Tuesday, 6 January 2009

Using a CD/DVD Distribution under Linux/Unix

To use a custom ISO distribution disk in a running *NIX O/S, the first step involves mounting the CD or DVD as a file system.

The next stage involves starting a “clean” shell and then setting the application search paths and library load paths.

If you don’t do this and you forget (or do not use) the complete directory listing when calling an application (e.g. calling “/bin/sh” against typing “sh” to start a shell), you cannot take reliance as to the security and integrity of the binaries and libraries being called.

An example of this process is listed below:

# mount -t iso9660 -o ro /dev/cdrom /mnt/cdrom

# /mnt/cdrom/bin/ksh

# PATH=“/mnt/cdrom/bin: /mnt/cdrom/sbin:$PATH”


# export PATH


When mounting the CD or DVD also ensure that you have called the device and not just assumed that this is set up correctly. It is possible that a rootkit could intercept mount function calls. Although an attacker could still bypass this methodology is much more difficult.

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