linux-kernel - Re: get_arg_page() && ptr

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Message-ID: <20180911152953.GB9450@redhat.com>
Date:   Tue, 11 Sep 2018 17:29:53 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Rik van Riel <riel@...hat.com>, Michal Hocko <mhocko@...e.com>,
        Stanislav Kozina <skozina@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: get_arg_page() && ptr_size accounting

On 09/10, Kees Cook wrote:
>
> On Mon, Sep 10, 2018 at 10:43 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > with this patch
> >
> >         #define MAX_ARG_STRINGS 0x7FFFFFFF
> >
> > doesn't match the reality. perhaps something like below makes sense just
> > to make it clear, but this is cosmetic.
>
> Part of the discussion from back then was basically "we don't have
> hard-coded limits so programs need to check dynamically themselves".
>
> I'd prefer to leave it all well enough alone since I don't want to
> introduce regressions here in the face of the many many Stack Clash
> style weaknesses.

I simply can't understand... Perhaps you too misunderstood me, I only
tried to say that count() can stop earlier, it is pointless to continue
to count the arg/env strings after argc + envc > _STK_LIM / 4 * 3 / 2,
copy_strings() will fail anyway.

Oleg.