_dsa you painfully hand-copied over, if you no longer need it, and kill your SSH sessions.

Epilogue

While this worked great, and I was able to get back in and see my router configuration, I wasn’t able to spot any problems.

That’s when I realized my Mac’s VPN configuration was hard-coding my old IP address and not the domain for my home network. Oops 🙁

Hope this helps someone!

Weird bugs: Django, timezones, and importing from eggs

Leave a Comment / Development

Every so often you hit a bug that makes you question your sanity. The past several days have been spent chasing one of the more confusing ones I’ve seen in a long time.

Review Board 1.7 added the ability to set the server-wide timezone. During development, we found problems using SSH with a non-default timezone. This only happened when updating os.environ[‘TZ’] to something other than our default of UTC. We’d see the SSH process (rbssh, our wrapper for SSH communication) break due to an EOF on stdin and stdout, and then we’d see the development server reload itself.

Odd.

Since this originated with a Subversion repository, I first suspected libsvn. I spent some time going through their code to see if a timezone update would break something. Perhaps timeout logic. That didn’t turn up anything interesting, but I couldn’t rule it out.

Other candidates for suspicion were rbssh itself, paramiko (the SSH library), Django, and the trickster god Loki. We just had too many moving pieces to know for sure.

So I wrote a little script to get in-between a calling process and another process and log all communication between them. I tested this with rbssh and with plain ol’ ssh. rbssh was the only one that broke. Strange, since it wasn’t doing anything obviously wrong, and it worked with the default timezone. Unless it was Paramiko somehow…

For the heck of it, I tried copying some of rbssh’s imports into this new script. Ah-ha! It dropped its streams when importing Paramiko, same as rbssh. Interesting. Time to dig into that code.

The base paramiko module imports a couple dozen other modules, so I started by narrowing it down and reducing imports until I found the common one that breaks things. Well that turned out to be a module that imported Crypto.Random. Replacing the paramiko import in my wrapper with Crypto.Random verified that that was the culprit.

Getting closer…

I rinsed and repeated with Crypto.Random, digging through the code and seeing what could have broken. Hmm, that code’s pretty straight-forward, but there are some native libraries in there. Well, all this is in a .egg file (not an extracted .egg directory), making it hard to look through, so I extracted it and replaced it with a .egg directory.

Woah! The problem went away!

I glance at the clock. 3AM. I’m not sure I can trust what I’m seeing anymore. Crypto.Random breaks rbssh, but only when installed as a .egg file and not a .egg directory. That made no sense, but I figured I’d deal with it in the morning.

My dreams that night were filled with people wearing “stdin” and “stdout” labels on their foreheads, not at all getting along.

Today, I considered just ripping out timezone support. I didn’t know what else to do. Though, since I’m apparently a bit of a masochist, I decided to look into this just a little bit more. And finally struck gold.

With my Django development server running, I opened up a separate, plain Python shell. In it, I typed “import Crypto.Random”. And suddenly saw my development server reload.

How could that happen, I wondered. I tried it again. Same result. And then… lightbulb!

Django reloads the dev server when modules change. Crypto is a self-contained .egg file with native files that must be extracted and added to the module path. Causing Django to reload. Causing it to drop the spawned rbssh process. Causing the streams to disconnect. Ah-ha. This had to be it.

One last piece of the puzzle. The timezone change.

I quickly located their autoreload code and pulled it up. Yep, it’s comparing modified timestamps. We have two processes with two different ideas of what the current timezone is (one UTC, one US/Pacific, in my case), meaning when rbssh launched and imported Crypto, we’d get a bunch of files extracted with US/Pacific-based timestamps and not UTC, triggering the autoreload.

Now that the world makes sense again, I can finally fix the problem!

All told, that was about 4 or 5 days of debugging. Certainly not the longest debugging session I’ve had, but easily one of the more confusing ones in a while. Yet in the end, it’s almost obvious.

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