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Date: Wed, 20 Feb 2013 01:01:25 +0400
From: Solar Designer <>
Subject: Re: Linux kernel race condition with PTRACE_SETREGS (CVE-2013-0871)

On Tue, Feb 19, 2013 at 12:40:50PM -0800, Julien Tinnes wrote:
> On Sat, Feb 16, 2013 at 2:49 AM, Solar Designer <> 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()).

Yeah.  To clarify why the vulnerability looks so bad to me: for our
kernel builds and usage, it appears to be the worst since CVE-2010-3081
(compat_alloc_user_space() missing sanity checks), although it is
probably trickier to exploit in the wild (due to the race).  There were
other local vulnerabilities in the Linux kernel discovered in those ~2.5
years, but they were in more obscure subsystems (which we generally
don't expose) or/and they required that the local attacker would execute
a SUID/SGID program.  This one, however, is in an (almost) core kernel
component and is self-contained (no dependency on the userland being
non-perfect), which makes it almost as bad as CVE-2010-3081, except that
it's a race.  On the other hand, CVE-2010-3081 did not affect 32-bit
only kernel builds, whereas this new vulnerability probably does.

> > 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.

Have you looked into whether 32-bit x86 kernel builds are affected to
the same extent?



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