Re: [ft-devel] More fuzzing for freetype2?

[Kostya Serebryany]

On Tue, Oct 6, 2015 at 9:46 AM, Ben Wagner <address@hidden> wrote:

I am interested in gx variation fonts being fuzzed. I've created an simple SIL licensed example font of this type, which can be found at https://skia.googlesource.com/skia/+/master/resources/fonts/Distortable.ttf , which is currently being used for testing Skia. Hopefully this can be a useful starting place for testing these sorts of fonts.

Thanks! 

I've inserted this file into the corpus, and it added 2 more control flow edges (out of ~15000).

Not much, but not zero. 

The current target function handles any kind of font, so it may be rather slow in finding problems specific to a single font type. 

For that we better write a separate target function. Would you like to help? 

--kcc 

 

On Oct 5, 2015 4:28 PM, "Kostya Serebryany" <address@hidden> wrote:

On Mon, Oct 5, 2015 at 7:22 AM, Alexei Podtelezhnikov <address@hidden> wrote:

On Sun, Oct 4, 2015 at 2:40 PM, Kostya Serebryany <address@hidden> wrote:
> The data shows that ~500 out of ~1000 functions were never executed.
> ...
> If we ever get close to ~90% function coverage...

About 50% coverage actually sounds reasonable for a given font format.
For example, Freetype has 3 hinters for different fonts. Of course, we
do not use them together. It took a while before the Fuzzer
"discovered" CFF space.

About two weeks on 20 CPU cores, to be precise. 

if I had a test input that uses CFF, it would have been much quicker. :) 

 

I might be totally off base here, but coverage
for a given font format would be more informative. FreeType supports a
large but limited number of font formats
http://freetype.org/freetype2/docs/index.html .

How do you identify that a given file belongs to one format or another?

Some magic in the beginning?

We can modify the target function to immediately reject all formats but one, and we'll get what you are asking for.  

This is where my knowledge about this domain area (fonts) ends and where I may need your help. 

--kcc 

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