On 2014-12-04 17:27, Mark Wielaard wrote:
[skip]
BTW. It is helpful to know which architecture you are running on. Some
issues only show on a 32bit architecture trying to parse a 64bit ELF file,
or on little/big endian systems parsing a different endian ELF file.
Yes, sorry, I'm using amd64 now. Maybe will switch to x86 later.
I'm not very familiar with elfutils. Which commands give the most code
coverage (and shortest run time)? I've used two commands so far:
objdump -rs
readelf -aAdehIlnrsSVcp -w
and crashes seem to differ for them.
That does give a biggest coverage. For eu-readelf -w you might want to use
-N, --numeric-addresses Do not find symbol names for addresses in DWARF data
which can increase the runtime a lot (we really need to not do a linear
search to lookup the addresses...).
Thanks for the tip!
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).
BTW does indended use of elfutils include the use against untrusted
files and do you track corresponding security issues?
I guess it isn't specifically intended for use against completely untrusted
files. But it happens of course. Also some of the elfutils libraries (libelf,
libdw) are used by tools that might process untrusted data. For example
systemd might use libdw to extract backtraces from core files - which should
normally be "trusted" because generated by the kernel, but there might be
bugs in the generation or they might refer to ELF or debug files that a
hostile user might have prepared. So we are actively working to make it
work robustly against anything thrown at it.
Nice to hear it!
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.
[skip]
I might be good to have a central place to store these results.
The mailinglist seems a little problematic and we might miss/overlook
some issues just posted to the list.
Sure, and mailing several megs of attachments to all the list is not
nice too. It's just there is no info about bug reporting on the project
page at https://fedorahosted.org/elfutils/ .
Do you have some location where you
can store them and any future files? Or could you open a bugzilla report
against elfutils and attach them there?
https://bugzilla.redhat.com/enter_bug.cgi?product=Fedora
I think the bugzilla is exactly fine for this. Filed here:
https://bugzilla.redhat.com/show_bug.cgi?id=1170810
--
Alexander Cherepanov
