On Fri, Mar 29, 2024 at 04:46:54PM -0500, Michael Catanzaro wrote:
> On Fri, Mar 29 2024 at 04:10:53 PM -05:00:00, Michael Catanzaro
> <mcatanzaro@redhat.com> wrote:
> >OK, I am going to ask Product Security to edit their blog post to
> >remove the incorrect information. I will CC you on that request.
>
> Or maybe I should rephrase this as a "request for clarification,"
> because maybe they know something that we don't. E.g. the Ars
> article [1] says
>
> "The build environment on Fedora 40, for example, contains
> incompatibilities that prevent the injection from correctly
> occurring. Fedora 40 has now reverted to the 5.4.x versions of xz
> Utils."
>
> [1] https://arstechnica.com/security/2024/03/backdoor-found-in-widely-used-linux-utility-breaks-encrypted-ssh-connections/

Yeah that's just a confused report.  This is how it actually happened:

(1) We built 5.6.0 for Fedora 40 & 41.  Jia Tan was very insistent in
emails that we should update.

(2) We got reports later of a valgrind test failure.  I also saw it
myself in my own projects that use liblzma.  We notified Jia Tan of
this.

(3) Since the valgrind failure pointed to something with ifuncs, using
'./configure --disable-ifuncs' was used to fix this in F40 & F41.

(4) xz 5.6.1 was released with a fix for the valgrind failure.

(5) Fedora 40 was now in beta so we kept 5.6.0 + --disable-ifuncs.
Fedora 41 was updated to 5.6.1 (enabling ifuncs again).

And now with the benefit of hindsight ...

In step (1) we worked in good faith with upstream.  Given how
obfuscated the injection is, it's very unlikely we would have found
the problem even if we'd spent days inspecting the tarball.  (And the
initial step of injection is *not* in git, so forget about reviewing
git commits.)

The valgrind failure (2) was caused by a bug in the back door.

Disabling ifuncs in (3) disabled the back door, because I think it
relies on ifuncs to do its malware, but in any case the obfuscated
injection script explicitly skips injection if ifuncs are disabled.

Step (4) fixed the back door valgrind failure.

The Fedora 40 beta freeze in (5) meant we got lucky for F40, not so
much for F41.

Rich.

> Now, that's a secondary source, and I'm not confident if it is true,
> but perhaps Product Security had time to analyze the build logs
> before publishing and found something that we don't know about.
> Richard, what do you think?
>

--
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