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    SubjectRe: [PATCH] ptrace: use safer wake up on ptrace_detach()
    On Wed, 2 Feb 2011 11:34:02 +0100
    Tejun Heo <tj@kernel.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@redhat.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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