codeblog code is freedom — patching my itch

May 24, 2006

easy wordpress anti-spam

Filed under: Blogging,Networking,Security — kees @ 11:06 pm

After getting about 40 moderation requests a day, I figured I should spend some time finding some anti-comment-spam plugins for WordPress. After digging around a while, I found one that doesn’t require JavaScript, doesn’t perform vision tests, but works just fine for the kind of comment-spam-bot that seemed to have taken a liking to my blog (even though no spam ever appeared in my comments ever…)

I found lr2Spam which has a great setup, but an incomplete final step. I merged it with ideas I saw in the RBL measures plugin, and got some good results. By replacing lr2Spam’s comment_post with pre_comment_content (see the WordPress Plugin API), I was able to redirect spammers away from from my site with PHP’s header("Location: [URL]") technique. (This is what I borrowed from the RBL plugin.) The patch is almost as big as lr2Spam itself (both are very small). Honestly, I’m surprised it works at all. Someone wrote a comment-spam bot that can’t correctly parse a totally valid HTML form, but does correctly handle a 302/Location redirect. Weird.

I thought briefly about redirecting all the spammers to[IP] but then realized their requests’ referer header would show my URL still. On further thought, I realized that comment-spam is very different from email spam because the bot has to implement a much larger set of protocol elements. Since they must respect the 302/Location redirect, someone who is getting hit really hard with comment spam could effectively DDoS somone’s link by redirecting to somewhere with big files. Say, for example, instead of using above, I used Every spam bot in their network would start a giant-ass download from after hitting my anti-spam system. Ewww.

Implemented early on May 20th, after 4 days, I’ve seen 250 comment spam attempts from 162 unique IP addresses (most in China — maybe they need to turn their firewall around). The volume of spam isn’t big when compared to my daily email spam statistics, but each one of those would have been an email in my inbox, asking for moderation. Interestingly, they all stopped on May 23rd. Maybe they got a clue.

© 2006, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

May 22, 2006

TiVoConnect dissector for Ethereal

Filed under: Multimedia,Networking — kees @ 9:03 pm

Over the weekend, I coded up a protocol dissector in Ethereal for the TiVoConnect Discovery Protocol. The protocol is very simple, but I still wanted the satisfaction of seeing it listed by name when scanning through my home network captures while debugging Galleon/TiVo traffic.

Ethereal has great developer documentation. It was easy to find and got me coding right away with a skeleton dissector. I just love the projects with these kind of to-the-point examples. The only thing I felt was missing from their README.developer was something showing that the dissector routine could return gboolean, letting a dissector reject being attached to a given packet.

There were other clearly written dissectors that I used for reference: DNS, Yahoo, and Syslog. They seemed to answer most of the more subtle questions I had about rewriting column text, scanning the packet, and dealing with other special cases.

Hopefully the patch will get accepted. I even did the randomized testing the wiki recommended. :)

© 2006, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

May 18, 2006

bleeding-edgeness matrix

Filed under: General — kees @ 11:22 pm

At least two times in recent history, I’ve wondered “is this the most recent version” of some piece of software, immediately followed by “which distro has the most recent version?” As I recall, these were for:

I had discovered both to be woefully behind “most recent” for a number of distributions. In my mind popped a vision of a chart/table/matrix of software on one axis and distros on the other, showing which had what versions of things. And little boxes where I could rank the “bleeding-edgeness” of a distro.

While hunting around, I found something almost like my vision. The distrowatch website is pretty damn cool. It wasn’t really set up to compare bleeding-edgeness between different distros, just different versions of a distro. For example, here’s Ubuntu’s matrix.

I exchanged some email with the author, and it sounds like he just uses a mess of custom scripts to poll version numbers of some of the more “big-name” software packages, common to most distros. Needless to say, mdadm and f-spot did not make the cut. I’d love to be able to add more “tracked packages” via some kind of web UI. A URL plus a regex to extract a version from; almost the same as what’s needed for WWW-PkgFind to operate. :)

From the pkgfind man page description:

… scans a web or ftp site for newly posted files and
downloads them to a local filesystem. … The motivation for this script is to poll places where developers post patches to software we’re testing.

© 2006, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

May 16, 2006

catching up on Stargate

Filed under: Blogging,Health — kees @ 10:50 pm

I’ve been catching up on Stargate SG-1 ever since Bryce recommended it. I’d been resisting it, but with no more Firefly, Farscape, or StarTreks left to watch, it was inevitable.

At one point during my catch-up, I realized that I was watching 4 separate time-lines of the show. SciFi was showing new episodes on Fridays, a set of 3-in-a-row on Mondays, and a third chronology running Tue, Wed, Thu. On top of this, Fox(?) was playing re-runs on Fridays as well. About 30 episodes in, I totally lost it, and could not keep things straight. (“What? Where’d Daniel Jackson go? Who’s this guy?”)

To my rescue was my ever-faithful to serve as a base check-list for which shows I’d seen already, and the fantastic Stargate Wiki Episode Guide to help me remember which I’d already seen. (They even have full transcripts of the episodes! That’s dedication!)

It looks like very few of season 2 has aired, so I will have to turn to either the library or Netflix to fill the gaps. Once SG1 is gone, I will have to switch my daily exercise routine back to Buffy the Vampire Slayer. :)

© 2006, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

May 12, 2006

sourceforge CVS re-check-out solution

Filed under: Blogging — kees @ 9:54 pm

SourceForge migrated to their new CVS server infrastructure recently (due to a catastophic disk failure of the old system), and told everyone that they had to re-check-out all their trees:

Hostname for CVS service

This change will require new working copies to be checked out of all
repositories (so control files in the working copy will point to the
right place). We will be updating the instructions we supply, but
instructions that your team has written within documentation, etc. will
need to be updated.

cvs co gaim

would be changed to

cvs co gaim

With 14 projects hosted there, with potentially multiple CVS modules in each, this wasn’t the best way for me to deal with the change. I had relocated several CVS trees at OSDL last year, so I went digging for my command line to do the updates. I was disappointed they didn’t suggest it in their email, so I offered my solution via their Tracker. Someone else (on Cygwin even) confirmed that it worked for them, and SourceF orge summarily closed the ticket (hence making it disappear from the Tracker where other people were seeking help). I can find no record of a change made to their documentation. In effect, they just eliminated my help (though they did thank me first).

It would be nice if SourceForge ran some kind of forum or Wiki on their site so people could help each other. I’ll have to remember this for the next Advisory Council.

© 2006, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

May 4, 2006

mythtv listing-update time-rotation

Filed under: Multimedia — kees @ 7:33 pm

A few months ago, zap2it‘s renewal survey included a set of questions that were not questions, but rather pleas that people move their database updates to a non-standard time. The default install of MythTV has a hard-coded time in the middle of the night to contact the zap2it servers for TV listing updates. Unfortunately, this means zap2it’s servers were (are?) getting crushed on the hour, across 4 time-zones, in the middle of the night.

To solve this little problem in MythTV, I turned off the built-in “mythfilldatabase” execution, and moved to doing it via crontab. zap2it said they had virtually no load during the day-time, so I moved the update to a little after noon, sticking the following in /etc/cron.d/mythtv-backend:

09 12 * * * mythtv mythfilldatabase –quiet

It dawned on me today while messing around with the “at” scheduler that I could actually randomize when during the day the mythfilldatabase runs. If you wanted to run the job anywhere in a 12 hour (720 minute) period after 9am, you could do it this way:

0 9 * * * mythtv echo “mythfilldatabase –quiet” | at + $(( RANDOM % 720 )) minutes

(My bash manpage says the low-order bits of $RANDOM are as random as the high-order bits, so this is “safe”. If you don’t trust your version of bash, you could use $(( 720 * RANDOM / 32767 )) instead. IANAMG*, YMMV, OMGPONIES.)

*I Am Not A Math Geek

© 2006, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

careful with mysql downgrades

Filed under: Multimedia — kees @ 1:59 am

I ran into a nasty bug while attempting to downgrade a MySQL database. I had been running my MythTV machine on Debian Unstable, but recently reinstalled to Ubuntu. This has the unfortunate consequence of going from MySQL 4.1 to MySQL 4.0. The “mysqldump” option “–compat=mysql40” kind of forgets to include the “auto_increment” flag for tables creation. This caused my subsequent MythTV 0.18 to 0.19 upgrade attempt to instantly bomb, since all the INSERTs expecting the PRIMARY KEY to increment as new stuff was inserted … didn’t.

Once I split the dumps into tables (-t) and data (-d) with different “–compat” levels and hand-edited the tables, everything was “fine” again. I actually got the whole system up and on its feet again, with no loss of Stargate SG-1 episodes. ;)

So, now all I have to fight with is Xv on an old S3 card. Looks like new versions of Xorg don’t aim Xv to the right place. And, mysteriously, the S3 card’s Xv implementation lacks the XV_SWITCHCRT attribute, so I can’t just use “xvattr” to fix it, like I do I my laptop. Aaagh.

I wonder if something like the xorg.conf’s Option MonitorLayout “TV,CRT” might help it? I’ll try that tomorrow.

© 2006, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

May 3, 2006

fun with OpenID

Filed under: Blogging,Security,Web — kees @ 6:04 pm

While I can’t log into NetFlix or Amazon with OpenID (or other federated login systems), I still wanted to try it out. The goal is to easily write comments on people’s blogs, edit Wiki pages, etc, all without having to keep logging in every time. So far, so good.

First step was to decide between running my own OpenID server or not. I went with “not”, since there really isn’t an installable OpenID server yet (there are only support libraries, it seems). Since I was given a permanent account with LiveJournal for some XSS testing I did for them, I figured I’d just use their stuff. I wanted to use “” as my login everywhere, so I just added two lines to my HTML source:

<link rel=”openid.server” href=”” />
<link rel=”openid.delegate” href=”” />

Poof. Done. I used Videntity to verify that it was all working. Nifty stuff.

My only complaint is that it’s not clear how to get an end-to-end secure login. I can log into LiveJournal securely, but the OpenID server they run doesn’t seem to operate over HTTPS. Future study is needed. :)

© 2006, Kees Cook. This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 License.
Creative Commons License

Powered by WordPress