Re: Fuzzing elfutils

[Alexander Cherepanov <cherepan at mccme dot ru>]

On 2014-12-05 11:58, Mark Wielaard wrote:
> On Fri, 2014-12-05 at 02:10 +0300, Alexander Cherepanov wrote:
>> On 2014-12-04 17:27, Mark Wielaard wrote:
>>> But I found that using such broad coverage makes the search space for the
>>> fuzzer really, really big. It can take days for the fuzzer to generate a
>>> somewhat valid data for some of the section types. It is imho better to
>>> not use -a or -w, or a combination of flags for different headers or data
>>> sections, but to create a minimal valid ELF file with just one kind of
>>> section or segment and then let the fuzzer run on that with just one
>>> specific flag (or --debug-dump=xxx).
>>
>> I think this is specific to AFL which you seem to use. For it, I agree
>> with your approach. But I'm not sure how useful such an advanced fuzzer
>> at this stage. I'm still using zzuf. Right now it gives more crashes
>> than I can pipe through valgrind. You can get similar behavior with AFL
>> if you specify -dn options (or perhaps you can use just -d).
>
> Yes, that is true. I have been using afl. And it is good to throw some
> other fuzzers at it. The reason you are so successful is because till
> now we concentrated on readelf and libelf. Clearly the other tools need
> fuzzing too. And we do know debuginfo (-w), libdw, has some known
> issues. One of which I just fixed in response to your testcases (see the
> patch posted, I haven't pushed it yet, to see if there are any
> comments).

Ok, I've switched to mjw/pending branch. I hope it's the right branch to 
have all your latest fixes?

> I hope to get to the other main libdw debug issue (leb128
> parsing) soon. After that hopefully you will have a bit more of a
> challenge :)

Well, I've uploaded some more crashes for the current (i.e. mjw/pending) 
readelf. Some of them could be duplicates of the previous unfixed ones.

>>> We don't specificly track any security issues, we just treat them as bugs
>>> to be fixed and do a new release when enough/important bugs have been fixed.
>>> There have been people who have filed CVEs against elfutil bugs though.
>>> I don't have any experience with filing CVEs though.
>>
>> I see. For now, I've added 'Security' keyword to the bug in the
>> bugzilla. This should get attention of the security team. Otherwise I
>> can ask for CVEs later in oss-security mailing list.
>
> Thanks, some guidance on how to deal with these issues would be
> appreciated. Sadly at the moment there are just too many to special case
> them. So for now just report issues and we try to fix them asap.
>
> The short term plan is to do a new release (elfutils 0.161) after the
> next weekend. Get as many bugs fixed before Friday 12th, do some
> additional testing during the weekend and have a release the 15th. This
> is not a very special release, just our periodic ~3/4 month release
> cycle. It will have a lot of robustness fixes though. But I doubt we
> will have fixed all crashers found by then. We will try though.

I'll reply to this a bit later.

-- 
Alexander Cherepanov