Re: [PATCH] handle ext3 directory corruption better

From: Steve Grubb
Date: Sat Oct 21 2006 - 11:34:22 EST

>I've been using Steve Grubb's purely evil "fsfuzzer" tool, at

Oops, I didn't know this was going to be mentioned and deleted the file. The
current release is 0.5 and I've symlinked it to the address Eric mentioned
above. That said, I would like to say a couple things about the program.

Bugs found by fuzzing falls into 2 categories, robustness and security. Its
very possible to overflow stacks or find signed/unsigned conversion problems
which can be exploited by malicious users. It is also expected by people that
the OS tolerate errors. If you have defective media, you may need to access
the drive in attempt to salvage what you can. Or maybe someone walks by with
specially doctored USB stick and jams it in your desktop computer while you
are away. The automounter then mounts and reads the initial directory...boom.

To help find these kind of problems, I worked on a program, fsfuzz, that can
create all sorts of errors. The initial idea for the program comes from LMH.
The tool saves the image that crashed your machine so that you can replay the
problem and study it. This program has killed all the file systems it
currently supports in the latest rawhide kernel - except swap. Virtually
every file system in the current kernel can be used to oops or lockup a
machine. Currently supported filesystems include:


The way that the program works falls into this general pattern, it creates an
initial file system image, corrupts it, then loopback mounts it, and tries
various operations. If that passes, it corrupts the image in a different way
and repeats.

The initial image is created in one of 2 ways, either dd a file or mkdir a
directory depending on what the filesystem creation tools call for. To
corrupt the image, a version of mangle is used. Mangle is a program that
corrupts about 10% of the data and favors bytes with a value > 128 to induce
signed/unsigned problems. The corrupted image is exercised by a program
called run_test. I separated it from the main program so that you can replay
a test and debug what is happening.

So, to wrap up...anyone that has anything to do with file system development
may want to give this tool a try to see how robust any given file system is.
The program can be grabbed here:

There is a README file that explains more about using it. I am taking patches
if you have any ideas about supporting file systems not already covered or
ideas for new tests to exercise different filesystem operations.

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