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FreeBSD/WPA

Since I got my Mac some of my FreeBSD projects have been languishing on the back burner. Two are important, getting an IPSEC tunnel using IKE between FreeBSD (racoon) and OpenBSD (isakmpd frontended by ipsecctl) and getting WPA going. A couple of months ago I replaced WEP with wpa in my home wifi setup. There’s no arguing that the security is better and on the Mac it’s drop dead simple. I never understood what was going on in FreeBSD I understand it now. WPA appears to be divided into two parts like IKE. One part runs on the client and another in the Wireless AP. FreeBSD includes a program called wpa_supplicant which manages the WPA key exchange for you. To handle this it also has to manage the wireless interface. The automatic setup is actually pretty easy. I found this which helped me out. I wanted to understand what was going on under the hood. It turns out the setting up the config per the original article is the first step. Then run:

wpa_supplicant -B -Dbsd -iath0

as root. This handles the WPA negotiation. When ifconfig reports that you are connected you can run dhclient ath0 to connect.

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Dav backended web servers

My father-in-law asked a question about email the other day that perplexed me. We recently got him a Mac and he was complaining about the “spinning beach ball of death” when he tried to send a message. It turns out that the message was 50 full sized digital photos for my brother-in-law. After he explained that detail it made sense that Mail was choking. I told him that the mail was simply too big and that the better way to share the pictures would be to post them in a website. I also promised to come up with a solution for him in a week or so and give him a helping hand getting everything posted.

Normal people would look at Picasa or Flickr or something but neither of those sites interest me. Most of the photo sites on the web  want you to sign up which infringes on my privacy. They grant you some promotion through search engines for the privilege but Bapa doesn’t need the world to be able to see his photo album. To my “Open source guy” brain the immediate solution would be to create the site and then setup something like coppermine or gallery2 but both of those solutions require me to teach Bapa how to post to a photo web site. Picasa and Flickr have the same issue.

Fortunately for me, Bapa has a Mac. The Mac has a set of wonderfully integrated tools for doing exactly this sort of thing. I decided that the easiest thing to do would be to Apache and mod_dav to grant access to some web space. And then use apache to publish a site from within the web space. The Apache config is actually pretty simple. You use two virtual hosts. One points to the backend and one points the actual site. Here’s the apache2 config for the backend:

<VirtualHost *:80>
    ServerName      backend.example.com
    ServerAlias     backend

    ServerAdmin     webmaster@example.com

    DocumentRoot    /home/www/sites/backend.example.com/
    DAVLockDB       /var/www/DavLockDb

    <Directory "/home/www/sites/backend.example.com/Dav/">
        Dav On
        AuthName    "Photo DAV Fileshare"
        AuthType    Basic
        AuthLDAPURL ldap://ldap-slave.example.com/ou=people,dc=example,dc=com?uid
        <LimitExcept GET HEAD OPTIONS PROPFIND>
            require valid-user
        </LimitExcept>
    </Directory>

    ErrorLog        /home/www/sites/backend.example.com/log/error_log
    CustomLog       /home/www/sites/backend.example.com/log/access_log common
</VirtualHost>

The goal here is to provide DAV access to the web sites storage so the Macintosh toolkit sees it as just another place to store files. The Directory setting tell Apache to provide the Dav directory and everything below it as a shared file system using the DAV protocol. In this case authentication is provided via LDAP but that could easily be changed to .htaccess files.

The actual web sites virtual host config is here.The trick is in setting DocumentRoot to be a subdirectory of the Dav provided above.

<VirtualHost *:80>
    ServerName      photos.example.com
    ServerAlias     photos

    ServerAdmin     bapa@example.com
    DocumentRoot    /home/www/sites/backend.example.com/Dav/photos

    ErrorLog        /home/www/sites/backend.example.com/log/error_log
    CustomLog       /home/www/sites/backend.example.com/log/access_log common
</VirtualHost>

The result is that Bapa can attach the file structure that contains his photo share as a DAV imported file system from his Mac (Finder: Go -> Connect to Server – http://backend.example.com/Dav/photos. Then tell iWeb to publish his website into that space et voilá: his pages are magically published to the web under photos.example.com.

This is about 90% of your setup. You will want to secure things to make sure that they aren’t easily broken. Apache accesses the Dav as user: www so it’s pretty important to make sure that the DAV directory is protected from tampering by having it owned by root:

# mkdir -p /home/www/sites/backend.example.com/Dav/photos
# chown root:root /home/www/sites/backend.example.com/Dav
# chmod 775 /home/www/sites/backend.example.com/Dav
# chown root:www /home/www/sites/backend.example.com/Dav/photos
# chmod 775 /home/www/sites/backend.example.com/Dav/photos

These permissions setup the Dav share so that an object stored in the root of the Dav may only be deleted or removed by its owner. The DocumentRoot of the photos site can be written into by the www user. This isn’t meant as absolution security as much as a means to keep down support calls.

Caveats

In this example I’m doing nothing to protect Bapa’s password from interlopers on the net. In reality you would want the DAV to be provided over https to protect the password. A VPN connection is another possibility.

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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…”

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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.

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Trackback Spam

Someone is attempting to spam my blog pretty heavily through trackbacks. This is stupid. It’s never going to work since I have so few comments here anyhow that I moderate all of them. It only serves to annoy me by generating an email saying that I have comments to moderate. My original thought was to block inbound packets from the offenders. It would be pretty simple. Add a table to my firewall config and then use a little shell script magic (grep, awk etc) to pull the addresses from the log an load them into the table. But a quick pass through sort confirmed that these attacks were coming from mostly different addresses. For now I’ve disabled trackbacks by disabling the php file that supports them. Next up change my mail filter to quarantine the emails appropriately. Sigh.

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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.

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Should I use SPF?

Should I use SPF? What is SPF? Will SPF reduce the amount of spam that I get to my domain? There’s a lot of talk about SPF as a means of preventing spam these days and though it was originally designed to do that I’d have to put it down as a miserable failure at spam prevention. Does that mean that you shouldn’t use it? The juries still out on that one.

SPF stands for Sender Policy Framework. It’s a means of specifying where mail from a specific domain will come from. The implementation is an ugly kludge that overloads DNS TXT records. Through the overloaded records a remote server which is receiving a mail that claims to be from your domain can determine if it is real or a forgery… …maybe. It turns out that mailing lists that forward mail without rewriting the envelope headers as well as older mailers like mutt which still have a bounce forwarding feature will most likely false positive (e.g. receive an SPF fail).

SPF probably won’t reduce the amount of spam you receive. In fact don’t be surprised if you start to receive or are currently receive quite a bit of spam that passes the SPF tests. Many of the “more reputable” spammers, the ones sending spam using real mailservers and not hijacked windows machines on a botnet, use SPF to fool your spam filter into thinking that a piece of spam is a legitimate mail.

Should you use SPF? That depends on what you want. If you want a spam free inbox then look elsewhere. Under no circumstances should you ever assume that a piece of mail that is marked SPF fail is spam. In fact you are better off ignoring it when you test to determine the level of spammyness of your inbound mail stream. SPF does have one big positive and this is big enough that I recommend that people use it if they can.

It turns out that if you do enable SPF on your domain then spammers will no longer be able to forge messages from you as spam. To the postmaster of the domain this means that a large chunk of the those bounce messages from tens of thousands of people who don’t exist don’t get sent to you. You know what I mean the mail from postmaster@yahoo.com that says that mail from johnbigbooty@example.com to drlizardo1287341@yahoo.com failed because there is no drlizardo128341. If you enable SPF the smarter spammers will not put your domain into the from field of an outgoing spam since then people can tell it’s a forgery.

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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.

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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……

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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.