Old Code does die

I have a very old VA Linux 2200 box that I use a firewall. I recently upgraded it a later version of OpenBSD but it appears that I’ve found a regression in the X Server. This machine uses the Intel 440Gx Chipset with an integrated Cirrus Logic CL GD5480 Video adapter. It looks like the support for the video adapter has fallen out of Xorg 7.2 since the old OpenBSD could drive this box at 1280x1024x16bpp even though the box only has 2M of video RAM (If you do the math, don’t ask me I’m trying to found out how myself).  The new driver can’t do this. I’ve spent a few hours trying to find Doco for the chipset in Xorg but the man page is another one of those “This section needs to be completed things…”

Use the source, Luke!

I wrote earlier about SASL and postfix. One side affect of my setup has been that I get these spurious warnings in my logs.

Apr 4 10:22:19 corellia postfix/smtpd[69626]: auxpropfunc error invalid parameter supplied

I’ve been meaning to throw some time at this problem for a while now but everything works so I haven’t. Upgrading my infrastructure to the latest Open and FreeBSD’s has me using newer packet filtering code with more capabilities so what was once a non-problem has become a pain in the neck. This problem is tied to another feature of cyrus sasl that if find annoying. The configuration for postfix and cyrus is handled through a file called smtpd.conf. This file is stored in /usr/local/lib/sasl2/smtpd.conf. This is annoying for one because under Unix configuration files like this belong in /etc. But for two because the file is poorly documented at best. Reading the source for postfix shows that this is handled by the smtpd_sasl_path. It’s already well documented that this variable isn’t a path, it’s the base file name for the configuration file. This is fixed in postfix 2.5. The warning comes from the initialization of the ldapdb component of sasl. Even though I’m not using it I have to specify the parameter ldapdb_uri.

Keeping up to date with FreeBSD

I use FreeBSD for nearly anything that needs a server. It’s got quite a bit to offer. Anyone who actually knows FreeBSD knows that it’s dead simple keep up to date. I’ve used this basic technique for several years.  The steps are pretty simple and can be found here with additional instructions for dealing with multiple machines here.  I’ve pretty much followed this method for years including updating a machine located in a remote close with an NFS mounted /usr/{src,obj} over an IPSEC link. I recently added a new wrinkle that I think is pretty cool. My build box is an HP/Compaq DL360 with hardware RAID. I’ve pretty much standardized on this hardware. A client clued me into this simple technique. Long story short he had to move a data center from Chicago to CT and he chose to do it by stocking up on spare RAID drives. He cloned a server by pulling a working drive from a working server and replacing it with a spare. He shipped the pulled drive via courier to the new data center. Installed it in the correct slot on the same kind of server chassis booted the new clone up. At this point the clone server now saw it’s drive array missing the other drive. He was obviously mirroring. On insertion of the new drive the clone server hardware did an automatic rebuild. I apply the same technique to FreeBSD. I build a new server from the lastest snapshot then go through the source update process. Next I pull one of the drives and put the pull aside replacing it with a spare.  Et voila. Now I have a save point on that Drive. I can install it in the server alone an reboot. and I’m right at the point where I have built and installed the world and have just finished running mergemaster. This is an excellent starting point for building a fresh server.

Lil’ Bobby Tables

A while back I found xkcd. I found it through a mailing list but this post grabbed my attention. Here’s a recent comic which made me think about the way that popular web applications use SQL databases. If you don’t get it the
Mom in the comic executed a classic SQL injection attack against her son’s school. (BTW I didn’t want to spoil the joke. You can see the previous sentence by highlighting it with your mouse.) In any case this is a common attack method against many current web applications and it shows just how naively many of the programmers are of SQL in general. There are two practical ways to defend against this attack. The most obvious is to validate your SQL before you pass it to the database engine. One that requires a little more thought would be to disallow the web database user from being able to DROP TABLES in the first place. Any real web application should expect a database with at least two users, root, or dba and webuser, or www. Root should be allowed to do anything to the database but his credentials need to be protected. If your web application has grown to the point where you’ve split your database server from your webserver for performance purposes. Allowing the root or dba level of access from localhost only is a good start. Webuser should be able to SELECT on your applications tables. He should be able to INSERT, UPDATE, and DELETE on a limited subset of tables as your database will allow. He may need to be able to CREATE a temporary table and possible DROP the same but that’s a job that’s really better done by a stored procedure. E.g. create a stored procedure that does the needed manipulation and then allow the webuser the privilege to call the stored. Obviously what you can do here depends on your database. I know that Postgresql can grant these very fine grained security settings. If I recall correctly MySQL is a little more course but is still workable.

Hylafax: Ugh

I tried to setup hylafax today. I had it going a few years ago. I even had a neat hack where I would have it take all inbound faxes, convert them into pdf and store them in directory accessible from the web. It was pretty cool. I figured I’d re-create that and maybe add some Python-Fu to have an outbound directory but alas it wasn’t meant to be. I ran around in circles for three hours trying to eliminate the problems but got no-where until I installed efax and right off the bat the fax just worked. That eliminated the problems of (The modem broke between last time and now, the modem doesn’t like the VoIP line, and my new HP A-I-O doesn’t like the fax modem) leaving Hylafax is misconfigured. Here we go again, another mailing list……

More stuff about Postgresql that should be obvious.

I’ve been scratching my head on this one for far too long. I have a query under Postgresql which retrieves the distance between too points given the knowledge of their zipcodes. This work because I have an incomplete table of mileages between arbitrary three digit zipcode pairs. Each time I use this table my queries take a long time and I could never understand why. It has to do with the type that postgresql assigns to computed text fields. I was doing something like this:

SELECT * FROM worklist INNER JOIN partial_zipcode_mileage ON SUBSTRING(worklist.origin_zipcode, 1, 3) = partial_zipcode_mileage.origin_partial_zipcode...

The issue here is the type of the expression: SUBSTRING(worklist.origin_zipcode, 1, 3) as compared to the type of the field partial_zipcode_mileage.origin_partial_zipcode. The latter is a SQL CHAR(3) since it will always hold 3 characters. Postgresql assignes the first expression a type of TEXT since it has know way to know how bit a field you actually want. This prevents the postgresql engine from using the index and this, my query takes along time. Substitute SUBSTRING(worklist.origin_zipcode, 1, 3)::char(3) in the statement and all is happy.

Exception trapping in pl/pgsql.

Learned a new trick with postgresql stored procedures today. This will probably appear to be obvious but it’s new to me. You can do exception trapping in pl/pgsql by you can also ignore some errors. The form is:


BEGIN
DROP TABLE foo;
EXCEPTION
WHEN undefined_table THEN NULL;
WHEN OTHERS THEN
RAISE NOTICE, ('Notice: ' || SQLSTATE || ' - ' || SQLERRM);
END;

Most MTA’s should offer SSL/TLS

Most MTA’s should offer Opportunistic TLS by default

I think that the time has come for most SMTP MTA servers to offer STARTTLS session protection by default. I see two reasons for doing this. Firstly, it takes a short amount of extra time and a little more CPU horsepower and that’s a resource that spammers cannot control. Secondly, opportunistic TLS brings email security a little more in line with the security model that most users expect.

Spammers

The majority of spammers out there are relying on stealing CPU time on machines that they don’t own. I don’t see them moving to TLS at the client side anytime soon. On the other hand legitimate email senders usually aren’t sending mail in such bulk that the cost of encrypting the session would be an onorous penalty. The practical end result of this would be differentiation of mail at the inbox. We would get mail from servers that used TLS to encrypt the session and mail from servers that didn’t. Assuming that the MTA server flagged the mail on this axis by adding a header, the end result is a hook for a statistical spam filter to use.

Users expectation

The second advantage would be a little added security in email during the transport from client MTA to server MTA. If everyone adopted opportunistic TLS encryption of the wire then sending email would better approximate the users expectations for security. Compared to physical mail email without TLS is like sending a postcard. No one sends postcards where security is a requirement because it’s obvious that everyone between the point where you drop the mail in the postbox and  the point of delivery  can just read the mail. Most users don’t expect that this is the case with email right now.

The advantage of opportunisticaly encrypting the mail is that we have a situation that we can grow into. If some server doesn’t do TLS in transport the mail still gets delivered.

Greylisting + MS Exchange 2003

I’m using greylisting to filter spam. It works quite well. If you aren’t of the technique this is how it works. Greylisting filters spam by testing the RFC compliance of the server that is trying to send mail to you. RFCs 2821 and 821 describe the meat and potatoes of sending email on the internet. The RFCs both specify that the receiver may tell the sender to queue the message and retry later because the receiver is temporarily out of resources. Greylisting exploits this to sift spam from legitimate email because many Spam sending programs cannot queue mail. As a method of spam detection Greylisting is great because it takes almost no resources on the receiving side to filter. Other methods of filtering are not so resource friendly. I find that Greylisting is rejecting over my inbound 90% of the spam. I used to say that it did this with 0 false positives but after reading these two threads I’m not so sure:

Leave it to Microsoft to rain on the parade.

I’m not going to stop Greylisting. It’s just been too effective at spam removal for me to even consider going without. I’m also aware of several people who are using Exchange to contact me who have not run across this problem. For me the solution to this potential problem is to contact some of the people who I know that are running Exchange and see what their awareness is on this problem.

Templating in Joomla and WordPress

Vindaloo backgroundI haven’t been writing in a while. It’s not because I don’t love it, I’ve been ramping up on a couple of projects and quite frankly that’s what I’ll be doing in about 10 minutes.

Among other things I’ve been using the Gimp to generate a new template for Vindaloo.com. I need to give credit where it’s due here. The person to talk to about this is Al Gordon. Vindaloo will be moving to Joomla soon. I’m writing a white paper on spam prevention and a few other things. I want to have a common theme for both this site and my Joomla site so I need to learn templating for both Joomla and WordPress. For Joomla the best thing seems to be PhotoShop and Dreamweaver. for the Open Source Developer who is on a budget. You can trade more time for less money and use the Gimp and Nvu. Nvu has a Mambo/Joomla Template Generator which is okay. If you are using FreeBSD and nvu make sure to get the latest copy of the port. I submitted a patch a month or so ago to enable Cascades, nvu’s CSS editor which is okay. Software:

Tutorials: