Friday, May 30, 2008

warning: SASL authentication failure: cannot connect to saslauthd server: No such file or directory

There's nothing quite like being in a complete coding frenzy, communicating with your customers to get feedback on critical bugs, and your mail server going to SMTP heaven on you.

The Setup
My MTA (postfix) is set up to do secure SMTP-AUTH and TLS via Cyrus SASL library (a.k.a. saslauthd via the sasl2-bin package) on an Ubuntu box.

Postfix SASL support (RFC 4954, formerly RFC 2554) is used to authenticate remote SMTP clients to the MTA and the Postfix SMTP client to a remote SMTP server.

The Error
I originally set things up via the Postfix-SMTP-AUTH-TLS-Howto and everything was working fine until earlier today when I started seeing the following log entries when trying to send mail vi the MTA:
May 30 03:03:36 pyxidis postfix/smtpd[2840]: connect from unknown[x.x.x.x]
May 30 03:03:37 pyxidis postfix/smtpd[2840]: setting up TLS connection from unknown[x.x.x.x]
May 30 03:03:40 pyxidis postfix/smtpd[2840]: Anonymous TLS connection established from unknown[x.x.x.x]: TLSv1 with cipher AES128-SHA (128/128 bits)
May 30 03:03:40 pyxidis postfix/smtpd[2840]: warning: SASL authentication failure: cannot connect to saslauthd server: No such file or directory
May 30 03:03:40 pyxidis postfix/smtpd[2840]: warning: SASL authentication failure: Password verification failed
May 30 03:03:40 pyxidis postfix/smtpd[2840]: warning: unknown[x.x.x.x]: SASL PLAIN authentication failed: generic failure
May 30 03:03:46 pyxidis postfix/smtpd[2840]: lost connection after AUTH from unknown[x.x.x.x]
May 30 03:03:46 pyxidis postfix/smtpd[2840]: disconnect from unknown[x.x.x.x]
The Solution
I checked and the saslauthd process was happily running. Next up I had a peek in /var/spool/postfix/var/run/saslauthd/ (which I had previously created as per the HOWTO above) but there were no *mux* files to be seen as there should have been.

I then dawned on me that postfix runs in a chrooted jail and that saslauthd for some reason had stopped writing the required info to the chrooted jail where postfix was running. A quick look at the saslauthd rc script and its default file showed that it no longer had the required config to do this properly.

Why? Dunno. I'll have to go do some snooping a little later.

For now thought the fix was as simple as modifying the OPTIONS variable in the /etc/defaults/saslauthd config file to be something like this:
OPTIONS="-c -m /var/spool/postfix/var/run/saslauthd"
Restart saslauthd and things start appearing where they should and mail is back in business.

Cacti Segfaults

I recently did a cacti installation for a customer and ended up skipping step #3 from the Install and Configure Cacti guide.

Step in question:
shell> mysql cacti 
Why would I have skipped this very crucial step you might say?

Well, the installation was done in two sessions with enough time having elapsed between the initial and final sessions that I had gotten hazy on what was and wasn't done. I had created the database but just never took the next step.

After completing the rest of the configuration I fired Cacti but via my browser and php promptly did a segfault and lay there on the ground haemorrhaging. From my recent experience php has a propensity to do this in two specific cases:
  • Something went awry with a database connection or using a database resource
  • You're pushing the php boundaries with recursive regexps in a pre_match*() function
Once I sat down and went through each of the steps required to set the beastie up I realized I simply needed to import the db schema and initial data to get things going.


Saturday, May 24, 2008

Tales from the (PHP and Perl) Crypt - AES Encryption in MySQL

I was looking for a way to share encrypted information between two systems where a table in MySQL was the integration point.

The one system is based on php while the other component is a perl daemon.

Let's get cryptic
My first stab at this was a perl based solution using the Crypt::CBC and Crypt::Blowfish libraries plus a shared secret/key. This meant I had to develop a perl script which I called from php to do the encryption which is a rather inelegant solution.

At first I could not find the right libs in php to get this done but later stumbled upon the
Mcrypt suit off php and MCrypt perl functions that allow you to do encryption between the two different subsystems.

Unfortunately this means you have double the amount of hassle when it comes to updates and ensuring things Just Work™.

Move it back to the source
Some more checking brought me to the MySQL AES encryption functions that are built into MySQL. They provide the best cryptographic algorithms MySQL currently has to offer and are pretty respectable from a academic encryption perspective.

This means en/decryption is dealt with at one integration point across all languages involved which is much more elegant.

Tales from the Crypt
The MySQL AES encryption functions allow you to en/decrypt data quite easily. To encrypt a string you simply issue the following, assuming your shared secret is lesser-spotted-mountain-squid:
mysql> INSERT INTO test_table (test_column) VALUES(AES_ENCRYPT('this is a super-secret message', 'lesser-spotted-mountain-squid'));
Query OK, 1 row affected (0.09 sec)

mysql> SELECT * FROM test_table;
| test_column |
| Aÿ„1
ý#ôärO™é=:Žï ¼Ñ†kWA |
1 row in set (0.00 sec)
Et voila!

One thing you need to keep in mind is that the field you want to store your encrypted data in must be a MySQL
BLOB data type.

Sucking our super secret string back out into a usable form is as simple as:
mysql> SELECT AES_DECRYPT(test_column, 'lesser-spotted-mountain-squid') AS top_secret FROM test_table;
| top_secret |
| this is a super-secret message |
1 row in set (0.00 sec)
The security lesson
This is rather obvious but your security is only as strong as the weakest link in the chain. In this specific case I did not want to have clear text data in the db and achieved that amicably.

Because my secret is in clear text in two different systems I am rather exposed if those systems are not as secure as they could be. Lucky for my they are pretty much locked away from daylight so I'm not too concerned.

Tuesday, May 6, 2008

Ubuntu 8.04 and PAM SMB Password

For those of you who have taken the plunge to Ubuntu v8.04 (Hardy Heron) you may have noticed that your auth.log is being filled with the following:
May  4 03:17:01 example CRON[10796]: PAM adding faulty module: /lib/security/
May 4 04:17:01 example CRON[10799]: PAM unable to dlopen(/lib/security/
May 4 04:17:01 example CRON[10799]: PAM [error: /lib/security/ cannot open shared object file: No such file or directory]
What's up?
For some reason the Ubuntu gods have decided by default to include PAM configuration for the PAM SMB password module without actually installing the PAM SMB password module.

Hence the complaints in your logs.

Make it go away!
Sure, simply install the libpam-smbpass package or edit two config files on your system like this:

$ perl -p -i -e 's/(password\s+optional\ nullok use_authtok use_first_pass)/#$1/' /etc/pam.d/common-password
$ perl -p -i -e 's/(auth\s+optional\ migrate)/#$1/' /etc/pam.d/common-auth

You can find some more info on this boog here.

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I love solving real-world problems with code and systems (web apps, distributed systems and all the bits and pieces in-between).