I follow the main feeds of a couple social news sites (namely Digg, Reddit and Muti). When I find an article which I like, I go back and vote it up on the site. However, when I come across good articles via other sources, I don't submit them to these news sites (or try to find out if they've already been submitted) simply because it's too much effort.

When I started aggregating my activity on these sites on my blog and on FriendFeed, I needed a way to share pages that I didn't get to via one of these social news sites. I ended up setting up Delicious because I found a plugin for Konqueror which made it easy to bookmark pages.

I still wanted to solve the original problem though, and so started looking for an easy way to submit links to these sites from Konqueror. Konqueror has a feature called service menus which allows you to add entries to the context menu of files. I then needed to work out how to submit links to these services, which turned out to simply involve loading a URL with a query parameter specifying the link you want to share.

I created entries for Reddit, Digg, Muti, Delicious, Facebook and Google Bookmarks. These take you to the submission page of the service where you can fill in the title¹. Digg and Reddit will show existing submissions if the link has already been submitted.

I often share links on IRC, and wondered if I could integrate that with my menu. It turns out that WeeChat has a control socket, and I could send messages by piping them to the socket. I therefore wrote a script which prompted me for a headline or excerpt using kdialog, and then sent the link to the specified channel. My menu now looks like this:

If you want to set this up yourself, download share.desktop and put it in ~/.kde/share/apps/konqueror/servicemenus. If you want the icons, download shareicons.tar.gz, extract them somewhere, and fix the paths in social.desktop². To setup the IRC feature (assuming you're using WeeChat), download postirc.sh and save it in ~/bin/. You will need to change the commands in social.desktop depending on the servers and channels you wish to use.

When I first started using Linux four years ago, one of the most useful features I discovered was circular scrolling on touchpads. (For those that don't know, this allows you to scroll up and down by moving your finger in a circle.) Traditional scrolling now feels very clumsy, and I find it awkward when using a laptop which doesn't have this feature (such as those running Windows). According to the changelog for the XOrg/XFree86 Synaptics driver, this feature was added in February 2004.

I happened to come across the news today that Synaptics have added a feature called ChiralTouch Technology to the latest version of their Windows drivers. This so-called "technology" provides "the ability to scroll continuously with a circular motion." This basically means that they have finally gotten round to implementing a very useful feature which Linux users have had for over four years.

In some respects proprietary software is way behind FOSS in terms of features and usability, and this example also shows how proprietary software uses ideas which were first implemented in FOSS.

When I occasionally read IRC logs saved by irssi, I find the lack of colouring rather annoying and find that I can't read them very quickly. I finally got round to writing a syntax highlighting plugin for Vim in order to correct this. The colours could probably do with some improvement, but it's much better than before.

In case anyone else finds this useful, I have attached the plugin to this post. To use it, save irssilog.vim in ~/.vim/syntax/ and enter the following command to use it with the current file.

:set syntax=irssilog

If you want Vim to automatically detect the file type, add the following to ~/.vim/ftdetect/irssilog.vim¹.

au BufRead,BufNewFile */irclogs*.log    set filetype=irssilog

I've been using an external harddrive to store backups of my laptop for a while now. At first I manually created a set of compressed tar archives about once a month. That was a bad system though because it used a lot of space and was a mission to retrieve files from backups. I then started using pdumpfs, which can do incremental backups by hard linking files which haven't changed. The problem I found with it however was that if a file's ownership or timestamps changed it wouldn't be hard linked even if the content hadn't changed.

I therefore set out to find a better backup solution. My requirements were as follows.

1. Incremental backups
2. Easy to access specific files from backups
3. Able to delete certain backups, preferably arbitrarily¹
4. Compression
5. Encryption

I finally settled on storeBackup which supports everything except number 5. It works similarly to pdumpfs, except it stores ownership and timestamp data separately and therefore can still hard link identical files even if these change. It compresses on a per file basis, which makes it easy to access specific files (as opposed to having to find them in an archive). Old backups can be deleted arbitrarily since they are only related by hard links. I then added encryption by backing up to an encfs encrypted directory.

Due to a very restrictive firewall at the CHPC, I need to run a VPN to get access to things like email, Jabber and SSH. This however degrades my web browsing experience, since that gets tunnelled as well. I therefore wanted a setup where only ports which are blocked get tunnelled through the VPN, while everything else goes out normally.

The routing part was fairly straightforward, which consists of an iptables rule to mark certain packets, and an alternate routing table for these marked packets. I first created a name for the new table by adding the following to /etc/iproute2/rt_tables.

10  vpn

I then added a default route to the new table specifying the IP address of the VPN server and the VPN interface, and a rule to use this table for packets marked by iptables.

ip route add default via 10.8.0.3 dev tun0 table vpn
ip rule add fwmark 0x1 table vpn

The following iptables rule will mark packets destined to the listed port numbers. Note that this is for packets originating from the firewall host — if you want this to apply to packets forwarded for other hosts it must be in the PREROUTING chain.

iptables -t mangle -A OUTPUT -p tcp -m multiport --dports 22,995,587,5223 -j MARK --set-mark 0x1

The actual routing worked, but packets were being sent with the wrong source IP. I therefore needed to NAT packets going out on the VPN interface (the IP address is the local IP of the VPN connection).

iptables -t nat -A POSTROUTING -o tun0 -j SNAT --to 10.8.0.4

I could then see packets going out on the VPN interface with the correct source IP as well as the replies, but it still wasn't working. I eventually discovered that rp_filter must be disabled in order for this to work.

echo 0 > /proc/sys/net/ipv4/conf/tun0/rp_filter

The CHPC installed a new network this past weekend as part of the SANReN project. The new network consists of Cisco equipment, including their NAC (or "Clean Access") system. This requires all clients to authenticate before they are allowed access to the network, and can also enforce a configured security policy (such as requiring operating system updates and anti-virus).

The system works as follows. By default, the ports on the switch are in an "unauthenticated" VLAN. When a client is connected, it is provided with an IP address (via DHCP) in an "unauthenticated" subnet. The system then presents a captive portal which requires the user to authenticate with a username and password using their browser. If the authentication is successful, the port is moved to a different VLAN (depending on the user's access level), and the switch briefly disconnects the link which causes the client to negotiate a new IP address (in a different subnet).

Before the portal presents the login page it requires that a Java applet be run on the client. The applet gathers various bits of information about the client (including the operating system) and submits this information to the portal. (I assume that the portal uses this information to determine what policies must be enforced. In our setup, Windows machines must have the Clean Access Client installed, while Linux and Mac OS X machines are simply allowed access.) The portal then presents the login page.

Being a geek, I wasn't very happy to go through this rigmarole everytime I connected to the network. (I also couldn't use my normal browser since the applet didn't work in it.) So I set out to automate the process. Initially I tried to script everything (including the Java applet) but then I noticed that the output of the applet wasn't sent with the login form submission. The only other information the form contained was a session key and random string, both of which were present on the HTML page which contained the applet. A manual test confirmed that the login page could be submitted successfully as long as the session key and random string were correct — the applet could be bypassed.

I quickly scripted the login process using a bash script and wget. I then installed it in /etc/network/if-up.d after adding some logic to only execute if the current IP address was on the unauthenticated network. The result is that I can plug in the cable, and my machine automatically authenticates to the system.

While searching for information about the Clean Access system, I came across this Slashdot article about a guy who was suspended from university for bypassing the Clean Access checks. I only realised last night that this is exactly what my script does!¹ I haven't tested it on Windows yet, but the only possible change I can think of is to change the user agent. Seriously Cisco, the fact that I managed to bypass the applet simply by submitting the login form programmatically is ridiculous.

I have attached my script to this post. The way in which I have parsed the HTML page is rather ugly and likely to only work on this specific version of Clean Access. I plan to rewrite it in Python sometime.

Update: I have rewritten the script in Python, which should be a bit more solid since it parses the HTML using a DOM. The script requires libxml2dom and ipy. After configuring the parameters it can be dropped in /etc/network/if-up.d² where it should run automatically.

Unfortunately Windows is still a necessary evil sometimes: I keep a Windows virtual machine for times when it's absolutely necessary, and I still give my friends Windows tech support. I still like to do things properly, and so I wanted to create a Windows XP install CD with Service Pack 3 slipstreamed in¹. I had two CDs to do, and slipstreamed the first one using a Windows VM, but then got curious and wondered if I could do it without Windows.

The answer is that it is possible using Wine to run the service pack installer. I followed this blog post (which was interesting since it's in French), but I then found another blog post which explains it in English. The steps are as follows:

1. Copy contents of original CD to harddrive.
2. Extract the service pack using cabextract.

3. Use Wine to run the service pack installer.

   wine ~/sp3/i386/update/update.exe /integrate:~/xp/
   

4. Use geteltorito to extract the bootloader from the original CD

5. Make sure that all the filenames are upper case.

   convmv -r --upper --notest ~/xp/*
   

6. Create the new CD image. I did this in K3b with the following settings.

   • Boot emulation: none
   • Boot load segment: 0x7c0
   • Boot load size: 0x4
   • Generate Joilet extensions
   • Omit version numbers in ISO9660 filenames (nothing else enabled under "ISO9660 Settings"
   • ISO Level 1
7. Test in a virtual machine

It seems to be quite particular about the ISO9660 settings and the upper case filenames, so if it doesn't boot check the settings.

I was looking through a list of DNS record types, and noticed the SSHFP and CERT records. I then proceded to implement these in my domain... just because I can ;-)

SSH Host Keys

The SSHFP record is used to publish the fingerprint of a host's SSH key. When an SSH client connects to a server for the first time, it can verify the host's key by checking for this DNS record. The format of the record is specified in RFC 4255, but there is also a tool which will generate the records for you.

$ sshfp -s mammon.gorven.za.net
mammon.gorven.za.net IN SSHFP 1 1 5e6772b6962f3328a0d73f7765097b7622f21447
mammon.gorven.za.net IN SSHFP 2 1 00e59b1843421f13d75e21abb06bf032a6e60b8b

The SSH client needs to be configured to check these records. Specifying "VerifyHostKeyDNS ask" in ~/.ssh/config will make the client look for SSHFP records, but will still prompt you to accept the key. (It will output a messaging saying that it found a matching key.) Specifying "VerifyHostKeyDNS yes" will skip the prompt if the record exists and matches the key presented by the server.

GPG Keys

The CERT record is used to publish public keys or fingerprints. It can be used for PGP, X.509 or SPKI keys. It is specified in RFC 4398, and there is very little mention of it other than this blog post I found. To generate records you need the make-dns-cert tool which is part of GnuPG. It isn't distributed in the Ubuntu package however, and so I had to compile GnuPG from source.

To determine the name of the record to use, convert your email address into a domain name by replacing the ampersand with a dot¹. To publish your entire public key, run the tool as follows.

$ make-dns-cert -k ~/pubkey -n michael

The first parameter specifies the file containing your public key in binary format, and the second parameter specifies the domain name to use. To publish a reference to your public key, run the tool as follows.

$ make-dns-cert -f BF6FD06EA9DAABB6649F60743BD496BD6612FE85 -u http://michael.gorven.za.net/files/mgorven.asc -n michael

The first parameter specifies the fingerprint of your key, and the second parameter the URL at which the public key can be found. It is also possible to only publish the fingerprint or only the URL. Simply add the record which the tool outputs to your zone file².

There is also another method to publish GPG keys called PKA. The only documentation I can find is a specification in German linked from the blog post mentioned above. I still managed to set it up though. This method uses a TXT record (similar to SPF). Here is my record.

michael._pka.gorven.za.net. TXT
"v=pka1\;fpr=BF6FD06EA9DAABB6649F60743BD496BD6612FE85\;uri=http://michael.gorven.za.net/files/mgorven.asc"

This specifies the fingerprint and URL, just as with the second CERT method above. In order to get gpg to check DNS for keys, you need to specify "--auto-key-locate cert,pka" on the command line or in the configuration file.

I discovered that OpenVPN supports connections through an HTTP proxy server. This makes it possible to establish a VPN from a completely firewalled network where the only external access is through a proxy server¹. It takes advantage of the fact that SSL connections are simply tunnelled through the server and aren't interfered with like unencrypted connections.

The server setup is almost identical to a normal configuration, except that the tunnel must use TCP instead of UDP (since the proxy server will establish a TCP connection). Since most proxy servers only allow SSL connections to certain ports, you will also need to change the port number that the server listens on. The best is 443 since that is used for HTTPS, but if the server is also running a web server on port 443, then 563 is probably the next best choice. This port is assigned to NNTPS, and is allowed by the default Squid configuration. The following two lines enable TCP connections and change the port number.

proto tcp-server
port 563

The client configuration is also very similar. It simply needs to enable TCP connections, set the correct port number, and specify the proxy server.

remote vpn.example.com 563
http-proxy cache.saix.net 8080
proto tcp-client

OpenVPN can also authenticate to the proxy server using either Basic or NTLM authentication. To enable this add "stdin basic" or "stdin ntlm" to the http-proxy line. This will prompt for the username and password when the VPN is started. For more details see the OpenVPN documentation.

I have been using Gmail for a while now, and really think that it's about the best email provider out there. I recently moved my mail over from Google Apps to my own server, but I wanted the major features that I liked. I've always used a desktop mail client and used POP3 and SMTP to receive and send mail.

These are the features I particularly like:

1. Secure access with TLS/SSL
2. Outgoing SMTP with authentication
3. Messages sent via SMTP are automatically stored in the mailbox
4. Messages downloaded via POP3 are still stored on the server
5. IMAP and Web access

I therefore set out to recreate this setup as closely as possible. The first two are satisfied by a standard Postfix setup with TLS and SMTP AUTH. The last one is done with Dovecot and Roundcube.

To automatically store sent messages on the server, I used Postfix's sender_bcc_maps to BCC messages I send to myself, and the following Procmail recipe to move these messages to the Sent folder.

:0
* ^Return-Path.*me@example.com
.Sent/

To make POP3 access independent from IMAP, I first configured Dovecot to use a different mail location for each as follows.

protocol imap {
    mail_location = maildir:~/Maildir
}
protocol pop3 {
    mail_location = /var/mail/%u
}

I then used the following Procmail recipe to send incoming messages to both locations.

DEFAULT=$HOME/Maildir/
:0c:
/var/mail/mgorven

At the moment this is only setup for my user, but it should be possible to do it for all users by creating a global procmailrc and telling Postfix to deliver all mail using Procmail. This is working fairly well. The only part missing is that Gmail can archive or mark messages as read when they are downloaded via POP3, whereas in my setup POP3 and IMAP are completely independent.