Getting Started with the Linux Intrusion Detection System

Sometimes file permissions aren't enough. LIDS gives you kernel-level access control that goes beyond filesystem settings.
Setting Up a LIDS-Enabled Server

This article assumes that you have installed LIDS and its associated administration tools.

We will set up a system with tight security settings, and the services that will be allowed to run are MySQL, Apache and Bind.

The sample commands below assume that the Apache installation resides in /usr/local/apache, with a log directory of /var/log/httpd, and also assumes your Apache configuration directory is /etc/httpd. MySQL is assumed to be installed in /usr/local/mysql. Obviously, you'll want to change the commands to suit your installation if it differs.

It is beyond the scope of this article to cover everything necessary to secure your system completely. However, these examples of how access control is administered in LIDS should get you started.

Setting Up a System

After you restart LIDS, you can begin adding access controls to various system binaries and libraries. The following sets the /sbin, /bin, /usr/bin and /lib to read-only:

lidsconf -A -o /sbin -j READONLY

lidsconf -A -o /bin -j READONLY

lidsconf -A -o /usr/bin -j READONLY

lidsconf -A -o /lib -j READONLY

Next, we define some additional access controls for /opt, /etc and /usr/local/etc, which should be read-only, and we deny all access to /etc/shadow and the boot manager file:

lidsconf -A -o /etc -j READONLY

lidsconf -A -o /usr/local/etc -j READONLY

lidsconf -A -o /etc/shadow -j DENY

lidsconf -A -o /etc/lilo.conf -j DENY

Because we have denied all access to /etc/shadow, the system will not be able to authenticate logins, thus we need to allow login and vlock to have read-only access to the file. Additionally, su also should have read-only access to the /etc/shadow file:

lidsconf -A -s /bin/login -o /etc/shadow -j READONLY

lidsconf -A -s /usr/bin/vlock -o /etc/shadow -j READONLY

lidsconf -A -s /bin/su -o /etc/shadow -j READONLY

We need to set some other access controls for su, in order for it to work with UIDs and GIDs, and access the /etc/shadow file:

lidsconf -A -s /bin/su -o CAP_SETUID -j GRANT

lidsconf -A -s /bin/su -o CAP_SETGID -j GRANT

lidsconf -A -s /bin/su -o /etc/shadow -j READONLY

Now, we need to allow init, login and associated applications to have write access to log files:

lidsconf -A -o /var/log -j APPEND

lidsconf -A -s /bin/login -o /var/log/wtmp -j WRITE

lidsconf -A -s /bin/login -o /var/log/lastlog -j WRITE

lidsconf -A -s /sbin/init -o /var/log/wtmp -j WRITE

lidsconf -A -s /sbin/init -o /var/log/lastlog -j WRITE

lidsconf -A -s /sbin/halt -o /var/log/wtmp -j WRITE

lidsconf -A -s /sbin/halt -o /var/log/lastlog -j WRITE

lidsconf -A -s /etc/rc.d/rc.sysinit -o /var/log/wtmp -i 1 -j WRITE

lidsconf -A -s /etc/rc.d/rc.sysinit -o /var/log/lastlog -i 1 -j WRITE

Now, we set up access control for root's home folder. We allow only the bash history file to be appended:

f -A -o /root -j READONLY

lidsconf -A -s /bin/bash -o /root/.bash_history -j APPEND

Finally, we allow the init program to kill processes on shutdown:

lidsconf -A -s /sbin/init -o CAP_INIT_KILL -j GRANT

lidsconf -A -s /sbin/init -o CAP_KILL -j GRANT

Now, we allow fstab and init scripts to mount filesystems, kill processes and unmount filesystems:

lidsconf -A -s/etc/fstab -o CAP_SYS_ADMIN -j 1 -j GRANT

lidsconf -A -s /etc/rc.d/init.d/halt -o CAP_INIT_KILL -i 1 -j GRANT

lidsconf -A -s /etc/rc.d/init.d/halt -o CAP_KILL -i 1 -j GRANT

lidsconf -A -s /etc/rc.d/init.d/halt -o CAP_NET_ADMIN -i 1 -j GRANT

lidsconf -A -s /etc/rc.d/init.d/halt -o CAP_SYS_ADMIN -i 1 -j GRANT

Setting Access Controls for the Apache Web Server

Apache needs to have setuid and setgid capabilities. We also need to allow Apache to access log files and deny other applications from accessing the httpd binary:

lidsconf -A -s /usr/local/apache/bin/httpd -o CAP_SETUID -j GRANT

lidsconf -A -s /usr/local/apache/bin/httpd -o CAP_SETGID -j GRANT

lidsconf -A -o /etc/httpd -j DENY

lidsconf -A -s /usr/local/apache/bin/httpd -o /etc/httpd -j READONLY

lidsconf -A -o /usr/local/apache -j DENY

lidsconf -A -s /usr/local/apache/bin/httpd -o /usr/local/apache -j READONLY

lidsconf -A -o /var/log/httpd -j DENY

lidsconf -A -s /usr/local/apache/bin/httpd -o /var/log/httpd -j APPEND

lidsconf -A -s /usr/local/apache/bin/httpd -o /usr/local/apache/logs -j WRITE



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Access controls for Jboss server.

Anonymous's picture

Hi Irfan,

Your post had been very useful. Thanks first.

I was given the task of binding port 443 to JBoss server.

i have granted the NET_BIND capability on 443 port to Jboss/bin/ subject. But the problem persists with exception as Permission denied :443

Can u pls help wid this.

More Information on LIDS please

Matt's picture

Hello Irfan.

I liked your article on LIDS, but am a bit confused by the phrase:

"It is recommended that the LIDS patch be applied only to the original kernel source, not to the distribution-specific source".

I use Suse Linux 10. Does your statement mean I must somehow 'retrofit' a vanilla kernel into my distribution? This would be something well beyond my capabilities and I presume Novell wouldn't like it much either.

Where can I find LIDS?