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diff --git a/docs/image-fuzzer.txt b/docs/image-fuzzer.txt new file mode 100644 index 0000000000..e73b182859 --- /dev/null +++ b/docs/image-fuzzer.txt @@ -0,0 +1,239 @@ +# 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. + +For now only header fields and header extensions are generated. + + +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. |