linux-kernel - Re: [PATCH] tracing: do not leak kernel addresses

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Date:   Thu, 26 Jul 2018 09:32:07 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     rostedt@...dmis.org
Cc:     salyzyn@...roid.com, LKML <linux-kernel@...r.kernel.org>,
        mingo@...hat.com, kernel-team@...roid.com, stable@...r.kernel.org
Subject: Re: [PATCH] tracing: do not leak kernel addresses

On Thu, Jul 26, 2018 at 8:22 AM Steven Rostedt <rostedt@...dmis.org> wrote:
>
> On Thu, 26 Jul 2018 08:14:08 -0700
> Mark Salyzyn <salyzyn@...roid.com> wrote:
>
> > Thank you Steve, much appreciated feedback, I have asked the security
> > developers to keep this in mind and come up with a correct fix.
> >
> > The correct fix that meets your guidelines would _not_ be suitable for
> > stable due to the invasiveness it sounds, only for the latest will such
> > a rework make sense. As such, the fix proposed in this patch is the only
> > one that meets the bar for stable patch simplicity, and merely(!) needs
> > to state that if the fix is taken, perf and trace are broken.
> >
> > Posting this patch publicly on the lists, that may never be applied, may
> > be the limit of our responsibility for a fix to stable kernel releases,
> > to be optionally applied by vendors concerned with this CVE criteria?
> >
>
> The patch breaks the code it touches. It makes it useless.

Doesn't that depend on kptr_restrict, or would it be broken if
kptr_restrict was set to 0?

> If you want
> something for stable, add a command line parameter that just disables
> the creation of that file. Otherwise you will break usespace and that
> will be a definitely NAK from Linus, and for stable itself. This is a
> very minor security issue, and does not justify breaking userspace
> applications. I would be very upset if a new stable release broke both
> perf and trace-cmd's ability to read certain trace events.

I don't disagree.

-- 
Thanks,
~Nick Desaulniers