Posts Tagged → admin
Finger print reader vs. encrypted home
Modern Linux distributions allow you to encrypt your home directory. When logging in the user’s password is used to decrypt the home directory. This works great unless you are using one of the many other options that PAM offers for authentication. PAM (Pluggable Authentication Modules) is an extensible authentication system, currently standard on most modern Unix systems including Linux.
On my Thinkpad notebooks I am used to the comfort of the finger print reader instead of having to type and remember passwords. As far as I know support for decrypting the home directory using your finger print has not been developed yet. Thus my preferred solution is:
- For initial login after use a password and decrypt home. This happens very seldom anyway.
- For everything else (sudo, screensaver, etc.) use the finger print reader
- Whenever the finger print is not available (ssh, injured finger, etc.) fall back to password
Luckily using pam this can be easily achieved. The solution below has been tested on Ubuntu but it should work with slight adoptions on most linux distributions. If you have configured an alternative authentication method like a finger print reader (or if your distribution or an setup script has done this for you) you will probably have edited /etc/pam.d/common-auth. Copy this file now e.g. to /etc/pam.d/common-auth-pass-only and remove the lines that you added during configuration in the new file. I am using fprint so I had to remove the following line:
auth [success=3 default=ignore] pam_fprintd.so
Now configure your login manager to use the password-only-configuration by substituting
@include common-auth through @include common-auth-pass-only. Your login manager is probably configured in one of those files:
/etc/pam.d/lightdm /etc/pam.d/gdm /etc/pam.d/kdm
You might want to do the same for /etc/pam.d/sshd or others as well.
If you know about a way to support the finger print reader during initial login in combination with an encryted home I’d be happy to hear about it in the comments.
VPN (IPsec) tunnel between a pfSense 2.0 router and a FRITZ!Box
We have a pfSense 2.0 router at our coworking space which is hooked up to a pretty fast VDSL line so I thought it would be a fun idea to connect my home network (where I’m using a FRITZ!Box 7390) to the work LAN using a secure and permenent VPN tunnel.
Doing a quick Google search yields results for the 1.2 version of pfSense which is outdated and does not use DynDNS hostnames for both ends, so I did a quick writeup of my own.
Prerequisites
First things first, create permanent hostnames for your pfSense and your FRITZ!Box. If your DSL provider has assigned permanent IP addresses, that’s fine. If they didn’t you’ll probably need something like DynDNS. Last time I checked, you could still get free accounts, otherwise it’s just a few bucks a year – probably a good investment. You’ll need to configure both the pfSense and the FRITZ!Box to update your DynDNS hosts whenever their IP address changes, but that’s pretty straight forward so I won’t cover it here. Fun fact: you can add CNAME records to your company domain pointing to your DynDNS host, so it looks even more professional. We use vpn.launchco.com for instance – how cool is that?
You’ll also need two different primary subnets for your networks, i.e. if your home network lives in 192.168.178.0/24, which is the standard network a FRITZ!Box uses, your work network has to use something else, like 192.168.1.0/24, which is by the way the standard that pfSense uses – so you should be safe if you’re like me a big fan of sticking with sensible vendor defaults.
Now, with the permanent hostnames and subnets in place, let’s get down to business.
Setting up pfSense
We’re using IPsec, so let’s head to VPN -> IPsec first and click the [+] icon on the bottom right to add a new phase 1 entry.
Fill the form in accordance to what you see on the following screenshot:
Obviously, replace your-fritz.dyndns.org with the permanent hostname assigned to your FRITZ!Box as well as your-pfsense.dyndns.org with the one on your pfSense box. The Pre-Shared Key should be a long random string. Don’t worry, you won’t have to remember it. You’ll just save that in the FRITZ!Box later and then you can forget about it.
Next up, we need a phase 2 entry. For that, click the [+] icon next to a label that says Show 0 Phase-2 entries and fill the form like below:
Here, you just need to make sure that you replace 192.168.178.0 with the actual subnet your FRITZ!Box uses. Again, if you’ve sticked with the default when setting up the box, this setting should be right for you.
That should be it for the pfSense. After saving it’ll probably ask you to apply or reload the configuration. This is safe to do now.
Setting up the FRITZ!Box
Now, let’s finish this by configuring a VPN entry in your FRITZ!Box. From my perspective, this part is much easier, because I’m just pasting code instead of fiddling with screenshots – yay!
Fire up your favorite text editor and paste the following code:
Make the necessary modifications according to the comments in the file. Then, open the FRITZ!Box configuration interface in your browser and head to Internet -> Freigaben -> VPN, use the browse button to select the file you just created and click on VPN-Einstellungen importieren.
That’s it – you’re done. In my first trials I had to go back to the pfSense interface and navigate to Status -> IPsec to click on a small [>] (“play”) button to get things rolling. Maybe you need this, maybe it just works without it.
Getting the connection up after a restart of either of the two routers sometimes fails which is most probably due to the fact that DynDNS updates have not yet propagated when the VPN tries to connect. In this case, just be patient; both boxes will keep retrying to open VPN connections and you can always stop/start on both ends yourself. Once a connection is made, the tunnels are usually stable and rock-solid. Enjoy!
How to build an 8 TB RAID5 encrypted time capsule for 500 Euros
So I wanted to buy a NAS that can act as a time capsule for Apple computers and run a proper Linux at the same time. I also wanted to be able to run the occasional Windows or Linux VM and I wanted to have a lot of storage. As I knew the thing was going to be in our coworking space, it also needed to have disk encryption.
Here’s how I built this for just under €500.00 using standard components and free open source software.
Selecting the hardware components
I found the HP ProLiant MicroServer (see Review and more Picures) to deliver great value for the price. At the time of writing, you can buy it for €209.90 if you’re in Germany like me.
The N36L (which I bought) comes with a single 250GB hard drive which obviously did not meet my “a lot of storage” requirement. So I bought 4 identical Seagate Barracuda Green 2000GB SATA drives which would add another €229.92 to the bill if you bought them today. I am not an expert in hard drives, but the Seagate Barracuda brand was familiar and “Green” sounds good as well.
If you don’t want your new server to host virtual machines at some point, you can probably get out your credit card and check out right now. If you’re like me though, you’d add another 2 bars of 4GB Kingston ValueRAM PC3-10667U CL9 (DDR3-1333) to your cart. The two of them together are just €44.24, so it’s no big deal anyways.
All components together will set you off €484.06. The rest is based on open source software (Debian mostly) which is free as in beer. More about that after the break.
Bazaar over chrooted sftp
How to set up bzr for chrooted sftp users
How to restrict a user’s access to sftp://.../var/bzr
For the prototyping editor itself and for a lot of our clients’ projects we are heavy Bazaar users at pidoco° to manage our distributed workflow. When we started some years ago we just installed bzr on one of the test servers where all of the developers had ssh access anyway. We put the repositories in /var/bzr and used sftp to checkout/push/pull source changes. This was handy as a sftp server comes with openssh installed.
As the team grew over the years we got to a point where we wanted to give new developers access to the bzr repositories without giving them full ssh access. However we did not want to have to change all the urls for existing repositories. Luckily this can be achieved easily since Debian Lenny.
Per Server Settings
On our scm server we have a user group called bzr that grants read/write access to most of the repositories (except of some personal or release branches) to all users with bzr access. And now we added the group sftponly. All users in this group will be restricted to sftp access only instead of a full shell.
sudo addgroup sftponly sudo addgroup bzr
You probably have to add ‘/usr/lib/sftp-server’ to /etc/shells to make it a valid shell, eg. like this:
root@host # echo '/usr/lib/sftp-server' >> /etc/shells
The following settings in /etc/ssh/sshd_config force the internal sftp server to be used by openssh and change the root directory for all users in the group sftponly to /var/chroot. Make sure to restart sshd afterwards.
Subsystem sftp internal-sftp
Match Group sftponly
ChrootDirectory /var/chroot
AllowTCPForwarding no
X11Forwarding no
ForceCommand internal-sftp
Up to now our repositories have been in /var/bzr. These need to be moved to /var/chroot/var/bzr to let the sftponly users access them. /var/chroot needs to have root:root as owner for openssh to work correctly. For the existing ssh users we add a symbolic link to keep the old paths working:
sudo mkdir /var/chroot sudo chown root:root /var/chroot sudo mkdir /var/chroot/var sudo mv /var/bzr /var/chroot/var sudo ln -s /var/chroot/var/bzr /var/bzr
Per User Settings
giving the user username sftp access, but nor ssh access:
USERNAME=username # give the user a name
sudo adduser ${USERNAME} # add user and data to system
sudo usermod -s /usr/lib/sftp-server ${USERNAME} # disallow ssh/bash, allow ssh/ftp (sftp)
sudo adduser ${USERNAME} bzr # allow group access to most bzr folders
sudo adduser ${USERNAME} sftponly # disallow access to /, allow access to /var/bzr
This changes user’s shell to sftp-server.
Result
As a result of these settings both normal ssh users as well as restricted users in the sftponly group can use the same url for their shared repositories
bzr checkout sftp://my.domain/var/bzr/my_repository. By using chroot however users in the group sftponly are restricted to using sftp and can only access the folders in the bzr subdirectory.
Sources
In the Debian Administration Weblog you can find information on how to setup an OpenSSH SFTP chroot() with ChrootDirectory and on how to restrict users to SFTP only instead of SSH.