FSFUZZ

This is a quick start guide to fsfuzz.


BUILDING
========
To build from the repo after cloning:

cd fapolicyd
./autogen.sh
./configure
make

You do not need to install the program anywhere, just use it
right where you unpack it.


USAGE
=====
To get started fuzzing file systems, the program expects
that you have a /media directory. It uses that one for
mounting test images in. It will try to create mount points
there, so if you don't have a /media directory, create one.

The main program is ./fsfuzz. If you do not give it arguments,
it will cycle through all the file systems and test each one
individually. You can also test a specific file system by passing
its name on the command line. To see the supported file systems
type "./fsfuzz --help". The file systems supported can vary based
on the utilities you have installed.

The fsfuzz program uses ./run_test to actually exercise a file
system image. When fsfuzz is running, it writes to syslog the 
command line for ./run_test. This is so that when it finally
crashes, you can lookup what the command was and re-test. There
should be an image in the ./cfs directory.

So, for example, you had a crash fuzzing iso9660. You might find
this in syslog "./run_test iso9660 16" This tells run_test that
you are fuzzing is09660 files and the 16th image is what was last
run.

A simple program ./run_last will run the last image as long as
there is only one image in the cfs directory...which is usually
the case. If you find an image that you like and want to keep,
move it out of the cfs directory because subsequent runs of 
./fsfuzz will erase the files.

WARNING: This program can cause your kernel to oops. ITS WHOLE
PURPOSE IS TO PROVOKE THE COMPUTER TO DO BAD THINGS. If you are
using a journalling file system for all your important data, for
the most part you will be OK running this on your machine. But its
impossible to know what hole in the OS you will trigger and what its
consequences are. If you don't run with a journalled file system 
and many processes are active and some writing to disk, there
is a real good chance that you could screw up your computer. YOU
HAVE BEEN WARNED! 


CURRENT FILE SYSTEMS
====================
cramfs, ext2/3/4, btrfs, gfs2, hfs, iso9660, jffs2, msdos, reiserfs,
romfs, squashfs, swap, vfat, xfs, and ecryptfs over other file systems.


EXTENDING
=========
If you want to add support for a file system not already covered,
this is what you want to do. 

1) First, look for its filesystem creation program. In a lot of
cases, its called mkfs.filesystem-name. Add an optional test for
that program and include the filesystem's name in the list.

2) Next, does the filesystem have any minimum size requirements? If
so, you may need to make an adjustment to prep_fs function. Look at
xfs as an example.

3) After that comes the most important step, you need to create a file
system creation scriptlet in the big switch/case block. Filesystems fall
into 2 categories. The kind that can be created from a file and the kind
that are created from a directory. For the kind that can be created from
a file, use xfs as the recipe. For the kind that are created from a 
directory, use cramfs as a recipe.

4) In order for the tests to find more bugs, the file system should
be populated with initial data. This happens naturally if the file
system is created from a directory. However, if the file system is
created from a file, you will have to add the file system name to 
a case statement at the bottom of the prep_fs function.

5) In the main loop, you may have to add a modprobe statement to make
sure the module is loaded. Look at xfs again for the basic recipe.

6) Share the code !

Have fun...

-Steve