linux-kernel - Re: [PATCH] ptrace: use safer wake up on ptrace

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Date:	Wed, 2 Feb 2011 11:33:42 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Roland McGrath <roland@...hat.com>, oleg@...hat.com,
	jan.kratochvil@...hat.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH] ptrace: use safer wake up on ptrace_detach()

On Wed, 2 Feb 2011 11:34:02 +0100
Tejun Heo <tj@...nel.org> wrote:

> Hello,
> 
> On Tue, Feb 01, 2011 at 09:38:28PM -0800, Andrew Morton wrote:
> > On Tue,  1 Feb 2011 21:33:31 -0800 (PST) Roland McGrath <roland@...hat.com> wrote:
> > 
> > > > Am unable to work out why you tagged it for backporting.  It fixes some
> > > > observed bug?  Perhaps a regression?
> > > 
> > > No observed bug, only theoretical ones (AFAIK, never even a ginned-up
> > > synthetic test case has been demonstrated).  Certainly not a regression,
> > > since it has been this (wrong) way since the dawn of time.  I don't think
> > > this first change is dangerous for -stable, but I have seen no positive
> > > rationale for pushing it there.
> > > 
> > 
> > OK, thanks.  I shall destabilize my copy of this patch.
> 
> It can be used as an attack vector.  I don't think it will take too
> much effort to come up with an attack which triggers oops somewhere.
> Most sleeps are wrapped in condition test loops and should be safe but
> we have quite a number of places where sleep and wakeup conditions are
> expected to be interlocked.  Although the window of opportunity is
> tiny, ptrace can be used by non-privileged users and with some loading
> the window can definitely be extended and exploited.
> 
> The chance of this problem being visible under normal usage is
> extremely low so no wonder there is no related bug report but that is
> very different from being safe against targeted attacks.
> 
> As the likelihood of causing user noticeable breakage is very low, I
> think we better push it through -stable.
> 

We're learning some lessons about changelogging here :(

I added this:

: This bug can possibly be used as an attack vector.  I don't think
: it will take too much effort to come up with an attack which triggers
: oops somewhere.  Most sleeps are wrapped in condition test loops and
: should be safe but we have quite a number of places where sleep and
: wakeup conditions are expected to be interlocked.  Although the
: window of opportunity is tiny, ptrace can be used by non-privileged
: users and with some loading the window can definitely be extended and
: exploited.

to the changelog so the -stable maintainers can understand why we're
sending this patch at them.

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