linux-kernel - Re: [rfc 3/3] prctl: Add PR_SET_MM codes to tune up mm

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Date:	Wed, 30 Nov 2011 00:37:14 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Andrew Vagin <avagin@...nvz.org>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Vasiliy Kulikov <segoon@...nwall.com>
Subject: Re: [rfc 3/3] prctl: Add PR_SET_MM codes to tune up mm_struct entires

On Wed, Nov 30, 2011 at 12:29:51AM +0400, Cyrill Gorcunov wrote:
...
> > 
> > arg3 needs to be significantly more carefully validated. find_vma() doesn't
> > say that vm_start <= addr, only that vm_end > addr. This effectively
> > bypasses all the vma checks (mmap_min_addr, max process size, etc), with
> > some pretty crazy side-effects, I think.
> > 
> 
> Yes, I know it needs some more testing, but apart from vma bounds (yup,
> good point with find_vma, I'll fix) I thought about what else should be
> checked? I think VMA prototype should be checked to fit "code", "data"
> templates, ie code should be at least readable and execytable, but what
> about data and stack and brk, should stack be executable? That is the
> point where I've got a bit confused and though putting RFC out might be
> a good idea to collect opinions.

On the other hands these fields are set up by elf hanlder code, which
does mmap these areas, so we have to check that particular member
belongs to existing VMA and never cross user-space area, and together
with root-only approach would not it be enough? I'm sure missing something
that is why I'm asking.
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