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

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Date:   Tue, 11 Sep 2018 17:25:31 +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 10:21 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> > Could you explain what this patch actually prevents from? Especially
> > now that we have stack_guard_gap?
>
> One of the many Stack Clash abuses was that it was possible to jump
> over the stack gap with outrageous environment variables that got
> expanded in stupid ways by, IIRC, glibc or the dynamic linker. The
> point here was to be defensive in the face of future weaknesses, and
> try to be robust in the face of crazy execs but workable under normal
> (but large) execs.

IOW, unlimited arg size makes many interesting attacks possible.

This is clear, I was confused because I thought this patch fixes some
particular problem not explained in the changelog.

Thanks,

Oleg.