OVERVIEW
========

vlock is a denial of service tool.  Linux allows any user logged into the
virtual console to lock the system completely.  vlock takes this one step
further and potenially grants this ability (and potentially other, even more
hazardous ones) to any user through the use of plugins.

The default installation sets permission that allow only users in the vlock
group to run dangerous modules.  Others will still be able to lock their own
console or terminal and run plugins that are considered secure.

This behavior is configurabe through ./configure option or by editing
config.mk.

DETAILS
=======

vlock-main allows plugins to extend its functionality.  These plugins are
separated into two groups:  modules and scripts.  Both are only loaded from
locations that are specified at compile time.  It is extremely important that
these directories are only writable by privileged users.

MODULES
-------

Modules are shared objects that are loaded into vlock's address space.  Because
vlock will most likely be installed setuid-root care must be taken that these
modules are secure themselves and that access to potentially dangerous modules
is limited to trusted users.  UNDER NO CIRCUMSTANCES MUST UNPRIVILEGED USERS BE
ALLOWED TO PUT THEIR OWN MODULES INTO VLOCK'S MODULE DIRECTORY.  Doing this
would allowing them to run any code they want with elevated privileges, i.e.
as root.

SCRIPTS
-------

Scripts may be any kind of executables located in vlock's script directory.
They are run with with lowered privileges, i.e. the same as the user who
started vlock, in a separate process.  They also don't have direct access to
the terminal vlock runs on and thus may be considered a relatively secure
alternative to modules.  For any privileged operations they want to perform
they have to use helpers such as sudo.  Although less dangerous than modules
vlock's script directory must still be protected the same as the module
directory.
