linux-kernel - Re: [RFC][PATCH 7/7] kref: Implement using refcount

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Message-ID: <20161116092414.GA2071@kroah.com>
Date:   Wed, 16 Nov 2016 10:24:14 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will.deacon@....com>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        Arnd Bergmann <arnd@...db.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        David Windsor <dave@...gbits.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 7/7] kref: Implement using refcount_t

On Wed, Nov 16, 2016 at 10:07:37AM +0100, Ingo Molnar wrote:
> 
> * Greg KH <gregkh@...uxfoundation.org> wrote:
> 
> > On Wed, Nov 16, 2016 at 09:31:55AM +0100, Ingo Molnar wrote:
> > > So what I'd love to see is to have a kernel option that re-introduces some 
> > > historic root (and other) holes that can be exploited deterministically - 
> > > obviously default disabled.
> > 
> > Ick, I don't want to have to support nasty #ifdefs for
> > "CONFIG_TOTALLY_INSECURE" type options in code logic for the next 20+
> > years, do you?
> 
> I'd write it in C, not CPP, so it would be an 'if', but yeah, it would be extra 
> code otherwise.
> 
> So I'd restrict this strictly to cases:
> 
>  - Where the maintainer absolutely agrees to carry it.
> 
>  - Where it's still easy to do technically - for example a single unobtrusive 
>    'if' condition or so, in cases where the current upstream code still has a 
>    similar structure conductive to the re-introducion of the bug. Such testcases
>    can be dropped the moment they interfere with active development.
> 
>  - Plus an additional approach could be that some of the typical holes can be
>    reproduced in completely separate code that is not seen by anyone who doesn't 
>    want to see it.

Ok, but in looking at a number of "security" fixes over the past year or
so, I don't think that many of them would really work well for this.
Just look at all of the "don't reference a NULL pointer" bugs for an
example of that.

> I doubt many bugs have 20 years life times in face of frequent code reorganization 
> - and if code is static for 20 years then there won't be much extra maintenance 
> overhead, right?

Hah, you obviously are not in charge of maintaining the tty layer :)

Anyway, if you want to try this for the next type of security "issue" in
your area of the kernel, be my guest, but I think it's going to be a lot
harder than you think.

thanks,

greg k-h