239 lines
9.4 KiB
Text
239 lines
9.4 KiB
Text
# Specification for the fuzz testing tool
|
|
#
|
|
# Copyright (C) 2014 Maria Kustova <maria.k@catit.be>
|
|
#
|
|
# This program is free software: you can redistribute it and/or modify
|
|
# it under the terms of the GNU General Public License as published by
|
|
# the Free Software Foundation, either version 2 of the License, or
|
|
# (at your option) any later version.
|
|
#
|
|
# This program is distributed in the hope that it will be useful,
|
|
# but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|
# GNU General Public License for more details.
|
|
#
|
|
# You should have received a copy of the GNU General Public License
|
|
# along with this program. If not, see <http://www.gnu.org/licenses/>.
|
|
|
|
|
|
Image fuzzer
|
|
============
|
|
|
|
Description
|
|
-----------
|
|
|
|
The goal of the image fuzzer is to catch crashes of qemu-io/qemu-img
|
|
by providing to them randomly corrupted images.
|
|
Test images are generated from scratch and have valid inner structure with some
|
|
elements, e.g. L1/L2 tables, having random invalid values.
|
|
|
|
|
|
Test runner
|
|
-----------
|
|
|
|
The test runner generates test images, executes tests utilizing generated
|
|
images, indicates their results and collects all test related artifacts (logs,
|
|
core dumps, test images, backing files).
|
|
The test means execution of all available commands under test with the same
|
|
generated test image.
|
|
By default, the test runner generates new tests and executes them until
|
|
keyboard interruption. But if a test seed is specified via the '--seed' runner
|
|
parameter, then only one test with this seed will be executed, after its finish
|
|
the runner will exit.
|
|
|
|
The runner uses an external image fuzzer to generate test images. An image
|
|
generator should be specified as a mandatory parameter of the test runner.
|
|
Details about interactions between the runner and fuzzers see "Module
|
|
interfaces".
|
|
|
|
The runner activates generation of core dumps during test executions, but it
|
|
assumes that core dumps will be generated in the current working directory.
|
|
For comprehensive test results, please, set up your test environment
|
|
properly.
|
|
|
|
Paths to binaries under test (SUTs) qemu-img and qemu-io are retrieved from
|
|
environment variables. If the environment check fails the runner will
|
|
use SUTs installed in system paths.
|
|
qemu-img is required for creation of backing files, so it's mandatory to set
|
|
the related environment variable if it's not installed in the system path.
|
|
For details about environment variables see qemu-iotests/check.
|
|
|
|
The runner accepts a JSON array of fields expected to be fuzzed via the
|
|
'--config' argument, e.g.
|
|
|
|
'[["feature_name_table"], ["header", "l1_table_offset"]]'
|
|
|
|
Each sublist can have one or two strings defining image structure elements.
|
|
In the latter case a parent element should be placed on the first position,
|
|
and a field name on the second one.
|
|
|
|
The runner accepts a list of commands under test as a JSON array via
|
|
the '--command' argument. Each command is a list containing a SUT and all its
|
|
arguments, e.g.
|
|
|
|
runner.py -c '[["qemu-io", "$test_img", "-c", "write $off $len"]]'
|
|
/tmp/test ../qcow2
|
|
|
|
For variable arguments next aliases can be used:
|
|
- $test_img for a fuzzed img
|
|
- $off for an offset in the fuzzed image
|
|
- $len for a data size
|
|
|
|
Values for last two aliases will be generated based on a size of a virtual
|
|
disk of the generated image.
|
|
In case when no commands are specified the runner will execute commands from
|
|
the default list:
|
|
- qemu-img check
|
|
- qemu-img info
|
|
- qemu-img convert
|
|
- qemu-io -c read
|
|
- qemu-io -c write
|
|
- qemu-io -c aio_read
|
|
- qemu-io -c aio_write
|
|
- qemu-io -c flush
|
|
- qemu-io -c discard
|
|
- qemu-io -c truncate
|
|
|
|
|
|
Qcow2 image generator
|
|
---------------------
|
|
|
|
The 'qcow2' generator is a Python package providing 'create_image' method as
|
|
a single public API. See details in 'Test runner/image fuzzer' chapter of
|
|
'Module interfaces'.
|
|
|
|
Qcow2 contains two submodules: fuzz.py and layout.py.
|
|
|
|
'fuzz.py' contains all fuzzing functions, one per image field. It's assumed
|
|
that after code analysis every field will have own constraints for its value.
|
|
For now only universal potentially dangerous values are used, e.g. type limits
|
|
for integers or unsafe symbols as '%s' for strings. For bitmasks random amount
|
|
of bits are set to ones. All fuzzed values are checked on non-equality to the
|
|
current valid value of the field. In case of equality the value will be
|
|
regenerated.
|
|
|
|
'layout.py' creates a random valid image, fuzzes a random subset of the image
|
|
fields by 'fuzz.py' module and writes a fuzzed image to the file specified.
|
|
If a fuzzer configuration is specified, then it has the next interpretation:
|
|
|
|
1. If a list contains a parent image element only, then some random portion
|
|
of fields of this element will be fuzzed every test.
|
|
The same behavior is applied for the entire image if no configuration is
|
|
used. This case is useful for the test specialization.
|
|
|
|
2. If a list contains a parent element and a field name, then a field
|
|
will be always fuzzed for every test. This case is useful for regression
|
|
testing.
|
|
|
|
The generator can create header fields, header extensions, L1/L2 tables and
|
|
refcount table and blocks.
|
|
|
|
Module interfaces
|
|
-----------------
|
|
|
|
* Test runner/image fuzzer
|
|
|
|
The runner calls an image generator specifying the path to a test image file,
|
|
path to a backing file and its format and a fuzzer configuration.
|
|
An image generator is expected to provide a
|
|
|
|
'create_image(test_img_path, backing_file_path=None,
|
|
backing_file_format=None, fuzz_config=None)'
|
|
|
|
method that creates a test image, writes it to the specified file and returns
|
|
the size of the virtual disk.
|
|
The file should be created if it doesn't exist or overwritten otherwise.
|
|
fuzz_config has a form of a list of lists. Every sublist can have one
|
|
or two elements: first element is a name of a parent image element, second one
|
|
if exists is a name of a field in this element.
|
|
Example,
|
|
[['header', 'l1_table_offset'],
|
|
['header', 'nb_snapshots'],
|
|
['feature_name_table']]
|
|
|
|
Random seed is set by the runner at every test execution for the regression
|
|
purpose, so an image generator is not recommended to modify it internally.
|
|
|
|
|
|
Overall fuzzer requirements
|
|
===========================
|
|
|
|
Input data:
|
|
----------
|
|
|
|
- image template (generator)
|
|
- work directory
|
|
- action vector (optional)
|
|
- seed (optional)
|
|
- SUT and its arguments (optional)
|
|
|
|
|
|
Fuzzer requirements:
|
|
-------------------
|
|
|
|
1. Should be able to inject random data
|
|
2. Should be able to select a random value from the manually pregenerated
|
|
vector (boundary values, e.g. max/min cluster size)
|
|
3. Image template should describe a general structure invariant for all
|
|
test images (image format description)
|
|
4. Image template should be autonomous and other fuzzer parts should not
|
|
rely on it
|
|
5. Image template should contain reference rules (not only block+size
|
|
description)
|
|
6. Should generate the test image with the correct structure based on an image
|
|
template
|
|
7. Should accept a seed as an argument (for regression purpose)
|
|
8. Should generate a seed if it is not specified as an input parameter.
|
|
9. The same seed should generate the same image for the same action vector,
|
|
specified or generated.
|
|
10. Should accept a vector of actions as an argument (for test reproducing and
|
|
for test case specification, e.g. group of tests for header structure,
|
|
group of test for snapshots, etc)
|
|
11. Action vector should be randomly generated from the pool of available
|
|
actions, if it is not specified as an input parameter
|
|
12. Pool of actions should be defined automatically based on an image template
|
|
13. Should accept a SUT and its call parameters as an argument or select them
|
|
randomly otherwise. As far as it's expected to be rarely changed, the list
|
|
of all possible test commands can be available in the test runner
|
|
internally.
|
|
14. Should support an external cancellation of a test run
|
|
15. Seed should be logged (for regression purpose)
|
|
16. All files related to a test result should be collected: a test image,
|
|
SUT logs, fuzzer logs and crash dumps
|
|
17. Should be compatible with python version 2.4-2.7
|
|
18. Usage of external libraries should be limited as much as possible.
|
|
|
|
|
|
Image formats:
|
|
-------------
|
|
|
|
Main target image format is qcow2, but support of image templates should
|
|
provide an ability to add any other image format.
|
|
|
|
|
|
Effectiveness:
|
|
-------------
|
|
|
|
The fuzzer can be controlled via template, seed and action vector;
|
|
it makes the fuzzer itself invariant to an image format and test logic.
|
|
It should be able to perform rather complex and precise tests, that can be
|
|
specified via an action vector. Otherwise, knowledge about an image structure
|
|
allows the fuzzer to generate the pool of all available areas can be fuzzed
|
|
and randomly select some of them and so compose its own action vector.
|
|
Also complexity of a template defines complexity of the fuzzer, so its
|
|
functionality can be varied from simple model-independent fuzzing to smart
|
|
model-based one.
|
|
|
|
|
|
Glossary:
|
|
--------
|
|
|
|
Action vector is a sequence of structure elements retrieved from an image
|
|
format, each of them will be fuzzed for the test image. It's a subset of
|
|
elements of the action pool. Example: header, refcount table, etc.
|
|
Action pool is all available elements of an image structure that generated
|
|
automatically from an image template.
|
|
Image template is a formal description of an image structure and relations
|
|
between image blocks.
|
|
Test image is an output image of the fuzzer defined by the current seed and
|
|
action vector.
|