Sunday, April 19, 2009

Installing SE Linux on Debian/Lenny

I have set up my own APT repository for SE Linux packages.

gpg --keyserver hkp:// --recv-key F5C75256
gpg -a --export F5C75256 | apt-key add -

To enable the use of my repository you must first run the above two commands to retrieve and install my GPG key (take appropriate measures to verify that you have the correct key).

deb lenny selinux

Then add the above line to /etc/apt/sources.list and run “apt-get update” to download the list of packages.

Next run the command “apt-get install selinux-policy-default selinux-basics” to install all the necessary packages. After that is done you need the file /.autorelabel to exist for the next boot to cause the filesystems to be labeled. The file /boot/grub/menu.lst needs to have “selinux=1” on the end of the line which starts with “# kopt=” (and the kernel command-lines for each kernel). You can do this manually but the recommended thing to do is to run the command selinux-activate, if given no parameters it will apply all the necessary tweaks to enable SE Linux (it changes PAM configuration files, GRUB configuration, and creates /.autorelabel.

Note that if you use gdm then the file /etc/pam.d/gdm needs to have the line moved to before the GNOME key lines. I need to update the selinux-basics package for this.

Then reboot and the filesystems will be relabeled. The relabel process will cause a second automatic reboot of the machine (it needs to be rebooted so that init gets the correct context). After that is finished the machine will be running in “permissive mode“, this means that SE Linux will log the actions that it would deny, but they will still be performed.

To put the machine in “enforcing mode” you can run the command “setenforce 1“, this means that SE Linux actually controls access to the machine. When you are confident that the machine is working correctly you can edit the file /etc/selinux/config and change the SELINUX= line to specify that it is in “enforcing” mode. The script selinux-config-enforcing will do this for you (with no parameters if configures SE Linux to be in enforcing mode at the next boot). If you need to override this (for example if critical files get the wrong labels and prevent booting) then the kernel command-line option enforcing=0 will override it. I will add a new command selinux-config-enforcing to the selinux-basics package to manage this (it will hopefully be there for Lenny).

If you use Postfix then you need to run it without chroot, the command postfix-nochroot will configure Postfix to not use chroot and will restart it. This script is included in the selinux-basics package but will hopefully be in Postfix for Lenny+1 (I think that many people who don’t use SE Linux will be able to use it).

In summary here are the commands you need:
apt-get install selinux-policy-default selinux-basics

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