CLI

Slow SSH login

tl;dr – my SSH client was attempting an IPV6 connection; my internet connection does not support IPV6

So. For a couple of weeks now, on and off, I’ve been trying to track down the source of my personal server being slow to log in via SSH.  IT was slow… say… 98% of the time, and 2% of the time it was fast.

I thought maybe it was compromised somehow (and I did find some xmlrpc pingback reflection attacks being done using a site of mine… which I fixed) but it didn’t appear to be so.

Then I thought maybe it was some sort of network exhaustion. But my bandwidth, and my tcp connections as reported by netstat all looked very low.

I had some swap used, so I thought maybe there was something important in swap slowing the system down.

I checked the usual suspects (dns resolvers, etc) and nothing. I checked my 2 factor authentication setup. Again nothing. I checked my sshrc script. Nada.

Turning to google and the various .*exchange(like)? site answers I tried setting usedns to no, and GSSAPIAuthentication to no. I cleared out some hosts.deny|allow entries, I even disabled some dynamic things in PAM for SSH, and finally turned PAM authentication off completely.  disabled and configured the server not to use avahi

Nothing worked. Everything looked good… sshd loglevel was set to verbose and not giving me any signs… using ssh -v to connect didn’t show me anything out of the ordinary

Well that’s not true. It showed the problem but it wasn’t an “error”, so to speak, and so I didn’t immediately notice it.

It turns out that, since my server has an IPV6 address my ssh client was attempting to connect to it via IPV6 first.  This is problematic because my internet connection has no such support.

Setting “AddressFamily inet” for “Host *” in .ssh/config fixed things right up.

I want to say this started happening right around the time I upgraded to OSX Yosemite (GM candidate), but I couldn’t swear to that.

Debian, ProFTPD, FTPS, TLS, SSL, and SSL23_GET_SERVER_HELLO:unknown protocol

Recently I needed to test against an FTPS server. No big deal, I thought to myself, I’ll just set one up real quick. Boy did I end up having a hard time with that. Not because the task was actually hard but because there’s a bit of a general haziness about the whole idea of what FTPS is. More on that later.

The first thing I did was setup my Debian ProFTPD server via the included /etc/proftpd/tls.conf. Restarted ProFTPD, and then tried curl -v -v -k ‘ftps://localhost’ which immediately resulted in the following error

* About to connect() to localhost port 990 (#0)
*   Trying 127.0.0.1... Connection refused
* couldn't connect to host
* Closing connection #0
curl: (7) couldn't connect to host

Oh, right, It’s listening on port 21 not port 990… curl -v -v -k ftps://localhost:21/ which gave me this error

* About to connect() to localhost port 21 (#0)
*   Trying 127.0.0.1... connected
* Connected to localhost (127.0.0.1) port 21 (#0)
* successfully set certificate verify locations:
*   CAfile: none
  CApath: /etc/ssl/certs
* SSLv3, TLS handshake, Client hello (1):
* error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol
* Closing connection #0
curl: (35) error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol

Believe it, or not, I got stuck here for more than an entire day. Which is kind of embarrassing. I googled the hell out of this issue, and got lots of advice which centered about generating appropriate certs, and using “openssl s_client -connect 127.0.0.1:21” to test (which resulted in, essentially, the same error: “14996:error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol:s23_clnt.c:607:” )

With the help of a friend from work we found what I had been overlooking. You see FTPS can mean one of two very different things.

FTPS can mean FTP with explicit SSL. This is where you connect to FTP, then give a command to encrypt the session after the initial plaintext connection has been established.

FTPS can also mean FTP with implicit SSL. This is where you connect to the ftp server and the connection is encrypted before any commands are sent (this is like having HTTP on port 80 and HTTPS on port 443, except using 21 and 990 for FTP.)

The two types of FTPS are not compatible with one another. Apparently FTPS/Implicit is no longer a part of the standard, but still “around” and “supported” by “things”. And curl thinks you mean this when you give it a url of ftps://something. FTPS/Implicit is also the kind of stream that “openssl s_client -connect 127.0.0.1:21” would test. FTPS/Implicit is not the configuration setup by /etc/proftpd/tls.conf. Which is why my testing failed, frustratingly, for so long.

Since ProFTPD uses FTPS/Explicit by default… how do you test? With very similar commands to the ones I used previously (lending to the confusion…)

openssl s_client -connect 127.0.0.1:21 -starttls ftp

curl -v -v -k --ftp-ssl ftp://localhost:21/

Ok. Now I’m able to setup and test an FTP/E server. What if I also need to setup and test an FTP/I server too? Thats pretty simple. in ProFTPD 1.3.3rc2, the mod_tls module was enhanced to support implicit FTPS via the UseImplicitSSL TLSOption. So by adding “TLSOption UseImplicitSSL” on an appropriately new version of ProFTPD and mod_tls you can have a server that works with “curl -v -v -k ftps://localhost:21/” and “openssl s_client -connect 127.0.0.1:21”

I hope that this saves someone else the headaches that going through all of this gave me. Had I read through the ProFTPD TLS howto carefully, instead of just searching for what I thought I needed, I would have solved this all much more quickly.

AirPort ♡ Free IPV6 From TunnelBroker.net

After signing up for a (free) account on tunnelbroker.net and creating a (free) tunnel with my ipv4 address as the endpoint I was able to easily configure my AirPort Extreme. View your tunnel, then click on “Example Configurations” and then “Apple Airport.”

In TCP/IP prefs for my MacBooks Network/AirPort Preferences I have “Configure IPv6” set to “Automatically” Then BOOM “ping6 en.blog.wordpress.com” works just fine.

IPv6 without needing my ISPs support and it didn’t cost me an extra dime. Happy World IPv6 Day

OnLive, Max, Xbox360 controller

Did you know that the OnLive OSX app has its own built in drivers that work out of the box with your wired Xbox360 controllers? I found this to be fantastic, but I had already installed the tattiebogle.net controller driver it works, but it conflicts with OnLives use of the device so I couldn’t use it where I wanted to use it. There were no handy instructions on uninstalling them, so I did it manually. Here’s how: back-up and then delete the /System/Library/Extensions/360Controller.kext and /System/Library/Extensions/Wireless360Controller.kext directories from your mac (you’ll need to be root to do this.) after a reboot the driver is gone and OnLive will recognize it. hope this helps someone.

Linux AFP server going slow?

Recently I found that it was taking appauling amounts of time to transfer files to/from my debian file server setup with netatalks AFP. I upgraded to the latest version to no avail, but this trick helped out quite a lot — http://www.netafp.com/tn003-slow-afp-read-performance-90/

Incidentally I believe, unscientifically, that it also helped my OnLive game latency quite a lot (on OSX)

elockd [more] publicly available

I’d call this an 0.5 release. It’s now in the code repo that we at Automattic use to put out little open source tools.

I’ve fixed several bugs with the code since the first time that I posted about it. It can handle at least 2k active connections, and at least 100k shared and exclusive locks (split 50/50) and can handle every single connection orphaning its locks at the same time for both shared and exclusive locks.

It’s a pretty good bit of code… not bad for under a week in my spare time.

I suppose that I should explain what it is and does. And why I care.

The idea behind lockd was to build a network oriented daemon which would handle arbitrary locking of… things. The idea was to mix the ease of Memcached with the atomic chewy goodness of MySQls named locks. It’s really handy to have something like this that can be depended upon when you have a very large distributed environment to keep things from stepping on its own toes.

Only one client can have an exclusive lock, and only the lock owner can release it. any client can inspect that exclusive lock to see if it’s held or not. If the owner disconnects from the server then all of the owned locks are released.

Any number of clients can acquire a shared lock, and the result of the locking action includes the number of other owners sharing that lock. The response for the first lock request would be 1 lock acquired, while the second lock request for the lock would be 2 lock acquired (i.e. two people have this lock.) Likewise releasing the lock decrements it, and inspecting the lock shows the number of open handles to that lock. All of an owners shared locks are also released on disconnect.

Oh, did I mention that it also keeps stats for you to use in your munin graphs? Yea. That too.

So… some obvious questions I’m sure you’re wondering:

1: why not just use Memcached? Well Memcached has no knowledge of the state of your connection. I want a lock that goes away if the parent process disconnects for any reason. You could do this with timed keys in Memcached but you run two risks: the first being that you might not get around to updating the lock and resetting its ttl before it expires leaving another process able to lock erroneously, and the second being that given enough data flowing through the cache your lock might simply be pushed off the back end of the cache by newer data — something that I don’t want. Also shared locks would be difficult here.

2. Why not just use MySQL named locks? You can only hold one named lock per connection, and there is no concept of shared named locks.

3. Why not use filesystem locks? Those tend to be difficult for people to code properly, depend on various standards implementations, cant do counted shared locks, and most importantly aren’t network enabled.

4. Whats the big deal about shared locks? They’re super powerful — great for rate limiting, etc.

5. Wasn’t there already something out there for this? I’m not going to say “no,” but I will say “not that I saw when I looked”.

6. Why did you rewrite it in erlang, was the PHP version bad? Yes, sort of, the PHP version played some interesting tricks to achieve a thread-like operational state, but I believe that there are timing issues because of those tricks that cause it to crash in as-of-yet unknown circumstances at high load. The PHP version is also slow when there are a very high number of clients or locks. Erlang was, essentially, born for this particular purpose since it sports great concurrency models immutable variables, and the way that the gen_* things work out I get atomicity built in even with all these concurrent clients grabbing at stuff.

7. Whats the API look like? It looks nice and clean…

“g $key
” — get exclusive $key
“r $key
” — release exclusive $key
“i $key
” — inspect exclusive $key
“sg $key
” — get shared $key
“sr $key
” — release shared $key
“si $key
” — inspect shared $key
“q
” — show stats

elockd

I’ve been working on an erlang port of my php locking daemon in erlang (which is a more appropriate language for this kind of thing.) And I have it all tricked out (ok partially tricked out but hey it’s my first real erlang project and i’ve only spent 2 afternoons on it.)

The api is completely the same between the two (read: simple), and it works great (in my tests.) It supports both exclusive and shared locks, orphaning on disconnect works great for both, stats are working, it’s all running under a supervisor to restart anything that stops, I *think* i’ve done the code well enough that hot code swapping should work as expected. I know there’s a lot of “how an erlang application is packaged” stuff that I don’t know yet.

If i had to describe in a one-liner what this does i would say that lockd is MySQL named locks meets Memcached.

I’m kind of annoyed, however, that “erl -s esuper” doesn’t run the stupid thing, I have to actually run esuper:start(). to get it going. I’ll have to figure that out. You would think that running some precompiled beams/modules/functions/args would be super easy from the outside a-la-init-script, and it probably is but I’m missing something.

Comments on the code are welcome. It’s a pretty cool little thing — my [lack of] mad erlang skills aside.

When I’m ready I’ll be testing it in production, and putting it in a public repo.

Using PHP and OpenSSH with username/password auth

It turns out that this is actually a tricky problem. It’s super easy to use the OpenSSH command line stuff via PHP when you have key based authentication set up, but it’s not at all easy to use when you want to go the user/pass route. This is for a couple of reasons:

First you cannot specify the password on the command line. Second you cannot use the php process controls directly to give the password (well this isn’t 100% true, if you want to recompile your PHP binary with pty support then you probably could bypass everything I’m about to say and just use proc_open straight). And there’s a third reason that I’ll get to in a bit.

OpenSSH supports getting a password from an executable program via the SSH_ASKPASS environment variable — with two notable gotchas. First this only works if you also specify a DISPLAY environment variable, and second it does NOT work if the controlling process has a tty or pty.

The code below works… but if you just paste it into a script file and run it directly with php ./myscript.php it fails. Why?

function ssh_user_pass_port_forward( $hostname, $username, $password, $localport, $remotehost, $remoteport ) {
	$descriptorspec = array(
	        0 => array("pipe", "r"),  // stdin is a pipe that the child will read from
	        1 => array("pipe", "w"),  // stdout is a pipe that the child will write to
	        2 => array("pipe", "w")   // stderr is a file to write to
	);
	$script = tempnam( '/tmp/', 'askpass-');
	file_put_contents( 
		$script, 
		"#!/bin/bash
echo -n ".escapeshellarg( $password ) 
	);
	chmod( $script, 0755 );
	$env = array( 
		'DISPLAY' => '0', 
		'SSH_ASKPASS' => $script 
	);
	$forward = sprintf(
		"%d:%s:%d",
		$localport,
		$remotehost,
		$remoteport
	);
	$command = sprintf(
		"/usr/bin/ssh -n -o StrictHostKeyChecking=no -l %s -L %s -N %s",
		escapeshellarg( $username ),
		escapeshellarg( $forward ),
		escapeshellarg( $hostname )
	);
	return proc_open( $command, $descriptorspec, $pipes, getcwd(), $env);
}

The answer is that you are running it, and you’re running it from a shell which has a tty or pty attached, and the script inherits those and OpenSSH sees this and then ignores the SSH_ASKPASS variable completely. The trick to testing/using this code is to execute it without running it from a terminal. If you execute the command below (roughly) it looks like it hangs. but if you open another terminal you should be able to use the port forward just created.

ssh myserver.com “php /path/to/myscript.php”

This is because since you’re sshing for the sole purpose of running that command and not using a shell the system doesn’t allocate you a pty like it would normally. I’m guessing that executing it via an http request would do something similar.

Since I previously posted some hard-won advice for working with ssh2_* in php I thought I would share this equally tricky bit that I’d also figured out in the process.

Remember that there is ALWAYS more than one way to skin a problem, and every problem can be skinned with enough effort.

Again, this is itch-scratch-ware, YMMV, this is meant as a starting point on a journey to a solution and not a drop-in-works-everywhere bit of code. It’s just the hard stuff. The useful stuff is still up to you 😉