linux-kernel - Re: [PATCH] mmap: add sysctl for controlling ~VM

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Message-ID: <26032.1313623355@turing-police.cc.vt.edu>
Date:	Wed, 17 Aug 2011 19:22:35 -0400
From:	Valdis.Kletnieks@...edu
To:	Roland McGrath <mcgrathr@...gle.com>
Cc:	Mel Gorman <mel@....ul.ie>, Will Drewry <wad@...omium.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Al Viro <viro@...iv.linux.org.uk>,
	Eric Paris <eparis@...hat.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Nitin Gupta <ngupta@...are.org>,
	Hugh Dickins <hughd@...gle.com>,
	Shaohua Li <shaohua.li@...el.com>, linux-mm@...ck.org
Subject: Re: [PATCH] mmap: add sysctl for controlling ~VM_MAYEXEC taint

On Tue, 16 Aug 2011 10:07:46 PDT, Roland McGrath said:

> I think the expectation is that the administrator or system builder
> who decides to set the (non-default) noexec mount option will also
> set the sysctl at the same time.

On the other hand, a design that requires 2 separate actions to be taken in
order to make it work, and which fails unsafe if the second step isn't taken,
is a bad design. If we're talking "expectations", let's not forget that the
mount option is called "noexec", not "only-really-noexec-if-you-set-a-magic-sysctl". 

I'll also point out that we didn't add a sysctl in 2.6.0 to say whether or not
to still allow the old "/lib/ld-linux.so your-binary-here" hack to execute binaries
off a partition mounted noexec - we simply said "this will no longer be permitted".

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