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Re: Linux kernel race condition with PTRACE_SETREGS (CVE-2013-0871)
From: Julien Tinnes <julien () cr0 org>
Date: Tue, 19 Feb 2013 12:40:50 -0800

On Sat, Feb 16, 2013 at 2:49 AM, Solar Designer <solar () openwall com> wrote:
I haven't looked into this closely yet, but at first glance it looks
like the worst Linux kernel vulnerability in a few years.

The good news is that the race is not trivial to win in an exploit. It
also requires access to ptrace() (but unfortunately most distros don't
limit ptrace()).

For distro
vendor kernels (rather than mainline, which was patched almost a month
ago), this is a 0-day.  We need to figure out a few things:

What's the oldest affected kernel version?

I didn't spend much time looking at that, but I think it may pre-date 2.6.

Which "stable" and distro vendor kernels are affected?  This does not
appear to be e.g. on Red Hat's Bugzilla yet ... but it's already on HN:

I don't know, but probably all / most ?

Are all architectures affected?  The ptrace code in the kernel is
naturally somewhat arch-specific, so _maybe_ not all are affected.

We don't know of any other architecture other that x86 affected, but
again, I don't think anyone spent time trying to figure this out. It's
possible that the same mistake was made on another architecture.

The mainline commits from January are by Oleg Nesterov of Red Hat.  Why
wasn't(?) the issue handled with due severity within Red Hat, then -
such that Red Hat would at the very least have a statement on whether
and which of their kernels are affected by now.  My guess is that the
full severity of the issue might not have been understood by Oleg at the
time, but it's only a guess.

That's the eternal debate :) Since upstream doesn't want to handle
security and disclosure, I sure wish that distro vendors could
regroup, step-up and do it.

As for why it took so long for me to send this e-mail after the patch
went public: there is no good answer, mostly we were busy with other
things. Sorry about that.

Julien


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